This paper describes the effectiveness of the geometric multi-grid method in a current density analysis using a numerical human body model. The scalar potential finite difference (SPFD) method is used as a numerical method for analyzing the current density inside a human body due to contact with charged objects in a low-frequency band, and research related to methods to solve faster large-scale simultaneous equations based on the SPFD method has been conducted. In previous research, the block incomplete Cholesky conjugate gradients (ICCG) method is proposed as an effective method to solve the simultaneous equations faster. However, even though the block ICCG method is used, many iterations are still needed. Therefore, in this study, we focus on the geometric multi-grid method as a method to solve the problem. We develop the geometric-multi-grid method and evaluate performances by comparing it with the block ICCG method in terms of computation time and the number of iterations. The results show that the number of iterations needed for the geometric multi-grid method is much less than that for the block ICCG method. In addition, the computation time is much shorter, depending on the number of threads and the number of coarse grids. Also, by using multi-color ordering, the parallel performance of the geometric multi-grid method can be greatly improved.

The present study proposes a quasi-static finite-difference time-domain (FDTD) method for dosimetry in humans due to contact current at low frequencies (10 kHz). Our attention focused on wave sources which can reduce computational time. The computational time was found to be reduced using a voltage source of a step function with smooth start. The computational time required for the proposed method was smaller than a quasi-static FDTD method proposed in a previous study. Comparison between our computational results and those in a previous study suggested the effectiveness of our proposal. The difference in in-situ electric field due to different human models was a factor of 2 or so.

The radio-frequency protection guideline of Japan recommend the limits of contact current for contact hazard due to an ungrounded metallic object under an electromagnetic field in the frequency range from 10 kHz to 15 MHz. To arrange the standard measurement methods of contact current in Japan, the contact body impedance for the Japanese in the frequency range from 75 kHz to 15 MHz is obtained, and the simplified equivalent circuit is determined using nonlinear least squares method. In addition, the human body impedance is obtained from numerical simulation using the impedance method and voxel human model, and compared it with measured one.