3.3.2.3 Cut flower structure fabrics

The cut fabrics are obtained by cutting fabrics containing metal fibers or metallized fibers into different shapes. The planar fabrics are formed into the threedimensional structure through some support, and the cut flower units of fabrics become scattering units for radar waves, which are a kind of flexible, lightweight, wide-band radar stealth fabric.

three-dimensional state and the state in which the fabric is flattened is as shown in

The reflection coefficient of cut flower structure fabric. (a) The reflection coefficient of three-dimensional cut

flower fabric and (b) The reflection coefficient of flat cut flower fabric.

Cut flower structure fabric. (a) Three-dimensional cut flower fabric and (b) Flat cut flower fabric.

From the test results, it can be found that the reflection coefficient of the flat structural unit and the uneven structural unit are very large in a wide frequency range, and the coefficient of the uneven cut flower fabric can reach 10 dB at 2 GHz, and the flat cut flower fabric is 5 dB. In the test results, mainly because of the antenna used in the test, the results of the test in the frequency bands less than 3 GHz and greater than 17 GHz are not regular enough. The irregularity of the structural unit produces a strong scattering for electromagnetic waves, making the reflection coefficient smaller. However, the main difference in the structural unit of unevenness and flatness is the difference in the position of the resonance peak that appears. This is because when the mesh structure becomes flat, the size of the unit structure becomes small, so that the resonance peak shifts toward the higher

By adopting the method of embedding the heat shrinkable yarns, the textured

The stainless steel fibers and the cotton fibers in a ratio of 40/60 were blended into a yarn of 116dtex linear density, and high heat-shrinkage polyester yarns with a shrinkage ratio of 53.7% in the boiling water and a linear density of 167dtex are embedded in the warp and weft directions. Mixed yarns and polyester yarns are

structure containing metal fibers or metallized fibers can be obtained, which imparts good electromagnetic wave scattering properties to the fabric.

Figure 25.

Figure 25.

Figure 24.

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

frequency.

201

3.3.2.4 Uneven surface structure fabrics

The stainless steel/polyester/cotton blend fabric with a stainless steel content of 20% is cut as shown in Figure 24. The reflection coefficient of the fabric in the

Figure 23. The silver-plated fiber spacer fabric and its reflection coefficient.

Figure 24. Cut flower structure fabric. (a) Three-dimensional cut flower fabric and (b) Flat cut flower fabric.

Figure 25.

3.3.2.2 The three-dimensional spacer fabrics

Electromagnetic Materials and Devices

The woven velvet fabric for decoration and its reflection coefficient.

width, even up to 18 GHz.

Figure 22.

3.3.2.3 Cut flower structure fabrics

wide-band radar stealth fabric.

The silver-plated fiber spacer fabric and its reflection coefficient.

Figure 23.

200

multiple reflections happen in the intermediate layer.

The silver fiber spacer fabric is prepared on the warp knitting machine, of which the silver-plated filaments with a fineness of 83dtex are used in the middle layer, and the upper and lower surfaces are all made of polyester fibers, as shown in Figure 23. The silver-plated fibers make the radar waves absorption, reflection, and

The silver-plated fiber spacer fabric has a significant resonance peak, which should be related to the thickness of the intermediate layer of the fabric, and indicates that the shielding effect on the radar wave is not mainly due to the reflection radar wave mechanism. The reflectivity of silver-plated fiber spacer fabric is generally inferior to that of velvet fabrics, but its resonance peak can reach 30 dB, and when the reflection coefficient is below 5 dB, it has a wide band-

The cut fabrics are obtained by cutting fabrics containing metal fibers or metal-

The stainless steel/polyester/cotton blend fabric with a stainless steel content of 20% is cut as shown in Figure 24. The reflection coefficient of the fabric in the

lized fibers into different shapes. The planar fabrics are formed into the threedimensional structure through some support, and the cut flower units of fabrics become scattering units for radar waves, which are a kind of flexible, lightweight,

The reflection coefficient of cut flower structure fabric. (a) The reflection coefficient of three-dimensional cut flower fabric and (b) The reflection coefficient of flat cut flower fabric.

three-dimensional state and the state in which the fabric is flattened is as shown in Figure 25.

From the test results, it can be found that the reflection coefficient of the flat structural unit and the uneven structural unit are very large in a wide frequency range, and the coefficient of the uneven cut flower fabric can reach 10 dB at 2 GHz, and the flat cut flower fabric is 5 dB. In the test results, mainly because of the antenna used in the test, the results of the test in the frequency bands less than 3 GHz and greater than 17 GHz are not regular enough. The irregularity of the structural unit produces a strong scattering for electromagnetic waves, making the reflection coefficient smaller. However, the main difference in the structural unit of unevenness and flatness is the difference in the position of the resonance peak that appears. This is because when the mesh structure becomes flat, the size of the unit structure becomes small, so that the resonance peak shifts toward the higher frequency.

