FR2733311A1 - Fibre=optic camouflage system for vehicle or personnel - Google Patents

Abstract

The fibre optics network (1) has a grid of fibre optic cables (3) with a section having the sleeve removed and fed from an input point (2). Different infra-red bands are generated and radiated from one of the optical lines. The system measures the background radiance in the different infra-red band and sets the radiated levels to provide camouflage. The optical cables are embedded in a flexible outer section.

Description

SELF-ADAPTIVE CAMOUFLAGE DEVICE
The present invention relates to a self-adaptive camouflage device. It applies in particular to the protection of vehicles, men or fixed sites in battlefields against all types of threats and observation devices, whatever the weather conditions and the time of day or night .

 Faced with the various threats from the battlefields, vehicles, men and fixed sites must protect themselves. Several types of protection systems are known to provide protection by camouflage.

 In the field of visible wavelengths, it is known to use paints, nets, smoke bombs or active systems for example. Camouflage paints are deposited on the objects, for example a sand color for the desert and green or brown for the European landscapes. This protection is permanent, but only has the effect of reducing the contrast of the object in relation to the background. It therefore has reduced effectiveness.

 There are camouflage nets mainly used to camouflage stationary machines or fixed sites. Again, the effect is to decrease the contrast from the background. This protection therefore also has reduced effectiveness, and moreover it is not permanent.

 Another type of camouflage protection uses visible smoke bombs. It is mainly used to perform certain tactical maneuvers or to protect oneself from a near threat. This protection has a temporal nature, of a limited duration, and if it camouflages the object to be protected, it is particularly identifiable by the visible cloud that it creates.

 A certain number of active systems use the so-called "chameleon" effect which implements electrochromics, of the conductive polymer or liquid crystal type for example, and which consists in taking the color of the background on which the objects to be camouflaged are observed. This technique is similar to those used by certain animal species.

It is only effective in the visible domain.

In the infrared wavelength range, certain camouflage systems developed consist of multilayer structures of low emissivity. They are described in particular in patents
US 4,953,922 and US 5,077,101. The wide band infrared chameleon effect is more difficult to implement because it requires either heating the surface of the objects to be camouflaged, to increase their emissivity, or to cool it, to decrease their emissivity, and this without degrading the visible camouflage.

 None of the aforementioned solutions is entirely satisfactory in all the infrared and visible bands because the operational and meteorological conditions are variable, the sky can for example be cold or hot, the background cold or hot, and it can in particular whether or not there is sunshine.

 The object of the invention is to overcome the aforementioned drawbacks, in particular by making it possible to camouflage objects as a function of the environment in which they evolve.

 To this end, the invention relates to a device for camouflaging an object on a background with respect to an observer, characterized in that it comprises at least one network of optical fibers covering the object and diffusing waves whose wavelength depends on the bottom temperature and whose power depends on the background emittance, and a network control system.

 The main advantages of the invention are that it makes it possible to camouflage objects in all the observation bands which can currently be used, that it makes it possible to protect objects simultaneously in several observation directions associated with hot or cold bottoms, with in in this case the use of a cooling system for example, that it allows implementation on fixed or stationary systems without disturbing the operation of these systems, and that it allows modulation of the camouflage an object according to its movement on variable backgrounds.

Other characteristics and advantages of the invention will appear on reading the following description made with reference to the appended drawings which represent:
- Figures la and lb, an illustration of the principle of a device according to the invention by a possible embodiment;
- Figure 2, an example of assembly of optical fibers of a network line
FIG. 3, a block diagram of a first possible embodiment of a system for controlling a network of optical fibers;
- Figures 4a, 4b, 5 and 6, possible embodiments of the device according to the invention in panel;
- Figures 7, 8, 9 and 10, possible embodiments and examples of application of devices according to the invention;
- Figure 11, a block diagram of a second possible embodiment of a system for controlling a network of optical fibers.

