Local pressure field distribution of bistable PMUTs for distance sensing

This work presents both the directivity pattern and distance dependence of the pressure field of a piezoelectric micromachined ultrasonic transducer (PMUT). The PMUT comprises a silicon membrane and an integrated piezoelectric transducer based on aluminum nitride (AlN) and exploits bistability to achieve large displacements during snap-through between the two ground states. Snap-through is initiated by a short rectangular pulse train burst, and the resulting sound pressure pulse is recorded. The impact of the number of excitation signal pulses as well as the number of averaged measurement events on the sound pulse shape is studied to find an optimal balance between short sound pulse duration and high maximum sound pressure. Sound reflectance measurements finally demonstrate the feasibility of bistable PMUT devices for future ultrasonic ranging applications.