Piezocrystal-polymer composites: New materials for transducers for ultrasonic NDT

Piezoceramic-polymer composite materials are finding increasing acceptance in ultrasonic transducers for NDT. However, new piezocrystal materials are also becoming available, such as lead zinc niobate doped with lead titanate (PZN-PT). Made into piezocomposite, they have significant theoretical performance advantages. Although the new materials are presently more expensive than piezoceramic, their prices have recently fallen dramatically, making them viable for high-end NDT. In this paper, the authors first review the background to the new piezocrystals then report their experience in piezocomposites made with them. The authors describe how they have predicted the main piezoelectric properties of these piezocomposites, establishing a robust design process. The composite fabrication method is outlined and the properties for four different single-crystal volume fractions are reported. Prototype elements have been realised in the form of coupons approximately 5 mm × 10 mm suitable for dual-element probes and these probes have been evaluated on test objects of various materials, including a steel block, an aluminium block and a carbon fibre reinforced composite (CFRC) panel. The results confirm that the theoretical performance advantages can be achieved in practice, including doubling the gain-bandwidth product compared with conventional piezoceramic-polymer composite. It is concluded that applications such as ultrasonic spectroscopy, inspection of difficult materials and multi-element imaging arrays may benefit significantly.