 The figure illustrates it by a possible embodiment, the principle of a camouflage device according to the invention. The latter comprises a network 1 of optical fibers. This network 1 covers an object to be camouflaged with respect to an observer, the human eye or an infrared camera for example. The object is placed in front of a background which can be for example a landscape, the ground or the sky in particular. the background reflects a certain power per square meter called emittance and which depends in particular on the fourth power of its temperature and its emissivity. It also emits a wavelength directly proportional to its temperature. This wavelength can be in the visible range, in the near infrared range also called infrared band I and whose wavelengths go up to 2.7 pm approximately, from the more distant infrared range called infrared band II and whose wavelengths are up to about 5 pm, or from the most distant infrared range called infrared band III and whose lengths waves go up to around 12 pm.

 On the side of the observer, that is to say on the side opposite to the object which they cover, the optical fibers of the network 1 have their sheath cut so as to let diffuse the visible or infrared optical waves which they convey to through these sheath cuts, this diffusion being carried out towards the observer. Detectors, not shown, detect for example the background temperature and its emittance and supply this information, in the form of electrical signals for example, to a processing system which controls one or more laser sources connected to input 2 of the network 1 and supplying its optical fibers so that the waves circulating in these fibers have a wavelength corresponding to the bottom temperature and a power corresponding to its emittance. The wavelength can be in the visible or infrared range.

 The network 1 consists of one or more lines 3 unrolled linearly or intersecting to form a net for example.

 Each line contains one or more optical fibers. To be as efficient as possible, it is advantageous for the network to be able to broadcast wavelengths sweeping the widest possible range towards the observer, for example, the visible range and the infrared bands I, II and III. mentioned above, that is to say a domain whose wavelengths range from approximately 0.4 μm to 14 μm. Since a single optical fiber is not suitable for all these wavelengths, each line 3 of the network 1 can contain several optical fibers, each adapted to a well-defined frequency band, so as to scan the entire aforementioned field. For this, the association of the different frequency bands of each optical fiber is equal to this domain. For this purpose, each line 3 can contain, for example three optical fibers, a first dedicated to the visible and near infrared or infrared band I region, a second dedicated to the infrared band il and a third dedicated to the 'infrared band III.

 The maximum interval d between two adjacent lines 3 of the network 1 can for example be such that it is less than or equal to the resolution of an infrared camera located at a certain observation distance. For example, for a camera placed 1000 m from network 1, this interval can be around 10 cm. The network 1 can be a linear network at regular intervals or a crossed network for example.

 FIG. 1b, presents an enlarged view of an example of interlacing 4 in the case of a crossed network. Two branches of the network each composed of three optical fibers 5, 6, 7, 5 ', 6', 7 ', intersect at a weaving point 8 for example.

 FIG. 2 describes an example of assembly of optical fibers 21, 22, 23 of a line 3 of a network 1. Line 3 is seen in cross section, it contains three optical fibers. A first 21 is dedicated to the visible and near infrared, a second 22 is dedicated to 'infrared band II and a third 23 is dedicated to' infrared band II. The sheath 24 of each fiber is removed on a part of each of them, lengthwise, so as to cause a controlled leak of visible or infrared light. Arrows 25 illustrate the scattering of the optical waves towards the outside of the line 3. This scattering is directed towards observers of the object to be camouflaged.

 The sheath 24 could be entirely removed from each fiber, however this would not allow the light scattering to be oriented and would constitute a loss of energy, the scattering of light towards the object to be camouflaged being in particular not necessary.

 To be kept assembled, the optical fibers 21, 22, 23 are for example embedded in a flexible polymer material, constituting a coating 26, transparent for all the waves likely to be conveyed by these fibers. This material can for example be polyethylene, polypropylene or polystyrol-coacrylonitrile.

