Flnite-difierence Time-domain Method Research Articles

APPLICATIONS OF THE DISCRETE GREEN'S FUNCTION IN THE FINITE-DIFFERENCE TIME-DOMAIN METHOD

In this paper, applications of the discrete Green's function (DGF) in the three-dimensional flnite-difierence time-domain (FDTD) method are presented. The FDTD method on disjoint domains was developed employing DGF to couple the FDTD domains as well as to compute the electromagnetic fleld outside these domains. Hence, source and scatterer are simulated in separate domains and updating of vacuum cells, being of little interest from a user point of view, can be avoided. In the developed method, the fleld radiated by an FDTD domain is computed as a convolution of DGF with equivalent current sources measured over two displaced Huygens surfaces. Therefore, the computed electromagnetic fleld is compatible with the FDTD grid and can be applied as an incident wave in a coupled total- fleld/scattered-fleld domain. In the developed method, the DGF waveforms are truncated using the Hann's window and windowing parameters assuring accuracy of computations are pointed out. The error of the fleld computations varies between i90dB and i40dB depending on the DGF length and excitation waveform. However, if the DGF length is equal to the number of iterations in a simulation, the presented DGF-based techniques return the same results as the direct FDTD method.

DESIGN BLUETOOTH AND NOTCHED-UWB E-SHAPE ANTENNA USING OPTIMIZATION TECHNIQUES

In this article, an optimized E-shaped patch antenna for Bluetooth (2.4{2.484GHz) and UWB (3.1{10.6GHz) applications with WLAN (5.15{5.825GHz) band-notched characteristics is proposed. The dimensions of the E-shaped antenna structure in addition to the position of the slotted C-shape in the ground plane are optimized using recent optimization techniques such as Modifled Particle Swarm Optimization (MPSO), Bacterial Swarm Optimization (BSO), and Central Force Optimization (CFO). The optimization algorithms were implemented using MATLAB-software and linked to the CST Microwave Studio to simulate the antenna. Next, the efiects of the Laptop structure on the antenna radiation characteristics are considered. Finally, the antenna structures are simulated by the flnite difierence time domain method (FDTD) to validate the results. The measured results exhibit good agreement with the simulation from CST and the Finite Difierence Time Domain (FDTD) program written with matlab.

TIME-REVERSAL MICROWAVE IMAGING BASED ON RANDOM CONFIGURATION OF TRANSMITTERS OR RECEIVERS

Imaging techniques based on time reversal method are particularly suitable for detection of targets embedded in a strongly scattering media. Generally in time reversal imaging technique we need to know the Green's function of the medium and the exact locations of the transmitter and receiver antennas. We introduce a target imaging method in which imaging is made with an arbitrary placement of the transmitting or receiving antennas. Numerical simulations are used to illustrate the capabilities of the proposed algorithms in difierent scenarios. We use the two-dimensional flnite difierence time domain method in our simulations. The numerical simulations are done for a typical through-the-wall scenario. We also present results in which the same method is used for tracking targets behind the wall.

NOVEL TRIANGULAR METAMATERIAL DESIGN FOR ELECTROMAGNETIC ABSORPTION REDUCTION IN HUMAN HEAD

In this paper, a novel triangular metamaterial (TMM) structure, which exhibits a resounding electric response at microwave frequency, is developed by etching two concentric triangular rings of conducting materials. A flnite-difierence time-domain method in conjunction with the lossy-Drude model was used in this study. Simulations were performed using the CST Microwave Studio R ∞ . The technique of speciflc absorption rate (SAR) reduction is discussed, and the efiects of the position of attachment, the distance, and the size of the metamaterials on the SAR reduction are explored. The performance of the novel TMMs in cellular phones was also measured in the cheek and the tilted positions using the COMOSAR system. The TMMs achieved a 50.82% reduction for 1gm SAR. These results provide a guideline to determine the triangular design of metamaterials with the maximum SAR reducing efiect for a cellular phone.

