Dielectric Objects Research Articles

Decoupled Potential Integral Equations for Electromagnetic Scattering From Dielectric Objects

Recent work on developing novel integral equation formulations has involved using potentials as opposed to fields as unknown variables. This is a consequence of additional flexibility offered by potentials that enable development of well-conditioned systems. Until recently, most of the work in this area focused on formulations for analysis of scattering perfectly conducting objects. In this paper, we present well-conditioned decoupled potential integral equations (DPIEs) formulated for electromagnetic scattering from homogeneous dielectric objects. The formulation is based on decoupled boundary conditions derived for scalar and vector potentials. The resulting DPIE is a second kind integral equation, and does not suffer from either low frequency or dense mesh breakdown. Analytical properties of the DPIE are studied for spherical systems, and results provided demonstrate well-conditioned nature (and bounded spectrum) of the resulting linear system.

A novel diffraction tomographic algorithm with narrow observation angle

AbstractConventional diffraction tomography (DT) can be used to reconstruct objects with 360° coverage of observation angle. But solving inverse problem could be challenging when the full angle data are not available. In this paper, a novel diffraction tomographic algorithm with extrapolation method is proposed to detect two‐dimensional (2D) dielectric objects in cases where the observation stations are far away from the search domain and the observation angles are limited to a narrow range. Extrapolation is introduced to obtain more data in the frequency domain. Using this algorithm, all locations, shapes, and dielectric properties of targets can be reconstructed under 90° or even narrower observation angle. Due to the use of fast Fourier transform in the implementation, this algorithm is very fast although many iterations of extrapolation are needed. Images can be reconstructed with nearly real‐time performance. Simulation results are given to show the validity of the algorithm.

Ultra-Practical Guide to Ultrawideband [Book\/Software Review

This book contains nine chapters, progressing from an “Introduction to Ultrawideband, Short- Pulse Radio Systems” to “Transmitting, Receiving, and Arrays Antenna Design and Analysis.” It offers a comprehensive treatment of the methods, analysis, and practice of impulse and ultrawideband (UWB) systems and explores UWB sources, antennas, propagation, electromagnetic theory, and practical systems. It also includes practical guidance on how to build antennas and radio hardware for high-power wideband impulse signals and presents both theoretical and experimental results in the time frequency domain. Further, this book explains and discusses the scattering of UWB electromagnetic pulses by conducting and dielectric objects as well as the impulse response of objects; it also includes coverage of the propagation channel. The reader gains insight into the development of the high-power source of UWB radiation with megavolt effective potential on the base of combined antenna arrays. The book has been translated into English from Russian, with many listed references in Russian. This text covers both theory and practical information on UWB short-pulse radio systems. A UWB radio designer can use many of the examples as a starting point to ensure that he or she is beginning on the right foot. Various examples of test data, parameters, and charts can serve as checkpoint comparisons for an original design. Ultrawideband Short- Pulse Radio Systems is an extremely useful guidebook for any radio designer.

Reconstruction of Internal Field of Dielectric Objects for Noninvasive SAR Measurement Using Boundary Integral Equation

Reconstruction of the electromagnetic (EM) fields inside a dielectric object is investigated in order to develop a noninvasive specific absorption rate measurement. The proposed reconstruction method is based on the boundary integral equation (BIE) derived from the surface equivalence theorem that relates the equivalent EM currents on the surface enclosing the primary source to the radiated external fields. The EM currents are reconstructed by solving the discretized BIE using the field data sampled on the surface surrounding all of the target objects that consist of the dielectric phantom and radiating antenna. The field distribution inside the dielectric object is obtained from the reconstructed currents. A probe correction technique is also proposed to enable the application of this method to practical probe measurements. As the first step to the practical applications, the validity and usefulness of the proposed method are demonstrated numerically and experimentally using lossless and lossy homogeneous dielectric objects located near a dipole antenna, respectively. It is shown that the accuracy tends to deteriorate in the case of the lossy phantom, but this can easily be improved without significant modification of the proposed method.

