Compact piezoelectric transducers for lithotripsy

Abstract

Self-focusing piezoelectric transducers are widely used in extracorporeal shockwave lithotripsy. This application demands high focal pressure pulse amplitudes, small focal beamwidths and large penetration depths, which results in large transducers with typical dimensions of 350-mm focal distance and 500-mm diameter. Against the background of the development of smaller and therefore more economical devices it is still desirable to reduce the transducer size but keep the acoustic properties. This can be achieved only by an increased initial pressure amplitude at the transducer surface. Since the single piezoelectric elements are driven close to their electrical limit, a different mechanical design is necessary. Piezoelectric elements placed in a layered manner on both sides of a spherical cap could provide a significant increase of the pressure pulse amplitude generated at the transducer surface. Three-dimensional FEM simulations of the transducer structure including all important design parameters, like the electrical drive for both sides, show the ability of generating higher amplitudes by keeping similar pulse shapes. Measurements made on a prototype transducer with a diameter of 270 mm and a focal distance of 200 mm show comparable results to the standard single-layered design regarding peak focal pressure amplitude and spatial amplitude distributions.