What is the Advantage and Disadvantage of Custom EMF Fabric Manufacturer

2.1. Theoretical Calculation of EM Shielding Fabrics

The expression to measure shielding effect of materials are transmission coefficient T and Shielding Effectiveness (SE). The transmission coefficient T is the ratio of electric field intensity Et (or magnetic field intensity Ht) at a place with a shield to electric field intensity E0 (or magnetic field intensity H0) at the same place without a shield and the formula is as follows,

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T=EtE0=HtH0 (1)

SE refers to the shielding capability and effect of a shielding body against EM interference, which is often expressed logarithmically, as defined below [37],

SE=20lg(E0Et)=20lg(H0Ht)=10lg(P0Pt)=20lg1|T| (2)

where lg=log10; P0 is the power density without shielding; Pt is the power density with shielding body at the same place. For the convenience of calculation, the most used formula is SE=20lg(E0Et).

According to Figure 3, SE can be composed of reflection loss SER, absorption loss SEA and multiple reflection loss SEM.

SE=SER+SEA+SEM (3)

The current theoretical calculation methods of EM shielding fabrics are to directly equivalent the conductive yarns with shielding performance to metal plates, and then the equivalent calculation is carried out according to the fabric structures corresponding to metal plate structures, such as no pore, pore structure, metal grid, layered parallel array and other structures, so as to calculate SE of fabrics. Based on transmission line theory, there are three different mechanisms for EM waves attenuation by the shielding body: reflection attenuation, absorption attenuation and multiple reflection attenuation. Firstly, metal plates are classified into no pore, pore structure, metal grid, layered parallel array (as shown in Figure 4), then the theoretical formulas or semi-empirical formulas of EM shielding are derived based on transmission line theory and equivalent circuit methods [43,44,45,46].

According to the literature [47,48], under the condition of far-field plane waves, transmission coefficient of no pore metal plates is as follows,

(T=4ηeηme&#;γd(ηe+ηm)2/[1&#;(ηm&#;ηeηm+ηe)2&#;e&#;2γd]ηm=3.69×10&#;7fμrσrηe=377Ωγ=(1+j)πμfσ (4)

where ηe is the impedance of EM wave; ηm is the impedance of the metal plate; γ is the propagation constant of EM wave in metal; d is metal plate thickness; μr and σr are relative permeability and relative conductivity of metal plate; μ and σ are permeability and conductivity of metal plate. Combined with Equation (2), the SE of metal plate without poles can be obtained.

As for pore structure metal plates, the transmission coefficient of pores Th can be obtained according to the literature [49],

Th=4n(qF)3/2.(Circularpore) (5) Th=4n(kq&#;F)3/2.(Rectangularpore) (6)

where q is the area of a single circular pore; q&#; is the area of a single rectangular pore; n is the number of holes; F is the metal plate area; k=baξ23, a and b are short and long sides of rectangle pore, respectively; when the rectangle is square, ξ=1; when ba&#;5, ξ=b2aln0.63ba. The transmission coefficient of pore structure metal plate is Th=T+Th. Combined with Equation (2), SE of metal plate with pole structure can be obtained.

Henn et al. [50] first proposed that metallized fabrics were regarded as pores structure metal plates, and deduced the SE formulas of metallized fabrics by calculating the value of pores structure metal plates SE. Safarova et al. [51] used the above method to calculate metal fibers blended fabrics, analyzed the fabrics pore shape with image processing technology, approximated the irregular shape into a rectangle, and established the SE model about fabrics porosity, thickness and fibers volume.

The method of equivalent metal yarns to pores structure metal plates provides an idea for solving the SE of EM shielding fabrics. However, these models have certain limitations, requiring that the whole fabric has good electrical connectivity, resistance must equal to that of metal plates, fabrics must have a certain thickness, and the pores in fabrics need to be regular. In addition, simply approximating the shape of a single pore to a rectangle or a circle will cause a large error. When metal fibers content is too low, these models are not applicable, which is not conducive to the development of EM shielding fabrics.

SE formulas of metal mesh can be obtained from Literature [52].

