Effects of Ytterbium Oxide Nanopowder Particle Size on the Acoustic Properties of Silicone Rubber Lens for Medical Echo Array Probe

The effects of Yb 2 O 3 powder particle size, namely, 2000, 16, and 8 nm, on the physical and acoustic properties of a high-temperature-vulcanization (HTV) silicone (Q) rubber have been investigated in order to develop an acoustic lens material with a low sound velocity ( c ) and acoustic attenuation coefficient (α). The Yb 2 O 3 -doped HTV Q rubber with the large particle size of 2000 nm showed a density (ρ) of 1.6 × 10 3 kg/m 3 , with c = 828 m/s, characteristic acoustic impedance ( Z ) = 1.32 × 10 6 kg·m -2 ·s -1 , α= 1.32 dB·mm -1 ·MHz -1 , and an α-figure of merit (FOM) (α × c ) of 1090 at 5 MHz at 37 °C. For the Yb 2 O 3 -doped Q rubber with the small particle size of 8 nm, ρ= 1.57 × 10 3 kg/m 3 , c = 864 m/s, Z = 1.36 × 10 6 kg·m -2 ·s -1 , α= 0.68 dB·mm -1 ·MHz -1 , and α-FOM = 590. The 16 nm Yb 2 O 3 -doped Q rubber had intermediate values of α= 0.88 dB·mm -1 ·MHz -1 and α-FOM = 760. These results show that there is a clear dopant particle size dependence on the acoustic properties of Yb 2 O 3 -doped HTV Q rubbers. The 8-nm-doped HTV Q rubber also showed an excellent mechanical properties for practical application. Microstructure observation revealed that the low-α rubber shows a uniform Yb 2 O 3 nanopowder distribution in the HTV Q rubber matrix.