Slow waves in locally resonant metamaterials line defect waveguides

Abstract

Many efforts have been devoted to wave slowing, as it is essential, for instance, in analog signal computing and is one prerequisite for increased wave/matter interactions. Despite the interest of many communities, researches have mostly been conducted in optics, where wavelength-scaled structured composite media are promising candidates for compact slow light components. Yet their structural scale prevents them from being transposed to lower frequencies. Here, we propose to overcome this limitation using the deep sub-wavelength scale of locally resonant metamaterials. We experimentally show, in the microwave regime, that introducing coupled resonant defects in such metamaterials creates sub-wavelength waveguides in which wave propagation exhibit reduced group velocities. We qualitatively explain the mechanism underlying this slow wave propagation and demonstrate how it can be used to tune the velocity, achieving group indices as high as 227. We conclude by highlighting the three beneficial consequences of our line defect slow wave waveguides: (1) the sub-wavelength scale making it a compact platform for low frequencies (2) the large group indices that together with the extreme field confinement enables efficient wave/matter interactions and (3) the fact that, contrarily to other approaches, slow wave propagation does not occur at the expense of drastic bandwidth reductions.

Soda Cans Metamaterial: A Subwavelength-Scaled Phononic Crystal

“…Being robust to disorder is a great advantage compared to phononic crystals, in which most of the experimental realizations suffer from fabrication imperfections. Eventually, parametric experiments again performed in the microwave range demonstrate very interesting applications for this kind of waveguides: thanks to the S-shaped dispersion relation the waves can travel very slowly with unprecedented bandwidth-group index product [86]. In the latter experiment a perfect matching to co-axial lines is performed, demonstrating the ability to connect this component to other types of networks.…”

Locally polarized wave propagation through crystalline metamaterials

“…This bandgap can be used to induce defects straightforwardly in the medium, the latter being inclusions with a higher resonance frequency which fall in the previous bandgap frequency range. Its high versatility has been used in recent studies to create subwavelength cavities 35 , ultra-compact waveguides 36 and delay lines 37 .…”

Exploring bandgap generation mechanism of phonon crystal

“…The researches of the formation mechanisms of the phonon crystal bandgap by many scholars show that there are two types of them [4][5][6][7][8][9][10][11][12][13][14]: Bragg scattering mechanism and Local resonance mechanism. Compared with the Bragg scattering mechanism, the localized resonance mechanism considered that the scatterer resonance mode and the substrate vibration mode are coupled to each other to generate a bandgap [4,[9][10][11][12][13][14], which is the key factor in the bandgap formation [4,9,[15][16][17][18]. The Bragg scattering mechanism considered that the periodic arrangement of structures plays a leading role, which focused on the process analysis of elastic wave or acoustic wave propagation in structure [5-8, 19, 20].…”