On the absorption coefficient of porous corrugated surfaces

A classical way of improving acoustical absorption performances of porous materials is the use of corrugated surfaces; this use can obtain lower cut-off frequencies and also improve the overall absorption over a wide frequency range. An analytical approximation is presented for the calculus of the absorption on this kind of surfaces, where the thickness gradient is represented as a series of steps. Reflection coefficient of every step is obtained and will contribute to the net reflection coefficient. Theoretical results will be presented and shown to agree with experimental data.