FR2465187A1 - Infrared radiation generator of consumable type - comprising emissive refractory material layers of approximate black body properties, heat source and source initiator - Google Patents

Abstract

Appts. is described for emitting at a determined moment and for a limited time period, a radiation in the IR wave band, consisting of (a) a no. of layers of porous refractory material having emissive properties near to those of a black body, the outer faces of these layers forming the emissive surfaces; (b) a source of thermal energy distributed between the layers of porous refractory providing heat to raise the temp. sharply in a limited time; and (c) appts. for initiating the operation of the source of thermal energy. Used in inside guidance systems; cisprojectile markers, and as infrared lures or baits to decory a potential adversary. The emissive surfaces are perfectly defined. The source may emit at regular or irregular intervals according to desired programme.

Description

The invention relates to the technique of infrared radiation sources (I.R.) and in particular an I.R. radiation generator, of the consumable type, capable of emitting, at a determined time, a given level of radiation for a predetermined time.

Frequently, the problem arises of producing I.R. radiation generators, also called I.R. sources, whose emission time can be controlled, and capable of delivering levels. power of several hundred watts during a predetermined period of time, between a few seconds and several minutes.

 A first problem is that of producing T. sources? , intended to be mounted on test targets which are used in the testing of weapon systems equipped with electro-optical (EO) devices, such as passive missile guidance systems, devices aiming or detection, proximity rockets, etc ... These sources I.R must best reproduce the thermal radiation characteristics of real targets and their radiation diagram must be able to be modulated in order to meet the operational requirements of such tests .

A second problem is that of making sources
IR intended to "mark" projectiles, or missiles, in order to facilitate their detection in order to ensure their capture at the start of the trajectory or even their pursuit on the firing trajectory. These sources must have characteristics such that the detection of the projectile takes place without ambiguity in the shooting environment.

 Finally, a third problem, in the context of activated countermeasures I.R, is that of producing active lures I.R in order to lure a possible adversary, with the aim of ensuring a sufficient passing distance of a projectile or of triggering @ dearly prematurely firing the military charge of this projectile.

 In all the applications which have just been stated, as a general rule, the emission of the source I.R must be able to be triggered at a determined time. IR sources intended to be mounted on test targets must be able to emit for a period of time greater than one minute and the power level of the emitted radiation must be in the range of hundreds of watts. On the other hand, the operating time of active lures I.R can be shorter, of the order of seconds or a few tens of seconds with power levels which are at higher values of the order of kilowatt or more Furthermore, the consumable nature of these sources I.R implies that the cost of production remains reasonable, this cost not having to be obtained at the expense of operational reliability.

 Several devices are currently known for emitting radiation located in the I.R portion of the electromagnetic spectrum. Among these devices, there may be mentioned a device, more particularly suitable for marking test targets and projectiles, consisting of an open reservoir inside which is stored a block of powder, the combustion of which is the source of radiation. thermal.

The main drawback of this device lies in the position of the point of maximum luminance which is imperfectly defined. One can also cite a device more particularly intended to be used as active lure I.R; in this device, one of the faces of a metal sheet is coated with a bootable pyrotechnic composition, while the opposite face is coated with a dark colored material.

The main drawback of this device lies in the relatively low operating temperature.

 The object of the present invention is therefore to provide a generator of thermal radiation, of the consumable type, the emission of which can be triggered at a determined instant, the emissive surfaces of which are perfectly defined and, moreover, the source of calories. burns on closed fire.

This object is achieved by a generator which comprises - a plurality of layers of a porous and refractory material
which has emissive properties close to those of
black body, the external faces of these layers constituting
radiant emissive surfaces, - a source of heat energy distributed between the layers
of the material, - a means for initiating the combustion of the source
of heat energy.

The choice of the material that makes up the layers is dictated by the following considerations: the material must be permeable to the low gaseous residues released by the heat energy source, it must be non-combustible at the operating temperature of the heat energy source ; it can advantageously be flexible in order to allow the production of a generator of various shapes.

 The heat energy source must consist of an exothermic composition whose specific reaction heat is high and the reaction products must be transparent in the band of the electromagnetic spectrum corresponding to the infrared band of the generator operating.

te starting means can be constituted, for example, by a pyrotechnic device which causes a rise in temperature of the exothermic composition constituting the source of heat energy.

The invention also relates to a source whose radiation diagram can be modeled on demand by adapting the shape and the temperature of the emissive surfaces.

Another object of the invention is a generator of thermal radiation which can be launched at a distance from a target to be protected in order to create active decoys intended to reduce the efficiency of the electro-optical means available to a possible adversary.

