Impedance

The Impedance node adds an impedance boundary condition, which is a generalization of the sound-hard and sound-soft boundary conditions:

Here Zi is the acoustic input impedance of the external domain and it has the unit of a specific acoustic impedance. From a physical point of view, the acoustic input impedance is the ratio between the local pressure and local normal particle velocity.

The Impedance boundary condition is a good approximation for a locally reacting surface—a surface for which the normal velocity at any point depends only on the pressure at that exact point.

In the two opposite limits Zi → ∞ and Zi → 0, this boundary condition is identical to the Sound Hard Boundary (Wall) condition and the Sound Soft Boundary condition, respectively.

Impedance

The Impedance model available is User defined.

Enter the value of the Impedance Zi (SI unit: Pa·s/m). The default value is set to the specific impedance of air
1.2 kg/m3·343 m/s.