Multi-layered PZT/polymer composites to increase signal-to-noise ratio and resolution for medical ultrasound transducers. II. Thick film technology

For pt.I, see ibid., vol.46, no.4, p.961-71 (1999). 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. Thus, we have developed a multi-layer composite hybrid array that will not require post alignment. Starting from a 2-MHz, three-layer PZT-5H, thick film transducer designed for 1.5-D arrays, cuts are made only through the top layer and back-filled with epoxy, forming a composite layer on top of two ceramic layers. Finite element (PZFlex) simulations show that for a 2-MHz phased-array element with a single matching layer, the three-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. Composite hybrid arrays fabricated in our laboratory showed an improvement in SNR of 6 to 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.