Less Is More: Hollow‐Truss Microlattice Metamaterials with Dual Sound Dissipation Mechanisms and Enhanced Broadband Sound Absorption

Abstract Being a lightweight material with high design freedoms, there are increasing research interests in microlattice metamaterials as sound absorbers. However, thus far, microlattices are limited to one sound dissipation mechanism, and this inhibits their broadband absorption capabilities. Herein, as opposed to improving performances via the addition of features, a dissipation mechanism is subtractively introduced by hollowing out the struts of the microlattice. Then, a class of hollow‐truss metamaterial (HTM) that is capable of harnessing dual concurrent dissipation mechanisms from its complex truss interconnectivity and its hollow interior is presented. Experimental sound absorption measurements reveal superior and/or customizable absorption properties in the HTMs as compared to their constitutive solid‐trusses. An optimal HTM displays a high average broadband coefficient of 0.72 at a low thickness of 24 mm. Numerically derived, a dissipation theorem based on the superimposed acoustic impedance of the critically coupled resistance and reactance of the outer‐solid and inner‐hollow phases, across different frequency bands, is proposed in the HTM. Complementary mechanical property studies also reveal improved compressive toughness in the HTMs. This work demonstrates the potential of hollow‐trusses, where they gain the dissipation mechanism through the subtraction of the material and display excellent acoustic properties.