Predicting Lightweight Powders with Useful Sound Absorption Characteristics from Their Specifications

Powders that absorb sound by longitudinal vibration have either a gentle or sharp sound absorption curve at the first absorption peak frequency. Experiments were performed to investigate the conditions under which longitudinal vibration occurs in powders of various grain sizes and bulk densities. The sound absorption characteristics of the powders were then classified according to their specifications, and the sound absorption coefficients predicted by derived empirical equations were compared with the measured sound absorption coefficients. A threshold value for the areal density per grain layer was identified where lightweight powders at 0.0006 g/cm2 or less demonstrated useful sound absorption characteristics via longitudinal vibration. Powders with smooth (i.e., useful) and sharp (i.e., not useful) sound absorption curves could be further identified by the half-width value at 0.0974 < log f2 − log f1 < 0.119 decade. The bulk density can also be used to identify powders with useful sound absorption characteristics at 0.0868 < ρ < 0.124 g/cm3. A regression analysis was performed to obtain empirical equations expressing the relationship between the areal density per grain layer and first sound absorption peak frequency normalized by the layer thickness.