Piezoelectric materials for application in low profile interdigital transducer designs

This paper presents a comparative study between piezopolymer (PVDF) and piezo-platelet active layers in flexible interdigital transducer (IDT) designs for the generation of ultrasonic Lamb waves in thin plate structures. Initially, the pulse-echo response in steel was evaluated, where the piezo-platelet transducer demonstrates significant sensitivity advantage over the PVDF devices. The mechanical behaviour of each transducer was further investigated using a laser interferometer scanner to measure surface displacement and evaluate the extent of cross coupling and electrode pattern on the IDT response. Furthermore, finite element modelling has been utilised to evaluate the IDT coupling efficiency for the generation of a particular ultrasonic Lamb wave mode. Interestingly, it is shown that the properties of each transducer tend to be complementary with respect to a particular application. The piezo-platelet materials possess distinct advantages for generation of in plane, symmetric modes, especially for operation in composite plates, while the PVDF, although less efficient, has advantages with regard to cost and flexibility for the generation of anti-symmetric modes in metallic plates