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  • 1.
    Ebrahimpouri, Mahsa
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Rajo-Iglesias, Eva
    Sipus, Zvonimir
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Cost-Effective Gap Waveguide Technology Based on Glide-Symmetric Holey EBG Structures2018Ingår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 66, nr 2, s. 927-934Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a novel electromagnetic bandgap (EBG) structure, which can be used to manufacture low-cost waveguiding structures at high frequencies. The unit cell of the proposed EBG consists of glide-symmetric holes in parallel plate waveguide. Using this unit cell in groove gap waveguide technology has a number of advantages over pin-type EBG at high frequencies, such as acquiring higher accuracy because of larger periodicity as well as an easier and cheaper manufacturing process. The performance of the proposed waveguiding structure is demonstrated using both a straight and a double 90 degrees bent lines through simulation and measurement.

  • 2. Fei, Chao
    et al.
    Zhang, Junwei
    Zhang, Guowu
    Wu, Yujian
    Hong, Xuezhi
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. Zhejiang Univ, Ctr Opt & Electromagnet Res, State Key Lab Modern Opt Instrumentat, Hangzhou 310027, Zhejiang, Peoples R China.
    Demonstration of 15-M 7.33-Gb/s 450-nm Underwater Wireless Optical Discrete Multitone Transmission Using Post Nonlinear Equalization2018Ingår i: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 36, nr 3, s. 728-734Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we experimentally demonstrate an underwater wireless optical communication (UWOC) system using a 450-nm gallium nitride (GaN) laser and adaptive bit-power loading discrete multitone (DMT). To enhance the system capacity, a post nonlinear equalizer based on the simplified Volterra series is employed at the receiver to mitigate the nonlinear impairments of the UWOC system. By combining the adaptive bit-power loading with nonlinear equalization, 7.33-Gb/s DMT-modulated UWOC under 15-m tap water is achieved at a bit error rate below the 7% hard-decision forward error correction (FEC) limit 3.8 x 10(-3). The electrical signal bandwidth is 1.25 GHz, which corresponds to an electrical spectrum efficiency of similar to 6 bit/s/Hz. The capacity-distance product reaches 109.95 Gb/s-m in a single channel UWOC system with tap water. Compared with the linear equalization case, the system capacity at the FEC limit for 15-m underwater transmission is improved by similar to 18% with the nonlinear equalization. Furthermore, the impact of turbidity on the performance of UWOC system is investigated by measuring the signal-to-noise ratio (SNR) under different suspension concentrations of Al(OH)(3) and Mg(OH)(2). The results show that significant SNR gains (>3 dB for transmission distance up to 11 m) can be obtained by the nonlinear equalization over a wide range of water turbidity levels representing "clear ocean," "coastal ocean," and "harbor water," which demonstrates the robustness of the proposed scheme in various ocean environments.

  • 3.
    Ghasemifard, Fatemeh
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Dispersion Analysis of 2-D Glide-Symmetric Corrugated Metasurfaces Using Mode-Matching Technique2018Ingår i: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 28, nr 1, s. 1-3Artikel i tidskrift (Refereegranskat)
    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.

  • 4.
    Jürgensen, Jan Henning
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Brodersson, Anna Lilly
    Vattenfall Eldistribution AB.
    Nordström, Lars
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Hilber, Patrik
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Impact Assessment of Remote Control and Preventive Maintenance on the Failure Rate of a Disconnector Population2018Ingår i: IEEE Transactions on Power Delivery, ISSN 0885-8977, E-ISSN 1937-4208, Vol. 33, nr 4, s. 1501-1509Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents the impact of different explanatory variables such as remote control availability and conducted preventive maintenance, among others, on failure statistics of a disconnector population in Sweden using the proportional hazard model. To do so, 2191 work orders were analysed which included 1626 disconnectors and 278 major failures. Here, the results show that the remote control availability for disconnectors - an example of such Smart Grid technology - has a negative effect on the failure rate, whereas preventive maintenance has a positive impact. It is also shown that the disconnector age is not significant and that certain disconnector types have a significant and positive correlation towards failures when compared to other disconnector types. The results increase the understanding of disconnector failures to improve asset management.

  • 5. Sun, Fei
    et al.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. Centre for Optical and Electromagnetic Research, State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, China.
    Invisible gateway for both light waves and rays2018Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, nr 1, s. 165-172Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Considering that previous invisible gateways (an open entrance that only blocks electromagnetic waves) based on super-scatters designed by transformation optics cannot effectively work for narrow beams and light rays that do not touch negative refractive index material, we explore a new way to realize an improved invisible gateway that can give a good performance for both light waves and rays. In all previous invisible gateways, they require a finite thickness of the wall and the gateway. For the improved invisible gateway proposed in this study, there is no requirement on the thickness of the wall and gateway, i.e. the wall and gateway can be infinitely thin. Our study will go a further step to realize the invisible gateway in fiction.

  • 6.
    Jiang, Wei
    et al.
    Zhejiang Univ, Coll Opt Sci & Engn, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    Ma, Yungui
    Zhejiang Univ, Coll Opt Sci & Engn, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. Zhejiang Univ, Coll Opt Sci & Engn, State Key Lab Modern Opt Instrumentat, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China.
    Static Magnetic Cloak without a Superconductor2018Ingår i: Physical Review Applied, E-ISSN 2331-7019, Vol. 9, nr 5, artikel-id 054041Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Similar to its electromagnetic counterpart, magnetic cloaking also has very important technological applications. However, the traditional method to build a static magnetic cloak requires the use of superconducting materials as the diamagnetic component, which seriously limits the practical potential because of the cryogenic condition. We show that a diamagnetic active current boundary combined with a high-permeability magnetic inner shell (MIS) can be designed to solve this problem, rendering an ideal magnetic cloaking effect at zero frequency. We first theoretically prove that a current boundary could magnetically behave as a superconductor to external observers. Based on this phenomena, we introduce a high-permeability MIS made of magnetically ultrasoft metallic sheets (permeability mu > 10(3)) and experimentally prove that the bilayer combination can exactly balance out the disturbance to the external probing field and, meanwhile, have a large invisible inner space. We also show that the active boundary currents can be accordingly configured to overcome the permeability and frequency band limits, leading to a robust cloak over the entire quasistatic frequency region. Our work creates an efficient way to circumvent the traditional limits of metamaterials to build magnetic cloaks for ultralow frequencies. The active-passive hybrid approach could be generally extended to yield other artificial magnetic devices or systems as well.

