GB2375894A

GB2375894A - Radioabsorbing coating method for producing said coating and device for remote measuring in the UHF range reflection properties of coatings applied to objects

Info

Publication number: GB2375894A
Application number: GB0214795A
Authority: GB
Inventors: Stanislav Danilovich Leichenko
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-01-12
Filing date: 2000-12-21
Publication date: 2002-11-27
Anticipated expiration: 2020-12-21
Also published as: GB0214795D0; RU2155420C1; GB2375894B; WO2001052355A1; DE10085393T1

Abstract

The inventive radioabsorbing coating is made of a radioabsorbing material comprising the following: a synthetic glue 'Elaton" based on latex as plastic binder, and powdered ferrite or carbonyl iron as magnetic extender. The mixing ratio of the components in mass % is 80-20 of synthetic glue "Elaton" based on latex, and 20-80 of powdered ferrite or carbonyl iron. The coating is embodied in the form of layers (2-5) of the radioabsorbing material. The first layer is applied on a surface reflecting electromagnetic waves (1) and the remaining layers are applied successively to each other. The number of layers (2-5) of radioabsorbing material and the ratio of ingredients therein is selected on the condition that achieved the required value of an absorption factor (K<SB>c</SB>) of radioabsorbing material. The inventive method for producing the radioabsorbing material is performed in accordance with the invention and the controlling properties of said coating. In the device for remote measuring reflecting the properties of objects within the UHF range, the radioabsorbing elements have on their surface reflecting electromagnetic wave baffler which is embodied in the form of successively applied layers of the radioabsorbing material.

Description

Radio absorbing coating, method for preparation thereof and device for

remote measuring of reflective properties of the 5 coatings on objects in microwave band Field of the invention

The invention relates to radio engineering, in particular, to absorbers of electromagnetic waves (EMW) in 10 the band of ultrahigh frequencies (microwaves), and particularly to radio absorbing coating, method for preparation thereof and a device for remote measuring of reflective properties of the coatings on objects in microwave band.

Background art

The radio absorbing coatings (RAC) may be non-magnetic and magnetic coatings. Non-magnetic RAC can be subdivided on gradient (absorbing), interference and combined type 20 RAC. Gradient RAC have multilayer structure with smoothly varying or step change of complex dielectric and magnetic permeability on thickness thereof. The upper (input) layer usually comprises a material having dielectric permeability value close to one, the other alternating layers being made 25 from solid dielectrics with high and low dielectric permeability [FR,A,2736754, FR,A,2737347]. For increasing EMW absorption coefficient and broadbandness of RAC its certain layers are filled with non-magnetic or magnetic fragments [US,A, 3754255, EP,A,0600387, EP,A,0828313]. EMW 30 energy absorption in such Roes occurs due to transformation thereof into other kinds of energy, mainly, into thermal energy. The gradient absorbers conditionally comprise spinous RAC, which increase EMW absorption coefficient because of multiple reflections of the waves from the

surface of spikes with absorption of wave energy at each rc ection [EP,A, 0689262, EP,A,0694987]. Interferential RAC consist of alternating layers of dielectric and electro-

conductive material or gratings of resonance elements, thus 5 thickness of the RAC is selected to be aliquot to quarter-

wavelength of the microwave radiation [RU,A,2006999, SU,A,1786567, US,A, 5627541, RU,A,21192161. Energy of incident microwave radiation is attenuated in such RAC due to interference of radiowaves reflected from the metal 10 surface of the substrate covered by the RAC and from the conducting layers (the radiowaves combine in antiphase).

Main deficiencies of the non-magnetic RAC are awkwardness thereof, relatively narrow band, use of toxic materials and substances at manufacture thereof, complexity 15 in manufacture, that restricts the area of operating conditions of their application.

The magnetic RAC being basically constituted of fine-

dispersed ferrite materials are partially not inherent to these deficiencies. An antiradar coating is known prepared 20 from a mixture of spherical magnetized particles with size of 0.5-20 microns in form of powdery iron or glass globules covered with magnetized material and dielectric binder, thus the magnetized particles comprise approximately 80% by weight of the mixture, and a thermostable silicone 25 composition is used as the binder. This radio absorbing material ensures attenuation of EMW energy on 12 - 20 dB in 2 - 10 GHz band with thickness of the coating approximately 1 mm (0.040") [US,A,4173018]. The drawback of this RAC is predominance of magnetic filler (80%) therein resulting in 30 considerable weight and brittleness of the coating.

A composition is known for attenuation radar radiation containing siloxane polymer with polymeric cross-linking agent for it used as a binder, carbonyl iron powder, component on the basis of platinum and inhibitor, thus

amount of the carbonyl iron powder in the composition comprises 50 - 90 % by weight. The composition has increased thermal stability at temperatures up to 285 C [US,A,5764181]. Deficiency of this RAC is its high weight 5 and brittleness, as well as considerable cost.

The closest engineering solution to the claimed invention is a radio absorbing material containing synthetic adhesive <<Elaton>> on the basis of latex as polymeric binder, and powdery ferrite or carbonyl iron as 10 magnetic filler at components ratio of, by mass: synthetic adhesive <<Elaton>> on the basis of latex 80-20, powdery ferrite or carbonyl iron 20-80.

Adhesive <<Elaton>> has following composition: synthetic latex 90-99% 15 industrial casein 0.03-3% benzoic acid 0.1-0.4% aqueous ammonia 0.06-0.3% This radio absorbing material ensures attenuation of EMW energy on 7 - 18 dB in the microwave band with 20 thickness of the coating of the order of 1 mm. Advantages of this coating is simplicity of preparation process of the composition and coating a surface of the protected object, nontoxicity and availability of the components, high adhesive properties, that ensures a broad range of 25 operating conditions in its application [RU,A,2107705].

