Novel Metasurfaces for Manipulating Classical Waves and Observing Topological Effects

Over the last several years, metasurfaces have become one of the fastest-growing research fields in modern theoretical and applied electromagnetics and acoustics. In this thesis, we will demonstrate our work in developing novel metasurfaces for manipulations of electromagnetic waves and acoustic waves at different frequency bands. The first project is a metasurface for ultrasonic waves which could focus the reflected waves with a tunable focal length which is linearly dependent on the frequency of incident waves. The second project is a metasurface for microwaves which could convert the circular polarization of the incident waves with near-unity efficiency. The third project is a metasurface which could act as a tunable high-efficiency absorber for low-frequency acoustic waves. The forth project is an acoustic metasurface which allows ventilation while at the same time maintaining a high-efficiency absorption. The fifth project is an electromagnetic metasurface which could support non-leaky valley-Hall effects and we directly observe many features of valley-Hall topological edge states using this metasurface. In summary, these novel metasurfaces could have potential applications in acoustic and electromagnetic engineering due to their ease of fabrications, small thickness and high structural stability.