## 3 Results and Discussions
### Microwave Absorption Properties  
To relieve the microwave absorption mechanism of the GO/FeSiAl/epoxy compound, the influence of GO amounts on reflection loss, impedance matching, and the attenuation constant was studied. The electromagnetic properties were tested through the coaxial method within the frequency range of 0 GHz to 18 GHz to reveal the relationship between the complex permeability real part (\(\mu^{\prime}\)), the complex permeability imaginary part (\(\mu^{\prime\prime}\)), the relative complex permittivity real part (\(\epsilon^{\prime}\)), the relative complex permittivity imaginary part (\(\epsilon^{\prime\prime}\)), and the amount of GO in the compounds, as shown in Figure 6.  
Figure 6a shows a decreasing trend of \(\epsilon^{\prime}\) with increasing GO amounts, responding to the ability of the material to store charge decreases. This can be explained through the micro-capacitance model [37]. Neighboring FeSiAl presented in the matrix can be seen as two flat plates of micro-capacitor. While GO conducts electricity very well and has poor ability to stores electrons, therefor cannot form a micro-capacitor structure within itself or with FeSiAl [38]. Thus, the addition of GO will destroy the micro-capacitor between the FeSiAl and leads to a decrease in charge storing ability. In Figure 6b, the \(\epsilon^{\prime\prime}\) values exhibit an obvious peak in sample GF-1 and sample GF-2 with fewer or no GO. As the amount of GO increases, more peaks appear at higher frequencies. These peaks can be ascribed to the interfacial polarization resonance, indicating more GO-FeSiAl interface in the system as well as defects and functional groups on the surface of GO resulting in higher interfacial polarization. This contributes to higher microwave absorption at higher frequencies [39; 40]. As the frequency rises, \(\mu^{\prime}\) shows a collectively decreasing trend (Figure 6c). This may be explained by high-frequency fields resulting in polarization hysteresis and dielectric relaxation. This trend slows down as more GO is added. The complex permeability imaginary part (\(\epsilon^{\prime\prime}\)) of GF-1 and GF-2 with a lower amount of GO presents a pronounced and sharp peak at 0.3 GHz, which is attributed to the magnetic capacity of the FeSiAl consuming electromagnetic energy, as shown in Figure 6d. The high-frequency shift to 2 GHz and widening of peaks for samples with a higher GO amount may be ascribed to the suppression of eddy current resulting from the lower electric conductivity of GO-FeSiAl compared to pure FeSiAl [41]. Figure 5: FTIR spectra of GO and GF-3. According to the transmission line theory, \(\varepsilon_{r}\) (\(\varepsilon_{r}=\varepsilon^{\prime}-je^{\prime\prime}\)) represents relative complex permittivity and \(\mu_{r}\) (\(\mu_{r}=\mu^{\prime}-j\mu^{\prime\prime}\)) represents relative complex permeability. The reflection loss properties (RL) of the GO/FeSiAl epoxy compound can be calculated from \(\varepsilon_{r}\) and \(\mu_{r}\) through the following equations:  
\[RL=20\lg\left|\frac{z_{in}-z_{0}}{z_{in}+z_{0}}\right| \tag{1}\]  
\[Z_{in}=Z_{0}\sqrt{\frac{\mu_{r}}{\varepsilon_{r}}}\tan\left(j\frac{2\pi fd}{c} \sqrt{\mu_{r}\varepsilon_{r}}\right), \tag{2}\]  
where \(Z_{in}\) is the normalized impedance of the sample, \(Z_{0}\) is the free space impedance, f is the frequency of the incident microwave, \(c\) is the velocity of light in free space, and d is the thickness of the testing sample. The 3D projections of the reflection loss of the epoxy composites from 0 mm to 5 mm thickness and of the 0 GHz to 18 GHz frequency variation are shown in Figure 7. The black contour range of the effective bandwidth indicates an RL value below \(-10\) dB (90% absorption). All the epoxy composites have a fairly wide area to within this standard. In the sample with pure silylated FeSiAl (Figure 7a), the maximum reflection loss is \(-30.75\) dB at 0.5 GHz and at a 4.95 mm thickness, with an efficient bandwidth of 0.4 GHz.