The reason precluding deriving of the below mentioned engineering result at use of this coating is in the following. Properties of the RAC obtained with use of the described material depend on the size of particles of the 30 powdery magnetic filler and on the thickness of layer of the coating, that should be equal in all points of the coated surface. Particular size of the particles of the powdery magnetic filler in the composition is selected by calculation for suppression microwave radiation with

particular wavelength. Since batches of powders with particular grade, having absolutely equal size of the particles, do not exist, properties of the obtained RAC will always differ from the calculated values. Thickness of 5 the layer can not be hold identical in all points in process of application of the radio absorbing material on a surface placed vertically, under an angle or having curvature, since there occurs sags of the material, particles of the powdery magnetic filler being heavier 10 displace downwards. If deviations of parameters of the RAC from calculated values appear unacceptable, it should be removed, thus a new one should be prepared and applied, and that entails unproductive expenditures of forces and funds.

It is known a method for manufacture an electromagnetic 15 waves absorber including coating of a metal substrate by a first layer of dielectric and forming a grating of resonance elements thereon, consequent application on the obtained grating of a second layer of dielectric and grating of resonance elements, and so on up to N layers of 20 dielectric and gratings of resonance elements, application a protective layer of dielectric on the last grating of resonance elements, thus the resonance elements in process of forming of each grating are formed in accordance with wavelength matching the subband of absorbed frequencies, 25 and thickness of each layer of dielectric increases from layer to layer proportionally to the wavelength matching the subband of absorbed frequencies according to the relation An = (An - An1J/8 30 where An is central wavelength matching the absorbed subband of frequencies; n = 1, 2. ., N is a sequence number of the layer of dielectric and the absorbed subband of frequencies; dielectric permeability of the dielectric.

Thus the layers of the dielectric and the gratings of the resonance elements are made separately and are stacked sequentially, thud the gratings of resonance elements are formed of electro conductive material with help of 5 perforated templates or with use of printing method.

Operations of forming gratings of resonance elements can be automatized, that generally simplifies technology of manufacture thereof [R0,A,2119216) .

The reason precluding deriving of the below mentioned 10 engineering effect at use of the known method for manufacture of EMW absorber is absence of operations of instrumental monitoring of thickness of layers of dielectric therein, value of absorption coefficient of EMW energy by layers and the RAC as whole, in consequence of IS that the properties thereof may not meet the required values. It is known a device for remote measuring of the reflective properties of objects of irregular shape in the microwave band of radiowaves containing a microwave 20 generator, a mixer, an amplifier, a receiving-transmitting antenna, a laser target designator, a first and a second video cameras, a picture monitor, a frequency modulator, a power divider, a circulator, an analog-to-digital converter, a synchronizer, a calculator, radio absorbing 25 elements. The output of the microwave generator is connected to the input of the power divider, which first output is connected to the first input of the mixer, and second output is connected to the first arm of the circulator, which second arm is connected to the receiving 30 transmitting antenna and third arm is connected to the second input of the mixer which output is connected to the amplifier which output is connected to the first input of the analog-to-digital converter which output is connected to the first input of the calculator, and outputs of the

first and the second video cameras are accordingly connected to the second and third inputs thereof. The first output of the calculator is connected to the input of the first video camera, the second output is connected to the 5 input of the second video camera, the third output is connected to the input of the laser target designator, the fourth output is connected to the input of the synchronizer, the fifth output is connected to the picture monitor. The first output of the synchronizer is connected 10 to the second input of the analog-digital converter, and the second output is connected to the input of the frequency modulator which output is connected to the input of the microwave generator. A parabolic mirror antenna or sharp pointed pyramidal horn is used as a receiving 15 transmitting antenna which is installed on a portable rack and is fixed with possibility of displacement on height, angle of elevation and azimuth. The receiving-transmitting antenna, the laser target designator and the first video camera are rigidly connected therebetween and their optic 20 axes are adjusted, and the second video camera is installed so, that its optic axis is directed on the tested object and is perpendicular to the optic axis of the receiving-

transmitting antenna. The radio absorbing elements are made as mats, rugs, shields, curtains, aqueous foam installed or 25 applied on the surfaces and pieces enclosing the tested object and also near to the sendingreceiving antenna.

The described device ensures remote measuring of both local characteristics of dissipation of EMW energy in the microwave band, and integrated scattering pattern of 30 different objects, that allows to obtain radio-portraits of objects, including large dimension and complicated configuration objects under different angles of sight [RU,A, 2111506].

Possibilities of obtaining the mentioned below engineering result with help of this device are restricted for the following reasons. In order to determine properties of the RAC and possible adjusting thereof during 5 application of the RAC on the surface of the object, it is necessary to know the precise place where they deviated from the required parameters. The used parabolic mirror antenna forms a floodlight beam, thus the resolution element on the distance represents a cylinder having about 10 60 cm in diameter and about 30 cm in height. This volume is perceived by the radar as a unit space element, therefore inside this volume it is impossible to discriminate, for example, a <<bright>> point and to define its coordinates on the surface of the irradiated object with binding to any 15 characteristic element, if linear dimensions of this point are less than the diameter of the beam. The radio absorbing elements used in the device are made with use of conventional radio absorbing materials, for example, HV-3, having following deficiencies: considerable weight, 20 hardness, fragility. Use of foam as disposable means increases labor efforts for carrying out the test.

Disclosure of the invention

Object of the claimed invention is the problem of 25 developing a radio absorbing coating effectively working in a broad band of microwave radiowaves and having small thinness, creating a method for preparation such coating, allowing to perform instrumental control over parameters of the coating in process of application thereof on the 30 surface of a protected object, as well as creating a device for remote measuring of the reflecting characteristics of the coatings on the objects in microwave band of radiowaves with use of such radio absorbing coating.

