A miniature FUS transducer based on an acoustic Fresnel lens for integration with a surgical robot

Abstract

• A novel focused ultrasound transducer based on a Fresnel lens fills a size gap for robotic integration. • Four piezoelectric materials are evaluated for the single driving disc. • Additive manufacturing materials are evaluated for the acoustic lens and housing. • A novel focal zone steering mechanism is demonstrated that is based on frequency steering . A new focussed ultrasound surgery (FUS) transducer for soft tissue ablation is proposed, with a miniaturised configuration that can be readily integrated with a surgical robot. The transducer fills a gap in FUS technology at this size, with capability for acoustic focus steering within a very simple transducer configuration. Miniaturisation is enabled by the incorporation of an acoustic Fresnel lens as the focussing element driven by a single piezoceramic disc. The transducer housing and Fresnel lens are made from photopolymer resins in a mask stereolithography (mSLA) printer and a microballoon filled epoxy backing layer is added to approximate an air backing. In this study, four versions of the miniature FUS transducer were fabricated and tested, each incorporating a different piezoceramic material: a soft PZT, a specialised composition for high intensity focused ultrasound, a low acoustic impedance porous PZT, and a lead free piezoceramic. It is shown that the FUS transducer containing the porous piezoceramic disc, which has lower piezoelectric and coupling coefficients than the other materials, achieves the highest focal zone intensity. Through finite element analysis (FEA) and experimental characterisations of the acoustic field, the FUS transducer is demonstrated to be capable of both creating and steering a focal intensity suitable for tissue ablation.