Optical Biotelemetry using Indirect Light Transmission

The optical biotelemetry using free-space light transmission in a closed space has many advantages over the conventional telemetry techniques using radio waves. There are some reports on the optical telemeters using direct light transmission, but few are found which use the indirect light scattered from a ceiling, a floor and walls. Since the latter technique does not require the line-of-sight transmission, it enables us to realize the non-restraint measurement of biological signals. In order to examine the possibility of this technique, the distribution of the indirect light in a room was calculated by a computer simulation. The distribution is uniform enough to carry out the telemetry with one receiver in the room with the dimension of W4.2XL6.4XH2.7m. The minimum received power was -28.0dBm with the transmitter power of 1 watt, which was about a half of the maximum power. To verify the possibility shown in the theoretical analysis, an optical biotelemetry system using the indirect light transmission was developed. 3 ECG's and a body temperature are multiplexed in time domain and modulated into a PIM pulse sequence. Light emitters placed on both shoulders emit the light of about 1 watt when the pulse is on. The system can be operated over 100 hours without replacing batteries. To examine the practical usefulness of this technique in clinical application, the optical biotelemetry from a freely moving subject is carried out with the developed system. A stable data acquisition was demonstrated even from the subject in exercise.