Test, modeling, and analysis of air-coupled ultrasonic transducer based on piezoelectret film

Piezoelectrets, a new type of electromechanical transducer material with low acoustic impedance and high piezoelectric d(33) and g(33) coefficients, are promising candidates for developing high-performance air-coupled ultrasonic transducers. In this work, we design polypropylene-piezoelectret-film based air-coupled transducers (ACTs) with two different structures and investigate the influence of boundary conditions of the film with experimental measurement, electromechanical equivalent circuit modeling (EECM), and finite element analysis (FEA) for both inverse and direct piezoelectric effects. The experimental data are in great agreement with the results of EECM and FEA. The resonant frequency of the ACT with a free-front-clamped-back (FFCB) film is about half of that of the device with a free-front-free-back (FFFB) film, the response peak of the FFCB device is higher than that of the FFFB device, and the -3dB bandwidth of the former is much narrower than that of the latter. The results show that the experimental measurements can be predicted by EECM and FEA, which can provide the basis for the development of high-performance air-coupled ultrasonic transducers based on piezoelectret films.