Immersive metamaterial experimentation: implementation of a virtual periodic boundary condition

  • Thomsen, Henrik Rasmus (ETH Zürich)
  • Zhao, Bao (ETH Zürich)
  • Colombi, Andrea (ETH Zürich)

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Studying elastic wave propagation phenomena in the laboratory is a key aspect of many research disciplines. However, laboratory experiments are often plagued by modal responses of the system caused by e.g., free, or clamped boundaries. Furthermore, wave propagation within the structure is often difficult to interpret due to boundary reflections. Thus, experimentation is often constrained to high frequencies resulting in wavelengths much smaller in length than the size of the object. Immersive wave experimentation (IWE) was recently proposed to overcome such laboratory- and sample-size related limitations plaguing conventional wave propagation experimentation (Vasmel, 2016). Through modification of the physical boundary conditions encountered in the laboratory, wave propagation in the physical experimental under investigation is linked to a desired virtual domain. The method can be used in a wide range of applications, such as cloaking and holography (Börsing et al., 2019, as well as virtual extension (Thomsen et al., 2019) and modification (Becker et al., 2020) of the finite physical domain encountered in the laboratory. We demonstrate the first user-case of elastic IWE applied to the field of metamaterial research. Metamaterials are architected structures carefully designed to guide, focus and attenuate mechanical waves at diverse length scales. Our iterative workflow is used to successfully remove unwanted boundary reflections from a graded metamaterial and to create a virtual geometric periodicity in the elastic experiment. The technique described allows for the ad-hoc treatment of boundary conditions in metamaterial experimentation with arbitrary mechanical or acoustic properties, enabling reflection suppression, virtual periodicity, and the introduction of fictitious boundaries. Furthermore, the method can be used to immerse a physical experimental domain in an arbitrary larger numerical domain. Thus, facilitating a hybrid simulation setup with the potential of reduced scale modelling in areas where the analogue, real-size models are prohibitively expensive.