Effects of Ceramic Nanopowder Dopants on Acoustic Attenuation Properties of Silicone Rubber Lens for Medical Echo Probe

The effects of fine ceramic powder dopants, namely, TiO2, Al2O3, BaSO4, Fe2O3, ZrO2, and Yb2O3 with primary particle sizes of 16–100 nm, on the acoustic properties of silicone rubber have been investigated, in order to develop an acoustic lens material for medical echo probes with a low acoustic attenuation (α). Silicone rubber doped with Yb2O3 powder having a high density (ρ) of 9.2×103 kg/m3 and an average particle size of 16 nm showed a lower acoustic attenuation than silicone rubber doped with other powders. The materials showed ρ=1.54×103 kg/m3, a sound velocity (c)=882 m/s, an acoustic impedance ρ·c (Z)=1.36×106 kg m-2 s-1, and an acoustic attenuation α=0.93 dB mm-1 MHz-1 at 37 °C. Silicone rubber doped with Fe2O3 powder having ρ=5.2×103 kg/m3 and an average particle size of 30 nm showed the highest α=2.36 dB mm-1 MHz-1 and Z=1.47×106 kg m-2 s-1. Microstructure observation of the rubber by scanning microscopy revealed that the α of the powder-doped rubber is not only determined by the primary particle size of the powders but also by the dispersion and agglomeration of the secondary particles in the rubber matrix. The discovery of the process parameter required to reduce the α of the nanopowder-doped silicone rubber has an important practical consequence.