F Transducers-A Performance omparison of Single-Layer and ultilayer Structures

To improve the pulse-echo sensitivity of a piezopolymer transducer while preserving its broad band- width property, several multilayer transducer design ap- proaches have been suggested. This paper presents formulae derived to describe three types of multilayer transducers: a folded multilayer-, Barker-coded, multilayer-, and switch- able Barker-coded multilayer transducer. The pulse-echo responses of the multilayer transducers under various ex- citation 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 switch- able Barker coded transducer design outperforms all other transducer designs analyzed with respect to the axial res- olution and overall sensitivity in the medical imaging fre- quency range. To verify the simulation results, several pro- totypes of multilayer Barker coded transducers were fabri- cated and tested in water. A good agreement between the experimental results and the corresponding computer pre- dictions was achieved.