High frequency imaging transducers from hollow spheres

Single element transducers were designed and built using shelf sections of piezoelectric hollow spheres. The shell sections provide inherent focal depths and allow for the easy production of low f-number transducers. Because of the low f-numbers, these transducers have improved lateral resolution compared to other transducers operating at the same frequency. Spheres were mass-produced using the sacrificial core technique and had diameters of 1-3 mm and wall thickness from 20 to 120 /spl mu/m. The lead titanate transducers described here had thickness mode resonance frequencies ranging from 25 MHz to 70 MHz. Electromechanical properties and pulse-echo response of these transducers were evaluated. Skin images taken with an Ultrasonic Backscatter Microscope at 55 MHz are also presented.