Lossy Dielectrics Research Articles

Experimental Investigation on Flanged Parallel-Plate Dielectric Waveguide Probe for Detection of Conductive Inclusions in Lossy Dielectric Medium

A flanged parallel-plate dielectric waveguide probe (PPDW) for microwave detection and localization of small inclusions in a lossy dielectric medium, based on detecting the contrast in dielectric properties between the inclusion and embedding medium has been proposed. In this paper, experimental evaluation of this probe for the detection and localization of small conductive inclusion is presented. Investigations were performed on solid lossy dielectric phantoms with conductive spherical inclusions representing tumors embedded. Preliminary experimental results demonstrate the potential of the PPDW to detect and locate a small inclusion exhibiting significant difference in dielectric properties from the host medium, embedded at reasonable depth.

Debye Model Fitting for Time-Domain Modeling of Lossy Dielectrics

In this paper, we will show a systematic procedure for fitting a Debye model to tabulated data of dielectric constant and loss tangent at discrete frequency points. Our approach is based on generation of a guaranteed passive RC macromodel, satisfying Kronig-Kramers relations for complex permittivity. We present for the first time an RC vector fitting method.

COMPLEX IMAGE SOLUTION OF SAR INSIDE A HUMAN HEAD ILLUMINATED BY A FINITE-LENGTH DIPOLE

This paper uses the accurate and computationally efficient complex image technique (CIT) to find the electric field and SAR distributions inside a human head illuminated by a finite-length dipole. The human head model used consists of 3 planar layers of lossy dielectrics. The accuracy of the results is verified by comparison with HFSS software. It was found that the CIT requires about 1 minute and 16 MB of RAM, while HFSS requires about 2 hours and 1.5 GB of RAM to find the SAR distribution using a 2.19 GHz Core 2 Due PC. The CIT method can also efficiently solve other types of antennas on other planar head models.

MODAL ANALYSIS OF MULTILAYER CONICAL DIELECTRIC WAVEGUIDES FOR AZIMUTHAL INVARIANT MODES

By using fleld expansion in terms of the Legendre polynomials and Schelkunofi functions, Maxwell's equations in the spherical coordinate system are cast into a matrix form which lends itself to the analysis of a multilayer conical waveguide. The matrix formulation is then used to obtain an eigen-value problem whose eigen-values are the allowable wave-numbers for propagation in the radial direction. To verify the proposed numerical approach, it is used to evaluate the resonance frequency of a partially fllled spherical resonator. The computed resonance frequencies are then compared with those obtained using commercial software based on the flnite- element method. The computation time is enormously reduced using the semi-analytical method of this work. Although results are shown for lossless isotropic dielectrics, the method is also applicable to conical waveguides made of lossy dielectrics even with negative permittivity.

Optimum electromagnetic heating of nanoparticle thermal contrast agents at rf frequencies

Enhanced heating of nanoparticles for applications such as thermoacoustic imaging and therapeutic heat delivery is considered. The optimum electrical conductivity to achieve maximum electromagnetic energy deposition in a given nanoparticle is obtained, with emphasis on rf frequencies, where plasmon resonances associated with negative permittivity are generally not possible. Spheres, coated spheres, nanowires, and carbon nanotubes are considered. In all cases, it is found that relatively small conductivity values (e.g., σ⪡1 S/m for spheres) provide the maximum absorption of rf energy, and thus maximizes heat production in the nanoparticle. Therefore, lossy dielectrics may be a better choice for maximizing nanoparticle heat production than metallic particles.

Analysis of hybrid EM wave absorber using thin corrugated dielectric lossy sheet based on equivalent permittivity representation

AbstractThe 10‐m and 3‐m semianechoic chambers are in widespread use for the electromagnetic compatibility (EMC). The hybrid EM wave absorber consisting of the sintered ferrite tiles and the dielectric lossy materials has been usually used for these semianechoic chambers. In the past, Suetake, Naito, and Shimizu's studies played a key part in providing the basis for the hybrid EM wave absorber. The reflectivity of the hybrid EM wave absorber can be calculated from the multilayered approximate structure. In particular, each layer occupied partly by the dielectric lossy materials can be replaced by the homogeneous plate having the equivalent relative complex permittivity, which is determined through the synthesized capacitance model in the large wavelength range. But, there was a problem that the equivalent relative complex permittivity differs with the process of the synthesized capacitance model.We propose a new method which can be applied to the equivalent relative complex permittivity by the finite difference method (FDM). Moreover, the reflectivity of the hybrid EM wave absorber using the thin corrugated dielectric lossy sheet is calculated and measured. As a result, it is confirmed that the measured reflectivity agrees with the calculation one. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(7): 12–20, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10082

