Integrated micro-displacement sensor and its application to photoplethysmographic sensor

Photoplethysmography (PPG) has been widely and commonly used, as it has a wide range of information such as stress level, heart rate interval, respiration rate, blood vessel hardness etc. It is necessary to control contact force between a PPG sensor and measurement part (skin surface), in order to obtain accurate PPG signal. We suggest new sensor module which can measure both pulse wave and contact force. A sensor module has a micro integrated displacement sensor chip with optical source, photo diodes, and op-amp circuits, and a gum flame with a mirror. One photodiode can detect reflecting light from a mirror and measure gum flame displacement, which is displaced by a contact force. On the other hand, some of the incident light penetrates into a finger, and the scattering light, which have biological signal (pulse wave) are detected by one photodiode. In this paper, we fabricate multifunctional sensor module and attempt to simultaneously measure the pulse wave and contact force.