SE=Aa+Ra+Ba+K1+K2+K3 (7)

where Aa is absorption loss of pores; Ra is reflection loss of pores; Ba is multiple reflection loss; K1 is the modification item related to the unit area and the number of pores K2 is the modification item related to skin depth; K3 is the modification item for coupling of adjacent pores. The calculation formula of each item was shown in Table 1, and the data was derived from [52].

Table 1.

Symbols The Calculation Formula Instructions Aa 27.3dw,(rectangular);32dD,(circular) d is the depth of pores, cm; D is the diameter of a circular hole. Ra 20lg|1+4K24K| Rectangular pores: K=j6.69×10&#;5fw
Circular pores: K=j5.7×10&#;5fw Ba 20lg|1&#;(K&#;1K+1)210&#;0.1Aa| f, MHz K1 &#;10lg(a&#;n),r&#;w r is the distance between shield and field source;
a is the area of a single pore, cm2;
n is the number of pores per square centimeter K2 &#;20lg(1+35p&#;2.3) P=WidthofconductorbetweenholesSkindepth K3 20lg[coth(Aa8.686)] &#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;&#;

It is difficult to accurately calculate the SE of metal grids. For the convenience of calculation, under approximate conditions, the SE of metal materials with good electrical conductivity mainly comes from reflection loss, and the absorption loss can be ignored. Engineering calculation of SE can be obtained that [53],

SE=20lg1s[0.265×10&#;2Rf]2+[0.265×10&#;2Xf+0.333×10&#;8f(lnsa&#;1.5)]2 (8)

where s is the pitch of the metal grid; Rf is AC resistance per unit length of metal grid; a is metal fibers radius; Xf is the reactance per unit length of the metal grid.

Chen et al. [54] made polypropylene fibers woven with copper wire and stainless-steel wire conduct fabrics, respectively, proposed the metal grid structure, and calculated conduct fabrics SE by using the formulas of metal grid structure from the literature. In the frequencies range of 30 MHz&#;1.5 GHz, the measured values were quite different from theoretical values, which may be caused by poor contact or low conductivity of fabrics at yarn intersections. Cai et al. [55] used a metal grid structure model to calculate the SE of stainless-steel fibers blended fabrics. When the content of stainless-steel fibers was 5%, 10% and 15%, respectively, the calculated results were close to experimental results under low frequencies conditions. Rybicki et al. [56] established an equivalent circuit model of conductive grid yarns based on a periodic metal grid structure, believing that SE depends on grid size, thickness and resistivity of grid material. Compared with simulation experiments, this method had certain feasibility.

Although the structure of metal mesh is close to real 2D fabrics in shape, the method requires that the intersecting points of fabrics grid should be conductive, the pores should be regular, and the content of conductive fibers should not be too low. Moreover, the yarns containing metal fibers are a mixture of metal fibers and other fibers, which will affect its EM parameters and cause large errors. This method is not suitable for the large degree of buckling or 3D fabrics, which will limit the development of EM shielding fabrics structure to a certain extent.

Other optimization methods to calculate SE include Sabrio&#;s metal parallel array method, as shown in Figure 4 [57]. The metal grid was divided into two periodic arrays of parallel metal plates with different angles, and SE of each periodic array metal plate can be calculated. Liang et al. [58] derived a SE model of 2D metal fibers blended woven fabrics base on this method. According to the comparison between theoretical values and measured values, yarn diameter, electrical conductivity and weaving Angle all have a certain influence on SE. Whether the fabric is conductive at the yarn crossing point has no effect on this model, which has high applicability.

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Yin et al. [59] established the SE model of plain weave fabrics by the way of the weighted average based on fabrics buckling surface equation and fabrics structure. This model explained the mathematical relationship between SE and the parameters of plain weave fabrics such as pitch, thickness and fiber volume content. The trend of this model was basically consistent with the experiment, which provided a theoretical reference for the effective design of EM shielding fabrics with a large degree of buckling.

