RU2125327C1 - Absorbing coating for attenuation of reflected electromagnetic waves; capacitance element for absorbing coating; inductance element for absorbing coating - Google Patents

Abstract

FIELD: radar equipment, military objects. SUBSTANCE: absorbing coating is designed as heterogeneous coating comprising pieces which are arranged in alternating order over surface. Some pieces reflect incident wave with quarter phase advance; other pieces reflect it with quarter phase delay. In addition each piece absorbs part of incident radio waves. First pieces are designed as coating which is made from fine metal or graphite particles, pure graphite or as special capacitance element for absorbing coating. Second pieces are designed as coating which is made from fine ferromagnetic particles or as special capacitance element for absorbing coating. Attenuation of reflected wave is achieved not only by partial absorption abilities of each piece but also by mutual attenuation of waves reflected from different pieces. Capacitance element of absorbing coating is designed as coating with significant capacitance features. Due to its design incident wave causes only bias currents which phase advances incident wave by quarter of phase. In addition capacitance element can heavily absorb incident waves, if it is made from several (at least two) capacitance layers. Both single-layer and double-layer elements are transparent for radio waves. Inductance element of absorbing coating is designed as thin-film coating which is made from fine ferromagnetic particles reinforced with metal grid or carbon fiber. It generates reflected wave with quarter phase delay with respect to incident wave. EFFECT: decreased possibility of detection of military objects by enemy's radars, possibility of application over arbitrary shapes, thus elimination of need to alter shape of objects to increase their antiradar masking. 3 cl, 4 dwg

Description

 The invention is applied in the fields of technology associated with the use of electromagnetic radiation, and can reduce the clogging of the environment by reflected radio waves.

 In the military field, it can increase the secrecy of military and transport equipment in aviation, astronautics or the navy from being detected by enemy radars.

 Capacitive and inductive elements of the absorbing coating, reinforced with high-strength fibers, can be used as a structural material and to create radiolucent structures.

 Currently available absorbent coatings are based on the ability to absorb incident radiation in finely dispersed components: metal, graphite and ferromagnetic dust, as well as pure graphite. They are analogues of the present invention.

 The disadvantage of such coatings lies in the very principle of absorption of incident radiation by them.

 In the case of finely dispersed fillers, the incident radio waves create alternating magnetic fields and electric displacement currents in the surface absorbing layer. The energy of these fields and currents is absorbed by a finely dispersed coating. These alternating currents themselves create around themselves an alternating electromagnetic field - a reflected wave. Thus, the condition for the absorption of radio emission is the presence of currents in the absorbing medium and, as a consequence, the presence of a reflected wave.

 In the case of a graphite coating, penetration of electromagnetic radiation, especially in the high-frequency region, into the depth of the coating due to the capacitor coupling between the graphite layers is achieved, which provides better absorption of radio waves compared to disperse coatings. However, in this case, the currents generated in graphite create a reflected wave.

 Capacitive and inductive elements of the absorbing coating have no analogues in technology.

 An absorbing coating for attenuating the reflected radio waves by the antiphase reflection of the incident waves allows not only to absorb the incident wave, but also significantly attenuate the reflected wave.

 The coating is a non-uniform surface. It consists of capacitive and inductive elements alternating between each other in all directions of this surface. Capacitive elements form a reflected wave, which is ahead of the phase shift wave incident at ninety degrees. The inductive elements of the absorbing coating form a reflected wave, which lags in phase shift from the wave incident by ninety degrees. In addition, each of the coating elements is capable of independently absorbing part of the incident radiation. Radio waves reflected from various coating elements are in antiphase to each other and therefore mutually weaken each other.

 The capacitive element of the absorbing coating is designed to form a reflected wave, which is ninety degrees ahead of the incident wave and partially absorbing the incident radiation. It is a single layer or multilayer surface. Each layer consists of many thin flat conductive plates (hereinafter referred to as flakes). The flakes have the regular shape of a rectangle, trapezoid, triangle, hexagon, circle - the same for all flakes of the capacitive element. Over the entire surface of the layer, the flakes are arranged in regular rows and columns. The planes of the flakes coincide with the plane of the layer in which the flakes are located. The axis of symmetry of the flakes of one row or column are on the same line. All adjacent layers of the capacitive element are offset relative to each other so that the dividing lines of the rows and columns of one layer are above the symmetry axes of the flakes of the adjacent row or layer. All adjacent layers are separated by standard capacitor dielectric materials.

 Thus, each flake is a lining for several capacitors at once, the second lining of which is the nearest flake from adjacent layers of the capacitive element. All such capacitors of the capacitive element are capacitively coupled to each other.

 The incident radio wave causes, on the first, surface layer, a displacement of the electric charges in the flakes along the directions of the intensity of the alternating electric field. In turn, the displacement of charges on the outer layer causes the displacement of charges in the remaining layers, since all layers have capacitive coupling between themselves. Thus, the energy of the electromagnetic field penetrates deep into the element, which contributes to its intense absorption in the dielectric like a graphite coating. The bias currents on the surface of the capacitive element are ahead in phase shift of the incident wave by ninety degrees and form a reflected wave with the same phase shift.

 Capacitive elements of the absorbent coating can be single-layer. In this case, the rows of scales partially overlap each other. Each row closes the adjacent one by half its width and, accordingly, it is itself closed by another adjacent row by the same amount. In addition, all rows are offset relative to adjacent rows along the row by half the width of the column. The construction of scales in such a capacitive single-layer element is similar to the structure of fish scales. Each element flake serves as a capacitor plate, forming capacitors with four scales from adjacent rows.

