Finite Difierence Research Articles

Numerical and Analtyical Solutions of a Model of Population Dynamics

The study presents numerical and approximate analytical approximations to a model of population dynamics with unbounded mortality function. The mathematical model involves a nonlocal boundary condion. A fi nite difierence method is implemented for the numerical solution while the homotopy analysis method (HAM) is applied to obtain the approximate series solution. The HAM solution contains an auxiliary parameter which provides a convenient way of controlling the convergence region of series solution. Results are presented for typical test problem provided in literature. Comparison of the results of both methods show validity and eficiency of the methods.

STUDY OF EM WAVE ABSORPTION AND SHIELDING CHARACTERISTICS FOR A BONSAI TREE FOR GSM-900 BAND

Electromagnetic (EM) wave absorption characteristics for a Bonsai tree are investigated at GSM-900 band. Finite Difierence in Time Domain (FDTD) method is hybridized with Friis transmission equation to carry out all the required EM simulations. The tree has been modelled using CT scan based 3D dataset considering difierent electrical parameters. Maximum local electric (E) fleld, magnetic (H) fleld, Speciflc Absorption Rate (SAR) and Shielding Efiectiveness (SE) have been calculated for the tree placing at distance of 5m away from a radiating Base Station Antenna (BSA) with 20W input power. The maximum local E fleld, H fleld, 1-g SAR and SE obtained by the simulation are found to be 70.1V/m, 0.09A/m, 0.135W/kg and 13.18dB, respectively. Plants are found to be good natural electromagnetic radiation shield.

MACROMODEL BASED DG-FDTD FOR CALCULATING LOCAL DOSIMETRY IN A VARIABLE AND HIGHLY MULTISCALE PROBLEM

This paper proposes a method to estimate human exposure to electromagnetic fleld radiation in a variable and highly multiscale problem. The electromagnetic fleld is computed using a combination of two methods: a rigorous time domain and multiscale method, the DG-FDTD (Dual Grid Finite Difierence Time Domain) and a fast substitution model based on the use of transfer functions. The association of these methods is applied to simulate a scenario involving an antenna placed on a vehicle and a human body model located around it. The purpose is to assess the electromagnetic fleld in the left eye of the human body model. It is shown that this combination permits to analyse many difierent positions in a fast and accurate way.

RECONFIGURABLE ANTENNA FOR RFID READER AND NOTCHED UWB APPLICATIONS USING DTO ALGORITHM

In this article, the approach involving Dynamic Threshold Optimization (DTO) algorithm is considered to optimize a new compact reconflgurable antenna to be applied to triple band Radio Frequency Identiflcation (RFID) and to ultra wideband (UWB) antenna with multiple bands notched. The antenna is implemented by using the existing techniques, such as loading an L-type band-stop fllter, inserting a split ring resonator (SRR) as well as connecting L branches to the radiation disk proposed by us. In case of RFID applications, triple-band RFID 915/2450/5800MHz are achieved separately. The results prove that this kind of antenna can be applied in RFID reader to avoid interference with other wireless systems. RF MEMS switches are used to reconflgure the antenna to be suitable for the application in the notched UWB communication systems. The DTO algorithm program is implemented using MATLAB-software and linked to the CST Microwave studio software to simulate the antenna. In addition, the optimized antenna is assessed using the Finite Difierence Time Domain (FDTD) program written with MATLAB to validate the results. The experimental results for the RFID and UWB antennas show good agreement with simulated ones. The radiation patterns are satisfactorily omnidirectional across the antenna's operation bands.

GAIN ENHANCEMENT OF REFLECTOR BASED IMPULSE RADIATING ANTENNAS: AN INNOVATIVE APPROACH

Conventional re∞ector based Impulse Radiating Antennas (IRA's) are designed with conical taper transmission line feed. A novel feed design approach is used to enhance gain of the IRA without increasing diameter of the re∞ector. This paper discuses conventional and new IRA designs of difierent input impedances. IRA with conventional feed and with new dipole feed is designed for both 200› and 100› input impedance category. The IRA with new feed design ofiers better gain compared to conventional IRA for both 200› and 100› input impedance category. These antenna designs are analyzed using the Finite Difierence Time Domain (FDTD) method and the result obtained shows that IRAs with new dipole feed ofiers better gain than IRAs with conventional feed for respective input impedance category without any compromise in time domain characteristics. A half IRA with new feed with input impedance of nearly 50› was realized and measured to establish the advantage of new dipole feed IRA.

