Metamaterials, recognized as advanced artificial materials endowed with distinctive properties, have found diverse applications in everyday life, military endeavors, and scientific research. Starting from monolayer metamaterials, multilayer ones are increasingly researched, especially in the field of electromagnetic wave absorption. In this article, we propose a multilayer metamaterial-absorber (MA) structure comprising two resonant layers crafted with copper and FR-4 dielectric. The presented multilayer MA structure exhibited an absorption greater than 90% in a frequency range from 4.84 to 5.02 GHz, with two maximum absorption peaks at 4.89 and 4.97 GHz. The bandwidth of the multilayer MA surpassed that of the individual single-layer MAs, with extension fractions reaching 360% and 257%, respectively. Through the simulation and calculation, the field distribution and equivalent circuit model elucidated that both individual magnetic resonances and their interplay contribute significantly to the absorption behavior of the multilayer MA. The absorption of the proposed multilayer MA structure was also investigated for the oblique incidence in the transverse electric (TE) and transverse magnetic (TM) modes. In the TE mode, the absorption intensity of two maximum peaks was maintained at over 93% up to an incident angle of 40 degrees and dropped to below 80% at an incident angle of 60 degrees. In the TM mode, the absorption was more stable and not significantly affected by the incident angle, ranging from 0 to 60 degrees. An absorption greater than 97% was observed when the incident angle increased from 0 to 60 degrees in the TM mode. Additionally, the approach in our work was further demonstrated by adding more resonant layers, making 3- and 4-layer structures. The results indicated that the absorption bandwidths of the 3- and 4-layer structures increased by 16% and 33%, respectively, compared to the bilayer structure. Furthermore, we analyzed the thermal distribution within the MA to understand the dissipation of absorbed electromagnetic energy. This research offers valuable insight into the augmented MA through a multilayer structure, presenting the implications for microwave applications like electromagnetic shielding, as well as in the design of MAs for terahertz devices and technologies, including emission and thermal imaging. These findings contribute to the advancement of knowledge in enhancing the absorption capabilities across various frequency ranges, expanding the potential applications of metamaterials.

This study explores the design and performance of a bilayer graphene metamaterial absorber (MA) operating in the GHz range. The structure is developed based on a single-layer MA, which consists of graphene ink layer on an FR-4 dielectric substrate, backed by a continuous copper plate. To enhance absorption performance, a second graphene-FR4 layer with identical dimensions is added, forming a bilayer configuration. Our proposed bilayer graphene MA structure achieves an absorption exceeding 90% with an impressive bandwidth of 8.43 GHz, covering the frequency range from 6.07 GHz to 14.5 GHz. The structure maintains high absorption even at large incident angles and remains insensitive to polarization angles due to its symmetrical design. Additionally, we analyze the absorption mechanism of the bilayer metamaterial structure through surface current distribution and magnetic field investigations. These comprehensive analyses provide valuable insights into the underlying mechanisms responsible for the enhanced absorption in bilayer metamaterial structures. Furthermore, we have successfully fabricated this material, demonstrating its potential for applications in electromagnetic wave shielding technologies and GHz-range devices.

This work investigates the design and performance of a bilayer graphene metamaterial absorber operating in the GHz region. We initially analyzed a single-layer metamaterial absorber composed of a conductive ink graphene structure on a FR-4 dielectric substrate backed by a continuous copper sheet. Subsequently, a second graphene-FR4 layer of identical dimensions was added to create a bilayer structure. While the number of absorption peaks increased, they remained isolated, failing to achieve the desired broadband effect. To overcome this limitation, we explored graphene layers with varying surface resistances. Our findings demonstrate that the bilayer graphene metamaterial absorber achieves an absorption exceeding 90% with a remarkable bandwidth of 9.1 GHz, spanning frequencies from 6.21 GHz to 15.31 GHz. This significant bandwidth expansion is attributed to the synergistic interactions and contributions between the graphene and metal layers within the structure. To gain a deeper understanding of the underlying absorption mechanism, we investigated the surface current distribution, the impact of conductivity, and the individual contributions of each layer. Additionally, we examined the influences of both incident angle and polarization angle on the absorption performance of the proposed bilayer MA. These comprehensive analyses provide valuable insights into the mechanisms responsible for the enhanced absorption observed in multilayer metamaterial structures. Our work holds relevance and might be useful to develop electromagnetic wave shielding technologies and devices operating in the GHz frequency range.