Fine pitch non-uniform multilayered linear ultrasound phased arrays for medical imaging: Design and testing

Due to their higher transmit efficiency and better received SNR compared to single layer technology, multilayer transducers with uniform layers (MLU) are currently in research and use. Altering the intrinsic geometrical or material homogeneity (i.e. different thicknesses of the constitutive layers, piezoceramic/piezocomposite or piezoceramic/piezopolymer stacks) will increase the available degrees of freedom in transducer design. The paper presents parametric modeling and experimental results related to the development of a CTS 3203 HD based fine pitch 2.5 MHz multilayered phased array with non-uniform thickness of the constitutive layers (MLNU). As reference transducers, a uniform multilayered phased array developed in parallel and a customly produced single layer phased array (SLPA) were used. Based on pulser-receiver pulsed excitation measurements, MLNU prototypes exhibited a 12% and 15 % higher transmit and receive respectively bandwidth at -6dB (BW_-6dB) at centre frequency (f_c) compared to MLU. In receiving, the second harmonic level was ~ 15 dB down with respect to the f_c. Considerable surface heating was measured in the case of MLNU. Using resistors placed in parallel with the active elements decreased MLNU equilibrium temperature by 47% while transmit and receive relative sensitivities improved by 38% and 22% respectively. Due to its lower input impedance, MLNU required low inductance series tuning components. As a result, for a similar round-trip sensitivity MLNU exhibited a 2 times higher BW_-6dB compared to SLPA.