PMUTs (piezoelectric micromachined ultrasonic transducers) are microsystems with piezoelectric elements that sense their environment by means of acoustic signals. They are smaller and thus have a higher resolution and are easier to integrate than conventional bulk transducers, which are used today in medical imaging, for example. This will enable the development of medical technology, endoscopic in-vivo applications (in the body) or ultrasonic radar systems for the mobility of the future and intelligent industrial machines in the future.
The PMUTs are deflected by an electrical voltage and cause a gas or liquid to vibrate. This acoustic signal is reflected by a structure under investigation. The reflection of the acoustic signal in turn hits the PMUT. The micromechanics on the PMUT are vibrated and the piezoelectric layer generates a sensor signal. From the transit time difference of excitation of the PMUT and measurement of the reflected signal, the distance to an object is determined.
The signal from ultrasonic transducers, unlike bulk transducers, is directional and can be focused. Arrays can be arranged in almost any shape, allowing PMUTs to be flexibly adapted to customer-specific requests. Operating frequencies are typically between 100 kHz and 10 MHz. In liquids, excitation voltages in the low-voltage range are sufficient for excitation and conventional amplifiers for evaluation of the sensor signal. Another advantage of microtechnological production is the small installation space. By using AlN as transducer material, Fraunhofer ENAS avoids lead-containing transducer materials.