Abstract
Single-layer metallic rings are the effective structure cell which are widely used to design single-band and multiband perfect metamaterial absorbers owning to their electromagnetic resonance. However, the absorbers based on the single-layer metallic rings have a common shortcoming, that is the narrow absorption bandwidth. To overcome the limitations, here we proposed a single-layer, flexible and broadband terahertz metamaterial absorber, which consists of four sub-cells with multiple metal rings and a metal ground plane separated by a dielectric layer. By enhancing the coupling response between adjacent metallic rings and merging the adjacent resonant peaks of multi-resonators, we experimentally observed broadband characteristics at the terahertz band. The average absorption of 88% from 0.63 to 1.34 THz and the relative absorption bandwidth of 95% at the incident angle of 15o for TE polarization. Correspondingly, for TM polarization the absorption of more than 80% from 0.61 to 1.1 THz with the relative absorption bandwidth of 80% were also observed. The results went far beyond the previous single-layer absorbers based on metal rings and were much better than the fractal-cross structure reported recently [Kenney et al., ACS Photonics 4, 2604 (2017)]. We had reason to believe that the presented terahertz metamaterial absorber with broad absorption bandwidth and simple structure can find important applications in communication, stealth, energy harvesting systems and so on.
Highlights
The rapid development of science and technology in terahertz wave, which designated band of frequencies from 0.1 to 10 terahertz,[1] has spawned a series of significant applications, such as medical imaging,[2] explosive detection,[3] biological sensing,[4] and wireless communications with ultrahigh data rate.[5]
We propose a broadband terahertz metamaterial absorber formed by sub-cells of four square metallic rings with different sizes and a metal ground plane separated by a flexible dielectric layer
The electromagnetic coupling response between adjacent metallic rings can be enhanced by adjusting the structural dimensions of the square rings and the dielectric layer
Summary
The rapid development of science and technology in terahertz wave, which designated band of frequencies from 0.1 to 10 terahertz,[1] has spawned a series of significant applications, such as medical imaging,[2] explosive detection,[3] biological sensing,[4] and wireless communications with ultrahigh data rate.[5]. Metamaterials are candidates for developing high-performance terahertz devices owing to the strong interaction between electromagnetic wave and artificial structures.[6,7,8,9] For example, metal ring structure has been widely used to design metamaterial absorber in THz band because the strong electromagnetic resonance response can generate the perfect absorption peak.[10,11,12,13] these perfect metamaterial absorbers have advantages in applications such as filtering, high-resolution terahertz imaging and sensing, they still suffer from narrow operation bandwidth, which is a fundamental obstacle in broadband applications such as high-efficiency signal detection, communications and stealth technology. By means of four fractal resonators in one unit cell, a broadband THz metamaterial absorber with the average absorption of 83% from 2.82 THz to 5.15 THz and the relative absorption bandwidth of 65% has been experimentally reported.[23] It follows that the absorption bandwidth by engineering multiple resonating structures in single-layer unit cell still has a lot of room for promotion. The proposed absorber may provide a method for absorption engineering to realize bandwidth enhancement in the terahertz wave and generate more significant functions
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