Controlling electromagnetic waves with active graphene devices
The dynamic control of electromagnetic waves forms the basis of modern communication technologies. Although sources of microwaves can be controlled by electrical means, the active control of microwaves in the free space has been a challenge due to the lack of an active material. Graphene, the 2-dimensional crystal of carbon, provides a unique platform to control light-matter interaction in a broad spectrum. This thesis describes a new approach to control microwaves using large area active graphene devices. Our strategy relies on electrostatic tuning of the density of high mobility charge carriers on an atomically thin graphene electrode which operates as a tunable metal in microwave frequencies. We developed a method to synthesize large area graphene (20x20 cm2) by chemical vapor deposition. Using large area graphene electrodes, we demonstrate a new class of active surfaces capable of real-time electrical control of reflection, transmission, and absorption of microwaves over a broad spectrum. These active devices allow us to fabricate electrically tunable microwave surfaces such as switchable radar absorbing surfaces and tunable metamaterials with modulation depth of 50𝑑𝐵 and operation voltage of 3𝑉. Large modulation depth, simple device architecture, and mechanical flexibility are the key attributes of the graphene-enabled active microwave surfaces that could find a wide range of applications ranging from active signal processing to adaptive camouflage.