Tunable waveguide and cavity in a phononic crystal plate by controlling whispering-gallery modes in hollow pillars

Abstract

We investigate the properties of a phononic crystal plate with hollow pillars and introduce the existence of whispering-gallery modes (WGMs). We show that by tuning the inner radius of the hollow pillar, these modes can merge inside both Bragg and low frequency band gaps, deserving phononic crystal and acoustic metamaterial applications. These modes can be used as narrow pass bands for which the quality factor can be greatly enhanced by the introduction of an additional cylinder between the hollow cylinder and the plate. We discuss some functionalities of these confined WGM in both Bragg and low frequency gaps for wavelength division in multiplexer devices using heteroradii pillars introduced into waveguide and cavity structures.

Phononic Crystal Plate with Hollow Pillars Actively Controlled by Fluid Filling

“…This new structure was first studied in [22]. In this section, we give some additional results with respect to the conclusions of [22].…”

“…The quality factor of the WGMs can be further increased by adding a full cylinder between the hollow pillar and the plate, so that the elastic energy is better confined in the hollow pillar part [22]. This new structure was first studied in [22]. In this section, we give some additional results with respect to the conclusions of [22].…”

“…By introducing an inner hole in the pillar, two new branches of WGMs with quadrupolar shape occur in the dispersion curves that do not appear in the native PnC; their fields are localized in the upper part of the pillars around the hollow. The quality factor of the WGMs can be further increased by adding a full cylinder between the hollow pillar and the plate, so that the elastic energy is better confined in the hollow pillar part [22]. This new structure was first studied in [22].…”

“…Using Brillouin light scattering experiments, Graczykowski et al [21] showed significant changes in the hypersonic phonon propagation due to the presence of local resonances in phononic crystal made of a square lattice of holes and pillars in/on silicon membrane. Very recently, Jin et al [22] explored confined whispering-gallery modes (WGMs) by considering hollow pillars on a thin plate. The confined WGMs with high quality factors allow for manipulating the acoustic waves for guiding and filtering applications in both Bragg and low frequency band gaps.…”

Pillar-type acoustic metasurface

“…This has been demonstrated both numerically and experimentally, with 1D stripes periodically engraved on the surface of a lithium niobate substrate 8 and more recently with 2D phononic crystals made of a periodical array of cylindrical pillars deposited on a thin and homogeneous slab. [9][10][11][12][13][14][15][16][17][18] This last structure deserves special attention. Indeed, a pillar exhibits both compressional (monopolar) and bending (dipolar) resonances that may lead to negative dynamic effective modulus and mass density respectively.…”