 This goal is achieved by performing a generator, launched by a vector, and triggered at a given time on its path, this generator being constituted by a plurality of emissive surfaces which are deployed from the moment of ejection.

 Other characteristics and advantages which the invention provides will appear more clearly in the detailed description which follows, which is made with reference to the appended figures and which gives, by way of explanation, but in no way limiting, several embodiments of a generator. thermal according to the invention.

In these figures - Figure 1 shows a schematic view of a generator
of thermal radiation and shows the essentials
emissive surfaces and the source of heat energy.

- Figure 2 shows a cutaway view of an IR generator
of circular shape more particularly intended to be
used as IR tracer - Figure 3 shows a schematic view of a means cons
with a deflector, allowing to reinforce the intensity
and the energy of the radiation emitted by one of the faces of the eur gene.

FIG. 4 represents a means, constituted by a deflector,
allowing to model the diagram of the emitted radiation.

- Figure 5 shows a generator of IR radiation,
cylindrical configuration, allowing to widen the diagram
of the radiation emitted.

- Figure 6 shows an execution mode of a generator
according to the invention, making it possible to increase the duration
effective emission of IR radiation - Figure 7 represents an IR radiation generator
comprising a plurality of emissive layers, for the purpose
increase the duration of the program.

FIG. 8 represents a means, consisting of cells,
allowing to distribute and maintain in place the consti
kills from the calorific energy source.

- Figure 9a shows an IR radiation generator
consisting of a plurality of emissive surfaces which are
stacked in a container.

- Figure 9b shows the generator of Figure 9a after
ejection of the container and deployment of the emissive surfaces.

- Figure 10a shows a crucible radiation generator
shape whose emissive surfaces are rolled up in a container.

- your figure 10b represents the IR radiation generator
of Figure 10a after ejection of the container and 'bending
of emitted areas.

FIG. 1 represents a sectional view of a thermal radiation generator showing the essential elements which constitute the generator, the latter comprises - two discs, 10 and 20, made of a porous material and
refractory with emissive properties close to
those of the black body: the external faces of these discs
constitute the radiating emissive surfaces.

- A layer, 30, of an exothermic composition, which is re
part uniformly between the internal faces of the discs 10
and 20: this layer then constitutes the energy source
generator heat.

- A device (not shown) allowing to provoke
locally a rise in temperature of the composition
exothermic: this device constitutes the starting means
of the exothermic reaction.

your discs 10 and 20 can be made of a material such as carbon felt, this material is produced industrially in different thicknesses: carbon felt has emissive properties close to those of the black body, it conducts heat and electric current, its specific density t of the order of 0.14 is low, its texture gives it a high permeability to gaseous products and a great mechanical flexibility thus making it possible to produce layers of complex shape, the carbon felt can be easily cut to small thicknesses, 5 mm for example, its resistance to breakage, in particular to tearing, is high; finally, its combustion kinetics allow it to be used up to temperatures exceeding 20,000 C.

The exothermic composition which constitutes the source of heat energy and causes the temperature rise of the discs can be an oxidoreductive couple such as an intimate mixture of magnesium (Mg) and ferric oxide (Fe203) which, for example, in stoichiometric proportion (31.4% Mg and 68.6 Fe20 mode) releases an amount of heat of the order of
23 1000 calories per gram of matter. reaction product
MgO has a transmission factor of the order of 90% in the IR band, 3 to 57 (m
To give a certain mechanical rigidity to the generator thus formed or, in other words, to avoid deformation of the discs, the assembly can be trapped in a case whose faces are formed by a mesh, for example, made of steel or any refractory material .

 The operation of the generator is as follows: at a given instant, the temperature of the exothermic composition is raised locally, thus the exothermic reaction stethes with the entire layer 30 which delivers a flow of heat through the disks 10 and 20, the significant rise in the temperature of these discs gives rise to IR radiation which is emitted outside the generator.

the intensity of the radiation emitted is proportional to the effective area of the discs: the luminance is a function of the temperature rise of the discs of the carbon felt, this temperature rise depends on the nature and the
mass of the exothermic composition used and the mass of the felt layers. The radiation pattern emitted is of the Lambertian type. Various means will be described later, which allow this radiation pattern to be modeled, in particular by adapting the shape of the emitted surfaces and by the addition of reflectors judiciously placed in the vicinity of the emissive surfaces.

 The operating time of such a generator can be adapted to the problem posed, as will be described later: either by modifying the quantities of the products which constitute the exothermic composition, or by a judicious arrangement of the layers of carbon felt or else or by adding reflectors.

