Noise Robust Optical Sensor for Driver's Vital Signs 2011-01-1024
We have developed a built-in vital sign sensor, which allows drivers to noninvasively measure their heartbeat and pulse wave just by gripping the steering wheel in the usual manner. Unlike conventional vital sign sensors used in clinical practice, such as an electrocardiogram sensor for measuring the heartbeat and photoplethysmogram sensor for measuring the pulse wave, our system requires no preparation or gel. One of the major issues we have successfully addressed is the suppression of mechanical vibration and electrical noise affecting the pulse wave sensor, which is far more susceptible to disturbances than heartbeat monitoring, especially while driving. To address this issue we have developed several new techniques: an active type optical sensor using a 525 nanometer green light-emitting diode which enhances the signal-to-noise ratio (SNR) of the pulse wave signal, an anti-vibration mounting mechanism for the sensor module which reduces vibration from the steering wheel, and a heartbeat signal-triggered ensemble averaging signal processing technique to recover a clean pulse wave from a noisy signal. As a result, we successfully achieved a 27 dB improvement in the SNR and have succeeded in recovering a clean 42 dB pulse wave from a noisy signal while the driver is at the wheel.