GB2280735A

GB2280735A - Method of screening static or moving targets

Info

Publication number: GB2280735A
Application number: GB8803030A
Authority: GB
Inventors: Juergen Burbach; Josef Schneider; Johannes Grundler; Guenter Hoff
Original assignee: Buck Chemisch Technische Werke GmbH and Co
Current assignee: Buck Chemisch Technische Werke GmbH and Co
Priority date: 1987-02-19
Filing date: 1988-02-10
Publication date: 1995-02-08
Anticipated expiration: 2008-02-10
Also published as: GB8803030D0; FR2705168B1; FR2705168A1; DE3800521C1; GB2280735B

Description

2280735 6 METHOD OF SCREENING STATIC OR MOVING TARGETS The subject of the

invention is a method of screening static or moving targets, particularly military targets, from location.by means of an electro-magnetic radiation which lies within the range of wavelengths from 1 mm to 1 m, by the production and arrangement, known per se. of a gaseous. nebulous or liquid screen over the target, round the target or on the targetg which screen at least partially absorbs the electromagnetic radiation emitted from a radar detector to locate the target.

The present-day camouflaging and screening of static or moving targets, such as military targets above all, is based not only on constructive measures on the particular object, such as the use of electrically nonconducting materials or avoiding corners, but also on the use of socalled window. namely metallic or electrically conducting foils, flakes or fibres., which are so distributed, by suitable means, in the air above the particular target to form a cloud that as a result, the target is screened from the incident radar radiation. Such a window curtain, 1 however. also marks the target at the same time with an extensive powerful signal which originates from the window acting as tuned aerials or wide-band aerials. Thus in this case, the particular detector can always recognize, by the radar beam reflected from the window curtain, that an object to be protected is being camouflaged. Further clouds of window leading away from the target therefore have to be continuously formed as new dummy targets in order to deflect the radar location from the actual target. In addition, projectiles or rockets equipped with radar homing heads can locate the target afresh after flying through the particular cloud of window and finally also hit it with the greatest probability. With the modern, intelligent missiles or rockets guided in the final phases, the camouflaging or screening of static or moving targets by conventional means is becoming increasingly ineffective or even dang erous for the target.

It is therefore the object of the invention to provide a method of camouflaging static or moving targets, particularly military targets. from location by an electromagnetic radiation in the radar wave band (millimetre to metre wave band), whereby the target can be so screened, by forming suitable screens such as clouds of gas or clouds of mist inter alia, that as little radar radiation as possible or none at all.'of the incident wavelength, is reflected in the direction of incidence. Thus the screen should dampen, namely absorb, the incident radar radiation as far as possible so that practically no location of the target is possible. Thus it is intended, by this means, to replace the conventional camouflaging of the target by means of clouds of window by a completely new principle of screening which cannot be detected for location by electromagnetic radiation in the radar wave band and is thus invisible. Devices equipped with radar homing heads or with combat radar should therefore no longer be able to detect any target at all for lack of any reflection, which can be evaluated from the point of view of detection, from such a screen.

In the method of the type mentioned at the beginning, the above problem is now solved, according to the invention, in that in order to produce the screen, gaseous and/or liquid inorganic and/or organic-chemical compounds are used which a) as a result of the excitation of molecular rotation absorb a monochromatic electromagnetic radiation from the wave band from 1 mm to I m and then radiate it in the form of a diffuse polychromatic electromagnetic radiation and b) are composed of at least three non-linearly arranged atoms per molecule and/or c) have a quasi-continuous rotational absorption spectrum and/or - 4- d) have a dipole- moment of 0.1 to 10 Debye units, preferably at least about 2 Debye units and/or e) have a moment of inertia of 15 x 10-40 to 1000 x 10-40 g - cm 2 9 and, in the case of gaseous compounds, those compounds are used which ensure a damping of the incident intensity of at least 5 dB/m at normal pressure and room temperature.

Thus the method according to the invention is based on recognition of the fact that in order to form the screen, which is, for example a cloud of gas or a cloud of mist of the particular gaseous or liquid chemical compound to be used, over the target or round the target, a multicavity areal foil member or sponge in which the particular gaseous or liquid chemical oompound is disposed, or a protective layer in the form of an emulsion in which the particular liquid chemical compound or possibly also a gaseous chemical compound is included and which can, for example be disposed on the particular target in the form of a coating, a system is used which absorbs as completely as possible the monochromatic electromagnetic radiation emitted in order to home on the target and converts it into a diffuse polychromatic electromagnetic radiation so that neither the screen nor the object to be protected thereby can be located by radar.

