In recent years there has been a rise in the popularity of metamaterial concepts, based on the so-called local resonance phenomenon, used to control the propagation of electromagnetic, acoustics and elastic waves in artificially engineered media. While the momentum initially focused on the subwavelength bandgaps generated by the resonance, the research has delivered new forms of wave control, encompassing tailored graded designs to obtain spatially varying refraction index, wide bandgaps and mode conversion. In the field of photonics and acoustics this transition has already taken place and a new graded design allows for bespoke management of the propagation of light, micro-waves and sound. Elastic waves, are characterized by different compressional and shear wave speeds resulting in mode conversions at the interfaces. On the one hand this makes elastic metamaterials complex to model and requires the use of computational elastodynamics techniques, but on the other hand it opens up new possibilities in the wave control area not achievable in the electromagnetic or acoustic case. Among the various metamaterial configurations, resonant metasurfaces are particularly well suited to lens design, non-reciprocal devices, random media, and tailored modal conversions of guided to body waves. Results discussed in this talk cover various resonant mechanical systems, materials and lengthscale as well as frequency bands to highlight the broad applicability of abovementioned concepts.

Reference :

• G.J. Chaplain, R.V. Craster, J.M. De Ponti, A. Colombi, A. Clare, M. Clark, R. Patel and R.J. Smith. Tailored elastic Umklapp surface to body wave conversion. https://arxiv.org/abs/1912.05373
• R. Zaccherini, A. Colombi, A. Palermo, V.K. Dertimanis, A. Marzani, H.R. Thomsen, B. Stojadinovic, and E.N. Chatzi. Locally resonant metasurfaces for shear waves in granular media. http://arxiv.org/abs/1912.00617
• J.M. De Ponti, A. Colombi, R. Ardito, F. Braghin, A. Corigliano, R.V. Craster. Graded metasurface for energy harvesting. New J. Phys. (IF : 3,8), 2019.