Lossy Dielectric Objects Research Articles

Numerical framework for modeling quantum electromagnetic systems involving finite-sized lossy dielectric objects in free space

The modified Langevin noise formalism [A. Drezet, Phys. Rev. A 95, 023831 (2017); O. D. Stefano, S. Savasta, and R. Girlanda, J. Mod. Opt. 48, 67 (2001)] has been proposed for the correct characterization of quantum electromagnetic fields in the presence of finite-size lossy dielectric objects in free space. The main modification to the original one [T. Gruner and D.-G. Welsch, Phys. Rev. A 53, 1818 (1996); H. T. Dung, L. Kn\"oll, and D.-G. Welsch, Phys. Rev. A 57, 3931 (1998)] (also known as the Green's function approach for a bulk inhomogeneous lossy dielectric medium) was to introduce another fluctuating source in reaction to the radiation loss. Consequently, the resulting electric field operator is now determined by (i) boundary-assisted and (ii) medium-assisted fields on an equal footing, which originate from radiation and medium losses, respectively. However, due to the lengthy mathematical manipulation and complicated concepts, the validity of the modified Langevin noise formalism has not been clearly confirmed yet. In this work, we propose and develop a numerical framework for the modified Langevin noise formalism by exploiting computational electromagnetic methods. Specifically, we present utilization of the finite-element method to numerically solve plane-wave-scattering and point-source-radiation problems whose solutions are boundary-assisted and medium-assisted fields, respectively. We numerically validated the modified Langevin noise model calculating the Purcell factor of a two-level atom inside or outside a lossy dielectric slab. The proposed numerical framework is particularly useful for analyzing the dynamics of multilevel atoms near plasmonic structures or metasurfaces in the open space.

Characteristic Mode Formulations of Composite PEC and Lossy Dielectric Objects

Lossy dielectric substrate affects the performance of a nearby perfect electric conductor (PEC) antenna. This letter presents a set of formulae for characteristic mode analysis (CMA) of composite PEC and lossy dielectric objects. It is based on the volume-surface integral equation and substructure treatment that separates the radiation and dissipation powers of the composite structure. A narrow PEC plate (that represents a dipole antenna) is placed in proximity of a thick, lossy dielectric material, and CMA of this structure is presented as an example. The separation gap between the PEC and dielectric objects affects the resonance and radiation efficiency of the antenna, and it is shown that CMA accurately captures those effects. The influence of dielectric loss on the modal orthogonality is discussed. Since the PEC item dominates over the coupling one in the substructure operator, the computed modes maintain good orthogonality with low-loss dielectrics. Owing to the physical insights of CMA, it has many potential applications associated with lossy materials.

Microwave Radiometric Coherence Imaging: A Novel Electromagnetic Imaging Technique

A new microwave (MW) imaging technique for the reconstruction of complex permittivity profiles of lossy dielectric objects is proposed. The proposed technique is based on partial coherence in thermal radiation of objects and is distinct from interferometric radiometry used for high-resolution imaging of brightness temperature. This is a unique feature of the method that distinguishes it from other MW imaging methods for permittivity reconstruction, where the underlying physical phenomenon is electromagnetic scattering by the probed object. Equations governing the imaging method are presented, and its potential for complex permittivity reconstruction in two dimensions is demonstrated with simulations.

Effects of frequency-dependent surface impedance on the vacuum electronic terahertz sources

When the working frequency of vacuum electronic device reaches the terahertz frequency, the ohmic loss has a significant impact on the vacuum electronic device. To study the effect of the ohmic loss on the working characteristic of the vacuum electronic terahertz devices, this paper implements the frequency-dependent surface impedance boundary condition (SIBC) in the 3 dimensional particle in cell code UNIPIC-3D. Conformal mesh is adopted in the code to overcome the staircase error in traditional particle in cell method. By using the surface impedance boundary, we eliminate the need to study the field inside the lossy dielectric objects which require extremely small grid cells for numerical stability. In comparison with constant parameter SIBC, the dispersive SIBC is applicable over a very large frequency bandwidth and over a large range of conductivities. The correctness of the implementation is verified by simulating the lossy resonant cavity and circular waveguide, the simulated power loss is comparable with the theoretical predication. High power vacuum electronic devices of terahertz regime are attracting extensive interests due to their potential applications in science and technologies. The impulse-wave relativistic surface wave oscillator (SWO) and low-voltage continuous-wave planar grating backward wave oscillator (BWO) both made of copper are numerically studied by using UNIPIC-3D and dispersive surface impedance boundary condition. Numerical results show that the strongest field is very close to the slow wave structure where the beam-wave interaction occurs and that terahertz wave generates both in these two devices. The distributed wall loss has a considerable effect on the devices: the output power has a significant decrease and the startup time becomes longer, but the working frequencies of the two devices keep unchanged. To improve the efficiency of relativistic SWO, a resonant reflector is proposed between the diode and the slow wave structure. Numerical results show that the working frequency of the device with a resonant reflector keeps unchanged as the original one, but the output power increases to 60 MW from 41 MW of the original one when the ohmic loss is considered.

