Use the Impedance condition to prescribe an impedance at a solid boundary according to the Ingard–Myers formulation. For the boundary mode interface, gradients in the out-of-plane direction(s) are implemented in a consistent manner using the solved for or prescribed wave number(s).

For the boundary mode interface only the Ingard–Myers option can be selected as the Impedance model. Enter a value or expression for the Specific impedance Zn (SI unit: Pa·s/m). The default value is lpfbm.rho0*lpfbm.c0 which corresponds to the specific characteristic impedance of the medium at rest.