 The first optical fiber 21 is for example plastic, polymethyl methacrylate. The second optical fiber 22 is for example made of fluorinated glass, zirconite tretrafluoride or indium trifluoride. The third optical fiber 23 is for example made of tellium halide. These optical fibers 21, 22, 23 have for example a diameter of approximately 500 μm.

They are arranged, with the coating 26, on a support 27 for example. This support can be flexible or rigid, it is for example made of kapton, aluminum or steel. The coating 26 can be placed directly on an object to be camouflaged.

 FIG. 3 presents a block diagram of a possible embodiment of a system for controlling a network of optical fibers of a device according to the invention. It comprises means 31 for detecting the bottom in which the object to be camouflaged is located. These means 31 detect in particular the temperature or the color of the background as well as its emittance according to methods known to those skilled in the art. The detection means 31 supply processing means 32 with electronic signals, in voltage for example, representative of the elements of the background detected, that is to say its temperature or its color and its emittance. The processing means 32 are connected to control means 33 of laser sources 34, 35, 36. In the embodiment of FIG. 3, the device according to the invention comprises three laser sources, but it could however contain them more or less. The example of embodiment given is adapted in particular to the type of line presented in FIG. 2 containing three optical fibers dedicated to three different frequency bands, each laser source supplying an optical fiber of a line 3 of the network 1. For this purpose , they are connected to one or more lines 3 depending on whether the network 1 contains several lines or not. These connections are made for example by optical connectors not shown.

 Figures 4a and 4b show another example of a possible embodiment of a device according to the invention constituting a camouflage panel. Figure 4b is a sectional view of Figure 4a.

 An optical connector 41 for example connects the network 1 of optical fibers to laser sources such as those 34, 35, 36 shown in FIG. 3. The network 1 is for example made up of a single line 3 arranged in a serpentine. However the network 1 could be different, it could for example consist of crossed lines 3 as illustrated in FIG. 1. The network 1 for example is placed in a metallic formwork 42.

This is painted for example the color of the object to be protected, a vehicle in particular. The network 1 of optical fibers is for example disposed on a layer 43 having a reflecting metallic surface facing an observer relative to which the object is to be camouflaged. This reflecting surface 43 decreases, as the case may be, the contrast between the background on which the network 1 of optical fibers is disposed and that on which the object to be camouflaged is located, therefore decreases the difference in emittance between these backgrounds. This can in particular make it possible to reduce the power emitted by the optical fibers, and therefore to use lasers of lower power. The effect is further improved by using for example a surface 42 with variable emissivity, depending on the background in particular. Indeed, the reflection coefficient Re of a surface being given by the relation Re = e - where s represents the emissivity of this surface, the variation in emissivity therefore varies the reflection. Furthermore, the emittance of a given surface, representing the power emitted per square meter (W / m2) by this surface, is directly proportional to the emissivity, as shown by the following relation: R = r T4
R being the emittance of the surface retaining the constant of the black body
T being the temperature of the surface and being the emissivity of the surface.

 This emissivity could for example vary according to discrete or continuous values.

 A thermal insulator is for example placed between the metallized surface 43 and the bottom 45 of the formwork 42. This in particular prevents in certain cases that the heat of the object to be camouflaged, a vehicle for example, heats the network 1 of optical fibers which would emit then a radiation parasitizing the camouflaging effect The bottom 45 of the formwork 42 comprises for example a reflecting surface oriented towards the object to be camouflaged so as in particular to further reduce the radiation of the object towards the network of optical fibers. These are for example, grouped together in a line or several lines 3 similar to that illustrated in FIG. 2. In the case of a network 1 consisting of a line 3 arranged in a serpentine, the end of the latter is for example connected to a mirror 46.