Discrete Quasi-Helmholtz Decomposition for 3-D High-Contrast Lossy Dielectric Problems

By applying Loop-Star decomposition of basis functions to form orthogonal transformation matrices, an efficient method for the analysis of electromagnetic scattering from three-dimensional dielectric and lossy objects, especially with high-contrast parameters to the background media, has been presented in this letter. The analysis of the diagonal blocks of the impedance matrix shows that the vector potential and scalar potential subspaces scale differently in relation to the material parameters, which may have a negative effect on the conditioning of the matrix and iteration efficiency. Therefore, new equations corresponding to the exterior and interior equations have been presented, respectively, by constructing discrete quasi-Helmholtz projection operators, based on the traditional dielectric integral formulations, i.e., Poggio–Miller–Chang–Harrington–Wu–Tsai. Numerical examples show that the proposed method is effective for high-contrast lossy dielectric objects by improving the condition number and decreasing the number of iterations.

Placement‐insensitive flexible RFID antenna for ‘peel‐and‐stick’ applications

Radio-frequency identification (RFID) systems with ‘peel-and-stick’ labels are currently limited to tracking items with nearly electromagnetically transparent material properties. This limitation stems from the antenna choice for these labels – a dipole variant. A ground plane edge treatment along with a feed slot with unique tuning capabilities is investigated as an alternative RFID antenna option. Ease of fabrication was maintained as a priority in all design decisions. The measured antenna displays true placement insensitivity with a constant impedance when attached to metal, lossy dielectric, or electromagnetically-transparent objects.

Analysis of Direct and Inverse Problems Related to Circular Waveguides Loaded With Inhomogeneous Lossy Dielectric Objects

An integral-equation-based analysis for direct and inverse problems related to circular waveguides loaded with inhomogeneous and arbitrarily shaped lossy dielectric material is introduced. The problem is formulated as a system of integral equations composed of the well-known data and object equations, which contain the dyadic Green's function (DGF) of the empty circular waveguide. Both the direct and inverse algorithms are based on this 3-D system of equations. In the direct problem, the scattering parameters are calculated using the scattered electric fields caused by the inhomogeneous lossy dielectric objects located in circular waveguide, while in the inverse algorithm, the scattered fields are assumed to be known and used for the determination of the complex permittivity variation of the object loaded in the waveguide through a Newton-type iterative approach. In both algorithms, the integral equations are solved via a method-of-moments-based discretization, where the accurate integration of the DGF at each discrete 3-D cell is achieved by a special integration technique. The validity region and the reliability of the direct and inverse algorithms are examined analytically and numerically through elaborative examples.

Research on RF Tag Performance on Metal Media and Design of Slotting Tag

Passive radio frequency (RF) tags in the UHF and microwave bands have recently drawn considerable attention with their great potential for use in inventory management, parcel and postal tracking. However, much more basic research is needed to increase the range and reliability of a passive RF tag’s radio link, particularly when the RF tag is placed onto a lossy dielectric object or a metallic surface. This paper presents two new useful forms of the radio link budget that describe the power link of an RF tag system when the tag is attached to an object, then the effects of a metal plate to antenna parameters when the antenna is horizontally placed near the plate. Furthermore, according to a series of tests for measuring the performance of an RF tag, relationship between distance from tag to a sheet of copper surface and readability is discovered. Moreover, the magnifying effect of an extra metal layer to readability is found too. Finally, according to the results of experiments, a design method of slotting RF tag which can be used to identify the goods location is proposed. This method can not only eliminate negative effect of metal disturbance, but enhance readability, which considers the convenience for use and manufacture cost as well.

Multilevel fast multipole method based on a potential formulation for 3D electromagnetic scattering problems

A combination of the multilevel fast multipole method (MLFMM) and boundary element method (BEM) can solve large scale photonics problems of arbitrary geometry. Here, MLFMM-BEM algorithm based on a scalar and vector potential formulation, instead of the more conventional electric and magnetic field formulations, is described. The method can deal with multiple lossy or lossless dielectric objects of arbitrary geometry, be they nested, in contact, or dispersed. Several examples are used to demonstrate that this method is able to efficiently handle 3D photonic scatterers involving large numbers of unknowns. Absorption, scattering, and extinction efficiencies of gold nanoparticle spheres, calculated by the MLFMM, are compared with Mie's theory. MLFMM calculations of the bistatic radar cross section (RCS) of a gold sphere near the plasmon resonance and of a silica coated gold sphere are also compared with Mie theory predictions. Finally, the bistatic RCS of a nanoparticle gold-silver heterodimer calculated with MLFMM is compared with unmodified BEM calculations.

