Air-coupled piezoelectric transducers with active matching layers

This work deals with the design of air-coupled piezoelectric transducers using active matching layers. In the proposed scheme, the active matching layer is the outer one and is made of a ferroelectret film. This kind of material has shown a stable piezoelectric response together with very low acoustic impedance, that make them an ideal candidate for this dual use: outer impedance matching layer and transducer material. Central frequency of the transducer is determined by the location of the λ/4 resonance of the active matching layer: 0.35 MHz. The transducer has been tested in conventional pulse-echo mode and also in a dual mode: the piezoceramic is used as transmitter and the ferroelectret film is used as receiver. Performance of both operational modes are compared with a conventional air-coupled piezoelectric transducer with centre frequency at 0.25 MHz. Other uses of this technology are also discussed.