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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.
    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.
    Pourrahimi, Amir Masoud
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
    Electric Conduction in Mineral Oil based ZnONanofluids under Intense Electric FieldsManuscript (preprint) (Other academic)
    Abstract [en]

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

  • 5.
    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.

  • 6.
    Ariza Rocha, Oscar David
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Dynamic transformers rating for expansion of expansion of existing wind farms2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Distribution system operators face the challenge to connect users rapidly to the grid and the opportunity to reduce costs for new connections. A method to enhance network operation and planning is dynamic transformer rating (DTR), which considers load and temperature variations to increase the rating of the transformer while maintaining in safe operation.

    This project investigates DTR application to an existing population of transformers connected to a wind park and proposes a method for adding new turbines to the grid using installed transformers. Five transformer locations and nine units belonging to E.ON AB are used to find the potential of DTR for network expansion.

    A weather analysis reveals that simultaneous high wind speeds and high temperatures seldom occur. An aging estimation based on the IEC 60076-7 standard shows that the transformers for wind power applications are underused. Considering the transformer thermal model, a sensitivity analysis shows that the parameters that mostly affect the aging rate are the moisture content, the hot spot factor, and the top-oil temperature rise. The maximum load to assure aging below 50 years is calculated for each transformer for different maximum hot-spot temperature levels showing that increasing the maximum allowed temperature reduces curtailment and increases aging. A single node analysis depicts the optimal expansion of wind power from a generator perspective, and a network analysis introduces further restrictions to the network. As a result, the optimal increase factor is around 30 to 50 % and is larger for higher hot-spot temperature limits.

    Accurate weather measurements and transformer parameters are necessary to make a proper estimation of transformer aging to unlock transformer potential. To use fiber optic temperature sensors in new transformers and on-site temperature measurements can increase the rating of the transformer. A maximum allowed temperature of 110◦C is conservative and limits the potential of the transformer for wind power applications. Finally, society benefits from DTR in wind power applications because there is a more efficient use of resources and additional renewable energy can be introduced to the network.

  • 7.
    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.

  • 8.
    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.

  • 9.
    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.

  • 10.
    Bagheriasl, Mohammad
    et al.
    Sorbonne Univ, L2E, UR2, F-75005 Paris, France..
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Valerio, Guido
    Sorbonne Univ, L2E, UR2, F-75005 Paris, France..
    Bloch Analysis of Artificial Lines and Surfaces Exhibiting Glide Symmetry2019In: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 67, no 7, p. 2618-2628Article in journal (Refereed)
    Abstract [en]

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

  • 11. 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. 

  • 12. Bantavis, P. I.
    et al.
    Kolitsidas, Christos
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Empliouk, T.
    Le Roy, M.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Kyriacou, G. A.
    A Cost-Effective Wideband Switched Beam Antenna System for a Small Cell Base Station2018In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 66, no 12, p. 6851-6861, article id 8485638Article in journal (Refereed)
    Abstract [en]

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

  • 13.
    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.

  • 14.
    Becerra Garcia, Marley
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Aljure, Mauricio
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Nilsson, Janne
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Assessing the production and loss of electrons from conduction currents in mineral oil2019In: 2019 IEEE 20th International Conference on Dielectric Liquids (ICDL), IEEE Computer Society, 2019Conference paper (Refereed)
    Abstract [en]

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

  • 15.
    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.

  • 16.
    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.

  • 17.
    Becerra Garcia, Marley
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, S-10044 Stockholm, Sweden.;ABB Corp Res, S-72226 Vasteras, Sweden..
    Pettersson, Jonas
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Franke, Steffen
    INP Leibniz Inst Plasma Sci & Technol, D-17489 Greifswald, Germany..
    Gortschakow, Sergey
    INP Leibniz Inst Plasma Sci & Technol, D-17489 Greifswald, Germany..
    Temperature and pressure profiles of an ablation-controlled arc plasma in air2019In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, no 43, article id 434003Article in journal (Refereed)
    Abstract [en]

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

  • 18.
    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.

  • 19.
    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.))
  • 20.
    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.
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Additive Manufactured Three Dimensional Luneburg Lens for Satellite Communications2019In: 13th European Conference on Antennas and Propagation, EuCAP 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, article id 8739803Conference paper (Refereed)
    Abstract [en]

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

  • 21.
    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.

  • 22.
    Brazalez, Astrid Algaba
    et al.
    Ericsson AB, Ericsson Res, Gothenburg, Sweden..
    Manhohni, Lars
    Ericsson AB, Ericsson Res, Gothenburg, Sweden..
    Johansson, Martin
    Ericsson AB, Ericsson Res, Gothenburg, Sweden..
    Mattsson, 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.
    Implementation of a compact Ka-band parallel plate Luneburg lens based on a hybrid dielectric/metasurface unit cell2019In: 13th European Conference on Antennas and Propagation, EuCAP 2019, IEEE, 2019, article id 8740306Conference paper (Refereed)
    Abstract [en]

    The complete implementation and numerical validation of a compact cost-effective multiport parallel plate Luneburg lens antenna operating at 28 GHz is described in this paper. The lens design consists of two parallel plates separated by a gap where each of them contains a metasurface structure based on a new type of combined dielectric/holey unit cell periodically arranged in a glide-symmetric configuration. The required refractive index is achieved by a combination of coarse control by adding a dielectric in the gap, and fine tuning by changing the height of the holes. The simulations of the final prototype including a flare to ensure a smooth wave transition from the parallel plate configuration to air, as well as a coaxial-to-waveguide-to-parallel plate feeding, show a 20% bandwidth for 11.5 dB return loss, and the crosstalk remains below -15 dB for the same frequency band.

