Effects of Fine Metal Oxide Particle Dopant on the Acoustic Properties of Silicone Rubber Lens for Medical Array Probe

The effects of fine metal oxide particles, particularly those of high-density elements (7.7 to 9.7 times 10
³
kg/m
³
), on the acoustic properties of silicone rubber have been investigated in order to develop an acoustic lens with a low acoustic attenuation. Silicone rubber doped with Yb
₂
O
₃
powder having nanoparticle size of 16 nm showed a lower acoustic attenuation than silicone rubber doped with powders of CeO
₂
, Bi
₂
O
₃
, Lu
₂
O
₃
and HfO
₂
. The silicone rubber doped with Yb
₂
O
₃
powder showed a sound speed of 0.88 km/s, an acoustic impedance of 1.35 times 10
⁶
kg/m
²
s, an acoustic attenuation of 0.93 dB/mmMHz, and a Shore A hardness of 55 at 37degC. Although typical silicone rubber doped with SiO
₂
(2.6 times 10
³
kg/m
³
) shows a sound speed of about 1.00 km/s, heavy metal oxide particles decreased the sound velocities to lower than 0.93 km/s. Therefore, an acoustic lens of silicone rubber doped with Yb
₂
O
₃
powder provides increased sensitivity because it realizes a thinner acoustic lens than is conventionally used due to its low sound speed. Moreover, it has an advantage in that a focus point is not changed when the acoustic lens is pressed to a human body due to its reasonable hardness.