EP0912875B1 - Camouflage structure - Google Patents

Abstract

To ensure that a camouflage structure will not lose its effectiveness even in changing temperatures (day/night, sunshine/clouds) when protecting against reconnaissance in the IR range, the camouflage structure features varying emissivity tendencies in the atmospheric windows II (3-5 um) and III (8-14 um). In other words, the emissivity in the IR range is not constant and at a certain level, but it has an increasing or decreasing tendency in at least one selected spectral range.

Description

Technical field

The invention relates to a tam structure according to the preamble of claim 1 and a Camouflage net with such a tam structure. A camouflage structure of this kind is e.g. from the FR 2,716,038 known.

State of the art

The most comprehensive camouflage of objects, systems and people is a central aspect of every military countermeasure. It works therefore, the clarification in the visible, in the (near and far) IR range (IR = infrared) and preferably also to prevent or at least complicate it in the radar range. Camouflage layers that perform this task more or less well are based on the principle known for a long time.

In order to be able to achieve a good camouflage coating, the camouflage effect must naturally extend to the entire range of wavelengths that can be detected by sensors. In the infrared there is in particular the atmospheric window II (3 - 5 µm) and III (8 - 14 µm) covering spectral range. (see e.g. Electro-Optics Handbook, Technical Series EOH-11, RCA Corporation, 1974, p. 91, paragraph 2).

GB-565.238 already has a tam coating with an effective broadband effect known from the visible to at least in the IR spectral range. The camouflage effect is achieved by having an upper coating; which for the camouflage in the visible Area is responsible for making infrared radiation transparent, and that an underlying primer reflects the infrared radiation in the desired manner.

The known coating thus consists of a primer and one applied thereon Camouflage paint (pigment layer), which in the visible area as the natural Background (for example chlorophyll) reflected. The primer is in the area reflecting the terrestrial thermal radiation and the top layer for even this spectral range transparent. The pigment layer must therefore be a binder use the one in the spectral ranges of the atmospheric windows II and III has good transparency.

DE-PS 977 526 discloses camouflage in visible light, in the infrared region and is effective in radar targeting. A camouflage net is used for camouflage in the radar area provided with an electrically conductive sub-layer (primer). It can either a metal paint (metallic paint) or a glued one Trade metal foil. In any case, the primer is designed so that it is relevant Wavelength range is well reflective. Consequently, the homogeneous reflects metallic primer (due to the low surface resistance of at most a few ohms) in the radar range. On the primer are scattering and absorbent layers applied. The top layer is preferred applied a camouflage color effective in the visible range in a manner known per se.

Another camouflage coating is known from DE 725 253. For an optimal Camouflage, which extends over both the visible and the long-wave range, will underlay the visible camouflage coating with a long wave Area reflective layer proposed (see e.g. page 2, lines 19 - 32), which is made of a metal foil (see page 2, example 4) or a metallic color (see Page 2, lines 33-43). An aluminum foil has (since it has a homogeneous metallic coating) has a very good conductivity, i.e. a strong reflective Effect for electromagnetic radiation in the radar range. The well-known topping is So designed so that it automatically reflects in the radar range.

To improve camouflage in the radar range, foils with slits can be used (see e.g. US 3.069.796 or DE 1.088.843).

About the from the above State of the art technical principles came also the later attempts to realize an improved camouflage (see e.g. EP 0 058 210, Pusch) not significantly, so that there is still a need for reconnaissance-resistant disguise exists.

The FR 2.716.038 deals with a camouflage, which is a material with an intrinsic has selective emissivity. The goal is to keep the emissions of the covered machine in significantly disruptive. The material used has the effect that the Maximum of the emission is shifted into a band which has a low atmospheric Transmission has. The material of high selective emissivity is in a solid Low emissivity material embedded.

GB 1,605,131 describes a camouflage consisting of a reflective Background and a color, the pigments camouflaging in the visible and in the near infrared and their binders in atmospheric windows II and III have an emissivity of has less than 90%. The emissivity of the surface is determined by using different layers of color structured in an irregular pattern.

GB 1,605,187 and DE 27 59 657 A1 have the object of a camouflage net which varies the emissivity of the camouflage coating across the surface, e.g. between 50% and 90% in atmospheric window II and between 60% and 95% in atmospheric window III.

From DE 36 14 017 A1 camouflage results, which is based on interference effects. The thickness of the camouflage layer is chosen so that the heat radiation in the II. And III. Window is reduced. It is also pointed out that average emissivities of 30-70% are preferred over extreme values. According to the curves shown in Fig. 2 the reflectance varies.

