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  • 1.
    A. Mouris, Boules
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Teknisk informationsvetenskap.
    Ghauch, Hadi
    Department of COMELEC, Institut Mines-Telecom, Telecom-ParisTech, Paris, 91120, France.
    Thobaben, Ragnar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Teknisk informationsvetenskap.
    Jonsson, B. Lars G.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Multi-tone Signal Optimization for Wireless Power Transfer in the Presence of Wireless Communication Links2020Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 19, nr 5, s. 3575-3590Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we study optimization of multi-tone signals for wireless power transfer (WPT) systems. We investigate different non-linear energy harvesting models. Two of them are adopted to optimize the multi-tone signal according to the channel state information available at the transmitter. We show that a second-order polynomial curve-fitting model can be utilized to optimize the multi-tone signal for any RF energy harvester design. We consider both single-antenna and multi-antenna WPT systems. In-band co-existing communication links are also considered in this work by imposing a constraint on the received power at the nearby information receiver to prevent its RF front end from saturation. We emphasize the importance of imposing such constraint by explaining how inter-modulation products, due to saturation, can cause high interference at the information receiver in the case of multi-tone signals. The multi-tone optimization problem is formulated as a non-convex linearly constrained quadratic program. Two globally optimal solution approaches using mixed-integer linear programming and finite branch-and-bound techniques are proposed to solve the problem. The achieved improvement resulting from applying both solution methods to the multi-tone optimization problem is highlighted through simulations and comparisons with other solutions existing in the literature.

  • 2.
    Ahmad, Ikhlas
    et al.
    Univ Engn & Technol, Dept Telecommun Engn, Mardan, Pakistan..
    Rehman Khan, Wasi Ur
    Univ Engn & Technol, Dept Telecommun Engn, Mardan, Pakistan..
    Ullah, Sadiq
    Univ Engn & Technol, Dept Telecommun Engn, Mardan, Pakistan..
    Mufti, Naveed
    Univ Engn & Technol, Dept Telecommun Engn, Mardan, Pakistan..
    Alharbi, Abdullah G.
    Jouf Univ, Fac Engn, Dept Elect Engn, Sakaka 42421, Saudi Arabia..
    Hussain, Niamat
    Sejong Univ, Dept Smart Device Engn, Seoul 05006, South Korea..
    Alibakhshikenari, Mohammad
    Univ Carlos III Madrid, Dept Signal Theory & Commun, Leganes 28911, Madrid, Spain..
    Dalarsson, Mariana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Highly Compact GCPW-Fed Multi-Branch Structure Multi-Band Antenna for Wireless Applications2022Ingår i: International Journal of Antennas and Propagation, ISSN 1687-5869, E-ISSN 1687-5877, Vol. 2022, s. 1-9, artikel-id 1917807Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, we present a highly compact multi-branch structure multi-band antenna with a grounded coplanar waveguide (GCPW)-fed structure printed on 26 x 13 x 1.6 mm(3) sized FR-4 substrate having dielectric constant epsilon r of 4.3 and loss tangent delta of 0.02. In the proposed antenna, five branches are extended from the main radiator to provide multi-band behavior. Two branches are introduced at the upper end of the main radiator, effectively covering the lower bands, while the other three branches are introduced near the center of the main radiator to extend operation to higher bands. The designed antenna covers five different bands: 2.4 GHz, 4.5 GHz, 5.5 GHz, 6.5 GHz, and 7.8 GHz, with respective gain values of 1.34, 1.60, 1.83, 1.80, and 3.50 dBi and respective radiation efficiency values of 90, 88, 84, 75, and 89%. The antenna shows a good impedance bandwidth, ranging from 170 MHz to 3070 MHz. The proposed antenna is simulated in CST Microwave Studio, while its performance is experimentally validated by the fabrication and testing process. The antenna has potential applications for IoT, sub-6 GHz 5G and WLAN (both enablers for IoT), C-band, and X-band services.

  • 3.
    Alex-Amor, Antonio
    et al.
    Univ Malaga, Dept Lenguajes & Ciencias Computac, Malaga 29071, Spain.;Univ Politecn Madrid, Informat Proc & Telecommun Ctr, Madrid 28040, Spain..
    Ghasemifard, Fatemeh
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Valerio, Guido
    Sorbonne Univ, Lab Genie Elect & Elect Paris, CNRS, F-75252 Paris, France.;Univ Paris Saclay, Cent Supelec, CNRS, Lab Genie Elect & Elect Paris, F-91192 Gif Sur Yvette, France..
    Ebrahimpouri, Mahsa
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Padilla, Pablo
    Univ Granada, Dept Teoria Senal Telemat & Comunicac, Granada 18071, Spain..
    Fernandez Gonzalez, Jose Manuel
    Univ Politecn Madrid, Informat Proc & Telecommun Ctr, Madrid 28040, Spain..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Glide-Symmetric Metallic Structures With Elliptical Holes for Lens Compression2020Ingår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 68, nr 10, s. 4236-4248Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, we study the wave propagation in a metallic parallel-plate structure with glide-symmetric elliptical holes. To perform this study, we derived a mode-matching technique based on the generalized Floquet theorem for glide-symmetric structures. This mode-matching technique benefits from a lower computational cost since it takes advantage of the glide symmetry in the structure. It also provides physical insight into the specific properties of Floquet modes propagating in these specific structures. With our analysis, we demonstrate that glide-symmetric structures with periodic elliptical holes exhibit an anisotropic refractive index over a wide range of frequencies. The equivalent refractive index can be controlled by tuning the dimensions of the holes. Finally, by combining the anisotropy related to the elliptical holes and transformation optics, a Maxwell fish-eye (MFL) lens with a 33.33% size compression is designed. This lens operates in a wideband frequency range from 2.5 to 10 GHz.

  • 4.
    Alex-Amor, Antonio
    et al.
    Tech Univ Madrid, Informat Proc & Telecommun Ctr, Madrid 28040, Spain..
    Ghasemifard, Fatemeh
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Valerio, Guido
    Sorbonne Univ, UR2, Lab Elect & Electromagnetisme, F-75005 Paris, France..
    Padilla, Pablo
    Univ Granada, Dept Teoria Senal Telemat & Comunicac, Granada 18071, Spain..
    Fernandez-Gonzalez, Jose M.
    Tech Univ Madrid, Informat Proc & Telecommun Ctr, Madrid 28040, Spain..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Elliptical Glide-Symmetric Holey Metasurfaces for Wideband Anisotropy2020Ingår i: 2020 14th European Conference on Antennas and Propagation (EUCAP 2020), Institute of Electrical and Electronics Engineers (IEEE) , 2020Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a mode-matching technique to study the dispersive features of periodic structures composed of glide-symmetric elliptical holes. As a difference from purely numerical methods, our formulation provides physical insight on the Floquet harmonics. At the same time, the computational cost is reduced compared to general purpose commercial software. The fields inside the holes are described by means of Mathieu functions and subsequently used to compute the full 2-D dispersion diagrams. With the presented analysis, we demonstrate that glide-symmetric periodic structures with elliptical holes offer anisotropic refractive indexes over a wide range of frequencies.

  • 5.
    Alex-Amor, Antonio
    et al.
    Univ CEU San Pablo, Informat Technol Dept, Madrid 28668, Spain..
    Palomares-Caballero, Angel
    Telemat & Comunicac Univ Granada, Dept Teoria Senal Telemat & Comunicac, Granada 18071, Spain..
    Mesa, Francisco
    Univ Seville, Dept Appl Phys 1, Escuela Tecn Super Ingn Informat, Seville 41012, Spain..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Padilla, Pablo
    Telemat & Comunicac Univ Granada, Dept Teoria Senal Telemat & Comunicac, Granada 18071, Spain..
    Dispersion Analysis of Periodic Structures in Anisotropic Media: Application to Liquid Crystals2022Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 70, nr 4, s. 2811-2821Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article presents an efficient method to compute the dispersion diagram of periodic and uniform structures with generic anisotropic media. The method takes advantage of the ability of full-wave commercial simulators to deal with finite structures having anisotropic media. In particular, the proposed method extends the possibilities of commercial eigenmode solvers in the following ways: 1) anisotropic materials with nondiagonal permittivity and permeability tensors can be analyzed; 2) the attenuation constant can easily be computed in both propagating and stopband regions, and lossy materials can be included in the simulation; and 3) unbounded and radiating structures, such as leaky-wave antennas (LWAs), can be treated. The latter feature may be considered the most remarkable since the structures must be forcefully bounded with electric/magnetic walls in the eigensolvers of most commercial simulators. In this work, the proposed method is particularized for the study of liquid crystals (LCs) in microwave and antenna devices. Thus, the dispersion properties of a great variety of LC-based configurations are analyzed, from canonical structures, such as waveguide and microstrip, to complex reconfigurable phase shifters in ridge gap-waveguide technology and LWAs. Our results have been validated with previously reported works in the literature and with commercial software CST and HFSS.

  • 6.
    Alex-Amor, Antonio
    et al.
    Univ Politecn Madrid, Informat Proc & Telecommun Ctr, E-28040 Madrid, Spain.;Univ Granada, Dept Teoria Senal Telemat & Comunicac, E-18071 Granada, Spain..
    Valerio, Guido
    Sorbonne Univ, CNRS, Lab Genie Elect & Elect Paris, F-75252 Paris, France.;Univ Paris Saclay, Cent Supelec, CNRS, Lab Genie Elect & Elect Paris, F-91192 Gif Sur Yvette, France..
    Ghasemifard, Fatemeh
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Mesa, Francisco
    Univ Seville, Microwaves Grp, Dept Appl Phys 1, Escuela Tecn Super Ingn Informat, E-41012 Seville, Spain..
    Padilla, Pablo
    Univ Granada, Dept Teoria Senal Telemat & Comunicac, E-18071 Granada, Spain..
    Fernandez-Gonzalez, Jose M.
    Univ Politecn Madrid, Informat Proc & Telecommun Ctr, E-28040 Madrid, Spain..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Wave Propagation in Periodic Metallic Structures with Equilateral Triangular Holes2020Ingår i: Applied Sciences, E-ISSN 2076-3417, Vol. 10, nr 5, artikel-id 1600Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper studies wave propagation in a periodic parallel-plate waveguide with equilateral triangular holes. A mode-matching method is implemented to analyze the dispersion diagram of the structure possessing glide and mirror symmetries. Both structures present an unexpected high degree of isotropy, despite the triangle not being symmetric with respect to rotations of 90 degrees. We give some physical insight on the matter by carrying out a modal decomposition of the total field on the hole and identifying the most significant modes. Additionally, we demonstrate that the electrical size of the triangular hole plays a fundamental role in the physical mechanism that causes that isotropic behavior. Finally, we characterize the influence of the different geometrical parameters that conform the unit cell (period, triangle size, hole depth, separation between metallic plates). The glide-symmetric configuration offers higher equivalent refractive indexes and widens the stopband compared to the mirror-symmetric configuration. We show that the stopband is wider as the triangle size is bigger, unlike holey structures composed of circular and elliptical holes where an optimal hole size exists.

