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Schematic of the experimental setup used for investigating the propagation of surface phonons in a periodic array of pillars on a semi-infinite substrate. The nickel pillars shown as an inset have a radius of 3.2 μm and a height of 4.7 μm. They are arranged according to a square lattice with a pitch of 10 μm. Two chirped interdigital transducers generate and detect surface phonons thanks to the piezoelectric properties of the lithium niobate substrate. The yellow color under the pillars represents the thin copper film used to insure electrical contact during the electroplating process necessary for pillar growth.
Measured electrical transmission S 12 as a function of frequency for (a) a pair of chirped interdigital transducers (IDTs) operating in a delay line configuration without PC, hence serving as a reference, (b) with a triangular lattice PC, (c) with a honeycomb lattice PC, and (d) with a randomly distributed pillar array. The grey region represents the common position of the locally resonant band gap. Optical microscope images of each pillar array are shown as insets.
Band structure of a periodic array of nickel pillars on a lithium niobate substrate computed using a finite element method along ΓK of the highest symmetry directions of the first Brillouin zone. The array is arranged according to (a) triangular and (b) honeycomb lattices with a pitch a = 10 μm. The radius of the pillar is r = 3.2 μm and the height is h = 4.7 μm. The grey region indicates the radiative region, or sound cone of the substrate.
Measured electrical transmission S 12 as a function of frequency for chirped interdigital transducers (IDTs) operating in a delay line configuration without (reference in black dotted line) and with randomly distributed pillar arrays with different heights (4.7 μm in blue, 4.1 μm in red, and 3.5 μm in green).
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