A Bandwidth-Tunable Array of Piezoelectric Micromachined Ultrasonic Transducers with Various DC Bias Voltage Combinations

Conventional multi-frequency piezoelectric micro-machined ultrasonic transducer (PMUT) arrays depend on various geometric radii of the units to achieve a wide bandwidth, resulting in low spatial utilization and relatively complex fabrication process due to non-uniform unit sizes. In this paper, we present a bandwidth-tunable PMUT array with uniform geometric design through various DC bias combinations of the five channels (three units per channel). The tunable bandwidth provides usage flexibility to enhance the axial resolution with a broader bandwidth or improve emission intensity by narrowing the bandwidth. Finite Element Analysis (FEA) simulation results demonstrated that applying DC biases from −24 V to 24 V on a single water-coupled PMUT could cause a resonant frequency shift of 25 kHz, from 126 kHz to 151 kHz. Experimental results further verified that, with DC biases applied from −15 V to 15 V, a single liquid-coupled PMUT channel was able to achieve a resonant frequency shift of 14.2 kHz, from 64.9 kHz to 79.1 kHz. Eventually, by applying a DC bias combination of 0 V and 9 V to two specific channels, the bandwidth was enhanced significantly to 179.9%, highlighting the potential of our bandwidth tuning methodology in advanced therapeutic applications and non-destructive testing.