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  • 1.
    Aljure, Mauricio
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Becerra Garcia, Marley
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Karlsson, Mattias
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymeric Materials.
    Erratum to: Aljure, M.; Becerra, M.; Karlsson, E.M. Streamer inception from ultra-sharp needles in mineral oil based nanofluids2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 11, article id 2900Article in journal (Refereed)
    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.

  • 2.
    Aljure, Mauricio
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Becerra Garcia, Marley
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. ABB Corp Res, Vasteras, Sweden..
    Karlsson, Mattias E.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    On the injection and generation of charge carriers in mineral oil under high electric fields2019In: JOURNAL OF PHYSICS COMMUNICATIONS, ISSN 2399-6528, Vol. 3, no 3, article id UNSP 035019Article in journal (Refereed)
    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.

  • 3.
    Aljure, Mauricio
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Becerra Garcia, Marley
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Karlsson, Mattias E.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Polymeric Materials.
    Streamer Inception from Ultra-Sharp Needles in Mineral Oil Based Nanofluids2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 8, article id 2064Article in journal (Refereed)
    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.

  • 4.
    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, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. 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 Array2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 41, p. 34817-34821Article in journal (Refereed)
    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.

  • 5.
    Augustin, Tim
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. KTH Stockholm.
    Becerra, Marley
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Magnusson, Jesper
    ABB Corporate Research, Västerås.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Parekh, Mrunal
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    System Design of Fast Actuator for Vacuum Interrupter in DC Applications2018In: 2018 28th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), Institute of Electrical and Electronics Engineers (IEEE), 2018, Vol. 2, p. 527-530Conference paper (Refereed)
    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.

  • 6.
    Augustin, Tim
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. KTH Stockholm.
    Becerra, Marley
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Nee, Hans-Peter
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Advanced Test Circuit for DC Circuit Breakers2018In: 20th European Conference on Power Electronics and Applications (EPE'18 ECCE EUROPE), 2018Conference paper (Refereed)
    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.

  • 7.
    Avula, Ramana R.
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Oechtering, Tobias J.
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Månsson, Daniel
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Privacy-preserving smart meter control strategy including energy storage losses2018In: Proceedings - 2018 IEEE PES Innovative Smart Grid Technologies Conference Europe, ISGT-Europe 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, article id 8571537Conference paper (Refereed)
    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.

  • 8. Bangalore, P.
    et al.
    Letzgus, S.
    Patriksson, M.
    Bertling, Lina
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Analysis of SCADA data for early fault detection with application to the maintenance management of wind turbines2016In: CIGRE Session 46, CIGRE , 2016, p. 1-10Conference paper (Refereed)
    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. 

  • 9.
    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, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. 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 Nanoparticles2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 13, article id 130401Article in journal (Refereed)
    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.

  • 10.
    Becerra Garcia, Marley
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Long, Mengni
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Schulz, W.
    Thottappillil, Rajeev
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    On the estimation of the lightning incidence to offshore wind farms2018In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 157, p. 211-226Article in journal (Refereed)
    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.

  • 11.
    Becerra Garcia, Marley
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Pettersson, Jonas
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Optical radiative properties of ablating polymers exposed to high-power arc plasmas2018In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 12, article id 125202Article in journal (Refereed)
    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.

  • 12.
    Becerra Garcia, Marley
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Saba, M. M. F.
    Liu, Lige
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Visacro, S.
    Using low-level currents measured during lightning events to estimate upward leader properties2018In: 34th International Conference on Lightning Protection, ICLP 2018, Institute of Electrical and Electronics Engineers Inc. , 2018Conference paper (Refereed)
    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.

  • 13.
    Bessman, Alexander
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Soares, Rudi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Software documentation for current-rippleequipment2018Report (Other (popular science, discussion, etc.))
  • 14.
    Björkqvist, Oskar
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Dahlberg, Oskar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Silver, Gustaf
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Kolitsidas, Christos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Wireless Sensor Network Utilizing Radio-Frequency Energy Harvesting for Smart Building Applications2018In: IEEE Antennas & Propagation Magazine, ISSN 1045-9243, E-ISSN 1558-4143, Vol. 60, no 5, p. 124-136Article in journal (Refereed)
    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.

  • 15.
    Brazalez, Astrid Algaba
    et al.
    Ericsson AB, Ericsson Res, Gothenburg, Sweden. attsson, Martin; Quevedo-Teruel, Oscar.
    Manholm, Lars
    Johansson, Martin
    Mattsson, Martin
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    A Ka-band glide-symmetric planar Luneburg lens with combined electric/metasurface for 5G communications2018In: 2018 INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION (ISAP), Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

    Here, we propose a cost-effective metasurface lens solution based on the use of metallic glide-symmetric unit cell combined with a dielectric sheet. Our solution reduces significantly the manufacturing and assembly complexity of previously investigated Ka-band Luneburg lens implemented in glide symmetry technology. The required refractive index for this unit cell has been studied for the geometrical parameters, and an efficient transition between different media in the parallel plate configuration of the lens is also investigated.

  • 16. Brazalez, Astrid Algaba
    et al.
    Manholm, Lars
    Johansson, Martin
    Quevedo-Teruel, Oscar
    Miao, Jingwei
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Investigation of a Ka-band Luneburg Lens Made of a Glide-Symmetric Holey Structure2017In: 2017 INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION (ISAP 2017), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    A Ka-hand 2D flat-profiled Luneburg lens antenna implemented with a glide-symmetric holey structure is presented. The required refractive index for the lens design has been investigated via an analysis of the hole depth and the gap between the two metallic layers constituting the lens. The final unit cell is described and applied to create the complete metasurface Luneburg lens showing that a plane wave is obtained when feeding at an opposite arbitrary point with a discrete source.

