Lossy Dielectrics Research Articles

Free-Space Time Domain Position Insensitive Technique for Simultaneous Measurement of Complex Permittivity and Thickness of Lossy Dielectric Samples

A novel time domain measurement technique is proposed to facilitate the simultaneous measurement of electrical properties (complex relative permittivity) and geometrical parameters (thickness) of the material under test (MUT). The overall process is noninvasive and noncontacting, which uses the measured scattering data of the MUT in the equivalent time domain or spatial domain. The effective time domain scattering data are employed to detect the primary and secondary peaks of the overall reflection and transmission coefficients. To this end, a novel algorithm is proposed to obtain the complex permittivity and thickness of the MUT in terms of extracted reflection and transmission power peaks. From the practical point of view, the main advantage of the proposed scheme is that one avoids the complicated calibration procedure normally required to define the reference plane. For increasing the accuracy of the overall reconstruction process, an automated optimization procedure based on parameter sensitivity analysis is proposed, which uses standard time gating procedure to implement the corresponding direct problem. The proposed technique is validated by extracting the relative permittivity, the dielectric loss (effective conductivity), and the thickness of various standard materials, such as polyethylene, Plexiglas, PVC, mortar, nylon, and so on, and comparing the extracted data with their values available in the literature.

Ultrathin phase-change coatings on metals for electrothermally tunable colors

Metal surfaces coated with ultrathin lossy dielectrics enable color generation through strong interferences in the visible spectrum. Using a phase-change thin film as the coating layer offers tuning the generated color by crystallization or re-amorphization. Here, we study the optical response of surfaces consisting of thin (5–40 nm) phase-changing Ge2Sb2Te5 (GST) films on metal, primarily Al, layers. A color scale ranging from yellow to red to blue that is obtained using different thicknesses of as-deposited amorphous GST layers turns dim gray upon annealing-induced crystallization of the GST. Moreover, when a relatively thick (>100 nm) and lossless dielectric film is introduced between the GST and Al layers, optical cavity modes are observed, offering a rich color gamut at the expense of the angle independent optical response. Finally, a color pixel structure is proposed for ultrahigh resolution (pixel size: 5 × 5 μm2), non-volatile displays, where the metal layer acting like a mirror is used as a heater element. The electrothermal simulations of such a pixel structure suggest that crystallization and re-amorphization of the GST layer using electrical pulses are possible for electrothermal color tuning.

Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space.

Kelvin probe force microscopy (KPFM) has provided deep insights into the local electronic, ionic and electrochemical functionalities in a broad range of materials and devices. In classical KPFM, which utilizes heterodyne detection and closed loop bias feedback, the cantilever response is down-sampled to a single measurement of the contact potential difference (CPD) per pixel. This level of detail, however, is insufficient for materials and devices involving bias and time dependent electrochemical events; or at solid-liquid interfaces, where non-linear or lossy dielectrics are present. Here, we demonstrate direct recovery of the bias dependence of the electrostatic force at high temporal resolution using General acquisition Mode (G-Mode) KPFM. G-Mode KPFM utilizes high speed detection, compression, and storage of the raw cantilever deflection signal in its entirety at high sampling rates. We show how G-Mode KPFM can be used to capture nanoscale CPD and capacitance information with a temporal resolution much faster than the cantilever bandwidth, determined by the modulation frequency of the AC voltage. In this way, G-Mode KPFM offers a new paradigm to study dynamic electric phenomena in electroactive interfaces as well as a promising route to extend KPFM to the solid-liquid interface.

Methodology for Coupling and Interference Prediction in Integrated-Circuit Substrates

This paper presents a methodology to evaluate different integrated-circuit substrate technology options in terms of interference coupling. It is based on the electromagnetic characterization of the different substrate configurations as radial multilayered dielectric lossy open waveguides and the selection of the propagation modes that effectively contribute to substrate coupling. In addition, attenuation patterns are obtained for different technologies, doping profiles, frequencies, and interference mechanisms in order to provide a tool for early interference prediction, electromagnetic compatibility performance evaluation and floorplan strategy definition.

