# Implementation of Atomically Thick Graphene and Its Derivatives in Electromagnetic Absorbers
## 2 Graphene-Based Quarter-Wavelength Absorbers
### Dielectric/Graphene Multilayer Absorbers  
Finally, there are also quarter-wavelength absorbers based on dielectric/graphene structure operating from THz to optical frequencies under wide absorption angle [72; 73; 74; 75; 76; 77]. Unlike the Salisbury, Jaumann and Dallenbach absorbers that require a metallic ground, the dielectric/graphene absorbers utilize one or more kinds of dielectrics as well as graphene to achieve EM absorption, as shown in Figure 5a-c. Slightly different from the absorbers with a metallic ground, the EM wave transmittance (\(T\)) has to be considered in these devices and the absorption (\(A\)) is calculated with Equation (7). Strong wave absorption is achieved when the transmittance is minimized and Fabry-Perot resonance occurs. The absorption performance of dielectric/graphene absorbers can also be tuned by varying the chemical potential of graphene [75; 76; 77]. No extra metallic electrodes are required in these devices as the graphene layers act as optical transparent electrodes for self-biasing, as shown in Figure 5b,c. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Year** & **Ref.** & **Type** & **BWmax** & **tmax** & **RLmin** & **fmin** & **tmin** \\  & & **(GHz)** & **(mm)** & **(dB)** & **(GHz)** & **(mm)** \\ \hline
2018 & [51] & rGO/FeNi & 5.6 (10.9–16.5) & 2 & \(-\)42.6 & 14.3 & 1.5 \\
2018 & [52] & rGO/MWCNTs/ZnFe\({}_{2}\)O\({}_{4}\) & \(>\)2.3 (15.7–18+) & 1 & \(-\)22.2 & 17.4 & 1 \\
2018 & [53] & Graphene/CoFeAl-LDH & 7.36 (10.4–17.76) & 2.5 & \(-\)23.8 & 14.2 & 2.5 \\
2017 & [18] & rGO/SiC & \(>\)4.2 (8.2–12.4+) & 3.7 & \(-\)40.7 & 10.9 & 3.5 \\
2017 & [50] & rGO/Co\({}_{0.2}\)Ni\({}_{0.4}\)Zn\({}_{0.4}\)Fe\({}_{2}\)O\({}_{4}\) & 10 (6.4–16.4) & 4 & \(-\)52.2 & 13.5 & 4 \\
2017 & [54] & rGO/CoFe\({}_{2}\)O\({}_{4}\) & 5 (12.2–17.2) & 2 & \(-\)53.6 & 11.4 & 2.5 \\
2017 & [55] & rGO/FeNi/CS & 5 (13–18) & 1.5 & \(-\)45.2 & 15 & 1.5 \\
2017 & [56] & rGO/ZnO & \(>\)4.2 (8.2–12.4+) & 4.8 & \(-\)27.8 & 9.57 & 4.8 \\
2017 & [57] & Graphene/NiO & 4.24 (12.48–16.72) & 1.7 & \(-\)59.6 & 14.16 & 1.7 \\
2016 & [47] & rGO/NiFe\({}_{2}\)O\({}_{4}\) & \(>\)3 (0.01–3+) & 2 & \(-\)68 & 1.11 & 2 \\
2016 & [49] & Graphene/SiOC & 3.9 (8.2–12.1) & 2.65 & \(-\)69.3 & 10.55 & 2.35 \\
2016 & [58] & Graphene/PANI/TiO\({}_{2}\) & 4.4 (12.2–16.6) & 1.5 & \(-\)45.4 & 14.4 & 1.5 \\
2016 & [59] & Graphene/Fe\({}_{3}\)O\({}_{4}\)/Fe & 6.2 (11.8–18) & 2 & \(-\)58 & 5.2 & 4.6 \\
2015 & [48] & Graphene Foam & \(>\)14 (4–18+) & 10 & \(-\)28 & 12.2 & 10 \\
2015 & [60] & GNSs/rGO-CoFe\({}_{2}\)O\({}_{4}\) & \(>\)4.2 (8.2–12.4+) & 2.5 & \(-\)21.8 & 11.8 & 1.25 \\
2015 & [61] & rGO/HGS & 4.1 (13.1–17.2) & 2 & \(-\)46 & 10.9 & 2 \\
2014 & [62] & rGO/FeNi & 3.3 (11–14.3) & 1.5 & \(-\)32 & 12.4 & 1.5 \\
2014 & [63] & Graphene/Fe\({}_{3}\)O\({}_{4}\)/SiO\({}_{2}\)/NiO & 5.1 (12.4–17.5) & 1.8 & \(-\)51.5 & 14.6 & 1.8 \\
2014 & [64] & rGO/ZnO & 6.3 (11.7–18) & 2.5 & \(-\)25.95 & 10.2 & 3 \\
2013 & [46] & rGO/PEDOT/Co\({}_{3}\)O\({}_{4}\) & 3.1 (9.4–12.5) & 2 & \(-\)51.1 & 10.7 & 2 \\
2013 & [65] & Graphene/Fe & 4.4 (9.7–14.1) & 2 & \(-\)45 & 7.1 & 3 \\
2013 & [66] & rGO/CuS/PVDF & 3.8 (8.9–12.7) & 2.5 & \(-\)32.7 & 10.7 & 2.5 \\
2013 & [67] & rGO/Fe\({}_{3}\)O\({}_{4}\) & 2.8 (10.4–13.2) & 2 & \(-\)26.4 & 5.3 & 4 \\
2013 & [68] & Graphene/Co\({}_{3}\)O\({}_{4}\) & \(>\)6.4 (11.6–18+) & 2.5 & \(-\)33.58 & 15.8 & 2.5 \\
2013 & [69] & Graphene/Fe\({}_{3}\)O\({}_{4}\) & 5 (10.8–15.8) & 3 & \(-\)40.3 & 7.04 & 5 \\
2012 & [45] & rGO/NBR & 4.5 (7.5–12) & 3 & \(-\)57 & 9.6 & 3 \\
2012 & [70] & Graphene/PANI & 5.6 (10.5–16.1) & 2.5 & \(-\)45.1 & 12.9 & 2.5 \\
2012 & [71] & rGO/Fe\({}_{3}\)O\({}_{4}\) & 4.9 (10.8–15.7) & 2 & \(-\)24 & 12.9 & 2 \\
2011 & [44] & rGO/PEO & \(>\)4.1 (13.9–18+) & 1.8 & \(-\)38.8 & 16.4 & 1.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Microwave absorption properties of graphene and its derivatives based composites.