The method of measuring heartbeat and pulse using LEDs has been adopted by Japanese universities and Toyota. As shown in the figure below, this method is to arrange a light-emitting module using an LED and a light-receiving module using a phototransistor in a portion where a finger or the like is touched, and it is easy to absorb light of a specific wavelength such as green by using hemoglobin in blood. The finger is illuminated and the reflected light is used to detect the pulse. This method is widely used. In June 2013, Nippon Wireless began selling a universal pulse sensor that integrates green LEDs and phototransistors in one package.
In addition, the University of Japan stated that the "phase shift method" technology developed by the university's tail stock professor was used in combination with the method of measuring pulse using LED. Japanese universities did not disclose specific mechanisms, but Professor Tail said that "the phase shift method can greatly improve the signal-to-noise ratio, so you can get a very accurate pulse waveform. Because of this, the pulse can be converted into blood pressure."
Since the exhibition at MEDICA2012, companies around the world have been consulting the phase shift method. Professor Tail has recently successfully integrated the core part of the data processing with phase shifting on a chip. He said that the chip size is currently 1cm2 square, but "the miniaturization of several mm squares has already been seen. It is installed in a portable terminal, so it is expected to realize the way to measure the pulse and blood pressure with a smart phone using the LED used as a flash. The University of Japan intends to launch the chip in cooperation with partners in 2013.
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