Electromagnetic Wave Modulation And Amplification Using Active Metasurfaces

Electromagnetic metamaterials(MTMs),are defined as artificially and effectively homogeneous electromagnetic structures with unusual properties not readily available in nature.MTMs have been widely investigated in recent years due to their unique reflection,transmission and absorption characteristics for electromagnetic waves.These wave manipulation capabilities can be further extended by introducing active elements into unit cell structures.This thesis focuses on free space EM wave modulation and amplification using active metasurfaces.In the aspect of EM wave modulation,we propose both a polarization-dependent and a polarization-independent metasurface modulator that work in the X band.As to EM wave amplification,we propose a metasurface whose reflection magnitude can be greater than 1 in a certain frequency band while the reflection phase can be dynamically adjusted.A reflectionless metasurface,whose transmission coefficient can be arbitrarily designed,is also proposed.The main contents include:1.Inspired by perfect metamaterial absorbers,we design a metasurface modulator that works in the X band.The resonance absorption frequency of the metasurface modulator can be tuned in 1 GHz range,which allows that a maximum of nearly 10 dB reflectance variation can be obtained for a certain frequency point in this range.An information transmission speed of 1 Mbit/s has been experimentally demonstrated using this modulator.In order to further increase the information transmission speed,we also propose a polarization-independent metasurface modulator by utilizing a symmetric unit cell.The information transmission speed can be doubled by independently modulating the two orthogonal-polarized incident EM waves.2.To eliminate the energy loss in MTMs,we introduce tunnel diodes into our metasurface's unit cell designs.A reflection phase tunable metasurface,whose reflection magnitude can be greater than 1 in a certain frequency band,is demonstrated.The amplification effect is achieved when the tunnel diode operates in the negative resistance region,while the reflection phase tunability is obtained by the integrated varactor diodes.In the last part,we propose a reflectionless metasurface whose transmission coefficient can be arbitrarily designed.