Radar Absorbing and Radiolucent Materials

RADIO-ABSORBING AND RADIO TRANSFER MATERIALS , nonmetallich. materials that provide absorption or transmission of electromagnetic. radio frequency radiation (105-1012 Hz) with min. its reflection. Spreading in the volume of these materials, electromagnet. radiation (EMR) creates a variable electr. the field, the energy of which is transformed into thermal energy almost completely in radio absorbing and minimally in radio transparent materials.

Radio absorbing materials. Along with dielectric and magnetic losses, dispersion, diffraction, interference, and total ext. reflection of radio waves causing add-on. weakening of the energy of electromagnetic radiation due to Rayleigh scattering, the addition of waves in antiphase, etc. Products made from such materials absorb electromagnetic fluxes. energy is tight 0.1-8.0 W / cm2; the range of workers tp - 60 - 1300 ° C; reflected radiation level 0,001-5%.

The basis of radio-absorbing materials are org. or not. (hl. obr. oxides and nitrides) islands, in which powders of graphite, metals and their carbides are introduced as active absorbing components.

Gradient radio absorbing materials are characterized by a multilayer structure that provides the specified change in dielectric. permeability in the thickness of the material. The outer layer is made of a solid dielectric with a dielectric. permeability e, close to 1 (for example, from phenolic plastic, hardened with quartz glass fiber), the subsequent ones - from dielectrics with higher e (eg, epoxy resin with e5 or the same resin with filler with e 25) and absorber powder (for example, graphite dust). The structure described contributes to the min. reflection of radio waves from the surface and an increase in their absorption as they penetrate deep into the material.

Interference Radio absorbing materials usually consist of a substrate and alternating dielectrics. and conductive layers. Metallic is used as a substrate. plate or nonmetallich. material with e 100 and the tangent of dielectric angle. loss tgd, close to 1. The dielectric layer, which is a binder, contains an absorber (eg, oxides of Fe), a conducting layer-metallisir. Fiber Such a structure provides for a phase shift of the wave reflected in the material by almost 180 ° and its damping.

Scattering radio absorbing materials provide multiple reflection and scattering of waves. Products from them - most often hollow pyramidal designs from expanded polystyrene, vnutr. walls to-rykh are covered with graphite, or pipes from fiberglass, covered outside with a layer of SiC.

Ceramics materials are, as a rule, highly sintered materials from low metal oxide metal oxides. resistance [eg, Ti3O4 and (AlTi) 2O3] or oxides and nitrides B and A1 with the addition of metals (W, Mo, Ti, Zr, Hf) or their carbides. Possess high heat conductivity, fur. durability and heat resistance. For shielding from high-intensity radio emission, multilayer materials are fabricated from A1 microspheres and Ba titanate interconnected by aluminophosphate cement. To the group of ceramics materials also include dense pyrolytic. carbon.

Ferrite materials, characterized by large magn. losses are characterized by high absorption, which allows their use in the form of lightweight elements, for example. thin-layer (up to 0.2 mm) coatings from FeO · Fe2O3 or MnO · Fe2O3 with an epoxy binder, or tiles mounted on metal. sheet and protected with fiberglass or a layer of plastic.

Radio absorbing materials are used in the form of coatings metallic. turns of aircraft, tanks, missiles and ships with the aim of their radar. masking, to protect people from exposure to high-intensity radio emissions, creating a radio-hermetic. anechoic test. chambers, energy absorbers in electronic devices, ensuring the radio compatibility of equipment parts.

Radio-transparent materials. The transparency of these materials is provided by a small dielectric. losses in the range of workers tp-60-1200 ° C (tgd 10-2-10-5, e 10) and low reflection of radio waves ( one%).

The basis of such materials are organic and inorganic dielectrics-plastics, ceramoplastics, ceramics, fused quartz, and cellars.

As radiotransparent plastics use hl. arr. fiberglass or fiberglass containing several. layers of glass, nylon fibers or fiberglass and impregnated silicone, polyimide or polyester resins. They are made by methods of processing polymeric materials that ensure the uniformity of the dielectric properties of the material (for example, impregnation, pouring, winding); t-ra long operation 300-500 ° C, tgd 10-2-10-3, e 3-5.

Ceramoplastics are made on the basis of: aluminophosphate ceramics reinforced with fiberglass; fiberglass impregnated with highly active colloidal SiO2; quartz or sapphire yarns and fabrics with binders used in fiberglass. Ceramoplastics with elevated. resistance to erosion under the influence of ext. the medium is obtained by plasma deposition on a plastic surface (before and after its curing) of a thin layer of refractory oxide, carbide or boride. Compared with plastics, they have greater strength and uniformity, they work in conditions of mp up to 650 ° C.

The basis of radiotransparent Kepram is high-temperature oxides A1 and Be, nitrides A1 and B; tgd 10-3, e4 (for boron nitride) and 10 (for alumina ceramics); thermal conductivity (in W / m · K) for А12О3 20, for BeO200, for BN 400. Products from oxide ceramics are obtained by the methods of slip casting, pressing, electrophoretic. and plasma spraying with afterbirth. high-temperature roasting, from boron nitride by chemical. deposition from the gas phase with the last. fur. processing. To enhance the fur. strength, heat resistance and reduction of wall thickness ceram. products in them during the formation of metal injected. rods, bars or grids.

Materials made of fused quartz and cellars based on Li and Mg oxides (Li2O-Al2O3-SiO2 and MgO A12O3 SiO2) are characterized by homogeneity, low coefficients. thermal extensions (5 · 10-7 degrees -1 for fused quartz, close to zero at the sieve), temperature stability (for MgO-SiO2-Al2O3), in the range working hours (-60-1200 ° C) decrease dielectric. permeability is approx. one%.

Radio-transparent materials are widely used in aerial fairings of airplanes and rockets under aerodynamic conditions. and thermal shock, rain, dust, gas erosion and ionizing radiation, as a partition-window in accelerators and electronic devices, to ensure the transmission of electromagnetic. energy.

Lit .: Shneiderman Ya. A., "Foreign Radio Electronics", 1971,? 2, p. 79-113; ibid., 1972, No. 7, p. 102-32; Batygin V.N., Metelkin II, Reshetnikov AM, Vacuum-dense ceramics and its junctions with metals, M., 1973; Mitsmakher M.Yu., Torgovanov V.A., Anechoic microwave oven chambers, M., 1982; Alimin B.F., "Foreign Radioelectronics", 1989, No. 2. p. 75-82.

V.N. Batygin, V. G. Bravinsky.