Modelling the Woven Structures with Inserted Conductive Yarns Coated with Magnetron Plasma and Testing Their Shielding Effectiveness

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Article Modelling the Woven Structures with Inserted Conductive Yarns Coated with Magnetron Plasma and Testing Their Shielding Effectiveness

Ion Razvan Radulescu 1,* , Lilioara Surdu 1, Razvan Scarlat 1, Catalin Constantin 2, Bogdana Mitu 2 , Cristian Morari 3 and Marian Costea 4

1 The National Research-Development Institute for Textiles and Leather—INCDTP, 030508 Bucharest, Romania; [email protected] (L.S.); [email protected] (R.S.) 2 The National Institute for Laser, Plasma and Radiation Physics—INFLPR, Magurele, 077125 Bucharest, Romania; catalin.constantin@inﬂpr.ro (C.C.); bogdana.mitu@inﬂpr.ro (B.M.) 3 The National Institute for Research-Development in Electrical Engineering—INCDIE ICPE—CA, 030138 Bucharest, Romania; [email protected] 4 Faculty of Power Engineering, University Polytechnica Bucharest, 060042 Bucharest, Romania; [email protected] * Correspondence: [email protected]

Abstract: The paper proposes the analytic modelling of flexible textile shields made of fabrics with inserted conductive yarns and metallic plasma coating in order to calculate their electromagnetic shielding effectiveness (EMSE). This manufacturing process is highly innovative, since copper plasma coating improves EMSE on the fabrics with inserted conductive yarns of stainless steel and silver with 10–15 dB in the frequency range of 0.1–1000 MHz, as shown by the measured EMSE values Citation: Radulescu, I.R.; Surdu, L.; determined according to the standard ASTM ES-07 via the Transverse Electromagnetic (TEM) cell. Scarlat, R.; Constantin, C.; Mitu, B.; Morari, C.; Costea, M. Modelling the On the other hand, modelling of EMSE for such conductive flexible shields gives an insight on Woven Structures with Inserted estimating EMSE in the design phase of manufacturing the shield, based on its geometric and Conductive Yarns Coated with electrical parameters. An analytic model was proposed based on the sum of EMSE of the fabric with Magnetron Plasma and Testing Their inserted conductive yarns and EMSE of the copper coating. The measurement results show close Shielding Effectiveness. Textiles 2021, values to the proposed analytic model, especially in case of fabric with conductive yarns having 1, 4–20. https://doi.org/10.3390/ stainless steel content. textiles1010002 Keywords: fabrics; silver yarns; stainless steel yarns; copper plasma coating; electromagnetic shield- Academic Editor: Philippe Boisse ing; far-field radiation

Received: 28 January 2021 Accepted: 12 March 2021 Published: 24 March 2021 1. Introduction

Publisher’s Note: MDPI stays neutral The shielding of electromagnetic non-ionizing radiation by means of flexible textile with regard to jurisdictional claims in materials is a well-established field of research in the current context. The use of various published maps and institutional affil- electronic devices, mobile phones and other gadgets has yielded significant pollution iations. from electromagnetic (EM) radiation in our environment [1]. Shielding is needed in many applications since non-ionizing radiation from various sources may cause interference (EMI) with other electronic devices or even cause harmful effects on human health [2,3]. Due to their advantages when compared to metallic shields, such as low weight, good mechanical strength, adaptability to various shapes of objects for shielding, as well as cost- Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. effectiveness, textile materials with electric conductive properties offer a proper solution This article is an open access article on these aspects [4]. distributed under the terms and Several papers tackle this innovative field of research and contributions in this re- conditions of the Creative Commons gard may be grouped in various topics. The main topic of research is new manufacturing Attribution (CC BY) license (https:// methods for EMI shielding textiles. Within the cited review paper [5], the following main creativecommons.org/licenses/by/ manufacturing technologies for EMI shielding fabrics are presented: applying intrinsic 4.0/).

Textiles 2021, 1, 4–20. https://doi.org/10.3390/textiles1010002 https://www.mdpi.com/journal/textiles Textiles 2021, 1 5

conductive polymers, incorporating metallic nanoparticles in coatings [6], embedding conductive ingredients into the spinning solutions of fibers and interweaving metallic yarns (silver, copper, steel) with other conventional textile yarns [7,8]. A second topic is given by imparting additional functionalities to EMI shielding: electroless plating was used to deposit Co and Ni coating on Tencel fabrics for enhanced EMI shielding properties and corrosion resistance properties [9]. Another new manufacturing method integrates silver nanowire networks and polyurethane protective layers into the fabrics structure, with outstanding washing durability and chemical stability properties [10]. A third topic of research provides improved or adapted methods for the determination of electric properties of conductive textiles, including electromagnetic shielding effectiveness (EMSE) [11]. A final identified topic of research in this field is modelling of the EMSE for various conductive textile structures. Shielding of EM radiation is an important topic in the field of electromagnetic compatibility [12–14]. The main analytic relations for modelling the shielding effectiveness are based on the models originating from the circuit method [15] and the impedance method [16]. In order to fulfill specific conditions occurring in the practical situations where electromagnetic shielding is required, additional analytic relations have been developed and adapted for different geometric shapes of electromagnetic shields under various physical premises. Estimation of the electrical properties in the case of fabrics is of great importance for the design of applications in relation to end-user requirements [16]. Since the process of manufacturing fabric samples involves a series of preparatory processes, modelling of electromagnetic shielding effectiveness (EMSE) means savings in terms of design duration, material resources and working time [17]. Two main technologies may be distinguished for imparting electrically conductive properties to textile materials. According to [18], the insertion of conductive yarns within the fabric structure (woven, knitted and nonwoven fabrics) and coating with conductive pastes of the plain fabrics. Various analytic relations for estimating the shielding effectiveness (EMSE) have been adapted for both types of technologies. For woven fabrics with inserted conductive yarns, due to their mesh grid structure, the impedance method with correction factors was adapted [19]. Moreover, another analytic relation establishes a weighted sum between the EMSE of the layer and the EMSE of the grid [20]. These relations were applied for Trans- verse Electromagnetic (TEM) cell measured fabric samples by [21], taking into consideration reflection as the main component of EMSE. Another shielding model was developed for mesh grid structures, based on the analogy with an RLC electric circuit with lumped elements [22]. Research work of estimating EMSE of mesh grid structures was accomplished by analogy with small aperture anten- nas [23]. A contribution to model EMSE for woven fabrics in shielding the near EM field based on the circuit method (introduced by H. Kaden [12,15]) was provided within [24]. Regarding the estimation of EMSE for coated fabrics, the main research direction goes for calculating the permittivity coefficient of the coating [18]. Various coating technologies and related analytic methods for estimation of EMSE were provided by [19]. In our research, both technologies for imparting conductive properties to fabrics were combined: fabrics with inserted conductive yarns were coated by magnetron plasma sputtering from a metallic target. Silver and stainless steel yarns were inserted in cotton woven fabrics and the as-obtained textiles were coated with copper thin films. The aim of our research is to model EMSE for this new type of conductive fabric with inserted conductive yarns in warp and weft direction and conductive plasma coating based on the sum of each conductive structure contributing to EMSE, namely the woven fabric with inserted conductive yarns and the copper coating on both sides of the fabric. The validation of these proposed analytic relations was conducted through electric sheet resistivity measurements and EMSE measurements via the TEM cell according to ASTM ES-07 standard. Textiles 2021, 1 6 Textiles 2021, 1, FOR PEER REVIEW 3