 Single-layer and two-layer capacitive elements are capable of not only absorbing and reflecting phase waves of radio waves, but can also be transparent to these waves. The incident electromagnetic radiation causes bias currents due to the fluctuation of charges in the flakes not only from the outside, but also from the back of the element. Therefore, both the outer and the reverse sides of the capacitive element form a reflected wave with a phase shift of ninety degrees relative to the incident.

 A multilayer capacitive element reinforced with high-strength mineral fibers can be used as a structural material with radio-absorbing properties. Single-layer and double-layer capacitive elements reinforced with high-strength mineral fibers can be used as a radiolucent structural material.

 The inductive element of the absorbing coating is intended for partial absorption of the incident radio wave and for the formation of the reflected wave, which is ninety degrees behind the phase shift from the wave. It is a single-layer surface made of composite material. The basis of the composite material is electrically conductive fibers or nets filled with a radiolucent cementitious composition with finely dispersed ferromagnetic fillers (iron oxides, platinum compounds). The inductive element of the absorbing coating can be reinforced with mineral and graphite high-strength fibers and used as a structural material with the properties of absorption of radio waves and the formation of a reflected radio wave, ninety degrees behind the incident wave.

 Capacitive and inductive elements can be glued to the protected surface of almost any shape, forming a protective absorbent coating. Reinforced elements can serve as material for the manufacture of casings, skins, fuselages or their parts without additional costs for their radar protection.

 The capacitive element (Fig. 3, 4) is a multilayer surface, consists of metal plates (Fig. 3, 4, item 3). Each layer is made up of metal plates (hereinafter “flakes”) arranged in regular rows and columns. Rows and columns of flakes in a layer are offset from rows and columns in adjacent (upper and lower) layers so that each flake with its corners forms capacitors with four flakes from the lower adjacent layer and four flakes from the upper neighboring layer. All layers of flakes are separated by standard capacitor dielectric materials.

 Capacitive elements made using printed circuit board technology can be very thin. For example, cathodic or thermal metallization allows to obtain flakes with a thickness of three to five micrometers, and chemical and galvanic - from two to three tenths of a micrometer. In any case, a ten-layer capacitive element, taking into account the thickness of the dielectric, can have a thickness of up to one tenth of a millimeter. For comparison - paint coatings are performed in the average range from two to five tenths of a millimeter. With this thickness, the capacitive element is a thin film that can be easily glued to the surface of the protected object.

 Since each flake in the capacitive element is a lining for several capacitors, the displacement of charges in the flake from the incident wave causes the displacement of charges on the flakes in the deeper layers of the capacitive element. According to the laws of electrical engineering, this current will outstrip the applied voltage by ninety degrees in phase. But since each flake is not only a receiving, but also a transmitting vibrator, the reflected wave will also be ahead of the incident one by ninety degrees. In addition to this technical result, the capacitive element is capable, like any capacitor, partially absorb the energy of the currents passing through it in the dielectric layer. Due to the multilayer nature of the element and a large number of scales, the energy of the incident wave penetrates into the element, where it is absorbed by the dielectric.

 The inductive element is a single layer surface of a composite material (Fig. 2). The basis of the composite is an electrically conductive, metal or graphite fiber mesh (Fig. 2, pos. 6), filled with a radiolucent cementing composition (Fig. 2, pos. 6), with finely dispersed ferromagnetic fillers (Fig. 2, pos. 7). It can have the thickness of a conventional paint coating, being made by the method of impregnation of whisker graphite crystals with a radio-transparent glue with ferromagnetic dust on a thin-film substrate. The required technical result is achieved due to the fact that the metal grid protruding outwardly serves as a transceiver antenna, and the element itself acts as an inductor in which the current lags the phase by ninety degrees from the voltage. In addition, ferromagnetic dust partially dissipates energy in the cementitious composition. As in the capacitive element, due to the mutual inductive coupling between the ferromagnetic particles, the energy of the incident wave is dissipated throughout the thickness of the inductive element.

 The absorbent coating (Fig. 1) is a non-uniform surface. It consists of inductive and capacitive elements, alternating among themselves in a checkerboard pattern over the entire surface (Fig. 1, pos. 1, 2). Capacitive and inductive elements form reflected waves that are in antiphase to each other. Thus, attenuation of the reflected wave due to antiphase reflection from various elements of the absorbing coating is achieved. In order to avoid interference amplification of waves reflected from various coating elements in separate directions, both the inductive and capacitive elements should have linear dimensions an order of magnitude smaller than the incident wavelength. For decimeter waves - centimeter.

 Since each of the elements making up the absorbing coating is capable of partially absorbing the radiation incident on it, the coating itself has this property as a whole.

Claims (3)

 1. The absorbent coating is a non-uniform surface in all directions and consists of capacitive and inductive elements alternating between each other in all directions of this surface.  2. The capacitive element is a layered surface, all layers of which are electrically separated by standard capacitor dielectric materials and are formed by planes of plates of symmetrical shape, arranged in the layer plane in regular rows and columns so that the intersection points of the lines of demarcation of one layer into rows and columns are opposite the centers symmetries of plates of adjacent layers.  3. The inductive element is a single-layer surface, the basis of which is a graphite fiber or mesh, filled with a radiolucent cementing composition with finely dispersed ferromagnetic particles embedded in it.

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