Design modelling and simulation of Piezo Micromachined Ultrasound Transducers (PMUT)
Piezoelectric micromachined ultrasonic transducers (PMUTs) are layered membranes with a piezoelectric active layer used for emitting and receiving ultrasonic waves. They have many potential applications: medical acoustic imaging and hydrophones exploit the in-water wave propagation of ultrasonic pulses; finger-printing recognition and range-finders use the in-air propagation. Further applications are represented by non-destructive testing, velocity sensing and 3D obstacle recognition. The possibility to measure distances is also interesting for Augmented Reality and Virtual Reality applications.
Conceptual scheme of PMUT working principle
Axonometric section of a PMUT starting configuration
Axonometric view of a packaged PMUT
We built a proper Multiphysics finite element (FE) model of both the electro-mechanical and the acoustic behaviour of the PMUT.
The model takes into consideration initial residual stresses and gives a realistic estimation of the fundamental frequency and of the PMUTs quality factor through the adoption of large deformation analyses and thermo-viscous modelling of the air, that induce the power dissipation in the so-called boundary layer at the fluid-structure interface.
Both un-packaged and packaged devices can be simulated.
Scheme of a multi-phyisics FE model for PMUT
Numerical and experimental results: effect of the fabrication process residual stresses
Sound Pressure Level SPL polar plot [dB] @ 3.5 cm from the center of the membrane in the vertical plane