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.

NUMERICALLY EFFICIENT TECHNIQUE FOR METAMATERIAL MODELING

In this paper we present two simulation techniques for modeling periodic structures with three-dimensional elements in general. The flrst of these is based on the Method of Moments (MoM) and is suitable for thin-wire structures, which could be either PEC or plasmonic, e.g., nanowires at optical wavelengths. The second is a Finite Difierence Time Domain (FDTD)-based approach, which is well suited for handling arbitrary, inhomogeneous, three-dimensional periodic structures. Neither of the two approaches make use of the traditional Periodic Boundary Conditions (PBCs), and are free from the di-culties encountered in the application of the PBC, as for instance slowness in convergence (MoM) and instabilities (FDTD).

WDM PERFORMANCES OF TWO- AND THREE-WAVEGUIDE MACH-ZEHNDER SWITCHES ASSEMBLED INTO 4X4 MATRIX ROUTER

The performance comparison of two conflgurations of broadband Mach-Zehnder Switches exploiting, respectively, two and three waveguides, assembled into 4 £ 4 matrices is reported in this paper. The simulations are performed by the Finite Element Method and the Finite Difierence Beam Propagation Method. In particular, we have found that, to parity of maximum insertion loss, about equal to 1dB for the single switch and 3dB for the 4£4 matrix, the proposed three-waveguide conflguration exhibits an almost doubled bandwidth ¢‚ = 115nm, making it suitable for e-cient routing of the Wavelength Division Multiplexing signals over photonic Networks on Chip.

TIME REVERSAL FOR SOFT FAULTS DIAGNOSIS IN WIRE NETWORKS

Time-reversal (TR) invariance of the wave equation in lossless transmission line (TL) is here introduced as an improvement for fault-detection techniques in wire networks. This new approach is applied to re∞ectometry in wire diagnosis. To test the e-ciency of this method, the reverse time algorithm simulated with FDTD (Finite Difierence Time Domain) is developed in a one dimension space. It uses a new signal processing and an adapted signal to the wire under test for diagnosing the fault in the wire. In addition, the interest of the convolution product between the incident signal and the output signal from this reverse time method will be also shown and applied in this paper. Through numerical simulations and experimental results measured on coaxial cable, the beneflts of this method have been illustrated.

EXPERIMENTAL RESULTS FOR MICROWAVE TOMOGRAPHY IMAGING BASED ON FDTD AND GA

The authors recently presented a novel microwave tomog- raphy method for creating quantitative images of the electromagnetic properties of the interior of unknown objects (1). This method is based on a time-domain inverse solver which uses the multi-illumination tech- nique and includes the dispersive and heterogeneous characteristic of the object. The Frequency Dependent Finite Difierence Time Domain ((FD) 2 TD) and Genetic Algorithm (GA) technique were utilized for determining unknown characteristics of the object. In the present pa- per, the calibration of measured data are described and image recon- struction results for preliminary experiments performed at the Uni- versity of Manitoba's Microwave Tomography Laboratory and at the Institut Frsenel are presented.

NUMERICAL INVESTIGATIONS OF ULTRA WIDEBAND STACKED RECTANGULAR DRA EXCITED BY RECTANGULAR PATCH

In this paper, a numerical study of a new ultra wideband (UWB) dielectric resonator antenna (DRA) is presented. The proposed structure consists of two stacked dielectric resonators excited by rectangular patch and operated from 3GHz to 11GHz (an impedance bandwidth of 115%), covering the full UWB spectrum. The analysis is carried out using the Finite Difierence Time Domain (FDTD) method and two commercial electromagnetic simulators. The numerical results are given and compared in terms of re∞ection coe-cients, radiation pattern and gain. The computed FDTD results are in good agreement with those of simulations.

EXTERNAL AND INTERNAL ELECTROMAGNETIC EXPOSURES OF WORKERS NEAR HIGH VOLTAGE POWER LINES

The major objective of the study was to assess the safety of electric line workers exposed to of a double circuit 132kV transmission line for difierent scenarios. The double circuit 132-kV, 60Hz transmission line has a power rating of 293 MVA and a maximum recorded peak load current of 603A. The charge simulation and the Biot Savart methods were used by EPRI workstation software to compute the external electric and magnetic flelds around a 132kV transmission line. We used the calculated external electric and magnetic fleld exposures to determine the induced electric fleld and induced current densities inside the human body. This was performed using the Finite Difierence Time Difierence computational algorithm in EMPIRE commercial software, with a 6mm voxel resolution. We used the Visible Human (VH) to investigate the internal induced electric fleld and circulating current densities in more than 40 difierent tissues and organs of the VH. We found that the worker exposure levels to extremely low frequency electromagnetic flelds are below the recommended IEEE international standards limits for the studied scenarios. In all scenarios the maximum induced current densities and electric flelds were in the bone marrow of the feet.

