3.2.3.2.2 The effect of the material of the metal fibers on SE

The metal fibers used in the fabric are different, and the different electrical conductivity of the metal may affect the electrical resistivity of the yarns and the

Figure 14. The shielding effectiveness of different types of yarns.

fabrics. For example, the electrical conductivity of copper fiber is 5.8 <sup>10</sup><sup>7</sup> S/m, and the electrical conductivity of aluminum is 3.54 <sup>10</sup><sup>7</sup> S/m. When the metal fiber content, linear density, and fabric specification parameters are the same, the SE of copper fiber fabrics are better than that of aluminum fiber fabrics.

The five grid samples with completely nonconducting period of 2 mm is shown in Figure 15, for which each grid sample of five different materials consisting of stainless steel bare wire (the diameter is 35 μm), core spun yarn and blended yarn of stainless steel/cotton (containing the stainless steel content of 30%), silver-plated nylon filament (the diameter is 50 μm), and bare copper wire (the diameter is 80 μm). The SE of the samples made of, respectively, stainless steel blended yarns, silver-plated filaments, and bare copper wires are substantially equal and higher that of the samples of core spun yarn and stainless steel bare wire.

#### 3.2.3.2.3 The effect of metal fiber content on SE

The two blended yarns with the stainless steel content of 20 and 30% are woven in both warp and weft directions, and the SE of the obtained sample in the range of 1–18 GHz are shown in Figure 16. It can be seen that except for the frequency range of 10 and 12–14 GHz, the SE of the fabric with 30% stainless steel content is 5 dB higher than that of the fabric with 20% stainless steel content, and the difference of SE in other frequency bands is unobvious. The content of stainless steel fibers has a certain effect on the shielding effectiveness of the fabric, but after reaching a certain level, the difference is not significant.

3.3 Electromagnetic scattering fabrics

Electromagnetic Function Textiles

DOI: http://dx.doi.org/10.5772/intechopen.85586

invisible for certain direction Radar.

for incident electromagnetic waves.

structures

structure.

197

Figure 16.

3.3.1 The mechanism of electromagnetic scattering fabrics

The shielding effectiveness of the fabrics with different content of stainless steel.

When electromagnetic waves radiate into the macroscopic object, which will causing induced electric charges and currents of the object, then the electromagnetic wave radiated into the object will be scattered into various directions. This process is called electromagnetic scattering [11, 12]. The electromagnetic scattering fabric is an electromagnetic functional material with the specific design structure, which makes the electromagnetic waves incident on the target are no longer reflected back along the way of the reflection of mirror, but radiated out into different directions. Thereby, it can reduce the radiated electromagnetic waves in the direction of propagation, and can make the human body and military targets

The textile technology is relatively mature in the preparation of threedimensional structural fabrics. Thus, it is very feasible to design the threedimensional structure of metallized fabrics which have good scattering properties

3.3.1.1 The electromagnetic wave scattering characteristics of linear column unit

When a simple harmonic uniform plane wave is incident on the threedimensional structure, the three-dimensional coordinate system XYZ shown in Figure 18 is selected. The XOY plane of the coordinate system coincides with the lower surface of the object, and the Z axis is perpendicular to the interface of the upper and lower surfaces. Electromagnetic waves are incident from the upper surface with the incident angle θ, and reflected waves and transmitted waves are generated at the interface of the upper surface. The transmitted waves enter the

As shown in Figure 17, the composite materials of the three-dimensional periodic structure can be simplified into two-phase dielectric materials when studying the transmission process of electromagnetic waves in the three-dimensional

It is assumed that the fibers are evenly distributed in the yarn. As the content of the metal fibers increases, the shielding effectiveness of the fabrics will increase, but when it is increased to a certain extent, the bending stiffness and flexural modulus of the yarns will increase, and the porosity among fibers during the fabric will increase. So the SE of the fabrics becomes slow down or even lower. Considering the cost, the content of stainless steel is generally 20–30% for fabrics containing stainless steel fibers.

