Piezoelectric Transducer Design for Medical Diagnosis and NDE

The number one technique for medical imaging and non-destructive evaluation (NDE) is ultrasound. This is due to its non-ionizing character, low cost and to the fact that images and measurements contain data linked to several physical and structural parameters of the explored media. The overall performance of an ultrasonic system is mainly determined by the transducer characteristics. Consequently, each application having its specific requirements, very different transducers need to be designed. Furthermore, the measurement techniques and imaging modalities are in constant evolution, requiring higher performance and versatility of the transducers. Not only must frequency bandwidth and sensitivity be increased, but transducers must also be able to operate in various modes such as pulse-echo (classical A, B or C modes), burst (Doppler or other velocity measurements) or harmonic reception (non-linear acoustics). Innovations such as ultrasound stimulated elastography and combination of different techniques such as ultrasound and MRI or ultrasound therapy and imaging are only possible if specific transducers are developed. The structure of a single-element ultrasonic transducer based on piezoelectric effect is first described, with particular focus on the influence of the constitutive materials on transducer performance. More complex transducers such as annular, linear, curved, phased, and 2D arrays are described and most important design issues discussed. Piezoelectric material issues relative to transducer applications are then addressed. Methods to characterize and models to predict transducer behaviour are presented, and several comparisons are shown to illustrate achieved performance. Finally, transducers designed for high-resolution imaging are presented, and other current developments briefly described. Some particularly interesting future trends are highlighted in the conclusion.