  • 7.
    Shayesteh, E.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Gayme, D. F.
    Amelin, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    System reduction techniques for storage allocation in large power systems2018Ingår i: International Journal of Electrical Power & Energy Systems, ISSN 0142-0615, E-ISSN 1879-3517, Vol. 95, s. 108-117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Semi-Definite Relaxation (SDR) techniques for AC optimal power flow (OPF) have recently been proposed as a means of obtaining a provably global optimal solution for many IEEE benchmark power systems. Solving the resulting semi-definite programs (SDP) can, however, be computationally intensive. Therefore new algorithms and techniques that enable more efficient computations are needed to extend the applicability of SDP based AC OPF algorithms to very large power networks. This paper proposes a three-stage algorithm for AC OPF based storage placement in large power systems. The first step involves network reduction whereby a small equivalent system that approximates the original power network is obtained. The AC OPF problem for this equivalent system is then solved by applying an SDR to the non-convex problem. Finally, the results from the reduced system are transferred to the original system using a set of repeating optimizations. The efficacy of the algorithm is tested through case studies using two IEEE benchmark systems and comparing the solutions obtained to those of DC OPF based storage allocation. The simulation results demonstrate that the proposed algorithm produces more accurate results than the DC OPF based algorithm.

  • 8. Sun, F.
    et al.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Waveguide bends by optical surface transformations and optic-null media2018Ingår i: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 35, nr 4, s. 944-949Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose what we believe is a novel method to design waveguide bends for metallic waveguides with arbitrary bending angles. The proposed method is based on a new theoretical branch from transformation optics that is referred as to optic surface transformation. Compared with waveguide bends designed by traditional transformation optics, the design process of our method can be made in a graphical way that is very simple and convenient. To realize any waveguide bend designed by the method proposed in this study, one needs only one homogeneous material, i.e., an optic-null medium (even if the bending angles are different for various cases). After some reductions, we find that the optic-null media here can be approximately realized by some anisotropic zero refractive index materials. 2D numerical simulations verify the performance of the designed waveguide bends. The design principle can be extended to the 3D case.

  • 9.
    Mazidi, Peyman
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. Comillas Pontifical University, Spain.
    Du, Mian
    Bertling Tjernberg, Lina
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Bobi, Miguel A. Sanz
    A health condition model for wind turbine monitoring through neural networks and proportional hazard models2017Ingår i: Journal of Risk and Reliability, ISSN 1748-006X, E-ISSN 1748-0078, Vol. 231, nr 5, s. 481-494Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, a parametric model for health condition monitoring of wind turbines is developed. The study is based on the assumption that a wind turbine's health condition can be modeled through three features: rotor speed, gearbox temperature and generator winding temperature. At first, three neural network models are created to simulate normal behavior of each feature. Deviation signals are then defined and calculated as accumulated time-series of differences between neural network predictions and actual measurements. These cumulative signals carry health condition-related information. Next, through nonlinear regression technique, the signals are used to produce individual models for considered features, which mathematically have the form of proportional hazard models. Finally, they are combined to construct an overall parametric health condition model which partially represents health condition of the wind turbine. In addition, a dynamic threshold for the model is developed to facilitate and add more insight in performance monitoring aspect. The health condition monitoring of wind turbine model has capability of evaluating real-time and overall health condition of a wind turbine which can also be used with regard to maintenance in electricity generation in electric power systems. The model also has flexibility to overcome current challenges such as scalability and adaptability. The model is verified in illustrating changes in real-time and overall health condition with respect to considered anomalies by testing through actual and artificial data.

  • 10.
    Mattsson, Martin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kolitsidas, Christos
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Silver, Gustaf
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Björkqvist, Oskar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Dahlberg, Oskar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A high gain Dual-Polarised Differential Rectenna for RF Energy Harvesting2017Ingår i: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 1609-1610Konferensbidrag (Refereegranskat)
    Abstract [en]

    A rectenna for radio frequency (RF) energy harvesting is presented in this paper. We introduce a novel technique for RF rectification that is based on differential field sampling and a Greinacher voltage doubler rectifier. The proposed rectification antenna is a dual polarized patch with 4 ports that operates for the WiFi frequency band of 2.4-2.5 GHz and has a gain of 6.75 dB at each port. The proposed novel topology doubles the amount of input power accepted for each polarization and then quadruples the overall output power. In addition we have a differential output voltage source that is typically required for the electronics connected to the harvesting system.

  • 11.
    Dahlberg, Oskar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kolitsidas, Christos
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Mattsson, M.
    Silver, Gustaf
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Björkqvist, Oskar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A Novel 32 Port Cube MIMO Combining Broadside and Endfire Radiation Patterns for Full Azimuthal Coverage - A Modular Unit Approach for a Massive MIMO System2017Ingår i: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 1641-1642Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we propose a novel 32 antenna port multiple-input-multiple-output (MIMO)-cube. The total volume of the cube is 320 x 320 x 120 mm(3) . On two faces, endfire radiating linear tapered slot antennas (LTSAs) are placed and on the remaining sides, a mix of both LTSAs and broadside patch antennas are placed. In total 16 LTSAs and 8 dual polarized patches are used. The LTSA is designed to operate at the GSM and 3G bands, from 1.7 to 2.3 GHz. A corrugation pattern is introduced along the edges of the LTSAs covering one face to increase directivity and decrease sidelobes. The LTSAs are placed in two different orientations in order to receive two polarisations. The patch antenna is dual band and dual polarized. It operates in the frequency bands 2.4-2.5 and 5.45-5.6 GHz where Wi-Fi communication is made. The spatial placement, with antennas on all sides of the cuboid, ensures full azimuthal coverage despite the high directivity of the antennas. Using different antennas on different faces of the cube further optimizes the volume efficiency of the cube for azimuthal coverage.

  • 12.
    Björkqvist, Oskar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kolitsidas, Christos
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Dahlberg, Oskar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Silver, Gustaf
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Mattsson, M.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A Novel Efficient Multiple Input Single Output RF Energy Harvesting Rectification Scheme2017Ingår i: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 1605-1606Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this work an implementation of an ambient radio frequency harvesting system utilizing multiple input single output approach is demonstrated. Measurements of typical ambient radiation have been conducted with respect to power levels and frequency to determine which communication signals are suitable for harvesting. The measurement campaign showed that the WiFi frequency band at 2.45 GHz is a good candidate for indoors applications. A Greinacher voltage doubler is used for the rectification. A multiple input single output - MISO scalable scheme approach is implemented that is able to provide a DC differential output voltage. Simulated and experimental results proved the MISO rectenna to be an efficient scheme for RF harvesting.

  • 13.
    Carrander, Claes
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Engdahl, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A semi-empirical approximation of static hysteresis for high flux densities in highly grain-oriented silicon iron2017Ingår i: 8th Joint European Magnetic Symposia (JEMS2016), Institute of Physics (IOP), 2017, artikel-id UNSP 012039Konferensbidrag (Refereegranskat)
    Abstract [en]

    In calculations and simulations regarding magnetic materials, it is important to have a have an accurate model of the hysteresis loop. The major loop, in particular, is used in many simulations. However, it is generally not possible to measure the true major loop, and it must therefore be approximated using a minor loop. There are several methods available for approximating magnetization curves, but they are primarily designed for paramagnetic materials, and are poorly suited to the highly grain-oriented steels used in modern transformers. Therefore, we propose two expressions for approximating the magnetization curves of grain-oriented silicon-iron steels. Both methods give close agreement with measurements and can be extrapolated to in order to describe the major loop.