  • 17.
    Bäckström, Hampus
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Design and Evaluation of V/UHF Satellite Communication Antennas for Naval Applications2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this master thesis, compact antenna design aimed towards naval applicationshave been designed, analyzed and evaluated. There is a recentinterest in the development of compact antennas to be used for smallersubmarine models, and with a smaller hull on a submarine, communicationand antenna systems must be adapted and minimized, which limitsantenna design. With two limiting cylindrical volumes with maximumallowed dimensions r = 10 cm, h = 50 cm and r = 5 cm, h = 90 cm,the antennas would operate on the upper to lower V/UHF band, radiatehemispherically and have a high RHCP purity. It was found that the mostappropriate antenna structure for both volumes was QHA design. Afterthe design and analysis process was completed, it was concluded that theshorter antenna design could meet all requirements set while the longerantenna design did not meet all requirements but could still establish agood communication link on the higher frequencies. Antenna prototypesbased on the produced design were constructed and measured and, despiteminor deviations, veried that the results obtained from this thesis werereliable.

  • 18. Chen, M.
    et al.
    Xue, S.
    Liu, L.
    Li, Z.
    Wang, H.
    Tan, C.
    Yang, J.
    Hu, X.
    Jiang, X. -F
    Cheng, Y.
    Xing, X.
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    A highly stable optical humidity sensors based on nano-composite film2019In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 287, p. 329-337Article in journal (Refereed)
    Abstract [en]

    We report a highly stable humidity sensor based on nanocomposite film obtained by depositing Au nanoparticles on the surface of 3-mercaptopropionic acid (MPA) capped CdTe quantum dots (QDs) and then modifying NaOH (CdTe@Au/NaOH). The CdTe@Au/NaOH film will form compound salts that can be dissolved or crystallized with humidity changes, resulting in a significant absorption variation of green light, which is very benefit for water vapor detection. In this study, we systematically investigated the influence on the performance of humidity sensing by varying the thickness of Au layer as well as the concentration of NaOH. Our results show that the quickest response-recovery time (˜less than 30 s) was found in the sensing film with the Au layer thickness of 20 nm and NaOH concentration of 1M, which can be ascribed to the combined effects of the better morphology and the yield of compound salts. The repeatable response and recovery measurements demonstrate that the designed sensors exhibit an ultralow humidity detection level with fast response-recovery time, high stability and reproducibility at room temperature. The simplicity, low fabrication cost, and wide working range of the humidity sensor will pave the way for its application in environments and gas detection.

  • 19.
    Chen, Qiao
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Southeast Univ, State Key Lab Millimeter Wave, Nanjing 210096, Jiangsu, Peoples R China..
    Ghasemifard, Fatemeh
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Dispersion Analysis of Coaxial Line Loaded with Twist-Symmetric Half-Rings2018In: 2018 IEEE International Workshop on Antenna Technology, iWAT2018 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

    A coaxial line with half-rings connected to its external conductor is proposed in this paper, to investigate the dispersion properties of a twist-symmetric electromagnetic configuration. We demonstrate that the propagating modes in a twist-symmetric structure are more linear than a conventional structure. Additionally, the bandgap at the Brillouin zone boundaries can be manipulated by tuning the relative angular orientation or translation of the rings. This tuning is equivalent to changing the order of the twist symmetry from 4- to 2-fold. Our proposed geometry finds potential application in fully-metallic reconfigurable filters and phase shifters.

  • 20.
    Chen, Qiao
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Southeast Univ, State Key Lab Millimeter Waves, Nanjing 210096, Jiangsu, Peoples R China.
    Ghasemifard, Fatemeh
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Valerio, Guido
    Sorbonne Univ, Lab Elect & Electromagnetisme, F-75005 Paris, France..
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Modeling and Dispersion Analysis of Coaxial Lines With Higher Symmetries2018In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 66, no 10, p. 4338-4345Article in journal (Refereed)
    Abstract [en]

    In this paper, 1-D periodic structures possessing higher symmetries are proposed and investigated in terms of their dispersion properties. The proposed structures are coaxial lines with coaxial rings periodically loaded on their inner or outer conductors. The higher symmetries, namely, glide and twist symmetries, are obtained by performing an additional geometrical operation within the unit cell of the periodic structure. We demonstrate that the propagating modes exhibit a lower frequency dispersion in higher symmetric coaxial lines. Moreover, the conventional stopbands of periodic structures at their Brillouin zone boundaries can be controlled by breaking the higher symmetry or changing the order of the twist symmetry. A circuit-based analytical method is proposed to calculate the dispersion diagram of the glide-symmetric coaxial lines. The results are validated with a full-wave simulation. Moreover, several prototypes of the twist-symmetric coaxial lines are manufactured and measured. A remarkable agreement is achieved between the measurements and simulations, validating the theoretical results. The proposed structures find potential applications in leaky-wave antennas and fully metallic reconfigurable filters and phase shifters.

  • 21.
    Chen, Qiao
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Valerio, G.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Dispersion analysis of polar glide symmetry with coaxial rings2018In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper (Refereed)
    Abstract [en]

    In this article, the dispersion properties of a coaxial transmission line with polar glide-symmetric rings are analyzed. This symmetry is obtained by introducing periodic polar rings on either the inner or outer conductor of a coaxial guide. By modifying the relative radii of both rings, we demonstrate that a zero bandgap with non-zero group velocity at the Brillouin zone boundary can be achieved. Such quasi-linear dispersion is analyzed by applying both a circuit-based method and full-wave simulations. A good agreement is achieved between the methods.

