Sound speed change with concentration in nano particle suspension

Based on the multi-scattering theory for the micro particles, sound speed of the TiO 2 nano particle suspension with ultra-low concentration was estimated. Good agreement was found between the estimated results and the experimental ones. The sound speed of 5 MHz ultrasound was measured with high accuracy, decreasing by about 0.15 m/s as concentration of suspension was changed in the range from 0.002 wt.% to 0.02 wt.%. From the experimental result, it is expected that the concentration of nano particle suspension is possibly estimated from the sound speed change.