Electromagnetic Field Analysis of Signal Transmission Path and Electrode Contact Conditions in Human Body Communication

Abstract

Human body communication (HBC) is a wireless communication method that uses the human body as part of the transmission medium. Electrodes are used instead of antennas, and the signal is transmitted by the electric current through the human body and by the capacitive coupling outside the human body. In this study, direction of electric field lines and direction of electric current through the human body were analyzed by the finite-difference time-domain method to clarify the signal path, which is not readily apparent from electric field strength distribution. Signal transmission from a transmitter on the subject’s wrist to an off-body receiver touched by the subject was analyzed for two types of transmitter electrode settings. When both the signal and ground electrodes were put in contact with the human body, the major return path consisted of capacitive coupling between the receiver ground and the human body, and the electric current through the human body that flowed back to the ground electrode of the transmitter. When the ground electrode was floating, the only return path was through the capacitive coupling of the floating ground. These results contribute to the better understanding of signal transmission mechanism of HBC and will be useful for developing HBC applications.