## 3 Results and Discussion
In addition, it can be clearly seen that, compared with the CNC, the \(\epsilon^{\prime}-\epsilon^{\prime\prime}\) curves of the CNCG present a relatively orderly state. For the CNCG, these relaxation processes are mainly caused by the synergy of interface polarization and dipole polarization [20]. On the one hand, Co particles, the Co-MOF-derived carbon layer, the PVP-K30-derived carbon layer, the 3D-graphene, and the paraffin wax have multiple interfaces with each other, and the charge accumulation at these interfaces causes strong interfacial polarization. On the other hand,  
Figure 7: The reflection loss curves of all composites. (**a**) The reflection loss curve of CNC; (**b**) The reflection loss curve of CNCG-1; (**c**) The reflection loss curve of CNCG-2; (**d**) The reflection loss curve of CNCG-3. under the action of incident wave, oxygen-containing functional groups, doped nitrogen, and other defects in the composite act as polarization centers to induce a large number of dipoles, which will cause strong dipole polarization. It is noteworthy that straight lines appear at the end of each \(\varepsilon^{\prime}-\varepsilon^{\prime\prime}\) curve (Figure 8b-d), indicating that conduction loss also plays an important role in the attenuation of incident wave, which is closely related to the properties of carbon in composite [21]. Magnetic loss is another important mechanism of microwave absorption. In general, magnetic loss is mainly caused by natural resonance, exchange resonance, and eddy current loss. If the eddy current loss is the dominant factor in the magnetic loss over a certain frequency range, the values of \(C_{0}\) (\(C_{0}=\mu^{\prime\prime}\left(\mu^{\prime}\right)^{-2}f^{-1}\)) remain essentially constant over that frequency range. Conversely, the main factors of magnetic loss are natural resonance and exchange resonance [22]. It can be seen from Figure 9 that the values of \(C_{0}\) are constantly changing in the frequency range of 2-18 GHz, which indicates that the main factors of magnetic loss of all composites are natural resonance and exchange resonance. Figure 9: The \(C_{0}\) curves of all composites. Microwave attenuation performance is directly determined by two factors: one is the reflection of microwaves on the surface of the material, the other is the absorption of microwaves inside the material. Generally speaking, the former is related to impedance matching (\(|Z_{\text{in}}/Z_{0}|\)), while the latter is related to attenuation constant (\(\alpha\)) [23]. In order to explore the relationship between the microwave absorption performance of the material and \(\alpha\) and \(|Z_{\text{in}}/Z_{0}|\), the \(\alpha\) and \(|Z_{\text{in}}/Z_{0}|\) of the CNCG were analyzed in detail. The \(\alpha\) can be calculated by the following Formula [24]:  
\[\alpha=(\varepsilon^{\prime\prime}u^{\prime\prime}-\varepsilon^{\prime}\mu^{ \prime}+(\left(\mu^{\prime\prime}\varepsilon^{\prime\prime}-\mu^{\prime} \varepsilon^{\prime}\right)^{2}+\left(\mu^{\prime}\varepsilon^{\prime\prime}+ \mu^{\prime\prime}\varepsilon^{\prime}\right)^{2})^{1/2}\sqrt{2}\pi f/c \tag{4}\]  
As can be seen from Figure 10a, when the frequency is in the range of 2-18 GHz, the values of \(\alpha\) of the CNCG show an increasing trend, and generally follow the order of \(\alpha\) (CNCG-3) \(>\alpha\) (CNCG-2) \(>\alpha\) (CNCG-1). It is worth noting that, although the values of the \(\alpha\) of the CNCG-3 are always greater than that of other composites, its microwave absorption performances are relatively weak compared with that of the CNCG-2, mainly due to the limitation of \(|Z_{\text{in}}/Z_{0}|\). Good \(|Z_{\text{in}}/Z_{0}|\) can ensure that the incident wave enters the material to the maximum extent. When the value of \(|Z_{\text{in}}/Z_{0}|\) is equal to 1, it means that the incident wave at this frequency point can completely enter the material [25]. Figure 10b compares the values of \(|Z_{\text{in}}/Z_{0}|\) of CNCG at the 1.79 mm thickness.