35-MHz linear array for medical imaging

This paper discusses the design, fabrication and testing of a 35 MHz linear ultrasonic array. The array features monolithic piezoelectric elements diced out of TRS 600FGHD fine grain high-density ceramic. A lossy urethane doped with gas filled microspheres is used as a kerf-filler to dampen inter-element acoustic propagation and reduce pulse length. The array incorporates a slotted single matching layer made from an unloaded epoxy. This matching layer also contributes to the reduction of pulse length and an increase in sensitivity. Array elements are spaced by a 50 mm pitch and interconnected via a flexible circuit. An 85 (Omega) transmission line coaxial cable is used to electrically match the array elements to the 50 (Omega) system electronics. The final 64-element array design is based on experimental results obtained from several four-element prototype arrays. An average center frequency of 34 MHz with a -6 dB bandwidth of at least 45% is achieved with the final prototype array. The maximum combined electrical and acoustical cross-talk for nearest and next nearest elements is less than -29 dB. The average -40 dB pulse length is 105 ns. The simple design and satisfactory performance of this array make it suitable for large-scale production.