A Novel Matching Layer Design for Improving the Performance of Transparent Ultrasound Transducers

Transparent ultrasound transducer (TUT) technology allows easy co-alignment of optical and acoustic beams in the development of compact photoacoustic imaging (PAI) devices with minimum acoustic coupling. However, TUTs suffer from narrow bandwidth and low pulse-echo sensitivity due to the lack of suitable transparent acoustic matching and backing layers. Here, we studied translucent glass beads (GB) in transparent epoxy as an acoustic matching layer for the transparent lithium niobate piezoelectric material-based TUTs (LN-TUTs). The acoustic and optical properties of various volume fractions of GB matching layers were studied using theoretical calculations, simulations, and experiments. These results demonstrated that the GB matching layer has significantly enhanced the pulse-echo sensitivity and bandwidth of the TUTs. Moreover, the GB matching layer served as a light diffuser to help achieve uniform optical fluence on the tissue surface and also improved the photoacoustic (PA) signal bandwidth. The proposed GB matching layer fabrication is low cost, easy to manufacture using conventional ultrasound transducer fabrication tools, acoustically compatible with soft tissue, and minimizes the use of the acoustic coupling medium.