Gradient acoustic metasurfaces are a class of subwavelength metamaterials that provide unprecedented opportunities to control the direction of reflected and refracted waves, including negative angles in accordance with the diffraction theory and generalized law of reflection. This opens new possibilities in designing metasurfaces for many practical applications in wave engineering. In this work, locally resonant acoustic metamaterials are considered as the building units of the metasurface, which owe their favorable properties to local resonances at the microstructural level. Non-trivial reflection angles are realized by introducing suitable phase modulations along the wave path. The required phase shift is achieved through the variation of geometrical and material parameters of the metamaterial unit cells. The negative reflection of ultrasound waves is demonstrated numerically by means of a finite-element analysis of a fluid-metasurface-solid structure. The results of this study provide new insights and detailed guidelines for designing metasurfaces for controllable acoustic wave reflection.

中文翻译：

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针对负反射的梯度局部共振声学超表面的设计

梯度声学超表面是一类亚波长超材料，它为控制反射波和折射波的方向提供了前所未有的机会，包括根据衍射理论和广义反射定律控制负角。这为波浪工程中许多实际应用的超表面设计开辟了新的可能性。在这项工作中，局部共振声学超材料被认为是超表面的构建单元，其有利的特性归功于微观结构水平上的局部共振。通过沿着波路引入合适的相位调制来实现重要的反射角。所需的相移是通过改变超材料晶胞的几何和材料参数来实现的。通过流体-超表面-固体结构的有限元分析，以数值方式证明了超声波的负反射。这项研究的结果为设计可控声波反射的超表面提供了新的见解和详细的指导。