Page 426 - Mechatronics for Safety, Security and Dependability in a New Era

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Intra-body communication, which uses human body as the propagation medium, is an alternative to
conventional radio transmission for short-range wireless communication and proposed as the optimal
method for PAN. Since the human body is an electrical conductor, intra-body communication may
become a novel wireless communication method with less power consumption and higher
communication security compared to conventional RF methods. Tt also allows a new communication
mode of human friendly man-machine interface, because information is transmitted only when body
contact is made.

Three types of intra-body communication are shown in Figure 1. The circuit type and capacitive
coupling type make a circuit with the surrounding environment, and are suited for communicating
with devices that are not attached to the human body (e.g. electronic money, keyless entry system).
Several research groups have already demonstrated intra-body communication devices of these types
such as Handa, et al. (1997) and Matsushita, et al. (2000). The propagation type does not require
external circuits and has more tolerance to external noise compared to the other two. It is suited for
communication between devices attached to the body (e.g. PAN).

Etectranugndic W«ne

Simple current type Capacitive coupling type Propagation type
Figure 1: Types of intra-body communication

The authors aim to propose a new wireless communication method intended for PAN. This research
focuses on clarifying an analytical model and the mechanism of intra-body communication of the
propagation type.

MODELING OF INTRA-BODY COMMUNICATION

Electrical properties of the human body
Electrical properties of the human body were measured to determine the most efficient frequency to
send signals. Sine waves of 1 V p. p generated by a function generator (transmitter) were applied to two
electrodes attached above the elbow. Two electrodes were also attached to the wrist of the same arm
and an oscilloscope (receiver) was used to read the received signal strength. Figure 2 shows that
maximum transmission gain is obtained around 10 MHz.

For experiments, special care is taken for electrical isolation between the transmitter and the receiver,
including the measurement devices. First, the signal ground is separated because a common ground
between the transmitter and the receiver may act as a wired return path for the signal. Such paths
would not exist in actual applications for intra-body communication. Using a common AC power line
also exhibits a much stronger coupling than the capacitive coupling between the human body and