Study On The Broadband Frequency Response Of Subwavelength Metamaterial

As artificial constructed materials, sub-wavelength metamaterials (SWM) are ofparticular importance in the electromagnetic and optical applications. Unlike thenaturally occurring or traditional composite materials, the electromagnetic properties ofSWM are not only determined by its composition (metal, insulator, semiconductor etc.),but also the arrangement of different meta-atoms. The quick development of SWM inrecent years revealed many exotic phenomena such as negative, zero, and ultrahighrefractive index. Moreover, SWM made a large variety of important applicationsbecome possible, including electromagnetic stealth, sub-diffraction super-resolution,smart electromagnetic communications.In practical applications, the major drawback of SWM is the limited bandwidth dueto the resonant characteristics. As part of the work in the designing of SWM, greatefforts have been done by the scientific community to enhance the bandwidth in recentyears.In this dissertation, we carry out elaborate research work concerning the bandwidthproblem of SWM. The main original work and valuable results of this dissertation are asfollows:1. Based on the effective media theory (EMT) and transfer matrix method (TMM),a mathematical-physical model for the designing of broadband absorber is established.It is found that the frequency dispersion of SWM is of particular importance for thebandwidth enhancement. Furthermore, a multilayer SWM is constructed to furtherincrease the bandwidth;2. In the designing of resonant wide-angle SWM absorber, the mechanism ofmode coupling is discussed. 3. Based on the frequency dispersion, an anisotropic SWM is constructed to obtainbroadband achromatic polarization conversion. Also, broadband anomalous reflection isnumerically demonstrated.4. Using the concept of coherent control, an ultra-broadband coherent perfectabsorber is demonstrated. The absorption can be near100%in the whole frequencyrange between0to5THz. By adjusting the phase shift between two inputs, theabsorption coefficient can be dynamically tuned.5. Combining the time-reversal symmetry and anisotropic SWM, an ultrabroadband coherent perfect rotator is demonstrated. The polarization conversioncoefficient can be near100%in the frequency range between [0,10THz]. It is alsodemonstrated that the output polarization state can be actively tuned by the phase shift.