Source: Sadeghpour, Sina, Bram Lips, Michael Kraft, and Robert Puers. "Flexible Soi-based Piezoelectric Micromachined Ultrasound Transducer (PMUT) Arrays." In 2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems & Eurosensors XXXIII (TRANSDUCERS & EUROSENSORS XXXIII), pp. 250-253. IEEE, 2019.
A flexible pMUT multi-array structure is realized based on Silicon-on-Isolator (SOI) technology. Six rigid islands of pMUT arrays are connected together by means of silicon springs (acting as hinges), which are fabricated by Deep Reactive Ion Etching (DRIE). This enables unseen ultra-miniaturization. Each island consists of a 3×3 pMUT array. Arrays are electrically connected through metal tracks on top of the hinges. Each single pMUT is 410μm in diameter with a resonance frequency of 426 kHz in air. The fabricated flexible array was wrapped around a 5×5mm 3D printed cube to create an omnidirectional transducer.