Electrohydrodynamic Model of Vesicle Deformation in Alternating Electric Fields

We develop an analytical theory to explain the experimentally observed morphological transitions of quasispherical giant vesicles induced by alternating electric fields. The model treats the inner and suspending media as lossy dielectrics, and the membrane as an impermeable flexible incompressible–fluid sheet. The vesicle shape is obtained by balancing electric, hydrodynamic, bending, and tension stresses exerted on the membrane. Our approach, which is based on force balance, also allows us to describe the time evolution of the vesicle deformation, in contrast to earlier works based on energy minimization, which are able to predict only stationary shapes. Our theoretical predictions for vesicle deformation are consistent with experiment. If the inner fluid is more conducting than the suspending medium, the vesicle always adopts a prolate shape. In the opposite case, the vesicle undergoes a transition from a prolate to oblate ellipsoid at a critical frequency, which the theory identifies with the inverse membrane charging time. At frequencies higher than the inverse Maxwell-Wagner polarization time, the electrohydrodynamic stresses become too small to alter the vesicle's quasispherical rest shape. The model can be used to rationalize the transient and steady deformation of biological cells in electric fields.

Theory of multiwall carbon nanotubes as waveguides and antennas in the infrared and the visible regimes

The propagation of azimuthally symmetric guided waves in multiwalled carbon nanotubes (MWCNTs) was analyzed theoretically in the midinfrared and the visible regimes. The MWCNTs were modeled as ensembles of concentric, cylindrical, conducting shells. The influence of intershell electron tunneling on the optical properties of MWCNTs was examined by focusing on a double-walled carbon nanotube (DWCNT). Longitudinal electrostatic waves exist in DWCNTs due to intershell tunneling. Conditions for weak influence of intershell tunneling in DWCNTs were identified, and an integral-equation approach for scattering by an MWCNT was formulated when those conditions prevail. Slightly attenuated guided waves and antenna resonances due to the edge effect exist for not-too-thick MWCNTs in the far-infrared and the midinfrared regimes. Interband transitions retard the propagation of guided waves and have a deleterious effect on the performance of a finite-length MWCNT as a nanoantenna. Propagation of surface-plasmon waves along an MWCNT with a gold core was also analyzed. In the near-infrared and the visible regimes, the shells behave effectively as lossy dielectrics to suppress surface-plasmon-wave propagation along the gold core.

Fabrication and electromagnetic characteristics of microwave absorbers containing carbon nanofibers and NiFe particles

The objective of this study is to develop microwave absorbers by using both dielectric and magnetic lossy materials. Carbon nanofibers (CNFs) were used as dielectric lossy materials and NiFe particles were used as magnetic lossy materials. Twelve kinds of composite specimens were fabricated and classified into dielectric, magnetic, and mixed types. Their complex permittivities and permeabilities in the range of 2–18 GHz were measured. Parametric studies to aid in the design of single-layered radar absorbing materials (RAMs) were performed. The mixed RAMs generally showed improved absorbing characteristics with thinner matching thicknesses. The present mixed RAM showed the 10 dB absorbing bandwidth of 4.0 GHz in the X-band (2.00 mm thickness) and 6.0 GHz in the Ku-band (1.49 mm thickness). The measured absorbing properties of selected specimens were in very good agreements with simulations.

Effect of Lossy Dielectric Overlays on the Read-Range of UHF RFID Tags

The effect of a lossy overlay on the read-range of UHF RFID tags is studied. The design of the tag antenna is optimized for long read-ranges and then the effects of a lossy overlay (cover) on its properties are studied. The tags are simulated with and without the lossy overlay material. The input impedance of tag antenna, power transmission coefficient and read-range are calculated and compared for the two cases of with and without overlay. Further, optimization of tag with lossy dielectric overlay is carried out. It is observed that even with the overlay of a lossy dielectric, read-range up to 9 m can be obtained by properly matching the antenna with the RFID IC.

