Structural Designs Of Metamaterials-based Broadband Electromagnetic Responses And Absorbers

Electromagnetic metamaterials are one of novel concepts in material community. Being different from the doping, coating, modification and other artificial methods, the properties of metamaterials are mainly controlled by the special artificial unit structure consisting of them, in which the wave coupling mechanisms dominate the responses. Presently, those novel properties of metamaterials such as negative permittivity and negative permeability are governed by the resonant behaviors of unit cells, and thus, the features of narrow bandwidths and dispersion are hard to be applied in engineering. To expand the working bandwidth and other band features, our work is then focusing on the structural design of unit cell and hopefully solving some of the above-mentioned problems. Starting from the classical metamaterials unit, the mechanisms of electric as well as magnetic coupling and response are analyzed first. Based on the recognitions of the relations between resonant features and structural designs, A multi-mode resonant phase mismatch method of varied components is proposed to realize broadband frequency independent effective negative permeability. By weakening the structural resonances, the effective negative permittivity can also be optimized with broadband and frequency independent features. Following those approaches, our "ring pairs" structure can achieve a broadband frequency independent negative permeability (-0.75) from 0.725 to 0.9 THz. Our "metal square" structure can obtain an effective negative permittivity (-0.3) with broadband and frequency-independent features (from 0.83 to 0.91 THz) In addition, those principles are adopted into an ultra-broadband THz absorber design. By introducing various plasmon resonances modes with special surfaces and cavity designs, our metamaterials absorber can have a broadband electromagnetic absorbance over 90% (>93.71% in average) from 1.64 to 5 THz, less sensitive to the incident orientation and polarization. The properties of our absorber can be further improved with optimization, i.e., an ultra-broad band (0.98-5 THz) and higher absorption efficiency beyond 90% (>96.46% in average).In summary, we successfully extend the working bandwidth of metamaterials with structural design methodology. With the ideas of the multi modes and resonance optimization methods, broadband electric and magnetic responses are obtained. We believe Our work could provide a new way to the engineering of broadband metamaterials and enrich metamaterials design once the rules are failed and not available.