  • 22.
    Chen, Qiao
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Yin, X.
    Wang, Lei
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Compact printed log-periodic dipole arrays fed by SIW horn2018In: IET Conference Publications, Institution of Engineering and Technology, 2018, no CP741Conference paper (Refereed)
    Abstract [en]

    Substrate integrated waveguide (SIW) horn is a good planar feeding structure for planar antennas and arrays. In this letter, a 18 printed log-periodic dipole array (LPDA) antenna fed by a compact SIW horn is presented. Some linear arrays of metal vias are embedded inside the SIW horn to correct the phase and amplitude distributions on the horn aperture. The measured gain of the proposed antenna is 9.61 dBi, the half power beam-width is 18.1, the FTBR is 17.55 dB, the cross polarization in the axis direction is 21.48 dB, and the side-lobe lever is -14.93 dB at 10 GHz. Good agreement between the simulated and the measured results is obtained.

  • 23.
    Cuaran, Jose
    et al.
    Univ Nacl Colombia, Elect Engn Dept, Bogota 111321, Colombia..
    Becerra Garcia, Marley
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Roman, Francisco
    Univ Nacl Colombia, Elect Engn Dept, Bogota 111321, Colombia..
    Lightning Attachment to UHV Power Transmission Lines: Effect of the Phase Voltage2019In: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 34, no 2, p. 729-738Article in journal (Refereed)
    Abstract [en]

    The self-consistent leader inception and propagation model is used to analyze the influence of the phase voltage on the attachment of lightning to ultra-high voltage power transmission lines (UHV-TLs). An UHV-ac line with shielding failures reported in the literature is used as a case study. It is shown that the length of upward leaders initiated fromconductors and their striking distances are longer under positive voltages than when energized with the opposite polarity. Therefore, the fraction of shielding failures of each conductor changes significantly with the phase angle in ac lines. However, it is found that the overall effect of voltage on lightning attachment can also be limited by the electrostatic screening produced by shield wires and their leaders. This proximity effect mainly reduces the velocity of upward leaders launched from energized conductors. Therefore, the effect of voltage on the lightning attachment process cannot be generalized since it is strongly coupled to the proximity of shield wires and their associated leaders. Thus, the lightning shielding performance should consider case-to-case variations in the upward leader velocity in different UHV-TLs designs, given not only by the line voltage but also coupled to the proximity of other wires and their launched leaders.

  • 24.
    Cui, Yue
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Bangalore, Pramod
    Greenbyte AB, Gothenburg, Sweden.
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    An anomaly detection approach based on machine learning and scada data for condition monitoring of wind turbines2018In: 2018 International Conference on Probabilistic Methods Applied to Power Systems, PMAPS 2018 - Proceedings, Institute of Electrical and Electronics Engineers Inc. , 2018Conference paper (Refereed)
    Abstract [en]

    This paper presents an anomaly detection approach using machine learning to achieve condition monitoring for wind turbines. The approach applies the information in supervisory control and data acquisition systems as data input. First, machine learning is used to estimate the temperature signals of the gearbox component. Then the approach analyzes the deviations between the estimated values and the measurements of the signals. Finally, the information of alarm logs is integrated with the previous analysis to determine the operation states of wind turbines. The proposed approach has been tested with the data experience of a 2MW wind turbine in Sweden. The result demonstrates that the approach can detect possible anomalies before the failure occurrence. It also certifies that the approach can remind operators of the possible changes inside wind turbines even when the alarm logs do not report any alarms.

  • 25.
    Cui, Yue
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Bangalore, Pramod
    Greenbyte AB, Gothenburg, Sweden..
    Bertling Tjernberg, Lina
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    An Anomaly Detection Approach Using Wavelet Transform and Artificial Neural Networks for Condition Monitoring of Wind Turbines' Gearboxes2018In: 2018 POWER SYSTEMS COMPUTATION CONFERENCE (PSCC), IEEE , 2018Conference paper (Refereed)
    Abstract [en]

    This paper presents an anomaly detection approach using artificial neural networks and the wavelet transform for the condition monitoring of wind turbines. The method aims to attain early anomaly detection and to prevent possible false alarms under healthy operations. In the approach, nonlinear autoregressive neural networks are used to estimate the temperature signals of the gearbox. The Mahalanobis distances are then calculated to measure the deviations between the current states and healthy operations. Next, the wavelet transform is applied to remove noisy signals in the distance values. Finally, the operation information is considered together with the refined distance values to detect potential anomalies. The proposed approach has been tested with the real data of three 2 MW wind turbines in Sweden. The results show that the approach can detect possible anomalies before failure events occur and avoid reporting alarms under healthy operations.

  • 26.
    Dahlberg, Oskar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Low-dispersive Leaky-wave Antennas: A Viable Approach for Fifth Generation (5G) mmWave Base Station Antennas2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this work, a method to achieve reduced beam-squint in fully metallic leaky-wave antennas is proposed and its applicability for high frequency, high gain, base station antennas in future communication networks is indicated.

    The antenna is built in gap waveguide technology, where the fundamental mode is allowed to leak by removal of one of the waveguide walls. The leakage is varied along the structure for reduced side lobes and a stable radiation pattern is obtained by coupling the leaked energy from the waveguide through a dispersive prism-lens.

    The gap waveguide is formed as a groove, sided by three rows of a glide-symmetric holey EBG-structure on one side, suppressing propagation of waves in that direction, and one row of vertical square pins, with tailored heights for optimal leakage, on the other. Beyond the single row of tailored pins, a prism-lens is placed. The prism lens is made of multiple rows of equally spaced and dimensioned, vertical square pins. The dispersive nature of the TE10-mode inside the waveguide is canceled by the oppositely dispersive prism-lens and a stable radiation beam (<1 degree beam-squint) is achieved over a 20% bandwidth.

    Two antennas are realized, both operating with a center frequency of roughly 60 GHz. The first design is optimized for single-beam operation such that the achieved efficiency is close to 90% across the band and the side lobe levels are below -20 dB. The second design is optimized for dual-beam operation such that two highly directive beams can be obtained, simultaneously or separately. The second design is placed in a 1D-array configuration for electrical beam-steering in one plane, and beam-switching in the orthogonal plane. The two antennas are simulated using CST Microwave Studio.

