Surface waves over periodically-spaced rectangular strips

Frequency- and time-domain measurements have been made on surfaces composed from parallel periodically-spaced rectangular strips (width: 0.0126 m, height: 0.0253 m) on an acoustically hard surface. The edge-to-edge spacing between the strips has been varied between 0.003 and 0.06 m. Frequency domain predictions show that when the spacing is small, these surfaces may be regarded as locally reacting rigid-framed hard-backed slit-pore layers with an effective depth slightly larger than the strip height, but when the spacing is comparable to the strip height or greater, the surfaces behave as periodically rough surfaces. Both frequency- and time-domain results show that surface waves of comparable magnitudes are created over the range of strip spacings studied but the frequency content of the acoustically induced surface waves decreases as the mean spacing is increased. It is found that surface wave dispersion is better predicted by the deduced effective impedance spectrum than by the slit-pore layer impedance model.