Combining multi-layers and composites to increase SNR for medical ultrasound transducers
Current 1.5-D and 2-D array elements suffer low capacitance resulting in high electrical impedance. The impedance mismatch between the 50Ω transmitter source impedance and the high impedance array elements decreases efficiency. Multi-layer PZT designs using interlaminar vias have been proposed to solve this problem by lowering the impedance of the array element. Another problem is the poor acoustic match of PZT to tissue, which can be improved with PZT/polymer composite designs. By combining multi-layer PZT and composite designs, new transducers can be developed to further improve SNR. Multi-layer 1-3 composite transducer array elements have been modeled with 3-D FEM simulations and fabricated at 0.9 MHz. Another new design is a 16 PZT layer 2-2 composite with inter-laminar electrodes. According to finite element (PZFlex) simulations, the array element will have a resonant frequency near 4 MHz and an impedance magnitude of 50Ω. Unlike conventional transducer arrays, this design operates in the transverse mode. Computer simulations show that despite the loss from operating in the transverse mode, this novel multi-layer 2-2 composite design will yield an overall SNR improvement relative to 2-2 composites and increased bandwidth relative to conventional PZT.