  • 27.
    Dahlberg, Oskar
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Ghasemifard, Fatemeh
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Valerio, Guido
    Sorbonne Univ, Lab Electron & Electromagnetisme, F-75005 Paris, France..
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Propagation characteristics of periodic structures possessing twist and polar glide symmetries2019In: EPJ Applied Metamaterials, ISSN 2272-2394, Vol. 6, article id 14Article in journal (Refereed)
    Abstract [en]

    In this article, we provide an overview of the current state of the research in the area of twist symmetry. This symmetry is obtained by introducing multiple periods into the unit cell of a periodic structure through a rotation of consecutive periodic deformations around a symmetry axis. Attractive properties such as significantly reduced frequency dispersion and increased optical density, compared to purely periodic structures, are observed. The direct link between the symmetry order and these properties is illustrated through numerical simulations. Moreover, polar glide symmetry is introduced, and is shown to provide even further control of the dispersion properties of periodic structures, especially when combined with twist symmetry. Twist symmetries can, with benefit, be employed in the development of devices for future communication networks and space applications, where fully metallic structures with accurate control of the dispersion properties are desired.

  • 28.
    Dahlberg, Oskar
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Pucci, E.
    Wang, L.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Fully-metallic, Low-dispersive, Leaky-wave Fed Lens Antenna for 60 GHz Base Station Applications2018In: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena, METAMATERIALS 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 90-92Conference paper (Refereed)
    Abstract [en]

    The guiding structure commonly employed in leaky-wave antennas is dispersive, resulting in beam-steering with frequency. This behavior reduces operational bandwidth in point-to-point communication applications. In this work, we present an approach that aims at increasing the operational bandwidth of leaky-wave antennas by the employment of a metasur-face lens.

  • 29. Dahlberg, Oskar
    et al.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Accurate and low-dispersive control of refractive properties in fully metallic waveguides possessing twist symmetry2018In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper (Refereed)
    Abstract [en]

    We here present a method of reducing the dispersive nature of periodic structures by utilizing twist symmetries. A dispersion study of four different 1D periodic structures is conducted to present the advantage of structures possessing twist symmetries. The analysis shows a clearly reduced frequency dependence of twist-symmetric structures, compared to more simple periodic structures. Additional advantage provided by twist symmetries is the accurate control of the refractive properties of the structures. Promising applications of twist-symmetric guiding structures are leaky-wave antennas, filters and phase shifters. 

  • 30.
    Dahlberg, Oskar
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Valerio, Guido
    Sorbonne Univ, Lab Elect & Electromagnetisme, F-75005 Paris, France..
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Fully Metallic Flat Lens Based on Locally Twist-Symmetric Array of Complementary Split-Ring Resonators2019In: Symmetry, ISSN 2073-8994, E-ISSN 2073-8994, Vol. 11, no 4, article id 581Article in journal (Refereed)
    Abstract [en]

    In this article, we demonstrate how twist symmetries can be employed in the design of flat lenses. A lens design is proposed, consisting of 13 perforated metallic sheets separated by an air gap. The perforation in the metal is a two-dimensional array of complementary split-ring resonators. In this specific design, the twist symmetry is local, as it is only applied to the unit cell of the array. Moreover, the twist symmetry is an approximation, as it is only applied to part of the unit cell. First, we demonstrate that, by varying the order of twist symmetry, the phase delay experienced by a wave propagating through the array can be accurately controlled. Secondly, a lens is designed by tailoring the unit cells throughout the aperture of the lens in order to obtain the desired phase delay. Simulation and measurement results demonstrate that the lens successfully transforms a spherical wave emanating from the focal point into a plane wave at the opposite side of the lens. The demonstrated concepts find application in future wireless communication networks where fully-metallic directive antennas are desired.

  • 31.
    Ding, Jiechen
    et al.
    Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    Lin, Zhili
    Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    Ying, Zhinong
    Nya Vattertornet, Sony Ericsson Mobile Commun AB, SE-22183 Lund, Sweden..
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    A compact ultra-wideband slot antenna with multiple frequency bands (vol 49, pg 3056, 2007)2008In: Microwave and optical technology letters (Print), ISSN 0895-2477, E-ISSN 1098-2760, Vol. 50, no 5, p. 1446-1446Article in journal (Refereed)
  • 32.
    Duvnjak Zarkovic, Sanja
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    On the Security of Electricity Supply in Power Distribution Systems2018In: 2018 IEEE International Conference on Probabilistic Methods Applied to Power Systems (PMAPS), IEEE conference proceedings, 2018, article id 8440489Conference paper (Refereed)
    Abstract [en]

    Security of electricity supply has become a fundamental requirement for modern societies. However, attempts to define and evaluate security of supply have differed from one another. This paper reviews relevant studies in order to give a comprehensive explanation of the security of supply concept. The paper includes theory, assessment, methodology, regulations, data and practical issues associated with the security of supply and power system reliability. Special focus is given to the methodologies used for improving the reliability and security of supply in power distribution systems.

  • 33.
    Ebrahimpouri, Mahsa
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH Royal Inst Technol, Sch Elect Engn, S-10044 Stockholm, Sweden..
    Brazalez, Astrid Algaba
    Ericsson AB, Ericsson Res, S-41756 Gothenburg, Sweden..
    Manholm, Lars
    Ericsson AB, Ericsson Res, S-41756 Gothenburg, Sweden..
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Using Glide-Symmetric Holes to Reduce Leakage Between Waveguide Flanges2018In: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 28, no 6, p. 473-475Article in journal (Refereed)
    Abstract [en]

    In this letter, a novel cost-effective flange is proposed to prevent the leakage created by undesired air gaps between flanges of two mating waveguides. The cause of an undesired gap can be surface curvature, dirt, human mistakes, or misalignment. Our proposal consists of machining glide-symmetric holes around the waveguide aperture on the flanges. Due to the glide symmetry properties, an identical pattern of the holes is possible at both sides, thus becoming glide-symmetric when they are mated together.

