Dispersion Characteristics And Their Applications Of Electromagnetic Metasurfaces

Metasurface,also called artificial electromagnetic surface,can be considered as two-dimensional or quasi-two-dimensional artificial composite structures formed by periodically arranged subwavelength structures which can produce exotic electromagnetic characteristics.By introducing unit cell structures with position related abrupt phase changes on the boundary conditions,electromagnetic wave propagation characteristics can be controlled flexibly by the elaborately designed metasurfaces according to the Huygens' theory.Furthermore,due to its subwavelength thickness and unit cell size,metasurface has the advantages of light weight,small size,and easy design procedures.This dissertation studies the electromagnetic frequency and spatial dispersion properties of metasurfaces used for tailoring the reflection and transmission of incident waves.By designing the unit cells of the metasurface with specific phase-frequency responses and spatial phase distributions,we have realized new kinds of electromagnetic devices with unique frequency responses for the control of reflected and transmitted waves.The main contents and contributions of the dissertation are as follows:1.The analysis of the electromagnetic dispersion characteristics of metasurface has been performed based on the generalized sheet boundary conditions and Huygens'theory.After that,a frequency filter for spatial wave based on reflective type metasurface which can perform frequency selective control of reflections are designed.It is composed of a single-layer reflective metasurface.The dispersion engineering technique for meta-atoms is used to control the frequency dependent phase gradient distributions.Based on that,a narrow pass band filter effect is realized at center frequency of 10 GHz.It has been proved that the newly proposed reflective metasurface can achieve narrow pass band filtering effect at X band according to the measured and simulated results2.The radar cross section(RCS)reduction by metasurface and characteristics of unit cell phase frequency response is theoretically studied.By tailoring meta-atom's frequency dispersion characteristics and proper design of unit cell distributions,a metasurface with frequency selective RCS reduction is realized.Specifically,two different kinds of metasurfaces with frequency selective RCS reduction are designed based on two types of anisotropic unit cell structures for single-and dul-polarized incidences,respectively.The former one use different sizes of unit cell structures to generate desired phase-frequency responses.While only one unit cell structure is used to generate two different phase-frequency responses for orthogonal polarizations in the latter one.Polarization-insensitive frequency selective diffusive scattering characteristics is realized by random distribution of the latter kind of unit cell with two orthogonal orientations.As a direct application,these kinds of metasurfaces are used as the ground plane or the reflector in antenna design to achieve out-of-band RCS reduction while maintain in-band high gain radiation characteristics.3.The dispersion characteristics of transmission type metasurface has been analyzed.Based on that,a metasurface with total transmission at center frequency band(around 12 GHz)and diffusive scattering at two side-bands(from 7.5 GHz to 11.5 GHz,and 12.5 GHz to 16 GHz)has been designed.It has potential use as a new type of radome with a center transmission band and broadband RCS reduction effect at whole working frequencies introduced by random distribution of the reflection phase4.Study of angle-selective multi-channel reflective surface has been performed.By the combination of metasurface and Van Atta array,a prototype device for incident angle dependent control of reflections has been designed.With this device,the angle of reflection can be controlled freely according to its incident angle.This new kind of electromagnetic device can be potentially applied in wireless communication,object identification and passive detection,etc.5.A multilayer metasurface with angle-selective multi-channel reflection capability has been realized by using intelligent optimization algorithms.It has been proved that the proposed structure can achieve good performs with incident angles ranging from positive 40° to negative 40°.Compared with the Van Atta array design,it has the advantages of simple structure,small thickness,and easy realization.