Anisotropic acoustic characterization of TPMS architected metamaterials via impedance-tube and multiscale modeling

Triply periodic minimal surfaces (TPMS) are a class of architected acoustic metamaterials valued for applications such as heat exchange, strain-energy absorption, and sound attenuation. By stretching the unit cell, TPMS exhibit anisotropic behavior, with properties varying by direction. Here, we apply a recently developed methodology to determine the effective density tensor and bulk modulus of manufactured TPMS samples using normal-incidence impedance-tube measurements. We also extract transport parameters for effective-fluid, semi-phenomenological models via a hybrid multiscale approach in COMSOL, solving boundary-value problems at multiple scales. To probe anisotropy, we fabricate samples with material axes rotated relative to their original orientation and compare measured apparent density and scattering coefficients to predictions from both the effective-density tensor and numerical homogenization. Our results demonstrate how precise characterization of anisotropic TPMS bulk absorbers enables targeted design strategies to maximize acoustic absorption.