Research groups at Tokyo University of Science, the University of Tokyo, and Tokyo Polytechnic University explained changes in transmission gain (relationship between distance and radio field strength) for various parameters of transmitter / receiver equipment using a simple equivalent circuit model for signal transmission of human body communication systems. Demonstrated what can be done.
Wireless technologies such as Wi-Fi and Bluetooth used in wearable devices that have become widespread in recent years are vulnerable to security.In addition, the human body that absorbs electromagnetic waves interferes with wireless communication.On the other hand, human body communication, which utilizes the human body itself as a passage for electromagnetic waves, enables high-reliability communication with low power consumption and robust security.This is because the "near-field electric field" that rapidly attenuates with distance is used for signal transmission, so electromagnetic fields are less likely to leak to the surroundings, and since the signal transmission path is only around the human body, electromagnetic interference from others is small and noise is low.
In the research, we constructed an equivalent circuit model (circuit model simplified for a certain characteristic) of signal transmission from the transmitter to the receiver via the human body and conducted characteristic analysis.This time, it is assumed that a user wearing a wearable device on his wrist touches a large installation device such as a ticket gate at a station to perform human body communication.An experiment was conducted using a transmitter (wearable device) in which both the signal electrode and the ground electrode were in contact with the human body, and a receiver (installed device) in which only the signal electrode was in contact with the human body.
As a result, as the two electrodes of the transmitter separate, the output impedance (difficulty in current flow) in the equivalent circuit model increases, and when the ground (ground) of the receiver increases, the capacitance coupling between the ground and the human body increases. It turned out that (the coupling of two circuits with electric capacity) becomes large.
The results of this research will streamline the development of human body communication technology with low power consumption and excellent confidentiality, and are expected to be applied to authentication information and medical healthcare fields.
Paper information:[IEEE Transactions on Biomedical Circuits and Systems] Equivalent Circuit Model Viewed from Receiver Side in Human Body Communication