The metal yarn was equivalent to the structure of no pores, pores, metal grid and so on, requiring yarn crossing point conductive, and fabrics need to have a certain thickness, which will limit fabrics design and development to a certain extent and there will be considerable limitations. The method equivalent to parallel metal array structure was more accurate and had no effect on whether the yarn crossing point was conductive or not, but this model was not suitable for 2D fabrics with a large degree of buckling and 3D fabrics. At present, the research on SE are limited to 2D fabrics, and there are few reports on 3D fabrics. 3D fabrics have greater development potential and stronger functions than 2D fabrics. The study of the influence of fabrics structure on SE will be the theoretical guiding significance to the development of 3D EM shielding fabrics.

2.2. The Experiment to Investigate EM Shielding Fabrics

The development of EM shielding fabrics can be generally processed by the method of surface metallization, metal coating or woven fabrics with conductive fibers, and then to investigate the influence of various parameters of EM shielding fabrics through experimental measurement.

The method of metal coating: Li et al. [60] conducted experimental tests on SE of silver-plated fiber fabrics, copper-nickel fiber fabrics and stainless-steel fiber blended fabrics. The results showed that, at the same frequency, the shielding effect of vertical polarization wave direction and horizontal or 45 degree polarization wave direction of silver-coated fiber fabric and the copper-nickel fabric was higher than that of stainless steel fiber blended fabrics, and the higher the folding degree, the greater the SE. Duan et al. [61] coated stainless steel electromagnetic shielding fabrics with carbon nanotubes, graphene, ferrite and nano nickel powder, respectively, and studied the effect of double-layer mixed coating on EM shielding fabrics. The test results showed that the best shielding effect was the double layer combination of graphene + ferrite and graphene + nickel, and the higher the coating thickness, the better the SE.

The method of surface metallization: Cheng et al. [62] experimentally studied the influence of different weft densities, warp densities, wire diameters and layering angles on EM shielding effect of copper-coated twill fabrics, and concluded that the number of conductive layers, warp and weft densities were positively correlated with SE. Liu et al. [63] prepared Ni/PPy (polymerization of pyrrole)/PET (polyethylene terephthalate) conductive fabrics with EM shielding effect by in-situ polymerization of pyrrole and electroless nickel plating, which had the abilities of flexible, lightweight and breathable. Conductive fabrics with higher fractal dimensions have higher thickness of conductive layer, higher conductivity and better EM shielding effect.

The method of braided fabrics with conductive fibers: Lopez et al. [64] explored the influence of metal fibers content on SE, studied the influence of EM waves frequencies and fabrics warp and weft density changes on SE, and showed that metal content index was positively correlated with SE. There was a negative correlation between electromagnetic frequencies and SE when metal content is constant. When fabrics metal index was the same, SE will not change regardless of yarn density. Liu et al. [65] conducted experiments on different types of EM shielding fabrics, and concluded that under the same parameters, SE of plain weave fabrics was better than that of twill weave fabrics, and SE of twill weave fabrics was better than that of satin weave fabrics, and indicated that fabrics porosity was the key factor to affect the SE. Liu then used the surface digital image analysis technology to analyze the surface of metal fabrics and establish the characteristic matrix, and found that the percentage content of metal fibers, porosity and arrangement direction all had a great influence on SE [66]. Yang et al. [67] tested various parameters of stainless-steel fibers blended fabrics on the influence of EM shielding. The results showed that stainless steel fibers content of fabrics was positively correlated with SE, fabrics compactness was negatively correlated with S, fabric with a small difference in warp and weft density showed better SE, and the SE of bidirectional blended yarns were better than that of unidirectional blended yarns.

A large number of experiments have qualitatively studied the factors affecting the EM shielding fabrics, and the general influence factors were the material properties, EM wave frequencies, polarization direction, metal yarns EM parameters, metal yarns arrangement spacing and arrangement, the coating thickness of metallizing fabrics, conductive yarns percentage content and porosity, etc. There are a few research on the influence of fabrics structures on EM shielding. There are many kinds of fabrics, and it cannot be ignored that the influence of different shielding fabrics structure on EM waves. With the diversity of fabrics structure, EM shielding fabrics will also develop in the direction of diversification. The research of 3D fabrics SE model or the influence of fabric structure on EM waves could be very important for the development and optimization of EM shielding fabrics.