FIG. 2 represents a mode of execution ~> ion of full IR radiation generator according to the invention: this generator is, more specifically, intended to equip a training target and it comprises - a metallic structure 40, of cylindrical shape, - two discs 10 and 20 made of a porous, reactive material
shut up like a carbon felt, for example felt
produced under the reference 8004 RVC 400 by the firm "Carbone
Lorraine ": the thickness, e, of each of the two discs,
may be of the order of 5 mm, - a layer 30 of an exothermic composition, distributed
evenly between the two discs 10 and 20: the composite
exothermic tion can be an oxidation-reduction couple such
than magnesium powder (Mg) thoroughly mixed
with ferric oxide (Fe203), - two grids 50 and 60 applied to each side
outer of the felt discs: the mesh size of these
grids can be of the order of cm and these grids can
be made of steel wire or a reactive material
keep silent at the operating temperature of the device, - two self-destructing films 50 and 60 arranged on
the outer faces of the felt discs for the purpose of assu
rer a device protection to external agents, no
humidity, - one or more nipples 90 to initiate the
exothermic reaction of layer 30: ignition of the
loot can be achieved by passing an electric coura: qt
supplied to power connections 95.

The assembly constituted by the stacking of the felt discs 10 and 20 of the exothermic layer 30, of the grids 50 and 60 and of the protective films 60 and 70 can be maintained in the metallic structure 40 by a threaded clamping piece 100
In an exemplary embodiment, the useful diameter of each of the discs can be 180 mm and the thickness e of the order of 5 mm. The heat energy source can be supplied by the stoichiometric composition of 2.74 g of magnesium and 6 g of ferric oxide which releases approximately a calorific energy of 8.800 calories approximately. your operating tests of such a generator indicate a peak liminance of the order of 2W / cm2 / sr in the spectral band 3 to 5 m; the IR radiation output from the device obeyed an ioi of the Lambertian type.

 In a device according to the invention, it is possible to extend the time during which the temperature rise Te of the felt discs can be kept high. As indicated above, the permeability to gaseous products of carbon felt makes it possible to use oxygen from the atmosphere.

2 MgO celle-ci fournit environ 5900 caljg de Mg. Si lron considère le générateur décrit précédemment, dont la source d'énergie calorifique était constitué de 2,74 de Mg et 6 g de Te203 et qu'on ajoute à cette composition 11,26 g de Mg, on dispose alors de 20 g de matière et, par voie de conséquence, un surplus d'énergie calorifique de 6.000 cal/g de Mg environ, qui, compte tenu de la quantité d'énergie d'environ 6.300 calories absorbée par les produits de réaction, conduit à une énergie calorifique utilisable de 60.000 calories environ. Ce complément de Mg permet de prolonger le palier d'émission à puissance maximale pendant un temps supérieur à deux minutes.To do this, an excess of magnesium is introduced into the exothermic composition, which reacts with oxygen according to the reaction 2 Mg + 02

2 MgO this provides approximately 5900 caljg of Mg. If we consider the generator described above, whose heat energy source consisted of 2.74 Mg and 6 g of Te203 and that we add to this composition 11.26 g of Mg, we then have 20 g of matter and, consequently, a surplus of calorific energy of 6,000 cal / g of Mg approximately, which, taking into account the quantity of energy of approximately 6,300 calories absorbed by the reaction products, leads to a calorific energy usable from around 60,000 calories. This additional Mg makes it possible to extend the emission plateau at maximum power for a time greater than two minutes.

 So far, we have only considered a plane generator whose radiation was emitted by the two output faces of the device. In certain applications for which the generator is used as an I.R tracer intended to simulate the propellant system of a training target, only the output energy of one of the faces is effectively exploited. This can be used to enhance the intensity and energy of the radiation emitted by the useful face. To do this, we have, as shown, schematically in Figure 3, a flat reflector located opposite the outlet face whose influence is not exploited. the radiation emitted by the disc 20 is returned by the reflector R, crosses all of the discs and reinforces the useful radiation, at the outlet of the disc 10. Your equilibrium equations of such a system will not be developed here, they indicate an increase emitted by the useful output face and jointly an increase in the effective duration of the emission.

However, it is desirable that the resulting increase in temperature Tc does not cause the vaporization of magnesium (magnesium evaporation temperature = 13 630 K), which would have the effect of taking an amount of heat from the amount of heat available.

We will now describe means for modeling the radiation diagram emitted by a generator according to the invention.

