Enhanced elastodynamic resonance via co-dipole metaclusters

Metamaterials exploit sub-wavelength microstructures to yield novel macroscopic material properties. Recently, the notion of a metacluster has emerged, which is a collection of resonators that interact in order to modify and possibly enhance the resonance. They can also be employed to modify and tune the far-field scattered response. This is particularly important with regard to metamaterial design. In the context of elastodynamics, Cotterill et al. [Proc. R. Soc. A 478(2263), 20220026 (2022)] considered the case of void metaclusters, thus permitting the modification of the so-called giant monopole resonance in elastodynamics. Here, we consider one of the original resonant configurations of metamaterial science in Liu et al. [Science 289, 1734 (2000)]; this structure consists of coated cylinders of circular cross section and gives rise to a strong dipole resonance for sufficiently soft coatings. We consider the nature of the interaction of two such identical resonators in close proximity, which we term the co-dipole metacluster. We show that, contrary to the giant monopole case, the frequency at which the resonance occurs is unchanged as compared to a single resonator. The amplitude of the resonance itself is enhanced significantly, however, by up to 5.7 times the enhancement observed when considering two non-interacting resonators. Furthermore, although the nature of the resonance remains dominated by a dipole response, both the enhancement and the far-field scattered response are now significantly affected by the incidence angle, in contrast to the single resonator.