Sound absorption characteristics of lotus-type porous copper fabricated by unidirectional solidification

Lotus-type porous copper with large number of unidirectional cylindrical pores was fabricated by unidirectional solidification of melt dissolving hydrogen in a pressurized hydrogen atmosphere. The sound absorption coefficient of the porous copper plate, which has many open pores, was measured by standing-wave method in the frequency range up to 4 kHz. The absorption coefficient increases with increasing frequency. The absorption coefficient increases with increasing porosity and specimen thickness, while it decreases with increasing pore diameter. In addition, it was understood that the absorption coefficient of lotus-type porous materials could be evaluated by using the attenuation constant.