## 2 Measuring Electromagnetic Shielding and Related Parameters  
Electromagnetic shielding is mostly measured according to the ASTM D4935-18 standard [19]. It is based on using a vector network analyzer combined with a test fixture in which, alternatingly, reference and test specimens are embedded, as shown in Figure 1[20]. In this so-called waveguide method, these specimens are placed in a coaxial specimen holder unit, as defined in the standard, and investigated by a setup as depicted in Figure 2[21]. Here, a network analyzer is coupled with the specimen holder where the outer conductor of the coaxial transmission line is extended throughout the whole holder unit (green parts), while the fabrics placed at the position of the sample cross section can shield the signal between the conductive parts. Measurements with the reference specimen are used to define the reference level with the space between the conductors being empty. This setup allows the reflected and the transmitted power, i.e., distinguishing between reflection and absorption losses[21]. Test frequencies are typically in the range of 30 MHz to 1.5 GHz[15; 20; 21; 22], but can also be extended to higher frequencies using appropriate waveguides[23]. Higher frequencies of around 3-30 GHz are typically used in digital telecommunication, satellite communication and waveguide communication, so that especially testing these frequencies is highly in-demand. Other existing standards are, e.g., related to durable relocatable shielded enclosures (ASTM E1851-15)[24], (IEEE 299-2006) enclosures and boxes[25], or EN 61000-4-21 (identical to IEC 61000-4-21)[26] which necessitates a special chamber, so that textile shielding fabrics are often investigated by the aforementioned ASTM D4935-18. Nevertheless, this standard is not unproblematic, due to the edge-contact requirements which may cause large measurement errors[27]. [PERSON] et al. thus suggested using a simple system in which the sample is placed between source antenna and receiving antenna, the latter of which is fully embedded in an absorber material to avoid diff  
Figure 1: **(a)** Reference and **(b)** load specimens used for EMI-shielding measurements, with dimensions given in millimetres. Reprinted from [20], copyright (2021), with permission from Elsevier. Figure 2: Schematic of the measurement setup for electromagnetic shielding according to ASTM D4935-18. Reprinted from [21], copyright (2019), with permission from Elsevier. receiving antenna [27]. They showed that a shielding effectiveness of up to 100 dB could be measured in a broad frequency range between 1 GHz and 8.5 GHz. Besides these potential edge contact problems, [PERSON] et al. mentioned the not fully defined specifications of the tester, such as unclear surface finish and end dimensions, while the ends, in addition, do not fit properly to standard connectors, in addition to the large mass of the tester around 18 kg [28]. They suggested a simplified design which could be attached to N-type standard connectors at the ends to the usual 50 \(\Omega\)/10 dB attenuators (cf. Figure 2), with significantly smaller samples of diameters 30.48 mm to also enable testing materials that are difficult to produce in larger quantities. For their tester, they calculated a theoretical cutoff frequency of 18.2 GHz and tested it up to 13.5 GHz and found satisfactory results for various materials. [PERSON] et al. used mathematical characterizations of SE testers similar to the standard one by investigating impedance mismatch and lossless network conditions [29]. They suggested a larger cross-section to avoid strong discontinuities in smaller testers due to the sample thickness and underlined the importance of high dimensional accuracy and improved surface finishing to avoid impedance mismatches. In contrast to these methods, [PERSON] et al. used an open-space method to investigate the electromagnetic shielding of conductive textile materials [30].