  • 14. Bantavis, P. I.
    et al.
    Kolitsidas, Christos
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Empliouk, T.
    Kyriacou, G. A.
    A Wideband Switched Beam Antenna System for 5G Femtocell Applications2017Ingår i: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 929-930Konferensbidrag (Refereegranskat)
    Abstract [en]

    This work introduces a wideband switched beam system for femtocell 5G base stations. The system consists of a 4 x 1 Vivaldi linear array and a 4 x 4 Butler matrix able to operate from 1.9-5.1 GHz. A soft surface is introduced along the outer edges of the vivaldi elements of the array for side lobes and back radiation suppression.

  • 15. Valerio, Guido
    et al.
    Sipus, Zvonimir
    Grbic, Anthony
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Accurate Equivalent-Circuit Descriptions of Thin Glide-Symmetric Corrugated Metasurfaces2017Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 65, nr 5, s. 2695-2700Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thin artificial surfaces that act as high frequency bandgap structures have been recently studied for the design of gap waveguides, hard surfaces, and planar lenses. Here, we propose a circuit-based method to analyze glide-symmetric corrugated metasurfaces that are embedded in a thin parallel plate waveguide. Our closed-form solution is based on rigorous analytical derivations. It achieves remarkable agreement with full-wave solvers, even when the waveguide thickness is extremely thin. In contrast, classical homogenization approaches are shown to be inaccurate for thin waveguides due to the interaction of higher order Floquet modes between the surfaces. Numerical results validate our theoretical analysis and show the utility of the proposed method.

  • 16. Zhan, Qiuqiang
    et al.
    Liu, Haichun
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Wang, Baoju
    Wu, Qiusheng
    Pu, Rui
    Zhou, Chao
    Huang, Bingru
    Peng, Xingyun
    Ågren, Hans
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. South China Normal University, China.
    Achieving high-efficiency emission depletion nanoscopy by employing cross relaxation in upconversion nanoparticles2017Ingår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, nr 1, artikel-id 1058Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Stimulated emission depletion microscopy provides a powerful sub-diffraction imaging modality for life science studies. Conventionally, stimulated emission depletion requires a relatively high light intensity to obtain an adequate depletion efficiency through only light–matter interaction. Here we show efficient emission depletion for a class of lanthanide-doped upconversion nanoparticles with the assistance of interionic cross relaxation, which significantly lowers the laser intensity requirements of optical depletion. We demonstrate two-color super-resolution imaging using upconversion nanoparticles (resolution ~ 66 nm) with a single pair of excitation/depletion beams. In addition, we show super-resolution imaging of immunostained cytoskeleton structures of fixed cells (resolution ~ 82 nm) using upconversion nanoparticles. These achievements provide a new perspective for the development of photoswitchable luminescent probes and will broaden the applications of lanthanide-doped nanoparticles for sub-diffraction microscopic imaging.

  • 17. Li, Borui
    et al.
    Sun, Fei
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Acoustic surface transformation realized by acoustic-null materials using bilayer natural materials2017Ingår i: APPLIED PHYSICS EXPRESS, ISSN 1882-0778, Vol. 10, nr 11, artikel-id 114001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a general method, known as acoustic surface transformation (AST), to design novel acoustic devices and study the realization of such devices by using naturally available materials in broadband acoustic frequencies. All devices designed by AST only need one anisotropic homogeneous acoustic-null material (ANM). We design the ANM by exploiting natural material-based metal-fluid structures and verify that by numerical simulation. Unlike traditional methods, no complicated mathematical calculations are needed. We only need to design the geometrical shapes of the input and output surfaces of the devices. The proposed method will pave a new road for future acoustic design.

  • 18.
    Carrander, Claes
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Mousavi, Seyedali
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Engdahl, Göran
    KTH, Skolan för elektro- och systemteknik (EES).
    An application of the time-step topological model for three-phase transformer no-load current calculation considering hysteresis2017Ingår i: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 423, s. 241-244Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In many transformer applications, it is necessary to have a core magnetization model that takes into account both magnetic and electrical effects. This becomes particularly important in three-phase transformers, where the zero-sequence impedance is generally high, and therefore affects the magnetization very strongly. In this paper, we demonstrate a time-step topological simulation method that uses a lumped-element approach to accurately model both the electrical and magnetic circuits. The simulation method is independent of the used hysteresis model. In this paper, a hysteresis model based on the first-order reversal-curve has been used. © 2016 Elsevier B.V.

  • 19.
    Malmström, Johan
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. Saab Surveillance, Sweden.
    Jonsson, Lars
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    An Effective Method for Antenna Placement on Platforms Based on the Reaction Theorem2017Ingår i: Proceedings of the 2017 19th International Conference on Electromagnetics in Advanced Applications, ICEAA 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 1547-1550, artikel-id 8065579Konferensbidrag (Refereegranskat)
    Abstract [en]

    Simulations for antenna placement on large platforms are computational costly. We here suggest a very effcient method for antenna placement optimization of low-scattering antennas. The method utilizes the reaction theorem to calculate the mutual impedance between the antennas based on precomputed electromagnetic fields. The method needs only one full-platform simulation together with post-processing of field data to estimate the coupling for all antenna positions in a given region. In the tested case, we see a speed-up with a factor of 2 000, compared to full-wave simulations of every antenna position to be evaluated.

  • 20.
    Liu, Lipeng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Becerra, Marley
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    An efficient model to simulate stable glow corona discharges and their transition into streamers2017Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, nr 10, s. 105204-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A computationally efficient model to evaluate stable glow corona discharges and their transition into streamers is proposed. The simplified physical model referred to as the SPM is based on the classic hydrodynamic model of charge particles and a quasi-steady state approximation for electrons. The solution follows a two-step segregated procedure, which solves sequentially the stationary continuity equation for electrons and then time-dependent continuity equations for ions. The validity of using the SPM to simulate glow corona discharges and their transition into streamers is demonstrated by performing comparisons with a fully coupled physical model (FPM) and with experimental data available in the literature for air under atmospheric conditions. It is shown that the SPM can obtain estimates similar to those calculated with the FPM and those measured in experiments but using significantly less computation time. Since the proposed model simulates efficiently the ionization layer without prior knowledge of the surface electric field or the discharge current, it is a computationally efficient alternative to calculations of glow corona discharges based on Kaptzov's approximation (KAM). The model can also be employed to efficiently calculate the conditions for the transition of glow corona into streamers, overcoming the limitations of KAM to provide such estimates.

  • 21.
    Liu, Lipeng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Becerra, Marley
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Application of the Position-State Separation Method to Simulate Streamer Discharges in Arbitrary Geometries2017Ingår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we extended the recent work of Liu and Becerra to employ the position-state separation (POSS) method to simulate filamentary streamer discharges. POSS is a semi-Lagrangian method, which solves convection-dominated continuity equations without numerical flux correction. An improved interpolation strategy for POSS is here introduced to overcome the excessive numerical diffusion of the method when very small time step is used. Several benchmark tests in the literature are used to validate the improved method. Numerical experiments show that POSS is an accurate, efficient, and robust numerical method to simulate streamer discharges in arbitrary geometries when combined with finite-element method.

