| The artificial electromagnetic(EM)absorber consisting of an impedance layer and the metallic ground is able to absorb the EM energy in a wide frequency band.The circuit analog absorber can be realized and the currents can be inspired in the impedance layer by placing it a quarter wavelength away from the metallic ground.Thus,the EM absorbing is achieved since the EM energy is transformed into other forms such as heat.After the research of the conventional reconfigurable methods such as mechanical and electrical reconfigurable,the liquid crystal and graphene are used in the reconfiguration.The research of this paper can be divided into four parts:1.A mechanical reconfigurable absorber is proposed.By rotating the circle metallic patch on the impedance layer,the equivalent capacitor can be adjusted.The reconfigurable principle is analyzed based on the equivalent circuit model(ECM),and the simulation results indicate that the absorbing frequency can be continuously adjusted from 10.5 GHz to 10.7 GHz.2.An electrically reconfigurable absorber is proposed based on the PIN diodes.By adjusting the bias of diodes,the equivalent resistance of the impedance layer can be changed.The ECM of this device are derived from the ECM of the Jerusalem cross,and the three absorbing states are achieved.3.A reconfigurable absorber based on liquid crystal is presented.By adjusting the bias of the liquid crystal,the effective dielectric constant of the substrate can be changed,and the reconfiguration is demonstrated utilizing the ECM.The simulated results indicate that the absorbing frequency can be adjusted within 10.5 GHz and 11.5 GHz.There are some mismatches between measurement and simulation,and the errors are analyzed.4.A reconfigurable absorber based on graphene is presented.By adjusting the bias of the graphene,the equivalent resistance of the impedance layer is changed.The simulated results indicate that the absorbing frequency can be adjusted within 3.1 GHz and 4.6 GHz. |
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