This problem cam be solved by radio absorbing coating comprising radio absorbing material, containing a synthetic adhesive <<Elaton>> on the basis of latex as polymeric binder and powdery ferrite or carbonyl iron as a magnetic filler 5 at components ratio, % by mass: synthetic adhesive <<Elaton>> on the basis of latex 80-20, powdery ferrite or carbonyl iron 20-80, according to the present invention, which is formed as layers of radio absorbing material, first of which is applied on the electromagnetic waves reflecting 10 surface, and the others are applied sequentially one on another, thus the number of the layers of the radio absorbing material is determined by required value of absorption coefficient of the radio absorbing coating according to the following relation: 15 Kc = Ko Nr where K: is the required absorption coefficient of the EMM radio absorbing coating, - empirical EMW absorption coefficient taking into account the relation of components of the applied radio 20 absorbing material and technological requirements of the coating of this material; N number of layers of the radio absorbing material.

The problem can also be solved by the method including application on a metal substrate of a first layer of the 25 absorber of electromagnetic waves, that is sequentially coated by other identical on composition layers of the absorber of electromagnetic waves, according to the invention, a radio absorbing material being used as absorber of electromagnetic waves containing synthetic 30 adhesive <<Elaton>> on the basis of latex as polymeric binder, and powdery ferrite or carbonyl iron as magnetic filler at components ratio, by mass: synthetic adhesive <<Elaton>> on the basis of latex 80-20, powdery ferrite or carbonyl iron 20-80, after applying first three-four layers

of the radio absorbing material with a particular relation of the ingredients, value of the absorption coefficient of the obtained radio absorbing coating is measured, compared with the estimated value for this number of layers of the 5 radio absorbing material with given relation of the ingredients, if this measured value of absorption coefficient exceeds the calculated value, a part of the upper layer of the radio absorbing material is removed up to obtaining the value of the required absorption 10 coefficient, and if it is less than the calculated one, a portion of the radio absorbing material is prepared with relation of the ingredients ensuring at application the required value of the absorption coefficient, thereupon the following three-four layers of the radio absorbing material 15 with particular relation of ingredients are applied, value of the obtained absorption coefficient of the radio absorbing coating is measured, compared with the estimated value for the given number of layers of the radio absorbing material with particular relations of the ingredients, and 20 using similar method the equalities of the measured and calculated absorption coefficients of the radio absorbing coating with given number of layers of the radio absorbing material is achieved, then the operations are repeated, thus the necessary number of layers of the radio absorbing 25 material are applied that ensures obtaining the required absorption coefficient of the whole radio absorbing coating. The required absorption coefficient of the radio absorbing coating Kc can be determined according to the 30 following relation: Kc = Ko N' where Ko is empirical EMW absorption coefficient taking into account the relation of components of the applied

radio absorbing material and technological requirements of the coating of this material; N - number of layers of the radio absorbing material.

And, finally, this problem can also be achieved by that 5 in the known device for remote measuring of reflective properties of objects in the microwave band of radiowaves comprising a microwave generator, a mixer, an amplifier, a receiving-transmitting parabolic mirror antenna with a feeding element, a laser target designator, a first and a 10 second video cameras, a picture monitor, a frequency modulator, a power divider, a circulator, an analog-to-

digital converter, a synchronizer, a calculator, radio absorbing elements, thus the output of the microwave generator is connected to the input of the power divider 15 which first output is connected to the first input of the mixer, and second output is connected to the first arm of the circulator which second arm is connected to the first input of the receiving-transmitting antenna, and third arm is connected to the second input of the mixer which output 20 is connected to the amplifier which output is connected to the first input of the analog-to-digital converter which output is connected to the first input of the calculator to which second and third inputs accordingly outputs of the first and second video cameras are connected, the first 25 output of the calculator is connected to the input of the first video camera, the second output is connected with the input of the second video camera, the third output is connected with the input of the laser target designator, the fourth output is connected with the input of the 30 synchronizer, the fifth output is connected with the picture monitor, the first output of the synchronizer is connected to the second input of the analog-to-digital converter, and the second output is connected to the input of the frequency modulator which output is connected to the

input of the microwave generator, the receiving-

transmitting antenna is installed on the portable rack and is fixed with possibility of displacement on height, angle of elevation and azimuth, and the receiving-transmitting 5 antenna, the laser target designator and the first video camera are rigidly connected therebetween and their optic axes are adjusted, and the second video camera is installed so, that its optic axis is directed on the tested object and is perpendicular to the optic axis of the receiving 10 transmitting antenna, thus according to the invention, the feeding element of the receiving-transmitting parabolic mirror antenna is provided with a device for reciprocating movement thereof coaxial to the optic axis of the antenna, a control block of displacement of the feeding element is 15 incorporated in the calculator, which output provides the sixth output of the calculator and is connected to the input of the device for displacement of the feeding element being the second input of the receiving-transmitting antenna, and the radio absorbing elements are formed as 20 flexible mats, rugs, curtains, domeand cone-shaped caps, with an electromagnetic waves reflecting shield installed on the surfaces thereof, for example, a metal mesh, sequentially covered by layers of the radio absorbing material including synthetic adhesive <<Elaton>> on the basis 25 of latex as polymeric binder and powdery ferrite or carbonyl iron as a magnetic filler at components ratio, % by mass: synthetic adhesive <<Elaton>> on the basis of latex 80-20, powdery ferrite or carbonyl iron 20-80, thus the number of layers of the radio absorbing material is 30 determined by the required value of absorption coefficient of the radio absorbing coating according to the following relation Kc = Ko N.

where Kc is the required absorption coefficient of the EMS radio absorbing coati K0 - empirical EMh absorption coefficient taking into account the relation of components of the applied radio 5 absorbing material and technological requirements of the coating of this material; N - number of layers of the radio absorbing material.

Brief description of the drawing"

10 The inventions will be further illustrated by description of particular examples of its embodiments and

accompanying drawings, on which.

Fig. 1 schematically represents a cross-sectional view of the radio absorbing coating.

