A COMPARATIVE STUDY OF AIR-COUPLED ULTRASONIC TRANSDUCERS BASED ON PIEZOELECTRIC COMPOSITES AND FERROELECTRET FOAMS.

This work presents a comparison in terms of sensitivity, bandwidth and signal to noise ratio (SNR) between air-coupled transducers made using two different transduction materials: 1-3 connectivity piezoelectric composites and polypropylene foam ferroelectret films. Center frequency is between 250 and 350 kHz and in both cases transducers are operated in through transmission mode under wideband excitation. Piezocomposite transducers include a stack of impedance matching layers to improve both sensitivity and bandwidth. Sensitivity of piezoelectric transducers is about -25 dB, while the sensitivity of the ferroelectret foam transducers is about -56 dB lower with similar differences in the SNR.