Predicting propagation from a point source over grooved ground using a modal model

International audience; A modal model, hitherto used to predict electromagneticand ultrasonic surface waves, is employed in deriving aneffective impedance for a grooved acoustically hard sur-face. This is inserted in the classical theory for propagationfrom a point source above an impedance plane to predictpoint-to-point propagation above regularly spaced grooveswith rectangular cross sections. Predictions of excess at-tenuation (EA) spectra obtained in this manner compareclosely with those obtained by a numerical method (BEM)but take a fraction of the time. The modal method is ex-tended to predict EA spectra above metasurfaces consist-ing of repeated arrays of variable depth grooves with dif-ferent depths of a low flow resistivity porous material ineach groove. The porous infill is predicted to reduce thenegative EA peaks associated with quarter wavelength res-onances in the grooves. By applying the modal model ef-fective impedance theory, porous-infill groove arrays havebeen designed to yield wideband excess attenuation spectrawith potential for reducing noise from surface transport.