  • 22.
    Ebrahimpouri, Mahsa
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Bespoke Lenses Based on Quasi-Conformal Transformation Optics Technique2017Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 65, nr 5, s. 2256-2264Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, a systematic method to design a quasioptimum lens profile based on quasi-conformal transformation optics technique for a given excitation is presented. This method is applied to a number of conventional antennas, such as an aperture and a log-spiral slot. In all these configurations, an increase of the directivity is observed. Furthermore, using this method, a quasi-optimum graded index lens for a broadband enhanced leaky slot excitation is designed and the results are compared with a hyperhemispherical lens with and without matching layers. Our proposed methodology demonstrates to be able to increase the directivity, to reduce the sidelobes and the cross polarization in a broad bandwidth from 20 to 70 GHz. Due to the continuously changed dielectric constant of the lens profile, reflections are also reduced considerably inside the lens.

  • 23. Hu, Mengzhu
    et al.
    Yang, Liu
    Dai, Hao
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Broadband Absorption and Efficient Hot-Carrier Photovoltaic Conversion based on Sunlight-induced Non-radiative Decay of Propagating Surface Plasmon Polaritons2017Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, artikel-id 4809Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Localized surface plasmon polaritons (SPPs), which can decay non-radiatively into hot carriers, have been widely employed to extend the responses of traditional semiconductor-based photocatalytic and photovoltaic devices to sub-bandgap photons. However, radiative decay is unavoidable and adverse to device performances. Here, we propose to take advantage of propagating SPPs, another form of SPPs, which possess non-radiative decay only. A special gold-titanium dioxide nanowire array with each nanowire capped with a nanocone is proposed. The adjacent nanocones forming top gradual openings attribute to efficient sunlight harvesting, while the neighbouring nanowires forming bottom nanoslots allow sufficient absorption due to the propagating SPPs. With the combined advantages, almost 100% of light is absorbed by a very thin gold film in the visible range, and 73% in the whole considered range of 400-1170 nm, superior to the nanocone cell based on localized SPPs, let alone the nanowire-based and planar counterparts. Therefore, much better photovoltaic conversion performance is achieved with short-circuit current density of 0.74 mA/cm(2) and open-circuit voltage of 0.41 V. This work confirms the superiority of non-radiative decay of propagating SPPs to the localized SPPs in terms of generation of hot carriers, providing a promising way of extracting electrons in metal into photocurrent.

  • 24. Yong, Z.
    et al.
    Gong, C.
    Dong, Y.
    Zhang, S.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. Zhejiang University.
    Broadband localized electric field enhancement produced by a single-element plasmonic nanoantenna2017Ingår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, nr 4, s. 2074-2080Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a novel design of a broadband plasmonic nanoantenna, investigate it numerically using finite-difference time-domain methods, and explain its performance using the analysis of charge distribution in addition to a multipole expansion. The custom-designed single-element nanoantenna consists of a modified gold ring structure with a bowtie-shaped spike inside. In contrast to the spectral response of extinction, the broadband localized electric field intensity enhancement is achieved over a bandwidth of 850 nm in the near infrared spectrum. Up to 26- and 22-fold field enhancements near the bowtie spike are obtained at the peak and even in the dip region of the extinction spectrum, respectively. Moreover, the nanostructure exhibits high tunability of its spectral features by modifying the structural parameters. We further demonstrate that the proposed nanoantenna can provide broadband spontaneous emission rates and quantum efficiency enhancements when a low-quantum efficiency emitter is introduced.

  • 25.
    Liu, Kexin
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Ghasemifard, Fatemeh
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Broadband metasurface Luneburg lens antenna based on glide-symmetric bed of nails2017Ingår i: 2017 11th European Conference on Antennas and Propagation, EUCAP 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 358-360, artikel-id 7928545Konferensbidrag (Refereegranskat)
    Abstract [en]

    A broadband metasurface Luneburg lens based on glide-symmetric bed of nails is designed. First, the Luneburg lens was re-shaped using quasi-conformal transformation optics. With this technique, the original circular focal curve of the lens is changed to a straight line. Afterwards, the refractive index distribution of the optically transformed lens is realized by changing the height of the pins in a bed of nails configuration. The complete Luneburg lens is simulated in CST Microwave Studio and the results demonstrate that the lens has 8-16 GHz bandwidth.

  • 26.
    Liao, Qingbi
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Ying, Zhinong
    Gustafson, Carl
    Channel Capacity Analysis of Different Mobile Antenna Array Topologies in the Outdoor Urban Environment for 5G mm Wave System2017Ingår i: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 1473-1474Konferensbidrag (Refereegranskat)
    Abstract [en]

    The 15 and 28 GHz frequency bands have been identified as interesting candidates for future 5G cellular communication systems. In this paper, based on ray-tracing simulations, we investigate the channel capacities at 15 and 28 GHz for a number of different array processing techniques, including beamforming, spatial multiplexing, and two types of hybrid beamforming. This is done for an 8 x 32 multiple input multiple output system, for the single user case. The hybrid beamforming techniques combines the beamforming and spatial multiplexing techniques, in order to reduce the number of analog-to-digital converters and thereby reducing the system complexity, while still maintaining multiplexing capabilities for improved system capacities. The achieved channel capacities the hybrid beamforming techniques with up to four parallel streams outperforms pure beamforming, but does not reach capacities close to that of full spatial multiplexing. This indicates that the outdoor channel can support multiplexing of more than four parallel data streams to a single user.

  • 27.
    Zhao, Kun
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Gustafson, Carl
    Liao, Qinghi
    KTH, Skolan för teknikvetenskaplig kommunikation och lärande (ECE).
    Zhang, Shuai
    Bolin, Thomas
    Ying, Zhinong
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Channel Characteristics and User Body Effects in an Outdoor Urban Scenario at 15 and 28 GHz2017Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 65, nr 12, s. 6534-6548Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of a user's body on channel characteristics for single user downlink transmission in an urban scenario for the fifth generation (5G) systems is investigated with ray-tracing at 15 and 28 GHz. Three different designs of user equipment (UE) antennas are fabricated and integrated into a mobile phone prototype, and their 3-D radiation patterns are measured both with and without a user. The user remains in Cellular Telephone Industries Association (CTIA) standard data mode and talk mode during measurements. The results show that the user's body will cause a strong shadowing loss and generate a large fluctuation on the received signal strength of the UE at both 15 and 28 GHz, which is crucial to channel modeling studies at frequencies above 6 GHz. In addition, the user's body effect on a linear array system in an UE is presented, and the main challenges for the future work are also addressed.

