Consecutively Strong Absorption from Gigahertz to Terahertz Bands of a Monolithic Three-Dimensional Fe₃O₄/Graphene Material

Abstract

With the booming microwave and terahertz technology for communication, detection, and healthcare, the consequently increasingly complicated electromagnetic environment is in urgent need of high-performance microwave and terahertz absorption materials. However, it is still a huge challenge to achieve consecutively strong absorption in both microwave and terahertz regimes. Herein, an ultra-broadband and highly efficient absorber for both microwave and terahertz bands based on the monolithic three-dimensional cross-linked Fe3O4/graphene material (3DFG) is first reported. The 3DFG shows an incredible wide qualified absorption bandwidth (with reflection loss less than −10 dB) from 3.4 GHz to 2.5 THz, which is the best result in this area by far. Furthermore, the remarkable absorption performance can be maintained under oblique incidence, different compressive strains, and even after 200 compression/release cycles. The designed highly porous structure for minimizing surface reflection combined with the micro–macro integrated high lossy framework results in the excellent absorptivity, as verified by the terahertz time-domain spectroscopy technique. With these, the 3DFG achieves an unprecedentedly average absorption intensity of 38.0 dB, which is the maximum value among the broadband absorbers. In addition, its specific average microwave and terahertz absorption value is over 2 orders of magnitude higher than other kinds of reported materials. The results provide new insights for developing novel ultra-broadband absorbers with stronger reflection loss and wider absorption bandwidth.

Transparent Perfect Microwave Absorber Employing Asymmetric Resonance Cavity

“…Note that the thickness of each layers are not drawn to scale in Figure , in order to better illustrate the intensive field and high absorption regions in the structure. In addition, recent development of absorbing materials or structures based on graphene with broad effective bandwidth is imperative for adapting to complex electromagnetic environment . As the microwave power is exclusively absorbed in the graphene layer in this GDS cavity, the effective way to improve absorption bandwidth is to add more graphene layers in the cavity separated by the silica on top of ultrathin doped Ag, which can introduce multiple resonances in different graphene layers at different frequencies, and the overlap of these resonances enables broadband absorption.…”

Recent progress in two-dimensional materials for terahertz protection

“…According to the electromagnetic transmission theory, the simplified transmission model of THz reflection loss could be established, as shown in Fig. 2a [34,35]. The incident THz radiation E 0 transmitted into the absorbing material from the air.…”

“…Metal When the THz radiation was normally incident to medium 2 (absorbing material) from medium 1 (air), according to the Fresnel formula, the reflectivity R and transmittance T at the interface could be expressed as follows [35][36][37]:…”

“…The THz wave would be attenuated with propagating a certain distance L in the lossy medium, so the intensity of THz radiation E L (ω) could be expressed as follow [35]:…”

“…where c is the speed of light (3 × 10 -8 m•s -1 ), ω is the angular frequency (rad•s -1 ), E 0 (ω) is the initial THz signal intensity. And the propagation loss , which was defined as the power ( , ) ratio of THz signal after a propagation length to the initial THz signal, could be expressed as follow [35]:…”