15 Fig.2 represents diagrams of the relation of the required (calculated) <<Am> and the measured <cB>> values of the absorption coefficient Kc of the EMW radio absorbing coating versus number N of layers of the radio absorbing material, where values of Kc in dB are put on the axis of 20 abscissae and the number N of layers are put on the axis of ordinates. Fig. 3 represents a block diagram of a device for measuring the EMW reflection factor.

Fig. represents a block diagram of a device for 25 remote measuring of the reflective properties of objects in the microwave band of radiowaves.

Fig. 5 schematically represents a device for displacement of the feeding element of the receiving transmitting parabolic mirror antenna.

30 Fig. 6 represents a flowchart of the control algorithm for displacement the feeding element of the receiving transmitting parabolic mirror antenna.

Best methods of carrying out the invention The radio absorbing coating according to the present invention schematically represented in Fig. 1 is provided in form of a plurality of layers of a radio absorbing 5 material sequentially applied one on another, thus the first layer is applied on EMW reflecting surface of the metal substrate 1. The first, the second and the third layers 2 are formed from a radio absorbing material, layer 3 is a first correcting layer, layers 4 are the following 10 layers of the radio absorbing material, layer 5 is a second correcting layer. The radio absorbing material includes a synthetic adhesive c<Elaton>> on the basis of latex as polymeric binder and powdery ferrite or carbonyl iron as magnetic filler at components ratio, % by mass: synthetic 15 adhesive <<Elaton>> on the basis of latex 80-20, powdery ferrite or carbonyl iron 20-80. This material was selected due to its high adhesion properties, inexpensiveness and availability of the ingredients, simplicity of preparation.

Size of the particles of the magnetic filler are determined 20 by the frequency band of the suppressed microwave radiation, and proportions of the ingredients are determined by the required value of the absorption coefficient of the EMW of the radio absorbing coating [RU,A,2107705]. Layers in the radio absorbing coating can 25 be homogeneous (e.g. layers 2, 4) or may differ by composition of the ingredients (e.g., layers 3, 5). Number of layers can be determined from the requirement of obtaining the required value of EMW absorption coefficient of the radio absorbing coating Kc according to the 30 following relation: Kc = Ko N. where go is empirical EMS absorption coefficient, N - number of layers of the radio absorbing material.

Adhesive <<Elaton>> has following composition:

Synthetic latex 90-99% Industrial casein 0.03-3% Benzoic acid 0.1-0.4% Aqueous ammonia 0.06-0.3% 5 The empirical EMW absorption coefficient Ho takes account of the components ratio of the applied radio absorbing material and technological requirements of application of this material, and can have the values from 0.0 to 1.0, but used in practice values of coefficient Ko 10 are usually in the range from 0.1 to 0.85. Thus, under normal room conditions (temperature from 18 C to 23 C, relative humidity 70-80%, pressure 700 mm of mercury) and at the components ratio in the composition of the synthetic adhesive <<Elaton>> on the basis of latex and powdery ferrite 15 or carbonyl iron of 50:50, = 0.53, and at the ratio of 20:80, Ko = 0.26. Introduction into construction of the

radio absorbing coating of layers (for example, layers 3, 5) differing by ingredients composition of the radio absorbing material is stipulated by the following reason.

20 The calculated dependence of Kc on the number of layers of the radio absorbing material has a smoothly varying envelope curve, as shown in Fig. 2 (histogram <<A>>).

Practically, the value of the EMW absorption coefficient (histogram <<B>>) may not coincide with the estimated value 25 for many reasons: dimensional spread of particles of the magnetic filler in the composition, irregularity of thickness of the layer at its application, deviation from the technological requirements of preparation of the coating, etc. For <<matching>> the value of the real Kc to 30 its calculated value correcting layers 3, 5 of the radio absorbing material are used. For example, on Fig. 1 correcting layer 3 is shown conditionally to be the fourth layer counting from metal substrate 1. Fig.2 shows, that the measured value Kc of the coating consisting of three

layers (histogram <<B>>), is less than its estimated value (histogram <<A> >). Selecting the components ratio in the composition of the radio absorbing material, correcting layer 3 is shaped and introduced into the coating, that 5 equalizes the measured and calculated values of Kc for the first four layers of the coating. In this example (Fig. 2) the radio absorbing coating contains also the 11-th and the 19-th correcting layers of the radio absorbing material.

Thus, due to introduction of correcting layers of the radio

10 absorbing material it is possible to prepare thin, on the order of 1 mm, radio absorbing coating with required (calculated) properties.

The radio absorbing coating according to the present invention works as follows. Due to the resistive properties 15 of the material a part of energy of the incident microwave radiation is absorbed by transformation to the energy of thermal motion of molecules in the material. Each particle of magnetic filler is surrounded by a thin layer of dielectric, and therefore it works as an elementary point 20 re-radiator with a broad radiation pattern. Because the particles are randomly oriented in the thickness of the material, radiation pattern of the re-radiation is also randomly oriented. This results in inconsiderable proportion of energy being reradiated in the direction 25 reverse to the incident microwave radiation. Thus the angle of incidence of the EMW weakly influences the radiation pattern of re-radiation. Besides, the claimed coating shows indistinct interferential properties at close to normal incidence of the microwave radiation. Particular thickness 30 of the coating and selection of electrical and dielectric parameters of the layers allow to provide phase shift on n/2 of the incident and reflected by the metal substrate EMW resulting in attenuation thereof due to addition in antiphase.

The method for preparation the radio absorbing coating and control over properties thereof consists in following.

