Electromagnetic Interference Shielding with Electrospun Nanofiber Mats--A Review of Production, Physical Properties and Performance  
Institute of Physics--Center for Science and Education, Silesian University of Technology, 44-100 Gliwice, Poland; [EMAIL_ADDRESS]  
Thin Films & Physics of Nanostructures, Bielefeld University, 33615 Bielefeld, Germany; [EMAIL_ADDRESS]  
Institute of Physics--Center for Science and Education, Silesian University of Technology, 44-100 Gliwice, Poland; [EMAIL_ADDRESS]  
Institute of with the electric (magnetic) field intensity without shielding \(E_{0}\) (\(H_{0}\)) and with shielding \(E_{t}\) (\(H_{t}\)), respectively [9]. The shielding effectiveness \(SE\) is defined as  
\[SE=20\log\frac{1}{T}=20\log\frac{E_{0}}{E_{t}}=20\log\frac{H_{0}}{H_{t}}=10\log \frac{P_{0}}{P_{t}} \tag{2}\]  
with the power \(P_{0}\) (\(P_{t}\)) for the measurement without (with) shielding [9]. The \(SE\) is composed of shielding due to reflection (\(R\)), absorption (\(A\)), and multiple reflections (\(M\)) [10]:  
\[SE=SE_{R}+SE_{A}+SE_{M} \tag{3}\]  
This formula indicates which materials may be suitable for electromagnetic shielding. Reflection losses \(SE_{R}\) will occur for electrically/magnetically conducting materials and be greater for higher conductivity and lower permeability; absorption losses \(SE_{A}\) occur upon interaction between electric or magnetic dipoles in the material with the electromagnetic field and are larger for high conductivity and high magnetic permeability; while multiple reflection losses \(SE_{M}\) are usually small and often neglected if the distances between reflecting surfaces or interfaces are much larger than the skin depth [11]. It must be mentioned that mobile charge carriers, i.e., electrons or holes, can result in reflection losses even if no percolation/conduction paths are formed, so that even materials that are not conductive on a macroscopic scale can cause reflection losses for electromagnetic waves [11]. This is especially important in case of integrating conductive nanoparticles in coatings or nanofibers where the filling may be insufficient to form percolation paths, or where the nanoparticles may be coated with an isolating shell to prevent them from oxidation. Sometimes, a deeper view into the shielding mechanisms is possible, especially in correlation with simulations. [PERSON] et al., e.g., subdivided the polarization properties of graphene-based hetero-structures into defects (vacancy, point defect and large-scale defect), polar groups and interfaces and underlined their importance for the EM properties of a dielectric material, in addition to the conductive properties of the material [12; 13]. These results were gained by measurements of the real and imaginary part of the complex dielectric permittivity at different temperature and frequencies as well as by first-principle calculations. Another important point is the skin effect, meaning that high-frequency electromagnetic fields can only penetrate into the surface region of a material, not into the bulk, where these skin depths decrease with increasing frequency, conductivity and permeability [11]. For metals such as copper or nickel, electromagnetic fields of 1 GHz frequency are reduced to 1/e at penetration depths around 0.5-2 \(\upmu\)m, showing that electromagnetic shielding can normally be performed by relatively thin shields. This is why many authors describe electromagnetic shields by textile fabrics, either woven, knitted or other macroscopic fabrics [14; 15; 16; 17; 18] or even nanofiber mats, as will be presented in this paper. This review is organized as follows: In the next sections, different measurement methods are presented, followed by a short description of the electrospinning technique and the different fibers and mats that can be produced in this way.