Maximization of Received Signal Power by Impedance Matching in Human Body Communication Receiver

Human body communication (HBC) utilizes human body as part of the transmission channel. The present paper deals with HBC between a transmitter worn on the user's wrist and an off-body stationary receiver touched by the user's finger. In this configuration, transmitter-human-body system can be regarded as a signal source as viewed from the receiver. The equivalent output impedance of this signal source mainly consists of resistance of human body and capacitive reactance among the receiver, human body, and the surrounding environment. Impedance matching was achieved by inserting an inductor to cancel the capacitive reactance and adjusting the input resistor to match the resistance of the equivalent output impedance. At frequency of 10 MHz, maximum received power was obtained with 40 μH inductor and 1.5 kΩ input resistance. This suggests that the output impedance of the transmitter-human-body system is 1500-j2500 Ω.