Ferroelectret Hydrophone

Ferroelectret films are soft cellular solids capable to trap dielectric dipoles within the pores. These dipoles together with the large material compressibility give rise to a measurable piezoelectric response. They have been used to produce air-coupled ultrasonic transducers (200 kHz to 600 kHz) and recent works have shown the possibility to use them in water immersion. The main advantage is the large bandwidth and the main drawback is the poor sensitivity. This suggests the possibility of using these materials for wide-band reception, in particular, to make hydrophones. Due to the very low acoustic impedance of ferroelectret films (about 0.08 MRayl), thickness resonances under water immersion are completely damped out. Therefore, unlike conventional PVDF hydrophones, no upper frequency limit in the frequency band of the FE film hydrophone is expected due to these resonances, being the only limit the attenuation in the material. Present work is aimed to study the response of FE film as hydrophone and to explore the frequency range of the reception band in water immersion operation.