Studies Of Terahertz Filters Based On Metamaterials

Metamaterial is a kind of artificial composite material, which has the periodic unit cell structure. Through rationally designing the size and shape of the unit cell structure, we can achieve various fascinating electromagnetic phenomena. Owing to these features, metamaterials can be widely used in the invisible cloak, super lens, negative refraction and other research fields. Because the terahertz wave devices based on metamaterials have great application prospect in terahertz imaging, spectrum, bio-sensing and other fields, the terahertz functional devices based on metamaterials such as terahertz filters, terahertz sensors, terahertz absorbers, and terahertz modulator, have been aroused intense research interest. Therefore, the further research on terahertz function devices can meet the application requirements and will promote the development of terahertz science and technology.In this thesis, we focus on the filter structure design based on the terahertz metamaterials, and study the transmission characteristics of the transmission spectrum. The main contents include:1. We report two novel high-quality-factor terahertz metamaterials based on asymmetric double split ring resonator (ADSRR) as unit cells. We numerically calculated the transmission spectrum through the proposed metamaterial structures. The simulation results show that we obtain an extremely sharp trapped-mode resonance with high quality factor Q and a new mix-mode resonance with relatively high quality factor Q. Through the surface current distribution at each resonance frequency, we analyze the mechanism of the trapped-mode resonance and the mixed-mode resonance. The quality factor and center resonance frequency of the resonances can be tuned by changing the gap position and vertical distance between the horizontal metal microstrip lines of the metamaterial unit cell. Through optimizing the design of the parameters of unit structure, the highest quality factor of trapped-mode resonance based on the first metamaterials structure is about 40, and the highest quality factor of the mixed-mode resonance of is about 16, which are approximate to 13 times and 5 times of the quality factor of the dipole resonance based on the symmetric structure, respectively. The highest quality factor of trapped-mode resonance based on the second metamaterial structure is about 38, and the highest quality factor of the mixed-mode resonance of is about 18, which are approximate to 13 times and 6 times of the quality factor of the dipole resonance based on the symmetric structure, respectively. In addition, we introduce the concept of FOM of resonance response. Through a detailed analysis of the FOM, an effective compromise between high quality factor and resonance intensity is achieved.2. We propose a broad stop-band terahertz filter structure based on metamaterials, which is made of metal-dielectric-metal (MDM) sandwich structure as the basic unit cell. We simulate the transmission spectrum through the proposed metamaterial structures. The numerical simulation results show that the MDM metamaterial structure is excited a broad stop-band resonance with a flat bottom in the terahertz frequency region, and the stop-band resonance possesses a notable spectral-filtering capability with a 0.56-THz-broad bandwidth and excellent band-edge transitions of 170% THz and 185% THz in the THz-gap region. In addition, we also deeply analyze the generation mechanism of stop-band resonance of MDM metamaterial structure and the influence of dimension parameters and dielectric constant of the unit cell structure on the stop-band resonance characteristics.