Metamaterial Absorber With Active Frequency Tuning

Metamaterials,due to their novel electromagnetic parameters which are designable,tunable and hardly found in nature,grant us a more effective way to control the electromagnetic waves,and find extensive applications in many areas like optical imaging,optical storage,microwave engineering,medical imaging and military technology.This thesis focuses on the metamaterial absorber(MA)with active frequency tuning.Based on the reported metamaterial absorber,we propose two kinds of tunable MAs in low and high frequency,respectively.On the basis of previous works,we further explore the MAs structure,and design and realize more three MAs:All polarized metamaterial absorber with active frequency tuning;Metamaterial absorber with active frequency band tuning;Metamaterial absorber with switchable electromagnetic energy absorption.The main contributions of this thesis are listed below:1.Utilizing the hardware condition of our lab,the TRL calibration and characterization is explored to measure the parameters of the microwave diode.The result of the simulation shows that this method provides high measurement accuracy within 5%error.2.Based on the previous MAs,a simple,thin,and tunable absorber is realized in low frequency.Adjusting the DC bias voltage of the varactors,the absorbing frequency can change from 2.0 GHz to 2.45 GHz,providing the tuning range of 0.45 GHz.The energy absorption is always above 60%.3.A metamaterial absorber with active frequency tuning in X-band is designed and realized.Adjusting by the DC bias voltage of the varactors,the range of the tuning frequency is 0.44 GHz,with the energy absorption above 95%.4.A kind of transmission line model is used to explain the work mechanism of the MA in X-band.The transmission line model can be divided into two methods:equivalent Slot-Line model and accurate Slot-Line model.Through the comparison of the simulation and calculation results,it is found that the transmission line model works well.5.More three MAs with new functions are proposed and realized:All polarized metamaterial absorber with active frequency tuning;Metamaterial absorber with active frequency band tuning;Metamaterial absorber with switchable electromagnetic energy absorption and reflection.(1)All polarized metamaterial absorber with active frequency tuning:all polarized MA is realized.No matter the wave is polarized along x or y axis,the absorption can reach 100%,with the frequency tuning range 0.36 GHz.The thickness of the MA is only 1/30 of the wavelength.(2)Metamaterial absorber with active frequency band tuning:Through controlling the DC bias voltage of the two cross structures,whose absorbing frequency are close to each other,the MA with tunable-10 dB band can be realized.The experiment result show that the band of 75%absorption can change from 0.3950 GHz to 0.7350 GHz,making the tunable range about 2 times.(3)Metamaterial absorber with switchable electromagnetic energy absorption and reflection:When the PIN is on,the structure is a perfect reflector.When the PIN is off,the structure is a perfect absorber.