Materials for acoustic matching in ultrasound transducers

Acoustic impedance (Z) and fabrication issues for matching layers in high frequency transducers were identified. Guided by a density/impedance relationship established for various polymers, glasses, ceramics and metals, few monolithic materials with Z in the range of 6-9 MRayls were found. Composites of gold- and silver-polymer resulted in the desired impedances, however, with increased attenuation. Issues of microstructural scale, homogeneity and particle size effects were noted including issues of percolation behaviour for conducting composites. Using PiezoCad, the effect of matching layer thickness and impedance variation of a 100 MHz transducer were modeled.