Beam Steering Based On Graphene

Graphene,an atomically thin layer of carbon atoms arranged in a honeycomb lattice,has arouse enormous interest due to its outstanding mechanical,thermal,and electrical properties.With the ability of being electrically tunable,graphene emerged as a promising candidate for the design of graphene-based tunable metasurfaces.Metasurfaces,a type of two-dimensional(2D)metamaterials composed of subwavelength building blocks,have proven to be a simple but effective way to control the amplitude,phase,and polarization of electromagnetic waves.The technology of metasurfacebased beam steering,with completive advantages,can find wide applications in science and engineering fields,such as communication system.This thesis contains the following contents:1.Circular SPP wavefront is transformed to three-,four-,five-and six-beams,respectively,based on ENZ graphene which is obtained by tuning its Fermi energy level(chemicalpotential).2.Two types of graphene-based resonators are designed and investigated,with their phaseshifts modulated by the Fermi levels of graphene which are controlled by external voltagegates.When the Fermi level of graphene varies from 0 eV to 1 eV,the phase range canreach more than 270 degrees and the amplitude is more than 0.5.We also analyze thepolarization property of the graphene resonator that usually depends on the direction withrespect to the polarization direction of the incident wave.The property of the resonator isnon-sensitive to the incidence polarization due to the structure symmetry.3.A graphene metasurface in reflection is designed.The metasurface can reflect incidentwave to a series of discrete reflection angles such as 43,31 and 24 degrees,respectively,at 1.75 THz,by designing the required phase profile of the metasurface using four phasesof 0 90 180 and 270 degrees.4.However,the obtained reflection angles are limited because the phase gradients of ametasurface are limited by the unit cell size,which cannot be infinitely small.Recently,anewly pattern shift theory based on convolution theorem is proposed to realize wide anglerange steering,enabling flexible and continuous manipulation of reflection angle.Weproposed and designed a tunable graphene metasurface with the capability to dynamicallysteer the reflection angle in a wide range.We achieved wide steering range from 5o to 70owith an interval less than 10o,which is demonstrated by numerical simulation results.5.We propose a method to steer a beam to nearly arbitrary direction.The procedures are asfollows: First,determine the phase profile that can make the waves interfereconstructively in the desired direction;second,according the phase profile obtained in thelast step,design the phase distribution of the meta surface using deliberately designedresonators at definite frequencies,then the metasurface can steer the beam to the desireddirection.We propose a method to achieve the arbitrary beam steering by using onlylimited phases.In this method,the calculated phases are replaced by the nearest phases inthe phase collection which is available to steer the beams.The deviation is tolerable andcan be further reduced by extending the phase collection.