Layered PVDF transducers for in-air US applications

Piezoelectric polymers are characterised by high dielectric losses and a low electromechanical coupling coefficient. Some successful attempts to improve the polymeric transducer performances, by using multilayered structures, in both the ultrasonic high frequency range and the audio frequency range have been reported. However, poor results were given on both mono-layer and multi-layer transducers, for in-air application, in the low ultrasonic frequency range. In this work, stratified curved transducers working in air at 50 to 90 kHz are investigated. By using the piezoelectric resonance method, the electrical parameters of the transducer equivalent model have been measured. Preliminary results on multi-layer free resonators, compared with those of mono-layer transducers, are given