[신간안내] Computational Electrodynamics (the finite difference time - domain method)

A review about the engineering design of optimal heat transfer systems using topology optimization

We introduce an approach to carry out layout optimization of metallic antenna parts An optimization technique first developed for the optimization of load-bearing elastic structures is adapted for the purpose of metallic antenna design The local conductivity values in a given region are used as design variables and are iteratively updated by a gradient-based optimization algorithm Given a set of time-domain signals from exterior sources, the design objective is here to maximize the energy received by the antenna and transmitted to a coaxial cable The optimization proceeds through a sequence of coarsely-defined lossy designs with successively increasing details and less losses as the iterations proceed The objective function gradient is derived based on the FDTD discretization of Maxwell's equations and is expressed in terms of field solutions of the original antenna problem and an adjoint field problem The same FDTD code, but with different wave sources, is used for both the original antenna problem and the adjoint problem For any number of design variables, the gradient is evaluated on the basis of only two FDTD simulations, one for the original antenna problem and another for the adjoint field problem We demonstrate the capability of the method by optimizing the radiating patch of both UWB monopole and microstrip antennas The UWB monopole is designed to radiate over a wide frequency band 1-10 GHz, while the microstrip patch is designed for single and dual frequency band operation In these examples, there are more than 20,000 design variables, and the algorithm typically converges in less than 150 iterations The optimization results show a promising use of the proposed approach as a general method for conceptual design of near-resonance metallic antennas

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Topology Optimization of Metallic Antennas

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.

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Implementation of the FDTD Method Based on Lorentz-Drude Dispersive Model on GPU for Plasmonics Applications

An optimization problem has been formulated to find a resonant current extremizing various antenna parameters. The method is presented on, but not limited to, particular cases of gain $G$ , quality factor $Q$ , gain to quality factor ratio $G/Q$ , and radiation efficiency $\eta $ of canonical shapes with conduction losses explicitly included. The Rao–Wilton–Glisson basis representation is used to simplify the underlying algebra while still allowing surface current regions of arbitrary shape to be treated. By switching to another basis generated by a specific eigenvalue problem, it is finally shown that the optimal current can, in principle, be found as a combination of a few eigenmodes. The presented method constitutes a general framework in which the antenna parameters, expressed as bilinear forms, can automatically be extremized.

Optimal Currents on Arbitrarily Shaped Surfaces

We present an approach to design from scratch planar microwave antennas for the purpose of ultra-wideband (UWB) near-field sensing. Up to about 120 000 design variables associated with square grids on planar substrates are subject to design, and a numerical optimization algorithm decides, after around 200 iterations, for each edge in the grid whether it should consist of metal or a dielectric. The antenna layouts produced with this approach show UWB impedance matching properties and near-field coupling coefficients that are flat over a much wider frequency range than a standard UWB antenna. The properties of the optimized antennas are successfully cross-verified with a commercial software and, for one of the designs, also validated experimentally. We demonstrate that an antenna optimized in this way shows a high sensitivity when used for near-field detection of a phantom with dielectric properties representative of muscle tissue.

Topology Optimization of Planar Antennas for Wideband Near-Field Coupling

In this paper, we investigate the use of fat tissue as a communication channel between in-body, implanted devices at R-band frequencies (1.7–2.6 GHz). The proposed fat channel is based on an anatomical model of the human body. We propose a novel probe that is optimized to efficiently radiate the R-band frequencies into the fat tissue. We use our probe to evaluate the path loss of the fat channel by studying the channel transmission coefficient over the R-band frequencies. We conduct extensive simulation studies and validate our results by experimentation on phantom and ex-vivo porcine tissue, with good agreement between simulations and experiments. We demonstrate a performance comparison between the fat channel and similar waveguide structures. Our characterization of the fat channel reveals propagation path loss of ∼0.7 dB and ∼1.9 dB per cm for phantom and ex-vivo porcine tissue, respectively. These results demonstrate that fat tissue can be used as a communication channel for high data rate intra-body networks.

Characterization of the Fat Channel for Intra-Body Communication at R-Band Frequencies

The human body can act as a medium for the transmission of electromagnetic waves in the wireless body sensor networks context. However, there are transmission losses in biological tissues due to the presence of water and salts. This Letter focuses on lateral intra-body microwave communication through different biological tissue layers and demonstrates the effect of the tissue thicknesses by comparing signal coupling in the channel. For this work, the authors utilise the R-band frequencies since it overlaps the industrial, scientific and medical radio (ISM) band. The channel model in human tissues is proposed based on electromagnetic simulations, validated using equivalent phantom and ex-vivo measurements. The phantom and ex-vivo measurements are compared with simulation modelling. The results show that electromagnetic communication is feasible in the adipose tissue layer with a low attenuation of ∼2 dB per 20 mm for phantom measurements and 4 dB per 20 mm for ex-vivo measurements at 2 GHz. Since the dielectric losses of human adipose tissues are almost half of ex-vivo tissue, an attenuation of around 3 dB per 20 mm is expected. The results show that human adipose tissue can be used as an intra-body communication channel.

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Intra-body microwave communication through adipose tissue

This paper presents a graphics processing based im- plementation of the Finite-Difierence Frequency-Domain (FDFD) method, which uses a central flnite difierencing scheme for solving Maxwell's equations for electromagnetics. The radar cross section for difierent structures in 2D and 3D has been calculated using the FDFD method. The FDFD code has been implemented for the CPU calcu- lations and the same code is implemented for the GPU calculations using the Brook+ developed by AMD. The solution obtained by using the GPU based-code showed more than 40 times speed over the CPU code.

https://www.jpier.org/pierb/pierb16/16.09060703.pdf

Emadeldeen Hassan

Papers

Topology Optimization of Metallic Antennas

Topology Optimization of Planar Antennas for Wideband Near-Field Coupling

Characterization of the Fat Channel for Intra-Body Communication at R-Band Frequencies

Intra-body microwave communication through adipose tissue

Electromagnetic Scattering Using GPU-Based Finite Difference Frequency Domain Method