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Publications (8 of 8) Show all publications
Frid, H. & Jonsson, B. L. (2018). Compensation of radome effects in small airborne monopulse arrays by convex optimization. In: IET Conference Publications: . Paper presented at 12th European Conference on Antennas and Propagation, EuCAP 2018, 9 April 2018 through 13 April 2018. Institution of Engineering and Technology (CP741)
Open this publication in new window or tab >>Compensation of radome effects in small airborne monopulse arrays by convex optimization
2018 (English)In: IET Conference Publications, Institution of Engineering and Technology , 2018, no CP741Conference paper, Published paper (Refereed)
Abstract [en]

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

Place, publisher, year, edition, pages
Institution of Engineering and Technology, 2018
Keywords
Airborne ESM, Convex optimization, Monoulse DOA estimation, Phased array antennas, Radomes, Economic and social effects, Active element patterns, Design parameters, DOA estimation, Large scan angle, Optimization approach, Sidelobe levels, Antenna phased arrays
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-247468 (URN)2-s2.0-85057296300 (Scopus ID)
Conference
12th European Conference on Antennas and Propagation, EuCAP 2018, 9 April 2018 through 13 April 2018
Note

QC 20190405

Available from: 2019-04-05 Created: 2019-04-05 Last updated: 2019-05-21Bibliographically approved
Shah, U., Reck, T., Frid, H., Jung-Kubiak, C., Chattopadhyay, G., Mehdi, I. & Oberhammer, J. (2017). A 500–750 GHz RF MEMS Waveguide Switch. IEEE Transactions on Terahertz Science and Technology, 7(3), 326-334
Open this publication in new window or tab >>A 500–750 GHz RF MEMS Waveguide Switch
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2017 (English)In: IEEE Transactions on Terahertz Science and Technology, ISSN 2156-342X, E-ISSN 2156-3446, Vol. 7, no 3, p. 326-334Article in journal (Refereed) Published
Abstract [en]

This paper reports on a submillimeter-wave 500-750 GHz micorelectromechanical systems (MEMS) waveguide switch based on a MEMS-reconfigurable surface to block/unblock the wave propagation through the waveguide. In the non-blocking state, the electromagnetic wave can pass freely through the MEMS-reconfigurable surface, while in the blocking state, the electric field lines of the TE10 mode are short-circuited that blocks the wave propagation through a WM-380 (WR-1.5) waveguide. A detailed design parameter study is carried out to determine the best combination of the number of horizontal bars and vertical columns of the MEMS-reconfigurable surface for achieving a low insertion loss in the non-blocking state and a high isolation in the blocking state for the 500-750 GHz band. Two different switch concepts relying either on an ohmic-contact or a capacitive-contact between the contact cantilevers have been implemented. The measurements of the switch prototypes show a superior RF performance of the capacitive-contact switch. The measured isolation of the capacitive-contact switch designed with an 8 μm contact overlap is 19-24 dB and the measured insertion loss in the non-blocking state is 2.5-3 dB from 500 to 750 GHz including a 400 μm long micromachined waveguide section. By measuring reference chips, it is shown that the MEMS-reconfigurable surface contributes only to 0.5-1 dB of the insertion loss, while the rest is attributed to the limited sidewall metal thickness and to the surface roughness of the 400 μm long micromachined waveguide section. Finally, reliability measurements in an uncontrolled laboratory environment on a comb-drive actuator with an actuation voltage of 28 V showed no degradation in the functioning of the actuator over one hundred million cycles. The actuator was also kept in the actuated state for ten days and showed no sign of failure or deterioration.

Place, publisher, year, edition, pages
IEEE, 2017
Keywords
RF MEMS, waveguide switch, micromachined waveguide, submillimeter-wave, rectangular waveguide, terahertz
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-197338 (URN)10.1109/TTHZ.2017.2670259 (DOI)000401094100012 ()2-s2.0-85014814859 (Scopus ID)
Funder
EU, European Research Council, 616846Swedish Foundation for Strategic Research , SE13-007
Note

