Abstract
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.
Highlights
Human body communication (HBC) is a wireless transmission method for wearable devices which uses human body as a part of the signal transmission channel
This standard states that HBC uses electric field communication (EFC) technology and its operation is centered at 21 MHz
The present study aims to provide some technical information for designing HBC devices
Summary
Human body communication (HBC) is a wireless transmission method for wearable devices which uses human body as a part of the signal transmission channel. HBC uses electrodes that are in contact with or placed close to the human body These electrodes are the equivalent of antennas in wireless communication. This study focuses on the third form, data transmission from a wearable device worn on the user’s wrist to an off-body stationary device touched by the user’s index finger. Transmission between a transmitter worn on the user’s wrist and an off-body stationary receiver touched by the user’s index finger consists of current flow through the finger and arm, and current flow through capacitive coupling between human body and receiver’s outer case, which is usually made of metal, and connected to the ground of the receiver circuit. The matched inductance and resistance corresponds to the equivalent capacitive reactance and resistance of the transmitterhuman-body signal source
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