3.2. Researches of Wave-Absorbing Fabrics Preparation

For the research of wave-absorbing fabrics development, the fabrics can be divided into coated wave-absorbing fabrics and structural base type wave-absorbing fabrics. Coated wave-absorbing fabrics mean the inside or surface of 3D fabrics are coated with wave absorbents, such as carbon black, graphite and ferrite resistance or magnetic medium materials. By separating wave absorbent materials and fabric stable structure, 3D structure fabric as the stable support structure and wave absorbent play a role in absorbing EM waves. Xie et al. [76] embedded carbon black (CB) into 3D woven fabrics composite as the wave absorbent. The results showed that the absorbing performance of composite was significantly improved. The introduction of 3D woven fabrics can reduce the complex dielectric constant of composite, thus improving the impedance matching of composite, reducing the reflection of EM waves and improving absorbing performance. Zou et al. [77] coated carbon nanotubes (CNTs) on NaOH-pretreated cotton fabrics by the method of non-adhesive dip coating. The surface morphology and modification of carbon nanotube functionalized fabrics were studied by scanning electron microscopy (SEM) and infrared spectroscopy. The effects of impregnation coating quantity, carbon nanotube concentration and impregnation temperature on the electrical conductivity, EM shielding effect and absorbing efficiency of cotton fabric were studied. The measurement results show that the absorption rate of EM wave was 65.7% by adding multilayer laminated fabric. Simayee et al. [78] mixed micromagnetic carbonyl iron powder with nano carbon black as the wave absorbent and coated it on polyester fabrics by the way of filling-drying curing and aluminum sputtering coating. The experimental results showed that the aluminized polyester fabrics coated with carbonyl iron powder and nano carbon black have better absorbability than those without aluminized polyester fabrics. Liu et al. [79] chose polyester woven fabrics as the basic fabrics. Ferrite and silicon carbide are wave absorbent at the bottom and surface, respectively. By optimizing EM parameters, the ferrite/sic double-coated polyester fabrics with absorbing properties were prepared. The results showed that the fabric had the best absorption performance at the frequency of 10 GHz.

The type of structural base wave-absorbing fabrics refers to the yarns or fiber bundles with wave-absorbing properties, such as nickel-iron fibers or carbon fibers are directly woven or woven into 3D fabrics based on stable structure, and then the wave-absorbing properties and influence parameters of 3D fabrics are tested by experiments. Ayan et al. used a vector network analyzer to conduct experimental tests on cotton fabric, carbon fabric and cotton-carbon fabric composites board within 3&#;18 GHz. The mechanical value of cotton fabric composite board was lower, but the EM wave absorption value in a certain frequency range was higher than that of carbon fabric composite board. Cotton-carbon fabric composites have better absorbing performance than pure carbon fabric composites in 12~18 GHz frequencies [80]. Fan et al. [81,82] tested three kinds of 3D woven carbon fiber/epoxy composites with different structures, and the experimental test results showed that the composite has good EM absorption and shielding efficiency, and its excellent mechanical properties and absorption capacity can be widely used in radar absorption structures. Xue, L et al. [83] studied 3D isotropic braided carbon fibers/glass fibers (CF/GF) bismaleimide composites and tested their EM absorbing properties under the condition of thermal oxygen aging. The results showed that the composites have better EM absorption properties than those without aging. Since the surface of the aged composite was not smooth due to thermal oxygen aging, which will cause a large number of cracks and voids. These cracks and voids caused more EM waves to react with the material surface, thus improving the absorbing performance. Tak, J et al. [84] proposed a wearable metamaterial microwave absorber, embedding two square ring resonators into the conductive fabric with a thickness of 1mm for indoor radar clear applications. At a specific frequency, the absorption peak was greater than 90%, and it had a good deformation effect, which can be easily worn on the body. Alonso-gonzalez et al. [85] fabricated a kind of frequency-selective surface 3D woven fabric, in which conductive yarns were woven into a cruciform frequency-selective surface. Due to the symmetry of surface, wave absorption performance was largely independent of polarization and incident Angle, which can achieve large broadband wave absorption. Compared with the traditional frequency selection surface, this type of frequency selection surface was more flexible and convenient, and provided the possibility of large-scale production. Bi et al. [86] prepared carbonyl iron/reductive graphene oxide /non-woven fabrics composite by the method of in-situ synthesis, which has excellent microwave absorption performance in the 2.91&#;5.1 GHz band, and its qualified absorption bandwidth reaches 9.2 GHz. This kind of flexible lightweight fabric composite can be used as a potential material for wearable EM absorption coatings and devices.

