Abstract
This paper investigates the acoustic Luneburg Lens (ALL) as a design framework for guiding acoustic wave propagation. In this study, an acoustic waveguide is proposed based on the characteristics of both acoustic wave focusing and collimation of cascaded ALLs. The continuous variation of the refractive index of the ALL is achieved by using lattice unit cells with a graded filling ratio. A cascaded ALL waveguide device is fabricated based on the additive manufacturing technique. The experimental results obtained with this device are consistent with the numerical simulations and theoretical calculations.
Highlights
Advances in the development of acoustic metamaterials in recent years have enabled the realization of novel acoustic functionalities, such as acoustic absorption,1,2 acoustic cloaking,3,4 acoustic wave trapping,5,6 acoustic focusing,7,8 and energy harvesting.9–11 In addition, there is a growing interest in the study of acoustic waveguides based on acoustic metamaterials.12,13 Most existing acoustic metamaterial waveguides are based on the tailoring of unit cells to achieve higher refractive indices or bandgaps
This paper investigates the acoustic Luneburg Lens (ALL) as a design framework for guiding acoustic wave propagation
The ALL used in the waveguide is based on variation of the filling ratio of lattice unit cells, which renders a graded change of the refractive index along the radial direction
Summary
Advances in the development of acoustic metamaterials in recent years have enabled the realization of novel acoustic functionalities, such as acoustic absorption, acoustic cloaking, acoustic wave trapping, acoustic focusing, and energy harvesting. In addition, there is a growing interest in the study of acoustic waveguides based on acoustic metamaterials. Most existing acoustic metamaterial waveguides are based on the tailoring of unit cells to achieve higher refractive indices or bandgaps. Otsuka et al. investigated a waveguide mechanism based on phononic band-gap structures, in which rows of defects were intentionally designed in phononic crystals to effectively guide sound waves Another method of achieving waveguides is based on cascaded Luneburg lenses. Mattheakis et al. proposed a theoretical design of an optical waveguide based on cascaded Luneburg lenses, which can be used for sensing and nonlinear optics applications This type of waveguide was later experimentally realized with periodic focusing of optical energy in a device by Smolyaninova et al.. When a point source is used for excitation, an ALL can convert the point source into a plane wave, and the neighbouring lens will focus the plane wave perfectly at a point on the other side of the lens In this way, the source energy can be guided to propagate along the desired direction, as shown, which indicates that the cascaded ALLs can serve as a waveguide for acoustic waves.
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