QC 20161214

Available from: 2016-12-03 Created: 2016-12-03 Last updated: 2018-03-22Bibliographically approved
Frid, H., Töpfer, F., Bhowmik, S., Dudorov, S. & Oberhammer, J. (2017). Optimization of Micromachined Millimeter-Wave Planar Silicon Lens Antennas with Concentricand Shifted Matching Regions. Progress In Electromagnetics Research C, 79, 17-29
Open this publication in new window or tab >>Optimization of Micromachined Millimeter-Wave Planar Silicon Lens Antennas with Concentricand Shifted Matching Regions
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2017 (English)In: Progress In Electromagnetics Research C, ISSN 1937-8718, E-ISSN 1937-8718, Vol. 79, p. 17-29Article in journal (Refereed) Published
Abstract [en]

This paper presents a study of planar silicon lens antennas with up to three stepped-impedance matching regions. The effective permittivity of the matching regions is tailor-made byetching periodic holes in the silicon substrate. The optimal thickness and permittivity of the matchingregions were determined by numerical optimization to obtain the maximum wideband aperture efficiencyand smallest side-lobes. We introduce a new geometry for the matching regions, referred to as shiftedmatching regions. The simulation results indicate that using three shifted matching regions results intwice as large aperture efficiency as compared to using three conventional concentric matching regions.By increasing the number of matching regions from one to three, the band-averaged gain is increasedby 0.3 dB when using concentric matching regions, and by 3.7 dB when using shifted matching regions,which illustrates the advantage of the proposed shifted matching region design.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-197335 (URN)
Note

QC 20161115

Available from: 2016-12-03 Created: 2016-12-03 Last updated: 2019-06-03Bibliographically approved
Becerra Garcia, M., Frid, H. & Vazquez, P. A. (2017). Self-consistent modeling of laminar electrohydrodynamic plumes from ultra-sharp needles in cyclohexane. Paper presented at Meeting of the Institute-of-Non-Newtonian-Fluid-Mechanics (INNFM), 2017, Llanwddyn, Wales. Physics of fluids, 29(12), Article ID 123605.
Open this publication in new window or tab >>Self-consistent modeling of laminar electrohydrodynamic plumes from ultra-sharp needles in cyclohexane
2017 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 29, no 12, article id 123605Article in journal (Refereed) Published
Abstract [en]

This paper presents a self-consistent model of electrohydrodynamic (EHD) laminar plumes produced by electron injection from ultra-sharp needle tips in cyclohexane. Since the density of electrons injected into the liquid is well described by the Fowler-Nordheim field emission theory, the injection law is not assumed. Furthermore, the generation of electrons in cyclohexane and their conversion into negative ions is included in the analysis. Detailed steady-state characteristics of EHD plumes under weak injection and space-charge limited injection are studied. It is found that the plume characteristics far from both electrodes and under weak injection can be accurately described with an asymptotic simplified solution proposed by Vazquez et al. ["Dynamics of electrohydrodynamic laminar plumes: Scaling analysis and integral model," Phys. Fluids 12, 2809 (2000)] when the correct longitudinal electric field distribution and liquid velocity radial profile are used as input. However, this asymptotic solution deviates from the self-consistently calculated plume parameters under space-charge limited injection since it neglects the radial variations of the electric field produced by a high-density charged core. In addition, no significant differences in the model estimates of the plume are found when the simulations are obtained either with the finite element method or with a diffusion-free particle method. It is shown that the model also enables the calculation of the current-voltage characteristic of EHD laminar plumes produced by electron field emission, with good agreement with measured values reported in the literature.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
Keywords
Dielectric Liquids, Blade Electrode, Flat-Plate, Injection, Field, Simulation, Charge, Conduction, Stability, Dynamics
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-221017 (URN)10.1063/1.5001000 (DOI)000418958300040 ()2-s2.0-85040032188 (Scopus ID)
Conference
Meeting of the Institute-of-Non-Newtonian-Fluid-Mechanics (INNFM), 2017, Llanwddyn, Wales
Funder
Swedish Foundation for Strategic Research
Note

QC 20180112

Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2018-02-12Bibliographically approved
Frid, H., Holter, H. & Jonsson, B. L. (2015). An Approximate Method for Calculating the Near-Field Mutual Coupling Between Line-of-Sight Antennas on Vehicles. IEEE Transactions on Antennas and Propagation, 63(9), 4132-4138
Open this publication in new window or tab >>An Approximate Method for Calculating the Near-Field Mutual Coupling Between Line-of-Sight Antennas on Vehicles
2015 (English)In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 63, no 9, p. 4132-4138Article in journal (Refereed) Published
Abstract [en]

