Real-Time Control of the Resonance Frequency of a Piezoelectric Micromachined Ultrasonic Transducer for Airborne Applications

Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) are promising for their small size and potential for integration. Because of manufacturing tolerances, there is typically a spread in the resonance frequencies of different devices. This, combined with narrowband when air-coupled, makes the use of multiple membranes very challenging, for example in applications like echo location or data communication. We leveraged the internal stresses to control the resonance frequency, by applying a proper bias voltage. The transducers used in this work are PZT-based PMUTs, with 100kHz nominal resonance frequency and ~1% fractional bandwidth in air. We designed and developed an analog frontend which is capable to apply a programmable voltage bias and, at the same time, perform one the following: excite a transducer with a pulse wave, acquire the free decaying oscillation, acquire the amplified received echo. The hardware blocks are managed by a microcontroller to create a discrete-time closed-loop, capable to set the resonance frequency to a desired value. We show that this control system is capable to control the resonance frequency of two unmatched transducers and set it to the same value. And then perform operations that require frequency matching (time-of-flight, data communication). This method enables also two- or three-dimensional echolocation, when applied to multiple transducers.