 FIG. 5 shows another embodiment of a device according to the invention similar to the previous one but in which the emissivity of the surface located under the network 1 of optical fibers varies by discrete values. The panel is seen there in section, only part of this section being represented. The formwork 42 always includes a thermal insulator 44, a bottom 45 reflecting towards the object to be camouflaged for example. Between these elements and the lines 3 of the optical fiber network is interposed a system 51 whose surface comprises for example two different emissivity zones, a first zone 52 is for example reflective, having an emissivity equal to approximately 0.05, and a second zone 53 has for example a higher emissivity, equal to approximately 0.5. For this purpose, the first zone 52 is for example made up of a layer of aluminum and the second zone 53 of a layer of alumina . These layers are arranged on a flexible rolling support 54 driven for example by two pulleys of which only one 55 is shown.

 Depending on the position of the support 54, one or the other zone 52, 53 is situated on the side of the lines 3 of the optical fiber network, that is to say on the side seen by the observer, the zone not seen being of the side of the bottom of the formwork 42.

The lines 3 of the network are placed on supports 56 fixed relative to the formwork 42. A thermal insulator 44 'is for example placed inside the system 51, the layers 52, 53 arranged on the flexible support 54.

FIG. 6 shows an embodiment of a device according to the invention similar to that described in FIG. 4 but where the surface located under the network of optical fibers has an emissivity which varies continuously,
The emissivity being for example electrically controlled. Only the thermal insulation 44, the variable emissivity layer and a line 3 of the network on its support 56 are shown. The thermal insulator is for example covered with a resistive circuit 61 connected to an electric generator 62 and has a mechanical mass 63. This circuit is for example covered with a layer of vanadium oxide 64 whose emissivity varies according to of the temperature.

This temperature variation is in particular controlled by the electric current supplying the resistive circuit 61 and delivered by the generator 52, the heat released by the resistive circuit being substantially proportional to the square of the current. The vanadium oxide layer could be replaced by any other layer whose emissivity varies in particular with temperature or directly depending on an electrical parameter.

 The various embodiments of the device according to the invention described in FIGS. 4, 5 and 6 make it possible to use camouflage panels capable of being fixed in particular on vehicles.

 Figures 7 and 8 illustrate two examples of camouflage devices according to the invention using these panels.

 FIG. 7 illustrates a use of these panels to camouflage an armored vehicle 71. Camouflage panels 72 of the type of those illustrated in FIGS. 4, 5 or 6 are fixed to the armored vehicle 72 so that it can be protected whatever or the angle of observation. The panels 72 are for example removable and interchangeable.

 FIG. 8 shows a camouflage net 81 for camouflaging a stationary vehicle 82. This net is composed of a network of optical fibers grouped for example by three in lines as defined by FIG. 2. These lines are braided so that sufficient mechanical consistency is obtained.

 A box 83 contains, for example, controls and optical sources grouping together elements such as those 31, 32, 33, 34, 35, 36 shown in FIG. 3. This net 81 is particularly suitable for camouflage in the visible or near range infrared.

 FIG. 9 shows a camouflage net 91 in particular adapted to the visible and to bands I, II and II of 'infrared. It consists of a network of optical fibers similar to that of FIG. 8 but this is arranged, glued for example, on a flexible support covered with a layer of variable and adaptable emissivity.

 The support can be made of flexible plastic covered with a layer of alumina, of the order of 1 μm for example. An emissivity layer 0.5 makes it possible to obtain an improvement in emissivity, which combined with the power of the waves emitted by the optical fibers, cancels the contrast between the background and the camouflage net 91. The color is for example adapted by the optical source supplying the optical fibers intended for the visible domain, either by fixed emission for example, or by frequency and spectrum modulation, in the latter case, in particular in order to disturb target acquisition systems.

 FIG. 10 shows a possible use of a device according to the invention for camouflaging an aircraft 101 in flight. For this use, networks of optical fibers and active layers with variable emissivity are for example integrated into the structure of the aircraft, in particular for aerodynamic reasons. The aircraft often flies on a cold background, clear sky. Therefore to reduce the contrast between the background and the aircraft, a cooling system can be added to it, for example using the circulation of fuel before combustion.

