Array of PVDF sensors for ultrasonic imaging in air

The advantages of ferroelectric polymer technology when building hemicylindrical ultrasonic transducers for airborne applications, have been already broadly investigated by the authors. The theory, experimentally confirmed, showed that the resonance frequency is inversely proportional to the bending radius. Based on this unique property a double frequency array sensor was built up in order to have a large bandwidth otherwise obtainable with more sophisticated and expensive fabrication technologies. In this work, the design is described of two interlaced series of transducers with the resonance frequency equal to 60 kHz and 86 kHz respectively. Experimental characteristics of the array elements have been derived and an imaging system based on the reflection tomography technique was gathered and tested in a laboratory environment. The overall system performance is reported via the point spread function image evaluated by the response to a thin steel wire. The spatial resolution is about 3 mm along both the lateral and axial direction