Design and characterization of focused ultrasound beam with MEMS array

Abstract

Ultrasound has recently received increased attention and acceptance as the therapeutic device. Especially non-invasive stimulation using focused ultrasound has been a promising field in therapeutic application. A non-invasive treatment has advantages over alternative surgical procedures or insertion of needles which carry with them the risk of infection and pain. With recent advancements in focused ultrasound (FUS) technique, focused acoustic energy can be delivered to specific areas of biological tissues, as small as a few millimeters in diameter. However, there are limitations in which conventional piezoelectric transducers used in above applications. Challenging issues in single bulk piezoelectric transducer, such as fixed focal depth, impedance matching layer, and high voltage requirement have been effectively handled by MEMS. A significant advantage of using the MEMS is that large transducer arrays can be implemented in a small area. This enables the delivery of high acoustic power to the target area without generating high pressure on the surface of the transducer. This thesis presents optimal configuration of MEMS array which effectively stimulate targeted local area, by using MATLAB code simulation based on Rayleigh-Sommerfeld integral. As a preliminary step, A 15 by 15 pMUT rectangular array was used to verify simulation model. Beam profile measurements on this transducer made in an acoustic tank were compared with the beam profile predicted by simulation. The results showed good agreement with the simulation results. The acoustic focal region (AFR), the region bounded by the intensity contour lying 3 dB below the peak intensity, was located 1.775mm in the z-axis direction from the surface of the transducer. At the AFR, I_spta from the simulation showed the largest value of 739 mW/