Effects of sound field on the fluidization of fine particles have been comprehensively examined by using fine powders (4.8-65 mu m average in size) including Al2O3, TiO2, glass beads and FCC catalyst. It is found that the fluidization quality of fine particles can be enhanced with the assistance of a sound field, resulting in higher pressure drops and a lower u(mf). The effect of sound on the fluidization of fine particles is strongly dependent on the particle properties (Geldart type and particle size) as well as the parameters of the sound field such as sound pressure level (or intensity) and frequency. Given a fixed sound frequency, the effect becomes more significant at a higher sound pressure level. For the present sound-aided fluidized bed system, there is a resonant frequency at about 100-110 Hz, at which the effectiveness of the sound wave in improving fluidization of fine particles is most remarkable. In addition, based on the different attenuation features of sonic waves in the gas-solid suspension of group C and A particles, a novel acoustic method is explored to distinguish group C from group A particles. (c) 2005 Elsevier B.V. All rights reserved.