2.2. Materials Materials and and Methods Methods TheThe stainless stainless steel steel yarns yarns of of type Bekinox BK 50/2 were were purchased purchased from from Bekaert Bekaert and and the silver yarns of type Statex 117/17 dtex were purchased from Statex Produktions- und the silver yarns of type Statex 117/17 dtex were purchased from Statex Produktions- und Vertriebs GmbH companies and used for fabric weaving. Cotton was used as a base material Vertriebs GmbH companies and used for fabric weaving. Cotton was used as a base ma- for the textiles. A copper target of 8 × 4 × 0.5 inches of purity 99.999% was purchased from terial for the textiles. A copper target of 8 × 4 × 0.5 inches of purity 99.999% was purchased K.J. Lesker and used in the magnetron sputtering system at The National Institute for Laser, from K.J. Lesker and used in the magnetron sputtering system at The National Institute Plasma and Radiation Physics (INFLPR). for Laser, Plasma and Radiation Physics (INFLPR). 2.1. Materials—Weaving 2.1. Materials—Weaving The woven fabrics based on cotton yarns with inserted conductive yarns were manu- facturedThe atwoven SC Majutex fabrics SRL,based Barnova on cotton Iasi. yarns Stainless with steel inserted yarns conductive (Bekinox BK yarns 50/2) were and man- silver ufacturedyarns (Statex at SC 117/17 Majutex dtex) SRL, were Barnova inserted Iasi. both Stainless in warp steel and yarns weft system(Bekinox on BK the 50/2) weaving and silverloom yarns of type (Statex SOMET 117/17 width dtex) 1.90 were m. The inserted woven both fabrics in warp were and designed weft system with plain on the weave weav- for inga simple loom andof type efﬁcient SOMET structure width of 1.90 EM m. shields, The woven while the fabrics basic were support designed yarn was with of plain 100% weavecotton for Nm a 50/2.simple Two and typesefficient of wovenstructure fabrics of EM with shields, inserted while conductive the basic support yarns of yarn stainless was ofsteel 100% (F1) cotton and silver Nm 50/2. (F3) resulted,Two types having of woven a mesh fabrics grid distancewith inserted of 5 mm. conductive yarns of stainless steel (F1) and silver (F3) resulted, having a mesh grid distance of 5 mm. 2.2. Materials—Magnetron Plasma Coating 2.2. Materials—MagnetronThe copper coating onto Plasma the Coating textile fabrics was performed at INFLPR into a dedicated stainlessThe copper steel spherical coating onto vacuum the textile chamber fabrics (K.J. was Lesker, performed East Sussex, at INFLPR UK), into pumped a dedicated out by stainlessan assembly steel of spherical a fore pump vacuum and chamber turbomolecular (K.J. Lesker), pump pumped (Pfeiffer, Memmingen,out by an assembly Germany), of a − forewhich pump allowed and theturbomolecular obtaining of apump base pressure(Pfeiffer), down which to 3allowed× 10 5 thembar. obtaining A constant of a argon base pressureflow (purity down 6.0) to 3 of × 5010− sccm5 mbar. was A constant continuously argon introduced flow (purity into 6.0) the of 50 chamber sccm was by contin- means uouslyof a Bronkhorst introduced mass into flow the chamber controller, by which means allowed of a Bronkhorst to establish mass the flow processing controller, pressure which −3 allowedaround 5to× establish10 mbar. the The processing chamber pressure is provisioned around with 5 × a 10 rectangular−3 mbar. The magnetron chamber sputtering is provi- sionedgun from with K.J. a rectangular Lesker, accommodating magnetron sputtering the high gun purity from copper K.J. Lesker, target. accommodating The discharge wasthe highignited purity by means copper of target. a radio The frequency discharge generator was ignited (13.56 MHz)by means provisioned of a radio with frequency an automatic gen- eratormatching (13.56 box MHz) for adaptingprovisioned the with impedance, an automatic and thematching deposition box for time adapting was set the to imped- ensure ance,coating and thicknesses the deposition in the rangetime was 1200–10,000 set to ensure nm on coating each side thicknesses of the textile in fabrics.the range Enhanced 1200– 10000deposition nm on uniformity each side of was the achieved textile fabrics. by rotating Enhanced the samples deposition during uniformity the deposition was achieved process by(200 rotating rotations/min). the samples during the deposition process (200 rotation/min). FigureFigure 1 presents a sketch of the experime experimentalntal set-up of the magnetron magnetron plasma equip- mentment of INFLPR. SampleSample F2F2 resulted resulted by by plasma plasma coating coating of F1of (stainlessF1 (stainless steel steel yarns) yarns) on both on bothsides sides with with 1200 nm1200 of nm Copper, of Copper, while sampleswhile samples F4, F5, F6F4, and F5, F7F6 resultedand F7 resulted by coating by F3 coating (silver F3yarns) (silver on yarns) both sides on both with sides 1200 with nm, 1750 1200 nm, nm, 5600 1750 nm nm, and 5600 10,000 nm nmand of10,000 copper, nm respectively. of copper, respectively.More details More regarding details the regarding experimental the planexperimental considered plan for considered the validation for ofthe the validation model is summarized in Figure2. of the model is summarized in Figure 2.

Figure 1. Sketch of the experimental set-up in INFLPR utilized for copper coating of textiles. Figure 1. Sketch of the experimental set-up in INFLPR utilized for Cu coating of textiles.

