Piezoelectric-Film-Based Wearable Respiratory Monitoring Device With Breathing Air Temperature Sensing and Heating Functions

This letter presents a novel wearable breath monitoring device created by micromachined thin-film technology. The device possesses precise respiratory rate sensing, breathing air temperature, and heating functions, which are all realized on one piece of barium titanate (BTO) film with different layout designs. The piezoelectric reverse trapezoidal cantilever produces large strain and converts it into voltage output when sensing breath airflow. The instant response at exhalation and inhalation provides useful breath parameters. The fabricated BTO film has an excellent positive temperature coefficient thermistor effect, which can serve as a temperature sensor. Using the piezoelectric effect of BTO film at electrical resonance with zero reactance, breath airflow can be heated with maximum power transfer, achieving the maximum heating effect. The fabricated BTO film device is assembled with a flexible printed circuit board with implementation of the charge amplifier circuit and packaged with a wearable housing to form a breath module. The subject wearing the developed module for testing verifies the device's functions.