Piezoelectric membrane sensor and technique for breathing monitoring

Airflow monitoring is an effective way to diagnose sleep disorders that are caused by complete or partial cessation of breathing during sleep. For monitoring airflow, a piezoelectric membrane sensor, consisting of a stainless steel foil, a piezoelectric ceramic film and a top electrode, has been developed using a sol-gel spray technique. This sensor has worked as a unimorph-type bending sensor, which could be attached beneath the nose and/or above the mouth using a clip or tape for monitoring breathing. A mathematical model for the sensor output with respect to the airflow speed has been developed using piezoelectric theory and Bernoullipsilas law. In addition, a respiration simulator system has been constructed in order to study the sensor response under different airflow conditions such as cycle, volume and temperature. Experimental results with the simulator showed that the sensor output voltage due to piezoelectric effect was proportional to the square of the airflow speed, which agrees with the mathematical model developed, under the experimental conditions employed. A calibration curve was obtained experimentally, which enables measurement of airflow variations quantitatively using the output voltage measured.