EP 0 198 283 A2 relates to a camouflage material that can be used in both atmospheric windows II and III as well as in the radar range is effective. In the The emissivity is specified as in the above mentioned atmospheric windows British Pusch patents mentioned. The camouflage effect is said to be in the radar range can be achieved by applying patterns or rectangles whose Dimension smaller than half a wavelength of the largest expected radar wavelength is. The result is a function of the wavelength of the radar radiation Reflection.

Presentation of the invention

The object of the invention is to provide a camouflage structure that also with changing Temperature conditions (day / night, sunshine / cloud cover) their effectiveness not lost to reconnaissance in the IR area.

The solution to the problem is defined by the features of claim 1.

It is noteworthy that the camouflage structure in atmospheric windows II and III unites each tends to have a different course of emissivity. In other words: The emissivity in the IR range is not simply constant at a certain level, but has at least one spectral range with increasing wavelength falling trend, with the atmospheric windows II and III a special one Importance.

Presentation of the invention

With the camouflage structure according to the invention, the thermal behavior (i.e. the Blackbody spectrum) imitated the soil, both when exposed to sunlight as well as cloudy weather. There is a major difference in this regard Camouflage structures, which show the temperature (or the IR spectrum) of the air layer close to the ground accept. Namely when the sky is clear is the temperature curve of the soil is significantly different from that of the air. Add to that the The fact that the temperature distribution of the air is much narrower than that of the floor. The adaptation to the air temperature is therefore considered as a whole do not lead to a similarly good camouflage effect as the adaptation to the floor temperature.

An important finding for the camouflage according to the invention is that the Zenith temperature is a significant parameter for the floor temperature or for its Is imitation. The quality of camouflage depends on how the zenith temperature is reflected becomes. It is especially the spectral properties of the atmosphere and the Solar radiation to take into account. However, these are not constant in the IR range. but depending on the wavelength. So the basic finding is that a camouflage structure has to be spectrally adapted, with the conditions being appropriately in the tendency to take into account adapted emissivity, if the camouflage effect should go beyond the known.

Trials have shown that it is special; is advantageous if the course of the Emissivity in the atmospheric window II is falling. The emissivity is So chosen so that - within the window II mentioned - for small wavelengths is higher than for large ones. The beneficial effect of this measure depends especially because the blackbody spectrum of the sun in the Range of 3 - 5 µm drops by about a decade. However, it is not necessary that the emissivity of the camouflage structure decreases to the same extent. It is enough if it this trend follows.

Good results can be achieved if the emissivity is in the upper wavelength range of the atmospheric window II at least 25%, in particular approximately Is 50% lower than in its lower wavelength range. That way an undesirable (not corresponding to the natural or real background) The gloss effect of the camouflage coating can be minimized.

In the atmospheric window III (especially in the range of 8-14 µm) the spectral emissivity may be slightly reduced. In the tendency their course can be constant his. In this sense, the value of the relative emissivity can range between Move 0.7 - 0.9 (e.g. by 0.8).

At night, the camouflage effect may be adversely affected by the tendency low zenith temperature is reflected too strongly, which in the reconnaissance as "black hole" becomes recognizable.

In the wavelength range between windows II and III (where the atmosphere is for IR radiation is impervious) the emissivity should be as high as possible. Advantageously it is higher than in atmospheric window III.

The camouflage structure according to the invention has at least two layers. The lower one is reflective in the IR range. The upper one mainly consists of a material which is transparent in the atmospheric window II, but not in the window III.

The top layer is e.g. a pigment coating, which is used for camouflage in the visible Area is responsible. The above-mentioned, transparent only in spectral areas Material of the top layer is then essentially by the (the color pigments including) binder (carrier or matrix made of plastic).

The lower layer (primer) mentioned is of a metallic type. As a preferred example be called aluminum. The primer can be as a metal foil or as a vapor-deposited or sprayed-on layer can be formed on a carrier material.

According to a particularly preferred embodiment, that of the upper layer facing interface of the primer structured three-dimensionally, so that the Emissivity of the camouflage structure in the atmospheric window II with increasing wavelength decreases. The three-dimensional structure mentioned can be e.g. generate by that a carrier formed from a fiber material (fabric) has a metallic coating becomes. But it is also possible to use a metal foil (or one coated with metal Film) with a fine embossing of the surface. Another Possibility exists e.g. in a brushed aluminum sheet as an underlayer use.

It can also be advantageous to store scattering bodies in the camouflage structure generate a diffuse scattering of the incident radiation in the range of 3 - 5 µm. In This area can be smooth metallic surfaces depending on the type of incident Radiation leads to strong unnatural reflections, so the camouflage can be clarified. Known matting agents can be used as scattering bodies serve with a suitable grain size.