GPU APPROACH FOR HERTZIAN POTENTIAL FORMULATION TOOL ORIENTED ON ELECTROMAGNETIC NANODEVICES

The time domain modeling and simulation of electromag- netic (EM) waves interaction with nanodevices, at high spatial and time resolution, requires high computational power. For the flrst time, in this paper we present an efiective implementation of the Hertzian Po- tential Formulation (HPF) on the Graphics Processing Units (GPUs), through the NVIDIA's CUDA (Compute Unifled Device Architecture) programming model. It accelerates the nanodevice EM simulations at nanometer scale harnessing the massive parallelism of the GPU based systems. This study is useful for similar electromagnetic codes includ- ing the Finite Difierence approaches. The results demonstrate that this GPU tool outperforms the CPU based HPF implementation, reaching a speedup from 30£ to 70£.

A SINGLE-FEED PLANAR ANTENNA FOR TERRESTRIAL DTV RECEPTION IN MOBILE COMMUNICATION

Japanese terrestrial broadcasting was completely con- verted to digital television (DTV) broadcasting on 470{710MHz as of July 2011. However, fading phenomenon resulting from standing waves is a factor in quality deterioration in TV and mobile commu- nication technologies. Suppression of this is needed for many kinds of technologies. A broadband single-feed planar antenna composed of two antenna components, a Broadband Planar Monopole Antenna (B- PMA) and a Broadband Planar Slot Antenna (B-PSA), is proposed for reducing deterioration of reception due to the fading across the DTV band. Re∞ection coe-cients and radiation patterns analyzed by the Finite Difierence Time Domain (FDTD) method and compared with measured results indicate that the proposed antenna is broad- band compared with a conventional antenna studied previously. A fleld experiment is conducted in the DTV band. The results of the fleld experiment indicate clearly that the proposed antenna e-ciently suppresses fading resulting from standing waves across the band.

SINGLE-FEED PLANAR ANTENNA FOR SUPPRESSING THE CHANGE IN RECEIVED SIGNAL LEVEL DUE TO STANDING WAVES IN MOBILE COMMUNICATION

The fading phenomenon resulting from standing waves is a factor in quality deterioration in mobile communication technologies (e.g., cellular phones and television receivers). Suppression of this fading phenomenon is needed for many kinds of technologies. A single-feed planar antenna composed of two antenna components, a Planar Monopole Antenna (PMA) and a Planar Slot Antenna (PSA), is proposed for reducing deterioration of reception due to the fading phenomenon. Re∞ection coe-cient and radiation patterns are analyzed by the Finite Difierence Time Domain (FDTD) method and compared with measured results. Results indicate that the proposed antenna has a resonant frequency with functions of the PMA and the PSA. The results of a fleld experiment at 583.76MHz in the Ultra High Frequency (UHF) band indicate that the proposed antenna e-ciently suppresses the fading phenomenon resulting from multipath propagation.

REALISTIC MODEL OF DISPERSIVE SOILS USING PLRC-FDTD WITH APPLICATIONS TO GPR SYSTEMS

A realistic model of ground soil is developed for the electromagnetic simulation of Ground Penetrating Radar (GPR) systems. A three dimensional Finite Difierence Time Domain (FDTD) algorithm is formulated to model dispersive media using N-term Debye permittivity function with static conductivity. The formulation of the algorithm is based on the concept of the Piecewise Linear Recursive Convolution (PLRC) in order to simulate the dispersion properties of soil as a two-term Debye medium. This approach of ground modeling enhances the accuracy and reliability of results obtained for GPR problems. The developed algorithm is validated when simulating practical GPR Systems used to detect difierent objects buried in Puerto-Rico and San Antonio clay loams. The proposed algorithm is employed to compare the impact of using two-term Debye model to simulate real soil on the coupling coe-cient between transmitting and receiving antennas due to the absence and presence of buried targets to that of using non-dispersive soil model. The efiect of soil moisture content on the performance of GPR system in detecting buried objects such as metallic and plastic pipes is investigated.

