A study of inversion layer transducers

Much recent interest has been expressed regarding inversion layer piezoelectric transducers. These are multi-layered devices, incorporating a reversal in piezoelectric polarisation in the stack thickness, creating the potential for extended bandwidth and enhanced even harmonic sensitivity in thickness drive structures. The transducer properties are determined in turn by the relative dimensions of the polarised zones, in addition to the mechanical load conditions at the transducer boundaries. This work presents an evaluation of different inversion layer configurations and piezoelectric materials, using the FE code PZFLEX as a virtual prototyping tool. The influence on non-uniform piezoelectric boundaries in lithium niobate transducers is addressed. The potential for multiple piezoelectric zones is also investigated, through modelling of three and more inversion layers through the transducer thickness. The influence of backing and matching on the transducer bandwidth and sensitivity is also considered. Experimental data is provided for lithium niobate plates and piezoelectric composite transducers, with the latter geared towards the enhanced detection of second harmonic backscatter in contrast agent imaging.