## 3 Results and Discussion
### Measurements of NiO/PANI/ZnNb\({}_{2}\)O\({}_{6}\) Composite's EMI Shielding Effect  
The measurements of shielding effectiveness, denoted as SE (shielding effect), were conducted utilizing a flanged coaxial EMI SE tester (Figure 4). Figure 3: SEM images of single-phase NiO and ZnNb\({}_{2}\)O\({}_{6}\): (**a**) NiO at \(\times\)2500, (**b**) ZnNb\({}_{2}\)O\({}_{6}\) at \(\times\)2500, (**c**) EDS analysis of NiO, (**d**) EDS analysis of ZnNb\({}_{2}\)O\({}_{6}\). The shielding effectiveness values of epoxy-based composites made of (NiO/PANI/ZnNb\({}_{2}\)O\({}_{6}\)) throughout the 0-8 GHz frequency range are demonstrated to vary with frequency in Figure 5. To guarantee precision, the measurements were made again using samples that were manufactured with a constant 1.4 mm thickness. The tester maintains a consistent 50 ohm impedance throughout its length. Initially, a reference measurement was taken without a sample. Subsequently, samples were inserted one by one, ensuring uniform pressure by pinching them at three points. The device transmitted output data to a computer, where the SE values were computed as the difference between measurements with and without the samples. The SE values of the composites were influenced by their geometry and orientation. Table 2 lists the microwave shielding effectiveness measurements of different materials that have been reported in previous works. Figure 4: Experimental setup for EMI shielding testing utilized in this study. Among the NiO/PANI/ZnNb\({}_{2}\)O\({}_{6}\) composites, it is evident that the epoxy-based composition of NiO-/ZnNb\({}_{2}\)O\({}_{6}\) (75-25% by weight) combined with Aniline at a 1/1 ratio exhibits superior microwave shielding effectiveness. According to Figure 5c, this particular composite produced the lowest recorded value of \(-\)41.16 dB at 6.24 GHz. For 1.27 GHz, 4.83 GHz, 6.86 GHz, and 7.51 GHz, it offered shielding effect values of \(-\)11.36 dB, \(-\)17.23 dB, \(-\)21.98 dB, and \(-\)24.68 dB, respectively. Additionally, it demonstrated a shielding effect of less than \(-\)10 dB throughout a broad spectrum, which included frequencies between 0 and 0.36 GHz, 3.16 and 4.43 GHz, 4.74 and 6.52 GHz, and 7.31 and 8 GHz. The shielding efficacy values of this composite material were consistently below \(-\)20 dB, for frequencies between 5.71 and 6.34 GHz. On the other hand, the epoxy-based composition of NiO-ZnNb\({}_{2}\)O\({}_{6}\) (50-50% by weight) combined with Aniline at a 1/1 ratio displayed the lowest shielding effectiveness value at \(-\)33.94 dB, occurring at a frequency of 5.64 GHz. Also, at 6.26 GHz, it obtained the second-lowest shielding efficacy rating, \(-\)31.91 dB. It recorded values below \(-\)10 dB in certain frequency bands, including 0 to 0.29 GHz, 4.74 to 6.52 GHz, 6.64 to 7.06 GHz, and 7.34 to 8 GHz (as shown in Figure 5b). This composite material consistently maintained shielding effectiveness below \(-\)20 dB, for frequencies from 5.43 to 5.79 GHz. Lastly, the epoxy-based composition of NiO-ZnNb\({}_{2}\)O\({}_{6}\) (25-75% by weight) combined with Aniline at a 1/1 ratio exhibited the lowest shielding efficiency value at \(-\)35.3 dB, occurring at 6.24 GHz. Additionally, it achieved shielding effectiveness values of \(-\)17.7 dB, \(-\)21.98 dB, and \(-\)23.57 dB at frequencies of 1.11 GHz, 6.85 GHz, and 7.5 GHz, respectively (as depicted in Figure 5a). This particular composite composition also demonstrated shielding effect values below \(-\)10 dB within specific frequency ranges, including the ranges 0 to 0.51 GHz, 0.78 to 1.81 GHz, 2.69 GHz to 3.8 GHz, 5.56 GHz to 6.51 GHz, 6.65 to 7.1 GHz, and 7.34 GHz to 8 GHz. Furthermore, it maintained shielding effectiveness below \(-\)20 dB, for the range from 6.11 to 6.32 GHz. One of the conductive polymers, polyaniline, was particularly selected, and it played an important role in increasing the impedance matching and contributing to the shielding efficiency of the recently created composites in certain frequency ranges by selectively selecting frequencies.