New Sm-PMN-PT Ceramic-Based 2-D Array for Low-Intensity Ultrasound Therapy Application

A two-dimensional (2-D) array with a small pitch (approximately 0.5\lambda in medium) can achieve complete 3-D control of ultrasound beams without grating lobes and enable the generation of multiple focal spots simultaneously, which is a desired tool for noninvasive therapy. However, the large electrical impedance of 2-D array elements owing to their small size results in a low energy transfer efficiency between a 2-D array and an electrical system, thereby limiting their practical applications. This article presents the development of a 1-MHz 256-element 2-D array ultrasonic transducer of low electrical impedance based on a new Sm-doped Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (Sm-PMN-PT) piezoceramic with ultrahigh dielectric permittivity. The electrical impedance of the array element is decreased by 3.4 times as the Sm-PMN-PT replacing commercial PZT-5H. Consequently, the output acoustic pressure of the 2-D array made of Sm-PMN-PT ceramic is approximately twice that of the 2-D array made of PZT-5H ceramic under the same excitation conditions. Array elements are spaced at a 1.1-mm pitch ( 0.71\lambda in water), enabling a large steering range of the ultrasound beam. A multiple-target blood-brain barrier opening in vivo is demonstrated using the proposed 2-D array with electronic focusing and steering. The obtained results indicate that the 2-D array made of Sm-PMN-PT ceramic is promising for practical use in low-intensity ultrasound therapy applications.