Influence of the prestressed layer on spherical transducer in sound radiation performance

To improve the acoustic radiation performance of the spherical transducer, a prestressed layer is formed in the transducer through fiber winding. The influence of the prestressed layer on the transducer is studied from the effects of the radial prestress (T-r) and acoustic impedance, respectively. First, a theoretical estimation of T-r is established with a thin shell approximation of the prestressed layer. Then, the acoustic impedance is measured to evaluate the efficiency of sound energy transmission within the prestressed layer. Further, the ideal effects of T-r on the sound radiation performances of the transducer are analyzed through finite element analysis (FEA). Finally, four spherical transducers are fabricated and tested to investigate their dependence of actual properties on the prestressed layer. The results show that with the growth of T-r, the acoustic impedance of the prestressed layer grows, mitigating the enormous impedance mismatch between the piezoelectric ceramic and water, while increasing attenuation of the acoustic energy, resulting in a peak value of the maximum transmitting voltage response (TVRmax) at 1.18 MPa. The maximum drive voltage increases with T-r, leading to a steady growth of the maximum transmitting sound level (SLmax), with a noticeable ascend of 3.9 dB at a 3.44 MPa T-r. This is a strong credibility that the prestressed layer could improve the sound radiation performance of the spherical transducer.