Airborne µm-Level Vibration Measurement with Thermophone and Phase Tracking Method

We propose a novel, high resolution, and compact non-contact vibration measurement system for heartbeat monitoring. Airborne ultrasound is employed as sensing modality, and displacement of body surface is measured by time of flight (TOF) principle. High spatial resolution is realized by combining cross correlation technique and the phase tracking method. Dedicated thermophone with specialized driving circuit is also fabricated to obtain a compact and wide-band ultrasound source. Our implementation is validated also by using micro-electrical-mechanical systems (MEMS) microphone, field programmable gate array (FPGA) and microcontroller. Displacement accuracy was evaluated by measuring stable target, and obtained distance resolution is less than 20 um, Measurement is also performed on actual human chest, heartbeat and respiration was clearly identified.