  • 7. Algaba-Brazalez, A.
    et al.
    Vidarsson, F. V.
    Zetterström, Oskar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Manholm, L.
    Johansson, M.
    Fonseca, N. J. G.
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Compact Polarization Transformation in a Geodesic Luneburg Lens Antenna2021Ingår i: 2021 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting, APS/URSI 2021 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2021, s. 1992-1993Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper describes the design of a compact polarizer that rotates the linear polarization of a fully metallic geodesic Luneburg lens antenna for applications requiring polarization diversity. The polarization rotation is achieved by loading the radiating aperture of the antenna with two metallic screens. The integrated antenna operates in the Ka-band, from 25 to 31 GHz, showing around 20% bandwidth with S11 below -10 dB, and a scanning range of 100°.

  • 8.
    Algaba-Brazalez, Astrid
    et al.
    Ericsson AB, Ericsson Res, Gothenburg, Sweden..
    Arnberg, Philip
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Zetterström, Oskar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Vidarsson, Freysteinn Vidar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Manholm, Lars
    Ericsson AB, Ericsson Res, Gothenburg, Sweden..
    Johansson, Martin
    Ericsson AB, Ericsson Res, Gothenburg, Sweden..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Crossover level improvement between beams in a geodesic lens antenna based on a generalized Luneburg lens2022Ingår i: 2022 16th European Conference on Antennas and Propagation (EuCAP), Institute of Electrical and Electronics Engineers (IEEE), 2022Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we propose a geodesic generalized Luneburg lens operating in the 60-GHz band, from 57 to 67 GHz, designed with the goal to improve the crossover level between beams with respect to previously reported fully metallic Luneburg lenses, while providing highly directive beams and wide scanning coverage. We have combined the use of a generalized Luneburg lens and the design of a compact feeding type based on ridge waveguide in order to achieve an optimum crossover level between beams keeping in mind manufacturing simplicity. The numerical evaluation of the final integrated lens design including 21 ridge waveguide feeding ports shows a vertical bar S-11 vertical bar parameter below -13.6 dB over the frequency band of interest, a scanning range of +/- 52 degrees, a realized gain higher than 19 dBi over the whole operating bandwidth, and a crossover level value between -3.5 dB and -4.2 dB from the lowest to the highest frequency of operation.

  • 9.
    Algaba-Brazalez, Astrid
    et al.
    Ericsson AB, Ericsson Res, Gothenburg, Sweden..
    Manholm, Lars
    Ericsson AB, Ericsson Res, Gothenburg, Sweden..
    Johansson, Martin
    Ericsson AB, Ericsson Res, Gothenburg, Sweden..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Overview of research on metalenses and geodesic lenses for 5G/6G applications in Ericsson2022Ingår i: 2022 INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION (ISAP), Institute of Electrical and Electronics Engineers (IEEE) , 2022, s. 103-104Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this contribution, we outline the challenges and opportunities of designing parallel-plate lenses implemented with metasurfaces (i.e. metalenses) or with geodesic surfaces (i.e. geodesic lenses), for next generation communication systems (5G and beyond). The requirements that we studied in our investigations are low scanning loss, high efficiency, high crossover level, polarization diversity, wide scanning range, low antenna profile, manufacturing simplicity, and cost-effectiveness. These requirements are key when designing and developing antennas for 5G and beyond.

  • 10.
    Alibakhshikenari, Mohammad
    et al.
    Univ Carlos III Madrid, Dept Signal Theory & Commun, Madrid 28911, Spain..
    Virdee, Bal S.
    London Metropolitan Univ, Ctr Commun Technol, Sch Comp & Digital Media, London N7 8DB, England..
    Benetatos, Harry
    London Metropolitan Univ, Ctr Commun Technol, Sch Comp & Digital Media, London N7 8DB, England..
    Ali, Esraa Mousa
    Amman Arab Univ, Fac Aviat Sci, Amman 11953, Jordan..
    Soruri, Mohammad
    Univ Birjand, Tech Fac Ferdows, Birjand 9717434765, Iran..
    Dalarsson, Mariana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Naser-Moghadasi, Mohammad
    Islamic Azad Univ, Dept Elect & Comp Engn, Sci & Res Branch, Tehran 1477893855, Iran..
    See, Chan Hwang
    Edinburgh Napier Univ, Sch Engn & Built Environm, 10 Colinton Rd, Edinburgh EH10 5DT, Midlothian, Scotland..
    Pietrenko-Dabrowska, Anna
    Gdansk Univ Technol, Fac Elect Telecommun & Informat, PL-80233 Gdansk, Poland..
    Koziel, Slawomir
    Gdansk Univ Technol, Fac Elect Telecommun & Informat, PL-80233 Gdansk, Poland.;Reykjavik Univ, Engn Optimizat & Modeling Ctr, IS-101 Reykjavik, Iceland..
    Szczepanski, Stanislaw
    Gdansk Univ Technol, Fac Elect Telecommun & Informat, PL-80233 Gdansk, Poland..
    Limiti, Ernesto
    Univ Roma Tor Vergata, Elect Engn Dept, Via Politecn 1, I-00133 Rome, Italy..
    An innovative antenna array with high inter element isolation for sub-6 GHz 5G MIMO communication systems2022Ingår i: Scientific Reports, E-ISSN 2045-2322, Vol. 12, nr 1, artikel-id 7907Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel technique is shown to improve the isolation between radiators in antenna arrays. The proposed technique suppresses the surface-wave propagation and reduces substrate loss thereby enhancing the overall performance of the array. This is achieved without affecting the antenna's footprint. The proposed approach is demonstrated on a four-element array for 5G MIMO applications. Each radiating element in the array is constituted from a 3 x 3 matrix of interconnected resonant elements. The technique involves (1) incorporating matching stubs within the resonant elements, (2) framing each of the four-radiating elements inside a dot-wall, and (3) defecting the ground plane with dielectric slots that are aligned under the dot-walls. Results show that with the proposed approach the impedance bandwidth of the array is increased by 58.82% and the improvement in the average isolation between antennas #1&2, #1&3, #1&4 are 8 dB, 14 dB, 16 dB, and 13 dB, respectively. Moreover, improvement in the antenna gain is 4.2% and the total radiation efficiency is 23.53%. These results confirm the efficacy of the technique. The agreement between the simulated and measured results is excellent. Furthermore, the manufacture of the antenna array using the proposed approach is relatively straightforward and cost effective.

  • 11.
    Alibakhshikenari, Mohammad
    et al.
    Univ Carlos III Madrid, Dept Signal Theory & Commun, Madrid 28911, Spain..
    Virdee, Bal S.
    London Metropolitan Univ, Ctr Commun Technol, London, England..
    Vadala, Valeria
    Univ Milano Bicocca, Dept Phys, I-20126 Milan, Italy..
    Dalarsson, Mariana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Gomez, Maria Elena de Cos
    Univ Oviedo, TSC Elect Engn Dept, Gijon 33203, Spain..
    Alharbi, Abdullah G.
    Jouf Univ, Fac Engn, Dept Elect Engn, Sakaka 42421, Saudi Arabia..
    Burokur, Shah Nawaz
    Univ Paris Nanterre, UPL, LEME, F-92410 Ville Davray, France..
    Aissa, Sonia
    Inst Natl Rech Sci INRS, Montreal, PQ H5A 1K6, Canada..
    Dayoub, Iyad
    Univ Lille, Univ Polytech Hauts France, CNRS, Inst Elect Microelect & Nanotechnol IEMN,ISEN,Cent, F-59313 Valenciennes, France.;Univ Roma Tor Vergata, Elect Engn Dept, Via Politecn 1, I-00133 Valenciennes, Italy..
    Falcone, Francisco
    Univ Publ Navarra, Dept Elect Elect & Commun Engn, Pamplona 31006, Spain.;Inst Smart Cities, Publ Univ Navarre, Pamplona 31006, Spain.;Tecnol Monterrey, Sch Engn & Sci, Monterrey, Mexico..
    Limiti, Ernesto
    Broadband 3-D shared aperture high isolation nine-element antenna array for on-demand millimeter-wave 5G applications2022Ingår i: Optik (Stuttgart), ISSN 0030-4026, E-ISSN 1618-1336, Vol. 267, artikel-id 169708Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper presents the results of a novel 3-D shared aperture 3 x 3 matrix antenna-array for 26 GHz band 5 G wireless networks. Radiation elements constituting the array are hexagonal-shaped patches that are elevated above the common dielectric substrate by 3.35 mm and excited through a metallic rod of 0.4 mm diameter. The rod protrudes through the substrate of 0.8 mm thickness. It is shown that by isolating each radiating element in the array with a wall suppresses unwanted electromagnetic (EM) wave interactions, resulting in improvement in the antenna's impedance matching and radiation characteristics. Moreover, the results show that by embedding hexagonalshaped slots in the patches improve the antenna's gain and radiation efficiency performance. The subwavelength length slots in the patches essentially transform the radiating elements to exhibit metasurface characteristics when the array is illuminated by EM-waves. The proposed array structure has an average gain and radiation efficiency of 20 dBi and 93%, respectively, across 24.0-28.4 GHz. The isolation between its radiation elements is greater than 22 dB. Compared to the unslotted array the improvement in isolation between radiating elements is greater than 11 dB, and the gain and efficiency are better than 10.5 dBi, and 25%, respectively. The compact array has a fractional bandwidth of 16% and a form factor of 20 x 20 x 3.35 mm(3).

