Analysis and design of piezocomposite ultrasonic transducers using finite element technique and surface displacement profiles

Ultrasonic transducers have found extensive applications in the fields of non-destructive testing, biomedicine, and SONAR. Piezocomposite ultrasonic transducers can offer significant advantages over their pure ceramic counterparts, but at the expense of increased manufacturing complexity and the introduction of additional resonant modes that may reduce transducer efficiency if the device is not carefully designed. Extensive work has been carried out over the last twenty years to characterise the behaviour of piezocomposite devices, resulting in many design guidelines, some of which are only applicable in a limited range of device structures. This Thesis presents a new theory of the generation of inter-pillar modes that is based upon the generation of Lamb waves in the piezocomposite plate. Through the use of finite element analysis and a scanning laser interferometer, the resonant mode displacement shapes of piezocomposite transducers are studied and analysed. Excellent correlation between modelled and experimental results is observed, and leads to the conclusion that Lamb waves, rather than Bragg scattering, are responsible for the generation of the high frequency inter-pillar modes. To facilitate these analyses, a comprehensive finite element modelling procedure that includes all piezocomposite microstructure effects as well as matching, backing and fluid loading effects was developed. Additionally, it was demonstrated that for low drive voltages, the acousto-optic effect has minimal effect on the through-water laser scanning of piezocomposite transducers. Finally, the analysis tools developed for the examination of piezocomposites were used to improve the design of an existing flexible ultrasonic transducer used for non-destructive te.sting. This resulted in a thinner, higher frequency, pulse-echo device capable of producing similar results to the original, while considerably reducing the complexity of the transducer. (author)