  • 23.
    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.

  • 24. 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.

  • 25.
    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.

  • 26.
    Capek, Miloslav
    et al.
    Czech Tech Univ, Prague, Czech Republic..
    Jelinek, Lukas
    Czech Tech Univ, Prague, Czech Republic..
    Schab, Kurt
    Santa Clara Univ, Santa Clara, CA 95053 USA..
    Gustafsson, Mats
    Lund Univ, Lund, Sweden..
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Ferrero, Fabien
    Univ Cote Azur, Nice, France..
    Ehrenborg, Casimir
    Lund Univ, Dept Elect & Informat Technol, Lund, Sweden..
    Optimal Planar Electric Dipole Antennas Searching for antennas reaching the fundamental bounds on selected metrics.2019In: IEEE Antennas & Propagation Magazine, ISSN 1045-9243, E-ISSN 1558-4143, Vol. 61, no 4, p. 19-29Article in journal (Refereed)
    Abstract [en]

    Considerable time is often spent optimizing antennas to meet specific design metrics. Rarely, however, are the resulting antenna designs compared to rigorous physical bounds on those metrics. Here, we study the performance of optimized planar meander line antennas with respect to such bounds. Results show that these simple structures meet the lower bound on the radiation quality factor (Q-factor) (maximizing single-resonance fractional bandwidth) but are far from reaching the associated physical bounds for efficiency. The relative performance of other canonical antenna designs is comparable in similar ways, and the quantitative results are connected to intuitions from small antenna design, physical bounds, and matching network design.

  • 27. 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.

  • 28.
    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.

  • 29.
    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.

  • 30.
    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.

  • 31.
    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.

  • 32.
    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.

  • 33.
    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.

  • 34.
    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.

  • 35.
    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.

  • 36.
    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.

  • 37.
    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.

  • 38.
    Dahlberg, Oskar
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Pucci, E.
    Ericsson AB, Syst & Technol, S-16480 Stockholm, Sweden..
    Wang, L.
    Hamburg Univ Technol, Inst Theoret Elektrotech, D-21079 Hamburg, Germany..
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Low-Dispersive Glide-Symmetric Leaky-Wave Antenna at 60 GHz2019In: 13th European Conference on Antennas and Propagation, EuCAP 2019, IEEE, 2019, article id 8740212Conference paper (Refereed)
    Abstract [en]

    In this work we demonstrate a method for producing low-loss, non-squinting, directive leaky-wave antennas (LWAs) for millimeter-wave frequencies. The scanning behaviour of the radiation pattern arises from the dispersive nature of the waveguide mode, which is leaking out when opening the wave guiding structure. We propose a method to cancel the dispersive behaviour, by allowing the leaked waves to refract in a dispersive prism-lens. The proposed method allows for fully metallic implementation of the antenna, resulting in low losses. Furthermore, high directivity is easily achieved with a simple feeding. The corresponding theory is outlined, and the proposed method is used to design an antenna operating at 60 GHz. The obtained bandwidth, with less than 1 degrees beam scanning, is 20% in simulations and the realized gain of the antenna is 17 dB across the entire bandwidth. The design is proposed as an alternative to obtain high gain antennas for 5G applications, in which low losses and narrow beams are expected to be key features for mm-waves.

  • 39. 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. 

  • 40.
    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.

  • 41.
    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)
  • 42.
    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.

  • 43.
    Duvnjak Zarkovic, Sanja
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Stankovic, Stefan
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Hilber, Patrik
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Reliability improvement of distribution system through distribution system planning: MILP vs. GA2019In: 2019 IEEE Milan PowerTech, 2019Conference paper (Refereed)
    Abstract [en]

    Distribution system planning (DSP) is very important because it can result in reliability enhancement and large cost savings for both utilities and consumers. DSP is a complex nonlinear problem, which can be solved with different optimization methods. This paper compares two such optimization methods, conventional (mixed-integer linear programming - MILP) and meta-heuristic (genetic algorithm - GA), applied to the DSP problem: construction of feeders in distribution power system from scratch. The main objective of DSP is to minimize the total cost, where both the investment and operational outage costs are considered, while the reliability of the whole system is maximized. DSP problem is applied to an actual distribution system. Solution methods are outlined, and computational results show that even though GA gives reasonably good results in faster computation time, MILP provides a better optimal solution with simpler implementation.

