Spectrum Analysis of Respiration and Heartbeat Signals Measured by A Non-Contact PVDF Piezoelectric Film Based Sensor

A very sensitive respiration sensor is developed using a simple poly-vinylidene difluoride (PVDF) piezoelectric film for monitoring the respiration activity of people who have sleep disorders such as sleep apnea syndrome (SAS). The respiration sensor is meant for at-home care use and is designed to be attached to a bed underneath a subject so that the respiration activity can be monitored without direct physical contact. A charge amplifier and a band elimination filter which were required for accurate respiration monitoring were also developed in this study. The output signals of the respiration sensor were measured while a subject repeated breathing and cessation every 30 s. In order to investigate the measured signal in detail, the measured signal was analyzed by using a fast Fourier transform algorithm. This confirmed that the measured signal contains not only the respiration signals but also the heartbeat signals of the subject. By using digital filters with appropriate cutoff frequencies, the respiration and the heartbeat signals were successfully separated.