 In FIG. 4, a planar generator has been shown in dry matic form, as described above: in order to widen the radiation diagram, we have arranged in the vicinity of the external surface of the carbon felt disc 20 , a deflector cone D which returns, obliquely, the output radiation from this disc 20. By adapting the shape and the location of the reflector D, it is possible to obtain radiation diagrams capable of satisfying the requirements of the problem posed.

 In figure 5 5 we have represented, in a schematic form, a means allowing a different approach to the problem of modeling the radiation diagram. In the exemplary embodiment shown, the layers of carbon felt are arranged to form a cylinder, the upper ace of which comprises two notches 10a and 20a, of carbon felt and the lateral face two layers 10b and 20b, of carbon felt ;; the exothermic composition 30a and 30b is distributed between the internal faces of the layers of carbon felt. te I.R radiation generator thus formed can be supplemented by the elements already described, a metal assembly structure, retaining grids, etc.

In FIG. 6, an embodiment has been shown of a generator in accordance with the invention, which makes it possible to increase the effective duration of emission of the IR radiation. According to this embodiment, the generator has n layers, here, for example, four layers, 30a to 30d, of an exothermic composition distributed between the internal faces of 5 disks of the carbon felt: 2 output disks 10 and 20 whose thickness is approximately 4.5 mm and 3 internal discs 11, 12 and 13 of a double thickness. An ignition device 90, placed at the level of the layer 30a makes it possible to trigger the operation of the generator, then gradually, the heat energy released initiates the exothermic reaction at the level of the layers 30b, 30c and 30d. the emissive assembly thus formed is maintained in a cylindrical metallic structure as shown in Figure 2; a pair of grids 50 and 60 completes this assembly and prevents mechanical deformation of the felt discs. In order to reinforce the radiation emitted by the upper disc 10, there is a reflector pl
R comprising orifices 110 for evacuating gaseous products possibly supplied by the exothermic reaction of the heat energy source. By modifying the thickness of the layers of felt, it is possible to vary the instant of ignition of the successive layers .

 In Figure 7, there is shown an embodiment of a generator according to the invention which comprises means for holding in place the powder which constitutes the exothermic composition when the generator is the subject of a level of intense vibration. According to this embodiment, the generator comprises 2 discs of carbide felt 10 and 20, and an internal disc 15 of carbon felt; between the discs 10 and 15 and the discs 20 and 15 are arranged two discs 16 and 17 in the thickness of which cells 120 have been provided. Inside these cells are sagasiné, intimately mixed, the constituents of the composition ion In the 120 alveoli, the exothermic composition is arranged either in bulk or encapsulated, or in the form of tablets. At the periphery of the cells are placed pyrotechnic devices 80a and 80b whose function is to initiate the exothermic reaction of the composition housed in the cells.

 FIG. 8 represents an alternative embodiment of the generator of FIG. 7. According to this alternative, the device for starting the source of heat energy is constituted by electrical means, the generator comprises: two layers of carbon felt 10 and 20 which constitute the emissive parts, two grids 50 and 60 which prevent the deformation of the carbon felt, two rings 70a and 80a to which are fixed self-destructible films, or waterproofing mats, 70 or 80, destructible from the temperature rise of the heat energy source. Between the disks 10 and 20 are arranged the heat energy source and the means for initiating the exothermic reaction. The heat energy source is placed in cells 120 in the form of a powder in bulk, in combustible sachets or in tablets.

your cells are formed by the superposition of perforated parts, the first part 150 in an electrically conductive carbon felt, a second and a third part 160a and 160b made of a refractory insulating material. At two diametrically opposite points of the part 150 sDnt fixed electrical contacts 170a and 170b which makes it possible to transfer an electric current through the part 150; under the effect of the passage of electric current, the room heats up and causes the ignition of the heat energy source.

All of the elements which have just been described are held by a structure 40 advantageously made of light alloy.

Sealed terminals 180a and 180b for supplying the electric current allow, through the electrical contacts 170a and 170b, the heating of the part 150. The assembly is completed by seals 190a and 190b.

We will now describe an IR radiation generator more particularly intended to be used as an IR decoy.
It will be recalled that the operating time of the IR decoy is limited to a few seconds and that the intensity of the radiation must be at the kilowatt / steradian level in the band 3 to 5 m. In the case of decoys, means must be sought to increase the temperature Tc of the emissive surfaces.