The radio absorbing material containing synthetic adhesive <<Elaton>> on the basis of latex as polymeric binder and 5 powdery ferrite or carbonyl iron as magnetic filler at components ratio, % by mass: synthetic adhesive <<Elaton>> on the basis of latex 80-20, powdery ferrite or carbonyl iron 20-80, is prepared in a mechanical mixer by stirring of the ingredients. Depending on the quantitative content of the 10 ingredients, time of agitation comprises from 7 to 15 minutes, then the mixer is switched in a condition of admixing with lowered on 75 from the nominal speed of rotation of the mixer. Monitoring of the composition on degree of homogeneity is performed before application 15 thereof, since the estimated value of absorption coefficient depends thereon, and local bunches and rarefaction of the particles of the magnetic filler in the mixture generally reduce absorption coefficient of the material. To this end a portion of the composition is 20 applied by a layer (0.7 - 1 mm) on the bottom of a flat dish and is covered by a radiotransparent unwettable material, e.g. a lavsan film. Measuring of the absorption coefficient is performed, as a rule, in nine points of the surface of the layer over the lavsan film (at the center, 25 in the corners and at ridges) with help of a device which block diagram is shown on Fig. 3.

The device includes microwave generator 6 which output is connected to the first arm of circulator 7 which second arm is connected to thesemiconductor cutout switch on a 30 p-i-n diode, and the third arm is connected with the detector 9. Semiconductor cutout switch 8 is installed in one end of a section of wave-guide 10 which other end is provided with radiator 11 executed as a detachable sectoral horn. The solid angle (a) of the sectoral horn 11 aperture

is determined by the required angle of irradiation of surface of the tested material. Thus, for normal irradiation 20 , under angle 45 = 0, and under angle 70 -30 . Output of detector g is connected to low 5 frequency (LF) block 12 of measuring and control. This block provides a computing mechanism on the basis of a microprocessor having ROM and RAM memories and an external input-output interface. The control outputs of block 12 are connected to the control inputs of microwave generator 1 10 and semiconductor cutout switch 8, and the information output to liquid crystals indicator 13. Operation of all elements of the device is controlled by the microprocessor according to the program stored in its memory.

Measuring of the absolute value of absorption 15 coefficient (IKE) is carried out automatically according to the algorithm stored in the ROM of block 12 according to the formula: I K1 1 - / -

where PI is power of the incident radio-frequency 20 radiation, P2 is power of the reflected radio-frequency radiation. After switching on the electric power unit, aperture of radiator 11 is pressed to the surface of the tested 25 material. Thus, semiconductor cutout switch 8 under action of the control signal from the microprocessor is in the locking (short circuit) mode of wave-guide 10. By pressing the button <<Start>> on the panel of LF block 12 the operator begins the process of measuring of IKE. Radio-frequency 30 radiation generated by microwave generator 6 is fed into the first arm of circulator 7, goes out from its second arm and is passed into the section of wave-guide 10 Since the semiconductor cutout switch 8 on p-i-n diode is in the locking mode of the wave-guide, the radio signal is

reflected therefrom practically lost-free, is returned into the second arm of circulator 7 and through its third arm goes to detector 9. From the output of detector 9 an LF signal is taken which is proportional to the power of the 5 incident radio-frequency radiation P1. This signal is normalized and digitized, and stored in the RAM of block 12. Then, by command of the microprocessor, semiconductor cutout switch 8 is switched in a transmission mode. Thus, the radio-frequency radiation passed the section of wave 10 guide 10 falls on the surface of the testing material under an angle determined by parameters of Pectoral horn 11.

Having lost a part of energy absorbed by the material, the radio signal is reflected, returned to the second arm of circulator 7 and through its third arm goes to detector 9.

15 On its output a LF signal is formed proportional to the power of the reflected signal Pa. After normalization and transformation to digital form it is stored in RAM of block 12. Thereafter the microprocessor evaluates loll according to the above stated formula, which value is displayed on 20 liquid crystals indicator 13. The process of measuring of the absorption coefficient of a layer of the <<wet>> radio absorbing material in a dish in one point takes no more than 2 - 3 seconds [RU,A, 21077051.

Degree of homogeneity of the composition and, hence, 25 readiness thereof to use is estimated on the value of dispersion D of the measured absorption coefficient, that for a normally prepared mixture should satisfy the requirement < a.d., 30 where a.d. - average of distribution.

If the obtained value of dispersion exceeds the limits, the causes thereof are analyzed, a new composition is prepared and its properties are similarly tested until the desired values of the mixture parameters are obtained.

After that, a radio absorbing coating on conducting surface of the protected object is formed by sequential application of layers of the radio absorbing material one on another. Application of the composition is performed 5 with help of, for example, an air paint-pulverizer for application of paintwork materials (PWM) with conditional viscosity up to 50 sec. Each layer is applied by the method of grating not allowing downflows and forming drops.

Thickness of a layer is 30 - 40 microns, time of drying of 10 a layer is 10 minutes at temperature 12 - 35 C and air humidity no more than 801.

After application of 3-4 layers the value of the obtained EMW absorption coefficient is measured with use of the above disclosed device and compared with the calculated 15 value of absorption coefficient which is determined from the following relation: Kc a Ko À N. where Kin is empirical EMS absorption coefficient taking into account the relation of components of the applied 20 radio absorbing material and technological requirements of the coating of this material; N - number of layers of the radio absorbing material.

If necessary, equality of the values of the measured and calculated absorption coefficients can be achieved for 25 a given number of layers of the radio absorbing coating (alignment of points of histograms <<B>> and <<A>>, accordingly, Fig.2) by grinding of the surface of the upper layer or by application thereon of an additional, so-

called, adjustment layer (position 3, Fig. 1). Then the 30 following three-four layers of the radio absorbing material are applied, the value of obtained absorption coefficient of the radio absorbing coating is measured, compared with the value of calculated absorption coefficient for the given number of layers taking into account parameters of

the correcting layer and, if necessary, equality of these values is achieved in a similar way. Depending on character of discrepancy of the values of measured and calculated absorption coefficients in process of forming of the radio 5 absorbing coating, the radio absorbing material of the adjustment layers can differ from the relatively previous and consequent layers, both in quantitative relation of the components and if size of particles of the magnetic filler.

