Design and characterization of metamaterials for terahertz region

Nebioğlu, Mehmet Ali
Metamaterials are manmade structures whose electromagnetic properties can be controlled with subwavelength inclusions. Due to this property metamaterials has gained importance in the terahertz region. Although terahertz radiation has many important applications in communication, astronomy, spectroscopy, imaging, biology and sensing, lack of materials which gives a response in this range decelerated development of devices to control and manipulate the terahertz waves. Metamaterials show a large potential to ll this gap since they have many applications such as superlenses, terahertz modulators, and antenna structures. Metamaterials are unique in that they exhibit a negative magnetic permeability and dielectric permittivity. Two dimensional metamaterials are called metasurfaces. These are two dimensional arti cial structures which show single negative metamaterial properties as opposed to three dimensional structures which show double negative properties. In this thesis, metasurface structures based on various conducting materials such v as copper, gold, indium tin oxide as well as yttrium barium copper oxide were designed, simulated and characterized especially for the terahertz region of the electromagnetic spectrum. Emphasis was placed on highly conducting materials, such as metals and superconductors. Extracted data of substrates were used to simulate metasurface structures using commercially obtained Computer Simulation Technology (CST) Microwave Studio program. Each metasurface structure was designed such that the frequency of the resonance lies in the terahertz region and this was veri ed by simulating the behavior of the structure in the terahertz region. Superconducting metasurface characterization was done with a closed cycle helium cryostat that was installed inside the terahertz time domain spectroscopy system. Experiments were done at 20, 40, 60, 70, 80, 84, 86, 90 and 298K. At di erent temperatures a shift in the resonance frequency and change in the resonance amplitude was observed. It was found that the simulation results were in good agreement with terahertz time domain spectroscopy results. The ability to measure both amplitude and phase allows this technique, terahertz time spectroscopy, to be used to extract metamaterial properties without prior knowledge of the structure shape.