  • 12.
    Aljure, Mauricio
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Becerra Garcia, Marley
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Karlsson, Mattias
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Polymera material.
    Erratum to: Aljure, M.; Becerra, M.; Karlsson, E.M. Streamer inception from ultra-sharp needles in mineral oil based nanofluids2018Ingår i: Energies, E-ISSN 1996-1073, Vol. 11, nr 11, artikel-id 2900Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The authors wish to make the following corrections to their paper [1]: i. On pages 13 and 14, the numbering of references from 17 to 30 is incorrect. References 17 to 30 should be renumbered from the original order below: 17. Liu, Z.; Liu, Q.; Wang, Z.D.; Jarman, P.; Krause, C.; Smith, P.W.R.; Gyore, A. Partial discharge behaviour of transformer liquids and the influence of moisture content. In Proceedings of the 2014 IEEE 18th International Conference on Dielectric Liquids (ICDL), Bled, Slovenia, 29 June–3 July 2014. 18. Yamashita, H.; Yamazawa, K.; Wang, Y.S. The effect of tip curvature on the prebreakdown streamer structure in cyclohexane. IEEE Trans. Dielectr. Electr. Insul. 1998, 5, 396–401. 19. Dumitrescu, L.; Lesaint, O.; Bonifaci, N.; Denat, A.; Notingher, P. Study of streamer inception in cyclohexane with a sensitive charge measurement technique under impulse voltage. J. Electrostat. 2001, 53, 135–146. 20. Pourrahimi, A.M.; Hoang, T.A.; Liu, D.; Pallon, L.K.H.; Gubanski, S.; Olsson, R.T.; Gedde, U.W.; Hedenqvist, M.S. Highly efficient interfaces in nanocomposites based on polyethylene and ZnO nano/hierarchical particles: A novel approach toward ultralow electrical conductivity insulations. Adv. Mater. 2016, 28, 8651–8657. 21. Li, J.; Du, B.; Wang, F.; Yao, W.; Yao, S. The effect of nanoparticle surfactant polarization on trapping depth of vegetable insulating oil-based nanofluids. Phys. Lett. A 2016, 380, 604–608. 22. Aljure, M.; Becerra, M.; Pallon, L.K.H. Electrical conduction currents of a mineral oil-based nanofluid in needle-plane configuration. In Proceedings of the 2016 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), Toronto, ON, Canada, 16–19 October 2016; pp. 687–690. 23. Primo, V.A.; Garcia, B.; Albarracin, R. Improvement of transformer liquid insulation using nanodielectric fluids: A review. IEEE Electr. Insul. Mag. 2018, 34, 13–26. 24. Jin, H.; Andritsch, T.; Morshuis, P.H.F.; Smit, J.J. AC breakdown voltage and viscosity of mineral oil based SiO2 nanofluids. In Proceedings of the 2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, Montreal, QC, Canada, 14–17 October 2012; pp. 902–905. 25. Jin, H.; Morshuis, P.; Mor, A.R.; Smit, J.J.; Andritsch, T. Partial discharge behavior of mineral oil based nanofluids. IEEE Trans. Dielectr. Electr. Insul. 2015, 22, 2747–2753. 26. Du, Y.; Lv, Y.; Li, C.; Chen, M.; Zhong, Y.; Zhou, J.; Li, X.; Zhou, Y. Effect of semiconductive nanoparticles on insulating performances of transformer oil. IEEE Trans. Dielectr. Electr. Insul. 2012, 19, 770–776. 27. Dung, N.V.; Høidalen, H.K.; Linhjell, D.; Lundgaard, L.E.; Unge, M. Effects of reduced pressure and additives on streamers in white oil in long point-plane gap. J. Phys. D Appl. Phys. 2013, 46, 255501. 28. McCool, J.I. Using the Weibull Distribution; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2012. 29. Lesaint, O.L.; Top, T.V. Streamer initiation in mineral oil. part I: Electrode surface effect under impulse voltage. IEEE Trans. Dielectr. Electr. Insul. 2002, 9, 84–91. 30. Becerra, M.; Frid, H.; Vázquez, P.A. Self-consistent modeling of laminar electrohydrodynamic plumes from ultra-sharp needles in cyclohexane. Phys. Fluids 2017, 29, 123605. to the following, corrected numbering: 17. Dumitrescu, L.; Lesaint, O.; Bonifaci, N.; Denat, A.; Notingher, P. Study of streamer inception in cyclohexane with a sensitive charge measurement technique under impulse voltage. J. Electrostat. 2001, 53, 135–146. 18. Liu, Z.; Liu, Q.; Wang, Z.D.; Jarman, P.; Krause, C.; Smith, P.W.R.; Gyore, A. Partial discharge behaviour of transformer liquids and the influence of moisture content. In Proceedings of the 2014 IEEE 18th International Conference on Dielectric Liquids (ICDL), Bled, Slovenia, 29 June–3 July 2014. 19. Yamashita, H.; Yamazawa, K.; Wang, Y.S. The effect of tip curvature on the prebreakdown streamer structure in cyclohexane. IEEE Trans. Dielectr. Electr. Insul. 1998, 5, 396–401. 20. Becerra, M.; Frid, H.; Vázquez, P.A. Self-consistent modeling of laminar electrohydrodynamic plumes from ultra-sharp needles in cyclohexane. Phys. Fluids 2017, 29, 123605. 21. Pourrahimi, A.M.; Hoang, T.A.; Liu, D.; Pallon, L.K.H.; Gubanski, S.; Olsson, R.T.; Gedde, U.W.; Hedenqvist, M.S. Highly efficient interfaces in nanocomposites based on polyethylene and ZnO nano/hierarchical particles: A novel approach toward ultralow electrical conductivity insulations. Adv. Mater. 2016, 28, 8651–8657. 22. Li, J.; Du, B.; Wang, F.; Yao, W.; Yao, S. The effect of nanoparticle surfactant polarization on trapping depth of vegetable insulating oil-based nanofluids. Phys. Lett. A 2016, 380, 604–608. 23. Aljure, M.; Becerra, M.; Pallon, L.K.H. Electrical conduction currents of a mineral oil-based nanofluid in needle-plane configuration. In Proceedings of the 2016 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), Toronto, ON, Canada, 16–19 October 2016; pp. 687–690. 24. Primo, V.A.; Garcia, B.; Albarracin, R. Improvement of transformer liquid insulation using nanodielectric fluids: A review. IEEE Electr. Insul. Mag. 2018, 34, 13–26. 25. Jin, H.; Andritsch, T.; Morshuis, P.H.F.; Smit, J.J. AC breakdown voltage and viscosity of mineral oil based SiO2 nanofluids. In Proceedings of the 2012 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, Montreal, QC, Canada, 14–17 October 2012; pp. 902–905. 26. Jin, H.; Morshuis, P.; Mor, A.R.; Smit, J.J.; Andritsch, T. Partial discharge behavior of mineral oil based nanofluids. IEEE Trans. Dielectr. Electr. Insul. 2015, 22, 2747–2753. 27. Du, Y.; Lv, Y.; Li, C.; Chen, M.; Zhong, Y.; Zhou, J.; Li, X.; Zhou, Y. Effect of semiconductive nanoparticles on insulating performances of transformer oil. IEEE Trans. Dielectr. Electr. Insul. 2012, 19, 770–776. 28. Dung, N.V.; Høidalen, H.K.; Linhjell, D.; Lundgaard, L.E.; Unge, M. Effects of reduced pressure and additives on streamers in white oil in long point-plane gap. J. Phys. D Appl. Phys. 2013, 46, 255501. 29. McCool, J.I. Using the Weibull Distribution; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2012. 30. Lesaint, O.L.; Top, T.V. Streamer initiation in mineral oil. part I: Electrode surface effect under impulse voltage. IEEE Trans. Dielectr. Electr. Insul. 2002, 9, 84–91. ii. On the last paragraph of page 9, the last sentence should be changed from: However, the results in [11] also show the consistent increase in the initiation voltage of prebreakdown phenomena in both polarities, as reported in Figure 11. to the following, corrected version: However, the results in [26] also show the consistent increase in the initiation voltage of prebreakdown phenomena in both polarities, as reported in Figure 11. iii. On the last paragraph of page 10, the third sentence should be changed from: Even though the existing hypotheses of the dielectric effect of NPs [8–10] were proposed for blunter electrodes (where charge generation before streamer initiation is less important [30]), they should still apply under the experimental conditions here reported. to the following, corrected version: Even though the existing hypotheses of the dielectric effect of NPs [5,6,16] were proposed for blunter electrodes (where charge generation before streamer initiation is less important [30]), they should still apply under the experimental conditions here reported. The authors would like to apologize for any inconvenience caused to the readers by these changes. The changes do not affect the scientific results. The manuscript will be updated and the original will remain online on the article webpage, with a reference to this Correction.

  • 13.
    Aljure, Mauricio
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Becerra Garcia, Marley
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. ABB Corp Res, Vasteras, Sweden..
    Karlsson, Mattias E.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH).
    On the injection and generation of charge carriers in mineral oil under high electric fields2019Ingår i: JOURNAL OF PHYSICS COMMUNICATIONS, ISSN 2399-6528, Vol. 3, nr 3, artikel-id UNSP 035019Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Charge injection and generation mechanisms under intense electric fields (up to 10(9)Vm(-1)) in mineral oil are assessed experimentally and numerically. For this, current-voltage characteristics under positive and negative polarities are measured in a needle-plane configuration using sharp needles (with tip radius R-tip <= 1.1 mu m). In addition, a state of the art electro-hydrodynamic (EHD) model is implemented to calculate the contribution of the different mechanisms on the high-field conduction currents in the liquid. In order to evaluate exclusively the contribution of field emission, experiments are also performed in vacuum. It is found that neither field emission nor field ionisation can explain the conduction currents measured in mineral oil. It is proposed that field molecular ionisation, as described by Zener tunnelling model for solids, and electron impact ionisation are the processes dominating the generation of excess electron-ion pairs in mineral oil under positive and negative polarity, respectively. It is also shown that Zener molecular ionisation alone grossly overestimates the measured currents when parameters previously suggested in the literature for mineral oil are used. Preliminary model parameters for these mechanisms that best fit the conduction currents measured in mineral oil are presented and discussed.

  • 14.
    Aljure, Mauricio
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Becerra Garcia, Marley
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Karlsson, Mattias E.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi, Polymera material.
    Streamer Inception from Ultra-Sharp Needles in Mineral Oil Based Nanofluids2018Ingår i: Energies, E-ISSN 1996-1073, Vol. 11, nr 8, artikel-id 2064Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Positive and negative streamer inception voltages from ultra-sharp needle tips (with tip radii below 0.5 m) are measured in TiO2, SiO2, Al2O3, ZnO and C-60 nanofluids. The experiments are performed at several concentrations of nanoparticles dispersed in mineral oil. It is found that nanoparticles influence positive and negative streamers in different ways. TiO2, SiO2 and Al2O3 nanoparticles increase the positive streamer inception voltage only, whilst ZnO and C-60 nanoparticles augment the streamer inception voltages in both polarities. Using these results, the main hypotheses explaining the improvement in the dielectric strength of the host oil due to the presence of nanoparticles are analyzed. It is found that the water adsorption hypothesis of nanoparticles is consistent with the increments in the reported positive streamer inception voltages. It is also shown that the hypothesis of nanoparticles reducing the electron velocity by hopping transport mechanisms fails to explain the results obtained for negative streamers. Finally, the hypothesis of nanoparticles attaching electrons according to their charging characteristics is found to be consistent with the results hereby presented on negative streamers.