Microwave absorbing properties of alternating multilayer composites consisting of poly (vinyl chloride) and multi-walled carbon nanotube filled poly (vinyl chloride) layers

The application of dielectric lossy absorbent, multi-walled carbon nanotubes (MWCNTs) filled polymer as a microwave absorbing material (MAM) is limited because of the high loading level. Optimizing the distribution of MWCNTs in a polymeric matrix was a key factor in obtaining better microwave absorption while keeping the MWCNT content low. According to the theory of transmission lines, we designed an alternating multilayer structure with MWCNTs distributed in the continuous and parallel layered spaces of a poly (vinyl chloride) matrix to improve its microwave absorbing properties. The effect of the layer number on the microwave absorbing capacity was studied by theoretical calculations and experimental measurements. The results showed that the −10 dB absorbing bandwidth and the absolute value of the minimum reflection loss of alternating layered samples were higher than those of a conventionally blended sample with the same MWCNT content and increased with the increasing layer number. This improvement of the microwave absorbing capacity was mainly attributed to the multi-reflection of microwaves between the layered interfaces. Interestingly, the matching frequency of the alternating layered MAMs could be adjusted by changing the layer number. The measured microwave absorbing properties were well predicted by the theoretical model. In addition, the mechanical properties improved with an increasing number of layers.

RADAR CROSS SECTION REDUCTION PROPERTY OF HIGH IMPEDANCE SURFACE ON A LOSSY DIELECTRIC

A detailed study on the performance of a high impedance surface on lossy dielectric is presented in this paper. It is observed that the structure, which is an array of square loops on a grounded dielectric, behaves as artificial magnetic condutor, narrowband absorber or perfect electric conductor depending on the dielectric loss. An equivalent circuit modelling is used to theoretically explain how this transition is happening. The observed narrowband absorption (bandwidth = 0.08GHz) of the thin (0.016λ) lossy dielectric is scalable to different operating frequencies by varying the structure parameters. The simulation studies on the effect of structural and dielectric properties on the characteristics of this HIS are also dealt with in this paper. Experimental investigation is in good agreement with simulated result and equivalent circuit modelling.

Charge Relaxation in Biological Tissues with Extremely High Permittivity

This letter presents a phenomenological model to describe charge relaxation (and the corresponding screening effect) in biological tissues, i.e., lossy dielectrics where a non-negligible conductivity and an extremely high relative permittivity (on the order of 50 × 10 6 ) may coexist. This situation is very peculiar and is not treated in textbooks. The model is used to study an open issue in electromagnetic dosimetry, namely the effect of charge relaxation on the motion-induced electric fields in the bodies of the operators working in magnetic resonance imaging environments.

A TE<sub>13</sub> Mode Converter for High-Order Mode Gyrotron-Traveling-Wave Tubes

A methodology to generate a circular TE13 mode for the operation of high-order mode (HOM) gyrotron-traveling-wave tubes is presented in this paper. A rectangular TE10 mode is efficiently converted into a circular TE13 mode using Y-type power dividers. Symmetric curved lossy dielectrics and dielectric rings are, respectively, positioned to suppress the potential coupling TE32 and TE71 modes according to their electric and magnetic field distribution properties. An HOM converter without dielectrics loaded was designed, constructed, and cold tested. Back-to-back transmission measurements exhibit good agreement with the results of computer simulations.

An effective 3D leapfrog scheme for electromagnetic modelling of arbitrary shaped dielectric objects using unstructured meshes

In computational electromagnetics, the advantages of the standard Yee algorithm are its simplicity and its low computational costs. However, because of the accuracy losses resulting from the staircased representation of curved interfaces, it is normally not the method of choice for modelling electromagnetic interactions with objects of arbitrary shape. For these problems, an unstructured mesh finite volume time domain method is often employed, although the scheme does not satisfy the divergence free condition at the discrete level. In this paper, we generalize the standard Yee algorithm for use on unstructured meshes and solve the problem concerning the loss of accuracy linked to staircasing, while preserving the divergence free nature of the algorithm. The scheme is implemented on high quality primal Delaunay and dual Voronoi meshes. The performance of the approach was validated in previous work by simulating the scattering of electromagnetic waves by spherical 3D PEC objects in free space. In this paper we demonstrate the performance of this scheme for penetration problems in lossy dielectrics using a new averaging technique for Delaunay and Voronoi edges at the interface. A detailed explanation of the implementation of the method, and a demonstration of the quality of the results obtained for transmittance and scattering simulations by 3D objects of arbitrary shapes, are presented.

