Optimization of PMUT array for vertebra kinetics imaging

MEMS technology, with its micrometer feature sized devices, is an ideal candidate to solve some of the crucial problems in wearable devices for human health monitoring. Ultrasonic imaging devices play a big role in in vitro human health monitoring. Wearable ultrasonic arrays can do imaging to monitoring bone kinetics, vessel pulsation, lung conditions and so on. Compared with other imaging modalities, ultrasound has the advantage of non-radiative, non-invasive and capability of realizing real time dynamic imaging. This research will focus on development of an ultrasound imaging system, which can be attached on the lower back of human body to monitoring the vertebra kinetics and use the biomarkers from the image to diagnose the low back pain disease, which is pervasive among aged population.

Classical ultrasound transducers consist of a thick layer of piezo material, sandwiched between two electrodes. Their miniaturized counterparts (PMUTs) allow for a much smaller form factor and easier integration with supporting electronics. A PMUT works on the principle of vibration of a membrane. These miniaturized drums contain a piezoelectric layer in their membrane that can generate and pick up mechanical deformation of the suspended membrane by applying or receiving an electrical signal over the piezoelectric layer. This allows PMUT to emit and receive ultrasound waves by respectively vibrating the membrane or detecting the deformation of the membrane by an incoming wave.

Fig 1: Sketch of PMUT cross-section and working principle.

By using smart arrays of these small transducers and controlling electrically them in an organized manner, complex ultrasound fields can be generated and received. It is this beamforming feature of arrays of transducers that is at the base of ultrasound imaging.

The goal of this thesis is to optimize single PMUT element to improve its transmission and reflection efficiency, and optimize the PMUT array targeted for a better vertebra image quality. The optimization can also concern the electronic system connecting the PMUT elements with the data acquisition device, PCBs and imaging data analysis. Depending on the students' interest, the balance between simulations and experimental work will be steered. Generally, this is a perfect topic for students eager to understand complex systems with a hands-on attitude and interest for MEMS devices. The work is estimated to be: 40% simulations/calculations (f.e COMSOL, Matlab or likewise), 30% characterization, 30% hardware design and implementation. Furthermore, this gives you the opportunity to work on cutting edge innovative technology in an application oriented project.

Fig 2: conceptual sketch showing PMUT array for vertebra imaging.

The broader context of this work is a collaboration between the MEMS team of Imec and the Robot-Assisted Surgery Research Group within department of Mechanical engineering of KU Leuven.