PVDF transducers-a performance comparison of single-layer and multilayer structures

To improve the pulse-echo sensitivity of a piezopolymer transducer while preserving its broad bandwidth property, several multilayer transducer design approaches have been suggested. This paper presents formulae derived to describe three types of multilayer transducers: a folded multilayer-, Barker-coded, multilayer-, and switchable Barker-coded multilayer transducer. The pulse-echo responses of the multilayer transducers under various excitation signals were calculated and compared with those achievable with an equivalent PZT transducer. Also, the influence of a tissue layer on the transducer responses was examined. The simulation results indicated that the switchable Barker coded transducer design outperforms all other transducer designs analyzed with respect to the axial resolution and overall sensitivity in the medical imaging frequency range. To verify the simulation results, several prototypes of multilayer Barker coded transducers were fabricated and tested in water. A good agreement between the experimental results and the corresponding computer predictions was achieved.