  • 28.
    Wang, Lei
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Yin, Xiaoxing
    Esquius-Morote, Marc
    Zhao, Hongxin
    Mosig, Juan R.
    Circularly Polarized Compact LTSA Array in SIW Technology2017Ingår i: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 65, nr 6, s. 3247-3252Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Typical linearly tapered slot antenna (LTSA) usually features a wideband and a high gain. However, its geometry size is large, especially very long in the tapering direction, which limits its application in compact antenna and array systems. This communication has minimized the tapered length to less than 0.19 lambda(0) when the aperture width is less than 0.35 lambda(0) both for horizontally and vertically polarized LTSA arrays. Moreover, the typical polarization of the LTSA is linear, which is perpendicular to the slot. In this communication, an X-band circularly polarized 1x8 LTSA array, made of cross-LTSAs, is proposed with the feeding of a substrate integrated waveguide horn. All the three different polarized LTSA arrays are designed and investigated both in simulation and experiment, and the simulation results agree well with the measured results.

  • 29. Zhang, J.
    et al.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. Zhejiang University, China.
    Cladding-free efficiently tunable nanobeam cavity with nanotentacles2017Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 25, nr 11, s. 12541-12551Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a cladding-free, efficiently tunable, high-quality factor (Q) nanobeam cavity with subwavelength-period nanotentacles (NT), adequately investigate the performance of the cavity, and study the directional heat transfer. By virtue of the excellent heat transfer of Si nanotentacles, a tuning range of more than 6 nm wavelength, with 24mW and 10 KHz switching rate, and 13 μs raising time is experimentally obtained. This result is about twentyfold better than the previous work by Fegadolli [ACS Photon. 2, 470-474 (2015)]. A potential 12nm tuning range with identical power is also theoretically suggested by modifying the silicon structure. With an optimized design, these nanotentacles are demonstrated to have a minimal effect to the cavity and are available to serve as photonic waveguides. This cladding-free design, with a simple fabrication process, is comparable to other proposals in which deep etching, suspended treatment, and troublesome heterogeneousintegration may be needed. Finally but importantly, this smart design can be applied to other photonic cavities, particularly cavities such as ring/disk resonators, in which we reasonably predict a better tuning efficiency due to the thermal circulation. We believe this design is fairly suitable for applications in which light-matter interaction is of primary importance, such as sensing, particle trapping, cavity quantum electrodynamics (CQED), and III-V/Si hybrid lasers with external cavities.

  • 30.
    Kubyshkina, Elena
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Unge, Mikael
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Communication: Band bending at the interface in polyethylene-MgO nanocomposite dielectric2017Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, nr 5, artikel-id 051101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Polymer nanocomposite dielectrics are promising materials for electrical insulation in high voltage applications. However, the physics behind their performance is not yet fully understood. We use density functional theory to investigate the electronic properties of the interfacial area in magnesium oxide-polyethylene nanocomposite. Our results demonstrate polyethylene conduction band matching with conduction bands of different surfaces of magnesium oxide. Such band bending results in long range potential wells of up to 2.6 eV deep. Furthermore, the fundamental influence of silicon treatment on magnesium oxide surface properties is assessed. We report a reduction of the surface-induced states at the silicon-treated interface. The simulations provide information used to propose a new model for charge trapping in nanocomposite dielectrics.

  • 31. Nikjoo, Roya
    et al.
    Taylor, Nathaniel
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Hollertz, Rebecca
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Wåhlander, Martin
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Malmström, Eva
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Comparison of Oil-impregnated Papers with SiO2 and ZnO Nanoparticles or High Lignin Content, for the Effect of Superimposed Impulse Voltage on AC Surface PD2017Ingår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 24, nr 3, s. 1726-1734Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Surface discharge behavior of modified oil-impregnated paper (OIP) with nanoparticles (NPs), has been investigated under AC voltage with superimposed impulses. Surface Partial Discharges (PD) can develop at an oil-paper interface and lead to its degradation. Modified paper, made from fibers with adsorbed nanoparticles, can affect the partial discharge behavior of a paper in combination with oil at the interface between oil and fibers. Papers with two different concentrations (2 wt% and 6 wt%) of silica (SiO2), and paper with silanized zinc oxide (ZnO) nanoparticles (1 wt%) have been studied. Papers with SiO2 NPs showed lower impulse-induced surface PD activity. However, thorough purification during the production of SiO2 filled papers was necessary to achieve a good performance. With less purification, paper with 2 wt% of SiO2 did not show such significant improvements. Paper with 6 wt% of SiO2 NPs showed a large number of AC surface PDs, but low influence of impulse voltage on subsequent PD. Papers containing 1 wt% of silanized ZnO showed reduced relative permittivity, but no significant difference in surface PD behavior. The effect of high lignin content in Kraft paper has also been studied. Paper with higher lignin content showed better surface PD characteristics under the impulse. Paper with low concentrations of pure SiO2 NPs, and paper with high lignin content thus appear good candidates for further studies to improve the surface PD behavior of OIP.

  • 32.
    Westerlund, Per
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Condition measuring and lifetime modelling of disconnectors, circuit breakers and other electrical power transmission equipment2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Elförsörjningen är viktig i det moderna samhället, så avbrotten bör vara få och korta, särskilt i stamnätet. En kortfattad historik över det svenska elsystemet presenteras. Målet är att kunna planera avbrotten för underhåll bättre genom att veta mera om apparaternas skick.

    Det är svårt att planera avbrott för underhåll och utbyggnad. Riskmatrisen är verktyg för att välja vad som ska underhållas och den kan förbättras genom att lägga till en dimension, sannolikhetens osäkerhet. Risken kan minskas längs med varje dimension: bättre mätningar, förebyggande underhåll och mer redundans. Antalet dimensioner kan igen bli två genom att följa linjer med samma risk, som är beräknade för betafördelningen.

    Denna avhandling tar upp tjugo studier av fel i brytare och frånskiljare med data om felorsak och livslängd. Den har också en översikt av ett fyrtiotal olika metoder för tillståndsmätningar för brytare och frånskiljare, som huvudsakligen rör de elektriska kontakterna och de mekaniska delarna.

    Ett system med IR sensorer har installerats på de nio kontakterna på sex frånskiljare. Målet är att minska antalet avbrott för underhåll genom att skatta skicket när frånskiljarna är i drift. De uppmätta temperaturerna tas emot genom radio och behandlas genom regression mot kvadraten av strömmen, då den bästa exponenten för strömmen visade sig vara 2,0. Förklaringsfaktorn $R^2$ är hög, över 0,9. För varje kontakt ger det en regressionskoefficient. Ju högre koefficienten är, desto mer värme utvecklas det i kontakten, vilket kan leda till skador på materialet. Koefficienterna ger en rangordning av frånskiljarna. Systemet kan också användas för att minska eller öka den tillåtna strömmen baserat på skicket.

    Slutligen förklaras ett ramverk för livslängdsmodellering och tillståndsmätning. Livslängdsmodellering innebär att koppla en fördelning för tiden till fel med varje delpopulation. Med tillståndsmätning avses att mäta en parameter och skatta dess värde i framtiden. Om den överskrider en tröskel, måste apparaten underhållas. Effekten av underhåll visas för fyra frånskiljare.

    En utveckling av riskmatrisen med osäkerheten, en sammanställning av statistik och metoder för tillståndsövervakning, ett system med IR-sensor vid kontakerna, en metod för termografiplanering och ett ramverk för livslängdsmodellering och tillståndsmätningar presenteras. De kan förbättra avbrottsplaneringen.

