Effect of Earth Ground and Environment on Body-Centric Communications in the MHz Band

Abstract

Body area network (BAN) research, which uses the human body as a transmission channel, has recently attracted considerable attention globally. Zimmerman first advocated the idea in 1995. Illustrations of the electric field streamlines around the human body and wearable devices with electrodes were drawn. In the pictures, the electrodes of the wearable devices constitute a closed circuit with the human body and the earth ground. However, analysis of the circuit has not been conducted. In this study, we model the human body shunted to earth ground in a radio anechoic chamber to analyze the electric field strength around it and clarify the effect of earth ground during BAN run time. The results suggest that earth ground has little influence on the human body and wearable devices. Only when the human body is directly grounded, the electric field near the feet area will decrease. The input impedance of the transmitter is approximately the same, and the received open-circuit voltage and current of the receiver are also the same. In addition, we elucidate that stable communications can be established by developing a closed circuit using earth ground as return path. When the external electronic devices and human body are shunted to earth ground, the received open-circuit voltage and current increase.