PMUT – a new generation of ultrasonic transducers
PMUT (piezoelectric micromachined ultrasonic transducer) are microsystems using piezoelectric materials for an acoustic mapping of the environment. Compared to bulk ultrasonic devices the PMUTs are better to integrate, e.g. for medical imaging devices. Furthermore, they are smaller with higher resolution. This development enables medical, endoscopic in vivo imaging devices and ultrasonic radar for autonomous mobility and industrial machines. In contrast to capacitive microsystems (CMUTs) the PMUTs require low voltages.
By actuating PMUTs with an electric voltage, an acoustic wave is transfered into the surrounding gas or fluid. Scanned objects will reflect the acoustic wave. The reflection signal will actuate the PMUT. The microsystems piezoelectric layer vibrates and generates a sensor signal. The distance of microsystem and object can be analyzed by measuring the time delay between actuating the PMUT and sensing the reflected signal. An array arrangement of PMUT sensors and actuators enables to map the environment.
The researchers of the Fraunhofer ENAS and the Center for Microtechnologies (ZfM) at the Chemnitz University of Technology use piezoelectric Aluminum nitride (AlN). This transducer material is highly suitable for the integration into existing MEMS processes. The moderate piezoelectric coefficient and low dielectric constant of AlN is optimal for applications, which require a combination of sensors and actuators.