A tunable function broadband absorber based on graphene fractal metasurface in the very long-wave infrared region

The combination of fractal structures with metasurfaces has proven to be an extremely effective method for achieving broadband absorption. A broadband absorber tunable in a very long wavelength infrared (VLWIR) region based on graphene of the Hilbert fractal pattern is proposed. The unique space-filling pattern of this structure enables the generation of gap plasmon resonance mode, thereby extending the absorber's bandwidth. The absorption spectrum can be dynamically adjusted by changing external parameters such as the azimuth angle, the graphene's Fermi level, and the relaxation time. Numerical simulations indicate that under optimal parameters, the proposed absorber achieves ultra-broadband absorption within the long-wave infrared target range (14-32 μm). The fractal absorber achieves consistently exceeded 90 % absorption in 15.2–30.6 μm with an average absorption of 95.73 %. Furthermore, the proposed absorber exhibits an excellent wide angle of incident stability. Our findings provide a novel strategy for designing fractal absorbers with broadband absorption capabilities in VLWIR. Our design has potential applications in VLWIR imaging and modulators, also can be applied to sensors, thermal emitters and photoelectric switches.