Dielectric Objects Research Articles

Novel Single-Source Surface Integral Equation for Scattering Problems by 3-D Dielectric Objects

A new single-source integral equation is proposed for the solution of electromagnetic wave scattering problems. The traditional volume electric field integral equation is reduced to the new single-source surface integral equation by representing the electric field inside the scatterer as a superposition of spherical waves emanating from its boundary. Such new integral equation formulation has been previously developed for the scalar and vector cases of 2-D scattering problems. In this paper, the 3-D form of this new single-source surface integral equation for scattering on homogeneous nonmagnetic dielectrics is proposed. Detailed description of the method of moments (MoMs) discretization and its resultant matrices is presented. In order to validate the new integral equation formulation and verify the accuracy of its MoMs discretization, its solution is compared against the analytical Mie series solution and fields computed using the commercial electromagnetic analysis software.

A Numerically Efficient Method for Predicting the Scattering Characteristics of a Complex Metallic Target Located Inside a Large Forested Area

An efficient electromagnetic model for the scattering analysis of targets placed in large natural environments is presented. A hybrid formulation combining volume and surface integral equations is used to describe forest environment (dielectric objects) in which metallic structures are present. A large part of the forest can be analyzed electromagnetically by using the characteristic basis function method, whose use enables us to simulate the problem at hand and significantly reduce the dimension of the linear system that needs to be solved.

Radiation of a charge in presence of a dielectric object: aperture method

We develop an original method for calculation of radiation from a charge moving in the presence of a dielectric object. The method can be applied to objects which are larger than the wavelengths under consideration. First, the field of a charge in an infinite medium (without external boundaries) is calculated. Further the field at the external boundary of the object (“the aperture”) is found using the Snell's and Fresnel's laws. At final step of this technique, we calculate the field outside the target using Stratton-Chu formulae (“aperture integrals”). Contrary to the ray-optic technique, this method is valid for the observation point with arbitrary wave parameter (including Fraunhofer area) as well as in neighborhoods of focuses and caustics. We apply the method developed to the cone with vacuum channel where the charge moves (axially symmetrical problem). As well, this problem is simulated using COMSOL Multiphysics. Comparing results of both techniques one can conclude that the aperture method can be applied even for relatively small objects which have the size of several wavelengths. It is important as well that the accuracy of calculations increases with an increase in the distance from the aperture.

Radiative heat transfer between spatially nonlocally responding dielectric objects

We calculate numerically the heat transfer rate between a spatially dispersive sphere and a half-space. By utilising Huygens’ principle and the extinction theorem, we derive the necessary reflection coefficients at the sphere and the plate without the need to resort to additional boundary conditions. We find for small distances nm a significant modification of the spectral heat transfer rate due to spatial dispersion. As a consequence, the spurious divergencies that occur in spatially local approach are absent.

Computational Electrodynamics - A Powerful Tool for Nanophotonics and Microscopy

ABSTRACTComputational electrodynamics simulations provide a critical complement to experimental investigations for the understanding of light-matter interaction in complex systems. Its success is due in part to its relative simplicity and ease of use, coupled with its broad applicability to many material systems and optical processes. First, we will review our recent work in nanophotonics. While computational electrodynamics has been, and continues to be, very widely used in plasmonics, there are significant issues in convergence and accuracy, which we have studied in detail, and which sometimes point to the need for parallel computing. With access to large computational resources, we are able to study complex arrangements of dielectric and plasmonic objects, including metallic nanoparticle distributions for color production, hybrid dielectric/plasmonic nanoantennas for enhancement of third harmonic generation, and metasurfaces for nonlinear light control and structuring. Second, we will discuss our computational electrodynamics simulations of nonlinear optical microscopy experiments. Our tool includes high numerical aperture light sources, propagation through heterogeneous media, nonlinear near-field interaction, subsequent propagation to the far field, and integration over a collecting lens. We have used this to unravel the image formation mechanisms in nonlinear optical microscopy, such as CARS and SHG microscopy. We find that the images are not a one-to-one density map of the object, but rather that the sub-micrometer to nanometer structure of the object, along with the coherence of parametric nonlinear optical processes, can be imprinted in the image in surprising ways.