  • 34.
    Ebrahimpouri, Mahsa
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    A bespoke lens for a slot log-spiral excitation2018In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper (Refereed)
    Abstract [en]

    In this paper, a bespoke lens has been designed for a slot log-spiral excitation. The performance of this lens is compared with a conventional hyper-hemispherical lens. Using the bespoke lens methodology, the specific electromagnetic properties of the slot log-spiral excitation are obtained and its phase fronts are transformed to flat phase fronts by a QCTO (quasi-conformal transformation optics) technique. The performance of the lenses is evaluated with the radiation properties. The bespoke lens produces an improvement in terms of directivity and side lobe levels.

  • 35.
    Eskandari, Hossein
    et al.
    Ferdowsi Univ Mashhad, Dept Elect Engn, Mashhad, Iran.;Ferdowsi Univ Mashhad, Commun & Comp Res Ctr, Mashhad, Iran..
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Attari, Amir Reza
    Ferdowsi Univ Mashhad, Dept Elect Engn, Mashhad, Iran..
    Majedi, Mohammad Saeed
    Ferdowsi Univ Mashhad, Dept Elect Engn, Mashhad, Iran..
    Transformation optics for perfect two-dimensional non-magnetic all-mode waveguide couplers2019In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 9, no 3, p. 1320-1332Article in journal (Refereed)
    Abstract [en]

    Here, we demonstrate that transformation optics can be used to produce 2-D non-magnetic waveguide couplers with no reflections. Our approach consists of using a scaling function for reflection suppression and introducing an auxiliary function in the transformation optics formulation to achieve a non-magnetic medium for coupling the TM polarization. To demonstrate the potential of this method, two non-magnetic waveguide couplers are designed. The first one satisfies the Brewster angle condition for any arbitrary incidence angle (TMn modes), extending the performance of couplers previously reported in the literature that only operate for TEM (TM0 mode), i.e. waves with normal incidence. Our method can be applied to match any given dielectric constant. Our results demonstrate that for a given mode (angle), we achieve a perfect match to a defined dielectric constant. The second design removes the dependence of the reflectionless condition to the incident angle at the boundary. Hence, this coupler works for all incident angles (TMn modes). It is used to compress all the modes into a region with a higher predefined refractive index.

  • 36.
    Estanqueiro, Ana
    et al.
    National Laboratory on Energy and Geology (LNEG).
    Ahlrot, Claes
    E.ON AB.
    Duque, Joaquim
    National Laboratory on Energy and Geology (LNEG).
    Santos, Duarte
    National Laboratory on Energy and Geology (LNEG).
    Gentle, Jake P.
    Idaho National Laboratory (INL).
    Abboud, Alexander W.
    Idaho National Laboratory (INL).
    Morozovska, Kateryna
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Söder, Lennart
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Kanefendt, Thomas
    Fraunhofer IEE.
    DLR use for optimization of network design withvery large wind (and VRE) penetration2018Conference paper (Refereed)
    Abstract [en]

    Due to the stochastic nature of wind and clouds,the integration of wind and PV generation in the powersystem poses serious challenges to the long-term planning oftransmission systems. Grid reinforcements always involverelevant direct costs while the average load factor of the windand solar PV dedicated transmission lines is usually low.Additionally, in very windy sites, the same high windresource that produces large amounts of wind generation andmay congest the transmission lines transporting it to distantconsumption centres may also have a beneficial effect inincreasing the transmission capacity of those lines. In fact, theoccurrence of wind not only contributes to the loading of theconnecting line, but also increases the line capacity, via theconvective cooling of the cables - one of the main heattransfer mechanisms in conductor heat balance; in otherwords, higher winds speeds contribute to faster cooling ofconductor and therefore higher conductor’s capacitypotential. In this paper the existing methodologies tocharacterize those thermal effects in electrical cables - usuallyreferred as dynamic line rating (DLR) - are applied to severalIEA Task 25 countries case studies to characterize thetechnical value of the dynamic operation of thermallycongested lines, as well as its potential economic benefits.

  • 37.
    Fei, Chao
    et al.
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Hong, Xiaojian
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Zhang, Guowu
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Du, Ji
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Gong, Yu
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    Evans, Julian
    Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Zhejiang Univ, Coll Opt Sci & Engn, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310058, Zhejiang, Peoples R China..
    16.6 Gbps data rate for underwater wireless optical transmission with single laser diode achieved with discrete multi-tone and post nonlinear equalization2018In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 26, p. 34060-34069Article in journal (Refereed)
    Abstract [en]

    In this paper, we experimentally demonstrate a 450-nm laser underwater wireless optical transmission system by using adaptive bit-power loading discrete multi-tone (DMT) and Volterra series based post nonlinear equalization. Post nonlinear equalization mitigates the nonlinear impairment of the UWOC system. By incorporating post nonlinear equalization with a 3rd-order diagonal plane kernel, the received signal-to-noise ratio (SNR) can be improved by similar to 2 dB compared with a linear equalization method. The measured transmission capacity of the UWOC system is 16.6 Gbps over 5 m, 13.2 Gbps over 35 m, and 6.6 Gbps over 55 m tap water channel, with bit error rates (BERs) below the standard hard-decision forward error correction (HD-FEC) limit of 3.8 x 10(-3). The used electrical signal bandwidth is 2.75 GHz, corresponding to electrical spectrum efficiency of similar to 6 bit/s/Hz. The distance-datarate product reaches 462 Gbps*m at 35 m tap water transmission. To the best of our knowledge, both the data rate and distance-data rate product are the largest reported for single laser diode.