E-polarized Diffraction Coefficients of a Composite Wedge Composed of a Perfect Conductor and a Lossy Dielectric

E-polarized Diffraction Coefficients of a Composite Wedge Composed of a Perfect Conductor and a Lossy Dielectric

Realization of 3 m Semi Anechoic Chamber by Using Crossed-Wedge Shaped Hybrid EM Wave Absorber Consisting of Thin Corrugated Dielectric Lossy Sheet

This letter proposes a new hybrid EM wave absorber with the crossed-wedge shape, which can be applied to 3m semi anechoic chambers. In this study, we designed a new hybrid EM wave absorber with the crossed-wedge shape, which consisted of the inorganic and organic thin corrugated dielectric lossy sheet containing organic conductive fibers. Then the 3m semi anechoic chamber is constructed in the size of 9.0m × 6.0m × 5.7m (L × W × H) using these absorbers, and also the normalized site attenuation (NSA) is measured according to ANSI C63.4 in the frequency range of 30MHz to 1GHz. As a result, the measured NSA is obtained within ±3dB of the theoretical one.

PEEC Modeling of Dispersive and Lossy Dielectrics

In this paper a general formulation is presented for the time-domain partial element equivalent circuit method in a general dispersive medium. The formulation is based on Debye and Lorentz models where the resulting model is passive. The incorporation of such models into a partial element equivalent circuit solver is described by both convolution techniques and equivalent circuits. The new circuit models can be applied in the frequency as well as the time domain. Numerical examples are given to validate the proposed formulation and to show that the proposed method is accurately capturing the physics of dispersive and lossy dielectrics.

Vacuum-Gap Capacitors for Low-Loss Superconducting Resonant Circuits

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Low-loss microwave components are used in many superconducting resonant circuits from multiplexed readouts of low-temperature detector arrays to quantum bits. Two-level system defects in amorphous dielectric materials cause excess energy loss. In an effort to improve capacitor components, we have used optical lithography and micromachining techniques to develop superconducting parallel-plate capacitors in which lossy dielectrics are replaced by vacuum gaps. Resonance measurements at 50 mK on lumped LC circuits that incorporate these vacuum-gap capacitors (VGCs) reveal loss tangents at low powers as low as <formula formulatype="inline"><tex Notation="TeX">$4\times 10^{-5}$</tex> </formula>, significantly lower than with capacitors using amorphous dielectrics. VGCs are structurally robust, small, and easily scaled to capacitance values above 100 pF. </para>

Potential of near-field microwave imaging in breast cancer detection utilizing tapered rectangular waveguide probes

Microwave imaging for medical applications has been of interest for many years. A novel near-field microwave non-invasive testing and evaluation (NIT&E) technique utilizing tapered rectangular waveguide probes is presented for breast cancer detection. Near-field microwave NIT&E techniques can be a successful candidate for the detection of breast cancer because of their potential in dealing with materials of low conductivity (i.e. lossy dielectrics like the breast tissue). The physical basis for breast tumor detection with microwave imaging is the contrast in dielectric properties of normal and malignant breast tissues. A method adopting Fourier transform matching (FTM) technique and utilizing the reflection coefficient at the aperture of a tapered rectangular waveguide sensor radiating into a breast is described resulting in microwave images that indicate the presence of a tumor. These images demonstrate the feasibility of detecting breast tumors using this approach.

Rigorous formulation for electromagnetic plane-wave scattering from a general-shaped groove in a perfectly conducting plane: comment

We show that the problem of scattering of an obliquely incident plane wave by a general-shaped groove engraved on a perfectly conducting plane, which was recently studied by Basha et al. [J. Opt. Soc. Am. A24, 1647 (2007)], was solved 11 years ago using the same formulation. This method was further extended to deal with a finite number of grooves and also with complex apertures including several nonlossy and lossy dielectrics, as well as real metals.

薄い波状誘電損失体を用いた複合電波吸収体の等価誘電率表現による解析

The 10m and 3m semi anechoic chambers are in widespread use for the electromagnetic compatibility (EMC). The hybrid EM wave absorber consisting of the sintered ferrite tiles and the dielectric lossy materials has been usually used for these semi anechoic chambers. In the past, Suetake, Naito, and Shimizu's studies played a key part in providing the basis for the hybrid EM wave absorber. The reflectivity of the hybrid EM wave absorber can be calculated from the multi-layered approximate structure. Especially, each layer occupied partly the dielectric lossy materials can be replaced by the homogeneous plate having the equivalent relative complex permittivity, which is determined through the synthesized capacitance model in the large wavelength range. But, there was a problem that the equivalent relative complex permittivity differs with the process of the synthesized capacitance model.We propose a new method which can be applied to the equivalent relative complex permittivity by the Finite Difference Method (FDM). Moreover, the reflectivity of the hybrid EM wave absorber using the thin corrugated dielectric lossy sheet is calculated and measured. As the result, it is confirmed that the measured reflectivity agree with the calculation one.