  • 15.
    Aljure, Mauricio
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Becerra Garcia, Marley
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Pourrahimi, Amir Masoud
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
    Electric Conduction in Mineral Oil based ZnONanofluids under Intense Electric FieldsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    The electric conduction processes in mineral oil based ZnO–C18 nanofluids under intense electric fields are investigated. For this, conduction currents are measured usinga needle-plane electrode configuration. Furthermore, an electrohydrodynamic (EHD) model is used here to discuss the charge generation mechanisms and the electronic properties of the ZnO–C18 nanofluids. The analysis of the conduction currents shows that ZnO–C18 nanoparticles increase the generation of charge carriers, and at the same time they augment the scavenging of quasi-free electrons compared with the measurements with mineral oil only. It is found that the existing nanoparticle electron scavenging model reported in the literature grossly underestimates the electron scavenging process here reported. A new analytical formulation for the nanoparticle electron scavenging process is proposed. The EHD model is also used to simulate the electric conduction processes just before negative streamer inception in mineral oil and ZnO–C18 nanofluids. It is shown that ZnO–C18 nanoparticles hinder the streamer initiation process by reducing the effective electric field at the tip of the needle. This electric field reduction is caused by the combined effect of the generation of charge carriers and the electron scavenging of ZnO–C18 nanoparticles.

  • 16.
    Amendola, Giandomenico
    et al.
    Univ Calabria, Dipartimento Ingn Informat Modellist Elettron & Si, I-87036 Arcavacata Di Rende, CS, Italy..
    Cavallo, Daniele
    Delft Univ Technol, Fac Elect Engn Math & Comp Sci, Dept Microelect, NL-2628 CD Delft, Netherlands..
    Chaloun, Tobias
    Ulm Univ, Inst Microwave Engn, D-89081 Ulm, Germany..
    Defrance, Nicolas
    Univ Lille, Univ Polytech Hauts de France, IEMN Inst Elect Microelect & Nanotechnol, CNRS,Cent Lille, F-59000 Lille, France..
    Goussetis, George
    Heriot Watt Univ, Inst Sensors Signals & Syst, Sch Engn & Phys Sci, Edinburgh EH14 4AS, Scotland..
    Margalef-Rovira, Marc
    Univ Lille, Univ Polytech Hauts de France, IEMN Inst Elect Microelect & Nanotechnol, CNRS,Cent Lille, F-59000 Lille, France..
    Martini, Enrica
    Univ Siena, Dept Informat Engn & Math, I-53100 Siena, Italy..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Valenta, Vaclav
    European Space Agcy, European Space Res & Technol Ctr, NL-2201 AZ Noordwijk, Netherlands..
    Fonseca, Nelson J. G.
    European Space Agcy, Antenna & Submillimeter Waves Sect, NL-2200 AG Noordwijk, Netherlands..
    Ettorre, Mauro
    Univ Rennes, CNRS, IETR, F-35000 Rennes, France..
    Low-Earth Orbit User Segment in the Ku and Ka-Band2023Ingår i: IEEE Microwave Magazine, ISSN 1527-3342, E-ISSN 1557-9581, Vol. 24, nr 2, s. 32-48Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Low-Earth orbit (LEO) constellations are revolutionizing the world of satellite communication (Satcom), providing new opportunities to manufacturers and operators and enabling innovative and attractive services to users.

  • 17.
    Amizhtan, S. K.
    et al.
    Indian Inst Technol Madras IIT Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Amalanathan, A. J.
    Indian Inst Technol Madras IIT Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Babu, Myneni Sukesh
    Indian Inst Technol Madras IIT Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Sarathi, R.
    Indian Inst Technol Madras IIT Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Kumar, Ganesh
    Indian Inst Technol Madras IIT Madras, Dept Ocean Engn, Chennai 600036, Tamil Nadu, India..
    Sangwai, Jitendra S.
    Edin, Hans Ezz
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Taylor, Nathaniel
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Experimental Study and ANN Analysis of Rheological Behavior of Mineral Oil-Based SiO2 Nanofluids2022Ingår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 29, nr 3, s. 956-964Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work reports an experimental and theoretical analysis of the rheological properties of mineral oil-based SiO2 nanofluid for their potential applications in transformer insulation. The flow electrification mechanism on the nanofluids with different surfactants such as cetyl trimethyl ammonium bromide (CTAB), oleic acid, and Span 80 is studied using a spinning disk technique. The results show a higher streaming current for the nanofluids with CTAB as a surfactant compared to oleic acid and Span 80. The rheological behavior of nanofluids is explored with the double gap concentric cylinder geometry. The variation of shear stress with shear rate follows a power law relationship along with a yield stress observed for all the nanofluids. A transition is seen from storage modulus to dominant loss modulus for the nanofluids during the frequency sweep analysis, whereas no transition is observed in the case of mineral oil. In addition, regression analysis using artificial neural network (ANN) algorithms are performed on the experimentally measured viscosity of the nanofluids in order to estimate theoretical parameters and provide insights into the streaming current formation. The desirable rheological characteristics of nanofluids are identified for achieving enhanced insulation performance in transformers.

  • 18.
    Amizhtan, S. K.
    et al.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Amalanathan, A. J.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Sarathi, R.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Edin, Hans Ezz
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Taylor, Nathaniel
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Impact of Magnetic Field on Corona Discharge Behavior of Mineral Oil Under AC Voltage2022Ingår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 29, nr 4, s. 1417-1424Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article reports an experimental investigation of the impact of magnetic field on corona discharge activity in mineral oil, using both ultrahigh-frequency (UHF) and fluorescence techniques under ac voltage. The results show that corona inception voltage (CIV) increased under ac voltage with varying harmonic frequencies without considering any phase shift and reduced marginally under magnetic field. In addition, the impact of the magnetic field shifted the dominating frequency of the UHF signal (0.9 GHz) obtained under ac voltage toward lower frequencies (0.3 and 0.6 GHz). Under high magnetic fields, the parameters such as rise time, fall time, and pulsewidth of the fluorescence signal increased in its magnitude compared to its effect without a magnetic field. Also, using both the UHF sensor and the fluorescence sensor, there was no clear difference in the phase-resolved partial discharge (PRPD) pattern caused by corona discharge (with and without magnetic field). Furthermore, the number of discharges is observed to be high under the impact of harmonic ac voltages with third- and seventh-order containing total harmonic distortions (THDs) of 4% and 40%.

  • 19.
    Amizhtan, S. K.
    et al.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Amalanathan, A. J.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Sarathi, R.
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Srinivasan, Balaji
    Indian Inst Technol Madras, Dept Elect Engn, Chennai 600036, Tamil Nadu, India..
    Gardas, Ramesh L.
    Indian Inst Technol Madras, Dept Chem, Chennai 600036, Tamil Nadu, India..
    Edin, Hans Ezz
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Taylor, Nathaniel
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Impact of Surfactants on the Electrical and Rheological Aspects of Silica Based Synthetic Ester Nanofluids2022Ingår i: IEEE Access, E-ISSN 2169-3536, Vol. 10, s. 18192-18200Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study reports experimental investigations of the effects of different surfactants (CTAB, Oleic acid and Span 80) on silica based synthetic ester nanofluids. The positive and negative potential observed for the ionic (CTAB) and non-ionic surfactant (Span 80) from zeta potential analysis indicates an improved stability. The optimization of nanofillers and surfactants is performed considering the corona inception voltage measured using ultra high frequency (UHF) technique and fluorescent fiber. Rheological analysis shows no significant variation of properties with shear rate, implying Newtonian behavior even with the addition of surfactant. In addition, the permittivity of the nanofluid is not much affected by adding surfactant but a marginal variation is noticed in the loss tangent with the effect of temperature. The fluorescence spectroscopy shows no change in the emission wavelength with the addition of silica nanofiller and surfactants. Flow electrification studies indicate an increase in the streaming current with the rotation speed and temperature, with a higher current magnitude observed in the case of nanofluids.

  • 20.
    Ao, Xianyu
    et al.
    South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China..
    Xu, Xinan
    South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China..
    Dong, Jinwu
    South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China..
    He, Sailing
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. South China Normal Univ, South China Acad Adv Optoelect, Ctr Opt & Electromagnet Res, Guangzhou 510006, Guangdong, Peoples R China.;Zhejiang Univ, Natl Engn Res Ctr Opt Instruments, Ctr Opt & Electromagnet Res, JORCEP, Hangzhou 310058, Zhejiang, Peoples R China..
    Unidirectional Enhanced Emission from 2D Monolayer Suspended by Dielectric Pillar Array2018Ingår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, nr 41, s. 34817-34821Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Monolayers of transition metal dichalcogenides show great promise for optoelectronic devices as atomically thin semiconductors. Although dielectric or metal nanostructures have been extensively studied for tailoring and enhancing emission from monolayers, their applications are limited because of the mode concentrating inside the dielectric or the high optical losses in metals, together with the low quantum yield in monolayers. Here, we demonstrate that a metal-backed dielectric pillar array can suspend monolayers to increase the radiative recombination, and simultaneously, create strongly confined band-edge modes on surface directly accessible to monolayers. We observe unidirectional enhanced emission from WSe2 monolayers on polymer pillar array.

  • 21.
    Ariza, David
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Beroual, Abderrahmane
    Methling, Ralf
    Gortschakow, Sergey
    Chamorro Vera, Harold Rene
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik.
    Electrical Conduction Currents Prior to Negative Streamer Inception in Mineral-Oil/Solid Interfaces2021Ingår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 28, s. 1300-1307Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper is an experimental study of the electrical conduction of mineral-oil/solid interfaces in negative polarity. This study is performed in a point-plane configuration immersed in mineral oil submitted to impulse voltages. The interface is assembled with an inclined solid in contact with the point electrode tip. Charge recordings and conduction currents of different combinations of mineral-oil/solid interfaces are reported. Different polymers and oil-impregnated papers are used as the solid materials. It is found that for voltages lower than the inception voltage, the injection of charge belongs to a weak injection regime. The spatial limitation with solids of similar permittivity as the mineral oil decreases the charge injection. The charge injection at mineral-oil/solid interfaces follow two conduction current type characteristics. Experiments with mineral-oil/PTFE interface shows the existence of a transition between both conduction current types if the applied voltage is increased.

