Negative refraction of longitudinal waves in a two-dimensional solid-solid phononic crystal

Negative refraction of elastic waves at the deep-subwavelength scale in a single-phase metamaterial

“…All of the reported experiments on NR of elastic waves in solid bulk media are based on Bragg scattering. Using a unit cell size El, NR of transverse and longitudinal waves was experimentally observed in 2D PCs made of cylindrical air cavities in an aluminium (Al) block at 470-530 kHz and steel rods embedded in an epoxy matrix at 750-860 kHz, respectively 21,22 . For elastic guided waves, Pierre et al 23 employed a 2D PC with a unit cell size E2.7 l and experimentally evidenced the NR of antisymmetric Lamb waves at 5.4-10.5 MHz.…”

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

“…16 Analysis has been performed on the width and the length of the focal spot, showing that, due to the impedance mismatch between the PC and the surrounding medium, the focal spot is degraded with respect to previous studies on the ideal case. 14 By looking carefully to the pressure field displayed on Fig. 5, one can notice a second focal point in the area above the flat lens.…”

“…14 Here, the prism shaped PC is immersed in water, in order to confirm that the longitudinal waves exhibiting negative refraction in the PC can be coupled to the surrounding fluid domain. The experimental setup is presented on Fig.…”

“…Indeed it is necessary for this kind of applications, that the phononic crystal lens be surrounded by a fluid medium. In a recent paper, C. Croënne et al 14 have shown theoretically and experimentally the negative refraction of a pure longitudinal elastic wave in a triangular array of steel rods inserted in an epoxy block. Preliminary analysis of the optimal conditions for elastic waves focusing in the surrounding fluid medium was also reported.…”

Beam paths of flexural Lamb waves at high frequency in the first band within phononic crystal-based acoustic lenses

“…[3][4][5][6][7][8] To a certain extent, the resolution of the focusing was beyond the diffraction limit with the evanescent waves being gathered at the focusing through the bound modes. 9,10 These studies of acoustic waves in fluids have inspired a series of works dealing with other polarized waves both on the negative refraction phenomenon [11][12][13] and on the focusing of negative-refractive PCs. [14][15][16][17][18] On the other hand, there has been a great deal of work on systems based onto a positive refraction process to realize the focusing.…”