Abstract
We propose and validate an approach to obtain an ultra-broadband terahertz absorber by taking the advantages of the absorption of the surface plasmon resonance in combination with the absorption of the intrinsic mode. The absorber is composed of a gold (Au) bottom layer and a patterned graphene embedded in TOPAS polymer, exhibiting ultra-broadband absorption by coupling the surface plasmon resonance and the intrinsic modes. The single-layer graphene is patterned to C4 symmetric regular polygons which are arranged in circle circumscribed polygons (CUPs) or circle inscribed polygons (CIPs) at the same periodicity for comparison. With the increase of the side number ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> ), the strongest and weakest coupling of the surface plasmon resonance and the intrinsic modes was achieved at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> = 4 (square) and ∞ (circle) for CUP and CIP arrangements, respectively. The optimum absorption bandwidth of 2.54 THz with relative absorption bandwidth of 109.5% above 90% absorption efficiency has been achieved for the circles with a diameter of 12.4 μm arranged at a gap distance of 1.0 μm. This design shows broader relative absorption bandwidth than previously reported single-layer graphene THz absorbers. Therefore, the proposed method would be highly valuable to design and manufacture ultra-broadband THz absorbers.
Highlights
THE electromagnetic wave absorber at terahertz (THz) frequency is an indispensable component in terahertz devices/systems for biosensing, imaging and communication [1], and can be used for terahertz stealth technology as well [2]
The graphene material shows obvious advantages in broadband absorbers according to its two-dimensional (2D) structural characteristics and the ability for dynamical control over the THz band absorption properties by doping or applying voltage [38, 39], making them be highly potential for applications in THz absorbers
We present an ultra-broadband THz absorber benefited from a simple graphene structure
Summary
THE electromagnetic wave absorber at terahertz (THz) frequency is an indispensable component in terahertz devices/systems for biosensing, imaging and communication [1], and can be used for terahertz stealth technology as well [2]. Broadband absorption of a graphene-based THz absorber is usually obtained by the combined contributions of the intrinsic mode of the F-P cavity and the surface plasmon resonance mode of the periodic structural units. Simulation results show that an absolute absorption bandwidth of 2.54 THz with relative absorption bandwidth of 109.5% above 90% absorption efficiency is obtained by optimizing the shape and size of the single-layer graphene metamaterial under the graphene chemical potential of 0.5 eV. The relative absorption bandwidth is broader than previously reported single-layer graphene metamaterial THz absorbers [35, 36, 43, 44], and the absorption efficiency can be dynamic adjusted in a wide range by varying the chemical potential. The optimized absorber is stable and insensitive to the incident angle, and the absorption efficiency is guaranteed within acceptable manufacturing error
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