Analysis of Current Density and Specific Absorption Rate in Biological Tissue Surrounding an Air-core Type of Transcutaneous Transformer for an Artificial Heart

This paper reports on the specific absorption rate (SAR) and the current density analysis of biological tissue surrounding an air-core type of transcutaneous transformer for an artificial heart. The electromagnetic field in the biological tissue surrounding the transformer was analyzed by the transmission-line modeling method, and the SAR and current density as a function of frequency (200k-1 MHz) for a transcutaneous transmission of 20 W were calculated. The model´s biological tissue has three layers including the skin, fat and muscle. As a result, the SAR in the vicinity of the transformer is sufficiently small and the normalized SAR value, which is divided by the ICNIRP´s basic restriction, is 7times10^-3 or less. On the contrary, the current density is slightly in excess of the ICNIRP´s basic restrictions as the frequency falls and the output voltage rises. Normalized current density is from 0.2 to 1.2. In addition, the layer in which the current´s density is maximized depends on the frequency, the muscle in the low frequency (<700kHz) and the skin in the high frequency (>700kHz). The result shows that precision analysis taking into account the biological properties is very important for developing the transcutaneous transformer for TAH