  • 33. Jiang, W.
    et al.
    Ma, Y.
    Yuan, J.
    Yin, G.
    Wu, W.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Deformable broadband metamaterial absorbers engineered with an analytical spatial Kramers-Kronig permittivity profile2017Ingår i: Laser & Photonics reviews, ISSN 1863-8880, E-ISSN 1863-8899, Vol. 11, nr 1, artikel-id 1600253Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electromagnetic (EM) materials with perfect absorption have long been investigated for their important applications in many practical technologies. The trial-and-error method has been mostly employed to achieve this target, either by varying the constituent compositions for traditional natural material absorbers or by running computer simulations for general metamaterial (MM) absorbers. In this work, the authors propose a new method with analytical guidance to build omnidirectional perfect absorbers inspired by the recently proposed spatial Kramers-Kronig (KK) nonreflecting dielectric profile. The subtle combination of the spatial and time dispersions in the metamaterial-engineered KK profile gives the desired broadband response property. More importantly, these features remain invariant when the sample is uniformly compressed or stretched with large thickness change, i.e., this particular broadband absorber is deformable, which has been firstly reported in the literature. The current results will pave a new way to design high-efficiency EM absorbers that could also be extended in general to manipulate waves for other fields or applications. (Figure presented.).

  • 34.
    Ebrahimpouri, Mahsa
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Rajo-Iglesias, Eva
    Design Guidelines for Gap Waveguide Technology Based on Glide-Symmetric Holey Structures2017Ingår i: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 27, nr 6, s. 542-544Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The behavior of a glide-symmetric holey periodic structure as electromagnetic bandgap is studied in this letter. A number of numerical simulations have been carried out in order to define the importance of each constituent parameter of the unit cell. Our proposed structure finds potential application in antennas and circuits based on gap waveguide technology for the millimeter band. The experimental verifications confirm the effects previously analyzed with the numerical studies.

  • 35.
    Ebrahimpouri, Mahsa
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Rajo-Iglesias, E.
    Design of microwave components in groove gap waveguide technology implemented by holey EBG2017Ingår i: 2017 11th European Conference on Antennas and Propagation, EUCAP 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 746-748, artikel-id 7928587Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, the feasibility of the implementation of microwave components in groove gap waveguide technology by glide-symmetry holey EBG is discussed. Using this technology, microwave components and antennas which were previously designed for hollow metallic waveguides can be manufactured in a cost-effective way at high frequencies. To show the viability of the proposed solution a phase shifter and a mode converter are designed as examples of typical components for antenna systems.

  • 36. Camacho, Miguel
    et al.
    Mitchell-Thomas, Rhiannon C.
    Hibbins, Alastair P.
    Sambles, J. Roy
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Designer surface plasmon dispersion on a one-dimensional periodic slot metasurface with glide symmetry2017Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 42, nr 17, s. 3375-3378Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this Letter, we explore the dispersion of spoof surface plasmons supported by a single-layer glide-symmetric structure. This structure consists of an infinitely long double-notched slot perforated in a metal layer. The presence of a degeneracy of the two lowest-order modes at the Brillouin zone boundary, which have non-zero group velocity is explained and experimentally demonstrated. Further, the dependence of the band structure when glide-symmetric configuration is broken is also explored.

  • 37.
    Nikjoo, Roya
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Taylor, Nathaniel
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Edin, Hans
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Dielectric response measurement by impulse stimulus on AC: Measurement considerations, and laboratory testing on a bushing2017Ingår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 24, nr 1, s. 511-518, artikel-id 7873509Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dielectric response (DR) measurement is commonly used for condition assessment of insulation systems of power components. A method for measurement of dielectric response using the stimulus of natural transients such as lightning and switching impulses was proposed in earlier work. Its desirable features include the ability to make measurements online over a range of frequencies, without requiring a voltage source. This article presents a laboratory demonstration of the method on a 150 kV service-aged transformer bushing, where the stimulus was a standard lightning impulse voltage superimposed on an AC voltage. Several aspects of the measurement and data processing that affect the results are studied experimentally and numerically. The results are compared with low-voltage frequency domain spectroscopy (FDS). Reasonable accuracy for monitoring changes in DR can be achieved by suitable choice of measurement circuit and data acquisition. The study suggests an approach for online monitoring of dielectric properties of power transformer bushings, and diagnostics of defects that affect the high frequency region of DR, such as moisture content.

  • 38.
    Chen, Feng
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Taylor, Nathaniel
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Balieu, Romain
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Kringos, Niki
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Dynamic application of the Inductive Power Transfer (IPT) systems in an electrified road: Dielectric power loss due to pavement materials2017Ingår i: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 147, s. 9-16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Inductive Power Transfer (IPT) technology is seen as a promising solution to be applied in an electrified road (eRoad) to charge Electric Vehicles (EVs) dynamically, i.e. while they are in motion. Focus in this study was placed on the dielectric loss effect of pavement surfacing materials on the inductive power transfer efficiency, induced after the integration of the technology into the physical road structure. A combined experimental and model prediction analysis was carried out to calculate this dielectric loss magnitude, based on which some preliminary conclusions as well as a prioritization of future focus needs were summarized in detail.

  • 39.
    Li, Bing
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Månsson, Daniel
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Effect of Periodicity in Frequency Responses of Networks From Conducted EMI2017Ingår i: IEEE transactions on electromagnetic compatibility (Print), ISSN 0018-9375, E-ISSN 1558-187X, Vol. 59, nr 6, s. 1897-1905Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we consider different types of networks, and investigate the characteristics of the frequency responses of loads, which are distributed in the networks. Without loss of generality, both frequency-independent and frequency-dependent loads are discussed, respectively. Beginning with a transmission-line (TL) network with frequency-independent loads, via the TL theory and Baum-Liu-Tesche equation, we demonstrate that the frequency responses are periodic in the frequency domain, where the periodicity is derived and verified. Subsequently, our study is extended to the complex networks that consist of multiple junctions and branches. By using the statistical method, we generate random loads with different attributes, i.e., resistive, inductive, or capacitive, and mainly study the effect of the number of branches and junctions on the frequency response of targeted load in various networks. From the perspective of protections for the targeted load in networks, results indicate that, for lossless and good dielectric (i.e., low-loss) media, it is crucial to consider the frequency responses at the critical frequencies in a periodical manner, rather than at a single frequency. Furthermore, it is worth noting that, the frequency response of targeted load behaves differently when varying the attributes of other loads in the network. The variation of network topology, i.e., increasing the number of junctions or branches, also influences the frequency response.

  • 40.
    Malmström, Johan
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Efficient Methods to Calculate Mutual Coupling between Generic Antennas on Large Platforms2017Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Denna avhandling behandlar metoder för att beräkna ömsesidig koppling mellan antennar. Den ömsesidiga kopplingen beskriver hur mycket av den energi som sänds ut i en av antennerna som tas upp av den andra antennen och är ett viktigt mätetal vid installation av antenner på plattformar, såsom flygplan. För att undvika störningar mellan de system som ansluts till antennerna så bör kopplingen vara så låg som möjligt. Risken för störning påverkas av både de system som ansluts till antennerna och utbredningsvägen mellan antennerna. Denna avhandling fokuserar på det senare.