  • 22.
    Ariza Rocha, Oscar David
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Dynamic transformers rating for expansion of expansion of existing wind farms2019Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Eldistributionsnätet står inför en utmaning att snabbt ansluta användare till nätet och en möjlighet att miska kostnaderna i nya ansultnigar. En metod för att förbättra nätverksdrift och planering är dynamisk lastbarhet hos transformatorer, eller dynamic transformer rating (DTR). Metoden beaktar belastings- och temperaturvariationer för att öka transformatorns lastbarhet samtidigt som den upprätthåller säker drift.

    Detta projekt undersöker tillämpningen av dynamisk lastbarhet till en befintling population av transformatorer kopplade till en vindkraftpark och föreslår en metod för att ansluta ytterligare turbiner till nätet med hjälp av befintliga transformatorer. Fem transformatorplatser och nio enheter som tillhör E.ON AB används för att undersöka potentialen för DTR inom tillämpningar för nätverksexpansion.

    En vänderanalysis avslöhar att både höga vindhastigheter och temperaturer sällan uppstår samtidigt. En uppskattning av åldrandet baserad på IEC 60076-7-standarden visar att transformatorer för vindkraftstillämpningar är underanvända. Med avseende på den termisk transformatormodellen visar en känslighetsanalys att parametrarna som påverkar minskning av livslängden mest är fuktinnehållet, hot spot-faktorn och ökning av top-olja-temperaturen. Den maximala belastningen för att säkerställa en åldring under 50 år beräknas för varje transformator, för olika värden på den maximala hotspottemperaturen. Detta visar att med ökning av den maximala tillåtna temperaturen minskar produktionsbortfall och ökar åldrandet.

    En-nods-analys visar den optimala expansionen av vindkraft från en producents perspektiv, och en nätverksanalys introducerar ytterligare begränsningar för nätverket. Detta resulterar i en optimal ökningsfaktor på cirka 30-50% och är större för högre värden på den maximala hotspottemperaturen.

    Noggranna vädermätningar och transformatorparametrar är nödvändiga för att göra en korrekt uppskattning av transformatorns åldrande. Att använda fiberoptiska temperatursensorer i nya transformatorer och platsspecifika temperaturmätningar kan öka transformatorns lastbarhet. En maximal tillåten temperatur på 110 ◦C är för konservativ och begränsar transformatorns potential för vindkraftstillämpningar. Samhället drar fördel av DTR i vindkraftstillämpningar eftersom det leder till en effektivare resursanvändning och att ytterligare förnybar energi kan introduceras i nätverket.

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  • 23.
    Ariza Rocha, Oscar David
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS). ABB Power Grids Research.
    Morozovska, Kateryna
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Laneryd, Tor
    ABB Power Grids Research.
    Ivarsson, Ola
    E.ON Energidistribution AB.
    Ahlrot, Claes
    E.ON Energidistribution AB.
    Hilber, Patrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Dynamic rating assists cost-effective expansion of wind farms by utilizing the hidden capacity of transformers2020Ingår i: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 123, artikel-id 106188Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dynamic rating of power transmission devices is a technology that allows better equipment utilization through real-time monitoring of the weather conditions and the load. Dynamic rating of transformers is a fairly new technology if compared to the dynamic rating of power lines, and has a high potential for significantly improving component utilization while lowering investment costs on installing new transformers.

    The following work investigates how to utilize already operational transformers, which are used for wind farm connection, for expanding wind generation capacity. Also, this paper shows improvements that dynamic transformer rating can bring to both power grid operators and wind farm owners by exploring the economic benefits of expanding wind parks without investing in new power transformers. Connecting additional wind turbines at sites with high wind potential after the wind park is already in exploitation can assist in lowering electricity price and provide a possibility of less risky investment in the wind energy sector. This paper uses transformer thermal modelling and wind farm expansion techniques such as convolution method and product method to investigate to which extent existing wind farms can be expanded using already installed transformer units.

    Five transformer locations and nine units are studied for finding the potential of dynamic transformer rating for network expansion applications. The analysis shows that the optimal expansion of wind power from a generator perspective is around 30%" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 16.2px; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">% to 50%" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 16.2px; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">%, although, it can be limited further by network restrictions. A possibility to use a large component, such as power transformer, closer to its full potential can provide material and cost savings for building new devices and decrease investment costs on manufacturing, transportation and installation of new units. Dynamic rating of power transformers can also increase the socio-economic benefits of renewable energy by lowering electricity price from renewables and incentivize an increased share of green power in electricity markets.

    Ladda ner fulltext (pdf)
    Dynamic rating for wind power
  • 24.
    Ariza Rocha, Oscar David
    et al.
    ABB Corporate Research, Västerås, Sweden. E.ON. Energidistribution AB, Malmö, Sweden.
    Morozovska, Kateryna
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Laneryd, Tor
    ABB Corporate Research.
    Ivarsson, Ola
    E.ON. Energidistribution AB, .
    Ahlrot, Claes
    E.ON. Energidistribution AB, .
    Hilber, Patrik
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Dynamic rating assists cost-effective expansion of wind farms byutilizing hidden capacity of transformersManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Dynamic rating of power transmission devices is a technology that allows better equipment utilization through real-time information about the system state. Dynamic rating of transformers is a fairly new technology if compared to dynamic rating of power lines, and has high potential for significantly improving component utilization while lowering investment costs on installing new transformers.

    Dynamic transformer rating increases the rating of the transformer considering load and temperature variations without affecting safe operation. Dynamic rating is highly suitable for being used in conjunction with renewable energy generation, specifically wind power. The following work investigates how to utilize existing transformers, which are under exploitation at wind farms, for expanding wind generation capacity. Also, this paper shows improvements that dynamic rating can bring to both power grid operators and wind farm owners by exploring the economic benefits of expanding wind parks while using dynamic rating. Connecting additional wind turbines with the same transformer at sites with high wind capacity after the wind park is already in exploitation can assist in lowering electricity price and provide a possibility of less risky investment in wind power.

    Five transformer locations and nine units are studied for finding the potential of dynamic transformer rating for network expansion applications. The analysis shows that the optimal expansion of wind power from a generator perspective is around 30 % to 50 %, although, it can be limited further by network restrictions. A possibility to use a large device, suchas power transformer, closer to its full potential can provide material and cost savings for building new devices and decrease investment costs on manufacturing, transportation and installation of new units. Dynamic rating of power transformers can also increase the socio-economic benefits of renewable energy by lowering electricity price from renewables and incentivize an increased share of green power in electricity markets.

    Ladda ner fulltext (pdf)
    fulltext
  • 25.
    Arnberg, Philip
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Petersson, Oscar Barreira
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Dahlberg, Oskar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Ghasemifard, Fatemeh
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    High Refractive Index Electromagnetic Devices in Printed Technology Based on Glide-Symmetric Periodic Structures2020Ingår i: Applied Sciences, E-ISSN 2076-3417, Vol. 10, nr 9, artikel-id 3216Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate the beneficial effects of introducing glide symmetry in a two-dimensional periodic structure. Specifically, we investigate dielectric parallel plate waveguides periodically loaded with Jerusalem cross slots in three configurations: conventional, mirror- and glide-symmetric. Out of these three configurations, it is demonstrated that the glide-symmetric structure is the least dispersive and has the most isotropic response. Furthermore, the glide-symmetric structure provides the highest effective refractive index, which enables the realization of a broader range of electromagnetic devices. To illustrate the potential of this glide-symmetric unit cell, a Maxwell fish-eye lens is designed to operate at 5 GHz. The lens is manufactured in printed circuit board technology. Simulations and measurements are in good agreement and a measured peak transmission coefficient of -0.5 dB is achieved.

  • 26.
    Augustin, Tim
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Becerra Garcia, Marley
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Magnusson, Jesper
    ABB Corporate Research, Västerås.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Parekh, Mrunal
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    System Design of Fast Actuator for Vacuum Interrupter in DC Applications2018Ingår i: 2018 28th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), Institute of Electrical and Electronics Engineers (IEEE), 2018, Vol. 2, s. 527-530Konferensbidrag (Refereegranskat)
    Abstract [en]

    One of the major challenges of DC circuit breakers is the required fast mechanical actuator. In this paper, a Thomson coil actuator system for a vacuum interrupter is designed. Active damping is used to decelerate the moving contacts. Challenges are discussed, especially concerning the power supply needed for the Thomson coil actuator. The design philosophy is explained and FEM simulation results are presented. The results indicate that a wide range of combinations of drive circuit capacitance and voltage fulfill the requirements for armature acceleration. However, active damping requires a very careful selection of drive circuit voltage and timing of applied damping.

    Ladda ner fulltext (pdf)
    fulltext
  • 27.
    Augustin, Tim
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Becerra Garcia, Marley
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Advanced Test Circuit for DC Circuit Breakers2018Ingår i: 20th European Conference on Power Electronics and Applications (EPE'18 ECCE EUROPE), 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    In future HVDC systems, many DC circuit breakers (DCCBs) will be required. In this paper, an advanced test circuit for DCCBs is described. A DC source is combined with a capacitor bank. In contrast to other test circuits, the proposed test circuit allows to replicate constant DC and temporary faults. In addition to conventional faults, this enables testing of auto-reclosing, proactive commutation, and complex test sequences combining all of these modes. The test circuit is easy to setup and also suitable for smaller research facilities. Experimental results from a down-scaled mock-up are included to demonstrate the capabilities of the test circuit.

    Ladda ner fulltext (pdf)
    fulltext
  • 28.
    Augustin, Tim
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Becerra Garcia, Marley
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. ABB Corporate Research, Västerås, Sweden.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Enhanced Active Resonant DC Circuit Breakers Based on Discharge Closing Switches2021Ingår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 36, nr 3, s. 1735-1743Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Direct current circuit breakers (DCCBs) have become a large research topic and are considered one of the critical components for future DC grids. Proposed DCCB concepts may be grouped into hybrid DCCBs and active resonant DCCBs. In this work, the enhanced active resonant (EAR) DCCB family is introduced. EAR DCCBs combine elements of hybrid and active resonant DCCBs. The EAR DCCB family consists of one unidirectional and six bidirectional concepts. All concepts feature proactive commutation. The main characteristic of the EAR DCCBs is that discharge closing switches are used instead of semiconductors with turn-off capability. Relevant discharge closing switch technology is reviewed, a laboratory prototype is explained, and experimental results are presented to demonstrate the feasibility of the proposed DCCB concepts.

