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3/ Cloaking and lensing in the plate and rod configuration

29 September 2016 ( maj : 7 October 2016 ), by Administrateur

Benefitting from the laboratory set-up and equipment facility at ISTerre, small-scale experiments will be performed with vertical rods attached to the plate in the configuration described in section "State of the art" Fig. 1. To complement experimental results at Institut Langevin, we will focus on cloaking and lensing effects with rods of different lengths and a spatial configuration of rods determined by numerical simulations (see WP3.1).

In practice, we ambition to perform numerous experiments by the PhD student funded by ANR through the META-FORET project. In particular, we first aim at creating a Luneburg lens (see example in WP3.1 Fig. 1a) that will refocus an incident plane wave on the other side of the forest of rods. Note, however, that Fig. 1a describes a Luneberg lens obtained with buried soft concrete inclusions that is different from a Luneburg lens obtained with vertical rods attached to the plate where each rod plays the role of a resonator. The spatial distribution of rods will be determined from conformal optics (see WP4.2) in combination with numerical simulation tests to adjust the rod height accordingly.

Following this first experimental demonstration, we ambition to reach full and perfect cloaking (that is to say no wave at the center of the cloak and a reconstruction of the incident wave outside of the cloak) with the excitation of flexural rod resonances inside of a bandgap driven by the compressional resonances of rods as classically observed in section "state of the art" Fig. 1a&b. Indeed, when the plate thickness becomes thinner, both flexural and compressional resonances of the rods are simultaneously excited by the A0 plate waves, the first one behaving as a dipole when the second one is a natural monopole. Choosing the proper frequency excitation, the combination of these two types of resonances may be the adequate route to reach a negative index of refraction that is a necessary ingredient to perform full cloaking, in a way similar to what a combination of thin straight wires and split ring resonators achieved back in 2000 for negative refraction in electromagnetic metamaterials.