How does Xiaomi 11 detect heart rate?
Heart rate is a very important health indicator and is the most direct reflection of heart health. Especially for sportspeople, it can reflect the physical condition when exercising, guide the intensity of exercise, and avoid sports injuries. So fitness people almost must have a heart rate watch or bracelet.
Xiaomi 11 adopts ultra-thin under-screen fingerprint, cleverly integrating the heart rate detection function into the under-screen fingerprint recognition module, without adding additional hardware or increasing the thickness of the body, it realizes the heart rate detection function with accuracy comparable to that of a heart rate watch, which is another major experience innovation of Xiaomi 11.
One transmitting, one receiving, one calculating: the principle of heart rate detection is not difficult to achieve. For high-end smartwatches and smart bands, heart rate detection technology is a necessary basic function. The heart rate detection method is mainly optical heart rate detection. The general principle is: hit a beam of light to the wrist skin, through the sensor to detect the intensity of the reflected light changes, combined with the algorithm to calculate the heart rate value.
Because the heartbeats, the blood flow in the blood vessels is a stream, and the blood volume in the vessels changes periodically. When the heart rate monitoring device emits light to the skin, a portion of it is absorbed by the blood in the blood vessels.
- The greater the blood volume, the more light is absorbed and the less is reflected.
- The lower the blood volume, the less light is absorbed and the more is reflected.
- The heart rate can be calculated based on the time interval of the change in the intensity of the reflected light.
Without additional hardware and increasing additional body thickness, Xiaomi 11 detect heart rate, detection is cleverly integrated into the under-screen fingerprint. Xiaomi 11 is not the first phone in the industry to carry heart rate detection. As early as 2014, some phones implemented heart rate detection by adding LED lights that emit light and sensors that detect reflected light to the back of the body.
The Xiaomi 11’s under-screen heart rate detection function is very clever, as it uses the AMOLED screen display unit as the light source and the optical fingerprint sensor as the receiver, integrating the heart rate detection function into the fingerprint module. No additional hardware, no increase in body thickness.
When heart rate detection is performed, the light provided by the screen enters the finger, and the optical fingerprint sensor detects the light intensity change reflected by the finger and then combines the professional algorithm (photoelectric volume pulse wave tracing method PPG) to extract the characteristic value of the light intensity change and calculate the time interval to achieve the purpose of heart rate detection.
Ultra-thin under-screen fingerprint + green light solution, accurate and unambiguous detection results. Xiaomi 11 uses an ultra-thin under-screen fingerprint module, which ultimately projects sufficient incoming light on the fingerprint sensor and has the strong anti-interference capability. And, when Xiaomi 11 heart rate detection works, it emits green light, which is easily absorbed by the body, presents a large change in reflected light, and is subject to little interference from ambient light, with a high signal-to-noise ratio and more accurate detection results.
Tested by Xiaomi Lab, the heart rate detection function of Xiaomi 11 has reached the performance level of flagship wearable watches. Tested by SGS laboratory, the accuracy of comparison with professional pulse oximeter reaches 2.11bpm. The accuracy of heart rate detection of common wearable devices such as bracelets and watches in the market is generally around 3bpm.