Absorption and radiation impedance of finite absorbing patches

A variational formulation is used to calculate the sound absorption in order to incorporate the interaction between several absorbing patches of arbitrary shape. In particular, this formulation is applied to small periodic patches. The absorption characteristics are governed by the radiation impedance, Z(r), which is a function of the absorber's geometry and the incidence angle, together with the surface impedance of the absorber. The behaviour of Z(r) is evaluated numerically for a number of typical configurations, and the effect on the statistical absorption coefficient, alpha(stat) is calculated. The evaluations stress that alpha(stat) is regulated by the interaction between Z(r) and the impedance of the absorber. A comparison is made of results from measurements and calculations performed on the measurement set-up