Development of high frequency annular arrays for medical imaging

A 3 mm, 50 MHz ultrasound annular array incorporating six equal-area elements was designed and fabricated. The array incorporated fine-grain lead titanate to reduce lateral coupling. The kerfs were diced to 30 microns using laser micromachining. A lens was used to provide an f-number of 3. The interconnect was achieved by sputter masking and application of silver epoxy. The average center frequency and bandwidth of the array elements was 55 MHz and 22%, respectively. The maximum nearest-element crosstalk throughout the passband was measured as -22 dB in water, and insertion loss varied from 11-29 dB. Imaging of an 8 μm wire target with one of the outer elements showed a practical imaging depth starting under 6 mm, which agreed well with simulations.