Attempt for optical BAN on human body

Fundamental study was conducted to apply the optical biotelemetry technique to the body area network (BAN). With this technique, we can expect many advantages over the conventional BAN with electric signal transmission. The bandwidth was evaluated to be 2.80 GHz. The optical signal reached the longer distance in the narrower channel due to the light-guide effect in diffuser. For a prototype of a practical system, an array of LEDs was attached to the wrist area and transmitted light was detected with an avalanche photodiode. The signal transmission (100 kHz, ASK) from the wrist to the fingertips was attained in an adult hand. In the experiment, the following facts were newly found. When the transmission range in the hand exceeds 70 mm, the intensity of radiation from the hand surface became larger than that of the internal propagation through the hand tissue. The transmission range became larger with the lower duty ratio of the optical ASK signal. These results provide useful information for the realization of the optical BAN as an application of optical biotelemetry.