 The optical fiber networks and the active layers are for example arranged so as to form several panels 102 covering most of the surface of the aircraft intended to be camouflaged. For the use of the camouflage device according to the invention to be effective in this application case, it is preferable in particular that the jets of hot gases leaving the reactors are themselves camouflaged since they participate in the infrared signature of an aircraft.

 FIG. 11 shows the block diagram of another possible embodiment of a system for controlling fiber optic networks contained in a camouflage device according to the invention, taking for example elements of the system presented in FIG. 3, but in particular suitable for a moving vehicle covered with camouflage panels of the type of those in FIGS. 4, 5 or 6.

 The detection means 31 consist for example of several detectors 111, 112, 113, 114, 115.

 These detectors are equal in number to the number of panels covering the vehicle to be camouflaged, five by way of example in the case of application of FIG. 11. Each detector is associated with a panel and detects the background on which the latter is located. . Each detector is for example operational in all the bands, that is to say visible and near infrared, infrared band Il and infrared Il, and for this purpose contains three elementary detectors, an elementary detector being for example assigned to each of these bands. For the visible and near infrared band, a voltage representative of the detected color is for example delivered by the corresponding elementary detector according to methods known to those skilled in the art. The elementary detectors assigned to the bands II and II of the infrared -red for example delivers voltages representative of the bottom temperature. These detectors also deliver the background emittance, ie its power per square meter radiated in the frequency bands.

 The detectors 111,112,113,114,115 are connected to the processing means 32 which exploit the electrical signals, in particular voltages, supplied by the detectors of the detection means 31. The processing means 32 define, from the signals delivered by the detection means 31, the wavelength and the power that the laser sources 34, 35, 36 must emit, a laser source being for example assigned to each of the aforementioned bands.

 The laser optical sources are for example tunable. They are for example composed of YAG lasers pumped diodes, frequency doublers and optical parametric oscillators known to those skilled in the art.

 The control means 33 contain, for example, logic control circuits 116 connected to the output of the processing means 32.

 The logic control circuits 116 have their outputs connected to the input of a control interferance circuit 116 connected to the inputs of the laser sources and in particular intended to amplify the control signals supplied by the logic control circuits 116.

 The outputs of the laser optical sources 34, 35, 36 are connected to first distribution means 118 making it possible in particular to distribute the optical waves in their corresponding optical fiber networks, in accordance with the results of the processing means 32. For this purpose, I ' input of the distribution means 118 is in particular connected to the logic control circuits 116. The distribution means 118 supply several optical fiber networks 11, 12, 13, 14, 15 intended to obtain an emittance and a coloring variable.

 Each network is for example arranged on a panel. The color and emittance emitted by an optical fiber network then corresponds to the background on which its panel is located.

 Second distribution means 119 control, for example, the emissivity of each of the panels or surfaces on which the optical fiber networks 11, 12, 13, 14, 15 are located. This control can be done, for example, by an electric heating current. a layer of vanadium oxide, as in the case of FIG. 6 in particular, of vanadium dioxide or of conductive polymers of polythiophene or polypyroll type for example, all of these compounds having an emissivity as a function of their temperature. This control can also be done by mechanical effect by the unwinding of a layer composed of half metal and half oxide or alumina, as in the case of FIG. 5 in particular. To control the distribution of the emissivity, in particular according to the parameters detected, the input of the second distribution means 119 is connected to the logic control circuits 116.

 As an option, in the case of camouflaging a moving vehicle, the control means 33 are for example connected to means for detecting the movements of the vehicle 121.

 If the vehicle is armored, for example, of the type shown in FIG. 7, the detection means 121 detect not only the overall linear movement of the vehicle but also the movements of all of its elements supporting a camouflage panel. The movement detection means 121 are connected to logic circuits for controlling the detectors 122 themselves connected to the detectors of the detection means 31. These logic control circuits 122 associated with the movement detection means 121 make it possible to correlate the position of the detectors of the detection means 31 to the movements of the vehicle.

