Near-field Thermal Radiation Characteristics Of Metamaterials Based On The Fluctuation Dissipation Theorem

The enhancement of near-field radiation exceeds the blackbody limit due to theexcitation of surface wave and photon tunneling, has attracted much attention duringthe past years. Metamaterials are artificial composite material and they possesspeculiar electromagnetic properties， such as the existence of electromagneticresonances and negative refraction. Based on the fluctuation-dissipation theorem,this dissertation presents detailed analysis of the near-field radiation formetamaterials.Firstly, using S-parameter retrieval method in effective medium theory, theelectromagnetic parameters of metamaterial with array of wires and split ringresonators and metal-dielectric-metal sandwich-like fishnet-structure are obtained.The dispersions of effective permittivity and permeability for the two metamaterialsare presented for further analysis the characters of near-field radiation.Secondly, based on the fluctuation-dissipation theorem, considering the electricresponses and magnetic response in metamaterials, the density of state (DOS) formetamaterial is derived using fluctuation dissipation theory, by separatelyconsidering electric response and magnetic response. Moreover, by consideringmagnetic effect, the reflection and transition coefficient expressions are newlyderived. The comparison of DOS between metamaterial and dielectrics arepresented.Finally, the analysis of near-field radiation for two typical metalaterials iscarried out. The analysis for the original metamaterial with array of wires and splitring resonators show the enhancement of DOS and the heat transfer at electric andmagnetic resonance frequency, the density of states variation with distance toelectromagnetic metamaterials plane, and other general physical mechanisms ofnear-field radiation for metamaterials. For metamaterial with fishnet-structure whichis closer to the actual engineering, by adjusting the structural parameters andconsidering the diffraction surface waves, new enhanced spectrum of near-fieldradiation can be added.