A Study of RF Power Attenuation in Bio-tissues
Andrew S. L. Lou,
Hon-Zon T. Chen
Implantable biomedical micro devices (or micro-implants) are believed to be useful in many clinical applications. Using wireless radio frequency (RF) techniques to transmit power and signals to micro-implants is the main stream in this research area. Depending upon among of signals to be transmitted to a micro-implant, the frequencies used by the wireless RF techniques vary. An issue is that the power attenuation in bio-tissues will change, when the RF power transmission frequency is altered. In this work, a wireless RF power transmission/receiving system was developed to study power attenuation in bio-tissues. Common radio frequency range applied in neural prosthesis (500 kHz ~ 2 MHz) was used to transmit power in a fashion of electromagnetic wave (EM) in the study. Studies of power transmission in air and in pork were conducted. Our study results prove that for the coil based power coupling technique, the received power is proportional to the power transmission frequency. However, the power attenuation rate of low frequency EM waves is less than that of high frequency EM waves. In addition, the study results demonstrate that the power attenuation for high ε medium is slower comparing with low ε medium. More importantly, we have developed power attenuation models for various transmission frequencies using regression analysis technique. We believe these models can be further evolved to become more generic so that they can be used to facilitate positioning the micro-implants.