Multifunctional Optical Sensor Module - Integrated Optical Micro Displacement Sensor and Its Application to a Photoplethysmographic Sensor with Measuring Contact Force

Photoplethysmography (PPG) is widely and commonly used, as it produces a wide range of information, such as stress level, heart rate interval, respiration rate, blood vessel hardness, etc. It is necessary to control the contact force between a PPG sensor and the measurement location (the skin surface), in order to obtain an accurate PPG signal. We propose new multifunctional sensor modules that can measure both pulse waves and contact force. The sensor module has a micro integrated displacement sensor chip with an optical source, photo diodes, and op-amp circuits, and a gum frame with a mirror. Some incident light penetrates into a finger, and the scattered light, which contains a biological signal (a pulse wave), is detected by one photodiode. The photodiode can also detect reflected light from a mirror, which is displaced by a contact force. In this paper, we fabricate a multifunctional sensor module and attempt to simultaneously measure the pulse wave and