Geometry-controlled focused ultrasound transducers fabricated by laser-assisted diamond turning of single-crystal PMN-PT.

Focused ultrasound transducer concentrates acoustic energy to enable inspection and treatment of localized target regions. To achieve precise control of focal zone, piezoelectric element is needed to be shaped as acoustically designed curvature. In this study, ultra-precision laser-assisted diamond turning approach was demonstrated as an effective manufacturing approach to fabricate a highly controlled curved structure. Four types of geometry were designed based on vibrational characteristics and were precisely fabricated using developed laser-assisted diamond turning approach. The machining quality and piezoelectric properties of the machined single-crystal PMN-PT were characterized, with a P-V form error below 2 μm and surface roughness Ra below 5 nm. Single-element piston-type ultrasound transducers were assembled and bandwidth characterization was conducted through pulse-echo evaluation. Especially, acoustic beam fields of focused ultrasound transducers were tested in both numerical and experimental methods. The machined elements exhibited the intended focusing effect, with the concave-convex model showing around 60% increase in intensity compare with flat shaped model, and a full width at half maximum(FWHM) of 2.98 mm at a focusing distance of 16.5 mm.