Abstract
Piezoelectrets, a new type of electromechanical transducer material with low acoustic impedance and high piezoelectric d33 and g33 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.
Highlights
Traditional contact testing technology faces many challenges due to increasingly complicated operating environments with the fast development of modern industry
The magenta line depicts the FFCB air-coupled transducers (ACTs), the resonant frequency (RF) is found at 226.6 kHz, which is 1.0% lower than that of the experiment and 1.0% higher than that of the equivalent circuit modeling (EECM), the −3dB bandwidth is 34.8 kHz in the range of 208.4 kHz–243.2 kHz, and the response peak (RP) reaches 1.0
The experimental measurements obtained using the LDV and pulse-echo method, the theoretical analysis based on the EECM, and the finite element analysis (FEA) of the 2-D axisymmetric model are used to study resonance and frequency response of ACTs in order to investigate the influences of the boundary conditions
Summary
Traditional contact testing technology faces many challenges due to increasingly complicated operating environments with the fast development of modern industry. The piezoelectric ceramic material and the ferroelectric polymer material have been used to develop ACTs. the acoustic impedance for the piezoelectric ceramic material can reach values higher than 3 × 107 Rayl, whereas it is only about 420 Rayl for the air medium. The acoustic impedance for the piezoelectric ceramic material can reach values higher than 3 × 107 Rayl, whereas it is only about 420 Rayl for the air medium Such a large contrast in the impedance usually results in quite a low energy conversion, which means that only a small part of energy of the ultrasonic wave can propagate into the air medium. Due to weak piezoelectric activity, the energy conversion efficiency of the ACT fabricated with the ferroelectric polymer is much lower than that of the piezoelectric ceramic ACT. We propose the theoretical analysis based on electromechanical equivalent circuit modeling (EECM) and carry out finite element analysis (FEA) to predict the features of the ACTs, such as resonance characteristics and bandwidth
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
