Tatsuya Kashiwa

The phase velocity error and stability condition of the three-dimensional nonstandard FDTD method

The nonstandard finite-difference time-domain (NS-FDTD) method, using a rectangular parallelepipeds structured grid, has been proposed to overcome the dispersion and anisotropic errors of the FDTD method. However, the numerical dispersion and the stability condition have not been examined. Furthermore, the method has been defined only in the isotropic grids. This paper investigates the numerical dispersion and the stability condition of the three-dimensional NS-FDTD method for isotropic and nonisotropic grids. The method is compared with the FDTD method. As a result, this method demonstrates highly accurate characteristics and high Courant stability condition.

Analysis of a hyperthermic treatment using a reentrant resonant cavity applicator for a heterogeneous model with blood flow

Hyperthermic treatment using a reentrant resonant cavity applicator is investigated. By solving time-dependent electromagnetic field-heat transfer equations for a heterogeneous model, temperature distributions in various organs are obtained. Calculated results show that it is indispensable to consider the blood flow to predict accurate temperature distributions during a hyperthermic treatment. Also, it is found that the necessity of measuring the electrical and thermal properties of the abdominal fat accurately as well as optimizing the heating system to avoid the concentration of electromagnetic energy around the abdominal fat-muscle interface.

Analysis of a hyperthermic treatment in a reentrant resonant cavity applicator by solving time-dependent electromagnetic-heat transfer equations

Investigates the analysis of a hyperthermic treatment. The time dependent electromagnetic-heat transfer equations are solved step-by-step considering the temperature dependencies of relative permittivity /spl epsiv//sub r/ and electric conductivity /spl sigma/. Close agreement between the calculated and measured temperature distributions is obtained. A technique to direct the electromagnetic energy toward a specific part of a homogeneous torso model is also noted.

Phase velocity errors of the nonstandard FDTD method and comparison with other high-accuracy FDTD methods

Several high accuracy finite-difference time-domain (FDTD) methods have been developed to overcome the phase velocity errors present in the FDTD method. The nonstandard FDTD method has been developed as one of those. The phase velocity errors of the method are investigated and the characteristics are compared with other high-accuracy FDTD methods. As a result, the numerical dispersion characteristics of the method are clearly shown and the extremely high-accuracy characteristic at the desired frequency is confirmed.

The nonstandard FDTD method using a complex formulation

In this paper, a complex nonstandard finite-difference time-domain (CNS-FDTD) method is proposed in order to simulate wave propagation in lossy media. To clarify the characteristics of the method, expressions for the numerical propagation constant and the stability condition are derived. It is found that the CNS-FDTD method is much more accurate and stable than the conventional finite-difference time-domain (FDTD) method. The method is applied to the analysis of a fin ferrite electromagnetic wave absorber with a periodic structure.

Resonant frequency analysis of reentrant resonant cavity applicator by using FEM and FD-TD method

A reentrant resonant cavity applicator is analyzed as a generalized eigenvalue problem by using the finite element method (FEM) with edge elements. The subspace iteration method is used to solve for selected eigenvalues. The resonant frequencies obtained are in good agreement with both the measured values and with the ones obtained using the finite-difference time-domain (FD-TD) method. Computation time and the amount of memory required are also discussed.

Nonstandard FDTD Method for Wideband Analysis

The nonstandard (NS) FDTD algorithm can compute electromagnetic propagation with very high accuracy on a coarse grid, but only for monochromatic or narrow-band signals. We have developed a wideband (W) NS-FDTD algorithm that overcomes this limitation. In NS-FDTD special finite difference operators are used to make the numerical dispersion isotropic, which is then corrected by a frequency-dependent factor. In WNS-FDTD the numerical dispersion is modeled as frequency-dependent electrical permittivity and magnetic permeability, and the Yee algorithm is augmented by correction terms in the time domain. We demonstrate the high accuracy of WNS-FDTD in example problems, and show that it gives better results than both the standard (S) FDTD and the FDTD(2,4) algorithms.

Effects of car body on radiation pattern of car antenna mounted on side mirror for inter-vehicle communications

Recently, the inter-vehicle communication systems have been proposed for the prevention of car crash. By the way, a radiation pattern of car antenna is changed by effects of car body and antenna positions. Therefore, it is important to know the influence of car body and antenna positions on radio wave propagation characteristics. In the numerical simulation, from a viewpoint of the reduction of computational cost, it is interested to consider a simplified car model that can obtain reasonable numerical results. In this paper, effects of car body on radiation pattern of car antenna mounted on a side mirror for inter-vehicle communications are investigated. As a first step in this work, both strict and simplified models of car body are considered. As the numerical simulation method, the FDTD method is used.

Scattering Analysis of Large-Scale Coated Cavity Using the Complex Nonstandard FDTD Method With Surface Impedance Boundary Condition

Recently, we reported on the basic advantages of the complex-type surface impedance boundary condition (CSIBC), however, its validity has not been confirmed for practical problems. In this paper, we show the formulation of CSIBC, which includes corners, and the complex nonstandard finite-difference time-domain (CNS-FDTD) method with the CSIBC is applied to the scattering analysis of a large cavity coated with radar absorbing materials. As a result, it is shown that the CSIBC formulation is highly efficient at reducing the computer load. For our 3-D model, the CSIBC reduced the computer load to roughly 1/64 that of the FDTD method.

Overlap Algorithm for the Nonstandard FDTD Method Using Nonuniform Mesh

In this paper, the overlap algorithm is applied to the nonstandard finite-difference time-domain (NS-FDTD) method using a nonuniform mesh in a 2-D space. The characteristics of the overlap algorithm are numerically examined and compared with a no overlap algorithm. The results show that the reflection rate from the interface of the two meshes using the overlap algorithm is less than -80 dB, which is smaller than that of the NS-FDTD method without the overlap. Consequently, it is shown that the overlap algorithm is more suitable for the NS-FDTD method when using a nonuniform mesh. The overlap algorithm is successfully applied to the analysis of a dielectric flat panel and a corrugated surface