A dual-mode proximity sensor with combination of inductive and capacitive sensing units

PurposeThe purpose of this paper is to present a dual-mode proximity sensor composed of inductive and capacitive sensing modes, which can help the robot distinguish different objects and obtain distance information at the same time. A systematic study of sensor response to various objects and the function of cooperation sensing is needed. Furthermore, the application in the field of robotic area needs to be discussed.Design/methodology/approachNumerical modeling of each sensing modes and simulations based on finite element analysis method has been carried out to verify the designed dual-mode sensor. A number of objects composed of different materials are used to research the cooperation perception and proximity sensing functions. In addition, the proposed sensor is used on the palm of a mechanical hand as application experiment.FindingsThe characteristics of the sensor are summarized as follows: the sensing range of inductive mode is 0-5.6 mm for detecting a copper block and the perceive range of capacitive mode is 0-5.1 mm for detecting a plastic block. The collaborative perceive tests validated that the non-ferromagnetism metals can be distinguished by inductive mode. Correspondingly, ferromagnetism metals and dielectric objects are differentiated by capacitive mode. Application experiments results reveal that both plastic bottle and steel bottle could be detected and differentiated. The experimental results are in agreement with those of simulations.Originality valueThis paper provides a study of dual-mode proximity sensor in terms of design, experiments and application.

Compressive Sensing Holographic Microwave Random Array Imaging of Dielectric Inclusion

Holographic microwave imaging is an innovative method to image biological objects based on their dielectric properties, which has the advantages of high spatial resolution. However, the image reconstruction method is always a critical issue in holographic microwave imaging. This research aims to investigate the feasibility and effectiveness of applying compressive sensing (CS) technique to the holographic microwave imaging for small dielectric object detection. This paper presents a compressive sensing holographic microwave random array imaging (CS-HMRAI) method for imaging of dielectric objects. A numerical system consists of various dielectric models and imaging processing model are developed to evaluate the proposed approach. The split Bregman (SB) and orthogonal matching pursuit (OMP) algorithms are applied to HMRAI for evaluation of small inclusions embedded in dielectric objects. Various experiments are conducted to identify lesions using the proposed CS-HMRAI method and results are compared with HMRAI and HMRAI via OMP methods. Both simulation and experimental results demonstrate that CS-HMRAI via SB can produce high-quality images and detect arbitrarily shaped small inclusions with random sizes and locations by using significantly fewer sensors and scanning times than the HMRAI and CS-HMRAI via OMP approaches. The proposed approach has the potential for further investigation for breast tumor detection in a fast and cost-effective manner.

A Time-Domain Propagator Numerical Method for Computational Electromagnetics

A new time-domain numerical method for full-wave electromagnetic scattering and propagation is presented. The propagator method can be described as a numerical integral operator technique for moving the electromagnetic field through numerical space at successive increments in time. The numerical equations are obtained by discretizing electric and magnetic field propagator integrals. A primary feature of the propagator method is that all six electromagnetic-field components are calculated at each numerical grid point and all components are in time synchronization. Constant spatial and time increments are maintained throughout an inhomogeneous numerical space by employing an extrapolation procedure that ensures causality. A simple and effective first-order absorbing boundary condition, described as the null boundary condition, is introduced. Examples, provided in one-, two-, and three-dimensions, include plane wave reflection from and transmission through a planar boundary, and scattering and radar cross sections for canonical dielectric objects.

Electromagnetic Imaging of Dielectric Objects Using a Multi-Directional Search-Based Simulated Annealing.

In this paper, we introduce a global optimization method that is a novel combination of the simulated annealing method and the multi-directional search algorithm. We demonstrate the use of the algorithm for a microwave-imaging system to obtain the electrical properties of objects. The proposed global optimizer significantly improves the performance and speed of the simulated annealing method by utilizing a nonlinear simplex search, starting from an initial guess, and taking effective steps in obtaining the global solution of the minimization problem. Due to the efficient performance of the proposed global optimization method, we are able to obtain the shape, location, and material properties of the target without considering any a priori information about them. The accuracy and applicability of the proposed imaging method is demonstrated with some numerical results in which two-dimensional images of multiple objects are successfully reconstructed.

Fast Operations for a Gabor-Frame-Based Integral Equation With Equidistant Sampling

We consider the computation time of a three-dimensional Gabor-frame-based spatial–spectral integral equation solver for scattering from dielectric objects embedded in a multilayer medium. Based on the Gabor frame, a new set of basis functions is proposed, together with a set of equidistant Dirac-delta test functions. Using this construction, we approximate the operations of Fourier transformation and pointwise multiplication by a method that is significantly faster than the original method. A numerical example is included where the computation time is reduced by a factor of 15, while preserving accuracy.

