3.4.2.1 The method for preparing frequency selective surface textiles

The researches mainly focus on the preparation of frequency selective fabrics with high-precision two-dimensional periodic structure produced by different textile processing techniques, which can be roughly divided into four categories [14].


In China, the team that studies the periodic structure of textile materials is mainly a joint research group composed of Professor Meiwu Shi in textile materials and Professor Qun Wang in electromagnetic materials. Based on preliminary sample preparation, theoretical simulation analysis, and the preliminary experimental results and research ideas of special electromagnetic functional textile materials, in the aspect of 2D FSF, various types of bandpass, band-stop filter fabrics, etc. have been prepared by weaving, electroless plating, embroidery, transfer printing, and so on. Through experiments, the effects of cell shape and dimensional changes, periodic spacing, and dielectric materials on transmission and reflection coefficients

The periodic structures produced by knitting and embroidery processes. (a) The samples of woven fabrics and

Screen printing and inkjet printing form a periodic structure. (a) The screen printing and (b) The inkjet

3.4.2.2 The comparison for frequency selective surface textile materials produced by

includes screen printing, laser processing, and computer embroidery [15].

The preparation of frequency selective surface for flexible materials mainly

The screen printing is to stretch and fix synthetic fibers, silk fabrics, or mental wire meshes on the frame, using the method of making the hand-painted film or photochemical plate to make the screen printing plate, and the metal ink is squeezed from the mesh of the pattern portion, which is a process for extruding onto a fabric to form a sample. Figure 34 shows a ring-shaped frequency selective surface of a complementary structure prepared by the screen printing method.

The complementary cross-type frequency selective surface prepared by the laser processing method is directly produced by laser processing on the flexible medium

have been studied.

205

Figure 32.

Figure 33.

(b) The samples of knitted fabrics.

Electromagnetic Function Textiles

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

printing.

different processing methods

Figure 30.

Continuous conductive yarns form a periodic structure in the fabric. (a) Woven in a square structure and (b) Woven in a square structure rectangle.

#### Figure 31.

The conductive material is adhered to the substrate to form a periodic structure.

#### Figure 32.

3.4.2 The processing of frequency selective surface textiles

Electromagnetic Materials and Devices

3.4.2.1 The method for preparing frequency selective surface textiles

The researches mainly focus on the preparation of frequency selective fabrics with

high-precision two-dimensional periodic structure produced by different textile processing techniques, which can be roughly divided into four categories [14].

1. Continuous conductive yarns form a periodic structure in the fabric. The continuous carbon fibers are directly woven into a square or rectangular periodic structure, as shown in Figure 30. Since the conductive carbon fibers are continuously present in the fabric, the structure is actually a conductive grid formed by the conductive yarns in the woven fabric. This structure is more suitable for the preparation of isotropic electromagnetic shielding fabrics, not a true frequency selective periodic structure, which is confirmed by the absence of resonance peaks in the test curves reported in the article.

2. The cut commercialized conductive material unit is directly bonded to the

3. Depositing conductive materials on the surface of fabrics by screen printing, inkjet printing, and other textile finishing techniques can form the conductive

4.The high conductive yarns are formed into a periodic structural unit by textile weaving processing techniques such as weaving, weft knitting, embroidery,

Continuous conductive yarns form a periodic structure in the fabric. (a) Woven in a square structure and

The conductive material is adhered to the substrate to form a periodic structure.

nonconductive fabric substrate, as shown in Figure 31.

structural unit, as shown in Figure 32.

and so on, as shown in Figure 33.

Figure 30.

Figure 31.

204

(b) Woven in a square structure rectangle.

Screen printing and inkjet printing form a periodic structure. (a) The screen printing and (b) The inkjet printing.

Figure 33.

The periodic structures produced by knitting and embroidery processes. (a) The samples of woven fabrics and (b) The samples of knitted fabrics.

In China, the team that studies the periodic structure of textile materials is mainly a joint research group composed of Professor Meiwu Shi in textile materials and Professor Qun Wang in electromagnetic materials. Based on preliminary sample preparation, theoretical simulation analysis, and the preliminary experimental results and research ideas of special electromagnetic functional textile materials, in the aspect of 2D FSF, various types of bandpass, band-stop filter fabrics, etc. have been prepared by weaving, electroless plating, embroidery, transfer printing, and so on. Through experiments, the effects of cell shape and dimensional changes, periodic spacing, and dielectric materials on transmission and reflection coefficients have been studied.

### 3.4.2.2 The comparison for frequency selective surface textile materials produced by different processing methods

The preparation of frequency selective surface for flexible materials mainly includes screen printing, laser processing, and computer embroidery [15].