In practice, multispectral camouflage is very often required. I.e. it is not enough to ensure the camouflage in the IR range, but at the same time there must be a radar camouflage be created. This allows good camouflage in the radar area achieve that on the one hand the resistance of the metallic coating is suitable is selected and, on the other hand, a three-dimensional shape of the camouflage area is given is.

The resistance in the radar range is to be dimensioned so that radar waves in a certain Extent will be absorbed. Practice shows that the (wavelength dependent) resistance is preferably in the range of 30-300 ohms. The resistance can be determined by the choice of the layer thickness, the material of the layer local breakthrough (holes) can be set. Instead of damping the electrical The magnetic field of the radar wave can also enter the field (e.g. by applying a magnetic layer).

In order to create a three-dimensional shape, a fabric or a Laminate a sheet cut (as known for example from US 3,069,796 or DE 1,088,843 is) be attached. This measure has also in the IR area a beneficial effect as it also helps to keep the zenith temperature in the different directions of observation is reflected.

From the following detailed description and the entirety of the claims there are further advantageous embodiments and combinations of features of the Invention.

Brief description of the drawings

Fig. 1

Eine schematische Darstellung einer Tarnstruktur mit einem Gewebe als Träger;

Fig. 2

eine schematische Darstellung einer Tarnstruktur in Form eines Laminats;

Fig. 3

eine schematische Darstellung eines erfindungsgemässen Verlaufes der spektralen Emissivität der Tarnstruktur.

The drawings used to explain the exemplary embodiment show:

Fig. 1

A schematic representation of a camouflage structure with a fabric as a carrier;

Fig. 2

a schematic representation of a camouflage structure in the form of a laminate;

Fig. 3

is a schematic representation of an inventive course of the spectral emissivity of the camouflage structure.

In principle, the same parts are provided with the same reference symbols in the figures.

Ways of Carrying Out the Invention

Fig. 1 shows the structure of the camouflage structure according to the invention in cross section. As a carrier a fiber fabric 1 is used. This is not only very robust and tearproof, but also has a three-dimensionally structured surface (in the micrometer range) 1.1. In principle, the surface is 1.1 by a variety of fine, more or less cylindrical fibers (made of polyester or the like) which are dense lie next to and on top of each other. This creates a three-dimensional quality, which in the manner described below for infrared radiation range from 3 - 5 µm can have a scattering effect.

The surface 1.1 is covered with a metal coating 2, which can be sprayed on, evaporated or possibly even spread on. According to a particularly preferred Embodiment not only serves to reflect (or scatter) infrared radiation, but also for camouflage in the radar area. The setting required for this Conductivity takes place on the one hand through the appropriate choice of material, on the other hand (and above all) by determining the layer thickness. The sheet resistance in the frequency range of radar waves is preferably in the range of a few a few to a few hundred ohms.

Because the (usually very thin) metal coating 2 on a carrier is applied with a three-dimensionally structured surface 1.1, it has on her Top 2.1 itself a corresponding structuring in the micrometer range.

At the top is a cover layer 3. Since this is in the visible wavelength range Should camouflage (in a known manner), it is designed as a pigment layer. Depending on the intended use of the camouflage, the color of the pigments is rather in the shade of gray or be in the green range.

The binder (decisive for the behavior of the top layer 3 in the infrared range) the pigment layer is in the sense of a preferred embodiment of the invention transparent for wavelengths of 3 - 5 µm (atmospheric window II), but not so for wavelengths from 8 - 14 µm (atmospheric window III).

The transparency of the top layer 3 can be adjusted by the choice of the layer thickness. Is the top layer 3 namely thin enough, then in the atmospheric window III in the end, nevertheless, a certain transparency (and consequently an emissivity at the desired height).

The camouflage structure according to the invention can also be formed by a laminate. On such is shown by way of example in FIG. 2. The bottom layer, which is not on one shown carrier can be applied or possibly the same as carrier material is a metal foil 4. It is covered with a cover layer 5, which is of the same design can be like that described with reference to FIG. 1.

To diffuse the incident infrared radiation to a desired extent scatter, are in the top layer 5 (or at the interface between metal foil 4 and Top layer 5) scattering body 6 embedded. These are particles whose size is at least in the range of the wavelength of interest (3 - 5 µm), so that it can develop a scattering effect. It can be advantageous if the statistical Particle size distribution is not too narrow (use of polydisperse matting agents).

The layer structure according to the invention is particularly suitable for camouflage nets. It These are fabric-like or foil-like tarpaulins, which cover the ones to be camouflaged Objects can be thrown. To have a good effect against radar reconnaissance To achieve these camouflage nets are preferably with a suitable leaf cut Mistake. When they are spread out, the ones cut out stand up Leaves open and develop a diffuse scattering effect in the radar range.

