## 3 Results and Discussion
### Electrical Properties  
According to the law of energy conservation [21], the electromagnetic (EM) waves passing through a medium are divided into a transmitted wave, reflected wave, and loss [40]. Reflection occurs at the interface between the medium and air [41]. According to impedance matching theory [42], a larger \(\varepsilon_{\mathrm{r}}\) of the material increases the EM wave reflection, with an ultimate reduction in its transmission efficiency due to polarization phenomena of the medium in the external electric field [43]. The dielectric constant (\(\varepsilon_{\mathrm{r}}\)) and dielectric loss factor (\(\delta\)) of the pure epoxy composite was 4.1, and for the quartz fiber/epoxy composite EQ-20, it was 3.31, 3.28 for EQ-25, 3.26 for EQ-30, and 3.26 for EQ-35. These measured \(\varepsilon_{\mathrm{r}}\) and \(\delta\) values were different from those estimated from the rule of mixture for composite property estimation [44]. The lowest value of \(\varepsilon_{\mathrm{r}}\) was 3.26 with quartz factors of 0.30 and 0.35. The results showed that \(\varepsilon_{\mathrm{r}}\) varied by 1.5% from 3.31. These decreasing values are due to the interfacial polarization of the composite. The dielectric constant became fixed and was not reduced further even with increasing quartz fiber fraction. Increasing the quartz fiber fraction packed the composite structure and reduced the local charge displacement towards the electric field. The epoxy resin embedded with quartz fibers formed a heterogeneous structure due to their organic-inorganic nature. Upon curing of the epoxy resin, space charge polarization was created with the compact interfacial boundaries and random movement of ions was restricted. Thus, ionic conductivity becomes lower with increasing dielectric dispersion in both the real and imaginary parts of \(\varepsilon_{\mathrm{r}}\). In the composites EQ-30 (0.30) and EQ-35 (0.35), due to the relatively lower resin action compared to EQ-20 and EQ-25, the curing reaction progressed quickly. Thus the epoxy/amine crosslinking contributed towards the dominancy of dipole relaxation over the ionic conductivity, which ultimately reduced the dielectric constant [45]. Moreover, these fiber-reinforced composites are composed of heterogeneous materials that behave differently when exposed to applied electric fields. If they become polarized, their structure leads to polarizability, consequently lowering their \(\varepsilon_{\mathrm{r}}\). \(\delta\) of the pure epoxy composite was 0.035, \(\delta\) of quartz fiber/epoxy composite EQ-20 was 0.030, EQ-25 was 0.028, EQ-30 was 0.021, and that of EQ-35 was 0.021. Increasing the material thickness leads to higher transmission losses, but it's worth noting that in this study, the thickness remained constant at 3 mm for all composite samples. The presence of quartz fibers changed the composite structure and thus \(\delta\) was further decreased upon increasing the fiber fraction. Pure epoxy composite exhibits a consistent structure, yet in quartz fiber/epoxy composites, the epoxy, interface, and the fibers collectively contribute to the occurrence of losses. Due to the fast curing, the higher crosslinking density and more stable composite structure resulted in a lower dielectric loss in these composites compared to the pure epoxy/amine composite. Increasing the fiber quantity caused the fibers to embed with epoxy more firmly and restricted the free movement of ions, resulting in a decrease in polarization and reduction in dielectric loss factors by up to 40% from 0.035. The minimum value of \(\delta\) was 0.021 for EQ-30 and EQ-35. This can be attributed to the fact that the minimum dielectric loss factor did not change even upon an increase in the quartz fraction. It is said that the addition of quartz fiber can significantly reduce the energy dissipation during transmissions of EM waves through this composite material [46]. The performance of wave transparent composites can be estimated by its dielectric loss factor (\(\delta\)) which is a significant indicator [47].