Design Of Electromagnetic Absorber Based On Surface Plasmons

Electromagnetic absorber is a kind of material which can absorb theincident electromagnetic wave with little reflection or transmission, it hasimportant applications in many fields such as stealth weapons, electromagneticshielding, blackbody source and solar cells. Plasmonic absorber is one of theemerging absorbers these years, and is attracting more and more attentionrecently for its novel absorbing mechanism and ultrathin structure. Theresearch of this thesis mainly focuses on the design of plasmonic absorber.The rectangular sandwich absorber is studied, which is composed of anarray of subwavelength rectangular metal patch on a thick metal layer,separated by an ultrathin dielectric layer. The unit cell of the absorber isequivalent to a resonant cavity, and the CSPR (Cavity surface plasmonresonance) model is set up. Similar to the metal-dielectric-metal waveguide andmicrostrip patch antenna, the field distribution in the cavity and the resonantconditions are derived. By investigating the inherent loss of the cavity and thecoupling between the mode and the incident field, the resonant absorption isanalyzed qualitatively. The CSPR model is verified by numerically calculatedthe resonant wavelength, resonant absorption and near field distribution of anabsorber with given structure parameters. The study also shows that theabsorber has wide-angle polarization insensitive absorption property.The effect of geometric parameters and material parameters on theresonant wavelength and absorption is investigated in detail, and someempirical methods of parameter choosing for absorber design are summarized.It is shown that the resonant wavelength and absorption are mostly affected bythe thickness of the dielectric layer and the width of the metal patch, so we canoptimize these two parameters when designing an absorber with highabsorption. With the CSPR model and the empirical methods, we present adesign method for a narrow-band wide-angle polarization insensitiverectangular sandwich absorber. As a proof, we design an absorber working at1140nm with resonant absorption of99.3%, we also fabricate and measure the corresponding sample, and the experimental results have the same trend withthe prediction.Finally, to extend the bandwidth of the absorber and reduce the processcost, we carry out some extension researches on the rectangular sandwichabsorber, the effect of high order modes, multisize structure, lossy dielectricand ordinary metal, patches with other shapes and the randomness of thestructure are investigated. The absorption property and possible fabricationmethod of a plasmonic absorber with random multisize circular ordinary metalpatches on the top are also studied.