Thus, in the method according to the invention, any gaseous and/or liquid inorganic and/or organic S_ compounds which have the capacity first to convert the energy of monochromatic radio waves and microwaves in the range of radar wavelengths into the energy of molecular rotation and then to radiate it in the form of diffuse polychromatic electromagnetic radiation are used as chemical compounds to form the particular screen.

The compounds to be used according to the invention are composed of at least three nonlinearly arranged atoms per molecule as a result of which all three principal moments of inertia of the particular molecule differ from zero and have a quasi-continuous rotational absorption spectrum. They have a dipole moment of the order of magnitude of 1 Debyeunitg namely in the range from, in general, 0.1 to 10 Debye units, 'the lower limiting value for the dipole moment of these compounds preferably being at least about 2 Debye units. Furthermore. the compounds suitable for use in the method according to the invention have a moment of inertia from 15 x 10-40 to 1000 X 10-40 2 g - em. Finally, when the compounds are gaseous under the conditions of use, according to the invention, preferably only those compounds are used which ensure a damping of the incident intensity of at least 5 dB/m at normal pressure and room temperature since otherwise the thickness of the screen to be.formed_would have to reach dimensions which could only be realized technically with difficulty.

6 Compounds with the features given above have, at a constant temperature, always an absorption maximum of a specific microwavelength and with a constant wavelength at a specific temperature, an absorption maximum. The compounds to be used according to the invention are therefore selected depending on the wavelength of the monochromatic electromagnetic radiation to be absorbed so that they absorb particularly strongly with a specific radar wavelength determined by the radar transmitter and at a specific temperature of use.

Depending on the electromagnetic radiation emitted to locate the particular object, mixtures of a plurality erent chemical compounds are preferably also used of difL to form the particular screen, which mixtures are selected depending on the wavelengths of a plurality of different monochromatic electromagnetic radiations to be absorbed. By this means,-mixtures of different compounds can thus be used and be so matched that these mixtures absorb particularly -strongly with a plurality of radar wavelengths and at various temperatures.

If clouds of gas and/or clouds of mist are preferably formed as screens by the method according to the invention, the particular preferably gaseous and/or liquid compounds used should not react chemically with atmospheric moisture under the conditions of use since such chemical reactions can alter the particular absorption behaviour in such a manner as to make it more difficult.

4--- In principle, all chemical compounds which satisfy the features given above can be used for the formation of suitable screens for the method according to the invention. Gaseous chemical compounds are usually preferred for the formation of gaseous screens. Screens in the form of mist can also be produced from liquid chemical compounds by appropriate finely-divided spraying and liquid chemical compounds are naturally used above all for the formation of liquid screens.

Asymmetrical low-molecular carbon halides or halogenated hydrocarbons are preferably used for the production of screens and may be used in liquid form or preferably in gaseous form. These include asymmetrical nowmolecular aliphatic, cycloaliphatic or aromatic chlorofluorocarbons or chlorofluorohydrocarbons which may possibly also contain bromine atoms, preferably in a minor proportion and which are either liquids or preferably gases. Such compounds are obtainable commercially under the names Frigene or Freone for example.

honochlorethane, 1,1-difluoroethane, 2-chlorine-1,1,1 trifluoroethane and 1-chlorine-1,1-difluoroethane have proved particularly suitable as halogenated hydrocarbons since these ensure a damping of radar radiation with a wavelength of about 3.2 mm of successively 10,2, 189 28 and 30 dB/m at normal pressure and room temperature. In addition, these halogenated hydrocarbons are also gaseous.

8 Further particularly suitable halogenated hydrocarbons and also carbon halides are 1,1-dichloroethylene, dibromodifluoromethane, 2-chloropropane, 2,-chloro-1,1,1-trifluoroethane, 1,-.1,2-trichlorotrifluoroethane and trichlorofluoromethane which, for example, ensure a damping of radar radiation with a wavelength of about 3,2 mm of successively 45, 29, 27, 19, 15 and 12 dB/5 mm layer thickness at normal pressure and room temperature and are liquids.

