Acoustic scattering from a suspended ceiling with perforated facing
This paper focuses on the scattering effect of a finite perforated plate suspended from a rigid backing. In the considered frequency range up to 5 kHz, the period of the perforation is much shorter than the trace wavelength of the incident wave on the structure. Therefore a perforated plate behaves as a flat homogeneous plate with uniform porosity. Thus only the specular reflected wave is transmitted from the perforated plate to far field, while the others exponentially decay. As a result the scattering effect is caused by the finiteness of the structure. It indicates that as the length of the specimen increases, the scattering coefficient approaches zero. Nevertheless, the perforated plate modifies the directional distribution of the reflected sound pressure by its absorption. It is well-known that, when the quarter wavelength of the sound wave is equal to the suspension height of the perforated plate, the absorption of the perforated plate is maximized. As the absorber efficiently removes energy from the specular reflection direction, the scattering coefficient rises. Finally, the peak and dip frequencies of the scattering coefficient well agree with those of the absorption coefficient.