3 shows a representation of the quantity S = 1 - ρ ( ρ = reflexivity), which for gray bodies corresponds approximately to the relative emissivity (E _r ) for a camouflage structure according to the invention as a function of the wavelength ( λ ). Of interest at this point is only the 3-14 µm wavelength range, which includes atmospheric windows II and III.

At the lower end of window II (i.e. at 3 µm) the emissivity is slightly less than 1.0 (e.g. between 0.65 and 0.9).

The emissivity decreases with increasing wavelength. In the present example it drops to almost half of the original value, i.e. to 0.3 - 0.45. The steepness the waste lies e.g. at one octave per micron, especially around one Decade per micrometer. In Fig. 3 is a small in the range between 4 microns and 5 microns Plateau recognizable.

From 5 µm, a strong increase to a maximum level begins. This is preferable at least as high as the emissivity in the atmospheric window III. In the present In this case, the maximum is in the range of 0.85-1.0. The trend is Emissivity curve - after rising to the maximum - remains consistently high.

The emissivity should be reduced in the atmospheric window III. In the present example it ranges between 0.75 - 0.85. Also in this wavelength range the trend is constant (i.e. neither rising nor falling).

3 shows only one of many possibilities. Especially in the area between Windows II and III do not necessarily need emissivity to a maximum Level to rise. It can e.g. also slowly and more or less continuously rise to the level desired in window III. Because the atmosphere in the Range between 5 µm and 8 µm is not permeable, the course of the emissivity is in this wavelength range is not very critical for the quality of the camouflage effect.

In the atmospheric window III, a constant course is shown in FIG. 3, one However, a tendency falling or increasing with increasing wavelength is not excluded. Of course, the course in window II can also have a different tendency exhibit.

It goes without saying that a specific measurement curve of a camouflage structure according to the invention will fluctuate within certain limits. Smaller modulations will be cannot be avoided. This is not so important for the invention on. The spacious course is important, i.e. the trend of the curve.

Surface areas with different camouflage structures can be combined on a camouflage net be (in the manner of a patchwork arrangement). It should be noted that the Emissivity according to the invention not at a single point on the network, but instead only considered as a whole (i.e. taking into account a larger area) is fulfilled.

Although camouflage nets are the preferred application, it is not excluded that the camouflage structure according to the invention on the surface of a housing a technical device or a building.

In summary, it can be stated that the invention creates a camouflage structure which, due to the wavelength-dependent emissivity, is one of the tamper effect can be optimally adapted to specific circumstances.

Claims (12)

1. Camouflage structure with a layer (2; 4) reflecting in the IR range with an emissivity which has a different course in the atmospheric windows II (3-5 µm) and III (8-14 µm), characterized in that the emissivity in the atmospheric window II has a falling tendency with increasing wave length.
2. Camouflage structure according to claim 1, characterized in that the emissivity in atmospheric window II (3-5 µm) drops by at least 25%, especially by 50% or more.
3. Camouflage Structure according to one of claims 1 to 2, characterized in that the emissivity in atmospheric window III (8-14 µm) tends to be constant and lies in a range from 0.7 to 0.9.
4. Camouflage structure according to one of claims 1 to 3, characterized in that the emissivity in the wave length range between atmosphcric windows II and III is at least as high as in atmospheric window III (8-14 µm).
5. Camouflage structure according to one of claims 1 to 4, characterized in that, above the first layer (2; 4), which reflects in the IR range, an upper, second layer (3; 5) is provided which basically consists of a material which is transparent in atmospheric window II (3-5 µm), but not in atmospheric window III (8-14 µm).
6. Camouflage structure according to one of claims 1 to 5, characterized in that the first layer (2; 4) reflecting in the IR range basically consists of metal, especially of aluminum.
7. Camouflage structure according to one of claims 1 to 6, characterized in that a upper boundary layer of the reflecting first layer (2; 4) is structured in three dimensions so that the emissivity in the atmospheric window II (3-5 µm) diminishes with increasing wave length.
8. Camouflage structure according to one of claims 5 to 7, characterized in that scattering elements (6) are embedded in the upper layer, or between the upper and the lower layers, in order to bring about a diffuse scattering of incident infrared radiation, especially in the 3-5 µm range.
9. Camouflage structure according to one of claims 1 to 8, characterized in that it has a pigment layer for camouflage in the visible range as a cover layer (3; 5).
10. Camouflage network with a camouflage structure with a layer (2; 4) reflecting in the IR range with an emissivity which has a different course in atmospheric windows II (3-5 µm) and III (8-14 µm), characterized in that the emissivity in atmospheric window II has a falling tendency with increasing wave length.
11. Camouflage network according to 10, characterized in that it is constructed as laminated or as a coated tissue.
12. Camouflage network according to one of claims 10 or 11, characterized in that it has a blade section for camouflage in the radar range.

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