High frequency (>20 MHz) spherically shaped ceramic transducers

Difficulty in obtaining well focussed efficient ultrasound transducers has limited the development of new high frequency applications of B-mode imaging. A method of fabricating high frequency spherically shaped lead zirconate titanate (PZT) transducers is described. A transducer is fabricated by bonding a malleable backing layer onto a thin (<100 μm) plate of PZT and then pressing the plate into a spherically shaped well. The backing layer distributes stresses across the material and allows the transducer to be formed without the development of macroscopic cracks. The characteristics of a 2 mm diameter 53 MHz PZT transducer with a 4 mm focal distance are described. This device demonstrated a two-way insertion loss of -25 dB with a 6 dB bandwidth of 30%. A lateral beam width at the focal region of 68 μm was measured. The theoretical diffraction limited beam width is 59 μm. Images of a resolution phantom and normal human skin demonstrate the potential of these transducers in a realistic clinical application