Vital Sign Sensing Technology

Epson's vital sign sensing technology


Vital sign sensing technology is a solution that uses a sensing device to measure the vital signs that are evidence of biological activity in humans. Epson has provided various kinds of value through photoelectric vital sign sensing technology that makes use of semiconductor and photoelectric technologies. These include activity level monitoring of footsteps, calories burned, sleep and other activities in daily life for the healthcare market, and exercise intensity visualization for the running gear market. This vital sign sensing technology shows promise for utilization in a wide range of applications. These include safeguarding children, the elderly, workers, and drivers of automobiles and other machinery, and early detection of infection with new types of viruses. Through its vital sign sensing technology, Epson is helping to safeguard people in various situations in life, and contributing to a safer and more secure society.

Basic principle of photoelectric vital sign sensing

Vital Sign Sensing

Photoelectric vital sign sensing is a measurement technology that makes use of the light absorbing properties of hemoglobin. The basic principle of measurement involves shining light from a green LED onto blood vessels under the skin. Light that is reflected without being absorbed by hemoglobin is captured by the photodetector. The captured light generates an analog signal within the photodetector, which is converted to a digital signal and monitored for infinitesimal changes in intensity. Pulse is measured by looking at the difference in the amount of reflected light that occurs as the blood vessels expand and contract with heartbeat.

During actual measurement, reflected light is generated by sources other than the LED, such as sunlight and room lighting. In order to perform accurate measurement, these sources must be eliminated. Also, if the person moves and wiggles the device, the reflected LED light will be scattered and generate body movement noise. Body movement noise will pollute the data, so this influence must also be accounted for.

Achieving low power consumption and high precision measurement through device structure and detection algorithm

Epson has been developing its original heart rate measurement technology for many years. Epson's vital sign sensing devices are made using proprietary semiconductor and optical technology. Sensing devices such as our photodetector have allowed us to realize high-accuracy and low power consumption heart rate measurement.

Vital Sign Sensing

To prevent decline in the measurement precision of the photodetector, we have created two types of original optical filter. These are an angle limiting filter, which employs a metallic microstructure to limit ray angle, and a spectral filter, which uses a multi-layer thin film to restrict wavelength.
The angle limiting filter cuts out reflected LED light at the skin surface or exterior that comes from angles, which are unrelated to pulse measurement. The multi-layer thin film filter, composed of dozens of layers on top of the angle limiting filter, shuts out external optical noise due to unnecessary wavelengths of intense light from sources such as the sun. This ensures only the LED reflected light needed for accurate measurement is captured, and maintains measurement accuracy. Effectively capturing reflected light also allows the amount of light emitted by the LED to be reduced. This decreases power consumption and makes it possible to use the device for a long period of time.

Epson vital sign sensors

Epson vital sign sensors

In addition, we are developing sensors (shown below) that can monitor the percentage of oxygen coupled with hemoglobin in the blood, while maintaining the low power consumption of a measurement device used primarily for continuous monitoring. Blood oxygen saturation is recognized as important for those with asthma and other respiratory diseases to manage their own health, for mountain climbers ascending high-altitude peaks, and for detecting the early signs of breathing difficulty caused by infectious diseases such as Covid-19. We have produced an easily deployable device by combining the red/infrared LEDs and photodetector used to measure blood oxygen saturation, in a compact package.

Also, we have improved measurement accuracy by incorporating an accelerometer and detection algorithm to detect and eliminate body movement noise caused by things such as arm movement.

Artifact Canceler

In addition to its vital sign sensors, Epson has numerous sensing devices that utilize its core proprietary sensing technology. We have also analyzed big data gathered through sensors over many years to accumulate a vast amount of data and algorithms. Epson intends to use its family of sensing devices and the new value obtained through analyzing big data to create an algorithm platform. This will form the core of our efforts to expand the world of smart sensing, and accelerate the creation of new usage scenarios. We will continue to support and safeguard people in all situations, and thereby help to create a safe, secure and sustainable society.

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