Radio-Absorbing Nonwoven Material with Intermediate Dispersed Carbon-Fiber Layers
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Fibre Chemistry, Vol. 52, No. 2, July, 2020 (Russian Original No. 2, March-April, 2020)
NONWOVEN MATERIALS RADIO-ABSORBING NONWOVEN MATERIAL WITH INTERMEDIATE DISPERSED CARBON-FIBER LAYERS V. G. Nazarov and A. V. Dedov
UDC 620.197
The frequency dependence of the reflection coefficient of nonwoven radio-absorbing material in which carbon fibers were distributed in two intermediate layers containing the same number of carbon fibers between layers of dielectric fibers was studied. A mechanism for the absorption of electromagnetic radiation in the materials was proposed. The effect on it of the carbon-fiber content in the intermediate layers was determined.
Nonwoven radio-absorbing materials (NRAMs) containing electrically conducting carbon fibers in a matrix of dielectric fibers is one solution to the problem of the electromagnetic compatibility of electrotechnical, electronic, and radio-electronic systems [1, 2]. These materials have low density and are resistant to external factors over broad temperature ranges and long operating times. Production of NRAMs using standard manufacturing technology of nonwoven needlepunch materials is complicated by the need for uniform mixing of the dielectric fibers with a small amount of carbon fibers, the content of which, as a rule, is ≤10%. The production technology for three-layer NRAMs with two cloths of dielectric polyester fibers and an intermediate layer of carbon fibers was developed by us (Fig. 1a). The intermediate layer was produced via filtration of an aqueous suspension of carbon fibers through a cloth followed by application of another cloth and piercing the assembled stacks with needles [2]. The proposed method for preparing three-layer NRAMs does not require mixing of the dielectric and carbon fibers. Variations in the electrophysical properties of the three-layer NRAMs can be regulated [2-9]. The quality of the three-layer NRAMs depends on the accuracy of the carbon-fiber contents and their uniform distribution on the surface of the dielectric polyester fiber cloth. An increase of the number of intermediate carbon-fiber layers to two separated by three layers of nonwoven material (five-layer NRAMs) was proposed by us to soften the technological requirements on the accuracy of the content and the uniformity of the distribution of carbon fibers on the surface of the nonwoven dielectric fiber material [5, 8]. Use of five-layer NRAMs with different amounts of carbon fibers in the intermediate layers was found to be efficient. The amount of carbon fibers in the intermediate layers increased in the direction of impingement of the electromagnetic radiation (EMR) into the material. The frequency range of EMR absorption was expanded [5, 8]. However, the problem of softening the requirement on the accuracy of the content and the distribution of the carbon fibers in the intermediate layer remained unresolved. The goal of the present work was to study the electrophysical properties of six-layer materials produced by stacking two three-layer NRAMs (Fig. 1b). Stacking of two
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