  • 38.
    Fonseca, Nelson J. G.
    et al.
    European Space Agcy, Antenna & Sub Millimetre Waves Sect, Noordwijk, Netherlands. iao, Qingbi; Quevedo-Teruel, Oscar.
    Liao, Qingbi
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    The Water Drop Lens: A Modulated Geodesic Lens Antenna Based on Parallel Curves2018In: ISAP 2018 - 2018 International Symposium on Antennas and Propagation, Institute of Electrical and Electronics Engineers (IEEE), 2018, article id 8627878Conference paper (Refereed)
    Abstract [en]

    This paper discusses the design of parallel plate waveguide geodesic nses based on parallel curves enabling low-profile beamformers with a ry wide angular scanning range. The proposed approach provides smooth ns profiles with additional degrees of freedom for the optimization of odesic lenses, enabling Gaussian beam but also shaped patterns. The tational symmetry of the lens results in a shape looking like water op ripples, also known as capillary waves, at the surface of a fluid, nce the water drop lens appellation.

  • 39. Frid, Henrik
    et al.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Compensation of radome effects in small airborne monopulse arrays by convex optimization2018In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper (Refereed)
    Abstract [en]

    The quality of small array antennas in airborne monopulse systems can be significantly reduced by the radome. We therefore present a convex optimization approach to minimize radome effects in monopulse arrays. This is achieved by using active element patterns in the optimization to determine the excitation weights. Simulation results for a BoR array with 48 elements and an extended hemispherical radome are presented. We demonstrate that it is possible to reduce the side-lobe level by 3.5 dB by taking radome effects into account in the optimization. This approach also results in an increased gain, particularly at large scan angles. Furthermore, the presented approach allows the monopulse slope to be indirectly specified as a design parameter. It is shown that the trade-off between the monopulse slope coefficient and the side-lobe level is approximately linear.

  • 40.
    Frid, Henrik
    et al.
    Saab Surveillance, Stockholm, Sweden.;KTH Royal Inst Technol, Osquldas Vag 10, SE-10044 Stockholm, Sweden..
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Determining Installation Errors for DOA Estimation with Four-Quadrant Monopulse Arrays by using Installed Element Patterns2018In: 2018 2nd URSI Atlantic Radio Science Meeting, AT-RASC 2018, Institute of Electrical and Electronics Engineers (IEEE), 2018, article id 8471377Conference paper (Refereed)
    Abstract [en]

    The four-quadrant monopulse array is widely used for direction of arrival (DOA) estimation. Errors in the angle estimate are introduced when installing the array on a platform, due to unwanted reflections in the platform, as well as reflection and refraction in the radome. These installation effects are captured in the installed element patterns, which can be computed using a number of computational electromagnetics methods. In this paper, we demonstrate that the error introduced in the DOA estimate can be determined from the installed element patterns. To illustrate how the method is used, we present results for two cases: (a) BoR-array without radome and (b) BoR-array with an extended hemispherical radome. The presented method can be applied for any installation configuration, as long as the installed element patterns can be computed.

  • 41.
    Ghasemifard, Fatemeh
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Periodic Structures with Higher Symmetries: Analysis and Applications2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, periodic structures with higher symmetries are studied. Their wave propagation characteristics are investigated and their potential applications are discussed. 

    Higher-symmetric periodic structures are described with an additional geometrical operation beyond a translation operator. Two particular types of higher symmetry are glide and twist symmetries. Glide-symmetric periodic structures remain invariant under a translation of half a period followed by a reflection with respect to a glide plane. Twist-symmetric periodic structures remain invariant under a translation along followed by a rotation around a twist axis. 

    In a periodic structure with a higher symmetry, in which the higher order modes are excited, the frequency dispersion of the first mode is dramatically reduced. This feature overcomes the bandwidth limitations of conventional periodic structures. Therefore, higher-symmetric periodic structures can be employed for designing wideband metasurface-based antennas. For example, holey glide-symmetric metallic structures can be used to design low loss, wideband flat Luneburg lens antennas at millimeter waves, which find application in 5G communication systems. In addition, holey glide-symmetric structures can be exploited as low cost electromagnetic band gap (EBG) structures at millimeter waves, due to a wider stop-band achievable compared to non-glide-symmetric surfaces. 

    However, these attractive dispersive features can be obtained if holey surfaces are strongly coupled, so higher-order modes produce a considerable coupling between glide-symmetric holes. Hence, these structures cannot be analyzed using common homogenization methods based on the transverse resonance method. Thus, in this thesis, a mode matching formulation, taking the generalized Floquet theorem into account, is applied to analyze glide-symmetric holey periodic structures with arbitrary shape of the hole. Applying the generalized Floquet theorem, the computational domain is reduced to half of the unit cell. The method is faster and more efficient than the commercial software such as CST Microwave Studio. In addition, the proposed method provides a physical insight about the symmetry of Floquet modes propagating in these structures. 

    Moreover, in this thesis, the effect of twist symmetry and polar glide symmetry applied to a coaxial line loaded with holes is explained. A rigorous definition of polar glide symmetry, which is equivalent to glide symmetry in a cylindrical coordinate, is presented. It is demonstrated that the twist and polar glide symmetries provide an additional degree of freedom to engineer the dispersion characteristics of periodic structures. In addition, it is demonstrated that the combination of these two symmetries provides the possibility of designing reconfigurable filters. Finally, mimicking the twist symmetry effect in a flat structure possessing glide symmetry is investigated. The results demonstrate that the dispersion properties associated with twist symmetry can be mimicked in flat structures.

     

  • 42.
    Ghasemifard, Fatemeh
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Dispersion Analysis of 2-D Glide-Symmetric Corrugated Metasurfaces Using Mode-Matching Technique2018In: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 28, no 1, p. 1-3Article in journal (Refereed)
    Abstract [en]

    In this letter, wave propagation in 2-D doubled corrugated metasurfaces, including glide-symmetric corrugated metasurfaces, embedded in a thin parallel plate waveguide have been analyzed using the mode matching method. The general dispersion equation for propagation at different directions is derived and dispersion surfaces have been obtained for three different cases. The results are in good agreement with reference results obtained using CST Microwave Studio. Moreover, the method is accurate and computationally much faster than CST Microwave Studio and similar commercial software.