  • 44.
    Ebrahimpouri, Mahsa
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Experimental Validation of a Bespoke Lens for a Slot log-spiral FeedManuscript (preprint) (Other (popular science, discussion, etc.))
  • 45.
    Ebrahimpouri, Mahsa
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    High Frequency Microwave and Antenna Devices based on Transformation Optics and Glide-Symmetric Metasurfaces2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The new generation of wireless communication networks intends to support data rate of Gbit/s. One solution to make it possible is to move upwards in frequency range to employ the unused spectrum in mm-wave frequencies. This brings new challenges in the design of hardware for the communication networks, namely high free space path loss and expensive manufacturing. In this thesis, transformation optics and glide symmetry are employed to address these new challenges for the design of high frequency microwave components and lens antennas.

    Transformation optics provides a systematic tool to manipulate electromagnetic waves in a desired way. In this thesis, this tool has been used to improve the radiation properties of conventional homogeneous three-dimensional lenses and compress the size of two-dimensional graded-index lenses.

    Glide symmetry is a subset of higher-order symmetries and is described by a translation followed by a reflection with respect to a defined plane. Periodic structures possessing glide symmetry exhibit interesting properties. In this thesis, four of these properties are explored and possible applications are discussed.

    First, it is demonstrated that the first mode in a glide-symmetric periodic structures is significantly less dispersive than the corresponding conventional non-glide structure. This property was employed to design fully metallic wideband metasurface-based antennas. The losses in this type of antennas are only ohmic which make them suitable for high frequency applications. Second, it is shown that anisotropic glide-symmetric periodic structures can provide higher levels of anisotropy compared to their conventional periodic counterparts. This property is employed to design compressed two-dimensional lenses. Third, it is demonstrated that glide symmetry can be used to match the impedance of two vastly different dielectric media in a parallel plate waveguide configuration by enhancing the magnetic properties. This property was used to match the profile of two-dimensional homogeneous lenses. Fourth it is shown that glide-symmetric holey metallic structures achieve a significantly wider stop-band compared to conventional non-glide periodic structures. This property is exploited to design cost-effective waveguiding structures and microwave components at mm-wave frequencies. Furthermore, using this property, a flange design that provides contact-less measurement at mm-wave frequencies is presented.

  • 46.
    Ebrahimpouri, Mahsa
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    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.

  • 47.
    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.

  • 48.
    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.
    Contact-less Measurement by Using Glide-symmetric Holes on Flanges2018In: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena, METAMATERIALS 2018, Institute of Electrical and Electronics Engineers Inc. , 2018, p. 105-107Conference paper (Refereed)
    Abstract [en]

    We present a cost-effective solution for contact-less measurement of waveguiding structures at high frequencies. Drilling glide-symmetric holey EBG (electromagnetic band gap) on the flanges, the leakage caused by undesired air-gaps, by the result of human mistakes or instrumental errors, between the flanges can be minimized considerably and contact-less measurement becomes possible.

  • 49.
    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.
    Ultrawideband Anisotropic Glide-Symmetric Metasurfaces2019In: IEEE Antennas and Wireless Propagation Letters, ISSN 1536-1225, E-ISSN 1548-5757, Vol. 18, no 8, p. 1547-1551Article in journal (Refereed)
    Abstract [en]

    This letter presents a method to realize anisotropic two-dimensional designs with wideband operation. Glide symmetry has been proven to increase the bandwidth and equivalent refractive index of periodic structures. Here, two anisotropic glide-symmetric unit cells are proposed and characterized. Our simulated results prove that these unit cells follow the general behavior of periodic structures possessing glide symmetry. Moreover, we demonstrate that higher level of anisotropy can also be achieved by glide symmetry. Combining our proposed anisotropic glide-symmetric unit cell and transformation optics, a 30% compressed Luneburg lens is designed. The lens operates from 1 to 13 GHz.

  • 50.
    Eskandari, Hossein
    et al.
    Ferdowsi Univ Mashhad, Dept Elect Engn, Mashhad, Razavi Khorasan, Iran..
    Majedi, Mohammad Saeed
    Ferdowsi Univ Mashhad, Dept Elect Engn, Mashhad, Razavi Khorasan, Iran..
    Attari, Amir Reza
    Ferdowsi Univ Mashhad, Dept Elect Engn, Mashhad, Razavi Khorasan, Iran..
    Quevedo-Teruel, Oscar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering.
    Elliptical generalized Maxwell fish-eye lens using conformal mapping2019In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 21, article id 063010Article in journal (Refereed)
    Abstract [en]

    A circular graded index lens is conformally transformed to an elliptical shape using a closed-form transformation. The proposed transformation is then employed to compress a Maxwell fish-eye and its generalized version. Since the transformation is conformal, the electromagnetic properties of the device are perfectly preserved after the transformation with fully isotropic and dielectric-only materials. Ray-tracing and full-wave simulations are carried out for several cases to verify the functionality of the optically transformed lenses in geometrical optics and wave optics regimes.

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