## 4 Conclusions  
In total, a facile method to fabricate series of Si-modified rGO@Fe\({}_{3}\)O\({}_{4}\)/PVDF-_co_-HFP composites was investigated. Meanwhile, the EMW absorption performance of samples illustrated that the lattice defects in graphene modified by silane coupling reagents have a significant influence on the optimized EMA performance. Notably, the optimal Si(2)-rGO@Fe\({}_{3}\)O\({}_{4}\)/PVDF-_co_-HFP with 30 wt % loading (S2-30 wt %) exhibits the high-performance EMA ability. The \(RL_{max}\) value of S2-30 wt % sample over the whole frequency range reaches \(-\)32.1 dB at 3.68 GHz at d = 7 mm and its maximum absorption bandwidth for RL \(<\)\(-\)10 dB is 4.8 GHz (13.2-18 GHz) at a thickness of 2 mm. On the basis of the proposed microwave attenuation mechanism, the high-efficiency EMA performance of S2-30 wt % sample mainly achieves from the interference absorption. Moreover, experimental results highlight that the interfacial polarization, dipole polarization and the higher degree of lattice defects in S2-30 wt % sample and synergistic effect of PVDF-_co_-HFP is beneficial to improving the dielectric loss. Simultaneously, its magnetic loss mainly originates the natural resonance effects of the Fe\({}_{3}\)O\({}_{4}\) NPs, contributing to achieving the impedance matching. It is undoubtable that construction of Si(2)-rGO@Fe\({}_{3}\)O\({}_{4}\)/PVDF-_co_-HFP composite could provide new possibility and strategy for the fabrication of the high-performance broadband EMA materials.  
**Supplementary Materials:** The following are available online at [[http://www.mdpi.com/1996-1944/13/4/933/s1](http://www.mdpi.com/1996-1944/13/4/933/s1)]([http://www.mdpi.com/1996-1944/13/4/933/s1](http://www.mdpi.com/1996-1944/13/4/933/s1)), Detailed TEM images of Si-modified rGO@Fe\({}_{3}\)O\({}_{4}\) (Figure S1); FT-IR spectra (Figure S2) and XPS patterns (Figure S3) of Si-modified GO, relative complex (S0-S2) electromagnetic patterns with different mass fraction loading (Figure S4-S6) and complex attenuation constants (Figure S7); \(|Z|\) modulus (Figure S8) of Si-modified rGO@Fe\({}_{3}\)O\({}_{4}\)/PVDF-_co_-HFP with 30 wt% loading; and frequency dependence of the electromagnetic parameters of the Si(2)- rGO@Fe\({}_{3}\)O\({}_{4}\)/paraffin wax composite (Figure S9).  
**Author Contributions:** Prepared the materials, Y.L. and C.W.; Writing--original draft preparation, Y.L.; Writing--review and editing, Y.D. and Y.L.; Supervision, Y.D.; Data analysis, Y.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This funding was funded by the National Natural Science Foundation of China (No. 3112520007).  
**Acknowledgments:** We would like to thank [PERSON] in Xi'an Jiaotong University who provided the sample tests, [PERSON] in Xi'an Jiaotong University who tested the TEM images, and [PERSON] in Technische Universitat Dresden who gave us some advice.  
**Conflicts of Interest:** The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Samples** & **Loading (wt \%)** & \(\mathbf{RL_{max}}\) (dB)** & **Thickness (mm)** & **EBD\({}^{\text{a}}\) (GHz)** & **Ref.** \\ \hline Ni/PVDF & 20 & \(-\)42.08 & 3 & 2.5 & [61] \\ MoS\({}_{2}\)/PVDF & 25 & \(-\)26.11 & 2.5 & 3.44 & [62] \\ Mesoporous Fe\({}_{3}\)O\({}_{4}\)/C & 40 & \(-\)18.0 & 2.0 & 2.0 & [63] \\ Graphene/ZnO & 50 & \(-\)45.1 & 2.2 & 2.5 & [64] \\ PEDOT/RGO/Co\({}_{3}\)O\({}_{4}\) & 50 & \(-\)51.1 & 2.0 & 3.1 & [65] \\ [Y\({}_{2}\)(MH)]\({}_{\text{k}}\)-DMF & 20 & \(-\)22.78 & 5.0 & 2.24 & [66] \\ Si(2)-rGO@Fe\({}_{3}\)O\({}_{4}\)/PVDF-_co_-HFP & 30 & \(-\)17.1 & 2.0 & 4.8 & This work \\ Si(2)-rGO@Fe\({}_{3}\)O\({}_{4}\)/PVDF-_co_-HFP & 30 & \(-\)32.1 & 7.0 & 2.88 & This work \\ \hline \hline \end{tabular} \({}^{\text{a}}\)EBD: Effective bandwidth (RL \(<\)\(-\)10 dB).  
\end{table}
Table 1: Comparison of microwave absorption performance of similar composite in the range of 2–18 GHz