The screens needed for the application of the method according to the invention may be any gaseous, nebulous or liquid substances which are disposed over the target, round the target or on the target. The steps for forming those screens which are based on the chemical compounds to be selected according to the invention, lie within the scope of the usual expert ability. Thus any known methods and apparatuses may be used for this, whereby clouds of gas or clouds of mist can be produced from the chemical compounds to be used according to the invention, at the particular place where they are to be used. As a result of the subsequent greater ease of distribution and the associated great reduction in volume of the equipment necessary for the filling, reception and subsequent distribution of the particular chemical compound, gaseous chemical compounds are best introduced under pressure into cylinders, bombs, grenades or other suitable devices so that they are present therein in the liquid state.

q Liquid chemical compounds can naturally likewise be introduced into such devices but here no pressure is necessary for their liquefaction. Pressure or other suitable aids are needed here, however, in order to distribute the liquids to form the desired mist or the desired cloud of gas over the target area or round the target area at the particular place where they are used. The selection and development of devices which are suitable for the production of suitable forms of application of gaseous or liquid chemical compounds and for forming corresponding screens likewise lie within the scope of the usual expert ability.

In order to screen static or moving targets, particularly military targets, from location by an electromagnetic radiation in the radar wave band, instead of forming clouds of gas or clouds of mist, protective devices may also be used wherein the particular gaseous or, because of the otherwise excessively large volume necessary, preferably the particular liquid chemical compound is included in any substances or materials in the form of which such protections can be disposed round the target and/or on the target. Multicavity areal foil members, the cavities in which contain the particular chemical compound, are suitable for this for example. Examples of such foil members are air-bed-like structures or foil members comprising a series of knop-like cavities such as are used inter alia for the packaging of fragile and sensitive (0 articles. Furthermore, the particular liquid chemical compound which is suitable according to the invention and, with restrictions, also a gaseous compound, can be incorporated in carrier substances which protect them from evaporation, forming emulsion-like pastes which can then be disposed on the particular target for example in the form of protective layers or protective coatings. Finally. liquid chemical compounds in particular and, with restrictions, also gaseous chemical compounds. can be included in spongelike or cage,-shaped formations and be used in this form. All such members may, if necessary. also be provided with a protective coating in order to prevent unwanted evaporation of the particular chemical compound.

Thus the practical application of the method according to the invention, namely the production of appropriate screens on the basis of the chemical compounds to be selected according to the invention, does not involve any problems for the expert and all that is essential according to the invention is that the corresponding screens are formed by following the teaching given herein, namely being based on chemical compounds in liquid or preferably gaseous form which satisfy the features given in detail.

Finding out chemical compounds which have a radarscreening effect for specific radar wavelengths and at specific temperatures of use and can therefore be used for the method according to the invention, does not involve any fundamental difficulties for the expert either, particularly with reference to the data and statements given above. All asymmetrically built-up chemical compounds actually have a dipole moment and fundamentally therefore can absorb radio waves or microwaves or convert them into diffuse polychromatic electromagnetic radiation, although the quantitative differeness in the absorption capacity may be fairly great. It is therefore only possible to determine purely empirically with which radar wavelengths and at what temperatures the liquid or gaseous compounds, which are fundamentally suitable for absorption. absorb particularly strongly. Above all, those chemical substances the molecules of which consist of at least three atoms should be Included in the narrower selection since such molecules, in contrast to diatomic molecules, frequently have no lined. rotational absorption spectrum but have a quasicontinuous rotational absorption spectrum. In the case of spectra with lines, the radar wavelength incident for the location might actually come in the gap between two absorption lines.

What is important for suitability for the method according to-the invention is that the particular chemical compounds are preferably gaseous or liquid substances since in gases or also in liquids with a low packing density of the molecules, the molecules can generally execute free or restricted rotation which is essential for the excitation (L, of molecular rotation needed for the method according to the invention. The atoms or molecules of solids, on the other hand, cannot execute any rotation so that their use is necessarily ruled out for the method according to the invention.

In the search for compounds which absorb particularly strongly with certain wavelengths and at certain temperatures, it must be borne in mind that the wavelength at which a certain kind of molecule has an absorption maximum at a fixed temperature increases with the moment of inertia or the moments of inertia of the molecule.At elevated temperatures, the maximum is shifted towards shorter wavelengths.