The screen printing is to stretch and fix synthetic fibers, silk fabrics, or mental wire meshes on the frame, using the method of making the hand-painted film or photochemical plate to make the screen printing plate, and the metal ink is squeezed from the mesh of the pattern portion, which is a process for extruding onto a fabric to form a sample. Figure 34 shows a ring-shaped frequency selective surface of a complementary structure prepared by the screen printing method.

The complementary cross-type frequency selective surface prepared by the laser processing method is directly produced by laser processing on the flexible medium

#### Figure 34.

to which metal materials are pasted. The patch type (slit type) sample torn off the excess metal (patch metal) at the gap to obtain the final sample, thus ensuring the process precision of the patch type frequency selective surface (Figure 35).

is simple and the production efficiency is the highest. It is suitable for mass production and exhibits better band resistance characteristics at the resonance frequency. The fabric-based frequency selective surface structure can be directly integrated into various textiles such as tents, clothing, and decorative products, and

3.4.3 The frequency selective textile materials with three-dimensional periodic structure

electromagnetic wave environments. Incident angle stability, multi-band, wide passband, miniaturization, flexibility, and active frequency selective surfaces are the research hotspots of frequency selective surface in recent years. The use of various processing techniques to convert a two-dimensional FSF into a threedimensional structure can bring more performance to the frequency selective sur-

The single-performance frequency selective surface can no longer meet complex

The 3D FSF consists of the structural unit (white part in Figure 37), the dielectric unit (black part in Figure 37), and the base medium (gray part in Figure 37). In the z-axis direction, the conical stereoscopic periodic structure composed of the structural unit and the dielectric unit and a composite structure of the dipole plane periodically loaded with a base medium structure. At the same time, the 3D FSF has

has the advantages of portability, maintenance-free, and low cost.

face [16].

Figure 37.

207

The multi-scale structure of 3D FSF.

Figure 36.

The computer embroidery processing.

Electromagnetic Function Textiles

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

The frequency selective surface with ring patch type is prepared by computer embroidery technology. According to the unit pattern and size of frequency selective surface period designed, the processing personnel uses the sample programming system to make the programming sample, and the needle position data of the design pattern is designed. Using these needle position data to control the computer embroidery machine, the silver-plated yarns are embroidered onto the fabric to produce the fabric material frequency selective surface (Figure 36).

The screen printing technology is more adaptable and can be applied to the flexible medium surface in printing; besides, the process is simple, the cost is low, and the quality is relatively stable. However, the screen printing processing has low production efficiency and is only suitable for small batch production, and the image accuracy produced is not high, which has a certain influence on the frequency response characteristics of the product.

The laser processing technology is characterized by high quality, high efficiency, and low cost. The laser processing is a kind of non-contact processing, and the frequency selection surface patterns at the sharp corners such as precise polygons can be obtained, and the products have high precision. Because the excess metal needs to be removed during the sample preparation processing to obtain the desired sample, the production efficiency of the product is affected.

The precision of computer embroidery technology when preparing flexible frequency selective surface is affected by the fineness of the needle, but the process

Figure 35. The laser engraving. (a) The patch type and (b) The aperture type.

Figure 36. The computer embroidery processing.

to which metal materials are pasted. The patch type (slit type) sample torn off the excess metal (patch metal) at the gap to obtain the final sample, thus ensuring the process precision of the patch type frequency selective surface (Figure 35).

The frequency selective surface with ring patch type is prepared by computer embroidery technology. According to the unit pattern and size of frequency selective surface period designed, the processing personnel uses the sample programming system to make the programming sample, and the needle position data of the design pattern is designed. Using these needle position data to control the computer embroidery machine, the silver-plated yarns are embroidered onto the fabric to

The screen printing technology is more adaptable and can be applied to the flexible medium surface in printing; besides, the process is simple, the cost is low, and the quality is relatively stable. However, the screen printing processing has low production efficiency and is only suitable for small batch production, and the image accuracy produced is not high, which has a certain influence on the frequency

The laser processing technology is characterized by high quality, high efficiency,

and low cost. The laser processing is a kind of non-contact processing, and the frequency selection surface patterns at the sharp corners such as precise polygons can be obtained, and the products have high precision. Because the excess metal needs to be removed during the sample preparation processing to obtain the desired

The precision of computer embroidery technology when preparing flexible frequency selective surface is affected by the fineness of the needle, but the process

produce the fabric material frequency selective surface (Figure 36).

The ways of screen printing processing. (a) The patch type and (b) The aperture type.

sample, the production efficiency of the product is affected.

The laser engraving. (a) The patch type and (b) The aperture type.

response characteristics of the product.

Figure 34.

Electromagnetic Materials and Devices

Figure 35.

206

is simple and the production efficiency is the highest. It is suitable for mass production and exhibits better band resistance characteristics at the resonance frequency. The fabric-based frequency selective surface structure can be directly integrated into various textiles such as tents, clothing, and decorative products, and has the advantages of portability, maintenance-free, and low cost.
