## 3 Results and Discussion
### Analysis of Typical Performances
#### 3.2.3 Dielectric Properties  
Dielectric properties (such as permittivity \(\varepsilon\)) are an important index for characterizing the electrical performances of dielectric or insulating materials. Permittivity is mainly divided into real and imaginary parts. The real part of permittivity (\(\varepsilon^{\prime}\)) characterizes the polarization property of the material in the electric field. Moreover, the imaginary part of permittivity (\(\varepsilon^{\prime\prime}\)) characterizes the energy loss (i.e., dielectric loss) in the process of polarization. Figure 9 shows the dielectric properties of samples. Polyethylene belongs to the non-polar polymers. The polarization of polyethylene is mainly electron polarization and atomic polarization. Due to its weak polarization property, its permittivity is small. The \(\varepsilon^{\prime}\) of LDPE is clearly increased after changing the preparation process. Compared with the pure LDPE with modified process, the \(\varepsilon^{\prime}\) of the composite is decreased slightly, but it is still higher than that of the original sample. In addition, the \(\varepsilon^{\prime}\) of all samples is increased slightly with the decrease in  
Figure 8: Effect of the charge traps in the interface region on carriers. Figure 9: Dielectric properties of samples. (**a**) Real part of permittivity. (**b**) Imaginary part of permittivity. frequency. This phenomenon is caused by the more sufficient polarization behavior of the dielectric in low-frequency regions, such as electron polarization and impurity polarization [48]. Dielectric loss is mainly caused by the steering polarization of the material. The non-polar polymer is theoretically without steering polarization. In other words, there is no dielectric loss in polyethylene. However, due to the impurities and structural defects in the material, current leakage can be caused [36; 39]. Thus, a part of the electrical energy is transformed into the heat energy, which is the conduction loss. Therefore, the dielectric loss of polyethylene in the low-frequency regions is mainly conduction loss. All samples have obvious dielectric loss in the low-frequency regions. Moreover, the dielectric loss of LDPE in low-frequency regions is the largest after changing the process. Compared with the pure LDPE with modified process, the dielectric loss of the composite is decreased slightly. In the intermediate-frequency regions, the \(\varepsilon^{\prime\prime}\) of LDPE is increased slightly by changing the preparation process or doping microcapsule. In addition, the dielectric loss is decreased with the increase in frequency. In the high-frequency regions, the \(\varepsilon^{\prime\prime}\) of LDPE is increased by changing the preparation process. Moreover, the dielectric loss can be increased further after the doping microcapsule. The DC conduction loss can be neglected in high-frequency regions [49]. Moreover, the steering polarization of polar molecules cannot be established in high-frequency regions. At the electric field, the charge traps in the material can capture, emit, and re-capture the carriers, and release energy in the form of photons and phonons, thus causing the dielectric loss [37; 49]. The higher the frequency, the faster the process of capturing and releasing the carriers by the charge traps, so the more energy is released. This leads to the increase in dielectric loss with the increase in frequency. Therefore, the dielectric loss of polyethylene in the high-frequency band is mainly the relaxation polarization of the charge traps. Compared with the different preparation processes, the crystallinity of LDPE with a modified process is decreased, loosening the internal structure of the sample. Loose internal structure can reduce the hindrance to the movement of molecular chains and the steering polarization of the polar impurity group. Thus, the polarization property of polyethylene is enhanced, increasing the \(\varepsilon^{\prime}\) (as shown in Figure 9a).