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FigureFigure 2. 2. TextileTextile samples samples considered considered for for the the validation validation of of analytical analytical model model of of EMSE. EMSE. 2.3. Textile Samples 2.3. Textile Samples The structural and physical properties of textile samples subjected to modelling and validationThe structural of electromagnetic and physical shielding properties effectiveness of textile samples (EMSE) subjected are presented to modelling in Table1 and for validationthe yarns andof electromagnetic Table2 for the fabrics, shielding emphasizing effectiveness the data(EMSE) of particular are presented significance in Table for 1 thefor themodelling. yarns and Table 2 for the fabrics, emphasizing the data of particular significance for the modelling. Table 1. Physical and electrical parameters for the yarns of woven fabrics. Table 1. Physical and electrical parameters for the yarns of woven fabrics. Linear Electric Linear Electric Relative Magnetic Optical Linear Parameters/Yarns Raw Material Resistance, Conductivity, Permeability, Diameter, DensityLinear Electric Linear Electric Relative Magnetic Per- Optical Di- Parameters/ Linear R [Ω/m] * σ [S/m] * µ (according to [16]) d [µm] Raw Material Resistance,l Rl Conductivity,y meability,ry μry ameter, Yarns Density M1 100% Cotton, spun yarn Nm 50/2[Ω/m] * -σy [S/m] 0* (according to 1 [16]) d [μ 293m] 100%80% Cotton, Cotton, 20% M1M2 stainless steel fibers,Nm 50/2Nm 50/2 - 2200 0 7769 1 8 293 273 spun(Bekinox yarn BK50/2) 80%Silver Cotton, coated 20% PA yarn, M3 140 × 2 dtex 220 121842 1 218 stainless(Shieldtex steel 117/17 fi- dtex) M2 Nm 50/2 2200 7769 8 273 * linearbers, resistance of individual yarn measured by multimeter; application of resistivity relation. (Bekinox BK50/2) Silver coatedTable PA 2. Structural and electric properties of the uncoated woven fabrics. 140 × 2 M3 yarn, (Shieldtex Fabric220 Density 121842 1 218 Float Repeatdtex Properties 117/17Yarn dtex) [no·yarns/10 cm] Distance between Fabric Specific SR6431:2012 (Standard)/ * linear resistanceType of individual yarn measuredEN1049-2:2000 by multimeter; applicationConductive of Yarns resistivity Thickness,relation. Mass, Fabric Samples Warp/Weft, h [mm] [g/m2] Warp Weft Warp, dwa Weft, dwe r [mm] ISO5084:2001 EN12127:2003 F1 M1, M2Table 2. 6:2 Structural 5:2 and electric 168 properties 150 of the uncoated woven 5 fabrics. 0.532 129 F3 M1, M3 6:2 5:2Fabric 168 Density 150Distance be- 5 0.490 118 Properties Float Repeat [no.yarns/10cm] tween Conduc- Fabric Thick- Specific Mass, (Standard)/ Yarn SR6431:2012 The correspondingEN1049-2:2000 scheme of the textiletive Yarns samples subjectedness, h to[mm] modelling and[g/m2] validation Fabric Sam- Type of electromagnetic shielding effectivenessWarp/Weft, (EMSE) r is presentedISO5084:2001 in Figure 2EN12127:2003. ples Warp Weft Warp, dwa Weft, dwe [mm] 2.4. Morphology and Structure of the Textile Sample F1 M1, M2 6:2 5:2 168 150 5 0.532 129 F3 M1, M3 6:2 The 5:2 scheme 168 of woven 150fabric with inserted 5 metallic yarns 0.490 and plasma coating 118 is presented in Figure3. The copper coating on the fabric with inserted metallic yarns does not createThe a continuouscorresponding surface scheme layer, of butthe rathertextile ansamples additional subjected electrically to modelling conductive and valida- grid on tionmetallically of electromagnetic the fabric yarns, shielding increasing effectiveness the fabric’s (EMSE) conductivity is presented and itsin shieldingFigure 2. properties.

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2.4. Morphology2.4. Morphology and Structure and Structure of the of Textile the Textile Sample Sample The schemeThe scheme of woven of woven fabric fabric with with inserted inserted metallic metallic yarns yarns and plasmaand plasma coating coating is pre- is pre- sentedsented in Figure in Figure 3. The 3. copperThe copper coating coating on the on fabric the fabric with with inserted inserted metallic metallic yarns yarns does does not not Textiles 2021, 1 createcreate a continuous a continuous surface surface layer, layer, but ratherbut rather an additional an additional electrically electrically conductive conductive grid gridon on 8 metallicallymetallically the fabric the fabric yarns, yarns, increasing increasing the fabric’s the fabric’s conductivity conductivity and itsand shielding its shielding proper- proper- ties. ties.

FigureFigureFigure 3. Scheme 3.3. Scheme of the of woven the woven fabric fabric fabric with withinserted with inserted inserted metallic metallic metallic yarns yarns yarnsand plasma and and plasma plasma coating. coating. coating.

OpticalOpticalOptical microscopy microscopymicroscopy images imagesimages are areevidencingare evidencingevidencing the the uniformthe uniform uniform covering covering covering of the of ofthe fabric,the fabric, fabric, both both both on on cottoncottonon cotton and and theand the metallic the metallic metallic yarns yarns yarns of of the theof fabric the fabric fabric structure structure structure (Figure (Figure (Figure 4a,b).4a,b). 4a,b).

(a) (a) (b) (b)

FigureFigureFigure 4. (a) 4.Macroscopic ((aa)) Macroscopic Macroscopic aspect aspect aspectand ( andb) and optical (b) ( boptical) microscope optical microscope microscope image image at imagemagnification at magnification at magniﬁcation 50× for 50× the for 50 ×thefor the wovenwovenwoven cotton cottoncotton fabric fabric with withinserted inserted silver silver yarns yarns and copper and and copper copper coating coating coating of 5600 of of 5600nm—F6. 5600 nm—F6. nm—F6.

SEMSEMSEM images images were were meant meant to evidence to to evidence evidence the stainlessthe the stainless stainless steel steel steeland andthe and silverthe the silver silveryarns yarns yarnsin the in in the the fabricfabricfabric structure structurestructure (Figures (Figures(Figures 5 and5 5 and and6). 6The ).6). The investigationThe investigation investigation of Cu of of coppercoated Cu coated coatedsamples, samples, samples, presented presented presented in in FigureinFigure Figure7, shows 7, 7shows, that shows thethat that film the the filmis compact film is compact is compact and coversand and covers the covers yarns the yarns the uniformly. yarns uniformly. uniformly. A rupture A rupture A of rupture the of the of film thefilmalong film along one along fiberone onefiber allowed fiber allowed allowedevaluating evaluating evaluating the film the filmthickness, the filmthickness, thickness, with with variations withvariations variations caused caused by caused the by the by Textiles 2021, 1, FOR PEER REVIEW theactual actual positioning positioning into intothe field the field of view. of view. Also, Also, the copper the copper coating coating seems seems to present to present a 6co- a actual positioning into the field of view. Also, the copper coating seems to present a co- lumnarcolumnarlumnar structure structure structure of the of deposit. ofthe the deposit. deposit.

FigureFigure 5. SEM image image of of fabric fabric with with inserted inserted stainless stainless steel steel yarns yarns F1 F1(250×). (250 ×).

Figure 6. SEM image of fabric with inserted silver yarns and copper coating of 5600 nm F6— (250×).

(a) (b)

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Figure 5. SEM image of fabric with inserted stainless steel yarns F1 (250×).

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Figure 5. SEM image of fabric with inserted stainless steel yarns F1 (250×).

Figure 6. SEM image of fabric with inserted silver yarns and copper coating of 5600 nm F6— (250×).

The SEM images reveal that the average distance between adjacent yarns is around 300 microns, while the distance between two adjacent metallic yarns is 5 mm. In this manner, a combined network of rectangles is formed: a small net originating from the first- order neighbors combining both cotton and metallic yarns, which are covered by Cu coat- FigureFigure 6. SEM image of of fabric fabric with with in insertedserted silver silver yarns yarns and and copper copper coating coating of of5600 5600 nm nm F6— F6—(250×). ing, and(250×). larger rectangles formed by the metallic yarns woven into the fabric.

(a) (b)

Figure 7. SEM image of fabric with inserted silver yarns and copper coating of 5600 nm F6. (a) (2000×) and (b) (8000×).

The SEM images reveal that the average distance between adjacent yarns is around 300 microns, while the distance between two adjacent metallic yarns is 5 mm. In this manner, a combined network(a of) rectangles is formed: a small net originating(b) from the first-order neighbors combining both cotton and metallic yarns, which are covered by copper coating, and larger rectangles formed by the metallic yarns woven into the fabric.

2.5. Electric Conductivity Measurements

The following relation was used for measuring electric conductivity (σm) in the case of the washer geometrical shape of the textile shields, tailored according to the requirements imposed by the ASTM ES-07 standard for the determination of the EMSE.