OPTIMAL PROGRAMS TO REDUCE THE RESISTANCE OF GROUNDING SYSTEMS

In this paper, some optimal programs have been proposed through the analyses of transient grounding resistance (TGR) to reduce the grounding resistance using the flnite-difierence time-domain method. First, the TGR of various electrode types, lengths and sectional programs is studied, and it is found that a ∞at bar is the most flnancially e-cient conductor to be used as grounding electrode. Enlarging grounding electrode length can reduce grounding resistance when it is shorter than the efiective length, but the reduction efiect declines as the length increases. Additionally, a series of small electrodes would lead to a much lower resistance than a single large one. Second, it is demonstrated that locally improving the soil near the grounding system is an e-cient way of reducing the grounding resistance. Improving a limited area soil surrounding the lifting line would reduce the peak resistance signiflcantly, while local enlarging electrodes surrounded soil conductivity can reduce the grounding system steady resistance obviously.

FDTD ANALYSIS OF THE DISPERSION CHARACTERISTICS OF THE METAL PBG STRUCTURES

Two dimensional metallic photonic band gap (PBG) structures, which have higher power handling capability, have been analyzed for their dispersion characteristics. The analysis has been performed using flnite difierence time domain (FDTD) method based on the regular orthogonal Yee's cell. A simplifled unit cell of triangular lattice PBG structure has been considered for the TE and TM modes of propagation. The EM fleld equations in the standard central-difierence form have been taken in FDTD method. Bloch's periodic boundary conditions have been used by translating the boundary conditions along the direction of periodicity. For the source excitation, a wideband Gaussian pulse has been used to excite the possible modes in the computational domain. Fourier transform of the probed temporal flelds has been calculated which provides the frequency spectrum for a set of wave vectors. The determination of eigenfrequencies from the peaks location in the frequency spectrum has been described. This yields the dispersion diagram which describes the stop and pass bands characteristics. Efiort has been made to describe the estimation of defect bands introduced in the PBG structures. Further, the present orthogonal FDTD results obtained have been compared with those obtained by a more involved non-orthogonal FDTD method. The universal global band gap diagrams for the considered metal PBG structure have been obtained by varying the ratio of rod radius to lattice constant for both polarizations and are found identical with those obtained by other reported methods. Convergence of the analysis has been studied to establish the reliability of the method. Usefulness of these plots in designing the devices using 2-D metal PBG structure has also been illustrated.

PARALLEL FDTD SIMULATION USING NUMA ACCELERATION TECHNIQUE

In this paper, we introduce a new non-uniform memory access (NUMA) acceleration algorithm for parallel flnite-difierence time-domain (FDTD) method on NUMA architecture workstation. We compare the performance of parallel FDTD method with and without the NUMA acceleration technique. An ideal test case and an engineering example show that the NUMA acceleration technique can e-ciently improve the computing performance of FDTD parallel applications.

DETUNING STUDY OF IMPLANTABLE ANTENNAS INSIDE THE HUMAN BODY

This study quantifles the detuning and impedance mismatch of antennas implanted inside the human body. Maximum frequency shifts caused by variations in the electrical properties of body tissues and difierent anatomical distributions were derived. The results are relevant to the design of implantable antennas. They indicate the bandwidth enhancement and initial tuning necessary for correct functioning. The study was carried out using electromagnetic modeling based on the flnite-difierence time-domain method and high- resolution anatomical models. Four anatomical computer models of two adults and two children were used. The implanted antennas operated in the Medical Implant Communication Service band. The most important detuning and impedance mismatch was found for subcutaneous locations and in areas where a layer of fat tissue was present. The maximum frequency shift towards higher frequencies was 70MHz. The frequency shift did not occur symmetrically around 403MHz, but was shifted towards higher frequencies.

DESIGN ANALYSIS OF NEW METAMATERIAL FOR EM ABSORPTION REDUCTION

A new triangular metamaterials (TMMs) is designed for electromagnetic (EM) absorption reduction at microwave frequencies in this paper. The reduction of EM absorption with a new TMMs attachment is investigated in this research. The flnite-difierence time-domain method with lossy-Drude model is adopted in this investigation. The method of EM reduction is presented and the efiects of position, distance, and size of metamaterials are analyzed. TMMs have achieved a 1.0923W/kg for SAR 1gm which is 45.44% reduction of the initial SAR value for the case of 1gm SAR.

