Pre-focused lead titanate > 25 MHz single-element transducers from hollow spheres

Miniature lead titanate (PT) hollow spheres with diameters in the 1 to 10 m m range and wall thicknesses of 20 to 120 mum have been fabricated. Shell s ections were used as components of pre-focused transducers. Spheres are pro duced using a new sacrificial core technique that produces hundreds of sphe res with a more uniform wall thickness than those produced by earlier metho ds. Shells produced from these spheres were found to have a wall thickness variation of about 10%. Despite this variation, bulk properties were estimated from capacitance and impedance data. Shells tested in this work had dielectric constants (1 kHz ) near 280 with loss factor of <2% and d(33) values of 68 pC/N. Thickness c oupling coefficients averaged 0.51 with mechanical quality factors of <15. A transducer fabricated from these sections of spheres had a round-trip ins ertion loss of -20.1 dB at the center frequency of 39.8 MHz and a 6 dB band width of 33%.