1 b σm = ln (1) 2 π h Rw a

where a is the inner diameter of the circle, b the outer diameter, h the fabric thickness and Rw—the measured resistance value by ohmmeter [Ω] (Figure8).

2.6. EM Shielding Effectiveness Measurements Electromagnetic shielding effectiveness (EMSE) measurement was accomplished according to the standard ASTM ES-07, via a transverse electromagnetic cell (TEM cell). EMSE is defined as: power of incident signal EMSE = 10 log [dB] (2) 10 power of transmitted signal Textiles 2021, 1, FOR PEER REVIEW 7

Figure 7. SEM image of fabric with inserted silver yarns and copper coating of 5600 nm F6. (a) (2000×) and (b) (8000×).

2.5. Electric Conductivity Measurements

The following relation was used for measuring electric conductivity (σm) in the case of the washer geometrical shape of the textile shields, tailored according to the requirements imposed by the ASTM ES-07 standard for the determination of the EMSE.

Textiles 2021, 1, FOR PEER REVIEW 1 7 σ = ln (1) 2 π ℎ where a is the inner diameter of the circle, b the outer diameter, h the fabric thickness and Rw—the measuredFigure 7. SEM resistance image of value fabric by with ohmmeter inserted silver[Ω] (Figure yarns and 8). copper coating of 5600 nm F6. (a) (2000×) and (b) (8000×).

2.5. Electric Conductivity Measurements

The following relation was used for measuring electric conductivity (σm) in the case of the washer geometrical shape of the textile shields, tailored according to the require- Textiles 2021, 1 ments imposed by the ASTM ES-07 standard for the determination of the EMSE. 10 1 σ = ln (1) 2 π ℎ whereThe a schemeis the inner of the diameter coaxial of TEM the cellcircle, is presentedb the outer in diameter, Figure9, h which the fabric also includesthickness the and shape of the samples tailored for testing the EMSE with this system. Figure 8. GeometricalRw—the measured (washer) resistanceshape of textile value shield by ohmmeter for standard [Ω ASTM] (Figure ES-07. 8).

The scheme of the coaxial TEM cell is presented in Figure 9, which also includes the

shape of the samples tailored for testing the EMSE with this system. FigureFigure 8. 8.Geometrical Geometrical (washer) (washer) shape shape of of textile textile shield shield for for standard standard ASTM ASTM ES-07. ES-07.

The scheme of the coaxial TEM cell is presented in Figure 9, which also includes the shape of the samples tailored for testing the EMSE with this system.

Figure 9. Scheme of the TEM cell and of the testing woven fabric sample. Figure 9. Scheme of the TEM cell and of the testing woven fabric sample. In order to be tested, fabric samples were tailored in annular shape having an outer In orderdiameter to be of tested, 100 mm fabric and samples an inner diameterwere tailored of 30 in mm annular and were shape ﬁxed having onto thean outer cell by means diameterof of colloidal 100 mm Agand paste an inner applied diameter on their of 30 borders. mm and The were measurement fixed onto the system cell by included means a signal of colloidalgenerator Ag paste Keysight applied E8257D,on their border a powers. The ampliﬁer measurement IFI model system SMX50, included the coaxial a signal TEM cell generatormodel Keysight 2000 E8257D, and an oscilloscopea power amplifier Tektronix IFI modelmodel MDO3102.SMX50, the Thecoaxial EMSE TEM measurements cell model 2000were and performed an oscilloscope within theTektroni frequencyx model range MDO3102. of 100 kHz The to EMSE 1 GHz, measurements in accordance to the were performedASTM ES-07 within standard. the frequencyEMSE was range measured of 100 kHz for each to 1 ofGHz, the sevenin accordance fabric samples. to the ASTM ES-07 standard. EMSE was measured for each of the seven fabric samples. 3. Results The results obtained for the electrical conductivity for the samples investigated ac- cordingFigure 9. to Scheme the scheme of the TEM depicted cell and in Figureof the testing2 are presentedwoven fabric in sample. Table3. It is noticed that the conductivity of the fabrics containing silver yarns are systematically higher than those of the fabricsIn order containing to be tested, stainless fabric steel samples yarns, withwere abouttailored one in order annular of magnitude; shape having at the an sameouter time,diameter the conductivity of 100 mm and increases an inner upon diameter copper of coating30 mm and of the were fabrics, fixed regardlessonto the cell of by the means type ofof yarns colloidal in the Ag structure paste applied (Figure on 10 their). borders. The measurement system included a signal generator Keysight E8257D, a power amplifier IFI model SMX50, the coaxial TEM cell Table 3. Experimental values for electrical conductivity. model 2000 and an oscilloscope Tektronix model MDO3102. The EMSE measurements were performedDimensions within (a/b/h the) frequencyR range of− 100R kHz =toR 1 GHz, inConductivity, accordance σto the Sample Shape measured electrodes w m ASTM ES-07 standard.[mm] EMSE was measured for [eachΩ] of the seven fabric samples.[S/m] F1 Circular 20/44/0.53 5.195 45.60

F2 Circular 20/44/0.53 1.835 129.09 F3 Circular 20/44/0.49 0.435 589.02 F4 Circular 20/44/0.49 0.255 1004.8 F5 Circular 20/44/0.49 0.185 1385.00 F6 Circular 20/44/0.50 0.133 1887.98 F7 Circular 20/44/0.51 0.115 2140.67 Textiles 2021, 1, FOR PEER REVIEW 8

3. Results The results obtained for the electrical conductivity for the samples investigated according to the scheme depicted in Figure 2 are presented in Table 3. It is noticed that the conductivity of the fabrics containing silver yarns are systematically higher than those of the fabrics containing stainless steel yarns, with about one order of magnitude; at the same time, the conductivity increases upon Cu coating of the fabrics, regardless of the type of Textiles 2021, 1 yarns in the structure (Figure 10). 11

2500

2000

1500

1000

Electrical conductivity [S/m] 500

0 0 2000 4000 6000 8000 10000 Copper thickness [nm]

Figure 10. Dependence of the electrical conductivity of the fabrics with inserted silver yarns on the Figurethickness 10. Dependence of copper layer. of the The electrical dot curve conductivity is just for eye of guiding the fabrics for the with obtained inserted trend. silver yarns on the thickness of Cu layer. The dot curve is just for eye guiding for the obtained trend. The graphs evidencing the electromagnetic shielding effectiveness in the case of stain- Textiles 2021, 1, FOR PEER REVIEW 9 Tableless 3. steel-basedExperimental fabrics values are for illustrated electrical in conductivity. Figure 11. They show in the frequency range from 105 to 107 Hz a shielding up to 22 dB for the plain textile, with a small increase of around 4 dB of shielding upon coatingDimensions with 1200 nm copper layer onto both faces ofConductivity, the material. σm Sample Shape Rmeasured − Relectrodes = Rw [Ω] (a/b/h) [mm] [S/m] F1 Circular 20/44/0.53 5.195 45.60 F2 Circular 20/44/0.53 1.835 129.09 F3 Circular 20/44/0.49 0.435 589.02 F4 Circular 20/44/0.49 0.255 1004.8 F5 Circular 20/44/0.49 0.185 1385.00 F6 Circular 20/44/0.50 0.133 1887.98 F7 Circular 20/44/0.51 0.115 2140.67