    Elektromagnetiska problem, t ex koppling mellan antenner, löses standardmässigt genom simuleringar med kommersiella programvaror. Simuleringarna blir dock mycket beräkningsintensiva för stora plattformar. Avhandling undersöker sätt att effektivt beräkna kopplingen. Syftet med arbetet har varit att ta fram metoder som kan användas i praktiska situationer.  

    En möjlig effektivisering är att införa approximationer som bidrar till att förenkla beräkningarna. Två typer av approximationer har undersökts, dels förenklade vågutbredningsmodeller och dels ekvivalenta representationer av antenner. Båda dessa approximationer har potential att ge minskade beräkningstider men lider av att storleken på felen som introduceras inte är predikterbara. Detta bidrar till en osäkerhet vid uppskattning av kopplingen mellan antenner som gör dem mindre intressanta att använda i tillämpningar.  

    Reaktionsteoremet, som beskriver hur kopplingen förmedlas via elektromagnetiska fält, har visat sig mycket användbart i detta arbete. För att kunna tillämpa det så har två nya formuleringar av teoremet härletts. Formuleringarna delar upp genererade fält i dess spridda komponenter och visar att vissa komponenter inte påverkar reaktionen. Reaktionsteoremet och de härledda formuleringarna används i två tillämpningar.  

    Den första tillämpningen visar på praktiska möjligheter att beräkna ömsesidiga impedansen mellan antenner på en gemensam plattform. Det visas även på en metod för att visualisera kopplingsvägar, något som ger viktig information om hur kopplingen mellan antennerna är spatialt fördelad.  

    Den andra tillämpningen som använder reaktionsteoremet föreslår en effektiv metod för att placera antenner på en plattform så att den ömsesidiga impedansen mellan antennerna minimeras. Metoden används som ett efterbehandlingssteg där indata är fältvärden beräknade med kommersiell mjukvara. Metoden möjliggör att beräknade fältdata kan återanvändas vilket signifikant minskar beräkningstiden.  

    De huvudsakliga resultaten från avhandlingen är samlade i totalt fem artiklar och konferensbidrag som har eller ska publiceras i internationella vetenskapliga tidskrifter eller på konferenser. 

  • 41. Hong, Y.
    et al.
    Hong, Xuezhi
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    Chen, Jiajia
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Optical Network Laboratory (ON Lab).
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Elastic all-optical multi-hop interconnection in data centers with adaptive spectrum allocation2017Ingår i: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 383, s. 478-484Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, a novel flex-grid all-optical interconnect scheme that supports transparent multi-hop connections in data centers is proposed. An inter-rack all-optical multi-hop connection is realized with an optical loop employed at flex-grid wavelength selective switches (WSSs) in an intermediate rack rather than by relaying through optical-electric-optical (O-E-O) conversions. Compared with the conventional O-E-O based approach, the proposed all-optical scheme is able to off-load the traffic at intermediate racks, leading to a reduction of the power consumption and cost. The transmission performance of the proposed flex-grid multi-hop all-optical interconnect scheme with various modulation formats, including both coherently detected and directly detected approaches, are investigated by Monte-Carlo simulations. To enhance the spectrum efficiency (SE), number-of-hop adaptive bandwidth allocation is introduced. Numerical results show that the SE can be improved by up to 33.3% at 40 Gbps, and by up to 25% at 100 Gbps. The impact of parameters, such as targeted bit error rate (BER) level and insertion loss of components, on the transmission performance of the proposed approach are also explored. The results show that the maximum SE improvement of the adaptive approach over the non-adaptive one is enhanced with the decrease of the targeted BER levels and the component insertion loss.

  • 42. Shi, Kezhang
    et al.
    Bao, Fanglin
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Enhanced Near-Field Thermal Radiation Based on Multilayer Graphene-hBN Heterostructures2017Ingår i: ACS Photonics, E-ISSN 2330-4022, Vol. 4, nr 4, s. 971-978Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Graphene-covered hexagonal boron nitride (hBN) can exceed blackbody thermal radiation in near-field due to the coupling of surface plasmon polaritons (SPPs) and hyperbolic phonon polaritons (HPPs). As previous research found that the thickness of hBN in a graphene-hBN cell can be very thin while still presenting strong radiation enhancement, multilayer graphene-hBN heterostructures are proposed in this paper to further enhance the near-field thermal radiation. We found that a heterostructure consisting of five or more graphene-hBN cells performs better than all existing graphene-hBN configurations, and the infinite cell limit exhibits 1.87- and 2.94-fold larger heat flux at 10 nm separation than sandwich and monocell structures do, respectively, due to the continuously and perfectly coupled modes. The heat flux is found to be 4 orders of magnitude larger than that of the blackbody. The effective tunability of the thermal radiation of the multicell structure is also observed by adjusting the chemical potentials of graphene with an optimized thickness of 20 nm on each hBN, which is instructive for both experimental design and fabrication of thermal radiation devices.

  • 43.
    Petersson, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. Saab Surveillance, Jarfälla, Sweden.
    Error Estimation in Retrodirective Channel Implementation2017Ingår i: IEEE International Conference on Microwaves, Communications, Antennas and Electronic Systems (COMCAS), Tel Aviv, Israel, 13-15 november 2017, IEEE conference proceedings, 2017, s. 120-125Konferensbidrag (Refereegranskat)
    Abstract [en]

    Cross-eye (CE) jamming is a technique of electronic attack that can provide self-protection of aircraft against guided missiles using monopulse type radar. Implementation of a CE jammer using a retrodirective channel in a non-reciprocal electronic warfare system requires an appropriate system design and a correction process to achieve reciprocity. This paper defines a model of a CE jammer that uses digital radio-frequency memories, Active Electronically Scanned Arrays (AESA), and a system correction process. Further, the paper defines a simulation procedure for jammer performance estimation and system evaluation. The procedure is demonstrated by performing a parameter sensitivity study where the effects of dynamic variations in AESA model parameters on CE performance are determined.

  • 44.
    Zhao, Kun
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. SONY Mobile Communications AB, Sweden.
    Ying, Z.
    He, Sailing
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Evaluation of combined TIS for high order MIMO system in mobile terminal2017Ingår i: 2017 11th European Conference on Antennas and Propagation, EUCAP 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 3684-3687, artikel-id 7928570Konferensbidrag (Refereegranskat)
    Abstract [en]

    The maximum ratio combined total isotropic sensitivity (TIS) of high order MIMO system in a real phone prototype is presented in this paper. The value of combined TIS is estimated through antenna pattern combination and verified by experiments. The impact from the order of MIMO system, the propagation model and the user body effect are investigated.

