Investigation of surface acoustic wave propagation in composite pillar based phononic crystals within both local resonance and Bragg scattering mechanism regimes

Abstract

We investigate the propagation of surface acoustic wave through phononic crystals (PCs) that consist of composite pillars, comprising of a cap metallic pillar and a bottom epoxy pillar on the semi-infinite substrate. The computation of band structures, together with measured transmission spectra, shows the important role of the bottom pillar in engineering the band structures for its Young’s modulus one order of magnitude smaller than that of the cap pillar. We also discuss the conditions of ignoring the influences of the bottom pillar in PCs featuring extremely high cap pillars. We finally modify the height of the bottom pillar to engineer the band structures of PCs, leading to, in both the simulation and experiment, Fano resonance-like transmission in the long wavelength regime.

Compact Waveguide and Guided Beam Pattern Based on the Whispering-Gallery Mode of a Hollow Pillar in a Phononic Crystal Plate

“…This is the consequence of the low Young's modulus of epoxy which is lower than that of steel and aluminum by one order of magnitude. A similar behavior has already been demonstrated for SAWs propagating in a set of steel pillars regularly glued on a semi-infinite aluminum substrate [19]. We then computed the band structure for the unit cell comprising hollow pillars A and B on the slab with the inner diameter d2 = 2.8 mm and the height of the steel pillar kept unchanged, hA = 2.4 mm.…”

“…To match the actual samples we used in the experiments, we have considered a cylindrical pillar made of steel (labelled A hereafter), glued with epoxy (material B) to a plate made of 6061-T6 aluminum (material C). The outer diameter of the pillar, the thickness of the glue layer, the thickness of the plate, and the lattice constant were respectively (in mm): d1 = 5, hB = 0.135 [19], tC = 1.5, and a = 6. Both the height of the steel pillar hA and the inner diameter d2 of the entire pillar (steel and epoxy) were left as free parameters.…”

“…Both the height of the steel pillar hA and the inner diameter d2 of the entire pillar (steel and epoxy) were left as free parameters. As regards the physical parameters of the different materials we used for the Young's modulus (in GPa) EA = 226, EB = 5.1, and EC = 67.7; for the Poisson's ratios A = 0.29, B = 0.38, and C = 0.35; and for the mass densities (in g.cm -3 ) A = 7.75, B = 1.2, and C = 2.7 [19][20][21].…”

“…Our experimental setup combines the air-coupled method [24] and the laser ultrasonic technique [19]. To generate the lowest-order antisymmetric Lamb mode A0 in the slab, upstream the PC, we utilized an unfocused air-coupled transducer (ACT) as an emitter.…”

Double-Negative Pillared Elastic Metamaterial

“…Owing to their locally resonant substructures, their effective parameters, including the mass density, the bulk, and the shear modulus, can be dynamically set to a positive, zero or negative value [1][2][3][4], enabling thus to manipulate the propagation of elastic waves in the subwavelength scale. In analogy to their electromagnetic counterparts, elastic metamaterials with simultaneously negative effective mass density (NMD) and elastic modulus (NEM) have attracted considerable attention notably because of their great potential for the negative refraction of elastic waves or the over-the-diffraction-limit imaging [5][6][7][8][9][10]. The double negativity can be realized either by combining two different substructures, each supporting a different resonant mode or by constructing a single structure where two resonances occur at a single frequency [11,12].…”