The graphs evidencing the electromagnetic shielding effectiveness in the case of stainless steel-based fabrics are illustrated in Figure 11. They show in the frequency range from 105 to 107 Hz a shielding up to 22 dB for the plain textile, with a small increase of around 4 dB of shielding upon coating with 1200 nm Cu layer onto both faces of the material. FigureFigureFigure 11. 11. Measured12Measured shows EMSEaEMSE comparison for for samples samples of with the with stainless measur stainless steeled EMSE yarnssteel (F1–F2).yarns values (F1-F2). for the silver-based fabrics, which exceed 45 dB for the frequency range from 105 to 108 Hz, even for the uncoated material.Figure At the 12 same shows time, a comparison one can notice of the that measured the additional EMSE values coating for the of silver-basedthe structure is 5 8 conductingfabrics, whichto enhanced exceed shielding 45 dB for theeffectivene frequencyss, rangewhich from is more 10 to important 10 Hz, even as the for Cu the coat- uncoated material. At the same time, one can notice that the additional coating of the ing thickness increases and present values exceeding 60 dB for 10 µm layer coating, for structure is conducting to enhanced shielding effectiveness, which is more important as 7 8 frequenciesthe copper up coating to 10 thickness Hz. At frequencies increases and above present 10 values Hz, exceedingone can notice 60 dBfor that 10 theµm layerCu layer thicknesscoating, has for a frequencies limited influence up to 107 onHz. the At frequenciesshielding efficiency, above 108 Hz, which one canremain notice in that the the range 30–40copper dB. layer thickness has a limited inﬂuence on the shielding efﬁciency, which remain in the range 30–40 dB.

Figure 12. Measured EMSE for samples with silver yarns (F3-F7).

4. The Model for Estimating EMSE The principle that states that for combinations of multiple electric shields, the overall EMSE is the sum of the EMSE of individual shields [19] was applied in order to model the shielding effectiveness of the fabrics with inserted conductive yarns and conductive coatings. As such, due to the fact that the structure of such shields includes the coating of one side, the fabric with inserted conductive yarns and the coating of the other side, the following relation is proposed for modelling of EMSE: = +2× (3) For EMSEgrid, the relation for electric conductive grid structures according to [19] and for EMSElayer, the relation of impedance method according to [13] are used. Geometric and electric parameters for both relations were applied related to the structure of the grid of inserted conductive yarns and the layer of coating. The following notations for electric and geometric parameters for these types of fabrics apply: σy—electrical conductivity of the metallic yarns [S/m] µy—magnetic permeability of the metallic yarns [H/m] σm—electrical conductivity of the fabric material [S/m]; µm—magnetic permeability of the material (for copper coating µm∼µ0 = 4π ∗ 10−7 H/m); h—fabric thickness [m] d—diameter of the metallic yarn [m] D—equivalent diameter of the electric conductor [m] r—distance between conductive yarns [m]

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Textiles 2021, 1 12 Figure 11. Measured EMSE for samples with stainless steel yarns (F1-F2).

FigureFigure 12. 12. MeasuredMeasured EMSE EMSE for samplessamples with with silver silver yarns yarns (F3–F7). (F3-F7).

4. 4.The The Model Model for for Estimating Estimating EMSEEMSE The principle that states that for combinations of multiple electric shields, the overall The principle that states that for combinations of multiple electric shields, the overall EMSE is the sum of the EMSE of individual shields [19] was applied in order to model EMSEthe shielding is the sum effectiveness of the EMSE of the of individual fabrics with shields inserted [19] conductive was applied yarns in and order conductive to model the shieldingcoatings. effectiveness As such, due toof thethe factfabrics that thewith structure inserted of conductive such shields yarns includes and the conductive coating of coatings.one As side, such, the fabricdue to with the insertedfact that conductive the structur yarnse of andsuch the shields coating includes of the other the coating side, the of one side,following the fabric relation with is inserted proposed conductive for modelling yarns of EMSE and: the coating of the other side, the following relation is proposed for modelling of EMSE: EMSEtotal = EMSEgrid + 2 × EMSElayer (3) = +2× (3) For EMSEgrid, the relation for electric conductive grid structures according to [19] and For EMSEgrid, the relation for electric conductive grid structures according to [19] and forfor EMSEEMSElayerlayer, the, the relation relation of of impedance method method according according to [ 13to] [13] are used.are used. Geometric Geometric and and electricelectric parameters parameters for for both relationsrelations were were applied applied related related to the to structurethe structure of the of grid the of grid of insertedinserted conductive conductive yarnsyarns and and the the layer layer of coating. of coating. The following The following notations notations for electric for and electric andgeometric geometric parameters parameters for these for these types types of fabrics of fabrics apply: apply: σy—electricalσy—electrical conductivity conductivity of the of metallic the metallic yarns [S/m] yarns [S/m] µy—magneticµy—magnetic permeability permeability of the of metallic the metallic yarns [H/m] yarns [H/m] σ —electrical conductivity of the fabric material [S/m]; m σm—electrical conductivity of the fabric material [S/m]; −7 µm—magnetic permeability of the material (for copper coating µm∼µ = 4π ∗ 10 H/m); µm—magnetic permeability of the material (for copper coating0 µm∼µ0 = 4π ∗ 10−7 h—fabric thickness [m] H/m); d—diameter of the metallic yarn [m] D—equivalenth—fabric thickness diameter [m] of the electric conductor [m] r—distanced—diameter between of the conductive metallic yarns yarn [m][m] t—thicknessD—equivalent of the copperdiameter coating of the [m] electric conductor [m] f —frequencyr—distance of between electromagnetic conductive (EM) ﬁeldyarns [Hz] [m]

For EMSEgrid, the model related to the woven fabrics with inserted metallic yarns, the following equation applies (4):

EMSEgrid = Aa + Ra + Ba + K1 + K2 + K3 (4)

where:

Aa = attenuation introduced by a particular discontinuity, dB Ra = aperture single reﬂection loss, dB Ba = multiple reﬂection correction term, dB K1 = correction term to account for the number of like discontinuities, dB K2 = low-frequency correction term to account for skin depth, dB K3 = correction term to account for the coupling between adjacent holes, dB Textiles 2021, 1 13

With following relations for these terms:

h A = 27.3 [dB] (5) a r

where: h—fabric thickness (depth of opening) [m] r = distance between conductive yarns (width of the rectangular opening perpendicular to E-ﬁeld) [m]

1 + 4K2 R = 20 log [dB] (6) a 10 4K where: K = j6.69·10−9 f ·r (7) K is valid for rectangular apertures and plane waves.

