The Electromagnetic Properties Of Chiral Metamaterial

Maxwell equations reveal that the electromagnetic (EM) parameters of material determines the behavior of EM wave propagation. Since the EM parameters of metamaterial can be designed and tailored, it has many peculiar properties hardly found in nature. Chiral metamaterial, as a new kind of metamaterial, can have strong chirality and cause cross coupling between the electric and magnetic fields, therefore provides more ways to manipulate EM wave propagation due to the additional material EM parameter, the chirality. Since Professor J. B. Pendry proposed that chiral metamaterial could be used to realize negative refraction in2004, it has attracted more and more attention. Thanks to the novel properties of chiral metamaterial, it can find extensive applications in many areas like microwave absorber, antenna design, and microwave devices. Therefore it is important to undertake extensively study of the chiral metamaterial.The presented thesis investigates the EM wave propagation characteristics of chiral metamaterial, as well as some relatively theoretical and experimental analysis, especially focuses on the asymmetric EM wave transmission within the chiral metamaterial. Based on the previous research results reported, a kind of chiral metamaterial structure is proposed that can achieve asymmetric transmission only for linearly polarized EM wave. Furthermore, we have designed and fabricated some corresponding chiral structures, investigated their chiral properties, and provided validations for the design rule of the chiral structures which ensures asymmetric transmission of linear polarization only. This thesis mainly concludes the following parts:1. With the help of the constitutive relations of chiral metamaterial and the classical EM theory, we have studied the EM equations of the wave propagating through chiral metamaterial, together with the reflection and transmission properties. Through analyzing the asymmetric transmission which arises from chirality, a kind of chiral metamaterial structure is proposed that could achieve asymmetric transmission only for linearly polarized EM wave.2. By employing two twisted Spilt-ring resonators (SRR), we designed and fabricated a kind of three-layered chiral structure. The SRR structure is found to be sensitive to the polarization of the incident wave, and the chiral structures are investigated to have different propagation EM properties for different twisted angles. The associated chiral EM properties are also investigated, e.g., the EM resonance, polarization conversion, and the optical activity. By analyzing the equivalent circuit model of the structures, we further investigated the physical mechanism for the resonant characteristic of the structures.3. For the investigation of the asymmetric transmission of linear and circular polarizations, we designed and fabricated different three-layered chiral structures with square SRRs and circular SRRs, respectively. We validated the design rule of the chiral structures ensuring asymmetric transmission of only linear polarization. The calculated and measured results all indicate that, when the chiral structure satisfies the design rule, it obviously has asymmetric transmission for linearly polarized wave, which can lead to remarkable difference for the transmission of identical linearly polarized incident EM waves with opposite directions. The property provides a new way to design and realize EM devices with one-way propagation phenomenon..