  • 43.
    Ghasemifard, Fatemeh
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Norgren, Martin
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Twist and Polar Glide Symmetries: an Additional Degree of Freedom to Control the Propagation Characteristics of Periodic Structures2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8Article in journal (Refereed)
    Abstract [en]

    New high-frequency 5G and satellite communication systems require fully-metallic antennas and electromagnetic components. These components can be implemented with truncated versions of periodic structures. In order to achieve the desired performance of these future devices, it is of crucial importance to have a precise control of the propagation properties, i.e. the frequency dispersion behavior and stop-bands. Here, we demonstrate the potential use of higher symmetries to diminish the frequency dispersion of periodic structures and control the width of stop-bands with a new type of fully-metallic transmission line, which is loaded with holes on a twist-symmetric configuration. Simulated and experimental results confirm the intrinsic link between the propagation characteristics and the symmetries of a periodic structure. Additionally, we provide a definitive explanation of the recently discovered polar glide symmetry and its potential combination with twist symmetries to produce low-dispersive materials and reconfigurable stop-bands. The promising properties of these structures are demonstrated with a fully-metallic reconfigurable filter, which could be used for future high-frequency 5G and satellite communication systems.

  • 44.
    Ghasemifard, Fatemeh
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Valerio, G.
    Norgren, Martin
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Analysis of wave propagation in plasmonic holey metasurfaces with cylindrical holes2018In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper (Refereed)
    Abstract [en]

    The wave propagation along a plasmonic holey metasurface when a metallic plate is located in its proximity has been analyzed using a mode matching technique. With this analysis, we demonstrate that decreasing the distance between the metallic plate and the holey surface excites nonresonant higher order modes in the structure. Therefore, considering only the dominant mode inside the holes, as the previous simpler models assumed, is not sufficient to analyze this type of metasurfaces.

  • 45.
    Ghorbani, Hossein
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Characterization of Conduction and Polarization Properties of HVDC Cable XLPE Insulation Materials2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    High voltage direct current (HVDC) cables with extruded insulation system were introduced in 1998. Since then this technology has been growing rapidly with many installations that are today operational at voltages up to 320 kV. With fast developments during the last few years, extruded DC cable systems for operation voltages as high as 640 kV are now commercially available.

    Due to the importance of DC conductivity in the distribution of electrical field across the cable insulation, a good understanding of the DC conduction physics is of key importance to the design of robust HVDC cables. Currently, crosslinked polyethylene (XLPE) is the dominating material used in the insulation system of extruded DC cables. Since XLPE includes peroxide decomposition products (PDP), understanding their role on conduction behavior of the insulation system has been of great interest. The PDP and other chemical species can move in the system through diffusion which makes the characterization of cable insulation more challenging. Besides, like other semi-crystalline polymers, morphology of the XLPE evolves with temperature and over time. These changes in the material pose challenges to their electrical characterization by requiring stringent control of parameters during preparation, storage and measurement.

    In this work, different electrical characterization techniques relevant to polymeric insulation materials are discussed highlighting their applications and limitations. A set of considerations during preparation, storage and measurement of polymeric samples is listed and implemented in the studies. The design and performance of a high voltage DC conductivity measurement setup is evaluated.

    Thick low density polyethylene (LDPE) and XLPE press molded plaque samples together with plaque samples extracted from cable insulation are prepared and studied using the high voltage DC conductivity measurement setup. Conductivity measurements are done both under static and dynamic temperature programs. Different preparations and test programs are used and the results are analyzed and compared.

    Investigations show that the type of protective press film used during press molding of samples can strongly influence the results and using polyethylene terephthalate (PET) film appears to lead to the higher measured conductivity levels. Studies with dynamic temperature program reveal a non-monotonic temperature dependence of apparent DC conductivity of samples with certain

    preparation which to the author’s best of knowledge has not been previously

    reported in the literature.

    Studies on XLPE and LDPE plaque samples with different heat-treatments show that the behavior of conductivity during thermal dynamics depends on the type of the press film. Upon degassing, samples pressed with PET film show a decline of conductivity at all temperatures and a reduction of the non-monotonic behavior. Based on the results from the experiments, a set of hypotheses as potential explanation of this behavior is put forward and discussed.

  • 46.
    Ghorbani, Hossein
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Influence of press films on conduction in polyethylene plaque samples2016In: Dielectrics (ICD), 2016 IEEE International Conference on, France: Institute of Electrical and Electronics Engineers (IEEE), 2016, article id 16250905Conference paper (Refereed)
    Abstract [en]

    Press molded plaque samples are commonly used for characterization of polymeric insulation materials. Such samples are prepared by pressing polymer granulates sandwiched between two layers of protective press films at high temperatures and pressures. Polyethylene terephthalate (PET) film is a common press film since it tolerates high temperatures, acts as a good diffusion barrier and can be separated from the molded polyethylene sample easily. In this work, studies are performed on the influence of the pressing film on the dielectric properties of press molded polyethylene insulation samples. Volume resistivity is measured under high voltage DC at different conditions on samples pressed using different press films and different preparations. Furthermore, PEA measurements under high voltage DC is performed on plaque samples press molded with different press films. It is found that press molding using PET film leads to a considerably higher apparent conductivity of the samples in comparison to using aluminum foil. Choice of press film, also influences the space charge measurement results. It is concluded that the influence of the press film used during sample preparation cannot be neglected and this effect should be evaluated carefully in material characterization research. According to the results in this work, aluminum foil seems to be a better option as a press film in comparison to PET press film.