The radar-absorbing compounds to be used for the method according to the invention may also, in principle, be mixed with other compounds provided they do not enter into any chemical reactions with these other compounds-, as for example with atmospheric humidity, since such reactions may alter the absorption behaviour adversely. R.egard must be paid to the fact that with pure compounds and also if the radarabsorbing compounds which are suitable according to the invention are diluted with other compounds which do not react chemically, the damping of the radar waves, measured in decibels per metre (dB/m) is proportional to the amount of radarabsorbing COMDound present in the unit of volume. The higher the damping of a compound is, the smaller the amount of it which is needed for the screening and hence for the protection of the particular target. In the wave band around 3.2 mm, which is particularly important militarily, or at frequencies around 94 Gc/s used for preference in radar homing heads, and at temperatures which lie in the range of + 300C about room temperaturet certain gaseous asymmetrical low-molecular carbon halides or halogenated hydrocarbons which can be selected from the group of Frigenes or Freons obtainable commercially, have particularly high damping values. The damping values which can be seen from the following Table i were found for a series of such gaseous compounds, among which the preferred substances have already been mentioned, at normal pressure and room temperature in the wave band just mentioned, the damping value of air, which is zero, likewise being given for comparison: Table I Serial No. Compound Damping in dB/m 1 CC12 2 -3.0 2 CBrClF 2 - 4.0 3 CC1 P 3 ---0.4 4 CBr P 3 OP4 (+ 1.2) 6 OF 3-0p2C1 - 3.2 7 OH 3-CH201 - 10.2 8 OF 3-C]E[2O1 - 28 9 OR 3 01 - 3.2 CH 3-CP2C1 - 30 11 CEP 2-CH3 - 18 12 CC1F2-CO1F2 - 3.4 13 CHC1P - 2 14 CHP 3 - 1.8 air 0 It should be noted in connection with the said damping values that a damping of 30 dB/m for example means that the intensity of the radar waves emitted from the transmitter is weakened by a layer of the gas I metre thick, on the way transmitter-object-receiver, altogether by the factor 10 6 in comparison with the intensity which would be recorded by the.-radar receiver without this layer of gas.

The damping values which can be seen from the following Table II were found for various liquid compounds which are suitable according to the invention and have likewise been mentioned already, at normal pressure and room temperature in the wave band around 3.2 mm which is particularly important militarily, for frequencies around 94 Gc/s and at temperatures which are in the range of + 300C about room temperature:

Table II

Serial No. Compound Damping in dB/5 mm H 20C12 - 45 16 0Br2 - 29 17 (CH 3)20Hel - 27 18 F 3 O-CH2C1 - 19 19 012PC-OC1P2 - 15 CC1 3 F - 12 air 0 Apart from their comparatively high or even extremely high damping values, the compounds from the group of Frigenes or Preons, to be used for preference in the method according to the invention, also have the advantage that they do not react with atmospheric humidity, are incombustible and non-toxic, are easy to handle and can be liquefied if necessary and in addition are available as commercial products.

In general, gaseous radar-absorbing compounds in particular and, with certain restrictions, also liquid ones have the characteristic that they can be blown out to form a cloud of gas serving as a screen or be sprayed to form a cloud of mist round and over the object to be protected, within a very short time and so during the approach of a missile equipped with a homing head.

The steps necessary for carrying out the method according to the Invention and for the selection of the particular chemical compounds which are needed in the course of this to form the desired screen can easily be determined by the expert with reference to the above statements so that further explanation is superfluous.

