Research On Graphene-based Tunable Attenuators And Flexible Attenuators

Graphene,as an ultra-thin two dimensional material formed by carbon atoms in honeycomb lattice,has been the focus of intensive efforts recently.Due to its interesting mechanical,optical,and electrical properties,graphene has a good prospect in the field of material science,chemistry,electronics and biomedicine.And the graphene-based devices not only have compact structures,but also have the property of electrical tunability,transparency and flexibility.Due to these excellent characteristics of graphene,graphene-based dynamically tunable attenuators and flexible attenuators have been researched in this thesis.The main points of this paper are as follows.Firstly,the methods of synthesis,transfer,measurement and electrical control of graphene have been summarized.Besides,the electromagnetic model of graphene has been analyzed and the tunability of graphene sandwich structure has been validated by experiments,which are the basis for our work.Secondly,a dynamically tunable coaxial attenuator based on graphene is presented.The mechanism of this attenuator is theoretically analyzed and an approximate formula to calculate attenuation with different parameters is proposed.We experimentally demonstrate that attenuation of the attenuator can be tuned from 3d B to 14.5d B with good flatness in broad operation frequency from 2GHz to 9GHz when graphene impedance is changed by different bias voltage.The theoretical calculation and simulation results have a good agreement with experimental results,while the|S₁₁|can always remain low level under-15d B.Thirdly,a substrate integrated waveguide（SIW）H-plane horn antenna with dynamically tunable graphene-based attenuator is presented.The return loss,gain and electric distribution of antenna have been simulated and analyzed.When the surface impedance of graphene is changed dynamically,the gain of antenna can be correspondingly tuned with low return loss.So the switchable horn antenna is in working state with the larger gain and in non-working state with the lower gain.Fourthly,two types of graphene-based flexible attenuators are proposed.The first one places the conformal graphene sheets on flexible spoof surface plasmon polaritons waveguide to realize dynamically tunable and flexible property.The second one is composed of stretchable coplanar waveguide transmission line loaded with graphene nanoplates and stretchable silicone substrate to realize dynamically tunable and stretchable characteristics.