Focused spherical transducers for ultrasonic imaging

Spherically focused transducers were from miniature thin-wall lead zirconate titanate hollow spheres (BBs). The spheres were prepared from slurries of soft PZT powders using a coaxial nozzle process, and had diameters ranging from 1 to 6 mm and wall thickness from 12 to 150 /spl mu/m. Two main vibrations modes, namely radial and thickness modes, were obtained around 1 MHz and 30-40 MHz, respectively. Focused transducers were prepared by machining sections of the hollow spheres. The transducers were characterized in pulse echo mode and by using finite element analysis (FEA). The results obtained from experiments were confirmed by FEA. The transducers were found to have a center frequency of /spl sim/48 MHz with a bandwidth of 22% and a minimum insertion loss of -44 dB.