Graphene‐Based Microwave Metasurfaces and Radio‐Frequency Devices

Abstract

Graphene, as a 2D material, has attracted significant attention due to its particular electronic band structure and unique physical properties. Metasurfaces integrated with graphene hold great promise for dynamic manipulation of the electromagnetic waves, where metasurfaces with strong resonances enhance the interaction with incident waves and in turn facilitate a deep modulation through electrical doping of graphene. However, the tunable surface conductivity of graphene is very frequency dependent that makes graphene behave significantly different in THz and microwave band. Due to the novel tuning method of graphene–electrolyte‐based sandwich structures, experimental studies of tunable microwave metadevices have aroused wide interests in the past few years. Herein, the recent progress of graphene‐based microwave metasurfaces and related devices, involved but not limited to tunable absorbers, dynamic beam steering, reconfigurable antennas, and attenuators, are reviewed, enriching the experimental developments of graphene in the microwave region.

High-sensitivity narrow-band CSRR-based Microwave Sensor for Monitoring Glucose Level

“…From DC to microwave frequencies, for typical values of µ c , the energy of the electromagnetic waves is insufficient to promote an electron from the valence band to the conduction band (interband transition) and the following condition exists ℏω < 2|µ c | [24]- [27]. Therefore, for the purpose of this work, in expression (1) it is possible to neglect the interband conductivity term and express the dynamic conductivity of graphene only through the contribution of intra-band conductivity which can be expressed as [26]:…”

Flexible and Dual‐Tunable Radar Absorber Enabled by Graphene

“…[ 24 ] In addition, some kinds of tunable RAs through combining graphene with an active metasurface has been reported. [ 25–31 ] In these kinds of hybrid structures, graphene is used only as an amplitude‐tuning layer by changing its effective sheet resistance, while frequency or phase is tuned still by controlling semiconductor devices including PIN diodes loaded in a periodic metallic metasurface, in which designing the feeding network to provide electrical excitation for lumped components such as varactor diodes and PIN diodes is still a complex task. Meanwhile, these tunable RAs including active semiconductor are bulky and not able to planarization, which is difficultly bent to conform with the carrier.…”

“…[24] In addition, some kinds of tunable RAs through combining graphene with an active metasurface has been reported. [25][26][27][28][29][30][31] In these kinds of hybrid structures, graphene is used only as an amplitude-tuning layer by changing its effective sheet resistance, while frequency or phase is tuned still by controlling semiconductor devices including PIN diodes loaded in a periodic metallic metasurface, in which designing Flexible and tunable radar absorbers (RAs) are in great demand both in stealth technologies and electromagnetic delusion for concealment of complex targets such as aircraft and unmanned aerial vehicle from radar detection. As a general approach, conventional lumped components such as varactor diodes and resistors are employed to achieve frequency and/or amplitude tunability of RAs.…”

Design of a switchable phase‐modulated metasurface with wide modulation bandwidth in S band

“…Metasurfaces have recently garnered extensive research attention owing to their excellent properties, such as their low profile, 4,5 lightweight structure, 6 and easy conformability 7,8 . There are many ongoing studies regarding various types of metasurfaces, including absorptive, 9 frequency selective, 10 absorptive/transmissive, 11,12 and phase cancelation metasurfaces, 13 among others 14 . Once these metasurfaces are designed and fabricated, their performances cannot be changed, and as a result, they are not adaptable in complex and changeable environments.…”

“…7,8 There are many ongoing studies regarding various types of metasurfaces, including absorptive, 9 frequency selective, 10 absorptive/transmissive, 11,12 and phase cancelation metasurfaces, 13 among others. 14 Once these metasurfaces are designed and fabricated, their performances cannot be changed, and as a result, they are not adaptable in complex and changeable environments.…”