The Anisotropic Acoustics node is used to define a fluid with properties that can be modeled with an effective anisotropic density. The feature can be used to model metamaterials in a homogenized manner or when modeling fibrous materials with anisotropic properties. The material properties are defined through an effective bulk modulus K and an effective density tensor ρ. The density variable can be defined as being isotropic (a scalar), a diagonal tensor, or a symmetric tensor. The resulting (generalized) Helmholtz equation solved in the frequency domain is then

where it should been emphasized that ρ−1 is here a tensor. The resulting system will have principal speeds of sound that are (square root of) the eigenvalues and directions that are the eigenvectors of the quantity c2 = ρ−1K.

Select the Coordinate system in which the density tensor is defined. The default is the Global coordinate system.

Enter the Effective bulk modulus K (SI unit: Pa) taken From material. For User defined enter other values or expressions for any or all options.

Enter the Effective density ρ (SI unit: kg/m3) taken From material. For User defined enter other values or expressions for any or all options. Also select the representation for the density tensor either Isotropic (the default), Diagonal, or Symmetric.