  • 47.
    Ghorbani, Hossein
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Long-term conductivity decrease of polyethylene and polypropylene insulation materials2017In: IEEE Transactions on Dielectrics and Electrical Insulation, ISSN 1070-9878, Vol. 24, no 3, p. 1485-1493Article in journal (Refereed)
    Abstract [en]

    This work summarizes the results of a number of DC conductivity measurement studies on polypropylene (PP), low density polyethylene (LDPE), and cross linked polyethylene (XLPE). The main observation is that under apparently time-constant external conditions (voltage, temperature, etc.) no steady-state direct current (DC) was established even after very long measurement times. Nevertheless, this behavior seems to exhibit some common systematic features, and since the experiments were performed with different equipment at different R&D labs in different years by different teams, simple measurement artefacts can be excluded. One observation is that there are two electric field regimes with slightly different behavior, separated by crossover field of about 10-15 kV/mm. In this work we focus on the high-field region, where the main observation is that the conductance slowly decays sub-linearly with time, I~ t-n, with 0.3 <; n <; 1, n mostly around 0.5. We provide experimental indications that this behavior is rather independent of the presence of 1) the voltage and 2) the peroxide decomposition products (in PE). The observations are in favor of an underlying thermally driven relaxation process related to structural changes (morphology, free volume) of the polymer. A main implication of the results is that the use of steady-state conductivity values for the characterization of certain polymer insulation is not appropriate and instead the decaying behavior of the conduction current must be considered.

  • 48.
    Ghorbani, Hossein
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Observation of non-monotonic dependence of leakage current with temperature during thermal cycling2016In: IEEE Electrical Insulation Conference (EIC), 2016, Montreal: Institute of Electrical and Electronics Engineers (IEEE), 2016, article id 16263557Conference paper (Refereed)
    Abstract [en]

    Conductivity under high voltage DC, is one of the most important characteristics of insulating materials used as insulation in HVDC applications. The volume conductivity of the insulation can be measured on press molded plaque samples by applying DC voltage and measuring the leakage current passing through the insulation. Such measurements are often performed at constant temperatures and constant voltage levels. In this work, the leakage current is measured on 1 mm thick press molded low density polyethylene (LDPE) and crosslinked polyethylene (XLPE) samples under DC voltage of 30 kV while the different temperature conditions including thermal cycling with temperatures between room temperature and 90 °C is applied. While the obtained results with constant temperature are in good agreement with the previously reported measurements, during thermal transients an interesting phenomenon was observed. Based on the theories and previously reported measurements, the leakage current is expected to have an Arrhenius dependence to temperature. But in the new experiments during thermal transients, the leakage current shows a non-monotonic temperature dependence and during heating and cooling, peaks are observed in the measured leakage current. It was discovered that the behavior of leakage current is influenced by the type of protective film used during sample preparation and using PET film leads to a higher apparent conductivity than using aluminum foil. A non-monotonic temperature dependence is observed in samples pressed using PET film while samples pressed with aluminum foil exhibit an Arrhenius temperature dependence.

  • 49.
    Gong, Chensheng
    et al.
    Zhejiang Univ, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res, East Bldg 5,Zijingang Campus, Hangzhou 310058, Zhejiang, Peoples R China..
    Liu, Wen
    Zhejiang Univ, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res, East Bldg 5,Zijingang Campus, Hangzhou 310058, Zhejiang, Peoples R China..
    He, Nan
    Zhejiang Univ, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res, East Bldg 5,Zijingang Campus, Hangzhou 310058, Zhejiang, Peoples R China..
    Dong, Hongguang
    Zhejiang Univ, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res, East Bldg 5,Zijingang Campus, Hangzhou 310058, Zhejiang, Peoples R China..
    Jin, Yi
    Zhejiang Univ, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res, East Bldg 5,Zijingang Campus, Hangzhou 310058, Zhejiang, Peoples R China..
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Zhejiang Univ, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res, East Bldg 5,Zijingang Campus, Hangzhou 310058, Zhejiang, Peoples R China.
    Upconversion enhancement by a dual-resonance all-dielectric metasurface2019In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 11, no 4, p. 1856-1862Article in journal (Refereed)
    Abstract [en]

    Upconversion nanoparticles (UCNPs) have drawn much attention in the past decade due to their superior physicochemical features and great potential in biomedical and biophotonic studies. However, their low luminescence efficiency often limits their applications. Here, we demonstrated a dual-resonance all-dielectric metasurface to enhance the signals emitted by upconversion nanoparticles (NaYF4:Yb/Tm). An averaged upconversion signal enhancement of around 400 times is detected experimentally. The electric and magnetic dipole resonances of the metasurface are designed to enhance the local excitation field and the quantum efficiency of the upconversion nanoparticles, respectively. Furthermore, the collection efficiency is enhanced due to the directional emission of the UCNPs on the metasurface. Our approach provides a powerful tool to extend the sensing application potential of upconversion nanoparticles.

  • 50. Gong, Y.
    et al.
    Yang, B.
    Zhang, D.
    Hong, X.
    Lu, Y.
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. South China Normal University, Guangzhou, China.
    Chen, Jiajia
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab). South China Normal University, Guangzhou, China.
    Crosstalk-aware multiple-AWG based optical interconnects for datacenter networks2018In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 426, p. 151-157Article in journal (Refereed)
    Abstract [en]

    This paper proposes a crosstalk-aware passive optical interconnect architecture based on multiple arrayed waveguide gratings (AWGs). With two-stage cascaded AWGs, it can realize the communications not only within but also among the clusters for large-scale datacenters. To overcome serious crosstalk in multiple-AWG based optical interconnects, crosstalk suppression schemes are proposed. Proof-of-concept experiments are carried out to verify the necessity and feasibility of the proposed crosstalk suppression schemes for multiple-AWG based optical interconnects.

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