VIE-ODDM-FFT Method Using Nested Uniform Cartesian Grid for the Analysis of Electrically Large Inhomogeneous Dielectric Objects

A hybrid method of the volume integral equation-based overlapping domain decomposition method and the fast Fourier transform (FFT)-based method (VIE-ODDM-FFT) using nested uniform Cartesian grid is proposed for the analysis of electrically large inhomogeneous dielectric objects whose usual fast algorithm models are too large for the user’s computer to accommodate. The integral equation is first built in the entire volumetric domain, and then the entire volumetric domain is partitioned into some nonoverlapping geometric subdomains. The SWG basis functions are used to expand the equivalent electric flux density in the entire domain. Then, several concepts such as basic subdomain, extended region, and complementary region are introduced. The subproblem in an extended region is quickly solved by using the FFT-based method with DILU preconditioner, and the action of the complementary region of an extended region on this extended region itself is quickly calculated by means of FFT. In this scheme, FFT acceleration is achieved by fitting Green’s function (FG) onto the nodes of one or more nested uniform Cartesian grid. The convergence of the outer iterative scheme of the proposed VIE-ODDM is investigated theoretically and numerically, and demonstrated to be very good and, hence, a very large problem can be effectively solved in an ordinary computer. Some numerical examples are provided to demonstrate the correctness, robustness, and efficiency of the proposed method.

Embedding Approach to Modeling Electromagnetic Fields in a Complex Two-Dimensional Environment

An approach is presented to combine the response of a two-dimensionally inhomogeneous dielectric object in a homogeneous environment with that of an empty inhomogeneous environment. This allows an efficient computation of the scattering behavior of the dielectric cylinder with the aid of the CGFFT method and a dedicated extrapolation procedure. Since a circular observation contour is adopted, an angular spectral representation can be employed for the embedding. Implementation details are discussed for the case of a closed 434 MHz microwave scanner, and the accuracy and efficiency of all steps in the numerical procedure are investigated. Guidelines are proposed for choosing computational parameters such as truncation limits and tolerances. We show that the embedding approach does not increase the CPU time with respect to the forward problem solution in a homogeneous environment, if only the fields on the observation contour are computed, and that it leads to a relatively small increase when the fields on the mesh are computed as well.

Electrical Impedance Spectro-Tomography Based on Dielectric Relaxation Model

An electrical impedance spectro-tomography consists of a quasi-adjacent sensing method and a frequency-time difference imaging for relatively complex dielectric object monitoring has been proposed. A quasi-adjacent sensing method is designed to measure an electrical impedance spectroscopy based on four-wire measurement technique at the multi-electrodes electrical impedance tomography sensor. A frequency-time difference imaging for spatial distribution monitoring is needed, as the electrochemical reaction incur during the short time meanwhile the spatial geometry tends to be constant. An artificial set of phantoms were made and the proposed technique was capable to show the Cole–Cole parameters as a dielectric relaxation model on each measurement pair. Compare with the adjacent method, using the quasi-adjacent method show Re(Z) is two times higher, Imag(Z) is ten times higher, and a higher and homogeneous sensitivity map area are 60% wider. A negative resistance at high-frequency measurement also can be eliminated successfully by using the proposed method.

Three-dimensional nanoscale imaging by plasmonic Brownian microscopy

AbstractThree-dimensional (3D) imaging at the nanoscale is a key to understanding of nanomaterials and complex systems. While scanning probe microscopy (SPM) has been the workhorse of nanoscale metrology, its slow scanning speed by a single probe tip can limit the application of SPM to wide-field imaging of 3D complex nanostructures. Both electron microscopy and optical tomography allow 3D imaging, but are limited to the use in vacuum environment due to electron scattering and to optical resolution in micron scales, respectively. Here we demonstrate plasmonic Brownian microscopy (PBM) as a way to improve the imaging speed of SPM. Unlike photonic force microscopy where a single trapped particle is used for a serial scanning, PBM utilizes a massive number of plasmonic nanoparticles (NPs) under Brownian diffusion in solution to scan in parallel around the unlabeled sample object. The motion of NPs under an evanescent field is three-dimensionally localized to reconstruct the super-resolution topology of 3D dielectric objects. Our method allows high throughput imaging of complex 3D structures over a large field of view, even with internal structures such as cavities that cannot be accessed by conventional mechanical tips in SPM.

Image systems for the reaction field inside spheroidal dielectric objects and applications

Charges inside a dielectric object embedded in a dissimilar dielectric medium polarize the surrounding medium, which in turn makes a contribution, called the reaction field, to the electric field inside the object. In this work, we develop complete image systems for the reaction field inside a prolate or oblate spheroidal dielectric object embedded in an infinite dissimilar dielectric medium. In either case, an image system consists of a point image and a symmetric surface image over an exterior confocal spheroid that passes through the point image. As an application, the point image is applied into the generalized image charge solvation model (GICSM) and is tested in simulations of liquid water, and the results are analyzed in comparison with those obtained from the ICSM simulation as references. The results indicate that, for both the prolate and oblate cases, the single point image charge approximation for the reaction field inside the dielectric cavity of the model is good enough for the GICSM to faithfully reproduce typical static and dynamic properties of the liquid water at least when the spheroidal cavity has relatively small eccentricity.