Computational Modeling of Electromagnetically Induced Heating of Magnetic Nanoparticle Materials for Hyperthermic Cancer Treatment

We present work on the computational modeling of electromagnetically induced heating in the hyperthermic treatment of cancer using ∞uid-dispersed magnetic nanoparticles. Magnetic nanoparticle hyperthermia can be used as a complement to chemotherapy or for direct targeting and destruction of tumors through heat treatment. The ability of nanoscale materials to provide an extremely localized therapeutic efiect is a major advantage over traditional methods of treatment. When an AC magnetic fleld is applied to a ferro∞uid, Brownian rotation and Neel relaxation of induced magnetic moments result in power dissipation. In order to achieve appreciable volumetric heating, while maintaining safe values of frequency and magnetic fleld strength, and to reduce the risk of spot heating of healthy tissue, it is necessary to determine an ideal range of input parameters for the driving magnetic fleld as well as the complex susceptibility of the ferro∞uid. We do this by the coupling of the solution of Maxwell's equations in a model of the tumor and surrounding tissue as input to the solution to the Pennes' Bioheat Equation (PBE). In this study, we solve both sets of equations via the Finite Difierence Time Domain (FDTD) method as implemented in the program SEMCAD X (by SPEAG, Schmid & Partner Engineering). We use a multilayer model of the human head made up of perfused dermal and skeletal layers and a grey-matter region surrounding a composite region of tumor tissue and the magnetic nanoparticle ∞uid. The tumor/ferro∞uid composite material properties are represented as mean values of the material properties of both constituents, assuming homogeneity of the region. The AC magnetic excitation of the system (within 100kHz{2MHz frequency range) is provided by square Helmholtz coils, which provide a uniform magnetic fleld in the region of interest. The power density derived from the electromagnetic fleld calculation serves as an input term to the bioheat equation and therefore determines the heating due to the ferro∞uid. Results for several variations of input parameters will be presented.

SHIFT-OPERATOR FINITE DIFFERENCE TIME DOMAIN ANALYSIS OF CHIRAL MEDIUM

Shift-Operator Finite difierence Time Domain (SO- FDTD) method is introduced as a new e-cient technique for simulating electromagnetic wave interaction with chiral medium. The dispersive properties of this medium are presented as polynomials of j!. These polynomials are converted to time domain by replacing j! by the time derivative operator. Then this time derivative operator is converted to the corresponding time shift operator which is used directly to obtain the corresponding update equations of electric and magnetic fleld components. The resulting update equations do not require time convolution or additional vector components. The present analysis does not require also any transformation. Signiflcant improvement is obtained in memory requirements by using this method while the computational time is nearly the same compared with other similar techniques like Z-transformation FDTD.

FDTD MODELING OF THE BREAST: A REVIEW

Microwave imaging is one of the most promising emerging imaging technologies for breast cancer detection. Microwave imaging exploits the dielectric contrast between normal and malignant breast tissue at microwave frequencies. Many UWB radar imaging techniques require the development of accurate numerical phantoms to model the propagation and scattering of microwave signals within the breast. The Finite Difierence Time Domain (FDTD) method is the most commonly used numerical modeling technique used to model the propagation of Electromagnetic (EM) waves in biological tissue. However, it is critical that an FDTD model accurately represents the dielectric properties of the constituent tissues and the highly correlated distribution of these tissues within the breast. This paper presents a comprehensive review of the dielectric properties of normal and cancerous breast tissue, and the heterogeneity of normal breast tissue. Furthermore, existing FDTD models of the breast are examined and compared. This paper provides a basis for the development of more geometrically and dielectrically accurate numerical breast phantoms used in the development of robust microwave imaging algorithms.

Eigenvalue Analysis of Waveguides and Planar Transmission Lines Loaded with Full Tensor Anisotropic Materials

An eigenvalue analysis of curved waveguides and planar transmission lines loaded with full tensor anisotropic materials is presented. This analysis is based on our previously established two-dimensional Finite Difierence Frequency Domain eigenvalue method formulated in orthogonal curvilinear coordinates. This is properly extended herein in order to accurately handle arbitrarily shaped curved geometries fllled or partially loaded with full tensor anisotropic materials. Numerous investigations are carried out involving all type of forward or backward propagating modes.