Spatial Fourier-transform method for measuring reflection coefficients at oblique incidence. II. Experimental results

A method using spatial Fourier transforms for measuring the plane-wave reflection coefficient at oblique angles of incidence has been proposed in an earlier paper [M. Tamura, J. Acoust. Soc. Am. 88, 2259–2264 (1990)]. The present paper gives experimental verification of the method. Experimental results are shown for two types of samples: a perfectly absorbing plane (an imaginary plane in the air) and a layer of a polyurethane foam backed by a hard plywood board. The measured results are generally in good agreement with the theoretical value (for the first sample) or with the results calculated from the acoustical parameters of the material (for the second sample). The agreement shows the usefulness of the method for measuring acoustic properties of absorbent materials.