More Like this

1. Chiral elasticity of the gyroid lattice

   https://doi.org/https://doi.org/10.1103/PhysRevLett.125.205502  

   Reasa, D. and (November 2020, Physical review letters)

   null (Ed.)

   The gyroid lattice is a metamaterial which allows chirality that is tunable by geometry. Gyroid lattices were made in chiral and nonchiral form by 3D printing. The chiral lattices exhibited nonclassical elastic effects including coupling between compressive stress and torsional deformation. Gyroid lattices can approach upper bounds on elastic modulus. Effective modulus is increased by distributed moments but is, for gyroid cylinders of sufficiently small radius, softened by a surface layer of incomplete cells. Such size dependence is similar to that in foams but is unlike most lattices. 

   more » « less
2. Flexible Cube Tilt Lattice with Anisotropic Cosserat Effects and Negative Poisson’s Ratio

   https://doi.org/10.1002/pssb.201800512  

   Rueger, Z. (January 2019, Physica status solidi)

   A 3D lattice structure consisting of pivoting cubes with flexible links at the corners is presented. It exhibits anisotropic negative Poisson’s ratio -0.54 and -0.75. Size effects occur in torsion and bending; these effects are consistent with Cosserat elasticity but not with classical elasticity. Cosserat elastic solids exhibit sensitivity to strain gradients; size effects occur in torsion and bending; also reduction in stress concentrations. The observed Cosserat effects also reveal anisotropy. 

   more » « less
3. Experimental study of elastic constants of a dense foam with weak Cosserat coupling

   https://doi.org/10.1007/s10659-018-09714-8  

   Rueger, Z. (January 2019, Journal of elasticity)

   A dense closed cell foam is studied to determine which continuum theory of elasticity is applicable. Size effects inconsistent with classical elasticity are observed. The material exhibits a characteristic length scale considerably larger, by more than a factor 6, than the largest observable structure size. The Cosserat coupling number N is shown to be small, via measurements of size effects in square section bars, comparison with size effects in round section bars, and determination of warp of a square section bar in torsion. For this material, the couple stress theory is excluded and the modified couple stress theory is excluded. Theories that force constants to their thermodynamic limits do not apply to this foam. The role of other generalized continuum theories is considered. 

   more » « less
4. Strong Circular Dichroism in Single Gyroid Optical Metamaterials

   https://doi.org/10.1002/adom.201902131  

   Kilchoer, Cédric; Abdollahi, Narjes; Dolan, James_A; Abdelrahman, Doha; Saba, Matthias; Wiesner, Ulrich; Steiner, Ullrich; Gunkel, Ilja; Wilts, Bodo_D (May 2020, Advanced Optical Materials)

   Abstract Over the past two decades, metamaterials have led to an increasing number of biosensing and nanophotonic applications due to the possibility of a careful control of light propagating through subwavelength features. Chiral nanostructures (characterized by the absence of any mirror symmetry), in particular, give rise to unique chiro‐optical properties such as circular dichroism and optical activity. Here, a gyroid optical metamaterial with a periodicity of 65 nm exhibiting a strong circular dichroism at visible wavelengths is presented. This bottom‐up approach, based on metallic replication of the gyroid morphology in triblock terpolymer films, generates a large area of periodic optical metamaterials. A strong circular dichroism in gold and silver gyroid metamaterials at visible wavelengths is observed. It is shown that the circular dichroism is inherently linked to the handedness of the gyroid nanostructure and its tuneability is demonstrated. The optical effects are discussed and compared to other existing systems, showing the potential of bottom‐up approaches for large‐scale circular filters and chiral sensing. 

   more » « less
5. Topological Surface States in a Gyroid Acoustic Crystal

   https://doi.org/10.1002/advs.202205723  

   Guo, Yuning; Rosa, Matheus_I_N; Ruzzene, Massimo (December 2022, Advanced Science)

   Abstract The acoustic properties of an acoustic crystal consisting of acoustic channels designed according to the gyroid minimal surface embedded in a 3D rigid material are investigated. The resulting gyroid acoustic crystal is characterized by a spin‐1 Weyl and a charge‐2 Dirac degenerate points that are enforced by its nonsymmorphic symmetry. The gyroid geometry and its symmetries produce multi‐fold topological degeneracies that occur naturally without the need for ad hoc geometry designs. The non‐trivial topology of the acoustic dispersion produces chiral surface states with open arcs, which manifest themselves as waves whose propagation is highly directional and remains confined to the surfaces of a 3D material. Experiments on an additively manufactured sample validate the predictions of surface arc states and produce negative refraction of waves at the interface between adjoining surfaces. The topological surface states in a gyroid acoustic crystal shed light on nontrivial bulk and edge physics in symmetry‐based compact continuum materials, whose capabilities augment those observed in ad hoc designs. The continuous shape design of the considered acoustic channels and the ensuing anomalous acoustic performance suggest this class of phononic materials with semimetal‐like topology as effective building blocks for acoustic liners and load‐carrying structural components with sound proofing functionality. 

   more » « less