Annular 1-3 piezocomposite high intensity focused ultrasound transducer of a concave geometry

Abstract

For medical therapeutic applications, we have developed a concave annular high intensity focused ultrasound (HIFU) transducer that is made of a 1-3 piezocomposite plate and operates at 3 MHz. The transducer has 16 annular channels, and the annuli have been designed to focus at the geometrical center of the sphere. The focal point can be controlled to scan a three dimensional volume by electronic and mechanical means. The focal point is moved along the normal axis of the transducer by electronically steering the sixteen annular channels. The focal point is also rotated back and forth by mechanically wobbling the piezocomposite plate with a kinematic linkage. The kinematic linkage is driven by an electric motor installed inside the transducer. The optimal combination of the number of channels, the width of the kerf between channels, and the width of each channel were determined by means of the OpQuest-Nonlinear programming algorithm and the finite element method. The objective of the optimization was to minimize the side lobe levels while focusing the ultrasound beam to a prescribed position. Based on the design, an experimental prototype of the transducer was fabricated and its performance was measured, which showed excellent agreement with the design.