Evaluation of Ground Loop Through the Floor in Human Body Communication

Human body communication (HBC) is a wireless transmission method that utilizes the human body as part of the transmission medium. A signal is transmitted by weak electric current through the human body and by capacitive coupling between transmitter, receiver, human body, and floor. Capacitive coupling with the floor is often included in the transmission models of HBC; however, its contribution is not well understood. This paper evaluated the contribution of the ground loop through the floor in HBC. The received signal strength was measured for two cases: two subjects shaking hands, and a subject touching an off-body receiver placed on a stand. The subjects each wore a transmitter or a receiver on their wrist. They stood on a carpet-covered metal floor, concrete floor, hardwood floor, and wooden chair to be above the floor. The variation of the signal attenuation was approximately 40 dB depending on which hand the subject used to shake hands or to touch the off-body receiver, while the variation caused by the different floor types was less than 5 dB. The attenuation obtained by numerical simulation showed similar results. These results show that the contribution of a ground loop through the floor was small.