2 ! (K − 1) Aa − 10 Ba = 20 log10 1 − 10 [dB] (8) (K + 1)2

K1 = −10 log10(S·n) [dB] (9) where: S—the area of each hole (sq cm) n—number of holes/sq cm

−2.3 K2 = −20 log10 1 + 35p (10) where: p = D/δy (11) The term K2 is the single correction factor of the analytic relation sum which encoun- ters the electric parameter of the yarns (electric conductivity and magnetic permeability), within the relation of skin depth. It is thus a factor with high sensitivity on the overall EMSE relation. The electric parameters were considered for the conductive yarn (not for the fabric), since the ratio p = D/δy is a property of the yarn. The skin depth of the yarn δy has the following electric parameters:

1 δy = p (12) π f µyσy

Since D is the diameter of the electric conductor and we have within the fabric structure two adjacent yarns√ (ﬂoat repeat 2:6 Warp and 2:5 Weft), with the diameter d, the resulting diameter is: D = d1d2, due to the elliptical shape of the two adjacent metallic yarns. d = d and d = d + l with l = 100 and d = fabric density in yarns/100 mm. 1 2 c c dwe we

K3 = 20 log10(cothAa/8.686)[dB] (13)

For EMSElayer, the model related to the shielding of the copper coating was given by the general expression of the impedance method according to [13]:

(Z + Z )2 Z − Z 2 0 m t/δm jβt −2t/δm −j2βt 0 m EMSElayer = 20 log + 20 log e ·e + 20 log 1 − e ·e (14) 4Z0Zm Z0 + Zm where:

δm—skin depth of copper coated fabric with inserted metallic yarns [m]; γ—propagation constant, α—attenuation constant, β—phase constant. Textiles 2021, 1 14

Textiles 2021, 1, FOR PEER REVIEW p p 11 γ = α = jβ = jωµm(σm + jωεm); for metals, due to σ >> ωε, γ = jωµmσm or p p γ = (1 + j) π f µmσm, then α = β = π f µmσm;

The following relations are set for the impedance of the textile shields (Zm) and the waveγ = impedanceα + jβ = ofjωμ free space(σ +jωε (Z0): ); for metals, due to σ >> ωε, γ = jωμ or γ =(1+j)πμ σ , then α=β=sπμ σ ; jωµ Z = m (15) The following relations are setm for the impedance of the textile shields () and the σm + jωεm wave impedance of free space (Z0): Z = 377 Ω (16) 0 jωμ (15) where: = σ + jωε ω = 2πf —angular frequency = 377 Ω (16) where:Since theω = textile2πf − angular shields considered frequencyin this work contain metal coatings and yarns, theSince conductivity the textile is assumedshields considered to be very large in this as work compared contain with metal air, meaning coatings that andσ myarns,>> the ωε. This condition is verified for the sample with lowest electric conductivity (F1) σm = conductivity is assumed to be very large as compared with air, meaning that σm >> ωε. 45.60 S/m (Table3) and ωε0 = 0.0556 S/m for f = 1 GHz. Hence, the condition σ >> ωε is Thisvalid condition for all samples. is verified The shieldfor the impedance sample with can belowest written electric as: conductivity (F1) σm = 45.60 S/m (Table 3) and ωε0 = 0.0556 S/m for f = 1GHz. Hence, the condition σ >> ωε is valid for s s all samples. The shield impedance canjωµ be written as:π f µ Z = m = (1 + j) m (17) m σ σ jωμ m πμ m = =(1+j) (17) σ σ In terms of skin depth of the coating, δm, the modulus of shield impedance is: In terms of skin depth of the coating, δm, the modulus of shield impedance is: √ (1 + j) 2 Zm(1= + j) √=2 [Ω] (18) = σm=δm σm δ[Ω]m (18) σδ σδ SkinSkin depth depth is is defined defined asas thethe distancedistance from from the the metal metal surface surface for whichfor which the current the current densitydensity drops drops at at 1/e 1/e from from the the value atat the the inner inne surface.r surface. From From (15) (15) and and (17), (17), the definition the definition of ofskin skin depth depth for for copper copper coating is is obtained: obtained: √2√ 1 δ = 2= 1 (19) δm = = (19) σ πpfμσ σmZm π f µmσm By applying the general Equation (3) for the calculation of EMSE for the samples involvedBy in applying the present the general study, Equationwe obtained (3) for the the red calculation curves in ofFiguresEMSE 13for and the 14 samples for the case of involvedfabrics with in the inserted present study,stainless we obtainedsteel yarns, the redand curves respectively in Figures the 13 redand curves14 for the in caseFigures of 15– 18 fabricsfor the with case inserted of fabrics stainless with steelinserted yarns, silver and respectivelyyarns, and thewith red different curves in CuFigures layer 15 thickness.–18 for the case of fabrics with inserted silver yarns, and with different copper layer thickness.

FigureFigure 13. 13. CalculatedCalculated ( (redred)) and measuredmeasured (blue (blue) values) values for for F1 (stainlessF1 (stainless steel steel yarns). yarns).

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Figure 14. Calculated (red) and measured (blue) values for F2 [(st. steel yarns) and 1200 nm Cu Figure 14. Calculated (red) and measured (blue) values for F2 [(st. steel yarns) and 1200 nm Cu Figurecoating]. 14. Calculated (red) and measured (blue) values for F2 [(st. steel yarns) and 1200 nm Cu coating].Figure 14. Calculated (red) and measured (blue) values for F2 (st. steel yarns) and 1200 nm copper coating].coating.

Figure 15. Calculated (red) and measured (blue) values for F3 (silver yarns). FigureFigure 15. 15. CalculatedCalculated ( (redredred)) and and measuredmeasuredmeasured (blue ((blue) values)) valuesvalues for forfor F3 (silverF3F3 (silver(silver yarns). yarns).yarns).

FigureFigure 16. 16. Calculated (redred) and measured (blueblue) values for F4 [(silver yarns) and 1200 nm Cu coat- Figure 16. CalculatedCalculated (red ( )) and and measured ( (blue)) values values for for F4 F4 (silver [(silver yarns) yarns) and and 1200 1200 nm copper nm Cu coat- Figureing].coating. 16. Calculated (red) and measured (blue) values for F4 [(silver yarns) and 1200 nm Cu coating].ing].

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Figure 17. Calculated (red) and measured (blue) values for F6 [(silver yarns) and 5600 nm Cu coat- FigureFigure 17. 17. CalculatedCalculated (red (red)) and and measured measured ((blueblue)) values values for for F6 F6 (silver [(silver yarns) yarns) and and 5600 5600 nm copper nm Cu coating]). ing]).coating.