Application of layers of the radio absorbing material is 10 finished upon reaching equality of the value of the measured absorption coefficient with the value required by the technical specifications on radio absorbing coating.

Thus, the claimed method allows to control the properties of the radio absorbing coating during its 15 forming, that essentially increases exactness of production with required parameters.

For measuring of the value of absorption coefficient and control over the properties of the radio absorbing coating in process of its application on the surface of 20 complicated configuration, and also for due detection of local defects of the applied coating, according to the invention, a device is proposed for remote measuring of reflective properties of the coatings on objects in the microwave band of radiowaves schematically represented in 25 Fig. 4.

This device contains connected in series microwave generator 14, power divider 16 which first output is connected to the first input of the mixer 17, and second output is connected to the first arm of circulator 18. Its 30 second arm is connected to the first input of receiving-

transmitting antenna 19, and the third arm is connected to the second input of mixer 17 to which output amplifier 20 and analog-to-digital converter (AD converter) 21 being sequentially connected, which output is connected to the

first input of calculator 22. The second input of calculator 22 is connected to the output of first video camera 23, the third input is connected to the output of second video camera 24. The first and the second outputs of 5 calculator 22 are connected to the inputs of first 23 and second 24 video cameras, accordingly, its third output is connected to the input of laser target designator 25, its fourth output is connected to the input of synchronizer 26, its fifth output is connected to picture monitor (PM) 27, 10 the sixth output is connected to the second input of receiving-transmitting antenna 19. The first output of the synchronizer 26 is connected to the second input of analog-

digital converter 21 r the second output is connected to the input of frequency modulator 15, which output is connected 15 to the input of microwave generator 14. The second video camera 27 is installed with its optic axis during the measuring being in the plane perpendicular to the optic axis of the receiving-transmitting antenna, and is pointed to tested object 29 (shown conditionally by dotted lines on 20 Fig.4). A parabolic mirror antenna is used as a receiving-

transmitting antenna 19, thus the parabolic mirror, first video camera 23 and laser target designator 25 are rigidly connected therebetween through adjusting platforms 28 and the optic axes thereof being in adjustment. The antenna is 25 installed, for example, on a portable (transportable) rack with possibility of displacement on height, angle of elevation and azimuth [RU,A,2111506].

The feeding element of the antenna is provided with possibility of reciprocative displacement coaxial its optic 30 axis, that ensures adjustment (focusing) of the size of spot on the surface <<illuminated>> thereby. displacement device of the feeding element of antenna can be provided, for example, as it is shown in Fig.5. Wave-guide 32 rigidly connected to parabolic mirror 31 is connected with feeding

element 34 by the second end thereof through corrugated section 33. First end of wave-guide 32, being the first input of receiving transmitting antenna 19, is connected to the second arm of circulator 18. Drive 35 is a stepper 5 electromotor rigidly mounted on wave-guide 32. Its actuator through driving link 36 is connected to feeding element 34, and the control input, being the second input of receiving-

transmitting antenna 19, is connected to the sixth output of calculator 29.

10 Radio absorbing elements 30 are formed as mats made on a flexible base, rugs, curtains, dome- and cone-shaped caps, with an electromagnetic waves reflecting shield, for example, a metal mesh installed on the surfaces thereof.

Layers of the radio absorbing material are sequentially 15 applied on this shield including the synthetic adhesive <<Elaton>> on the basis of latex as the polymeric binder and the powdery ferrite or carbonyl iron as the magnetic filler at components ratio, by mass: synthetic adhesive <<Elaton>> on the basis of latex 80-20, powdery ferrite or carbonyl 20 iron 20-80. The number of layers of the radio absorbing material is determined by required value of the absorption coefficient of the radio absorbing coating Kc according to the following relation: Kc = Ko À N. 25 where Ko is empirical EMW absorption coefficient taking into account the relation of components of the applied radio absorbing material and technological requirements of the coating of this material; N - number of layers of the radio absorbing material.

30 Radio absorbing elements 30 are placed on the surface of the ground near tested object 29, neighboring objects, fasting elements or supports under the object, on the object itself (for example, with the purpose to eliminate reflecting from a particular surface segment) for maximal

attenuation of the hindering re-radiations. Radio absorbing elements 30 are also placed near receiving-transmitting antenna 19 with the purpose of attenuation of the influence of side lobes of its radiation pattern.

5 The disclosed device provides measuring of the values of absorption coefficient of the radio absorbing coating under different aspect angles with binding of results of the measurements to structural elements of the object. It allows to select the bright points, to discriminate them on 10 the object and to form a radioportrait of the object, with help of the calculator, as a plurality of bright points on its surface [RU,A,2111506]. Tested object 29 is installed on a calculated distance from receivingtransmitting antenna 19, coordinate systems of the tested object and the 15 device being matched. Thus, coordinates of characteristic elements of the object (center of gravity, building axis, symmetry axis, separate details of construction, etc.) are determined and stored in respect to the origin of the system of coordinates, in which the device works.