 Thus, when a panel 72 changes position in particular, the detectors must also change position to capture the new corresponding background. The connection of the motion detection means 121 to the control means 33 makes it possible in particular to correlate the control of the laser sources with the movements of the vehicle.

 The logic control circuits 33 and the movement detection means 121 may for example be connected to the vehicle control computer 120. The latter calculates the movements of the vehicle, these connections make it possible in particular to correlate the position of the detection means 31 and the control of the laser sources with the movement forecasts given by the computer 120 and thus anticipate the movements.

 The optical fiber networks 11, 12, 13, 14, 15 can be arranged on camouflage panels or else be arranged in the form of camouflage nets.

Claims (17)

 1. Device for camouflaging an object on a background with respect to an observer, characterized in that it comprises at least one network (1) of optical fibers (3, 24) covering the object and diffusing waves (25) whose wavelength depends on the bottom temperature and whose power depends on the background emittance, and a network control system (1).  2. Device according to claim 1, characterized in that the optical fibers (24) are grouped in lines (3), each optical fiber of a line being assigned to a frequency domain.  3. Device according to claim 2, characterized in that in a line (3), a first optical fiber is assigned to the visible and near infrared range, a second optical fiber is assigned to the infrared range band II and a third optical fiber is assigned to the infrared band III domain.  4. Device according to claim 2, characterized in that the optical fibers (25) of a line (3) are embedded in a flexible material (26).  5. Device according to any one of the preceding claims, characterized in that a part of the sheath (24) of each optical fiber (25) is removed along its length so that each optical fiber diffuses a wave towards the 'observer.  6. Device according to any one of the preceding claims, characterized in that the network (1) is arranged on a support (42, 44) covered with a variable emissivity layer (51, 64), 'emissivity being controlled by depending on the background emittance.  7. Device according to claim 6, characterized in that the variable emissivity layer (64) is arranged on a resistive circuit (61) controlled by an electrical signal (62) and heating the layer (64), Its emissivity varying with its temperature.  8. Device according to any one of claims 1 to 5, characterized in that the network (1) is arranged on a support (42, 4 ') covered with a reflective layer (43).  9. Device according to any one of the preceding claims, characterized in that the network (1) is arranged in a formwork (42) to form a camouflage panel (72).  10. Device according to claim 9, characterized in that a thermal insulator (44, 44 ') is interposed between the bottom of the formwork (45) and the layer (43, 64).  11. Device according to any one of the preceding claims, characterized in that the network control system (1) comprises at least:  - means for detecting the temperature and the bottom emittance (31);  - processing means (32) connected to the detection means (32),  - laser sources (34, 35, 36) connected to control means (33) themselves connected to the processing means (32), each laser source supplying an optical fiber of a line (3).  12. Device according to claim 11, characterized in that the network control system (1) further comprises means for detecting the movements (121) of the object, the position of the detection means (31) and the command laser sources (34, 35, 36) being correlated to the movement of the object.  13. Device according to claim 12, characterized in that the object (71) is covered with camouflage panels (72), each panel being covered with a network (11, 12, 13, 14, 15) connected to distribution means (118) connected to the laser sources (34, 35, 36) and to the control means (33), and distributing the energy of the laser sources between the different networks (11,12,13,14,15).  14. Device according to claim 13, characterized in that the emissivity of the surfaces on which the optical fiber networks (11, 12, 13, 14, 15) are arranged is controlled by distribution circuits (119) connected to the means control (33) and distributing the emissivity control signals between the various panels (72).  15. Device according to any one of the preceding claims, characterized in that the lines (3) are braided to form a net.  16. Device according to any one of claims 1 to 14, characterized in that the network (1) consists of at least one line arranged in a serpentine.  17. Device according to any one of the preceding claims, characterized in that it is integrated into the structure of an aircraft.