Multi-layer composite hybrid transducer for medical ultrasound
Increasing transducer bandwidth and signal-to-noise ratio (SNR) is fundamental to improving the quality of medical ultrasound images. In previous work, we have proposed the use of multi-layer 1-3 PZT/polymer composites to increase both, but have encountered significant fabrication challenges. These difficulties include making the bond thickness between the layers small relative to the ultrasound wavelength and aligning the posts of the composite to increase coupling coefficient. Thus, we developed a multi-layer composite hybrid array that will not require post alignment. Starting from a 2 MHz 3 layer PZT-5H thick film transducer, cuts are made only through the top layer and back-filled with epoxy forming a composite layer on top of 2 ceramic layers. Finite Element (PZFlex) simulations show that for a 2 MHz phased array element with a single matching layer, the 3 layer hybrid structure increases the pulse echo SNR by 11 dB versus a single layer PZT element and improves -6 dB pulse echo fractional bandwidth by a factor of 1.4. A composite hybrid array fabricated in our laboratory showed improvement in SNR of 11 dB over a PZT control and an increase in -6 dB bandwidth by a factor of 1.1. Images from a phased array scanner confirmed these improvements.