A COMPACT 90° BENT EQUAL OUTPUT PORTS OF PHOTONIC CRYSTAL BEAM SPLITTER WITH COMPLETE BAND GAP BASED ON DEFECT RESONANCE INTERFACE

A compact 90 - bent equal output ports of photonic crystal (PC) beam splitter (BS) with complete band gap (CPBG) based on the efiect of defect resonance interface (DRI) in PC waveguides is designed and analyzed. The flnite-difierence time-domain method is adopted to simulate the relevant structures of defect mode in a two dimensional square lattice circular dielectric rods of anisotropic PC. The device size reduction and ∞exibility in polarization dependence compared with the conventional PCBS can be attributed to the same resonant frequency for both transverse-magnetic and transverse- electric polarization, because the PC structures designed here have a CPBG. The merit of our proposed PCBSs with identical lights at the output ports possess the short coupling length with direct coupling (the coupling length is the same as that of the width of DRI, 3a) and the short distance without cross-talk among the output ports (only three lattice constant, 3a), thus helping the design ∞exibility of the PCBSs in IOCs.

THE UNFOLDING OF BANDGAP DIAGRAMS OF HEXAGONAL PHOTONIC CRYSTALS COMPUTED WITH FDTD

The application of the flnite-difierence time-domain method with rectangular periodic boundary conditions to the analysis of a hexagonal photonic crystal results in a folded bandgap diagram. The aim of this paper is to introduce a new unfolding method, which allows unambiguously determining the position of the modes in a wave- vector space by taking the advantage of the fast Fourier transform of modal fleld distributions. Unlike alternative solutions, it does not require any modiflcations of the FDTD method and is based solely on the post-processing of the simulation results. The proposed method can be applied to any non-rectangular lattice types, such as hexagonal, face-centered cubic or body-centered cubic.

AN FFT-ACCELERATED FDTD SCHEME WITH EXACT ABSORBING CONDITIONS FOR CHARACTERIZING AXIALLY SYMMETRIC RESONANT STRUCTURES

An accurate and e-cient flnite-difierence time-domain (FDTD) method for characterizing transient waves interactions on axially symmetric structures is presented. The method achieves its accuracy and e-ciency by employing localized and/or fast Fourier transform (FFT) accelerated exact absorbing conditions (EACs). The paper details the derivation of the EACs, discusses their implementation and discretization in an FDTD method, and proposes utilization of a blocked-FFT based algorithm for accelerating the computation of temporal convolutions present in nonlocal EACs. The proposed method allows transient analyses to be carried for long time intervals without any loss of accuracy and provides reliable numerical data pertinent to physical processes under resonant conditions. This renders the method highly useful in characterization of high-Q microwave radiators and energy compressors. Numerical results that demonstrate the accuracy and e-ciency of the method are presented.

IMPLEMENTATION OF THE FDTD METHOD BASED ON LORENTZ-DRUDE DISPERSIVE MODEL ON GPU FOR PLASMONICS APPLICATIONS

We present a three-dimensional flnite difierence time domain (FDTD) method on graphics processing unit (GPU) for plasmonics applications. For the simulation of plasmonics devices, the Lorentz-Drude (LD) dispersive model is incorporated into Maxwell equations, while the auxiliary difierential equation (ADE) technique is applied to the LD model. Our numerical experiments based on typical domain sizes as well as plasmonics environment demonstrate that our implementation of the FDTD method on GPU ofiers signiflcant speed up as compared to the traditional CPU implementations.

EFFICIENT SIMULATIONS OF PERIODIC STRUCTURES WITH OBLIQUE INCIDENCE USING DIRECT SPECTRAL FDTD METHOD

A simple and e-cient joint algorithm of flnite difierence time domain (FDTD) and periodic boundary condition (PBC), called as the direct spectral FDTD method, has been investigated to study three-dimensional (3D) periodic structures with oblique incidence, where both the azimuth angleand the elevation angle µ are varying. The number of sampling points for the horizontal wave number can be determined by using an adaptive approach. As numerical results, the transmission and re∞ection coe-cients from split-ring resonators (SRRs) and a dielectric grating slab are computed to validate the accuracy and e-ciency of the direct spectral FDTD method. The computed results are in good agreement to the published ones obtained by other methods.

