Negative refraction of surface acoustic waves in the subgigahertz range

Abstract

We used the picosecond ultrasonic technique to experimentally demonstrate the negative refraction of surface acoustic waves in a two-dimensional phononic crystal. The sample is made of a square lattice of circular voids drilled at the surface of a thick silica substrate. The lattice parameter is of a few micrometers. Broad band surface acoustic waves with Fourier components in the gigahertz range were excited. The negative refraction is observed for Rayleigh waves with frequencies in the second band and propagating along the direction ⌫M in the reduced Brillouin zone. We then used a plane-wave expansion method to calculate the dispersion of the waves in our sample and to analyze our experimental data.

Watching surface waves in phononic crystals

“…Animating k-space is new to acoustics and should prove useful for characterizing SAW devices in telecommunications, for example. It may also be helpful in the analysis of acoustic metamaterials exhibiting, for example, negative refraction [35], extraordinary transmission [50] or cloaking phenomena [51].…”

“…Time-domain imaging of acoustic wave propagation in phononic crystals was first demonstrated in millimetre-scale structures and liquid/solid systems without the use of optics by means of focused transducers at megahertz frequencies [30][31][32]. More recently, the versatility of time-domain optical interferometry for ultrafast measurements of surface acoustic waves (SAWs) on micrometre-scale solid and solid/air phononic crystals has been demonstrated up to approximately 1 GHz [33][34][35][36][37][38][39]. In this paper, we review results obtained using such ultrafast time-domain imaging of the acoustic field on the surface of microscopic phononic crystals in two spatial dimensions in the range around 100 MHz-1 GHz.…”

Optical Characterization of Phononic Crystals in the Time Domain

“…So far Mach-Zender [36], Sagnac [37,38], and Michelson interferometers have been proposed [5,24,30,39,40]. Here we describe an example [24] based on a modification of a previously proposed Sagnac interferometer [37].…”

Negative refraction of elastic waves in 2D phononic crystals: Contribution of resonant transmissions to the construction of the image of a point source

“…Nevertheless, negative refraction of shear waves or of transverse waves was analyzed numerically in periodic arrays of holes drilled in a metal matrix. 9,10 More recently such phenomenon was reported for surface modes 11 or for plate modes 12,13 It is straightforward that superlenses based on solid matrix phononic crystals may have potential applications in the fields of medical imaging or ultrasonic beam-based therapy provided the negative refraction and then the focusing phenomenon involve longitudinal waves. Indeed it is necessary for this kind of applications, that the phononic crystal lens be surrounded by a fluid medium.…”