Figure 18. Calculated (red) and measured (blue) values for F7 [(silver yarns) and 10,000 nm Cu FigureFigure 18. 18. CalculatedCalculated ( (redred)) and measuredmeasured ( blue(blue) values) values for for F7 (silverF7 [(silver yarns) yarns) and 10,000 and 10,000 nm copper nm Cu coating). coating).coating. 5. Discussion 5.5. DiscussionDiscussion The novel structure of textile shields made of fabrics with inserted conductive yarns The novel structure of textile shields made of fabrics with inserted conductive yarns andThe metallic novel plasma structure coating of textile has a geometry shields made difﬁcult of to fabrics be modelled with inserted in order toconductive accurately yarns andandcalculate metallicmetallic the plasmaplasmaEMSE. coatingcoating Several analytichashas aa geometrygeometry models have difficultdifficult been toto applied bebe modelledmodelled in the planning inin orderorder phase toto accuratelyaccurately of calculatecalculatethis research thethe EMSE.EMSE. study, such SeveralSeveral as: analyticanalytic modelsmodels havehave beenbeen appliedapplied inin thethe planningplanning phasephase ofof thisthis- researchresearchThe impedance study,study, suchsuch method as:as: [12–14,16] - The circuit method [12,15] -- The The impedanceimpedance methodmethod [12–14,16][12–14,16] - - TheThe circuit impedance method method [12,15] with correction factors for conductive grid structures [12,19] - - TheThe circuit impedance method method [12,15] for multiple shields [19]. -- The The impedanceimpedance methodmethod withwith correctioncorrection factorfactorss forfor conductiveconductive gridgrid structuresstructures [12,19][12,19] - TheThe impedance proposed approach method tofor model multiple these shields structures [19]. was to add the EMSE of the three - conductive The impedance structures: method the metallic for multiple yarns inserted shields into [19]. the woven structure and the copper coatingTheThe proposed onproposed both sides approachapproach of the fabric. toto modelmodel thesethese structuresstructures waswas toto addadd thethe EMSEEMSE ofof thethe threethree conductiveconductiveThe proposed structures:structures: analytic thethe metallicmetallic model considers yarnsyarns inseinse bothrtedrted geometric intointo thethe woven andwoven electrical structurestructure parameters andand thethe of coppercopper coatingcoatingthe fabric onon bothboth with sidessides inserted ofof the conductivethe fabric.fabric. yarns and of the conductive coating. However, the analyticTheThe proposedproposed model distinguishes analyticanalytic modelmodel between considersconsiders the skin depth bothboth of geometricgeometric the yarn ( δandandy) and electricalelectrical the skin parametersparameters depth of ofof the fabric material (δ ). Both electrical parameters for the skin depth (electric conductivity thethe fabricfabric withwith insertedinsertedm conductiveconductive yarnsyarns anandd ofof thethe conductiveconductive coating.coating. However,However, thethe analyticand magnetic model permeability) distinguishes were between measured the and skin calculated depth of in the ﬁrstyarn phase (δy) forand the the metallic skin depth analytic model distinguishes between the skin depth of the yarn (δy) and the skin depth of the fabric material (δm). Both electrical parameters for the skin depth (electric conduc- of the fabric material (δm). Both electrical parameters for the skin depth (electric conduc- tivitytivity andand magneticmagnetic permeability)permeability) werewere measurmeasureded andand calculatedcalculated inin thethe firstfirst phasephase forfor thethe metallicmetallic yarnsyarns andand thethe coatedcoated fabrics.fabrics. TheThe geometricgeometric parametersparameters withwith highhigh sensitivitysensitivity werewere thethe thicknessthickness ofof thethe fabricfabric andand thethe diameterdiameter ofof thethe metallicmetallic yarn.yarn. TheThe equivalentequivalent diameterdiameter

Textiles 2021, 1, FOR PEER REVIEW 14

Textiles 2021, 1 17

of the two metallic yarns was computed as the diameter of the circle having the same area as the resulting ellipse formed by the two adjacent metallic yarns in the fabric structure. Theyarns distance and the between coated fabrics.the yarns The was geometric considered parameters for computing with high the sensitivity diameter were of the the ellipse, thickness of the fabric and the diameter of the metallic yarn. The equivalent diameter of which was given by the fabric density (dw). the two metallic yarns was computed as the diameter of the circle having the same area All geometric and electric parameters of the achieved shields were considered within as the resulting ellipse formed by the two adjacent metallic yarns in the fabric structure. proposedThe distance calculation between theof EMSE yarns: was considered for computing the diameter of the ellipse, - which Electric was given conductivity by the fabric and density magnetic (dw). permeability of the metallic yarns; - OpticalAll geometric diameter and electricof the metallic parameters yarns of the an achievedd equivalent shields diameter were considered of the withinelectric con- proposedductor; calculation of EMSE: - - DistanceElectric conductivity between metallic and magnetic yarns of permeability the woven of fabric, the metallic depending yarns; on float repeat and - weave;Optical diameter of the metallic yarns and equivalent diameter of the electric conductor; - - ElectricDistance conductivity between metallic and yarnsmagnetic of the permeability woven fabric, of depending the fabric; on ﬂoat repeat and weave; - Fabric thickness; - Electric conductivity and magnetic permeability of the fabric; - - ThicknessFabric thickness; of the plasma coated layer. - InThickness the case of thethe plasmafabrics coatedwith stainless layer. steel yarns (F1), the model estimates quite well the fabricIn the with case inserted of the fabrics yarns, with with stainless differe steelnces yarns in the (F1), range the model1–8 dB estimates over the quite whole fre- quencywell the range. fabric An with even inserted better yarns, fitting with of the differences measured in the EMSE range is 1–8obtained dB over for the the whole fabric with insertedfrequency yarns range. and An copper even better coating ﬁtting (F2) of by the the measured EMSEgrid EMSE and isthe obtained additional for the EMSE fabriclayer relation,with with inserted differences yarns and between copper coatingthe modelled (F2) by an thedEMSE measuredgrid and values the additional less thanEMSE 5 dB,layer as shown inrelation, Figure 19. with differences between the modelled and measured values less than 5 dB, as shown in Figure 19.

FigureFigure 19. 19. DifferenceDifference betweenbetween measured measured and and calculated calculated values values for fabrics for fabrics with stainlesswith stainless steel yarns steel yarns andand copper copper coating. coating.

InIn case case of of the fabricfabric with with silver silver yarns yarns (F3), (F3), the the model modelEMSE EMSEgrid underestimatesgrid underestimates the the measuredmeasured values, values, aa fact fact which which could could be explainedbe explained by the by two the parameters two parameters with high with sensitiv- high sensi- tivityity of of the the model—the model—the electric electric conductivity conductivity and the and equivalent the equivalent diameter ofdiameter the silver of yarn. the silver The electrical linear resistance of the silver yarn presented different values for different yarn. The electrical linear resistance of the silver yarn presented different values for dif- measurements, a fact explainable by its non-homogenous structure and the general terms ferent measurements, a fact explainable by its non-homogenous structure and the general of its specification (Rl < 1.5 kΩ/m) [25]. The measured value for silver yarn conductivity terms of its specification (Rl < 1.5 kΩ/m) [25]. The measured value for silver yarn conduc- introduced into the model is a potential factor of underestimated values of EMSEgrid relation. tivity introducedThe fabrics F4 into and the F5 model show a is significant a potential difference factor betweenof underestimated modelled and values measured of EMSEgrid relation.values of around 20 dB on the frequency range 105 to 107 Hz, which could be explained by 3 theThe low valuesfabrics of F4 the andEMSE F5 showlayer model a significant in case of difference 10 nanometer between values: modelled 1200 nm (F4)and andmeasured values1750 nm of (F5).around On 20 the dB other on hand,the frequency the EMSE layerrangemodel 105 hasto 10 significant7 Hz, which increasing could be values explained for by 5600 nm (F6) and 10,000 nm (F7), which makes that EMSE reaches the measured values the low values of the EMSElayer model in case of 103 nanometertotal values: 1200 nm (F4) and for F6 and F7, as shown in Figure 20. These results show that the steady increase of the 1750 nm (F5). On the other hand, the EMSElayer model has significant increasing values for fabric conductivity upon copper coating, of 3.2 times for F6 and 3.6 times for F7 with respect 5600 nm (F6) and 10,000 nm (F7), which makes that EMSEtotal reaches the measured values for F6 and F7, as shown in Figure 20. These results show that the steady increase of the fabric conductivity upon copper coating, of 3.2 times for F6 and 3.6 times for F7 with respect to the uncoated fabric, plays an important role in the model of the EMSElayer. These

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factsto the suggest uncoated a significant fabric, plays role an played important by the role conductivity in the model ofof the theEMSE componentslayer. These in factsthe model. Onesuggest has to a significant consider rolethat played this type by theof conductivitycomposite EM of the shield components is quite in difficult the model. to model One and thathas the to considerproposed that relation this type of of EMSE composite includes EM shield all the is parameters quite difficult of to the model electric and thatstructures ofthe this proposed composite relation shield. of EMSE includes all the parameters of the electric structures of this composite shield.