Homogeneous shrinking/amplifying device and its layered realization

Arbitrary regular/irregular shaped electromagnetic shrinking device and amplifying device with homogeneous, non-negative, anisotropic and genetic constitutive parameters are proposed and designed based on linear transformation optics, which provides the flexibility for device designing, and closer to the practical implementation. Furthermore, layered structure based on effective medium theory is utilized to remove the anisotropic property of the proposed device. Simulation results show that when with sufficient layers, both the layered shrinking device and amplifying device behave nearly as perfect as the ideal one. A dielectric or magnetic object placed inside the proposed device will be visually transformed into another object with a bigger/smaller size and different constitutive parameters are figured out clearly, making the proposed device have potential applications in military camouflage or other field of electromagnetic engineering system. The shrinking/amplifying scale is tailored by the ratio of b/c (b and c are the quasi-radius of the arbitrarily shaped polygon). Composing of alternatively isotropic layers with positive material parameters would dramatically reduce the fabrication difficulty and move the device a step further towards the practical application.

A multi-mode digital holographic microscope.

We present a transmission-mode digital holographic microscope that can switch easily between three different imaging modes: inline, dark field off-axis, and bright field off-axis. Our instrument can be used: to track through time in three dimensions microscopic dielectric objects, such as motile micro-organisms; localize brightly scattering nanoparticles, which cannot be seen under conventional bright field illumination; and recover topographic information and measure the refractive index and dry mass of samples via quantitative phase recovery. Holograms are captured on a digital camera capable of high-speed video recording of up to 2000 frames per second. The inline mode of operation can be easily configurable to a large range of magnifications. We demonstrate the efficacy of the inline mode in tracking motile bacteria in three dimensions in a 160 μm × 160 μm × 100 μm volume at 45× magnification. Through the use of a novel physical mask in a conjugate Fourier plane in the imaging path, we use our microscope for high magnification, dark field off-axis holography, demonstrated by localizing 100 nm gold nanoparticles at 225× magnification up to at least 16 μm from the imaging plane. Finally, the bright field off-axis mode facilitates quantitative phase microscopy, which we employ to measure the refractive index of a standard resolution test target and to measure the dry mass of human erythrocytes.

Slotted Folded Patch Antenna With Double-T-slots for Platform-Insensitive UHF Tag Design

A compact folded patch antenna, which has a dimension of 42 mm $\times50$ mm $\times1.6$ mm ( $0.128\lambda \times 0.152\lambda \times 0.0049\lambda $ ) is proposed. Multiple C-shaped slotlines are incorporated for tuning down the resonant frequency of the folded patch. A pair of double-T-slots, which acts as the impedance matching network, is etched at the center of the patch for achieving conjugate match between the antenna and the chip. By combining the analytical method and the particle swarm optimization algorithm, an equivalent circuit model is constructed for analyzing the impedance characteristics of the proposed tag antenna. With the use of 4 W EIRP, a maximum read distance of 11.5 m is achievable by placing the proposed tag antenna on a dielectric object. Also, the tag antenna is found to be able to reach ~5.2 m on metal. The operating frequency of the proposed tag antenna is very stable for both the dielectric and metallic objects, which is very desirable for practical applications.

Efficient Solution of Electromagnetic Scattering From Dielectric Objects via Characteristic Basis Function Method Based on Large-Size Blocks With Multilevel Subdivision

The characteristic basis function method (CBFM) based on large-size blocks with multilevel subdivision is proposed to improve the analysis of electromagnetic scattering from dielectric objects. The small-size blocks' strategy is widely used to alleviate the computational burden on generating the characteristic basis functions (CBFs) in the perfectly electrical conducting (PEC) object problems. However, when transplanted into the dielectric objects, this strategy performs poorly according to our empirical results. For adapting the CBFM to dielectric objects, the large-size blocks' strategy is proposed for the first time. Primarily, it remarkably reduces the number of CBFs required for the reduced matrix. Furthermore, the multilevel subdivision on the blocks is adopted to convert the full-rank impedance matrices of the blocks into hierarchical matrices, leading to great advantage in two aspects. In the CBFs' generation, the self-impedance matrices with hierarchical structure can be easily inversed by a recursive inversion algorithm based on the Sherman-Morrison-Woodbury (SMW) formula, which significantly cuts down the consumption in terms of CPU time and memory requirement. In addition, the hierarchical structure is taken advantage of by the multiscale adaptive cross approximation (MS-ACA) to accelerate the filling of the mutual-impedance matrices of the adjacent blocks. The numerical results of several dielectric objects are presented to demonstrate the accuracy and efficiency of the proposed method.