(G

Claims

Patent Claims

BU 24/28 1. A method of screening static or moving targets, particularly military targets, from location by an electromagnetic radiation which lies in the wave band from 1 mm to 1 m. by the production and arrangement, known per se. of a gaseous, nebulous or liquid screen over the target, round the target or on the target, which screen at least partially absorbs the electromagnetic radiation emitted by a radar detector to locate the target, characterised in that, in order to produce the screen, gaseous and/or liquid inorganic and/or organic chemical compounds are used which a) as a result of the e=itation of molecular rotation, absorb a monochromatic electromagnetic radiation from the wave band from 1 mm to 1 m and then radiate it in the form of a diffuse polychromatic electromagnetic radiation and a b) are composed of at least tree non-linearly arranged atoms per molecule and/or c) have a quasi-continuous rotational absorption spectrum and/or d) have a dipole moment of 0.1 to 10 Debye units, preferably at least about 2 Debye units and/or k 1 - e) have a moment of inertia from 15 x 10 -40 to 1000 X 10-40 g. CE2 1 and, in the case of gaseous compounds, those compounds are used which ensure a damping of the incident intensity of at least 5 dB/m at normal pressure and room temperature.
2. A method according to Claim 1, characterised in that the chemical compounds are selected depending on the wavelength of the monochromatic electromagnetic radiation to be absorbed.
3. JI method according to Claim 21 characterised in that mixtures of a plurality of different chemical compounds are used, which are selected depending on the wavelengths of a plurality of different monochromatic electromagnetic radiations to be absorbed.
4. A method according to any one of the preceding Claims. characterised in that clouds of gas and/or clouds of mist are produced as screens and for this purpose. chemical compounds are used which do not react chemically with atmospheric humidity.
5. A method according to any one of the preceding Claims, characterised in that-asymmetrical low-molecular carbon halides or halogenated hydrocarbons are used as chemical compounds.
6. A method according to Claim 5, characterised in that asymmetrical lowmolecular ali.-lhatic, cycloaliphatic or aromatic chlorofluorocarbons or chlorofluorohydrocarbons, which may possibly also contain bromine atoms, are used as chemical compounds.
?. A method according to Claim 5 or 6, characterised in that monochloroethane and/or 1,1-difluoroethane and/or 2-chloro-1,1,1trifluoroethane and/or 1-chloro-1,1-difluoroethane are used as chemical compounds.
8. A method according to Claim 5501 or 6, characterised in that 1,1dichloroethylene and/or dibromodifluoromethane and/or 2-chloropropane and/or 2-chloro-1,1,1-trifluoroethane and/or 1,1,2trichlorotrifluoroethane and/or trichlorofluoromethane are used as chemical compounds.
9. A method according to any- one of the -preceding Claims5 characterised in that clouds of gas, clouds of mist, protective covers or protective layers are produced as screens.

9. A method according to any one of the preceding j Claims, characterised in that clouds of gas, clouds of mist, protective covers or protective layers are produced as screens.

-1 M Amendments to the claims have been filed as follows Amendments to the claims have been filed as follows i. A method of screening static or moving targets, particularly military targets, from location by an electromagnetic radiation which lies in the wave band from 1 mm to 1 m, by the production and arrangement, known per se 5 of a gaseous, nebulous or liquid screen over the target, round the target or on the target, which screen at least partially absorbs the electromagnetic radiation emitted by a radar detector to locate the target, characterised Id' screen i_ p U in that sa comprises a com o nd or m-ij'ure of compounds selected from inorganic and which a) as a result of absorb a monochromatic organic chemical compounds the e=. itation of molecular rota-tr-ion,) electromagnetic radiation from the wave band from 1 mm to 1 m and then radiate it in the form of a diffuse polychromatic electromagnetic radiation and b) are composed of at least three non-linearly arranged atoms per molecule and.,-.

c) have a quasi-contirLuOus rotational absorption spectrum and'- cl) have a dipole moment of 0.1 to 10 Debye units, preferably at least about 2 Debye units andi 210 e) have a moment of inertia from 15 x 10-40 to 1000 x 10-40 g. cm 2 ' and, wherein where the screen is gaseous, said compound or mixture of compounds exhibits a damping of the incident intensity of at least 5dB/m at normal pressure and room temperature.

2. A method according to Claim 1, characterised in that the chemical compound or mixture of chemical compounds is selected depending on the wavelength of the monochromatic electromagnetic radiation to be absorbed.

3. A method according to Claim 2, characterised in that a mixture of a plurality of different chemical compounds is used the compounds being selected depending on the wavelengths of a plurality of different monochromatic electromagnetic radiations to be absorbed.

4. A method according to any one of the preceding claims, characterised in that clouds of gas and/or clouds of mist are produced as screens and for this purpose, the chemical compound or mixture of chemical compounds used does not react chemically with atmospheric humidity.

5. A method according to any one of the preceding claims, characterised in that assymmetrical low-molecular carbon halides and/or halogenated hydrocarbons are used as chemical compounds.

6. A method accordinE5 to Claim 5. characterised in A A that asymmetrical low-molecular ali-chatic, c7cloaliphatic and/or aromatic chlorofluorocarbons and/or chlorofluorohydrocarbons, which may possibly also contain bromine atoms, are used as chemical compounds.

7. A method according to Claim 5 or 6, characterised in that monochloroethane and/or 1,1-difluoroethane and/or 2-chloro-1,1,1trifluoroethane and/or I-chloro-1,1-difluoroethane are used as chemical compounds.

8. A method according to Claim 5 or 6, characterised in that i iaichloroethylene and/or dibromodifluoromethane and/or 2-chloropropane and/or 2-chloro-1,1,1-trifluoroethane and/or 1,1,2trichlorotriflioroethare and/or trichlorofluoromethane are used as chemical comDounds.