## 3 Results and Discussion
### Influence of PIP Cycle Numbers on the Microstructure and Properties of the Composites
From Figure 8a, it is clear that the \(\varepsilon^{\prime}\) values for the composites increase first and then decrease as the PIP cycle number increases, whose value is connected with the polarization relaxation, while the \(\varepsilon^{\prime}\) values of all samples decrease with increasing frequency apart from some slight rising. The decline tendency could be explained as following: the random dipoles within the sample would overcome the great resistance and exhibit preferential orientation paralleling to the external EM field, leading to the formation of dipole relaxation polarization, while there is not enough time for the rearrangement of the dipoles to respond to the rapidly changing external EM field, resulting in a declining tendency with the increase of frequency [29; 37]. Similarly, the \(\varepsilon^{\prime\prime}\) values for the composites shown in Figure 8b also increase first and then decrease with increasing PIP cycle number, whose value strongly depends on the electrical conductivity of the tested sample, and thus the variation tendency for \(\varepsilon^{\prime\prime}\) value should be attributed to the different content SiCC introduced after different PIP cycle numbers, which could be confirmed by the above result of density for different composites (in Figure 5). In addition, some peaks around at 4, 12, and 14 GHz should be ascribed to the resonance behaviors [38; 39]. Besides the above real and imaginary parts of complex permittivity, another critical electromagnetic parameter for an absorber is the dielectric tangent loss (tan\(\delta_{e}=\varepsilon^{\prime\prime}/\varepsilon^{\prime}\)), which presents the microwave attenuation capability, and thus the value of tan\(\delta_{e}\) was calculated and is displayed in Figure 8c. Likewise, the value of tan\(\delta_{e}\) increases first and then decreases with increasing PIP cycle number. The sequence for the average value of tan\(\delta_{e}\) for as-prepared composites is S3 \(<\) S2 \(<\) S1, and a higher tan\(\delta_{e}\) value for an absorber without magnetic medium might own a better EMW absorption property from a theoretical point of view. As for the polarization, there are four polarizations easily created within a heterostructure, including electronic, atomic, Debye (dipolar), and interfacial polarizations [40]. According to previous results, the electronic and atomic polarizations would only be formed at a higher frequency, which could be excluded in the present study. As for interfacial polarization, it can be formed in the interface of two different components, and thus the interfacial polarizations would be formed at SiOC ceramic/BPR-derived carbon, SiOC ceramic/carbon fibers, and BPR-derived carbon/carbon fibers to improve the EMW absorption performances of the composites. Finally, as for the Debye polarization, which could be analyzed by the following the Cole-Cole curves. Based on the Debye theory, the relationship between \(\varepsilon^{\prime}\) and \(\varepsilon^{\prime\prime}\) could be written as follows [29; 38; 41]:  
\[\left(\varepsilon^{\prime}-\frac{\varepsilon_{s}+\varepsilon_{\infty}}{2} \right)^{2}+\left(\varepsilon^{\prime\prime}\right)^{2}=\left(\frac{ \varepsilon_{s}-\varepsilon_{\infty}}{2}\right)^{2} \tag{5}\]  
Notably, the parameters listed in the above equation, including \(\varepsilon_{s}\) and \(\varepsilon_{\infty}\) refers to the static permittivity and relative dielectric constant at the high-frequency limit. From Equation (5), the relationship between \(\varepsilon^{\prime}\) and \(\varepsilon^{\prime\prime}\) should be a semicircle, namely the Cole-Cole semicircle. The number of the Cole-Cole semicircle corresponds to the number of Debye relaxation processes. The Cole-Cole curve of all as-obtained samples with different PIP cycle numbers at the frequency 2-18 GHz is displayed in Figure 8d. Clearly, at least four semicircles could be found among all the samples, indicating that various relaxation processes would be generated within all as-prepared composites.