Tunable, switchable, and one-way electromagnetic wave absorbers based on metamaterial structures

Abstract

Recently metamaterials have been employed to construct electromagnetic (EM) wave absorbers [1]. The idea of metamaterial absorber is to adjust the effective permittivity and permeability independently by varying the dimensions of electric and magnetic resonant components in the unit cell so as to match the effective impedance of the absorber to free space and achieve a large resonant dissipation at the meantime. Thus, wave transmission and reflection are minimized simultaneously and absorption is maximized. Although metamaterial absorber has relatively narrow bandwidth, it possesses many advantages such as high absorption, low density, and thin electric thickness. Moreover, the frequency response can be tailored or scaled from microwave to terahertz and infrared regimes through carefully designing the constituent resonant structures. Since the EM performance of the metamaterial absorber is entirely determined by the resonant structure in the unit cell, it is possible to change or control the absorber performance by incorporating active elements into the resonant unit cell [2-3]. In this presentation, we will report on several controllable metamaterial absorbers that are realized by integrating resonant unit cell structure with microwave varactors or diodes, as well as a one-way microwave energy absorber based on a composite metamaterial structure including chiral structure. These metamaterial absorbers with tunable, switchable or one-way performances could find application in many functional devices for manipulation of the EM wave propagation and the design concept could also be scaled to other frequency band such as terahertz or optical range.