How does the IR pulse sensor works ??
Principle of photoplethysmogram (PPG) Measurement !!
The pulse sensor is made using an infra-red emitter and detector. Light emitted by an infra-red emitter enters the skin and is diffusely scattered. The peak wavelength emitted by the emitter is typically in the range on 900nm < λ < 960nm. The detector placed on the other end captures a part of this diffused light. As light propagates through the tissues, a fraction of its intensity is absorbed by pulsating blood. Hence, when blood volume increases during the cardiac systole the captured intensity decreases creating a pulse-like photoplethysmogram (PPG) signal which reflects the blood volume changes in the arterioles. Furthermore, light absorptivity of haemoglobin (Hb) is significantly greater than that of oxyhemoglobin (HbO2) at 660nm. As arterial blood have high concentration of HbO2 and contrastingly, venous blood have high concentration of Hb, the sensor is able to detect the variation in both the systole and diastole stages.
