Periodic Reporting for period 1 - METAQUAKENG (METAMATERIALS IN EARTHQUAKE ENGINEERING)
Periodo di rendicontazione: 2018-09-01 al 2020-08-31
My aim was to critically explore the potential of using large scale metamaterials for elastic waves control, having as a main objective the design of an optimal device, its numerical validation and hopefully its experimental characterization to really show whether this is feasible or not. The approach I used is twofold: I employed inertial resonators (IRs) to engineer seismic shields based on low frequency stop bands for surface and bulk waves by converting them into evanescent waves, and I further looked at conformal mappings to design seismic carpet cloaks smoothly detouring surface waves around a group of buildings.
In this project I designed and developed large scale elastodynamic metamaterial devices based on subwavelength elements to mitigate the damage created by surface (Rayleigh) and bulk (coupled shear and pressure) solid mechanics waves due to any type of vibration in structural components or earthquakes. I took advantage of the internationally renowned modelling skills of the applied mathematics group of Prof. Richard Craster at Imperial College, as well as ideas of negative refraction and cloaking that have been initiated and developed by Sir John Pendry at the Physics Department of Imperial College at the turn of this century. So-called electromagnetic metamaterials are becoming well established in the wave physics community of optics and electromagnetism, but their elastodynamic counterparts are less well studied. Transferring the knowledge of electromagnetic metamaterials to large scale elastodynamic metamaterials, also known as seismic metamaterials, draw upon my experience in mechanical and civil engineering. Recent developments in photonic topological insulators, which are the electromagnetic wave counterparts of electronic topological insulators (metal insulators whose surface contains conducting states, that is electrons can only move along their surface), have been at the core of my research for the last year of my fellowship, with the design and numerical validation of the first topological seismic rainbow in an elastic plate of varying thickness with judiciously patterned square perforations. This novel device has great potential in energy harvesting, and can be considered the main theoretical achievement of my research project. However, thanks to the participation of Institut Fresnel in this project, and the collaboration with the team of Stéphane Brûlé at the Menard civil engineering company in Lyon, I have been able to conduct the first in-situ experiments for Rayleigh waves propagating within a doubly periodic array of ancient stones (known as menhirs) in Carnac, France.
Metamaterials themselves were only discovered at the turn of the century by Sir John Pendry; The field is thus relatively young and there is a lot of opportunity to take advantage of the enormous progress that has been made using those ideas of the last 20 years in optics and electromagnetism, but now in the field of elastic waves. An initial study that I performed, based on inertial resonators subwavelength elements, showed considerable promise. A key premise is that the notion of metamaterials is valid across scales and this observation is critical to allowing ideas to translate from nanostructured media in optics and plasmonics to structured soils in civil engineering.