Sapphire Glass PPG Sensor Window (Sensor Window)

Sapphire Heart Rate Glass

The PPG Sensor (Photoplethysmography Sensor) is a non-invasive optical device based on photoplethysmography. It measures physiological parameters such as heart rate and blood oxygen saturation by emitting light that penetrates the skin and detecting fluctuations in light intensity caused by changes in blood volume. ‌‌

The fundamental principle of PPG (photoplethysmography):

The sensor emits a beam of light (commonly green, red, or infrared) onto the skin and uses a photodetector to capture the light reflected or scattered back from subcutaneous blood vessels. As blood volume changes periodically with each heartbeat, its absorption of light also fluctuates. The intensity of the reflected light detected by the photodetector exhibits subtle fluctuations synchronized with the heartbeat (typically only 0.5% to 5%). By analyzing these variations in light intensity, physiological parameters such as heart rate and blood oxygen saturation (SpO2) can be calculated.

In high-end smartwatches, the PPG Sensor Window typically refers to the smooth, translucent area on the back of the watch that emits green or red light flashes, serving as the 'light gatekeeper' in the entire PPG monitoring process.

It is not the core component that actively emits or detects light, but rather ensures the accurate and efficient transmission of optical signals through three key functions: optical transmission, signal filtering, and component concealment. With its meticulously designed optical structure, it effectively allows signal light to pass while blocking interfering light, while also harmonizing with the device's aesthetic design, making it an indispensable part of the PPG sensor.

Advantages of sapphire glass for sensor windows (sapphire heart rate glass):

1. High hardness, wear-resistant and scratch-proof:

Sapphire boasts an extremely high hardness (Mohs scale 9, second only to diamond), making it highly resistant to scratches in daily use. This is crucial for sensor windows, as even minor scratches can scatter and block light, leading to signal attenuation and directly affecting the measurement accuracy of heart rate, blood oxygen, and other data. Using sapphire glass ensures the sensor maintains high light transmittance throughout the device's entire lifecycle.

2. Excellent optical performance with minimal signal loss:

Sapphire exhibits high transmittance across a broad spectrum from ultraviolet to infrared, which perfectly meets the requirements of PPG sensors (commonly using green, red, and infrared light). Additionally, its thermal conductivity is superior to that of ordinary glass, aiding in heat dissipation within the sensor and ensuring operational stability.

*The image shows the sapphire glass PPG sensor window (sapphire heart rate glass) customized by Jingyuan Optics for its customers.