Piezoelectric sensor and respiration simulator system for sleep monitoring

Apnea and hypopnea are sleep disorders whereby there is complete or partial cessation of breathing during sleep. Airflow monitoring is an effective way to diagnose such sleep disorders. The objective of this thesis is to investigate the feasibility of a piezoelectric unimorph bending sensor to detect and quantify airflow during breathing. Both the piezoelectric and pyroelectric responses of the sensor that produce output voltages due to airflow pressure and/or temperature variations have been investigated.;Experimental results with the simulator showed that the sensor output voltage due to piezoelectric effect was dependent on the square of the airflow speed, which agreed with the mathematical model developed, under the experimental conditions employed. A calibration curve was obtained experimentally, which enables to measure airflow variations quantitatively using the output voltage measured. The sensor output signals due to changes in air temperature could be used to qualitatively monitor presence or absence of airflow.;A mathematical model for the sensor output with respect to the airflow speed has been developed for the presented measurement configuration using piezoelectric theory and Bernoulli's law. In addition, sensor design parameters are theoretically investigated to find a suitable material for the sensor substrate and an adequate thickness ratio of the piezoelectric/substrate layers. A respiration simulator system has been developed in order to study the sensor response under different airflow conditions such as cycle, volume and temperature. The simulator is capable of isolating the pressure and temperature responses of the sensor so that these responses could be studied independently.