Fast and accurate solutions of electromagnetics problems involving lossy dielectric objects with the multilevel fast multipole algorithm

Fast and accurate solutions of electromagnetic scattering problems involving lossy dielectric objects are considered. Problems are formulated with two recently developed formulations, namely, the combined-tangential formulation (CTF) and the electric and magnetic current combined-field integral equation (JMCFIE), and solved iteratively using the multilevel fast multipole algorithm (MLFMA). Iterative solutions and accuracy of the results are investigated in detail for diverse geometries, frequencies, and conductivity values. It is demonstrated that CTF solutions are significantly accelerated as the conductivity increases to moderate values and CTF becomes comparable to JMCFIE in terms of efficiency. Considering also the superior accuracy of this formulation, CTF becomes suitable for fast and accurate analysis of scattering problems involving lossy dielectric objects.

Efficient Wideband Electromagnetic Scattering Computation for Frequency Dependent Lossy Dielectrics Using WCAWE

This paper presents a model order reduction algorithm for the volume electric field integral equation (EFIE) formulation, that achieves fast and accurate frequency sweep calculations of electromagnetic wave scattering. An inhomogeneous, two-dimensional, lossy dielectric object whose material is characterized by a complex permittivity which varies with frequency is considered. The variation in the dielectric properties of the ceramic BaxLa4Ti 2+xO 12+3x in the <1 GHz frequency range is investigated for various values of x in a frequency sweep analysis. We apply the well-conditioned asymptotic waveform evaluation (WCAWE) method to circumvent the computational complexity associated with the numerical solution of such formulations. A multipoint automatic WCAWE method is also demonstrated which can produce an accurate solution over a much broader bandwidth. Several numerical examples are given on order to illustrate the accuracy and robustness of the proposed methods.

Spectral Difference Between Microwave Radar and Microwave-Induced Thermoacoustic Signals

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This letter presents a spectral content comparison of the signals generated in the microwave radar (MR) and microwave-induced thermoacoustic (MIT) imaging systems. Two physical processes occur when microwave interacts with a lossy dielectric object. First, due to the contrast in the complex permittivity between the embedded object and background medium, reflection of microwave energy occurs at the interface. Second, due to the contrast in the absorption coefficient between the object and background medium and the consequent thermal expansion, microwave induces an acoustic wave. As a method of comparison between the inputs and outputs of the MR and MIT processes, we define the MR and MIT channels. We use a two-dimensional (2-D) example to demonstrate that the MR channel over the ultrawideband (UWB) spectrum from 3.1 to 10.6 GHz manifests different fading from the MIT channel over the ultrasonic spectrum from 0.32 to 1.10 MHz. The two output signals are distinctive, but they are co-registered to the same object. Hence, using the information provided by both could enhance the imaging modality. We apply this dual-physics scheme in the context of breast tumor detection. </para>

Imaging of dielectric objects buried under a rough surface via distorted born iterative method

A method is given for the shape, permittivity and conductivity reconstruction of lossy dielectric objects buried under rough surfaces using the Distorted Born Iterative Method (DBIM). The method is based on the refreshing of the Green's function of the two-part space media with rough interface by updating the complex permittivity of the reconstruction domain at each iteration step. The scattered field data are measured at multiple locations for multiple transmitters operating at a single frequency where both transmitters and receivers are located above the rough surface interface. The Green's function of the problem is obtained by using the buried object approach (BOA) method where the fluctuations of the rough surface from the flat one are assumed to be buried objects in a two-part space with planar interface. The performance of the method is tested by some numerical applications and satisfactory results are obtained.

Subsurface Sensing of Buried Objects Under a Randomly Rough Surface Using Scattered Electromagnetic Field Data

This paper proposes a new inverse method for microwave-based subsurface sensing of lossy dielectric objects embedded in a dispersive lossy ground with an unknown rough surface. An iterative inversion algorithm is employed to reconstruct the geometry and dielectric properties of the half-space ground as well as that of the buried object. B-splines are used to model the shape of the object as well as the height of the rough surface. In both cases, the control points for the spline function represent the unknowns to be recovered. A single-pole rational transfer function is used to capture the dispersive nature of the background. Here, the coefficients in the numerator and denominator are the unknowns. The approach presented in this paper is based on the state-of-the-art semianalytic mode matching forward model, which is a fast and efficient algorithm to determine the scattered electromagnetic fields. Numerical experiments involving two-dimensional geometries and TM incident plane waves demonstrate the accuracy and reliability of this inverse method