RF Design, Thermal Analysis, and Cold Test of a Ku-Band Continuous Wave Sheet Beam Traveling Wave Tube

RF circuit design, thermal analysis, fabrication, and measurement of a continuous wave (CW) high-power sheet beam traveling wave tube (SB-TWT) operating in the Ku-band were demonstrated in this paper. The slow wave structure circuit was constructed by double staggered grating waveguides (DSGWs), and the lossy dielectrics attached in the H-plane were applied to suppress parasitic oscillations. The Particle-in-cell simulation predicted that the CW SB-TWT can provide >20-kW output power in the band range of 16.2–18.5 GHz, with a maximum small signal gain of 38 dB. Microchannel cooling, which has been proved to be an efficient cooling method for microelectronic chip, very large scale integration, and power electronic modules with very high heat flux were introduced to improve the thermal capacity and heat dissipation ability. A thermal analysis of the RF circuit considering attenuated losses and electrons interception was studied in detail. Investigation shows that the RF circuit can operate with maximum $\sim 1$ -kW dielectric loss power (1.5 times of the loss power generated from the saturated output power at center frequency) and a maximum of 7% interception of electrons. Furthermore, an interaction circuit, including 23 DSGWs implanted with BeO–SiC to provide necessary attenuation, was fabricated and cold tested. Vector network analyzer RF measurement shows excellent performance and agrees very well with our prediction.

Experimental and Modeled Performance of a Ground Penetrating Radar Antenna in Lossy Dielectrics

The way in which electromagnetic fields are transmitted and received by ground penetrating radar (GPR) antennas is crucial to the performance of GPR systems. Simple antennas have been characterized by analyzing their radiation patterns and directivity. However, there have been limited studies that combine real GPR antennas with realistic environments, which is essential to capture the complex interactions between the antenna and surroundings. We have investigated the radiation characteristics and sensitivity of a GPR antenna in a range of lossy dielectric environments using both physical measurements and a three-dimensional (3-D) finite-difference time-domain (FDTD) model. Experimental data were from measured responses of a target positioned at intervals on the circumference of a circle surrounding the H-plane of the antenna. A series of oil-in-water emulsions as well as tap water were used to simulate homogeneous materials with different permittivities and with complex conductivities. Numerical radiation patterns were created utilizing a detailed 3-D FDTD model of the antenna. Good correlation was shown between the experimental results and modeled data with respect to the strength of the main lobe within the critical angle window. However, there are discrepancies in the strength of main lobe at shallow angles. In all the dielectrics, the main lobes are generally broad due to the near-field observation distance but, as expected, become narrower with increasing permittivity. These results provide confidence for further use of the FDTD antenna model to investigate scenarios such as larger observation distances and heterogeneous environments that are difficult to study experimentally.

Single-wire radio frequency transmission lines in biological tissue

We present an approach for implanting radio frequency transmission lines in biological tissue, using a single insulated wire surrounded by tissue as a variant of the Goubau single-wire transmission line (SWTL) in air. We extend the Goubau SWTL model to include SWTLs surrounded by lossy dielectrics such as tissue by assuming a propagating mode component in the tissue. We show that a thin wire of radius 63.5 μm, coated with biocompatible fluorinated ethylene propylene dielectric, exhibits a measured loss of only 1 dB/cm at a frequency of 915 MHz. The model fit to the measured insertion loss is within ±0.3 dB/cm across the 100 MHz to 3 GHz band. This SWTL presents excellent impedance matching to 50 Ω as evidenced by a measured median return loss better than 10 dB across the 100 MHz to 3 GHz range. This approach represents an alternative to near-field magnetic coupling for implanted systems where tissue displacement by a single, thin wire can be tolerated.

