Characteristic of absorbing sound in lotus-type porous copper fabricated by unidirectional solidification

Lotus-type porous copper with a high number of unidirectional cylindrical pores was fabricated by unidirectional solidification of melt dissolving hydrogen in a pressurized hydrogen atmosphere. The sound absorption coefficient of porous copper whose specimen face has many open pores was measured by a standing-wave method in the range up to the sound frequency of 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 size. In addition, it was understood that the absorption coefficient of lotus-type porous materials can be determined by using the attenuation constant.