Analytical Research And Design Of Ultra-broadband Perfect Absorber Using Metamaterial

In the past decade, Metamaterial, which is of great research interest and practical applied potential, has drawn extensive attention on account of its unique and intriguing electromagnetic properties. Based on Effective Medium Theory, we can describe this new material on macroscopic view, and provide a method to control the electromagnetic properties artificially. The new analysis and study demonstrate some promising applications as negative refraction with anisotropic medium and artificially control of the electromagnetic field.In this paper, we present a subwavelength electromagnetic rectangular resonator based on Effective Medium Theory, using stacks of dielectric-plasmonic bilayers to realize an anisotropic permittivity tensor. Concerning that the oft-overlooked loss components of the optical constants can be appropriately used for perfect absorption, we propose a theoretical analysis employing transmission line theory which match metamaterial optical constant to free space to realize a perfect absorber that strongly absorb the incident wave energy. We establish a full and accurate frame to calculate the absorption performance and energy loss with exact mathematical formulas. For further investigation, we extend our analysis to broadband absorption. The analysis has a instructive guidance in design of perfect broadband absorber in visible, infrared and terahertz spectral regions.The main content and contribution of the dissertation include:1. We construct a quasi-closed subwavelength electromagnetic rectangular resonators using stacked dielectric-plasmonic bilayer structures, in an analogy to the dielectric resonators formed by materials with large permittivity according to Effective Medium Theory. A fully study of the resonant frequency and the radiation/material loss Q-factors of the fundamental mode is represented.2. Based on the subwavelength electromagnetic rectangular resonator and transmission line theory, we establish an analytical framework providing exact formulas to calculate absorber geometrical sets for arbitrary incident wavelength to realize perfect absorption. For incident wave with long wavelength, we simplified the mathematical relationship between absorber size and resonant frequency.3. Taking advantage of that, we present a well-performed trapezoid array structure which could absorb relative broadband incident wave, covering visible, near-infrared, mid-infrared and terahertz spectral regions. Meanwhile, we introduce some critical conditions for perfect absorption and point out some constraints in design.4. We validate the proposed theoretical analysis through numerical simulations based on the finite-element method. The research of boundary conditions and transmission mode are also presented to demonstrate absorption performance. The good agreement of analytical and numerical results demonstrate that a broadband subwavelength absorber consists of multiple stacked dielectric-plasmonic bilayers can be designed.