Analysis of Electromagnetic Scattering From Combined Conducting and Dielectric Objects Above Rough Surface Using Hybrid SIE-KA-FMM Method

An efficient hybrid SIE-KA-FMM method is presented to analyze the electromagnetic scattering from combined conducting and dielectric objects above the rough surface. In this approach, the induced electric current on the rough surface is obtained by the Kirchhoff approximation (KA). The single integral equation (SIE) method is utilized to efficiently compute scattering from the composite target with markedly reducing the numbers of unknowns compared with the conventional coupled integral equation method. The fast multi-pole method (FMM) is incorporated for faster operation and less memory requirement. Several examples verify the validation of the hybrid SIE-KA-FMM method. The composite scattering characteristics of diversiform targets above the rough surface are obtained. Moreover, the numerical results with the different permittivity of dielectric part, polarization mode, working frequency, root mean square (RMS) and correlation length of rough surface, incident pitching/azimuth angle, and target height and target category have been analyzed to provide some useful conclusions.

$\mathcal {H}$-Matrix Accelerated Solution of Surface–Volume–Surface EFIE for Fast Electromagnetic Analysis on 3-D Composite Dielectric Objects

An efficient fast direct algorithm based on the hierarchical ( $\mathcal {H}$ -) matrices is presented for solution of the radiation problems on piecewise homogeneous dielectric objects using Method of Moment (MoM) discretization of the surface–volume–surface electric field integral equation (SVS-EFIE). The SVS-EFIE for the composite objects introduces independent surface electric current density on the boundary of each region. Therefore, different from the traditional Poggio–Miller–Chang–Harrington–Wu–Tsai formulation, in the SVS-EFIE, the object regions can be meshing independently according to their local properties which improves the flexibility and efficiency of the proposed method. It also makes the proposed algorithms appropriate for the analysis of both multiscale and large-scale composite structures. The numerical results from the proposed fast method are provided for the high-loss biological tissues from bioelectromagnetics applications and agree well with the analytical Mie series solution and commercial software. The CPU time and memory cost of the required $\mathcal {H}$ -matrix operations are analyzed in details and verified through several numerical experiments. The new computational framework allows for fast direct solution of 3-D radiation and scattering problems of moderate electrical size with $O(P^{\alpha } \log ^2 P)$ CPU time and $O(P^{\alpha } \log P)$ memory complexity, $P$ being the number of surface unknowns produced by the MoM discretization, and $1\leq \alpha \leq 1.5$ being a geometry-dependent parameter.

METHOD OF STRIP LINES’ TE MODES CHARACTERISTICS CALCULATION

The paper is devoted to the calculation of the electromagnetic field in a stripline based transmission line for the TE-modes. TE-mode is one of the closest to the main mode, especially at the high frequencies, and should be considered in the multiple-mode resonators. Moreover, TE-mode is the main mode in the slotline at ane frequency. The method of solving the electromagnetic field problem of computing the characteristics of TE-modes of the slotlines is proposed. The proposed method is based on a rigorous electrodynamic approach and has no restrictions on the geometric and electrophysical parameters of the lines. The problem is reduced to the eigenvalues and eigenvectors problem, which is solved by the 2D finite element method applied to the cross-section of the line. The resulting solutions provide the possibility of obtaining the distribution of the component of the electromagnetic field and calculate the integral characteristics of the stripline, such as effective dielectric permittivity, which defines wavelength in the line, and characteristic impedance, which describes the relation between current and voltage in the equivalent transmission line. The distribution of the electric field components in the slotline is shown. The results of the effective dielectric permittivity and characteristic impedance calculation for the slotline with various geometrical and electrophysical parameters at different operating frequencies are presented. The obtained values of the effective parameters are in good agreement with other known calculated and measured results. The proposed method can be applied to any structures of strip lines in an arbitrary medium with any dielectric or metal objects placed near the line. Thus, such a method is suitable for the analysis and design of micro mechanically tunable devices as well.

Ring of charge probed with Atomic Force Microscopy dielectric tip

We consider a dielectric sphere in the presence of a charged ring and derive expressions for their interaction force. New mathematical closed form expressions for electrostatic problems involving dielectric objects are always interesting, both for their intrinsic foundational value, and also for their practical use as test beds for numerical solutions. The chosen geometry is motivated by the importance to probe charged rings with Atomic Force Microscopy dielectric tips. The interaction forces obtained are further analyzed to identify notorious features of the force versus separation curves. This analysis provides practical guidelines to measure charge and size of rings from experiments.

