Minimisation of mechanical cross talk in periodic piezoelectric composite arrays

This paper describes an investigation into mechanical cross-talk within 1-3 and 2-2 connectivity piezoelectric composite array configurations, comprising a matrix of active piezoelectric elements embedded within a passive, polymeric, material. One way to take full advantage of the reported sensitivity and bandwidth improvements from single-crystal materials is to configure them as a piezoelectric composite. For this work, piezoelectric ceramic, lithium niobate and single-crystal pmn-pt materials are investigated as the active component in the piezocomposite array designs. Within these piezoelectric configurations, the generation of ultrasonic inter-pillar modes, which arise due to the periodicity of the active piezoelectric elements within the piezocomposite lattice, can be detrimental to the array performance. Consequently, finite element (FE) modelling, using PZFlex, is utilised to provide design techniques for the removal of these inter-pillar modes from the frequency band of interest and the realisation of unimodal piezocomposite transducer structures. Further FE modelling is used to generate dispersion data for 2-2, and doubly periodic 1-3, composite substrates. This dispersion data is used to design the linear arrays, with the objective of minimising mechanical inter-element cross-talk. A comparison between the FE predicted mechanical cross-coupling between array elements, for each composite material operating in air, is supported by experimentally measured data. Subsequently, the validated FE models are extended to include both operation into a solid load and the introduction of a backing material to simulate the operation of a practical NDE array transducer. The design techniques obtained from PZFlex are shown to produce arrays with low cross-talk and the extent of the cross-talk in manufactured and modelled ceramic and pmn-pt single-crystal arrays is compared