Impact of Resonance Frequency Spread on Beam Pattern of a Piezoelectric Micromachined Ultrasonic Transducer Array

PMUTs (Piezoelectric Micromachined Ultrasonic Transducers), are a type of MEMS (Micro-Electro-Mechanical Systems) that have gained interest in beamforming applications because of their compactness, which makes them ideal for portable sensor arrays or matrix. One of the requirements to apply standard beamforming techniques, is that the transducers shall be identical. This is not the case, because manufacturing tolerances particularly affect the resonance frequency. This study evaluates the impact of resonance frequency spread on the beam pattern of a PMUT array. Starting from characterization values of actual samples, we extracted parameters that enabled to carry out finite-element simulations of the beam patterns. Based on the results, we propose a method to evaluate the fitness for beam forming applications of a P MUT array affected by manufacturing tolerance, based on a single parameter. The proposed parameter is dependent only on the bandwidth and resonance frequency variance, while it is frequency-independent.