Three Directions Of Research On Electromagnetic Textiles

< p > < strong > metallization < a href= "http://www.91se91.com/news/index_c.asp > > textile > /a > pore size and cut-off frequency. < /strong > /p >

< p > according to the theory of small hole coupling in the principle of electromagnetic compatibility, the dimension is much smaller than that of the wavelength, so the slot is equivalent to the electric dipole and the magnetic dipole.

According to the theory and the electromagnetic leakage practice of metal plate holes, the factors affecting the shielding effectiveness of metal plate include electrical conductivity, thickness, pore shape, size and arrangement. The shielding effectiveness of metal mesh is related to the wire diameter, spacing and the resistance of unit length.

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< p > it can be seen that due to numerous factors, even a well structured metal plate or metal mesh can not establish a complete theoretical equation to express the relationship between the gap state and shielding effectiveness.

But one thing is clear: according to cut-off waveguide management theory, cut-off waveguide as a high pass filter can not pass through a certain shape structure below the cut-off frequency. As the observation window of household microwave oven, observers can observe the holes on metal mesh, but the electromagnetic wave of 2.45GHz in microwave oven does not leak out.

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< p > therefore, we first study the relationship between the different shapes, sizes and arrangements of the holes on the foil and their shielding effectiveness. At the high frequency end, the electromagnetic shielding effectiveness is tested by the arch method test system, and the flange coaxial method is used to detect the low-frequency ends. The basic conclusion is that the material and thickness of various metal foil have little effect on the electromagnetic shielding effectiveness.

The larger the diameter of the hole and the smaller the distance between the holes, the lower the shielding effectiveness of the conductor, and the lower shielding efficiency for the high frequency end.

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< p > on this basis, the porous fabric made of three kinds of porous fabrics woven in Figure 1 is metallized by electroless copper plating and nickel plating. The relationship between the hole size and electromagnetic shielding effectiveness is shown in Figure 3.

Obviously, the processing method, shown in Figure 2, can take into account the shielding effectiveness and thermal comfort of electromagnetic radiation protective clothing.

When necessary, laser drilling can also be used for thermoplastic synthetic fabrics to form more complex holes.

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Study on electromagnetic properties of textiles with < p > strong > plane periodic structure < /strong > < /p >

According to the frequency selective surface theory, periodically repeating non conducting elements (or pore elements) on a conductor plane will produce band-pass effect or high pass effect on the conductor plane. Periodically conducting the conductive units (or resistive units with poor electrical conductivity) on a dielectric plane will cause the dielectric plane to form P band effect or low pass effect.

The resulting frequency selective penetrating effect of electromagnetic waves is very meaningful in selecting useful signals and cutting off interference signals. This precise control of electromagnetic waves is more applicable than shielding interference.

How to make textiles have the frequency selective permeability function of electromagnetic waves has not been noticed.

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< p > there are more ways to establish < a href= "http://www.91se91.com/news/index_c.asp" > conductivity > /a > periodic structural units on the dielectric plane. For example, local electroless plating or electroplating, partial sputtering of conductive materials, local coating printing, adhesion of conductive materials or conductive polymer materials can be used.

These processes are very easy to implement both for traditional textile processes and for new technologies.

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< p > through a series of contrastive experiments, it can be seen that textile can establish periodic structure conductive units on its insulation surface by various means, or non-conductive units with periodic structure on its conductive surface, and make flexible band pass filters that can be selected through electromagnetic wave frequency. It can be applied to the accurate control of electromagnetic signal pmission and energy pmission, so as to achieve the purpose of blocking or clearing electromagnetic waves at specific frequencies.

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Electromagnetic properties of textiles with < p > strong > solid periodic structure < /strong > < /p >

Less than P > the establishment of a three-dimensional periodic structure unit on the fabric will form more effective electromagnetic fabric with frequency selective penetration.

There are many mature processing techniques for the establishment of three-dimensional periodic structure of textiles.

For example, the conductive fabric made of silver plated nylon filament on the plush loom is 8mm in length. The silvered filaments are consolidated in the ground when processing, so the silver plated filament is not linked to the bottom of the fabric and becomes a basic vertical U shaped conductor.

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< p > > < a href= > http://www.91se91.com/news/index_c.asp > plush fabric > /a > E8257D signal pmitter, E7405A spectrum analyzer as test equipment and arch method to measure the pmission power of the system. It shows that in a wide frequency range, most of the incoming electromagnetic waves enter into the floss, and repeatedly reflect and consume energy, only a very small proportion of electromagnetic energy can be reflected to the receiver.

That is to say, this state is related to fiber size, and the fiber size affects the incident impedance of electromagnetic wave on the surface of plush fabric, thus affecting the frequency selectivity.

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The above example of P > is a vertical villi with one end in a free state.

We also use warp knitted spacer fabric, with silver plated nylon filament as spacer yarn, and polyester filament as raw material for two ends, and separate the spacer yarns to two ends.

In order to obtain high scattering effect, that is, to reduce the emissivity and to achieve radar camouflage, we have set up the consolidation method of conductive spacer yarns. The conductive yarns are arranged in a group way. Each group of conductive yarns are arranged in a circular form, but the yarns are fixed on a small circumference on the bottom of the spacer fabric, while the spacer yarns are on the larger circumference on the top of the spacer fabric. Therefore, the separated yarns form an open and flat cone on the top of the spacer yarn to facilitate the scattering of electromagnetic waves to a wider range, so as to reduce the specific reflectivity of the specific direction and achieve the effect of radar camouflage.

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< p > in addition, the manufacture of left-handed materials by chemical metallization technology and textile processing technology is an important topic worthy of study.

Left-handed materials are called metamaterials because their properties exceed the materials in nature.

However, the left-handed material has been etched by the micro printed circuit board, such as the open resonator ring, and so on.

Therefore, little progress has been made in the construction technology of left-handed materials.

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< p > the existing chemical fiber textile processing technology can realize the three-dimensional periodic structure more easily.

For example, on the basis of metallizing the fiber surface to form metal columns, or local metallization to form an open ring resonator, and by twisting and twisting to achieve the chirality, using the weaving method of plush, velvet, towel and spacer fabric to make the fibers fixed in a relatively regular form, it is possible to realize the structure needed for left-handed materials, and this process is much easier, especially the line degree of these fibers can be conveniently coincide with the electromagnetic wave length which needs to produce double negative effects.

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< p > the research and development of left-handed materials based on textiles will be of great academic significance and application value.

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