Publications

2023

• Modeling acoustic space-coiled metacrystals
  
  • Zhou Hagström Joar
  • Pham Kim
  • Maurel Agnés
  SIAM Journal on Applied Mathematics, Society for Industrial and Applied Mathematics, 2023, 83 (6), pp.2499-2521. We present an effective model of “space-coiled metacrystals” composed of a periodic array of sound rigid blocks into which long slots have been coiled up. The periodic cell of the block contains a coiled slot whose straight parts are at wavelength scale, which enables the appearance of Bragg resonances. These resonances, which prevent high transmission, compete with the Fabry–Pérot resonances of the entire slot, which foster perfect transmission. This results in complex scattering properties driven by the characteristics of the turning regions that act as atoms in a one-dimensional coiled crystal. Using appropriate scaling and combining two-scale homogenization with matched asymptotic techniques, the modeling of such metacrystals is proposed. The resulting model is validated through a comparison with full-wave numerics in both harmonic and transient regimes. (10.1137/22M1527131)
  DOI : 10.1137/22M1527131
• Revisiting effective acoustic propagation in labyrinthine metasurfaces
  
  • Hagström Joar Zhou
  • Pham Kim
  • Maurel Agnès
  Wave Motion, Elsevier, 2023, 122, pp.103196. We revisit the modelling of labyrinthine metasurfaces with space coiling design. To do so, we use homogenization theory which allows us to replace the actual structure by a slab filled with an effective, homogeneous and anisotropic, medium. The effective medium is highly anisotropic as the propagation is allowed in one direction only and its effective refractive index is obtained unambiguously thanks to the resolution of a static cell-problem. The result is compared to a classical, two-step, model which follows the intuitive idea that a coiled labyrinth and a slot being its uncoiled version behave the same. Beyond the approximation of such statement (the evanescent fields triggered at the turning regions of the labyrinth are neglected), we stress the difficulty in defining unambiguously the length of the uncoiled labyrinth. (10.1016/j.wavemoti.2023.103196)
  DOI : 10.1016/j.wavemoti.2023.103196