Biosignals sensing by novel use of bidirectional microphones in a mobile phone for ubiquitous healthcare monitoring

This paper describes a novel application of the bidirectional audio microphones in mobile phones to measure biosignals for ubiquitous health monitoring. The bidirectional microphone has two pressure-detecting ports. A pressure-detecting film receives the differential pressure between the ports. We apply this idea to biosignal measurements for a mobile phone. We used the microphone as 1) a sphygmograph at the fingertip, 2) a stethoscope in which a delay time sensor of pulse wave arrivals from the neck near the carotid or chest near the heart to the fingertip, and 3) a bed sensing device for biosignals. When used as a sphygmograph, it detects the wave similar to the second derivative of the conventional optical pulse oxymeter output wave. When used as a stethoscope, it detects cardiac sound and the pulse wave and respiration. With two microphones, the delay time from the neck carotid to the fingertip is detected.