Spinodoid structures, also called spinodoid metamaterials, are non-periodic cellular structures that mimic the spinodal topologies that are observed during diffusion-driven phase separation processes. Spinodoid structures are computationally efficient to model and they can be fabricated using additive techniques; as a result, they offer an attractive way to design multifunctional structures that can simultaneously provide mechanical stiffness and noise reduction performance. In recent work, the normal incidence sound absorption behavior of four distinct spinodoid topologies was studied: isotropic, cubic, columnar, and lamellar. The isotropic and cubic topologies are essentially isotropic in terms of acoustical behavior, and they can be successfully modeled by using the rigid JCA approach, for example. However, in contrast, the columnar and lamellar materials are inherently strongly anisotropic. In the present work, the acoustical properties of printed examples of the latter materials were measured in two different orientations to determine their direction-dependent properties. Those properties were used as input to a transversely isotropic implementation of the Biot theory, which successfully models the two materials. The columnar material, in particular, is inherently locally reacting and may perform well in duct lining applications. In contrast, the lamellar material is non-locally reacting and its surface impedance will therefore be strongly angularly dependent.
Spinodoids, Additive manufacturing, Anisotropic, Acoustical modeling, Sound absorption
Acoustics and Noise Control
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