Acoustic Luneburg lens based on a gradient metasurface for spoof surface acoustic waves

Abstract

This letter presents the design and experimental demonstration of a gradient metasurface guiding spoof surface acoustic waves (SSAWs) in the manner of a Luneburg lens for sound. By correlating the propagation characteristics of SSAWs with the effective surface acoustic impedance, a straightforward concentric surface structure design is proposed to realize the required refractive index distribution. The results from both simulation and measurement show that grazing incident sound is converted into SSAWs propagating along the metasurface and focusing on the edge of the opposite side of the lens, which may find applications in direction detection and acoustic sensing.

Broadband flattened underwater acoustic Luneburg lens

“…Both circular and flattened Luneburg lenses for electromagnetic [10][11][12][13][14][15], acoustic [16][17][18][19][20][21][22][23][24][25][26] and mechanic * Author to whom any correspondence should be addressed. [27][28][29][30][31] waves have been realized by taking advantage of the metamaterials, which are man-made structures that allow the effective constitutive parameters much richer than nature materials.…”

“…[27][28][29][30][31] waves have been realized by taking advantage of the metamaterials, which are man-made structures that allow the effective constitutive parameters much richer than nature materials. However, most of the experiments on the acoustic Luneburg lens focused on the airborne sound [9,[18][19][20][21][22][23][24][25][26]. Water is another important sound medium, and the underwater acoustics plays a momentous role in underwater communications, imaging and positioning.…”