Respirometry Rate Measurement by Pyroelectric Effect of a Piezo Sounder—Monitor and Alarm by Single Device

This article describes a novel application of a piezoelectric sounder on an acoustic device as a respiratory detector. When human exhaled air at a temperature of 36.5 °C is blown onto the piezoelectric device in the sounder in a room of 26.4 °C, a peak voltage of 1–2 V directly appears without an amplifier. We herein present a theoretical model of how the device works, experimentally prove its validity, and show its potential to be used as a spirometry detector. The output voltage changes alongside the output of a medical spirometer for forced vital capacity test respiration. The device is noise robust under a variety of measurement conditions, including different masks, shields, snorkels, and sustained airway positive pressure devices. The S/N ratios for quiet sitting, walking, quick face swing, and mask movement were 38, 33.3, 32.3, and 30.9 dB, respectively. The piezoelectric sounder considered herein can return to the original function and generate an alarm if the measured reparation is abnormal.