    Ladda ner fulltext (pdf)
    fulltext
  • 29.
    Augustin, Tim
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Becerra Garcia, Marley
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. ABB.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Experimental Study of Enhanced Active Resonant DC Circuit Breakers2022Ingår i: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 37, nr 5, s. 5687-5698Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Enhanced active resonant (EAR) dc circuit breakers (DCCBs) are a novel type of DCCB that use a discharge closing switch as interruption medium. A technical limitation of discharge closing switches is the minimum voltage across the main gap required for successful triggering. A novel commutation process creating the minimum voltage internally is proposed, which allows to simplify the EAR DCCB configuration and to reduce its component count. In the prototype, the discharge closing switch is implemented with a TVG. Experiments show that the TVG can be triggered reliably down to a voltage of 50 V and that the discharge in the TVG is highly oscillatory at low current. The originally proposed EAR DCCB configuration has to be tuned such that the commutation to the TVG succeeds at low current. Conversely, the novel commutation process decouples the minimum voltage from the current level by adjusting the triggering delay. This allows reliable commutation irrespective of the operating conditions. It is shown that the novel commutation process does not adversely affect dc interruption. Proactive commutation operation and auto-reclosing strategies are demonstrated.

    Ladda ner fulltext (pdf)
    fulltext
  • 30.
    Augustin, Tim
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Parekh, Mrunal
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Magnusson, Jesper
    ABB.
    Becerra Garcia, Marley
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. ABB.
    Nee, Hans-Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elkraftteknik.
    Thomson-Coil Actuator System for Enhanced Active Resonant DC Circuit Breakers2022Ingår i: IEEE Journal of Emerging and Selected Topics in Power Electronics, ISSN 2168-6777, E-ISSN 2168-6785, Vol. 10, nr 1, s. 800-810Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Enhanced active resonant (EAR) dc circuit breakers (DCCBs) are a promising set of recently proposed DCCB concepts. As other DCCBs, EAR DCCBs still require a fast mechanical switch. The requirements on the actuator of the mechanical switch depend on the DCCB concept and the dc grid and are derived here for an EAR DCCB. Thomson-coil actuators (TCAs) can open and close mechanical switches sufficiently fast to satisfy the requirements. This work studies experimentally a TCA system with active damping for an off-the-shelf industrial vacuum interrupter used as mechanical switch in an EAR DCCB. The prototype is explained in detail, and extensive measurement results are presented, showing that active damping must be perfectly timed to be effective. A novel Thomson-coil (TC) driver is proposed and studied experimentally, which operates the TCA more efficiently by recycling energy during the actuation. Moreover, the novel TC driver reduces the capacitive storage by 50% and allows for faster recharging with lower charging current. Finally, the autoreclosing and proactive commutation operation of the TCA system and the interruption capability of the prototype EAR DCCB are demonstrated experimentally.

    Ladda ner fulltext (pdf)
    fulltext
  • 31.
    Avula, Ramana R.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Teknisk informationsvetenskap.
    Chin, Jun-Xing
    Power Systems Laboratory, ETH Zurich, Switzerland.
    Oechtering, Tobias J.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Teknisk informationsvetenskap.
    Hug, Gabriela
    Power Systems Laboratory, ETH Zurich, Switzerland.
    Månsson, Daniel
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Design Framework for Privacy-Aware Demand-Side Management with Realistic Energy Storage Model2021Ingår i: IEEE Transactions on Smart Grid, ISSN 1949-3053, E-ISSN 1949-3061, Vol. 12, nr 4, s. 3503-3513Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Demand-side management (DSM) is a process by which the user demand patterns are modified to meet certain desired objectives. Traditionally, DSM was utility-driven, but with an increase in the integration of renewable sources and privacy-conscious consumers, it also becomes a “consumer-driven" process. Promising theoretical studies have shown that privacy can be achieved by shaping the user demand using an energy storage system (ESS). In this paper, we present a framework for utility-driven DSM while considering the user privacy and the ESS operational cost due to its energy losses and capacity degradation. We propose an ESS model using a circuit-based and data-driven approach that can be used to capture the ESS characteristics in control strategy designs. We measure privacy leakage using the Bayesian risk of a hypothesis testing adversary and present a novel recursive algorithm to compute the optimal privacy control strategy. Further, we design an energy-flow control strategy that achieves the Pareto-optimal trade-off between privacy leakage, deviation of demand from a DSM target profile, and the ESS cost. With numerical experiments using real household data and an emulated lithium-ion battery, we show that the desired level of privacy and demand shaping performance can be achieved while reducing the ESS degradation.

    Ladda ner fulltext (pdf)
    fulltext
  • 32.
    Avula, Ramana R.
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Teknisk informationsvetenskap.
    Oechtering, Tobias J.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Intelligenta system, Teknisk informationsvetenskap.
    Månsson, Daniel
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Privacy-preserving smart meter control strategy including energy storage losses2018Ingår i: Proceedings - 2018 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, artikel-id 8571537Konferensbidrag (Refereegranskat)
    Abstract [en]

    Privacy-preserving smart meter control strategies proposed in the literature so far make some ideal assumptions such as instantaneous control without delay, lossless energy storage systems etc. In this paper, we present a one-step-ahead predictive control strategy using Bayesian risk to measure and control privacy leakage with an energy storage system. The controller estimates energy state using a three-circuit energy storage model to account for steady-state energy losses. With numerical experiments, the controller is evaluated with real household consumption data using a state-of-the-art adversarial algorithm. Results show that the state estimation of the energy storage system significantly affects the controller's performance. The results also show that the privacy leakage can be effectively reduced using an energy storage system but at the expense of energy loss.

    Ladda ner fulltext (pdf)
    fulltext
  • 33.
    Bagheriasl, Mohammad
    et al.
    Sorbonne Univ, L2E, UR2, F-75005 Paris, France..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Valerio, Guido
    Sorbonne Univ, L2E, UR2, F-75005 Paris, France..
    Bloch Analysis of Artificial Lines and Surfaces Exhibiting Glide Symmetry2019Ingår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 67, nr 7, s. 2618-2628Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Glide-symmetric structures have recently emerged as a smart choice to design planar lenses and electromagnetic bandgap materials. We discuss here the conditions under which a glide-symmetric structure is equivalent to a nonglide-symmetric structure with a reduced period. To this aim, we propose an analysis method based on network theory to efficiently derive the dispersive behavior of these periodic structures. Both phase and attenuation constants can be determined, with potential applications to both guiding and radiating structures. Retaining higher order modal interactions among cells helps to derive the dispersive behavior of periodic structures more accurately. Furthermore, we take advantage of the higher symmetry of these structures to decrease the computational cost by considering only one half or one-quarter of a unit cell instead of the entire cell. We study one and 2-D glide-symmetric structures and confirm the validity of our analysis with comparisons from commercial software.

  • 34. Bangalore, P.
    et al.
    Letzgus, S.
    Patriksson, M.
    Bertling, Lina
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Analysis of SCADA data for early fault detection with application to the maintenance management of wind turbines2016Ingår i: CIGRE Session 46, CIGRE , 2016, s. 1-10Konferensbidrag (Refereegranskat)
    Abstract [en]

    During the past decade wind turbines have proven to be a promising source of renewable power. Wind turbines are generally placed in remote locations and are subject to harsh environmental conditions throughout their lifetimes. Consequently, the failures in wind turbines are expensive to repair and cause loss of revenue due to long down times. Asset management in wind turbines can aid in assessing and improving the reliability and availability of wind turbines, thereby making them more competitive. Maintenance policies play an important role in asset management and different maintenance models have been developed for wind turbine applications. Typically, mathematical models for maintenance optimization provide either an age based or a condition based preventive maintenance schedule. Age based preventive maintenance schedules provide the owner with the possibility to financially plan for maintenance activities for the entire lifetime of the wind turbine by providing the expected number of replacements for each component. However, age based preventive maintenance schedule may not consume the operating life of the wind turbine components to the maximum. Condition based maintenance scheduling has the advantage of better utilizing the operating life of the components. This paper proposes a wind turbine maintenance management framework which utilizes operation and maintenance data from different sources to combine the benefits of age based and condition based maintenance scheduling. This paper also presents an artificial neural network (ANN) based condition monitoring method which utilizes data from supervisory control and data acquisition (SCADA) system to detect failures in wind turbine components and systems. The procedures to construct ANN models for condition monitoring application are outlined. In order to demonstrate the effectiveness of the ANN based condition monitoring method it is applied to case studies from real wind turbines. Furthermore, a mathematical model called preventive maintenance schedule with interval costs (PMSPIC) is discussed and its application to a case study within the maintenance management framework is presented. The case study demonstrates the advantage of combining both the age based and condition based maintenance scheduling methods. 

  • 35. Bantavis, P. I.
    et al.
    Kolitsidas, Christos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Empliouk, T.
    Le Roy, M.
    Jonsson, B. Lars G.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Kyriacou, G. A.
    A Cost-Effective Wideband Switched Beam Antenna System for a Small Cell Base Station2018Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 66, nr 12, s. 6851-6861, artikel-id 8485638Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A wideband switched beam antenna array system operating from 2 to 5 GHz is presented. It is comprised of a 4 × 1 Vivaldi antenna elements and a 4 × 4 Butler matrix beamformer driven by a digitally controlled double-pole four-throw RF switch. The Butler matrix is implemented on a multilayer structure, using 90° hybrid couplers and 45° phase shifters. For the design of the coupler and phase shifter, we propose a unified methodology applied, but not limited, to elliptically shaped geometries. The multilayer realization enables us to avoid microstrip crossing and supports wideband operation of the beamforming network. To realize the Butler matrix, we introduce a step-by-step and stage-by-stage design methodology that enables accurate balance of the output weights at the antenna ports to achieve a stable beamforming performance. In this paper, we use a Vivaldi antenna element in a linear four-element array, since such element supports wideband and wide-scan angle operation. A soft condition in the form of corrugations is implemented around the periphery of the array, in order to reduce the edge effects. This technique improved the gain, the sidelobes, and helped to obtain back radiation suppression. Finally, impedance loading was also utilized in the two edge elements of the array to improve the active impedance. The proposed system of the Butler matrix in conjunction with the constructed array can be utilized as a common RF front end in a wideband air interface for a small cell 5G application and beyond as it is capable to simultaneously cover all the commercial bands from 2 to 5 GHz.

