Estimation and experiment on acoustic properties of rice straw (estimation of sound absorption coefficient based on CT image)

The sound absorption characteristics of rice straw were estimated using micro-CT scan images and theoretical analysis. Since it is difficult to express the structure and dimensions of rice straw in a regular manner, the voids in the straw were approximated as clearance between two parallel planes based on the micro-CT scan images. Using the surface area of the straw and the volume of the voids, a theoretical estimation of the sound absorption coefficient of the straw was made. Propagation constants, characteristic impedance, and normal incident sound absorption coefficient were obtained for the derived clearance. Since the rice straw is tubular, the sound absorption coefficient was also obtained assuming that an arbitrary CT scan image is continuous in the thickness direction. In addition, the sound absorption coefficient was estimated from ordinary photographs taken of the sample incident surface. In the experiments, the sound absorption coefficient was measured using a two-microphone impedance tube. The theoretical values were close to the experimental value.