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Influence of the imaginary part of the dielectric layer on the bandwidth of metamaterial absorber and the design of broadband absorption

It is well known that dielectric layer imaginary part (or loss tangent of tan(δ)) plays a crucial role in modulating the absorption rate of metamaterial absorber (MA). However, there is not any systematic investigation into whether tan(δ) impacts resonance bandwidth of the MA. Herein, we investigated the dependence of resonance bandwidth of the MA on the change of tan(δ). Three kinds of absorbers with top layers of frequently used metallic patterns of square patch, cross, and strip were demonstrated. To facilitate comparison of the bandwidth, each case of tan(δ) was optimized for perfect absorption. Results proved that the bandwidths of the three absorbers were broadened greatly with tan(δ) increase. Their bandwidth enhancement factors are all at least 10. Based on this, this paper further makes some discussions on the design of broadband MA, which consists of three alternating stack of square patches and dielectric layers with large value of tan(δ) on top of a metallic board. >80% absorption of the resonance bandwidth of the triple-layer absorber can cover a frequency range of 3.689 THz. The relative resonance bandwidth of absorber can reach 138.893%, which is far higher than that of previous broadband absorbers using small value of tan(δ).