Sang-Gyu Ha

FDTD Dispersive Modeling of Human Tissues Based on Quadratic Complex Rational Function

We propose a dispersive finite-difference time domain (FDTD) suitable for the electromagnetic analysis of human tissues. The dispersion relation of biological tissues is characterized by a quadratic complex rational function (QCRF) that leads to an accurate FDTD algorithm in 400 MHz-3 GHz. QCRF coefficients are extracted by applying the complex-curve fitting technique, without initial guess. Numerical examples are used to illustrate the computational accuracy and stability of QCRF-based FDTD.

On the Numerical Stability of Finite-Difference Time-Domain for Wave Propagation in Dispersive Media Using Quadratic Complex Rational Function

Abstract Recently, based on a quadratic complex rational function, a simple and accurate finite-difference time-domain algorithm was introduced for the study of electromagnetic wave propagation in dispersive media. It is of great necessity to investigate the numerical stability of the quadratic complex rational function–finite-difference time-domain to fully utilize this finite-difference time-domain algorithm. In this work, using the von Neumann method with the Routh–Hurwitz criterion, the numerical stability conditions of the quadratic complex rational function–finite-difference time-domain are investigated. It is shown that the numerical stability conditions of the quadratic complex rational function–finite-difference time-domain are not same as those of the conventional finite-difference time-domain schemes.

Accurate FDTD modelling for dispersive media using rational function and particle swarm optimisation

This article presents an accurate finite-difference time domain (FDTD) dispersive modelling suitable for complex dispersive media. A quadratic complex rational function (QCRF) is used to characterise their dispersive relations. To obtain accurate coefficients of QCRF, in this work, we use an analytical approach and a particle swarm optimisation (PSO) simultaneously. In specific, an analytical approach is used to obtain the QCRF matrix-solving equation and PSO is applied to adjust a weighting function of this equation. Numerical examples are used to illustrate the validity of the proposed FDTD dispersion model.

FDTD Dispersive Modeling With High-Order Rational Constitutive Parameters

In this work, we present a dispersive finite-difference time-domain (FDTD) algorithm using a four-pole complex rational function (CRF). For the sake of a better curve fitting of the four-pole CRF dispersion model, we use a particle swarm optimization technique. We also discuss an efficient memory storage strategy using a state-space approach. The numerical aspects of four-pole CRF-FDTD, the numerical accuracy and the numerical stability, are investigated in detail. Numerical examples are used to validate four-pole CRF-FDTD and numerical stability issues are discussed in detail. We also discuss the computational accuracy and the computational efficiency of an arbitrary N-pole CRF-FDTD.

Complex rational function for frequency dependent complex permittivity of biological tissues

In this work, we accurately characterize frequency dependent complex permittivity of biological tissues in the frequency range from 100 kHz to 10 GHz. Toward this purpose, a fourth-order complex rational function (CRF) is employed for dispersive modeling of the relative permittivity of biological tissues. We also discuss how to improve the accuracy of their dispersion characteristics.

Three-dimensional efficient dispersive alternating-direction-implicit finite-difference time-domain algorithm using a quadratic complex rational function

Efficient unconditionally stable FDTD method is developed for the electromagnetic analysis of dispersive media. Toward this purpose, a quadratic complex rational function (QCRF) dispersion model is applied to the alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method. The 3-D update equations of QCRF-ADI-FDTD are derived using Maxwells curl equations and the constitutive relation. The periodic boundary condition of QCRF-ADI-FDTD is discussed in detail. A 3-D numerical example shows that the time-step size can be increased by the proposed QCRF-ADI-FDTD beyond the Courant-Friedrich-Levy (CFL) number, without numerical instability. It is observed that, for refined computational cells, the computational time of QCRF-ADI-FDTD is reduced to 28.08 % of QCRF-FDTD, while the L2 relative error norm of a field distribution is 6.92 %.

Non-Foster Matching Circuit for Wideband Anti-Jamming Small GPS Antennas

위성항법시스템은 민간 및 군수 분야에서 널리 사용되고 있는 유용한 시스템이다. 그러나 지구 상공 2만 km 이상 원거리 송신 신호로 인한 수신 감도 미약으로, 위성항법시스템의 신호는 항재밍 공격에 취약하다. 본 논문에서는 항재밍 소형 GPS 배열안테나 설계를 위한 선행 연구로 전기적으로 초소형인 GPS 안테나 소자를 효율적으로 정합하는 비 포스터 정합회로에 대한 연구를 수행하였다. 전기적으로 소형인 GPS 안테나는 높은 품질계수로 인해 방사 이득이 낮고, 광대역 정합이 어렵다. 이를 해결하기 위해 소형 GPS 안테나용 비 포스터 정합회로(non-Foster matching circuit)를 설계하였다. Linvill의 교차 결합쌍 트랜지스터로 구성된 네거티브 임피던스 변환기 회로를 제작하였으며, 시간 영역에서 안정도 검증을 통해 안정성을 확인하였다. 비 포스터 정합회로를 이용한 소형 GPS 안테나 무반사실 측정결과, 전면방향이득이 17 dB 이상 개선됨을 확인하였다.

On numerical aspects of FDTD dispersive modeling using a quartic complex rational function

Recently, based on a 2-pole complex rational function, an accurate and efficient finite-difference time domain (FDTD) algorithm was introduced for many types of dispersive media. In this work, we consider a dispersive FDTD method using a quartic complex rational function (QCRF). It is of great importance to investigate two numerical aspects: the numerical accuracy and the numerical stability. Numerical examples are used to illustrate these numerical aspects of QCRF-FDTD.

Study on Wideband Shielding Effects of Simple Building Structures Using FDTD Method

We perform a wideband radiated pulse coupling analysis of simple building structures using the finite-deference time-domain(FDTD) method. Toward this purpose, the building structures composed of concrete and window materials are assumed and we numerically model the electrical properties of each material. In this work, we apply a dispersive FDTD algorithm for the electromagnetic analysis of building structures and investigate their shielding effectiveness in the frequency range of 50 MHz to 1 GHz.

Dispersive FDTD Modeling of Human Body with High Accuracy and Efficiency

We propose a dispersive finite-difference time domain(FDTD) algorithm suitable for the electromagnetic analysis of the human body. In this work, the dispersion relation of the human body is modeled by a quadratic complex rational function(QCRF), which leads to an accurate and efficient FDTD algorithm. Coefficients(involved in QCRF) for various human tissues are extracted by applying a weighted least square method(WLSM), referred to as the complex-curve fitting technique. We also presents the FDTD formulation for the QCRF-based dispersive model in detail. The QCRFbased dispersive model is significantly accurate and its FDTD implementation is more efficient than the counterpart of the Cole-Cole model. Numerical examples are used to show the validity of the proposed FDTD algorithm.