Sleep-mask-type pulse wave and respiration rate sensor using a MEMS-based differential pressure sensing element

Noninvasive sensors have been widely used to measure pulse and respiratory waves, which are the primary measurement targets in sleep monitoring. Conventional noninvasive biometric sensing devices, including smartwatches, require the use of multiple sensing elements and face challenges in the direct and simultaneous measurement of pulse and respiratory waves. Recently, pressure sensors with micro-electromechanical systems (MEMS)-based sensing elements have attracted attention for their small size, high sensitivity, and broad applicability. These sensors detect minute vibrations on the body surface with changes in pressure for biometric sensing. In this study, we propose a sleep-mask-type sensor for sleep monitoring that measures pulse and respiratory waves. A MEMS differential pressure (DP) sensor chip serves as a sensing element, which is placed between two chambers, one open to the atmosphere and the other with a rubber membrane. The proposed sensor detects minute vibrations of the dorsal surface of the nose, which can be attributed to pulse and respiratory waves based on DP changes in the chambers. This paper presents the design, fabrication, and evaluation of the sensor with respect to capturing vibrations during sleep. The application of frequency filtering to the measured raw data confirmed that the pulse and respiratory waveforms could be directly and simultaneously measured, thereby rendering the proposed sensor suitable for sleep monitoring.