Circuit Models On The Electromagnetic Induced Transparency Based On Terahertz Metamaterial

Metamaterial is one of the hot topics in electromagnetic field in recent years. Usually, its unit size is smaller than the wavelength, so the metamaterial can be regarded as a continuous medium without considering the coupling between the units. The parameters such as equivalent permittivity and permeability can be used to describe the electromagnetic response of the metamaterial. The fascinating physical properties of metamaterial such as negative refraction, super resolution, electromagnetic black hole are mainly determined by its resonant characteristics. The resonant properties of metamaterials depend on the metal constructing the metamaterials, and the size and shape of metal structure.With the develepment of research, the coupling between the units in metamaterial is also considered for manipulate the electromagnetic wave flexibly and easily. One of the examples is the classic analogue to electromagnetic induced transparency phenomenon (EIT), which is a result of a quantum interference effects occurring in an atomic system. At present, this kind of studies mainly based on the electromagnetic simulation software, calculating the spectrum properties of metamaterials, are not able to analyze the effects of various parameters on the spectrum characteristics. Our work is to present quantitatively and semi-quantitatively through the circuit models, and give the relation between the unit coupling and the transmission spectrum.The main work of this thesis includes:1, we study the circuit model of the EIT and the relationship of two parameters:the coupling strength and the loss of EIT. Meanwhile, the experiments were carried out for testing the results from the circuit model. The experiment is divided into two types:the first experiment was fabricated using superconducting NbN, and adjusting the conductivity of NbN by changing the working temperature for different Ohmic loss of the structure. Another experiment is to change the distance between two resonators for tailing the coupling strength.2, the double-layer U-ring is a common structure to realize EIT. In this section, the capacitive and inductive coupling between two U-rings on different layer is analyzed by using circuit model. The way to adjust the coupling strength is changing the rotation angle between the two-layer U rings. The relationship between resonance frequency splitting and two circuit parameters including resistance and the coupling strength is analyzed.3, we design a conductive coupling between two resonators realizing the EIT. The total coupling includes not only the coupling between the bright and dark resonators, but also the energy transfer through the electric current. They all have the important contribution to the EIT behavior.4, we design and fabricate flexible metamaterial to produce EIT at THz band. The metal structure of the flexible metamaterial is fabricated on a very thin thickness substrate, which can avoid FP effect, and has an important application in THz devices.Through our work, we can analyze semi-qualitatively the influences of coupling between the units on the resonance characteristics of the metamaterials, and further understand the EIT properties dependent on the structure parameters.