  • 45.
    Silver, Gustaf
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Kolitsidas, Christos
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Björkqvist, Oskar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Matsson, M.
    KTH.
    Dahlberg, Oskar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Jonsson, B. Lars G.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Exploiting Antenna Array Configurations for Efficient Simultaneous Wireless Information and Power Transfer2017Ingår i: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 1083-1084Konferensbidrag (Refereegranskat)
    Abstract [en]

    Different patch antenna array configurations for Simultaneous Wireless Information and Wireless Power Transfer - SWIPT - were simulated and evaluated. The scope of the work is to provide configurations that can be used to minimise the interference between information and power transfer as well as provide some beamforming capabilities. Our assumption for all the evaluated structures are that two receive antennas are used for RF energy harvesting and one antenna is used for information exchange. The choice for two antennas for energy harvesting is based on that a differential DC output full-wave rectifier is used. Our analysis is based on patch antennas.

  • 46.
    Ariza, David
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Becerra, Marley
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Hollertz, Rebecca
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi, Fiberteknologi.
    Wågberg, Lars
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknologi.
    Pitois, Claire
    ABB AB Corporate Research.
    First Mode Negative Streamers along Mineral Oil-solid Interfaces2017Ingår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 24, nr 4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This document presents an experimental study on the propagation of first mode negative streamers along mineral oil-solid interfaces. Samples made of an oil impregnated kraft paper and a low-porosity paper made from cellulosic micro and nano fibrils, as well as different polymeric films (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF)) are used as the solid. A comparison of the length, charge and velocity of streamers for all different mineral oil-solid interfaces is reported. It is shown that streamers propagate longer and faster along mineral oil-solid interfaces with low surface roughness, low porosity and higher electrical permittivity than mineral oil. Those streamers show a quasi-continuous injection of charge in the early stage of their propagation. This quasi-continuous charge injection consists of a sequence of small charge steps separated by few tens of nanoseconds in between. In comparison, the streamers that propagate along surfaces with similar permittivity to the mineral oil have lower injection of charge and higher stopping voltage conditions than streamers propagating free in the liquid without any solid barrier.

  • 47.
    Liu, Lipeng
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Becerra, Marley
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Gas heating dynamics during leader inception in long air gaps at atmospheric pressure2017Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 50, nr 34, artikel-id 345202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The inception of leader discharges in long air gaps at atmospheric pressure is simulated with a thermo-hydrodynamic model and a detailed kinetic scheme for N2/O2/H2O mixtures. In order to investigate the effect of humidity, the kinetic scheme includes the most important reactions with the H2O molecule and its derivatives, resulting in a scheme with 45 species and 192 chemical reactions. The heating of a thin plasma channel in front of an anode electrode during the streamer to leader transition is evaluated with a detailed 1D radial model. The analysis includes the simulation of the corresponding streamer bursts, dark periods and aborted leaders that may occur prior to the inception of a propagating leader discharge. The simulations are performed using the time-varying discharge current in two laboratory discharge events of positive polarity reported in the literature as input. Excellent agreement between the simulated and the experimental time variation of the thermal radius for a 1m rod-plate air gap discharge event reported in the literature has been found. The role of different energy transfer and loss mechanisms prior to the inception of a stable leader is also discussed. It is found that although a small percentage of water molecules can accelerate the vibrational-translational relaxation to some extent, this effect leads to a negligible temperature increase during the streamer-to-leader transition. It is also found that the gas temperature should significantly exceed 2000 K for the transition to lead to the inception of a propagating leader. Otherwise, the strong convection loss produced by the gas expansion during the transition causes a drop in the translational temperature below 2000 K, aborting the incepted leader. Furthermore, it is shown that the assumptions used by the widely-used model of Gallimberti do not hold when evaluating the streamer-to-leader transition.

  • 48.
    Jürgensen, Jan Henning
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Scheutz Godin, Axel
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Hilber, Patrik
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Health index as condition estimator for power system equipment: A critical discussion and case study2017Ingår i: CIRED - Congrès International des Réseaux Electriques de Distribution, 2017., Institution of Engineering and Technology, 2017, Vol. 2017, s. 202-205, artikel-id 1Konferensbidrag (Refereegranskat)
    Abstract [en]

    Over the past decade, the health index has become an increasingly popular asset management tool in utilities. The health index as a condition indicator can improve the decision making process. However, it also has challenges which need to be considered during development and implementation. This paper addresses the advantages and disadvantages of the health index as a condition indicator in a critical discussion. Moreover, a case study is presented where a health index is calculated for three transmission power transformers. The case study illustrates that age and the load factor included in the health index calculation lead to an immoderately high health index for the transformers T2 and T3. Thus, the paper ageing of the transformer windings are used instead which results in a plausible condition representation of all three transformers. The case study also demonstrates that the observation of condition trends over time is lost if the health index is transformed into a linguistic expression.

  • 49. Shen, Z.
    et al.
    Xu, Bo
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Liu, Peng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Hu, Y.
    Yu, Y.
    Ding, H.
    Kloo, Lars
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Hua, J.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi. Dalian University of Technology (DUT), Dalian, China.
    Tian, H.
    High performance solid-state dye-sensitized solar cells based on organic blue-colored dyes2017Ingår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, nr 3, s. 1242-1247Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The development of novel photosensitizers with very high molar extinction coefficients and broad absorption spectra to enhance the light harvesting efficiency providing high PCEs for solid state dye sensitized solar cells (sDSCs) is a main target for improvement. In this work, two novel organic blue-colored dyes termed S4 and S5 with indeno[1,2-b]thiophene functionalized triphenylamine as the donor, 2,3-diphenylpyrido[3,4-b]pyrazine (PP) or 2,3-diphenylquinoxaline (QT) as the auxiliary acceptor and cyclopentadithiophene (CPDT) as the π-linker were designed and synthesized for sDSCs. S5 containing the QT unit as the electron-withdrawing group exhibits a high molar extinction coefficient of 6.3 × 104 M-1 cm-1 at 600 nm. Most importantly, the S5-based sDSCs shows record PCEs of 7.81% and 8.25% under one sun and 0.5 sun light intensities, respectively, exceeding the PCE of LEG4-based solar cells (7.34%). To the best of our knowledge, this is the first case where an organic blue-colored dye displays a PCE over 7.8% in sDSCs, thus representing record efficiencies for sDSCs. These results clearly show that molecular engineering is a viable way to develop blue-colored dyes with high molar extinction coefficients for use in highly efficient sDSCs. Also, blue-colored dyes open up co-sensitization strategies in combination with traditional organic dyes with yellow-red colours.

  • 50.
    Quevedo-Teruel, Óscar
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Valerio, G.
    Higher symmetries: A new degree of freedom for the design of periodic structures2017Ingår i: 2017 11th International Congress on Engineered Material Platforms for Novel Wave Phenomena, Metamaterials 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 271-273, artikel-id 8107916Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this presentation, we will introduce the concept of higher symmetries, including both glide and twist symmetries. We will describe the remarkable properties of higher symmetries, such as their ability to produce both large bandgaps and low dispersive media. Higher-symmetry structures provide a new degree of freedom for the design of periodic structures, and find potential application for bandgap waveguide technology, ultra-wideband flat lenses, and low-dispersive leaky wave antennas.

1