Calculating the mutual coupling between antennas on vehicles using full-wave simulations requires a vast amount of computer resources due to the electrical size of the structures. We therefore propose an alternative and approximate method to determine mutual coupling between antennas on vehicles for the case where there is line-of-sight (LOS) between the antennas. The proposed method is based on approximating the mutual coupling between LOS antennas on vehicles as near-field transmission between antennas in free space. We begin the analysis with a brief review of four methods for calculating the near-field free-space transmission. Of the investigated methods, we demonstrate that a nonsingular form of the near-field transmission integral originally proposed by Yaghjian (1982) is the most suitable for LOS antennas on vehicles. We introduce a modification to this method, in order to only use the antenna far-fields and geometrical separation to determine the mutual coupling. The comparison with full-wave simulations indicates that the proposed method has a good accuracy for LOS antennas. This paper ends with a full-scale mutual coupling calculation for two monopoles on an aircraft under LOS conditions, demonstrating a root mean square (rms) accuracy of 6 dB for frequencies up to 5 GHz, as compared with full-wave simulations.

Keywords
Aircraft antennas, aircraft reliability, electrically large structures, electromagnetic interference, near-fields
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-173969 (URN)10.1109/TAP.2015.2447003 (DOI)000360803400035 ()2-s2.0-84940973948 (Scopus ID)
Note

QC 20151006

Available from: 2015-10-06 Created: 2015-09-24 Last updated: 2017-12-01Bibliographically approved
Becerra, M. & Frid, H. (2014). Electrohydrodynamic motion due to space-charge limited injection of charges in cyclohexane. In: Proceedings of the 2014 IEEE 18th International Conference on Dielectric Liquids, ICDL 2014: . Paper presented at 2014 IEEE 18th International Conference on Dielectric Liquids, ICDL 2014, 29 June 2014 through 3 July 2014.
Open this publication in new window or tab >>Electrohydrodynamic motion due to space-charge limited injection of charges in cyclohexane
2014 (English)In: Proceedings of the 2014 IEEE 18th International Conference on Dielectric Liquids, ICDL 2014, 2014Conference paper, Published paper (Refereed)
Abstract [en]

A self-consistent numerical model is presented in order to study the electrohydrodynamic (EHD) motion generated by a stationary, space-charge limited injection of charge in the point-plane geometry. In this multiphysics model, the continuity equations for charge carriers and Poisson's equation are coupled with Navier-Stokes equations and the heat equation. This model is used to study the EHD motion of cyclohexane in the negative point-plane geometry for sharp points with tip radius of 0.2 μm. It is shown that the injection of charges from a very sharp point electrode results in the formation of a thin plume with high liquid velocity. The results show large differences in the liquid velocity close to the point electrode compared to the average velocity estimated by the well-known electrohydrodynamic mobility. The difference between the width of the charged core and the hydrodynamic plume is analyzed and presented. It is shown that the local heating of the liquid is strongly reduced by the convective losses generated by EHD motion. Finally, it is found that the liquid temperature in cyclohexane in the vicinitiy of sharp points under space charge limited injection can reach temperatures slightly above boiling temperature, without generating bubbles.

Series
IEEE International Conference on Dielectric Liquids, ISSN 2153-3725
Keywords
Charge injection, Electrohydrodynamic motion, liquid breakdown, streamer formation, Cyclohexane, Dielectric liquids, Electric space charge, Electrodes, Electrohydrodynamics, Poisson equation, Boiling temperature, Continuity equations, Electrohydrodynamic (EHD), Liquid temperature, Multi-physics modeling, Poisson's equation, Space-charge limited, Navier Stokes equations
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-167961 (URN)10.1109/ICDL.2014.6893115 (DOI)000360485100046 ()2-s2.0-84907897647 (Scopus ID)9781479920631 (ISBN)
Conference
2014 IEEE 18th International Conference on Dielectric Liquids, ICDL 2014, 29 June 2014 through 3 July 2014
Note

