Acoustic focusing by coiling up space

Abstract

We report the design of a gradient index acoustic lens by coiling up space, an entirely different, yet more direct approach compared with previous designs. The proposed model comprises a series of acoustic metamaterial units with curled channels. Acoustic waves propagate freely within the channels but their propagating phases can be delayed at will by adjusting the size of the units. The numerical results show that the designed acoustic metamaterial can mimic an acoustic gradient index lens with arbitrarily large refractive index and considerably high transmission efficiency. This may provide possibilities for the design and application of acoustic lenses.

High transmission acoustic focusing by impedance-matched acoustic meta-surfaces

“…Much effort has been devoted to reducing the impact of mismatched impedance. 6,8,9,11,15,20,[22][23][24][25][26][27][28][29] One way to do so is to utilize Fabry-Perot (FP) resonances, 6,8,15,20,22,29 which can increase the transmission energy because of the destructive interference between the multiple reflections of acoustic waves on the input and output surfaces of the acoustic lens. Because the resonant frequency of FP resonances is sensitive to the effective thickness of the acoustic lens, it may not be able to perfectly eliminate the reflection in real applications.…”

“…Space-coiling structures have been utilized in the design of gradient acoustic lenses. [6][7][8][9][10] With gradient acoustic lenses, acoustic radiation patterns, such as focusing, 6,[8][9][10][11] tunable transmission, 7,12,13 reflection, 10 and cylindrical-to-plane wave conversion, 9 can be manipulated. Very recently, acoustic meta-surfaces have been used in the design of acoustic lenses.…”

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

“…24,25 To now the focusing achievements for waves with different polarizations have been investigated. [26][27][28][29][30][31][32][33] The flat GRIN PC features a graded sound velocity, making it feasible to control the propagation of waves through processes as focusing, collimating, cloaking and so on. Moreover, GRIN PCs have been designed to focus waves at a subwavelength resolution, generally with a highly gathered energy at the focus which is quite different from the focusing through negative refraction.…”

Focusing and directional beaming effects of airborne sound through a planar lens with zigzag slits

“…In previous studies, curved lenses built by uniform structure units [1,[12][13][14][15] or planar lenses constructed from spatially gradient building blocks [16][17][18][19][20] are frequently proposed. In the former case the focusing effect stems from the curved shape of the lens, whereas in the latter case the focusing effect depends on the gradient distribution of the local refraction index.…”

“…It is of interest that the planar lens presented here also exhibits an excellent conversion from a Below we demonstrate that a nonuniform array of ZSs can minic the above secondary sources retrived from the reverse design. Recently, the ZS units have been extensively employed to design acoustic metamaterials [9][10][11]19,20] and metasurfaces [25][26][27][28] due to the flexibility in tailoring the propagation length of sound. As illustrated in Fig.…”