Powder agglomeration patterns at acoustic driving observed by sonoluminescence technique

A sonoluminescence (SL) technique gives a sensitive probe to detect spatial agglomeration patterns produced in powder mixtures subjected to acoustical ly driven plate. Studies of the surface-integrated SL intensity with increa sing driving amplitude yield data about variations of the packing density o n the surface of vibrating powders. Imaging of spatial distributions of the SL intensity enables direct measurement of the size of agglomeration patte rns. The size of the patterns is found to be similar to 10(2) mu m in a 3-m u m-sized powder at a driving frequency of about 4 MHz. The distribution of the average sonoluminescence intensity across the pattern is attributed to the density gradient while rapid variations in the SL intensity across the pattern are suggested to give the particle velocity distribution within th e pattern. The temporal changes of the SL intensity can be used to study ti me evolutions of dense powder arrangements. (C) 1999 American Institute of Physics. [S0021-8979(99)01302-X].