Graphene-based waveguide resonators for submillimeter-wave applications

Abstract

Abstract. Utilization of graphene covered waveguide inserts to form tunable waveguide resonators is theoretically explained and rigorously investigated by means of full-wave numerical electromagnetic simulations. Instead of using graphene based switching elements, the concept we propose incorporates graphene sheets as parts of a resonator. Electrostatic tuning of the graphene surface conductivity leads to changes in the electromagnetic field boundary conditions at the resonator edges and surfaces, thus producing an effect similar to varying electrical length of a resonator. Presented outline of the theoretical background serves to give phenomenological insight into the resonator behavior, but it can also be used to develop customized software tools for design and optimization of graphene based resonators and filters. Due to the linear dependence of the imaginary part of the graphene surface impedance on frequency, the proposed concept was expected to become effective for frequencies above 100 GHz, which is confirmed by the numerical simulations. Frequency range from 100 GHz up to 1100 GHz, where the rectangular waveguides are used, is considered. Simple, all-graphene based resonators are analyzed first, to assess the achievable tunability and to check the performance throughout the considered frequency range. Graphene-metal combined waveguide resonators are proposed in order to preserve excellent quality factors typical for the type of waveguide discontinuities used. Dependence of resonator properties on key design parameters is studied in detail. Dependence of resonator properties throughout the frequency range of interest is studied using eight different waveguide sections appropriate for different frequency intervals. Proposed resonators are aimed at applications in the submillimeter-wave spectral region, serving as the compact tunable components for the design of bandpass filters and other devices.

Tuning the Filter Responses with Graphene Based Resonators

“…The achievable tunability range for resonators completely covered with graphene, for the studied insert length of 0.324a, increased from 4% to about 12% with increase in frequency. Likewise, the insertion loss decreased [4]. However, loaded quality factors were lower than those in the metallic resonators.…”

“…Due to the linearly increasing inductive component of graphene surface conductivity with the increase in frequency, it is proven to be a good electromagnetic material for low-terahertz and terahertz frequencies. Graphene based waveguide resonators were studied at frequencies from 100 GHz up to 1100 GHz [4]. The achievable tunability range for resonators completely covered with graphene, for the studied insert length of 0.324a, increased from 4% to about 12% with increase in frequency.…”

“…Novel components and circuits are also being proposed, often relying on the design approaches using micromachining, metamaterials, new materials such as graphene, etc. In line with these current trends, we have proposed and studied the tunable graphene-metal combined waveguide resonators [4], where the graphene has been employed in order to achieve frequency tunability. Due to the nonlinear frequency dependence, around the desired central frequency, of the equivalent analytical models of E-plane discontinuities as well as pronounced losses in graphene, an accurate analysis required the full-wave EM numerical computations [4].…”

“…In line with these current trends, we have proposed and studied the tunable graphene-metal combined waveguide resonators [4], where the graphene has been employed in order to achieve frequency tunability. Due to the nonlinear frequency dependence, around the desired central frequency, of the equivalent analytical models of E-plane discontinuities as well as pronounced losses in graphene, an accurate analysis required the full-wave EM numerical computations [4]. The state-of-the-art commercial software package HFSS has been employed in the design procedures relying on the extensive design space mapping [5].…”

Design methodology for graphene tunable filters at the sub-millimeter-wave frequencies

“…Not only is the span of the available components broadened, but additionally, the theoretic basis for the utilization of similar concepts in a somewhat different setting is developed. Having that in mind, we have recently proposed and analyzed in detail graphene based tunable rectangular waveguide resonators [22]. Graphene has been proven as a very good material for sub-millimeter wave (low-terahertz) applications.…”