A piezoelectric micro-electro-mechanical system vector sensor with a mushroom-shaped proof mass for a dipole beam pattern

Vector hydrophones based on a micro-electro-mechanical system (MEMS) hold great promise for underwater communications, due to their potential for miniaturization and mass production. Piezoelectric materials have recently been utilized in the fabrication of MEMS-based vector hydrophones, as less power is typically required for their operation. Here, we propose a millimeter-scale piezoelectric MEMS vector sensor with a suspended cross-shaped beam and a mushroom-shaped proof mass configuration. This design was inspired by the bio-transducer of the lateral line of fish. Sensor fabrication involved piezoelectric Pb(Zr_0.52Ti_0.48)O₃ thin-film deposition by radio-frequency magnetron sputtering onto the beam structure, followed by a multi-etching process and assembly using a three-axis microassembly technique. The fabricated MEMS vector sensor showed a resonance frequency above the working frequency range, which was suitable for naval applications. The directivity of the proposed sensor was determined by dipole patterns in the x and y directions, with a maximum relative sensitivity difference of −42 dB at 1 kHz. Finite element analysis results for the resonance frequency and directivity were in good agreement with the experimental results, suggesting that the proposed vector sensor could be used in underwater communications as a vector hydrophone.