Figure 15. Shielding effectiveness of different materials with grid period spacing of 2 mm in order.

fabrics. For example, the electrical conductivity of copper fiber is 5.8 <sup>10</sup><sup>7</sup> S/m, and the electrical conductivity of aluminum is 3.54 <sup>10</sup><sup>7</sup> S/m. When the metal fiber content, linear density, and fabric specification parameters are the same, the SE of

The five grid samples with completely nonconducting period of 2 mm is shown in Figure 15, for which each grid sample of five different materials consisting of stainless steel bare wire (the diameter is 35 μm), core spun yarn and blended yarn of stainless steel/cotton (containing the stainless steel content of 30%), silver-plated nylon filament (the diameter is 50 μm), and bare copper wire (the diameter is 80 μm). The SE of the samples made of, respectively, stainless steel blended yarns, silver-plated filaments, and bare copper wires are substantially equal and higher

The two blended yarns with the stainless steel content of 20 and 30% are woven in both warp and weft directions, and the SE of the obtained sample in the range of 1–18 GHz are shown in Figure 16. It can be seen that except for the frequency range of 10 and 12–14 GHz, the SE of the fabric with 30% stainless steel content is 5 dB higher than that of the fabric with 20% stainless steel content, and the difference of SE in other frequency bands is unobvious. The content of stainless steel fibers has a certain effect on the shielding effectiveness of the fabric, but after reaching a

It is assumed that the fibers are evenly distributed in the yarn. As the content of the metal fibers increases, the shielding effectiveness of the fabrics will increase, but when it is increased to a certain extent, the bending stiffness and flexural modulus of the yarns will increase, and the porosity among fibers during the fabric will increase. So the SE of the fabrics becomes slow down or even lower. Considering the cost, the content of stainless steel is generally 20–30% for fabrics containing

copper fiber fabrics are better than that of aluminum fiber fabrics.

that of the samples of core spun yarn and stainless steel bare wire.

Shielding effectiveness of different materials with grid period spacing of 2 mm in order.

3.2.3.2.3 The effect of metal fiber content on SE

Electromagnetic Materials and Devices

certain level, the difference is not significant.

stainless steel fibers.

Figure 15.

196

Figure 16. The shielding effectiveness of the fabrics with different content of stainless steel.

### 3.3 Electromagnetic scattering fabrics

### 3.3.1 The mechanism of electromagnetic scattering fabrics

When electromagnetic waves radiate into the macroscopic object, which will causing induced electric charges and currents of the object, then the electromagnetic wave radiated into the object will be scattered into various directions. This process is called electromagnetic scattering [11, 12]. The electromagnetic scattering fabric is an electromagnetic functional material with the specific design structure, which makes the electromagnetic waves incident on the target are no longer reflected back along the way of the reflection of mirror, but radiated out into different directions. Thereby, it can reduce the radiated electromagnetic waves in the direction of propagation, and can make the human body and military targets invisible for certain direction Radar.

The textile technology is relatively mature in the preparation of threedimensional structural fabrics. Thus, it is very feasible to design the threedimensional structure of metallized fabrics which have good scattering properties for incident electromagnetic waves.

## 3.3.1.1 The electromagnetic wave scattering characteristics of linear column unit structures

As shown in Figure 17, the composite materials of the three-dimensional periodic structure can be simplified into two-phase dielectric materials when studying the transmission process of electromagnetic waves in the three-dimensional structure.

When a simple harmonic uniform plane wave is incident on the threedimensional structure, the three-dimensional coordinate system XYZ shown in Figure 18 is selected. The XOY plane of the coordinate system coincides with the lower surface of the object, and the Z axis is perpendicular to the interface of the upper and lower surfaces. Electromagnetic waves are incident from the upper surface with the incident angle θ, and reflected waves and transmitted waves are generated at the interface of the upper surface. The transmitted waves enter the

Figure 17. Dielectric column periodic three-dimensional structure.

Figure 18. The schematic diagram of electromagnetic wave incident three-dimensional structure.

periodic three-dimensional structure, and after being attenuated in the threedimensional structure, the reflected waves and the transmitted waves are again generated at the lower surface interface.