## 3.3.2.4 Uneven surface structure fabrics

By adopting the method of embedding the heat shrinkable yarns, the textured structure containing metal fibers or metallized fibers can be obtained, which imparts good electromagnetic wave scattering properties to the fabric.

The stainless steel fibers and the cotton fibers in a ratio of 40/60 were blended into a yarn of 116dtex linear density, and high heat-shrinkage polyester yarns with a shrinkage ratio of 53.7% in the boiling water and a linear density of 167dtex are embedded in the warp and weft directions. Mixed yarns and polyester yarns are

As Figure 28 shows, in the range of 2–18 GHz, for the fabrics containing the heat shrinkage yarns in both directions, as the processing temperature is lowered, the degree of the uneven structure of the fabrics is reduced, the unit size of the concave and convex structure becomes larger, which make the fabrics have poor scattering performance for radar waves. Besides, the reflection coefficients are becoming more and more higher and the difference is obvious. At a frequency of 14 GHz, the reflection coefficients of fabrics having heat treatment temperatures of 97, 75, 65, and 58°C and untreated fabrics, respectively, are 39, 27, 24, 10, and 4 dB. It can be seen from the shrinkage structure at different temperatures that the degree of wrinkles of the fabrics after treatment at 97°C is significantly higher than that of the wrinkles treated at other temperatures. The unevenness of the fabric structure causes the electromagnetic waves to form the diffuse reflection in the structure; meanwhile, the electromagnetic wave scattering forms multiple absorptions on the

adjacent two intersecting slopes.

Electromagnetic Function Textiles

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

stop, as shown in Figure 29.

Figure 29.

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(c) band stop; and (d) band pass.

3.4 Frequency selective surface textile materials

all electromagnetic waves of a specific frequency.

3.4.1 The structure and properties of frequency selective surface textile materials

Frequency selective surface (FSS) is an infinitely large periodic array structure that is one-dimensional, two-dimensional, etc. It is mainly divided into two types: patch type and aperture type, which have frequency selective characteristic for the propagation of electromagnetic wave in space. The patch type can totally reflect electromagnetic waves of a specific frequency, and the aperture type can transmit

The textiles are light, soft, and flexible in processing. Relying on the media of textile materials, textile processing technology will qualify the textile products to attain the filtering characteristics and light, soft, and other characteristics, which can be applied in more fields [13]. Flexible periodic array structure prepared by textile processing technology is called frequency selective fabric (FSF). According to the filtering characteristics, the frequency selective fabric can be divided into four frequency response characteristics: high pass, low pass, band pass, and band

The four frequency response characteristics of the frequency selective surface. (a) High pass; (b) low pass;

Figure 26. The original plain weave.

Figure 27. Stainless steel fabrics with concave structure embedded with high heat shrinkage wires.

woven into a plain fabric with a square weight of 127 g/m<sup>2</sup> (as shown in Figure 26). The fabrics are treated at different temperatures to obtain fabrics with different concave and convex structures, as shown in Figure 27.

It can be seen from Figure 27 that the fabrics have different degrees of unevenness at different heat processing temperatures. The higher the treatment temperature, the more obvious the uneven structure; the lower the treatment temperature, the smaller the uneven structure. At 58°C, the fabric has a smaller degree of shrinkage.

Figure 28. Comparison of reflection coefficients under different conditions.

#### Electromagnetic Function Textiles DOI: http://dx.doi.org/10.5772/intechopen.85586

As Figure 28 shows, in the range of 2–18 GHz, for the fabrics containing the heat shrinkage yarns in both directions, as the processing temperature is lowered, the degree of the uneven structure of the fabrics is reduced, the unit size of the concave and convex structure becomes larger, which make the fabrics have poor scattering performance for radar waves. Besides, the reflection coefficients are becoming more and more higher and the difference is obvious. At a frequency of 14 GHz, the reflection coefficients of fabrics having heat treatment temperatures of 97, 75, 65, and 58°C and untreated fabrics, respectively, are 39, 27, 24, 10, and 4 dB. It can be seen from the shrinkage structure at different temperatures that the degree of wrinkles of the fabrics after treatment at 97°C is significantly higher than that of the wrinkles treated at other temperatures. The unevenness of the fabric structure causes the electromagnetic waves to form the diffuse reflection in the structure; meanwhile, the electromagnetic wave scattering forms multiple absorptions on the adjacent two intersecting slopes.
