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%.