Fig. 1: Cardiorespiratory sound sensors and sensing mechanism.

a Illustration of the placement of sensors on the human body for lung and heart sound monitoring. b Image of the prototype of the sound sensor. c Inside view of the prototype with a printed circuit board. d Structure of the accelerometer-based on an asymmetric gapped cantilever structure. H is the distance between the layer of the piezoelectric beam and the neutral plane. e Built-in charge amplifier circuit for amplification of the piezoelectric signal