Surface-Volume-Surface EFIE for Electromagnetic Analysis of 3-D Composite Dielectric Objects in Multilayered Media

The surface-volume-surface electric field integral equation (SVS-EFIE) is generalized for the case of scattering problems on the composite nonmagnetic dielectric objects situated in planar nonmagnetic layered medium. The piece-wise homogeneous regions of the scatterer can be arbitrarily positioned with respect to the layers of stratification. The SVS-EFIE being a class of single-source integral equations is formed by restricting the surface single-source electric field representation in each distinct region of the scatterer through the volume-EFIE (V-EFIE) enforced on the boundary of that region for only the tangential component of the total field. As a result, the SVS-EFIE utilizes only the electric field dyadic Green's functions. This allows for its cast into the mixed-potential form using classical Michalski-Zheng's formulation and method of moments (MoM) discretization featuring easily computable integrals with singularities no stronger than 1/R, R being the distance from the source to the observation point in such integrals. The matrices of MoM discretization are represented inhierarchical form (as H-matrices) enabling solution of the scattering problems in multilayered media with O(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</sup> log N) CPUtimeand memory complexities, where α is a geometry-dependent constant ranging from 1 to 1.5 depending on the shape of the scatterer. While the MoM surface and volume meshes discretizing the regions of the scatterer are constructed to ensure that no mesh element crosses interfaces between the layers, the clusters of both the surface and volume elements in their respective recursive partitionings in the process of H-matrix construction are allowed to span multiple layers of the medium. Upon computation of the layered medium Green's function kernels with the discrete complex image method allowing clusters of elements to cross dielectric interfaces between the layers is shown to preserve compressibility of the corresponding H-matrix blocks.

Multifrequency Microwave Imaging for Brain Stroke Detection

Early diagnosis of stroke with timely treatment could reduce adult permanent disability significantly [1]. Conventional medical imaging tools such as X-ray, ultrasound, computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET) have been widely used for diagnosis of brain disease. However, each of these methods has some limitations. X-ray imaging produces harmful radiation to the human body and challenging to identify early-stage abnormal tissue due to the relatively small dielectric proprieties contrast between the healthy tissue and abnormal tissue at X-ray frequencies [2]. PET provides useful information about soft tissues, but it is expensive and produces poor resolution. CT and MRI are unsuitable for continuously monitoring strokes due to produce harmful radiations (CT), expensive (MRI), time-consuming and not easy to develop a portable system [3,4]. Therefore, develop a new screening method is urgently needed to improve the effectiveness of disease detection. <br/> Microwave imaging is a relatively new non-invasive and cost-effective method for imaging of breast and brain tissues, which has continuously attracted many researchers’ interests over the past two decades [5,6]. The authors previously developed a holographic microwave imaging (HMI) method for dielectric object detection with a particular focus on brain stroke [7]. This paper investigates the feasibility of multifrequency HMI for brain stroke detection. A numerical system was developed to demonstrate the proposed theory. Various experiments were carried out to evaluate the performance of the proposed method. Results of experiments carried out using multifrequency HMI have been compared with the results obtained by using single frequency HMI. Results showed that multifrequency HMI could detect strokes and provide more accurate results of size and location than the single frequency HMI algorithm.

Versatile Solver of Nonconformal Volume Integral Equation Based on SWG Basis Function

In this paper, a versatile solver of a nonconformal volume integral equation based on the Schaubert-Wilton-Glisson (SWG) basis function is presented. Instead of using a piecewise constant function, the robust conventional SWG basis function is chosen and used directly for discontinuous boundaries. A new map method technique is proposed for constructing SWG pairs, which reduces the complexity from ON2 to ONlogN compared with a brute-force method. The integral equation is solved by the method of moments (MoM) and further accelerated by the multilevel fast multipole algorithm (MLFMA). What’s more, the hybrid scheme of MLFMA and adaptive cross approximation (ACA) is developed to resolve the low-frequency (LF) breakdown when dealing with over-dense mesh objects. Numerical results show that when in analysis of radiation or scattering problems from inhomogeneous dielectric objects or in LF conditions, the proposed solver shows high efficiency without loss of accuracy, which demonstrates the versatile performance of the proposed method.