Surface Impedance Boundary Conditions in Time Domain for Guided Structures of Arbitrary Cross Section With Lossy Dielectric Walls

This paper presents a procedure to implement the concept of surface impedance boundary condition (SIBC) for lossy dielectrics in time domain. The SIBC formulation, validation, and results are obtained with a time domain numerical method, namely the transmission-line matrix (TLM). The formulation of surface impedance in frequency domain is converted to the time domain using a rational approximation followed by a bilinear transform with a canonical representation in the state-space. This surface impedance formulation has been implemented in TLM. Simulations show that the proposed model is valid for interfaces between air and a lossy dielectric, and arbitrary conductivity $\sigma$. An application that concerns mode propagation in a rectangular tunnel with lossy dielectric walls is shown. A comparison with an approximate method proposed by Marcatilli is presented. It confirms that the propagation in electrically large guided structures, such as tunnels with lossy dielectric walls, can be efficiently modeled by this approach.

Vesicle biomechanics in a time-varying magnetic field.

BackgroundCells exhibit distortion when exposed to a strong electric field, suggesting that the field imposes control over cellular biomechanics. Closed pure lipid bilayer membranes (vesicles) have been widely used for the experimental and theoretical studies of cellular biomechanics under this electrodeformation. An alternative method used to generate an electric field is by electromagnetic induction with a time-varying magnetic field. References reporting the magnetic control of cellular mechanics have recently emerged. However, theoretical analysis of the cellular mechanics under a time-varying magnetic field is inadequate.We developed an analytical theory to investigate the biomechanics of a modeled vesicle under a time-varying magnetic field. Following previous publications and to simplify the calculation, this model treated the inner and suspending media as lossy dielectrics, the membrane thickness set at zero, and the electric resistance of the membrane assumed to be negligible. This work provided the first analytical solutions for the surface charges, electric field, radial pressure, overall translational forces, and rotational torques introduced on a vesicle by the time-varying magnetic field. Frequency responses of these measures were analyzed, particularly the frequency used clinically by transcranial magnetic stimulation (TMS).ResultsThe induced surface charges interacted with the electric field to produce a biomechanical impact upon the vesicle. The distribution of the induced surface charges depended on the orientation of the coil and field frequency. The densities of these charges were trivial at low frequency ranges, but significant at high frequency ranges. The direction of the radial force on the vesicle was dependent on the conductivity ratio between the vesicle and the medium. At relatively low frequencies (<200 KHz), including the frequency used in TMS, the computed radial pressure and translational forces on the vesicle were both negligible.ConclusionsThis work provides an analytical framework and insight into factors affecting cellular biomechanics under a time-varying magnetic field. Biological effects of clinical TMS are not likely to occur via alteration of the biomechanics of brain cells.

Unified position-dependent photon-number quantization in layered structures

We have recently developed a position-dependent quantization scheme for describing the ladder and effective photon-number operators associated with the electric field to analyze quantum optical energy transfer in lossy and dispersive dielectrics [Phys. Rev. A, 89, 033831 (2014)]. While having a simple connection to the thermal balance of the system, these operators only described the electric field and its coupling to lossy dielectric bodies. Here we extend this field quantization scheme to include the magnetic field and thus to enable description of the total electromagnetic field and discuss conceptual measurement schemes to verify the predictions. In addition to conveniently describing the formation of thermal balance, the generalized approach allows modeling of the electromagnetic pressure and Casimir forces. We apply the formalism to study the local steady state field temperature distributions and electromagnetic force density in cavities with cavity walls at different temperatures. The calculated local electric and magnetic field temperatures exhibit oscillations that depend on the position as well as the photon energy. However, the effective photon number and field temperature associated with the total electromagnetic field is always position-independent in lossless media. Furthermore, we show that the direction of the electromagnetic force varies as a function of frequency, position, and material thickness.

