A Physical Explanation of Angle-Independent Reflection and Transmission Properties of Metafilms/Metasurfaces

In this letter, we illustrate that a metafilm (the two-dimensional equivalent of a metamaterial, also referred to as a metasurface) can be designed to have transmission and reflection properties that are independent of the angle of the incident wave. We show theoretically and discuss physically why this behavior occurs in certain metafilms. We show that by choosing an inclusion with sufficiently strong resonances, the angle dependence of the metafilm becomes negligible. Metafilms operating at microwave frequencies and composed of both lossless and lossy resonant spherical inclusions as well as electrical resonators are investigated. Numerical and spherical-harmonic mode-matching approaches are used to investigate the angular dependence of the reflection properties of these metafilms. Such angular-independent properties can have applications in extending the modes supported in a metafilm waveguide and have direct applications to photonics where, due to fabrication obstacles, optical metamaterials are often limited in construction to single and multiple stacked two-dimensional arrays of plasmonic structures.