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A virtual prototype focussed ultrasound surgery (FUS) transducer has been developed with finite element analysis (FEA) (OnScale, Redwood City, CA, USA) comprising a single piezocermic element and an acoustic Fresnel lens. The piezoceramic is supported by microbaloon filled epoxy to approximate an air backing. The transducer housing and Fresnel lens materials are photopolymer resins of the type used in mask stereolithography (mSLA) printers. The design is optimised in FEA for the materials used in the Fresnel lens and the active piezoceramic layer. Six piezoceramic materials produced by Meggitt A/S (Kvistgaard, Denmark) were characterised in FEA and the acoustic properties of the photopolymer resins were measured using a standard pulse-echo approach to find their sound speed and frequency-dependent attenuation. The piezoceramic materials characterised spanned four major types: soft (PZ29); hard (PZT4); a specialised composition for high intensity focused ultrasound (HIFU) (PZ54); and low acoustic impedance, porous (PZ36HD). Acoustic impedance matching between the active material and the lens allowed the porous piezoceramic with lower piezoelectric and coupling coefficients to reach a higher intensity, spatial peak temporal average, (I SPTA ) at the focus (3.6 kWcm−2) than the hard PZT (2.46 kWcm−2). The focal intensity improved when HIFU and soft PZT were used, producing 5.69 kWcm−2 and 6.35 kWcm−2respectively.

Lead zirconate titanate (PZT) piezoceramics exhibit non-linear behaviour when large electric fields are applied. This causes the material properties to change through heating and increased mechanical and electrical losses. These may contribute to unexpected device behaviour and ultimately to failure. It is therefore of fundamental importance to characterise piezoelectric materials under high-power driving conditions for applications requiring large electric field. Ten different PZT compositions were investigated in the work presented here. Length-thickness-extensional (LTE) d 31 -mode plates were characterized under small signal excitation through electrical impedance spectroscopy, with curve fitting software (PRAP, TASI, Ontario, CAN) used to obtain the material properties. Subsequently, a high-power characterisation system was assembled, including a signal generator (33210A, Agilent, CA, USA), power amplifier (2100L, E & I, NY, USA), AC current probe (P6022, Tektronix, ORE, USA), differential voltage probe (GE8115, GE, GER), and DAQ (USB6346, National Instruments, TEX, USA). Bespoke software was used to acquire the electrical impedance through fast sine wave frequency sweeps in the range 1–200 $V_{pp}$ . This enabled evaluation of material properties with large electrical excitation. Additionally, a 1-D laser Doppler vibrometer (OFV 303, Polytec, GER), was integrated into the set-up to determine the transient vibrational response and determine the mechanical quality factor.

We have designed, manufactured and tested a piezoelectric composite material to operate at temperatures above 400 degrees C. The material is a 1-3 connectivity composite with pillars of Z-cut lithium niobate in a matrix of alumina cement. The composite material produced shorter pulses than a monolithic plate of lithium niobate and remained intact upon cooling. Results are presented from room temperature and high temperature testing. This material could be bonded permanently to a test object, making it possible to carry out condition monitoring over an extended period. A new excitation method was also developed to enable remote switching between array elements.