Study on Electromagnetic Problems Involving Combinations of Arbitrarily Oriented Thin-Wire Antennas and Inhomogeneous Dielectric Objects with A Hybrid MoM-FDTD Method

In this paper, a novel iteration procedure of the hybrid method combining the frequency-domain MoM with the FDTD method is first presented. And then the microwave network theory is introduced into the MoM-FDTD method to calculate the mutual impedance and the isolation between antennas located near lossy dielectric objects. Numerical results have a good agreement with those obtained by the software FEKO, which validates the EMC analysis method presented in this paper. Last, interactions between human head and antenna are analyzed by the hybrid MoM-FDTD method. Not only are the near-field distributions in human head presented but also the disturbed far-field patterns of the antenna. The hybrid method in this paper supplies an effective approach to analyze the performance of antennas near inhomogeneous dielectric objects.

Enhancement of specific absorption rate in lossy dielectric objects using a slab of left-handed material

An enhancement of the specific absorption rate (SAR) inside a lossy dielectric object has been investigated theoretically based on a slab of left-handed medium (LHM). In order to make an accurate analysis of SAR distribution, a proper Green's function involved in the LHM slab is proposed, from which an integral equation for the electric field inside the dielectric object is derived. Such an integral equation has been solved accurately and efficiently using the conjugate gradient method and the fast Fourier transform. We have made a lot of numerical experiments on the SAR distributions inside the dielectric object excited by a line source with and without the LHM slab. Numerical experiments show that SAR can be enhanced tremendously when the LHM slab is involved due to the proper usage of strong surface waves, which will be helpful in the potential biomedical applications for hyperthermia. The physical insight for such a phenomenon has also been discussed.

A Moment Method Solution for the Shielding Properties of Three-Dimensional Objects Above a Lossy Half Space

In this paper, a moment method (MM) solution for analyzing the electromagnetic (EM) shielding properties of three-dimensional (3-D) lossy dielectric and magnetic objects over a lossy half space is presented. An MM, based on a volume formulation and a special Green's function in the spectral domain, is developed. Plane waves with TMz and TEz polarizations incident upon 3-D lossy material structures are demonstrated for the shielding effects of those bodies in the presence of a lossy ground. Some of the results are compared with those evaluated by applying the finite difference time domain method, and good agreements are obtained. The MM solution can be used to study the shielding problems for 3-D objects located above a lossy ground.

Numerical Modeling Of Microwave Heating OfDielectric Materials

Microwave heating has been established in industry for many years. The temperature distribution within irradiated materials is obtained by determining the electric field distribution. For this reason, modelling the geometry under the plane wave illumination is useful. To determine the temperature distribution, the transmission line analogy for plane wave propagation and reflection for normal incidence angle is used. The heating pattern in a multilayered slab material exposed to a uniform plane wave is obtained. The lossy dielectric object is modelled as an infinitive number of cascaded transmission lines terminated with a metal plate and the inner electric field is calculated.

Microwave Heating of Dielectric Lossy Objects

This work deals with microwave heating of dielectric lossy materials. The heating pattern in a multilayered slab material exposed to uniform plane wave is obtained. To determine the temperature distribution, the transmission line analogy for plane wave propagation and reflection for normal incidence angle is used The lossy dielectric object is modelled as a cascaded transmission line tenniruited with a metal plate and the inner electric field is calculated. The temperature distributions are presented for two different objects with different radii.

Scattering from lossy dielectric objects buried beneath randomly rough ground: validating the semi-analytic mode matching algorithm with 2-D FDFD

A new semi-analytic mode matching (SAMM) algorithm is verified by two-dimensional (2-D) finite difference frequency domain (FDFD) simulations of scattering resulting from uniform plane waves incident on randomly rough dielectric half-spaces containing buried dielectric targets. The SAMM algorithm uses moderately low-order modal superpositions of cylindrical waves, each of which satisfies the 2-D-Helmholtz equation in its appropriate region (air, ground, or mine) and then matches all nonzero electric and magnetic field components at each interface by inverting a highly overconstrained dense linear matrix equation by singular value decomposition. That is, the set of cylindrical mode coefficients is found which best fits the boundary conditions in a least squares sense. For smooth ground, coordinate scattering centers (CSCs) are chosen at the mine center and at its image above the plane to model scattering. For randomly rough ground, additional CSCs are located within the rough boundary layer. Excellent agreement between 2-D-FDFD and the 2-D version of SAMM is observed, with 2-D-SAMM being at least an order of magnitude faster. 3-D-SAMM is estimated to be four orders of magnitude faster than 3-D-FDFD, with drastically reduced memory requirements.