## 4 Results and Discussion
### The SE of Textile and 3D-Printed Fabrics  
The textile fabrics and 3D-printed samples were tested according to the following schedule:  
1. The fabric samples were mounted on the fixture within the test setup. 2. The elements of the \(\mathbf{S_{TA}}\) matrix were measured. 3. The elements of the \(\mathbf{S_{TS}}\) scattering matrix were determined by using the aforementioned Formulas (13) and (14). 4. The results were corrected based on the measurements of the theoretical \(SE\) for aluminum foil according to the formula  
\[S_{21}=S_{21\text{TS}}-S_{21\text{fm}}+S_{21\text{ft}}, \tag{15}\]  
Figure 6: Results of measurements and calculations of the \(S_{21}\) coefficient for the food-grade aluminum foil. where \(s_{21\rm{fm}}\) is the measured transmission coefficient of the aluminum foil and \(S_{21\rm{ft}}\) is the theoretical value of the transmission coefficient of the aluminum foil. The applied correction was used to minimize the influence of the test setup imperfections so that the corrected results for the aluminum foil agree with the theoretical calculations. The \(SE\) is evaluated by means of the Formulas (6)-(8). Figures 7 and 8 show the frequency behavior of the \(S_{21\rm{TS}}\) coefficient and \(SE\) of the materials under examination. As expected, according to the measurements of the sheet resistance values, only five samples (silver fabric, copper fabric, conductive yarn, magnetic yarn, magnetic+conductive yarn) among the materials tested in this study showed usable \(SE\) values. For the others, \(SE\) was approximately 0 dB in the examined frequency band. It should be mentioned that the magnetic yarn samples actually have too high a sheet resistance to be expected to be suitable for EMI shielding; a potential reason for this finding is discussed below. Generally, due to the applied corrections, the influence of the test setup was significantly reduced. The \(S_{21\rm{TS}}\) coefficients (Figure 7) show a similar frequency dependence to the \(S_{21\rm{}}\) values of the aluminum foil used for calibration (Figure 6). Here, again, the ripples due to the imperfections in the SMA/WR-90 transitions can be observed as well as the increase in  
Figure 8: Evaluated \(SE\) of the materials examined versus frequency. Figure 7: The \(S_{21 TS}\) measurement results of the examined conductive materials versus frequency. attenuation for frequencies below approximately 7 GHz. More importantly, the highest attenuation along the whole investigated frequency band was found for the silver-coated fabric, directly followed by the copper-coated fabric, as would be expected from the sheet resistance measurements (Figure 5). Interestingly, the crocheted fabrics from the conductive yarn, the magnetic+conductive yarns, and the magnetic yarn all show relatively similar values, while their sheet resistances varied by four orders of magnitude (cf. Figure 5). This can be explained by the structure of the magnetic yarns, which contain 20% conductive stainless steel fibers. These fibers are short (in the range of 10-20 mm) and thus do not often come into contact with neighboring conductive fibers in the PES fiber-based yarns, leading to a relatively low conductance for the whole yarn or crocheted fabric. At smaller scales, however, each single steel fiber has a conductance comparable to that of the silver coating on the conductive yarn. While the conductivity of silver is significantly higher than that of steel, the conductance is also influenced by an object's geometry, and the silver coatings on the fibers are in the range of 10-100 nanometers, while the steel fiber showed a thickness of 12-13 um. On the other hand, the textile fabrics with PEDOT:PSS coating and the 3D-printed conductive PLA sample both having lower sheet resistances than the magnetic stainless steel yarn did not show noteworthy EMI shielding, indicating that the conductive properties are not the only relevant parameter for EMI shielding effectiveness, as already discussed in several previous studies [12].