FigureFigure 20. 20. DifferenceDifference between between measured andand calculated calculated values values for for fabrics fabrics with with silver silver yarns yarns and and coppercopper coating. coating.

TheThe differences differences betweenbetween the the calculated calculated and and measured measuredEMSE EMSEvalues (fromvalues Figures (from 19 Figures 19–20)and 20 are) are due due to to the the fact fact thatthat thethe ideal ideal conditions conditions considered considered in the in theoreticalthe theoretical model, model, whichwhich is is based based onon the the isomorphism isomorphism between between the infinite the infinite plane shield plane placed shield in placed free space in andfree space the washer-shaped sample placed in a coaxial line, (homogenous material sample, perfect and the washer-shaped sample placed in a coaxial line, (homogenous material sample, electrical contact between sample and sample holder (TEM Cell)) are difficult to achieve perfectin practice. electrical The electricalcontact between contact between sample the and sample sample and holder sample (TEM holder Cell)) becomes are verydifficult to achieveimportant in practice. at high frequencies. The electrical Moreover, contact when between using the a coaxial sample TEM and cell sample for determining holder becomes verythe EMSEimportantof material, at high higher frequencies. transmission Moreover, modes appearwhen using at high a frequencies,coaxial TEM which cell canfor deter- miningaffect thethe measurement EMSE of material, results [11 higher]. Also, transmission given the composite modes structure appear ofat the high proposed frequencies, whichelectromagnetic can affect shieldsthe measurement (textile yarns, results conductive [11]. Also, yarns, given conductive the composite coating), otherstructure phe- of the proposednomena may electromagnetic occur that would shield not usuallys (textile occur yarns, in a perfectlyconductive homogenous yarns, conductive material; these coating), othercould phenomena affect the EMSE may. occur that would not usually occur in a perfectly homogenous material;6. Conclusions these could affect the EMSE. This paper proposes a novel type of textile shield: fabrics with inserted conductive 6.yarns Conclusions and metallic coating obtained by magnetron sputtering deposition. The results regardingThis paper the electromagnetic proposes a novel shielding type efficiencyof textile (EMSE) shield: offabrics these fabricswith inserted evidence conductive that yarnsthe metallic and metallic plasma coating coatings obtained applied by additionally magnetron on sputtering fabrics with deposition. inserted conductive The results re- gardingyarns contribute the electromagnetic with 10–15 dB shielding to overall efficiency EMSE in the (EMSE) frequency of these range fabrics 0.1–1000 evidence MHz and that the metallictherefore plasma significantly coatings enhance applied the materialadditionally functionality. on fabrics The with utilization inserted of flexible conductive textile yarns shields would open up new practical opportunities, and therefore the modelling of the contribute with 10–15 dB to overall EMSE in the frequency range 0.1–1000 MHz and there- electromagnetic shielding effectiveness (EMSE) is particularly important. As such, in the forepresent significantly paper, we consideredenhance the the combinationsmaterial functionality. of multiple electric The utilization shields originating of flexible from textile shieldsthe initial would fabrics open structure up new with practical metallic opportunities, yarns inserted and and the therefore coating of the fabric modelling on both of the electromagneticfaces with a conductive shielding copper effectiveness layer of various (EMSE) thicknesses. is particularly important. As such, in the presentEach paper, of the we contributions considered to the overallcombinationsEMSE was of analyticallymultiple electric determined shields according originating fromto the the equations initial fabrics 3–19, respectively structure withEMSE metallicgrid and EMSEyarnslayer inserted, and the and obtained the coating values of were fabric on bothcomputed faces with to model a conductive the shielding copper effectiveness layer of various of the fabricsthicknesses. with inserted conductive yarnsEach and of conductive the contributions coatings. to The the approach overall ofEMSE modelling was analytically is meant to be determined able to estimate according the property of EMSE in the design phase of the textile shield. Although there are still to the equations 3–19, respectively EMSEgrid and EMSElayer, and the obtained values were differences between calculated and measured results, it is considered that the analytic computed to model the shielding effectiveness of the fabrics with inserted conductive yarns and conductive coatings. The approach of modelling is meant to be able to estimate the property of EMSE in the design phase of the textile shield. Although there are still differences between calculated and measured results, it is considered that the analytic

Textiles 2021, 1 19

model based on adding the particular contribution to EMSE of the metallic grid and of the metallic coating gives a valuable guidance when designing this type of textile shield.

Author Contributions: Conceptualization: I.R.R., Methodology: B.M., I.R.R., Software: I.R.R., M.C., Validation: M.C., B.M., Formal analysis: R.S., L.S., C.M., C.C., Investigation: L.S., C.M., R.S., Re- sources: L.S., B.M., Data curation: C.M., C.C., Writing original draft preparation: I.R.R., writing review and editing: B.M., R.S., M.C., Visualization: B.M., C.C., Supervision: I.R.R., Project administra- tion: B.M., L.S., I.R.R., Funding aquisition: B.M., L.S., I.R.R., All authors have agreed to the published version of the manuscript. Funding: This research was funded by ERA-NET Manunet project Contract no. 28/2018 TexEMFiRe— “Manufacturing textiles with elec-tromagnetic shielding and fire-retardant properties by plasma based methods”. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Please consult TexEMFiRe website: http://texemfire.inflpr.ro/. Acknowledgments: Research work for this study has been performed within ERA-NET Manunet project Contract no. 28/2018 TexEMFiRe—“Manufacturing textiles with electromagnetic shielding and fire-retardant properties by plasma based methods”, Contract no. PN19310103/2019—“Micro and nano-structured materials, processes and systems with applications in emerging technologies” and PN19150101- Emerging research on lasers, plasma, radiation and their applications in the fields of smart specialization and public interest. Conflicts of Interest: The authors declare no conflict of interest.

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20. Neelakanta, P.S. Handbook of Electromagnetic Materials: Monolithic and Composite Versions and Their Applications; CRC Press: Boca Raton, FL, USA, 1995. 21. Neruda, M.; Vojtech, L. Electromagnetic shielding effectiveness of woven fabrics with high electrical conductivity: Complete derivation and verification of analytical model. Materials 2018, 11, 1657. [CrossRef][PubMed] 22. Rybicki, T. EMI Shielding and reflection from textile mesh grids compared with analytic models. IEEE Trans. Electromagn. Compat. 2018, 61, 372–380. [CrossRef] 23. Caro, A.L.; Vojtech, L. Modelling of Textile Reinforced Composites Barriers against Electromagnetic Radiation; TU Prague: Prague, Czech Republic, 2011. 24. Rădulescu, I.R.; Surdu, L.; Visileanu, E.; Costea, M.; Pătru, I.; Voicu, V. Modelling and testing the electromagnetic near field shielding effectiveness achieved by woven fabrics with conductive yarns. Ind. Text. 2018, 69, 169–176. 25. Technical Data Sheet Shieldex®117/17 Dtex 2ply, No.: 260121011717. Available online: https://www.shieldextrading.net/ products/yarns-threads/ (accessed on 19 March 2021).