Mg Alloy Matching Layers for Broadband PZT-5H/Epoxy 1-3 Composite Underwater Acoustic Transducers: Acoustic Characterization and Design Simulation

The acoustic impedance mismatch between piezoelectric materials and water loads remains a bottleneck that severely hampers the advancement of underwater acoustic transducers. In this work, we propose a novel design that utilizes magnesium (Mg) alloy as the matching layer for PZT-5H/Epoxy 1-3 composite underwater acoustic transducers. To assess the suitability of Mg alloy as a matching-layer material and provide basic data for transducer design, the microstructural dependence of the elastic and acoustic properties is systematically established for solution-treated, extruded, and forged GWZ932 (Mg-9Gd-3Y-2Zn-0.5Zr, wt.%) alloys. It is determined that the elastic coefficients and acoustic performance of the three Mg alloys are essentially independent of grain size, second phases, and texture, whereas the acoustic attenuation coefficient exhibited an increasing trend with grain size at 20 MHz. The three alloys exhibit nearly identical acoustic impedances of 11.01 ± 0.03 MRayl (solution treated), 10.94 ± 0.02 MRayl (extruded), and 11.02 ± 0.03 MRayl (forged). The performance of PZT-5H/Epoxy 1-3 composite transducers with four different matching-layer designs, including single-matching-layer designs (Mg alloy or Al alloy) and dual-matching-layer designs (Mg alloy + polymer or Al alloy + polymer), is simulated using a finite element method (FEM). The results demonstrate that the transducer with the Mg alloy + polymer dual-matching-layer design exhibits both optimal transmitting voltage response (TVR) and receiving voltage sensitivity (RVS) bandwidths, with −6 dB transmit and receive bandwidths of 188.7 kHz and 156.6 kHz, respectively. These simulation results indicate that the Mg alloy + polymer dual-matching-layer design is promising for use in broadband piezoelectric underwater acoustic transducers. This work presents a novel Mg-alloy-based matching-layer scheme, offering a new choice for the matching-layer design of underwater acoustic transducers.