  • 36.
    Bao, Fanglin
    et al.
    South China Normal Univ, Ctr Opt & Electromagnet Res, Guangdong Prov Key Lab Opt Informat Mat & Technol, South China Acad Adv Optoelect, Guangzhou 510006, Guangdong, Peoples R China..
    Shi, Kezhang
    Zhejiang Univ, Natl Engn Res Ctr Opt Instrumentat, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res,JORCEP,Coll Opt Sci &, Hangzhou 310058, Zhejiang, Peoples R China..
    Cao, Guanjun
    South China Normal Univ, Ctr Opt & Electromagnet Res, Guangdong Prov Key Lab Opt Informat Mat & Technol, South China Acad Adv Optoelect, Guangzhou 510006, Guangdong, Peoples R China..
    Evans, Julian S.
    Zhejiang Univ, Natl Engn Res Ctr Opt Instrumentat, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res,JORCEP,Coll Opt Sci &, Hangzhou 310058, Zhejiang, Peoples R China..
    He, Sailing
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. South China Normal Univ, Ctr Opt & Electromagnet Res, Guangdong Prov Key Lab Opt Informat Mat & Technol, South China Acad Adv Optoelect, Guangzhou 510006, Guangdong, Peoples R China.;Zhejiang Univ, Natl Engn Res Ctr Opt Instrumentat, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res,JORCEP,Coll Opt Sci &, Hangzhou 310058, Zhejiang, Peoples R China.
    Inhomogeneity-Induced Casimir Transport of Nanoparticles2018Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, nr 13, artikel-id 130401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a scheme for transporting nanoparticles immersed in a fluid, relying on quantum vacuum fluctuations. The mechanism lies in the inhomogeneity-induced lateral Casimir force between a nanoparticle and a gradient metasurface and the relaxation of the conventional Dzyaloshinskii-Lifshitz-Pitaevskii constraint, which allows quantum levitation for a broader class of material configurations. The velocity for a nanosphere levitated above a grating is calculated and can be up to a few microns per minute. The Born approximation gives general expressions for the Casimir energy which reveal size-selective transport. For any given metasurface, a certain particle-metasurface separation exists where the transport velocity peaks, forming a "Casimir passage." The sign and strength of the Casimir interactions can be tuned by the shapes of liquid-air menisci, potentially allowing real-time control of an otherwise passive force, and enabling interesting on-off or directional switching of the transport process.

  • 37.
    Becerra Garcia, Marley
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Aljure, Mauricio
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Nilsson, Janne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Assessing the production and loss of electrons from conduction currents in mineral oil2019Ingår i: 2019 IEEE 20th International Conference on Dielectric Liquids (ICDL), IEEE Computer Society, 2019Konferensbidrag (Refereegranskat)
    Abstract [en]

    The evaluation of the high-field generation and loss of charged carriers is a key step to simulate any prebreakdown process in a dielectric liquid. Currently, the electron generation in mineral oil has been widely described in terms of 'electric-field-dependent molecular ionization' and the electron loss is estimated using a fixed attachment time constant. This paper reports our next step towards the quantitative characterization of the production and loss of electrons in mineral oil. In this step, the electrical conduction measurements are performed in mineral oil for a needle-plane configuration (tip radius 3 μm) and submicrometric gap distances (ranging between 10 to 100 μm). Conduction currents in negative polarity are reported from 10-12 to 10-7A, from the ohmic to the space-charge limited regimes. In order to check the validity of existing simulation models for mineral oil, computer simulation is used to calculate the VI characteristic in the liquid considering electrohydrodynamic (EHD) motion. It is shown that the active zone where electrons are produced in front of the needle is around 10 μm long. Furthermore, it is found that electrons travel a similar distance before they attach into ions. It is also shown that the currents are grossly misestimated when parameters proposed in the literature to model generation and loss of electrons in mineral oil are used.

  • 38.
    Becerra Garcia, Marley
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Aljure, Mauricio
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. BioGRID Grupo de Investigación y Desarrollo en Ciencias, Tecnología e Innovación, SoPhiC Sociedad de Doctores e Investigadores de Colombia, Bogotá, Colombia.
    Pourrahimi, Amir Masoud
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Fiber- och polymerteknologi. Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Gothenburg, SE-412 96, Sweden.
    Roman, F.
    High field conduction in mineral oil based zno nanofluids prior to negative streamer inception2021Ingår i: Journal of Physics Communications, ISSN 2399-6528, Vol. 5, nr 4, artikel-id 045006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electric conduction under intense electric fields (up to ∼ 109 V/m) in nanofluids using surface-modified ZnO–C18 nanoparticles dispersed in mineral oil as host, is investigated with both experiments and numerical simulations. The measurements are used to estimate unknown parameters necessary to represent the generation and loss of electrons in an electrohydrodynamic model for mineral oil with and without ZnO–C18 nanoparticles in a needle-plane configuration. The model suggests that ZnO–C18 nanoparticles induce an enhanced field emission from negative needles, explaining the significantly larger conduction currents measured in the nanofluid compared with those in the host liquid. It is also found that the scavenging of electrons by ZnO–C18 nanoparticles is a process which is negligible compared with the loss of electrons due to attachment in mineral oil. It is shown that ZnO–C18 nanoparticles hinder the streamer initiation process by reducing the effective electric field at the tip of the needle. This electric field reduction is caused by the combined effect of enhanced electron injection through ZnO–C18 nanoparticles and strong electron attachment in mineral oil. Thus, the electric field on the needle tip reaches the same threshold value when the streamer is incepted in the nanofluid as in mineral oil, although at a larger voltage. Solid evidence indicating that the additional electron scavenging and the reduced electron mobility introduced by nanoparticles has no effect in the conduction currents and in the negative streamer inception in the tested ZnO–C18 nanofluids is shown.

  • 39.
    Becerra Garcia, Marley
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Long, Mengni
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Schulz, W.
    Thottappillil, Rajeev
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    On the estimation of the lightning incidence to offshore wind farms2018Ingår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 157, s. 211-226Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Field observations have shown that the frequency of dangerous lightning events to wind turbines, calculated according to the IEC standard 61400-24:2010, is grossly underestimated. This paper intends to critically revisit the evaluation of the incidence of downward lightning as well as self-initiated and other-triggered upward flashes to offshore wind power plants. Three different farms are used as case studies. The conditions for interception of stepped leaders in downward lightning and the initiation of upward lightning is evaluated with the Self-consistent Leader Inception and Propagation Model (SLIM). The analysis shows that only a small fraction of damages observed in the analysed farms can be attributed to downward lightning. It is also estimated that only a small fraction (less than 19%) of all active thunderstorms in the area of the analysed farms can generate sufficiently high thundercloud fields to self-initiate upward lightning. Furthermore, it is shown that upward flashes can be triggered even under low thundercloud fields once a sufficiently high electric field change is generated by a nearby lightning event. Despite of the uncertainties in the incidence evaluation, it is shown that upward flashes triggered by nearby positive cloud-to-ground flashes produce most of the dangerous lightning events to the case studies.

  • 40.
    Becerra Garcia, Marley
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Pettersson, Jonas
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Optical radiative properties of ablating polymers exposed to high-power arc plasmas2018Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, nr 12, artikel-id 125202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The radiative properties of polymers exposed to high-intensity radiation are of importance for the numerical simulation of arc-induced ablation. The paper investigates the optical properties of polymethylmethacrylate PMMA and polyamide PA6 films exposed to high-power arc plasmas, which can cause ablation of the material. A four-flux radiative approximation is first used to estimate absorption and scattering coefficients of the tested materials in the ultraviolet (UV) and in the visible (VIS) ranges from spectrophotometric measurements. The temperature-induced variation of the collimated transmissivity of the polymers is also measured from room temperature to the glass temperature of PMMA and the melting temperature of PA6. Furthermore, band-averaged absorption and scattering coefficients of non-ablating and ablating polymers are estimated from the UV to the short-wavelength infrared (SWIR), covering the range of interest for the simulation of arc-induced ablation. These estimates are obtained from collimated transmissivities measured with an additional in situ photometric system that uses a high-power, transient arc plasma to both illuminate the samples and to induce ablation. It is shown that the increase in the bulk temperature of PA6 leads to a strong reversible increase in collimated transmissivity, significantly reducing the absorption and scattering coefficients of the material. A weaker but opposite effect of temperature on the optical properties is found in PMMA. As a consequence, it is suggested that the absorption coefficient of polymers used for arc-induced ablation estimates should not be taken directly from direct collimated transmissivity measurements at room temperature. The band-averaged radiation measurements also show that the layer of products released by ablation of PMMA produces scattering radiation losses mainly in the VIS-SWIR ranges, which are only a small fraction of the total incident arc radiation. In a similar manner, the ablation layer of PA6 leads to weak absorption radiation losses, although mainly in the UV range.

  • 41.
    Becerra Garcia, Marley
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion. KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, S-10044 Stockholm, Sweden.;ABB Corp Res, S-72226 Vasteras, Sweden..
    Pettersson, Jonas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Franke, Steffen
    INP Leibniz Inst Plasma Sci & Technol, D-17489 Greifswald, Germany..
    Gortschakow, Sergey
    INP Leibniz Inst Plasma Sci & Technol, D-17489 Greifswald, Germany..
    Temperature and pressure profiles of an ablation-controlled arc plasma in air2019Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, nr 43, artikel-id 434003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experimental measurements of the spatial distribution of temperature and composition of ablation-controlled arc plasmas are a key to validate the predictions of metal evaporation and polymer ablation models. Thus, high-speed photography and space-resolved spectroscopic measurements have been performed to characterize a stable air arc plasma jet controlled by ablation of a polymer nozzle made of Polyoxymethylene copolymer (POM-C) or polyamide (PA6). The spectroscopic analysis is performed along a plane perpendicular to the arc jet axis for a current of 1.8 kA, corresponding to an estimated current density of similar to 65 A mm(-2). Temperature and partial pressure profiles of the plasma for copper, hydrogen and carbon in the gas mixture are estimated as an inverse optimization problem by using measured side-on radiance spectra and radiative transfer spectral simulations. It is shown that the generated ablation-controlled arc has a complicated, non-uniform gas composition. Thus, the generated arc jet has a thin metallic core with a lower almost constant hydrogen pressure, surrounded by a thicker hydrogen and carbon mantle at partial pressures slightly lower than atmospheric pressure. The separation of hydrogen and carbon in the core is a consequence of demixing of the polymer vapour in the plasma. It is found that the overall shape of the temperature and pressure profiles obtained for the arc plasmas with the POM-C and PA6 nozzles are similar although differ in peak values and width.