4 2 3 3
Cette réaction fournit une quantité de chaleur égaie à environ 2.400 cal/g de matière, les produits de réaction Al2O3 et KCC possèdent un facteur de transmission élevé (de l'ordre de 90 fo) dans la bande 3 à 5,4m; la réaction s'effectue e un temps très bref (de l'ordre de 1/10 de seconde) si toutes les précautions habituelles sont observées ; par contre la température d'ébullition du chlorure de potassium KCW est relativement faible 17730K. To increase the temperature rise of the emissive surfaces, various exothermic compositions can be envisaged, in particular those whose reaction is strongly exothermic, for example a mixture of potassium chlorate KClO4 and aluminum Al which react according to the reaction 3KClO4

4 2 3 3
This reaction provides an amount of heat equal to around 2,400 cal / g of material, the reaction products Al2O3 and KCC have a high transmittance (of the order of 90%) in the band 3 to 5.4m; the reaction takes place in a very short time (of the order of 1/10 of a second) if all the usual precautions are observed; on the other hand the boiling temperature of potassium chloride KCW is relatively low 17730K.

Other exothermic compositions, the reaction products of which have a high evaporation temperature, can be envisaged, for example, the conventional aluminothermic composition, chromium oxide CrO) and aluminum Al, which react according to the reaction.
Cr2O3 + 2Al

Al2O3 + 2 Cr this reaction provides an amount of heat equal to approximately 580 cal / g of material and the reaction products: alumina A2O3 and chromium Gold vaporize respectively at 32550 K and 29450 K.

 The generator constituting the IR lure must be able to be placed inside a vector in order to be effective at a considerable distance from the objective which wishes to protect itself from the effects of an adverse weapon, the caliber of a conventional launching means is around 70 mm and the useful length is between 170 and 300 mm.

 One means of obtaining relatively large emissive surfaces is to produce a generator consisting of a plurality of emissive surfaces which are joined together and then deployed when the projectile is released; for example, the lure can be constituted by flat surfaces which are automatically deployed.

 In FIG. 9e there is shown an I.R lure constituted by elementary planar generators G, of circular shape, which are stacked in a container 200; they are interconnected by springs 210.

 In Figure 9b, there is shown the lure of Figure 9a, after ejection of the container and deployment.

In FIG. 10a, a cruciform IR lure L has been represented which is wound on itself inside a container 200. As represented in FIG. 10b, so ejection causes its deployment and its locking, by means of springs 220. Each of the four emissive surfaces, in the example shown, has a length l and a width r
When the device uses a stoichiometric cOmpOSiTDn, the device can operate in an ambient environment deprived of oxygen.

 An infrared radiation generator, as described, can be produced in various configurations; for example, it may include emissive surfaces deployed as an umbrella and such a generator can be placed at the front or at the rear of a means for launching this generator.

 te generator, in the case of a decoy, pe be constituted by emissive surfaces arranged sue ~ 'envelope of a means of launching this generator.

 One embodiment of an infrared generator making it possible to approach a determined spectral distribution consists in combining complex emissive surfaces which differ in nature, thickness and the active surface of the layers of felt as well as in the composition of a source of heat energy.

The device according to the invention can be used as a marker, tracer or lure in the infrared band of the electromagnetic spectrum.

Claims (10)

REVEEDICATI0gE 1. Device make it possible to emit, at a determined instant and for a limited time, radiation located in the infrared band of the electromagnetic spectrum, device characterized in that it comprises in particular - a plurality of layers of a porous material refractory which has emissive properties close to those of  black body, the external faces of these layers constitute  emissive surfaces, - a source of heat energy distributed between the layers  of porous refractory material, source which provides a flow  of heat energy capable of raising, strongly and in  a limited time, the temperature of the layers of the material, - a means enabling the operation of the  heat energy source 2. Device according to claim 1, characterized in that the porous absorbent material is a carbon felt. 3. Device according to claim 1, characterized in that the source of heat energy is an exothermic composition whose reaction products have a high transmission factor. 4. Device according to claim 3, characterized in that the exothermic composition consists of the intimate mixture, in stoichiometric proportion of magnesium and ferric oxide. 5. Device according to claim 3, characterized in that the exothermic composition consists of the intimate mixture of magnesium and ferric oxide, with an excess of magnesium. 6. Device according to claim 1, characterized in that, on the outer faces of the layers, are disposed grids made of a refractory material. 7. Device according to claim 1, characterized in that it comprises a reflective plane arranged late and in the vicinity of one of the emlssive surfaces. 8. Device according to claim 1, characterized in that it comprises a deflector device arranged opposite and in the vicinity of one of the emissive surfaces. 9. Device according to claim 1, characterized in that the means for initiating the operation of the heat energy source is a pyrotechnic device. 10. Device according to claim 1, characterized in that the means for initiating the operation of a heat energy source consists of an auxiliary layer of carbon felt heated by the passage of an electric current.