APPLICATION OF THE IMPROVED MATRIX TYPE FDTD METHOD FOR ACTIVE ANTENNA ANALYSIS

An improved flnite-difierence time-domain (FDTD) method has been extended to analyze the antennas with complicated lumped/active networks in this paper. The improved FDTD method is based on a novel integral transform and the matrix theory. Combining the novel integral transform with Kirchhofi's circuit laws, the hybrid networks comprised of high order linear and nonlinear elements with arbitrary connection can be modeled by a stable matrix equation. An efiective model is built for linear lumped networks including internal independent sources. A wire antenna loaded with wideband match network and a two-element active patch antenna loaded with Gunn diodes are analyzed by the developed techniques. The analysis results indicate that the improved matrix-type FDTD method is not only sta- ble and accurate, but also time-saving in simulating the complicated hybrid networks.

WEAKLY CONDITIONALLY STABLE AND UNCONDITIONALLY STABLE FDTD SCHEMES FOR 3D MAXWELL'S EQUATIONS

To overcome the Courant limit on the time step size of the conventional flnite-difierence time-domain (FDTD) method, some weakly conditionally stable and unconditionally stable FDTD methods have been developed recently. To analyze the relations between these methods theoretically, they are all viewed as approximations of the conventional FDTD scheme in present discussion. The errors between these methods and the conventional FDTD method are presented analytically, and the numerical performances, including computation accuracy, e-ciency, and memory requirements, are discussed, by comparing with those of the conventional FDTD method.

TRANSIENT RESPONSES OF COAXIAL CABLES IN AN ELECTRICALLY LARGE CABIN WITH SLOTS AND WINDOWS ILLUMINATED BY AN ELECTROMAGNETIC PULSE

An improved flnite-difierence time-domain (FDTD) method is proposed for predicting transient responses of coaxial cables which are placed in an electrically large metallic cabin with arbitrary slots and circular windows on its wall. By integrating nodal analysis, multi-conductor transmission line (MTL) equation and FDTD method, we are able to accurately capture electromagnetic interference (EMI) efiects on the cables. Our developed algorithm is verifled by calculat- ing frequency-dependent transfer impedance of coaxial cables together with induced currents. Numerical calculations are further performed to show the near-end coupled current responses of braided and tubular cables, respectively, and the efiects of incident directions and polar- izations of the illuminated electromagnetic pulse are both taken into account.

WIRELESS COMMUNICATION IN BOXES WITH METALLIC ENCLOSURE BASED ON TIME-REVERSAL ULTRA-WIDEBAND TECHNIQUE: A FULL-WAVE NUMERICAL STUDY

In this paper, two full-wave simulators (one using flnite difierence time domain method and the other the method of moments) are developed, in order to analyze wireless communication in boxes with metallic enclosure based on time-reversal ultra-wideband (TR- UWB) technique. Impedance boundary conditions are exploited to model realistic metallic walls; and parallel computing is applied to relieve high computational resources requirements. Focusing in both space and time is exhibited by numerical results in arbitrarily shaped metallic boxes, which demonstrates the feasibility of TR-UWB communication in metallic boxes.

CAN MAXWELL'S FISH EYE LENS REALLY GIVE PERFECT IMAGING? PART II. THE CASE WITH PASSIVE DRAINS

We use both FEM (flnite element method) and FDTD (flnite difierence time domain method) to simulate the fleld distribution in Maxwell's flsh eye lens with one or more passive drains around the image point. We use the same Maxwell's flsh eye lens structure as the one used in recent microwave experiment (10): Maxwell's flsh eye lens bounded by PEC (perfect electric conductor) is inserted between two parallel PEC plates (as a waveguide structure). Our simulation results indicate that if one uses an active coaxial cable as the object and set an array of passive drains around the image region, what one obtains is not an image of the object but only multiple spots resembling the array of passive drains. The resolution of Maxwell's flsh eye is flnite even with such passive drains at the image locations. We also found that the subwavelength spot around the passive drain is due to the local fleld enhancement of the metal tip of the drain rather than the flsh eye medium or the ability of the drain in extracting waves.

EBG FREQUENCY RESPONSE TUNING USING AN ADJUSTABLE AIR-GAP

A new adjustable Electromagnetic Band-Gap (EBG) structure whose frequency response is controllable by adjusting spacer height is proposed. The flnite difierence time domain method is adopted for the simulations. Results show that the desired frequency response can be selected by adjusting the spacer height. The efiects of the air-gap on the polarization dependent and conventional EBG structures have been investigated both theoretically and numerically. The agreement between the theoretical calculations and numerical results is reasonably good.