| Summary: | 碩士 === 國立清華大學 === 工程與系統科學系 === 94 === When electromagnetic waves penetrate a system that is composed of periodically modulated dielectric material in space, it behaves like electrons in a crystal. Such systems are called Electromagnetic Crystals when they are used for microwave regime. Contrast to electrons in a crystal, in electromagnetic crystals we can fabricate an electromagnetic bandgap in which no propagating modes will exist.
The goal of this study is to solve band structures of square and triangular lattice by Finite Element Method（FEM）. Another structure, electromagnetic crystal slabs, are also considered due to its easy fabrication and integration with other planar microwave passive devices on a substrate. Here we adopt commercial EM simulation software－High Frequency Structure Simulator（HFSS）as our tools. After solving band structure, we construct a driven model to calculate S parameter of finite periods and compare with each other.
In experiment, we fabricate Electromagnetism Crystal Slabs with a square arranged air holes of different rows in Γ→X direction. By measuring S parameter using HP 8510C, we can see the formation of TM-like mode bandgap which occurs in 36－38 GHz. Comparison of the bandgap position between the measurement data, 36－38 GHz, and the simulation results, 35.6－37.5 GHz, shows that they agree with each other.
Besides, another structure is also obtained by changing the diameter of the air holes. We can find that when the diameter of air holes decreases from 0.6 mm to 0.5 mm, the bandgap center frequency of TM-like mode will shift from 37 GHz to 34.5 GHz. When the diameter of air holes decreases below 0.4 mm, the TM-like mode bandgap becomes unobvious.
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