Design and performance evaluation of terahertz passive and dynamic metasurfaces with potential application in 6G

Driven by the need for improved performance and higher data rates, wireless telecommunication technology has undergone continuous evolution since its inception. The next step of its evolution will bring us the sixth-generation (6G) wireless communication technology. Among a multitude of innovative technologies, metasurfaces have the potential to play an important role in realizing 6G technology. Consequently, artificially designed 2D materials, also known as metasurfaces, warrant special attention and detailed investigation into their performance, characteristics, and limitations. In this dissertation, investigations on terahertz static and dynamic metasurfaces have been performed. First, the design of a broadband static metasurface-based focusing device is presented, and its dispersion behavior is studied. Then, a low-Fresnel-number, broadband, and highly efficient focusing metamirror has been presented, its experimental evaluation has been presented, and the reasons for its high performance metrics have been discussed. Additionally, a metasurface-based focusing mirror has been presented to address the focal shift issue in low Fresnel number optics. It has been demonstrated that this metamirror, operating in broadband, is capable of correcting focal shifts more effectively than an ideal mirror. Finally, an air-gap tunable beam steering metadevice has been presented, experimentally evaluated, and its working principle and limitations have been explained in terms of the dynamic blazed grating mechanism. The results of the investigations on dispersion behavior of metasurfaces-based optics, benefits and limitations of low-Fresnel number optics, and mechanisms and limitations of dynamic metasurfaces are critical in designing metasurface-based optics and devices for the next generation wireless communication technology.