Fabrication and performance of a 40-MHz linear array based on a 1-3 composite with geometric elevation focusing

The fabrication and performance of a 256-element high-frequency (40-MHz) linear array is described. The array was fabricated using a high-frequency 1-3 PZT-polymer composite material developed in our laboratory. The spacing of the pillars in the composite was chosen to match the 40-mu m center-to-center element spacing of the array electrodes. The element electrodes were created using photolithography, and connections to the electrodes were made using ultrasonic wire bonding. The array was focused in the elevation direction by geometrically shaping the composite material using a cylindrical die with a 6-mm radius of curvature. The resulting transducer produced pulses with a -6 dB two-way bandwidth of 50% and a peak-to-peak pressure of 503 kPa when excited with a +/- 30 V monocycle pulse. The measured one-way (-6 dB) directivity for a single array element was 24 degrees and the -3 dB one-way elevation beamwidth was measured to be 130 mu m. The radiation pattern for a focused 64-element subaperture was measured by mechanically translating the aperture above a needle hydrophone. A -3 dB one-way beamwidth of 97 mu m was found at a depth of 6 mm. The one-way radiation pattern decreased smoothly to less than -30 dB at a lateral distance of 640 mu m.