Precision high-bandwidth out-of-plane accelerometer as contact microphone for body-worn auscultation devices

Abstract

This paper reports on the implementation and characterization of wafer-level-packaged accelerometer contact microphones having wide bandwidth (fres >10 kHz) and low-noise (<100 µgHz) for use as auscultation devices in body-worn sensor arrays. By using wide bandwidth capacitive accelerometers as contact microphones, the encapsulated sensor can detect not only internal sounds from organs but also body motions down to DC frequency levels, significantly reducing sensor size and fabrication cost of wearable technology for health monitoring. The out-of-plane micro-g accelerometers use nano-gap transducers (270 nm) for enhanced signal-to-noise ratio in a high resonant frequency microstructure with small form-factor. Fabricated devices were interfaced with off-the-shelf readout circuits and their performance was compared to commercially available piezoelectric contact microphones. Normal breath sounds in the range of 600-1000Hz along with phonocardiogram (PCG) and ballistocardiogram (BCG) signals are extracted by mounting the device on the chest.