  • 42.
    Becerra Garcia, Marley
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Saba, M. M. F.
    Liu, Lige
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Visacro, S.
    Using low-level currents measured during lightning events to estimate upward leader properties2018Ingår i: 34th International Conference on Lightning Protection, ICLP 2018, Institute of Electrical and Electronics Engineers Inc. , 2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Low-level currents measured prior to return strokes can potentially provide information about the properties of upward leaders during lightning flashes. However, these currents need to be properly analysed and interpreted in order to be useful for evaluating upward connecting leaders. In this paper, low-level currents measured before return strokes in two lightning events to two structures in Brazil are analysed and interpreted as case studies. The discharge current estimated from one of these events is used as input to a detailed thermohydrodynamic model with an extensive kinetic scheme for N2/O2 mixtures. The model allows the evaluation of the physical and chemical properties of upward connecting leaders. Estimates of the temperature, mass density, electric field and radius of the channel are presented for an upward connecting leader propagating in a lightning event. In addition, estimates of the axial density of electrons, ions and neutral particles (including NO and NO2) are also reported.

  • 43.
    Bessman, Alexander
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik, Tillämpad elektrokemi.
    Soares, Rudi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Software documentation for current-rippleequipment2018Rapport (Övrig (populärvetenskap, debatt, mm))
    Ladda ner fulltext (pdf)
    fulltext
  • 44. Bissal, A.
    et al.
    Eriksson, A.
    Magnusson, Jesper
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Engdahl, G.
    Hybrid multi-physics modeling of an ultra-fast electro-mechanical actuator2015Ingår i: Actuators, ISSN 2076-0825, Vol. 4, nr 4, s. 314-335Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The challenges of an HVDC breaker are to generate impulsive forces in the order of hundreds of kilonewtons within fractions of a millisecond, to withstand the arising internal mechanical stresses and to transmit these forces via an electrically-insulating device to the contact system with minimum time delay. In this work, several models were developed with different levels of complexity, computation time and accuracy. Experiments were done with two mushroom-shaped armatures to validate the developed simulation models. It was concluded that although the electromagnetic force generation mechanism is highly sensitive to the mechanical response of the system, the developed first order hybrid model is able to predict the performance of the breaker with good accuracy.

  • 45.
    Björkqvist, Oskar
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Dahlberg, Oskar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Additive Manufactured Three Dimensional Luneburg Lens for Satellite Communications2019Ingår i: 13th European Conference on Antennas and Propagation, EuCAP 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, artikel-id 8739803Konferensbidrag (Refereegranskat)
    Abstract [en]

    A method for designing gradient refractive index (GRIN) lenses with additive manufacturing or 3D-printing at K-u band is presented. To demonstrate the potential of the method, we designed a Luneburg lens using a single low-loss dielectric material available for 3D-printers. The gradient index is realized by varying the local material fill density of the lens. We demonstrate with full wave simulations that the structure is able to transform a spherical electromagnetic wave to a plane wave. When the lens is fed with a rectangular waveguide, the overall antenna has a gain of 23 dBi with side lobe levels of -12.5 dB in K-u band. This lens, when integrated with a circular polarized feeding system, could find application for ground satellite communications.

  • 46.
    Björkqvist, Oskar
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Dahlberg, Oskar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Silver, Gustaf
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Kolitsidas, Christos
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Jonsson, B. Lars G.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Wireless Sensor Network Utilizing Radio-Frequency Energy Harvesting for Smart Building Applications2018Ingår i: IEEE Antennas & Propagation Magazine, ISSN 1045-9243, E-ISSN 1558-4143, Vol. 60, nr 5, s. 124-136Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The scope of this article is to develop a modular radio-frequency (RF) energy-harvesting system for smart buildings that can act as a power source for sensing devices. Electromagnetic field-strength measurements at the main campus of the KTH Royal Institute of Technology in Stockholm, Sweden, were carried out to define the strength of the available ambient signals. Mainly two spectra were available for possible RF harvesting, i.e., two cellular bands [GSM1800 and third generation (3G)] and the 2.45-GHz Wi-Fi band. Based on these measurements, a modular approach for the system was adopted. The system is composed from two modules: 1) a Wi-Fi rectenna system composed of eight dual-polarized patch antennas and 16 rectifiers to produce eight differential voltage sources connected in series and 2) a cellular rectenna system composed of eight linear tapered slot antennas and eight rectifiers to produce four differential voltage sources connected in series. We propose an innovative multiple-input, single-output (MISO) wave rectifier that yields an efficient differential output. Both rectenna modules offer full azimuthal coverage and can operate either together or independently.

  • 47.
    Björkqvist, Oskar
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Zetterström, Oskar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Additive manufactured dielectric Gutman lens2019Ingår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 55, nr 25, s. 1318-1320Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this Letter, the design of a 3D printed fully dielectric Gutman lens is presented. The authors demonstrate the feasibility of using highly accessible and cheap additive manufacturing technology to produce a compact and high performing antenna lens. The lens is designed to operate at Ku band and utilises a flat feed surface that approximates the focal sphere. The flat feed surface allows for beam steering that requires only translational movement of the feed. The lens has a measured realised gain of 20 dBi with 3 dB scan loss at +45°. The lens finds applications in systems that require high gain antennas, such as the new generation of satellite and 5G communications and radar technology.

  • 48. Boriratrit, Sarunyoo
    et al.
    Fuangfoo, Pradit
    Srithapon, Chitchai
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Chatthaworn, Rongrit
    Adaptive Meta-Learning Extreme Learning Machine with Golden Eagle Optimization and Logistic Map for Forecasting the Incomplete Data of Solar Irradiance2023Ingår i: Energy and AI, ISSN 2666-5468, s. 100243-100243, artikel-id 100243Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Solar energy has become crucial in producing electrical energy because it is inexhaustible and sustainable. However, its uncertain generation causes problems in power system operation. Therefore, solar irradiance forecasting is significant for suitable controlling power system operation, organizing the transmission expansion planning, and dispatching power system generation. Nonetheless, the forecasting performance can be decreased due to the unfitted prediction model and lacked preprocessing. To deal with mentioned issues, this paper proposes Meta-Learning Extreme Learning Machine optimized with Golden Eagle Optimization and Logistic Map (MGEL-ELM) and the Same Datetime Interval Averaged Imputation algorithm (SAME) for improving the forecasting performance of incomplete solar irradiance time series datasets. Thus, the proposed method is not only imputing incomplete forecasting data but also achieving forecasting accuracy. The experimental result of forecasting solar irradiance dataset in Thailand indicates that the proposed method can achieve the highest coefficient of determination value up to 0.9307 compared to state-of-the-art models. Furthermore, the proposed method consumes less forecasting time than the deep learning model.

  • 49.
    Boriratrit, Sarunyoo
    et al.
    Khon Kaen Univ, Fac Engn, Dept Elect Engn, Khon Kaen 40002, Thailand.;Prov Elect Author Thailand PEA, Bangkok 10900, Thailand..
    Srithapon, Chitchai
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Fuangfoo, Pradit
    Prov Elect Author Thailand PEA, Bangkok 10900, Thailand..
    Chatthaworn, Rongrit
    Khon Kaen Univ, Fac Engn, Dept Elect Engn, Khon Kaen 40002, Thailand..
    Metaheuristic Extreme Learning Machine for Improving Performance of Electric Energy Demand Forecasting2022Ingår i: Computers, E-ISSN 2073-431X, Vol. 11, nr 5, artikel-id 66Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electric energy demand forecasting is very important for electric utilities to procure and supply electric energy for consumers sufficiently, safely, reliably, and continuously. Consequently, the processing time and accuracy of the forecast system are essential to consider when applying in real power system operations. Nowadays, the Extreme Learning Machine (ELM) is significant for forecasting as it provides an acceptable value of forecasting and consumes less computation time when compared with the state-of-the-art forecasting models. However, the result of electric energy demand forecasting from the ELM was unstable and its accuracy was increased by reducing overfitting of the ELM model. In this research, metaheuristic optimization combined with the ELM is proposed to increase accuracy and reduce the cause of overfitting of three forecasting models, composed of the Jellyfish Search Extreme Learning Machine (JS-ELM), the Harris Hawk Extreme Learning Machine (HH-ELM), and the Flower Pollination Extreme Learning Machine (FP-ELM). The actual electric energy demand datasets in Thailand were collected from 2018 to 2020 and used to test and compare the performance of the proposed and state-of-the-art forecasting models. The overall results show that the JS-ELM provides the best minimum root mean square error compared with the state-of-the-art forecasting models. Moreover, the JS-ELM consumes the appropriate processing time in this experiment.

  • 50.
    Borisoot, Kanjanapon
    et al.
    Department of Electrical Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand.
    Liemthong, Rittichai
    Business Development Engineer, Sermsang Power Corporation Public Company Limited, Bangkok 10300, Thailand.
    Srithapon, Chitchai
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Elektroteknisk teori och konstruktion.
    Chatthaworn, Rongrit
    Department of Electrical Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand;Center for Alternative Energy Research and Development, Khon Kaen University, Khon Kaen 40002, Thailand.
    Optimal Energy Management for Virtual Power Plant Considering Operation and Degradation Costs of Energy Storage System and Generators2023Ingår i: Energies, E-ISSN 1996-1073, Vol. 16, nr 6, s. 2862-2862Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Even though generating electricity from Renewable Energy (RE) and electrification of transportation with Electric Vehicles (EVs) can reduce climate change impacts, uncertainties of the RE and charged demand of EVs are significant challenges for energy management in power systems. To deal with this problem, this paper proposes an optimal energy management method using the Virtual Power Plant (VPP) concept for the power system considering solar PhotoVoltaics (PVs) and Electric Vehicle Charging Stations (EVCS). The Differential Evolution (DE) algorithm is applied to manage energy in the power system to minimize the operation cost of generators and degradation costs in Energy Storage Systems (ESS) and generators. The effectiveness of the proposed approach is examined and tested on the IEEE 24 bus Reliability Test System (RTS 24) using the MATPOWER tool on the MATLAB program for calculating Optimal Power Flow (OPF). In this study, two situations before and after applying the proposed method are considered. The simulation results demonstrate that a branch constraint violation occurs before using optimal energy management using the VPP concept. In order to solve this issue, the DE algorithm for optimal energy management using the VPP concept is applied by dividing the studied case into two subcases as follows. For the first subcase, two objectives consisting of the minimization of the generator operation cost and the minimization of the battery degradation cost in ESS are considered. In the second case, three objectives comprising the two mentioned objectives with the minimization of generator degradation cost are considered. The results demonstrate that branch constraint violations can be avoided by applying optimal energy management using the VPP concept. This study also suggests considering the generator degradation cost in the objective function, which can minimize the total costs by 7.06% per day compared with the total cost of the first case.

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