Novel Tunable Absorbers And High Power Protection Structure

The artificial electromagnetic structure has exotic electromagnetic properties that are not possessed by natural materials.Among various application of artificial electromagnetic structure,absorbers and high-power electromagnetic protection structures are two important branches.This paper focus on the research on tunable absorbers and high-power electromagnetic protection structures based on the semiconductor devices and graphene.The contents are as follows:1.The paper studies the exotic properties of the two-dimensional material graphene and applies it into the design of absorbers,Furthermore,the paper proposes a metamaterial absorber(MA)with multi modes and tunability characteristics in terahertz(THz)range.The dominant absorption mode and the absorption frequency can be modulated at the same time.Particularly,the absorption would not decrease significantly without the modulation.Compared to the earlier work,the proposed MA have more flexible modulation and wider modulation range.Therefore,it shows promising application potentials.2.The paper also proposes a novel design of dual broadband graphene metamaterial absorber with absorption strength tunability characteristics in terahertz range.Due to the asymmetric nested electrical split ring design,multiple resonances and broadband absorption are obtained simultaneously with simple structure.There are two broad high absorption bands(absorptance larger than 95%)from 1.4 THz to 1.9 THz and 4.5 THz to 5.1 THz respectively.Under the regulation of graphene chemical potential via electrostatic doping,the absorption strength can be controlled electrically from 95% to 10%.Furthermore,it owns a good tolerance of polarization angles and remains high absorption over a wide angles range of incidence up to 70°.The design scheme provides a new perspective to design dual broadband absorbers which is proposed for first time and is scalable to develop various graphene-based tunable broadband absorbers at other frequencies.3.A broadband switchable absorber from 3.5GH to 11.2 GHz is presented in this paper.Based on the switch ability of semiconductor device,multi-layer design is adopted to realize the independent control of absorption in operation band and switch ability in designed frequency band.For demonstration,the proposed absorber is investigated using circuit analogy method and the distributions of the surface current are also discussed in detail to explore the mechanism of broadband absorption.Numerical calculations are carried to investigate the specific performance and experiments are conducted to validate the design furthermore.4.A novel ultrawideband high-power protection structure in S-band is presented.The insertion loss is less than 1 d B for low-power signals in operating band,while the shielding effectiveness is more than 20 d B when exposed to HPM..