Surface-Volume-Surface Electric Field Integral Equation for Solution of Scattering Problems on 3-D Dielectric Objects in Multilayered Media

Generalization of the surface-volume-surface electric field integral equation (SVS-EFIE) for the solution of electromagnetic scattering problems on 3-D dielectric objects embedded in multilayered media is proposed. While having only a single unknown surface current density on the boundary of the scatterer, the SVS-EFIE also features only electric field dyadic Green’s functions in its integral operators. This property in conjunction with Michalski–Zheng’s formulation of the multilayered media electric field Green’s function allows for the formulation of SVS-EFIE in the mixed potential form for the solution of the scattering problems in layered media. In the proposed method of moments (MoM) discretization scheme, the gradient and divergence operators associated with the electric field Green’s function are shifted to the basis and test functions of the discretized integral operators. As a result, the proposed formulation features no derivatives acting on the components of the layered media dyadic Green’s function, hence, substantially alleviating the numerical evaluation of the pertinent Sommerfeld integrals. The proposed MoM formulation scalarizes reaction integrals containing the multilayered media dyadic Green’s function through the use shape function-based definition of the basis and test functions. The resultant MoM integrals feature no singularities stronger than $1/R$ . The validation of the proposed SVS-EFIE formulation and its MoM discretization is performed through a comparison of the computed fields against the fields produced using commercial electromagnetic analysis software.

Study Effect of Objects Orientation in the Mediums On GPR Signal Reflections Using FDTD Simulation

Ground penetrating radar (GPR) is a very effective tool for detecting and identifying objects below the ground surface. based on the propagation and reflection of high-frequency electromagnetic waves. The GPR reflection can be affected by many things like the type of objects orientation, their shapes ..ect. The purpose of this paper is to study by simulation the effect of objects orientation in two different mediums (dry and wet sand) on the GPR signal reflection using Reflexw software which is based on a numerical method known as finite difference in time domain (FDTD). The simulations that have been realized included a conductor and dielectric objects. The results obtained have led us to find that the propagation path, the reflection strength and the signal form change with the change of object orientation and nature. To confirm the validity of the results, we compared them with experimental results previously published by researchers under the same conditions.

Study Effect of Objects Orientation in the Mediums On GPR Signal Reflections Using FDTD Simulation

Ground penetrating radar (GPR) is a very effective tool for detecting and identifying objects below the ground surface. based on the propagation and reflection of high-frequency electromagnetic waves. The GPR reflection can be affected by many things like the type of objects orientation, their shapes ..ect. The purpose of this paper is to study by simulation the effect of objects orientation in two different mediums (dry and wet sand) on the GPR signal reflection using Reflexw software which is based on a numerical method known as finite difference in time domain (FDTD). The simulations that have been realized included a conductor and dielectric objects. The results obtained have led us to find that the propagation path, the reflection strength and the signal form change with the change of object orientation and nature. To confirm the validity of the results, we compared them with experimental results previously published by researchers under the same conditions.

Development of a bipolar electrostatic chuck module with a beam-array assembly using the multiple etching process

In this paper, we propose a successful fabrication method for a bipolar electrostatic chuck (ESC) device with a beam-array assembly, in order to achieve a fairly flat surface on the beam’s tip. A fabricated bipolar ESC device is expected to clamp a curved dielectric object due to its elastically-deformable beams, which are compliant with an object’s surface. As a fabrication process, the lithography technique including multiple etching processes against a single etching mask was performed to etch a three-layer material (conductor–dielectric–conductor). Due to the fairly flat surface of the beam’s tip (figure ), sufficient adhesional contact area with the target object for a large adhesional force can be obtained. In order to understand the adhesion performance of the device, an experimental force curve was measured and partially compared with the theoretical adhesional force calculated using finite element analysis. The Pascal-expression for future work dealing with a large surface area was also calculated, corresponding to stacked prototype modules.

Folded Antipodal Dipole for Metal-Mountable UHF Tag Design

A compact folded dipole antenna that consists of two C-shaped arms, which are placed in the antipodal constellation, is proposed for designing a metal-mountable miniature tag antenna in the UHF band. Here, each of the dipole arms is composed of four unequal line segments for reducing the current crowding effect and for improving the tag’s performance. Two inductive shorting stubs are introduced for tuning the tag’s resonant frequency. The proposed tag antenna is made using a flexible substrate and it is electrically small, having a circuit size of 50 mm $\times30$ mm $\times1.6$ mm ( $0.153\lambda \times 0.092\lambda \times 0.005\lambda$ ). It has been found that conjugate match can be easily obtained by adjusting the dimensions of the C-shaped arms and the inductive shorting stubs. When mounted on metal, the proposed tag antenna is able to achieve a maximum read distance of 9.1 m at the equivalent isotropic radiated power of 4 W. The proposed tag antenna is found to be platform insensitive and it can read beyond 7 m when placed on dielectric objects.