UCLA

Metasurface is a two-dimensional array of subwavelength elements that can manipulate the physical fields on the surface. Conventional periodic metasurfaces may face some physical constraints. For example, in metasurface gratings, the existence of specular reflection governed by the diffraction equation can diminish the grating efficiency. Besides, it is difficult to control the diffraction lobes and polarizations of the scattered wave. To overcome these limitations, we realize that breaking the periodicity of the elements will provide more flexibility to manipulate the scattering properties.

In this dissertation, we propose metasurfaces consisting of nonperiodic group cells optimized for desired scattering behaviors. Each group cell includes several locally periodic elements that are characterized by their reflection phase response under TE/TM or CP illumination. We first present nonperiodic metasurfaces used for retroreflection of oblique incident wave with linear polarization (TE/TM) and circular polarization (CP). For CP wave, both handedness reversal and handedness preservation cases are demonstrated. In the following chapter, we present nonperiodic metasurface beam splitter for TE and TM polarizations based on the same method. Last, we propose the anisotropic metasurface that can convert linear polarization to circular polarization. All the metasurface designs are implemented by PCB fabrication and can be easily scaled to millimeter-wave, THz, and optical frequencies.