Fig. 2: Design principle and characterization of the device.
From: Machine learning-assisted wearable sensing systems for speech recognition and interaction
a Cross-sectional view of the three-dimensional structure of the acoustic sensor based on SOI wafer. b Finite element simulation comparison of relevant parameters of acoustic sensors of PZT, AlN, ScAlN and the corresponding three shapes. c Photos of the front (I) and back (II) of the PMUT. d Optical microscope image of the prepared acoustic chip and close-up details of a microelement. e SEM cross-sectional view of the Mo/ScAlN/Mo film structure of the prepared acoustic chip. f Resonant frequency response of the electrical impedance magnitude and phase of the MEMS chip in air. g Sensitivity test curve of the packaged MEMS sensor in the low-frequency wide-band range in water. h Images display of the flexible device under undeformed (I), twisted (II), bent (III) and stretched (IV).