Improved hybrid FEM/MOM combining MLFMA for composite electromagnetic scattering

ABSTRACTA generalized hybrid scheme combining finite element method (FEM) and the method of moments (MOM) is first presented to investigate scattering from a 3-D dielectric object above a 2-D dielectric rough surface. The hybrid FEM/MOM scheme is divided into the FEM region for the object based on Helmholtz’s equation and the MOM region for the rough surface based on coupled integral function, which can greatly reduce the computed region. With the rough surface getting larger, the unknowns of the rough surface get more. So MLFMA is employed to reduce computation complexity of MOM region itself and coupling interaction matrices between MOM region and FEM region. Consequently, the iterative process can be greatly accelerated. This generalized hybrid FEM/MOM is very suitable for investigating scattering from composite model of a complex material object and electrically large dielectric rough surface. Some examples verify this generalized hybrid FEM/MOM in high efficiency, low storage requirement, high precision and generality.

3-D Radar Imaging Based on a Synthetic Array of 30-GHz Impulse Radiators With On-Chip Antennas in 130-nm SiGe BiCMOS

We report a 30-GHz impulse radiator chip for high-resolution 3-D radar imaging. In this paper, an asymmetrical topology in the cross-coupled pulsed VCO is introduced to minimize timing jitter of radiated impulses to 178 fs, which enables highly efficient spatial combining. The coherent combining over the air has been performed with two widely spaced impulse radiators. The shortest full-width-at-half-maximum pulsewidth of 60 ps is recorded. 3-D images of various metallic objects and dielectric objects are produced using a custom-designed synthetic array imaging system. A depth resolution of 9 mm and a lateral resolution of 8 mm at a range of 10 cm have been achieved. The impulse radiator was implemented in a 130-nm SiGe BiCMOS process technology with an area of 2.85 mm2 and an average power consumption of 106 mW.

Detection of micron size phantom of biological cell using concentric square ring metamaterial at microwave frequency

ABSTRACTThis paper presents simulation studies and theoretical analysis of sensing property of concentric square ring metamaterial biological materials. Phantom of dielectric cell having dimension 100 µm long and 25 µm in radius is considered. Sensor is designed using periodic arrays of split ring resonators and wires having negative permittivity and permeability at 16.694 GHz. Transmission parameters are extracted using CST MWS software. Change in resonance is observed on placing phantom close to the sensor due to the change in capacitance and inductance. Designed sensor can sense single phantom cell with 133 MHz of shift in resonance. Study shows that sensor has good sensitivity for detecting micron size dielectric objects.

Compressed Sensing for the Detection and Positioning of Dielectric Objects Inside Metal Enclosures by Means of Microwave Measurements

Based on compressed sensing and microwave measurements, we present a procedure for the detection and positioning of dielectric objects inside a metal enclosure, where the number of objects is unknown but assumed to be limited. The formulation features a convex quadratic optimization problem with 1-norm regularization, which allows for rapid detection and positioning given a precomputed dictionary. The dictionary consists of the scattering parameters computed from a single scattering object placed at the grid points of a structured grid that covers the entire measurement region. We test our method experimentally in a microwave measurement system that features a measurement region with a diameter of 11.6 cm. The measurement region is encircled by six aperture antennas, where each aperture is the end-opening of a rectangular waveguide operated from 2.7 to 4.2 GHz. We use acrylic-glass cylinders of radius 5.2 mm as scatterers and find that the compressed sensing method can correctly detect at least up to five scatterers with an average positioning accuracy of 3 mm. In addition, we investigate the performance of the method with respect to scarcity of data, where we omit scattering parameters or frequency points.

Numerical Analysis of the Potential Formulation of the Volume Integral Equation for Electromagnetic Scattering

AbstractWe present a discretization of the potential volume integral equation for electromagnetic scattering by dielectric objects. The equations are written for the vector and scalar potentials combined with the Lorenz gauge condition. The advantage of the potential formulation over the more conventional formulations, that is, the field, flux, or current formulations, is that the potentials are continuous across material interfaces enabling the use of fully continuous basis functions. The discretization with the fully continuous basis functions leads to a better conditioned system matrix compared to those of the other formulations discretized with the fully or partially discontinuous functions. Thus, it speeds up the iterative solution. The method is accelerated with the precorrected fast Fourier transform algorithm.