Henrik Frid

500–750 GHz submillimeter-wave MEMS waveguide switch

This paper presents a 500-750 GHz waveguide based single-pole single-throw (SPST) switch achieving a 40% bandwidth. It is the first ever RF MEMS switch reported to be operating above 220 GHz. The switch is based on a MEMS-reconfigurable surface which can block the wave propagation in the waveguide by short-circuiting the electrical field lines of the TE10 mode. The switch is designed for optimized isolation in the blocking state and for optimized insertion loss in the non-blocking state. The measurement results of the first prototypes show better than 15 dB isolation in the blocking state and better than 3 dB insertion loss in the non-blocking state for 500-750 GHz. The higher insertion loss is mainly attributed to the insufficient metal thickness and surface roughness on the waveguide sidewalls. Two switch designs with different number of blocking elements are fabricated and compared. The overall switch bandwidth is limited by the waveguide only and not by the switch technology itself.

Simulation of microbubbles during the initial stages of breakdown in cyclohexane

The formation of a vapor microbubble has previously been suggested to be the initial mechanism in the process of dielectric failure of dielectric liquids. The bubble is generated by a rapid, highly localized heating of a volume close to a highly stressed electrode, caused by electric currents in the liquid at high voltages. A numerical model is presented in order to investigate the dynamics of a single microbubble in the point-plane geometry in cyclohexane. A condition for the formation of a vapor bubble is discussed. Thereafter, a Computational Fluid Dynamics (CFD) model of two-phase flow with phase transition is used to study the dynamics of the bubble from generation to collapse, under a highly divergent electrostatic field in a subcooled liquid. The amount of subcooling in the simulations is 5 K, and it is found that convergence gets significantly weaker as the amount of subcooling increases. The bubble dynamics is also simulated considering the electrohydrodynamic (EHD) processes in the liquid and vapor phases. Finally, it is shown how the electrostatic forces on the dielectric will cause a bubble to detach from the electrode.

An Approximate Method for Calculating the Near-Field Mutual Coupling Between Line-of-Sight Antennas on Vehicles

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.

Electrohydrodynamic motion due to space-charge limited injection of charges in cyclohexane

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 Poissons 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.

On the modeling of the production and drift of carriers in cyclohexane

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 Poissons 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.

Closed-Form Relation Between the Scan Angle and Feed Position for Extended Hemispherical Lenses Based on Ray Tracing

This letter presents a closed-form relation between the scan angle and feed position for extended hemispherical lenses. This relation is derived using ray tracing, and it is valid for both large and small scan angles, in excellent agreement with full-wave simulations. It is demonstrated that the relation is linear in the small-angle limit, and the effective focal length determining the scan angle is presented. It is also demonstrated that the scan angle only depends on the geometrical configuration, and that it is independent of the lens material. To demonstrate the applicability of this scan angle relation to the design of focal plane arrays (FPAs), we demonstrate that it can be used to determine the FPA spacing that results in -3-dB overlap between switched beams. A comparison with full-wave simulations of lenses with varying materials and FPA elements demonstrates a root-mean-square (rms) accuracy of 0.27° for the scan angle estimation, and rms accuracy of 0.26 dB for the -3-dB overlap criterion between the central and adjacent beams. Finally, we present scaling rules, which show that the scan resolution is inversely proportional to the lens diameter, whereas the FPA spacing is independent of the total lens size.

Self-consistent modeling of laminar electrohydrodynamic plumes from ultra-sharp needles in cyclohexane

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 devia...

Approximate methods to determine the isolation between antennas on vehicles

The isolation between antennas needs to be considered when integrating antennas on vehicles, since poor isolation between antennas can cause interference between radio systems on-board. The electrical size of vehicles at gigahertz frequencies often limits the usage of full-wave methods. This paper therefore evaluates two efficient methods to approximate the antenna isolation; the non-singular transmission integral (NSTI) method and the geometric theory of diffraction (GTD). We present the first evaluation of NSTI for antennas outside line-of-sight (non-LOS). It is shown to provide a 6.5 dB RMS accuracy in the early non-LOS zone for an antenna position sweep on an aircraft at 2 GHz, and for frequency sweeps on a cube and cylinder, the latter only to 5 GHz. The GTD implementation gives a 4.4 dB RMS accuracy for cylinders and simplified aircraft models. Both investigated methods give remarkably accurate results, considering memory requirements and runtime, which makes them interesting for further investigations.

OPTIMIZATION OF MICROMACHINED MILLIMETER-WAVE PLANAR SILICON LENS ANTENNAS WITH CONCENTRIC AND SHIFTED MATCHING REGIONS

This paper presents a study of planar extended hemispherical lens antennas, fabricated from a high-resistivity silicon substrate. The high-permittivity lenses are matched to free-space using up to ...