20 The device operates as follows (Fig.4). Microwave generator 14 works in continuous mode and generates voltage of particular carrier frequency f0. Under action of frequency modulator 2 this frequency is periodically varied according to saw-tooth law from fo to fn' where fn fO + 25 Fin). Thus, a slowly varying linear frequency modulated (chirp) signal is formed on the output of microwave generator 14. The frequency-tuning band is determined by the required resolving capacity of the distance determination to local points of dispersion on the surface 30 of tested object. These parameters of the chirp signal are set by synchronizer 26 under the program stored in the ROM of calculator 22. Frequency modulator 15 can be provided, for example, as a pulse counting device with an integrator, which is reset after gathering a particular number of

impulses fed from synchronizer 26. The saw-tooth voltage from the output of frequency modulator 15 is fed to the microwave generator on a varicap changing its capacity and, correspondingly, frequency of oscillation according to the 5 saw-tooth law. From the output of microwave generator 14 the chirp signal is fed to power divider 16, from which first output one part of it goes to mixer 17 as a heterodyne signal, and the second part - from the second output - to the first arm of circulator 18 and further 10 through its second arm to receiving-transmitting antenna 19. Reflected from the surface of tested object 30 signal is returned to receiving-transmitting antenna 19, goes into the second arm of circulator 18 and appears on its third arm, getting into mixer 17. This signal is shifted in 15 relation to the radiated (heterodyne) signal on a particular time period and, accordingly, on frequency. A signal of intermediate frequency is formed on the output of mixer 17 which value is proportional to the distance to the point of the reflecting surface of the object. It is 20 determined considering, that each value of distance in space corresponds to a particular value of frequency modulation of the chirp signal. A particular range of change of the frequency of the chirp signal corresponds to the space occupied by tested object 29. Due to this, 25 resolution of bright points on distance on the surface of the object is provided.

After amplification in amplifier 20 signal of intermediate frequency is passed into analog-digital converter 21, where it is quantized on levels of amplitude 30 with frequency set by synchronizer 26. For example, two 8-

digit analog-digital converters of K1107 PV4 type with sampling rate 100 MHz can be used as analog-digital converter 21, that ensures operation in real-time mode. On the output of analog-digital converter 21 a stepped varying

voltage is formed as discrete time references characterizing amplitude of the received signal. This voltage is passed to calculator 22. With help of a keyboard or a manipulator of the mouse type the operator inputs into 5 calculator 22 parameters of the aspect angle of the irradiated point on the surface of object in respect to the device (receiving-transmitting antenna 19): azimuth, angle of elevation, height, distance, and also azimuth of the antenna, angle of elevation of the antenna, height of 10 installation of the antenna.

Calculator 22 performs correlation of signals on algorithms stored in the ROM using the known rules, described, e.g., in RU,A,2111506. In particular, superposition is carried out of the obtained frequency 15 references with optical image of the object that in digital form is fed from first 23 and second 24 video cameras.

These video cameras create images, accordingly, of the frontal projection and orthogonal thereto side projection of tested object 29. A visible (in red color) spot from the 20 beam of laser target designator 25 is indicated on both projections in the same point on the surface of object.

This laser spot is placed in the center of the spot of the radio beam in result of preliminary adjustments of the optic axes of receivingtransmitting antenna 19, first 25 video camera 23 and laser target designator 25. Comparing the images of orthogonal projections of the object, coordinates of the laser spot can be easily determined and, thus, obtained frequency references can be identified, i.e. frequency references can be attached to the relevant 30 elements of dispersion (bright points) on the surface of the object.

Calculator 22 according to the algorithm developed by the inventors forms a signal proportional to the scattering cross-section (SCS) or absorption (reflection) coefficient

of the surface segment of the object, restricted by the spot of radio beam, and also calculates parameters of the signal of a particular element of resolution (amplitude' azimuth, angle of elevation, distance, height). This 5 information is stored, simultaneously displayed on PM (display) 27 and operator can identify a relevant frequency reference with a particular point marked by the laser spot on the surface of object. The operator, keeping the same aspect angle of irradiation of the object, and changing the 10 azimuth, angle of elevation, height of installation of the receiving-transmitting antenna sequentially <<scans>> the interesting surface segments of the object, inspecting displacement of the radio beam by location of the laser spot. Then the receiving- transmitting antenna is 15 rearranged, the object is irradiated under a new aspect angle, and the process of measuring is repeated. The accumulated information on parameters of signals obtained at different aspects angle of irradiation of the object, is processed in calculator 22 for joint correlation resulting 20 in multidimensional signal describing the law of behavior of each bright point depending on change of the aspect angle of irradiation of the object. The program of representation of the result of measurements provides displaying on PM (display) 27 of the data which can be 25 presented as, for example, a graphical chart: distance -

SCS; three-dimensional image in coordinates: distance -

angle of elevation - SCS (for a particular azimuth), etc. The mode of <<narrow beam>> is provided in the device for more precise measurement of parameters of radio absorbing 30 of the coating both in the process of its application on the surface of object, and of the finished one, as well as detection of its local imperfections or bright points, which linear dimensions are relatively small. This mode allows to reduce the dimensional element of resolution and

to view smaller details. It is implemented by the control block in calculator 22 according to the algorithm, which flowchart is shown in Fig. 6. The control is carried Out by displacement of the feeding element of antenna 34 (Fig. 5) 5 as follows. According to the solved problem the operator performs a preliminary measuring in the mode of a floodlight beam. On the screen of PM 27 he marks a zone(s) in which more detail view is required of the segment of the radio absorbing coating on the surface of the object. By 10 superposition of a marker on the chosen point, which the beam should be focused on, the operator automatically sets a value of distance thereto. Calculator 22 translates this distance according to the table stored in its memory into number of steps for a stepper motor, and forms a relevant 15 control signal, which is passed to stepper motor 35. After completing the required number of steps, the stepper motor 35 by means of driving link 36 displaces the feeding element (horn) 34 of parabolic mirror 31 coaxially to its optic axis so that the beam is focused on the required 20 distance. After that the measuring is performed. When the focusing is not required anymore, feeding element 34 is returned into initial position (<<floodlight bee=> mode).

Use of the claimed group of inventions allows to obtain a high-quality radio absorbing coating due to performing an 25 objective instrumental monitoring at all stages of its preparation, that reduces influence of the human factor and technological errors on receiving optimal, including weight and size, properties at application on the protected object. Industrial applicability

The invention is mainly intended for lowering radar visibility of object of different assignment and configuration.

