DEVELOPMENT OF A PIEZOPOLYMER PRESSURE SENSOR FOR A PORTABLE FETAL HEART-RATE MONITOR

A piezopolymer pressure sensor has been developed for service in a por table fetal heart rate monitor, which will permit an expectant mother to perform the fetal nonstress test, a standard predelivery test, in h er home. Several sensors are mounted in an array on a belt worn by the mother. The sensor design conforms to the distinctive features of the fetal heart tone, namely, the acoustic signature, frequency, spectrum , signal amplitude, and localization. The components of a sensor serve to fulfill five functions: signal detection, acceleration cancellatio n, acoustical isolation, electrical shielding, and electrical isolatio n of the mother. A theoretical analysis of the sensor response yields a numerical value for the sensor sensitivity, which is compared to exp eriment in an in vitro sensor calibration. Finally, an in vivo test on patients within the last six weeks of term reveals that nonstress tes t recordings from the acoustic monitor compare well with those obtaine d from conventional ultrasound.