Low-intensity focused ultrasound (LIFU) has the potential to improve clinical outcomes and replace the currently available neuromodulation techniques. Currently, single-element transducers are typically used in LIFU to generate ultrasound with fixed focus. 

Normally, a two-dimensional (2D) array with a small pitch (approximately 0.5λ in medium) can achieve a complete three-dimensional control of ultrasound beams. However, the large electrical impedance of 2D array elements caused by their small size leads to a low energy transfer efficiency between a 2D array and an electrical system, thereby limiting their practical applications.  

Researchers from the Shenzhen Institutes of Advanced Technology (SIAT) of the Chinese Academy of Sciences developed a 1-MHz 256-element 2D array ultrasonic transducer of low electrical impedance based on a new Sm-doped Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (Sm-PMN-PT) piezoceramic with ultrahigh dielectric permittivity. 

The array elements were spaced at a 1.1 mm pitch (0.71λ in water), which enabled a large steering range of the ultrasound beam, and its electrical impedance was decreased as the Sm-PMN-PT replacing the commercial PZT-5H. 

The output acoustic pressure of the proposed 2D array was approximately twice that of the 2D array made of PZT-5H ceramic under the same excitation conditions.  

Blood-brain barrier (BBB) opening evaluation experiments using the proposed 2D array with electronic focusing and steering confirmed the ability of opening the BBB at multiple targets. The results indicated that the 2D array made of Sm-PMN-PT ceramic is promising for practical use in low-intensity ultrasound therapy applications. 

The study was published in IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 

Schematics of the designed 2D array transducer and major components (Image by ZHANG Zhiqiang)