Claims

1. A radio absorbing coating comprising a radio absorbing material, including a synthetic adhesive <<Elaton>> 5 on the basis of latex as polymeric binder and powdery ferrite or carbonyl iron as magnetic filler at components ratio, % by mass: synthetic adhesive <<Elaton>> on the basis of latex 80-20, powdery ferrite or carbonyl iron 20-80, characterized in that the coating is made as layers of 10 radio absorbing material, first of which is applied on the electromagnetic waves reflecting surface, and the other are applied sequentially one on another, thus the number of layers of the radio absorbing material is chosen to provide the required value of absorption coefficient of the radio 15 absorbing coating according to the following relation = Ko À N. where By is the required absorption coefficient of the EMW radio absorbing coating, Ko is the empirical EMW absorption coefficient taking 20 into account relation of the components of the applied radio absorbing material and technological requirements of the coating of this material; N - number of layers of the radio absorbing material.

2. A method for preparation of the radio absorbing 25 coating and control over properties thereof comprising application of the first layer of the radio absorbing material on a metal substrate which is sequentially coated by other identical on composition layers of the absorber of electromagnetic waves characterized in that, the radio 30 absorbing material is used containing synthetic adhesive <<Elaton>> on the basis of latex as polymeric binder, and powdery ferrite or carbonyl iron as magnetic filler at components ratio, % by mass: synthetic adhesive <<Elaton>> on the basis of latex 80-20, powdery ferrite or carbonyl iron

2g 20-80, after applying of the first three-four layers of the radio absorbing material with a required relation of the ingredients, value of the absorption coefficient of the obtained radio absorbing coating is measured, compared with 5 the estimated value for this number of layers of the radio absorbing material with given relation of the ingredients, if this measured value of the absorption coefficient exceeds the calculated value, a part of the upper layer of the radio absorbing material is removed up to obtaining the 10 value of the required absorption coefficient, and if it is less than the calculated value, a portion of the radio absorbing material is prepared with relation of the ingredients ensuring at application the required value of the absorption coefficient? thereupon following three-four 15 layers of the radio absorbing material with required relation of the ingredients are applied, value of the obtained absorption coefficient of the radio absorbing coating is measured, compared with the estimated value for the given number of layers of the radio absorbing material 20 with given relations of the ingredients, and similarly the equalities of the measured and calculated absorption coefficients of the radio absorbing coating with given number of layers of the radio absorbing material are achieved, then the operations are repeated, thus the 25 necessary number of layers of the radio absorbing material is applied which ensures obtaining the required absorption coefficient of the whole radio absorbing coating.

3. Method according to claim 2 characterized in that, the required absorption coefficient of the radio absorbing 30 coating Kc is determined according to the following relation, Kc = Ko À N. where Ko is empirical EMW absorption coefficient taking into account the relation of ingredients of the applied

4. A device for remote measuring of the reflective 5 properties of coatings on objects in microwave band of radiowaves containing a microwave generator (14), a mixer (17), an amplifier (20), a receiving- transmitting parabolic mirror antenna (19) with a feeding element, a laser target designator (25), a first and a second video cameras (23, 10 24), a picture monitor (27), a frequency modulator (15), a power divider (16), a circulator (18), an analog-to-digital converter (21), a synchronizer (26), a calculator (22), radio absorbing elements (30), thus output of the microwave generator (14) is connected to the input of the power 15 divider (16) which first output is connected to the first input of the mixer (17), and the second output is connected to the first arm of the circulator (18) which second arm is connected to the first input of the receiving-transmitting antenna (19), and the third arm is connected to the second 20 input of the mixer (17) which output is connected to the amplifier (20) which output is connected to the first input of the analogto-digital converter (21) which output is connected to the first input of the calculator (22) to which second and third inputs accordingly outputs of the 25 first and the second video cameras (23, 24) are connected, the first output of the calculator (22) is connected to the input of the first video camera (23), the second output is connected to the input of the second video camera (24), the third output is connected with the input of the laser 30 target designator (25), the fourth output is connected with the input of the synchronizer (26), the fifth output is connected with the picture monitor (27), the first output of the synchronizer (26) is connected to the second input of the analog-to- digital converter (21), and the second

output is connected to the input of the frequency modulator (15) which output is connected to the input of the microwave generator (14), the receiving-transmitting antenna (19) is installed on the portable rack and is fixed 5 with possibility of displacement on height, angle of elevation and azimuth, thus the receiving-transmitting antenna (19), the laser target designator (25) and the first video camera (23) are rigidly connected therebetween and their optic axes are adjusted, and the second video 10 camera (24) is installed so, that its optic axis is directed on the tested object and is perpendicular to the optic axis of the receivingtransmitting antenna (19), characterized in that, the feeding element of the receiving-transmitting parabolic mirror antenna (19) is 15 provided with a device.for reciprocating movement thereof coaxial to the optic axis of the antenna, and a control block of displacement of the feeding element is incorporated into calculator (22), which output provides the sixth output of the calculator (22) and is connected 20 to the input of the device for displacement of the feeding element being second input of the receiving-transmitting antenna (19), and the radio absorbing elements t30) are formed as flexible mats, rugs, curtains, dome- and cone-

shaped caps, with an electromagnetic waves reflecting 25 shield installed on the surfaces thereof, for example, a metal mesh, sequentially covered by layers of the radio absorbing material including synthetic adhesive <<Elaton>> on the basis of latex as polymeric binder and powdery ferrite or carbonyl iron as a magnetic filler at components ratio, 30 % by mass: synthetic adhesive <<Elaton>> on the basis of latex 80-20, powdery ferrite or carbonyl iron 20-80, thus the number of layers of the radio absorbing material is determined by the required value of absorption coefficient

of the radio absorbing coating according to the following relation Hi = Ko À N. where K: is the required absorption coefficient of the EMW 5 radio absorbing coating, To - empirical EMS absorption coefficient taking into account the relation of components of the applied radio absorbing material and technological requirements of the coating of this material; 10 N number of layers of the radio absorbing material.