Furthermore, the acoustic-structure interaction is imposed on the transducers acoustic interface and on the package surface boundaries, as well.ĭifferent numerical modelling techniques are proposed to solve PMUTs problems, reporting the main features, advantages and drawbacks of each of them. To this purpose a 3D Finite Element (FE) model is used to study the role of the vibrating package on the pressure propagation, considering its elastic properties. The effects of the protecting structure in the acoustic performance, are deeply investigated. The attention is focused on the effects of the residual stresses related to the fabrication process and the DC voltage bias, V$_$ equal to 12 V. Several multiphysics numerical models predict the behaviour of the stand-alone diaphragm and the array of transducers. The main purposes of the thesis regard the modelling and the simulation of the Piezoelectric PMUTs working behaviour, in order to deeply investigate the acoustic performances of this device. The possibility to replace the common piezoelectric bulk wave resonators with this novel technology, extremely increases the research interests in the study and the comprehension of its capabilities. Piezoelectric Micromachined Ultrasonic Tranducers (PMUTs), appeared in the first decade of the XXI century, consist of layered flexural plates with a piezoelectric thin film active layer, arranged in an array configuration, to emit and detect ultrasonic pressure waves. Piezo-MEMS technology has revolutionized the actuators and sensors world, leading the micromachining and miniaturization advantages in the ultrasound systems. Modern micromachining techniques allow for a much higher precision than the reticulation techniques, adopted for the fabrication of piezoelectric bulk ceramic elements and a more easily manageable fabrication of large 1D and 2D arrays that imply high resolution and real-time imaging capabilities, in spite of the very small amount of piezoelectric material. However, this technology is limited by the high probe manufacturing and material production cost. Nowadays, array of several piezoelectric bulk wave resonators are employed in the commercial ultrasound imaging probes, in order to generate 3D real-time images. It is a non-invasive diagnostic technique, adopted to obtain images of human tissues by means of the principle of pulse-echo, that avoids the use of X-Rays scan, a technique that could be harmful because of the exposition to radiation. Ultrasonography was the first and the most important civil ultrasound application appeared in the 1950s.
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