Slow-light enhanced absorption for bio-chemical sensing applications: potential of low-contrast lossy materials

Slow-light enhanced absorption in liquid-infiltrated photonic crystals has recently been proposed as a route to compensate for the reduced optical path in typical lab-on-a-chip systems for bio-chemical sensing applications. A simple perturbative expression has been applied to ideal structures composed of lossless dielectrics. In this work we study the enhancement in structures composed of lossy dielectrics such as a polymer. For this particular sensing application we find that the material loss has an unexpected limited drawback and surprisingly, it may even add to increase the bandwidth for low-index contrast systems such as polymer devices.

임피던스 경계 조건, 모멘트 법과 몬테 카를로 방법을 이용한 논의 산란계수 수치적 계산과 측정 데이터와의 비교

본 논문은 논에 대한 전파 산란 특성을 측정하고, 수치적 계산 결과와 비교함으로써 벼의 수치적 모델링에 대한 전파 산란 알고리즘을 제시하고자 한다. 임피던스 경계 조건과 dyadic 그린함수로부터 임피던스 표면 위(수면)의 손실 있는 유전체(벼)에 대한 적분 방정식을 유도하였고, 모멘트 법을 이용하여 유전체의 체적 전류를 계산하였다. 또한, 몬테 카를로 방법을 적용하여 입사 각도 및 편파에 따른 후방 산란 계수를 수치적으로 계산하였다. 1.85 GHz의 측정 시스템을 이용하여 논의 후방 산란 계수를 측정하였으며, 본 논문에서 제시한 알고리즘의 계산 결과와 비교, 검증하였다. A numerical algorithm for estimating precise backscattering coefficients of rice fields is proposed and its accuracy is verified in this paper. After a bunch of rice plants above water surface is modeled with a bunch of randomly oriented lossy dielectric bodies above an impedance surface and the equivalent volume currents of the lossy dielectrics are computed using the moment method. Then, the scattered fields of a rice field with many bunches are computed with a Monte Carlo method, and consequently the backscattering coefficient of the rice field is computed for various incidence angles and polarizations. Finally, the backscattering coefficient of a rice field is measured at 1.85 GHz using an R-band scatterometer system, and these experimental data are used to verify the numerical algorithm proposed in this paper. It is found that the numerical computation results agree well with the measurement data.

PEEC capacitance extraction of 3-D interconnects

As feature size of electronic devices decreases, fast and accurate capacitance extraction has become increasingly critical for verification and analysis as regard as electromagnetic compat- ibility and signal integrity issues. The partial element equivalent circuit method is implemented for three-dimensional capacitance extraction of interconnects and very large-scale integration circuits with multiple dielectrics. The electric field coupling due to free and bound charges are analysed and modelled separately thus allowing to distinguish their contribution. The proposed approach provides physical insight, totally compatible fast methods for accelerating matrix-vector products, allows an easy treatment of lossy and dispersive dielectrics and is well suited for applying model order reduction techniques. Modern electronic design is surely extremely challenging. It is known that power distribution and management, digital computing and radio frequency wireless communication have very different bandwidths, as well as voltage and current levels. In addition, today's mobile devices share the same printed circuit board and/or packaging substrate in a very dense design. The consequence of this fact is that parasitics and interference poses significant design challenges and deserves a special attention to electromag- netic compatibility (EMC) engineers to meet design requirements. Parasitics may compromise the signal fidelity and/or level and dominate the coupling in the case of elec- tromagnetic interference and immunity. Typically, coupling takes place through the electric field (capacitive coupling), magnetic field (inductive coupling) or through a common current return path. It is understood that design meeting EMC criteria has a critical need for methodologies and computer-aided design tools, which allow to predict para- sitic effects and capture coupling physics. Also it is extre- mely desirable to extract parasitic lumped element circuit models from a layout geometry. As the feature size of electronics in mobile devices has dramatically decreased, the interconnect is becoming a dominant factor in system delay and signal integrity (SI). An accurate and efficient electromagnetic modelling of three-dimensional (3-D) high speed interconnects and very large-scale integration (VLSI) circuits embedded in mul- tiple dielectrics is extremely important for the design and verification of nowadays systems on package and systems on-chip for communication systems. Circuit performances such as SI, EMC, delay, radiation, power consumption, reliability are strongly influenced by the electrical charac- teristics of interconnects. Among the other effects, timing verification requires accurate interconnect modelling of parasitic parameters especially as regard as the parasitic