QC 20150604

Available from: 2015-06-04 Created: 2015-05-22 Last updated: 2015-11-27Bibliographically approved
Becerra, M. & Frid, H. (2013). On the modeling of the production and drift of carriers in cyclohexane. In: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP: . Paper presented at 2013 IEEE Conference on Electrical Insulation and Dielectric Phenomena, CEIDP 2013; Shenzhen; China; 20 October 2013 through 23 October 2013 (pp. 905-908). IEEE
Open this publication in new window or tab >>On the modeling of the production and drift of carriers in cyclohexane
2013 (English)In: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP, IEEE , 2013, p. 905-908Conference paper, Published paper (Refereed)
Abstract [en]

The modeling of the mechanisms of generation, loss, multiplication and transport of charge carriers is vital for the simulation of the prebreakdown process in dielectric liquids. Unfortunately, there is a lack of suitable coefficients to describe the electron generation and transport of carriers in liquids, which hinders the development of numerical models with sufficient predictive power. In this paper, the drift-dominated continuity equations for electrons and ions are coupled with Poisson's equation in order to simulate the carrier production and drift in the liquid phase under positive and negative voltages in cyclohexane. The estimations of the model are compared with measurements of current-voltage characteristics and Trichel current pulses reported in the literature for needle-plane configurations. In the analysis, the electron generation mechanisms suggested for dielectric liquids are analyzed and discussed. It is found that estimations based on the Zener equation for field-dependent molecular ionization do not agree with measurements for negative sharp points. It is also shown that the proper estimation of the electric current in the liquid phase should consider a field-dependent attachment term as well as the electrohydrodynamic movement of the liquid.

Place, publisher, year, edition, pages
IEEE, 2013
Keywords
Carriers, Cyclohexane, breakdown
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-139056 (URN)10.1109/CEIDP.2013.6747092 (DOI)2-s2.0-84901742535 (Scopus ID)978-147992596-4 (ISBN)
Conference
2013 IEEE Conference on Electrical Insulation and Dielectric Phenomena, CEIDP 2013; Shenzhen; China; 20 October 2013 through 23 October 2013
Funder
StandUp
Note

QC 20140110

Available from: 2014-01-01 Created: 2014-01-01 Last updated: 2014-06-27Bibliographically approved
Frid, H. & Becerra, M. (2013). Simulation of Microbubbles during the Initial Stages of Breakdown in Cyclohexane. In: 2013 Annual Report Conference on Electrical Insulation and Dielectric Phenomena: . Paper presented at Conference on Electrical Insulation and Dielectric Phenomena CEIDP October 2013,Shenzhen (China) (pp. 901-904). IEEE conference proceedings
Open this publication in new window or tab >>Simulation of Microbubbles during the Initial Stages of Breakdown in Cyclohexane
2013 (English)In: 2013 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, IEEE conference proceedings, 2013, p. 901-904Conference paper, Published paper (Refereed)
Abstract [en]

The formation of a vapor microbubble has previouslybeen suggested to be the initial mechanism in the process ofdielectric failure of dielectric liquids. The bubble is generated bya rapid, highly localized heating of a volume close to a highlystressed electrode, caused by electric currents in the liquid athigh voltages. A numerical model is presented in order toinvestigate the dynamics of a single microbubble in the pointplanegeometry in cyclohexane. A condition for the formation ofa vapor bubble is discussed. Thereafter, a Computational FluidDynamics (CFD) model of two-phase flow with phase transition isused to study the dynamics of the bubble from generation tocollapse, under a highly divergent electrostatic field in asubcooled liquid. The amount of subcooling in the simulations is5 K, and it is found that convergence gets significantly weaker asthe amount of subcooling increases. The bubble dynamics is alsosimulated considering the electrohydrodynamic (EHD) processesin the liquid and vapor phases. Finally, it is shown how theelectrostatic forces on the dielectric will cause a bubble to detachfrom the electrode.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2013
Keywords
Bubble, breakdown, cyclohexane
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-139057 (URN)2-s2.0-84901743769 (Scopus ID)
Conference
Conference on Electrical Insulation and Dielectric Phenomena CEIDP October 2013,Shenzhen (China)
Funder
StandUp
Note

QC 20140110

Available from: 2014-01-01 Created: 2014-01-01 Last updated: 2014-01-10Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7812-9849

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