OPPOSITE ANGLE OF REFLECTION GENERATOR
special acoustic beam generator 14,24 14. And the acoustic metasurfaces composed by these building blocks are able to operate as powerful compact acoustic wavefront manipulation devices, such as planar acoustic lens, 22,23 22. Various types of acoustic meta-atoms have been designed, such as coiling-up space structures, 13–15 13. Similar to their electromagnetic counterparts, acoustic meta-atoms with desired phase shift can be realized by tuning the acoustic impedance values of the meta-atoms. Acoustic metasurface, which can be regarded as the counterpart of the electromagnetic metasurface, is another important research branch of the metasurfaces. The gradient metasurface, which is composed by the periodic supercell array, is pointed out to be governed by the generalized laws of reflection and refraction and it has been perfectly verified by both numerical calculations and experimental measurements. Besides these numerous functional wavefront manipulation devices that realized by the metasurface, metasurface itself can be applied as a good platform to study some nontrivial phenomenon, for example, the anomalous reflection and refraction that takes place at a gradient metasurface and optical Spin Hall effect 9,10 9. Basing on the appropriately designed subwavelength structures, metasurface is able to be fashioned into a compact planar profile of the subwavelength thickness and tailors the scattered wavefront into arbitrary desired shape, such as ultra-thin planar lens, 2,3 2. opens the gate to the study of the electromagnetic metasurfaces.
In recent years, metasurface has become a research hot spot due to its novel characteristics shown in wavefront manipulation. The present work enriches the content of the generalized law of reflection and provide new design methodology for functional acoustic wave modulation devices, such like directional ground acoustic cloaking and acoustic isolation devices. In this paper, we utilize the coiling-up space structures of deep subwavelength geometrical scale to construct the desired gradient acoustic metasurface and observe the apparent full-angle negative reflection phenomenon. Basing on the generalized law of reflection which is modified by a reciprocal lattice vector term, the negative reflection that beyond the critical angle is possible. A straightforward physical picture is presented here to understand such anomalous phenomena by considering the influence of the non-local effect that originates from the supercell periodicity on the gradient metasurface. We theoretically demonstrate that full-angle negative reflection can be realized by the gradient acoustic metasurface with a specific surface phase gradient value.
0 kommentar(er)
