ISO 20998-3:2017 gives guidelines for ultrasonic attenuation spectroscopy methods for determining the size distributions of one or more material phases dispersed in a liquid at high concentrations, where the ultrasonic attenuation spectrum is not a linear function of the particle volume fraction. In this regime, particle-particle interactions are not negligible.

ISO 20998-3:2017 is applicable to colloids, dispersions, slurries, and emulsions. The typical particle size for such analysis ranges from 10 nm to 3 mm, although particles outside this range have also been successfully measured. Measurements can be made for concentrations of the dispersed phase ranging from about 5 % by volume to over 50 % by volume, depending on the density contrast between the continuous and the dispersed phases, the particle size, and the frequency range^{[9] [10]}. These ultrasonic methods can be used to monitor dynamic changes in the size distribution, including agglomeration or flocculation.