Conditions for sound absorption caused by longitudinal vibration of lightweight powder

It has been reported that powder layers composed of powder materials with a grain diameter of several tens of micrometers exhibit significant sound absorption capabilities in the low-frequency range when the bulk powder density is low. In a previous study, a model considered factors like “powder vibration” and “sound wave attenuation due to gaps between powders.” The remaining challenge lies in the unknown conditions under which a powder with a high sound absorption coefficient is formed through the attenuation of acoustic energy due to the longitudinal vibrations of the powder. In this study, we aimed to estimate these conditions based on the grain size and bulk density. The relationship between the “areal density per grain layer,” expressed as “grain diameter X bulk density,” and the first-order sound absorption peak value revealed that the sound absorption coefficient increases as the areal density per grain layer decreases.