Electromagnetic Time Reversal Algorithms and Source Localization in Lossy Dielectric Media

The problem of reconstructing the spatial support of an extended radiating electric current source density in a lossy dielectric medium from transient boundary measurements of the electric fields is studied. A time reversal algorithm is proposed to localize a source density from loss-less wave-held measurements. Further, in order to recover source densities in a lossy medium, we first build attenuation operators thereby relating loss-less waves with lossy ones. Then based on asymptotic expansions of attenuation operators with respect to attenuation parameter, we propose two time reversal strategies for localization. The losses in electromagnetic wave propagation are incorporated using the Debye's complex permittivity, which is well-adopted for low frequencies (radio and microwave) associated with polarization in dielectrics.

Effect of Electric Current on Trijunction Equilibrium and Grain Rotation of Lossy Dielectrics

To understand the structural stability of lossy dielectrics under the action of an electric current, the effect of an electric current on the stress evolution, the change of chemical potential, and the electric energy stored in a grain boundary is examined. Analytical forms of the stress, chemical potential, and electric energy are obtained, which depend on the current density. The concept of an apparent grain boundary energy, which is a linear function of the square of the current density, is introduced. One needs to use the apparent grain boundary energy in analyzing the equilibrium state of a trijunction. An expression for the rate of grain rotation is proposed, which includes the contributions of the change of chemical potential and the electric energy in grain boundaries.

Analytical method for monostatic radar cross section calculation of a perfectly conducting wind turbine model located over dielectric lossy half space

Radar cross section (RCS) of a wind turbine has a key role for determining possible effects of wind farms on radar and navigation systems. Closed form expressions of the physical optics technique are applied to calculate monostatic radar cross section of an electrically large wind turbine model over a dielectric, lossy half space. The model is constructed with perfectly conducting canonical structures. First-order effects of the half space to the electromagnetic scattering mechanism are approximated with four-path model. Doppler spectrogram of the turbine model over lossy ground is obtained using short-time Fourier transform. The closed form expressions provide very-fast RCS calculations for different broadside directions and blade rotation speeds. Performance of this proposed method shows that it is suitable for real-time simulations that analyse the effects of the wind farms to the radar and navigation systems performance.

Airgap Interconnects: Modeling, Optimization, and Benchmarking for Backplane, PCB, and Interposer Applications

Frequency and time domain models are developed for backplane (BP), printed circuit board (PCB), and silicon interposer (SI) links using six-port transfer matrices (ABCD matrices) for bumps, vias and connectors, and coupled multiconductor transmission lines for traces. The six-port transfer matrix approach enables easy computation of the transfer function, as well as near-end and far-end crosstalk. The intersymbol interference is accounted for by computing the pulse response for the worst case bit pattern. Furthermore, the models developed here are used to optimize the data-rate and trace width for each of the links, so that the aggregate bandwidth obtained per joule of energy supplied to the link is maximized. The modeling and optimization approach developed here serves as a good platform to compare the air-gap interconnects against BP, PCB, and SI interconnects on lossy dielectrics. It is shown that air-gap interconnects can provide an aggregate bandwidth improvement of 3x-4x for BP links at a comparable energy per bit, and a 5x-9x improvement in aggregate bandwidth of PCB links at the expense of 20% higher energy per bit. For SI links, airgap interconnects are shown to provide a 2x-3x improvement in aggregate bandwidth and a 1x-1.5x improvement in energy per bit.

Use of Collisional Plasma as an Optimum Lossy Dielectric for Wave Absorption in Planar Layers, Analysis, and Application

Parameters of electromagnetic scattering for lossy plasma media are analytically computed for planar layered structures. The structures are backed with a perfectly electric conductor and minimal reflection is analyzed versus both incident wave angle and frequency. The physical specifications of plasma dielectric for the optimum reduction in reflection are obtained using genetic algorithm. Optimizations show a good prospect to use electromagnetic properties of cold collisional plasma as an optimum lossy dielectric. The achieved optimum plasma for the coating layer is an appropriate choice for radar cross section reduction over a wide range of incident frequencies and angles. Although the plasma layer alone can dissipate the wave satisfactorily, an applicable model within a confining layer is analyzed. The elctron density distribution is analyticaly investigated. Applications are analyzed in full wave, numeric, and analytical methods.