At present, the research on absorbents are relatively mature, however the fabrics with absorbents are lack of theoretical bases, such as the amount of absorbent and the position of absorbent can only be measured according to experience or experiment. Moreover, taking fabrics as the basic structure will affect the EM parameters of whole materials, and the EM waves absorption frequency of one single type of absorbent is narrow, which is not conducive to the development of fabric with wide absorption frequencies, and absorbent has the risk of instability and easy to fall off. As for the research on structure-based absorbing fabrics, most scholars only focus on absorbing fiber materials, such as metal modification of fibers or measurement of electromagnetic parameters of fibers. There is still a lack of reports on how the fabric structure affects EM wave absorption. The development direction of wave-absorbing fabrics will be &#;thin, light, wide, strong&#; &#;thin&#; refers to the thickness is becoming smaller, &#;light&#; refers to the mass is becoming smaller, &#;wide&#; means that fabrics can work in the ultra-wide band of EM waves, &#;strong&#; refers to the absorption performance, environmental resistance, temperature resistance and other aspects will be stronger. Different fabric structures have different effects on absorbing waves, and it is urgent to study the influence of fabric structures on wave absorption.

In today's world, electromagnetic radiation is present everywhere. From our mobile phones and laptops to Wi-Fi routers and power lines, we are constantly exposed to electromagnetic fields (EMFs). While the effects of long-term EMF exposure on human health are still being studied, many people are turning to EMF fabric as a means of protection. Here are some of the advantages of using EMF fabric:

Reduces Exposure to EMFs

The primary advantage of using EMF fabric is that it reduces your exposure to electromagnetic radiation. This is especially important if you spend a lot of time near electronic devices or if you live near power lines. EMF fabric is designed to block or absorb electromagnetic radiation, which means that it can help reduce the amount of radiation that reaches your body.

Protects Your Health

There is still a lot of debate around the potential health effects of EMFs. Some studies have suggested that long-term exposure to EMFs can increase the risk of cancer, reproductive problems, and other health issues. While the evidence is not conclusive, many people are choosing to err on the side of caution and use EMF fabric to protect their health.

Easy to Use

EMF fabric is extremely easy to use. You can buy it in a variety of forms, including sheets, blankets, and clothing. Simply wrap yourself in the fabric or drape it over your electronic devices to reduce your exposure to EMFs. Many people also use EMF fabric to line their walls or create a "shielding" area in their home.

Versatile

EMF fabric is versatile and can be used in a variety of different settings. It can be used in the home, office, or even on the go. Many people use EMF fabric to create a protective barrier around their bed or sleeping area, while others use it to shield their laptops or tablets while working.

Long-Lasting

EMF fabric is designed to last for a long time. It is made from high-quality materials that are designed to withstand wear and tear. This means that you can use it for years to come without having to worry about replacing it.

Cost-Effective

EMF fabric is a cost-effective way to protect yourself from electromagnetic radiation. While some products can be expensive, there are many affordable options available. This means that you can protect yourself and your family without breaking the bank.

Easy to Clean

EMF fabric is easy to clean and maintain. Simply wash it in cold water and hang it up to dry. You can also iron it on a low setting if needed. This makes it a convenient and practical solution for anyone looking to reduce their exposure to EMFs.

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