EP1804336A1 - Composite structure with several stacked layers subjected to electromagnetic radiation - Google Patents

Composite structure with several stacked layers subjected to electromagnetic radiation Download PDF

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Publication number
EP1804336A1
EP1804336A1 EP06126432A EP06126432A EP1804336A1 EP 1804336 A1 EP1804336 A1 EP 1804336A1 EP 06126432 A EP06126432 A EP 06126432A EP 06126432 A EP06126432 A EP 06126432A EP 1804336 A1 EP1804336 A1 EP 1804336A1
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EP
European Patent Office
Prior art keywords
electromagnetic radiation
plates
core material
composite structure
skin material
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP06126432A
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German (de)
French (fr)
Inventor
Philippe Le Brestec
Regis Bourloton
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Thales SA
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Thales SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
    • H01Q15/24—Polarising devices; Polarisation filters 
    • H01Q15/242—Polarisation converters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/02—Arrangements for de-icing; Arrangements for drying-out ; Arrangements for cooling; Arrangements for preventing corrosion
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/42—Housings not intimately mechanically associated with radiating elements, e.g. radome
    • H01Q1/422—Housings not intimately mechanically associated with radiating elements, e.g. radome comprising two or more layers of dielectric material
    • H01Q1/424—Housings not intimately mechanically associated with radiating elements, e.g. radome comprising two or more layers of dielectric material comprising a layer of expanded material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q1/00—Details of, or arrangements associated with, antennas
    • H01Q1/42—Housings not intimately mechanically associated with radiating elements, e.g. radome
    • H01Q1/425—Housings not intimately mechanically associated with radiating elements, e.g. radome comprising a metallic grid

Definitions

  • the present invention relates to a multilayer composite structure stacked whose heating remains limited under the effect of electromagnetic radiation. It applies for example in the fields of detection and telecommunications.
  • the loss factor tg ⁇ of a material reflects its ability to absorb a portion of the power of radiation to which it is exposed, this power being restored by the material by heat dissipation.
  • the higher the loss factor tg ⁇ of a material the more it heats up when exposed to electromagnetic radiation.
  • the vacuum which is a medium with a loss factor of almost zero
  • the air which is a medium with a loss factor that is still extremely low.
  • the loss factor increases with the density of the material, which is why solid materials have loss factors much higher than vacuum and air.
  • a polarizer is a conventional device in electronic scanning antennas that transforms horizontally polarized waves that pass through it into vertically polarized waves and vice versa.
  • a polarizer comprises a support on which is disposed a conductive grid, such as a meander grid or a grid of metal wires, the conductive grid having polarizing properties.
  • Current polarizers have very advanced functions that require the use of several superimposed grids and therefore the use of spacers between the grids.
  • Current solutions include the use of foamed spacers and epoxy glass grid supports, all of which are assembled into a sandwich composite structure.
  • a sandwich type composite structure is an assembly of at least two different materials in the form of plates, one called “core material” constituting the framework and providing the mechanical strength and the other called “skin material” constituting the protection and ensuring the structure.
  • the plates of the two materials are assembled by gluing.
  • the thickness of the core material plates is much greater than that of the skin material plates.
  • the skin material consists of epoxy glass printed circuits having a non-electric power copper pattern, this pattern acting as a polarizing gate.
  • the core material is a foam, the foam type materials being low density solid materials thus having the double advantage of having a light weight and a low loss factor. But under extreme conditions of use, at full transmission power and very high outside temperature of the order of 80 ° C for example, it is still common for these materials to heat up, potentially damaging all or part of the polarizer and even the antenna.
  • the composite structures used should not rise to temperatures too close to the glass transition temperature of the foam-type material, temperature "Tg".
  • Tg glass transition temperature of a foam is the temperature at which it goes from the vitreous state, that is to say from the solid state to which it is capable of acting as a spacer, to a state which can be described as rubbery, which is a softer intermediate state to which it is no longer capable of acting as a spacer.
  • the subject of the invention is a composite structure with several stacked layers subjected to electromagnetic radiation. It comprises a stack of plates of a core material, the core material plates being interposed between plates of a skin material having a conductive pattern. Each core material plate has recesses passing therethrough, the recesses of two adjacent core material plates being connected in pairs by a hole in the skin material plate separating them.
  • the amount of heat dissipated is an increasing function with the volume of material passed through. But it is mainly to disturb neither the operation of the antenna nor its design. Because the thickness of the composite structure is often a necessary feature for the proper functioning of the antenna, for example it may be a function of the wavelength issued. It can not be considered to reduce it, except perhaps in a few particular cases.
  • the external dimensions of the composite structure may be a constraint necessary for assembling the assembly. For example the composite structure can contribute decisively to the rigidity and compactness of the assembly.
  • a good way of reducing the volume of material passed through without modifying the external volume of the composite structure is to hollow out it, that is to say to make withdrawals of material which do not change its substance. external appearance.
  • the recesses are made in such a way as to optimize the evacuation of the heat dissipated towards the outside of the composite structure by natural aeration, in order to further reduce the heating.
  • the conductive patterns on the skin material plates can have a polarization rotation function of the electromagnetic radiation.
  • the skin material plates and the core material plates can be assembled by gluing.
  • each recess can be in the form of cylinders whose axis is normal to the plane of the plate.
  • the skin material plates may be epoxy glass, the core material plates may be polyurethane foam or polymethacrylimide and the conductive pattern on the skin material plates may be copper.
  • the holes of the different skin material plates may be aligned.
  • the main advantages of the invention are that it does not modify the external dimensions of the structure to which it is applied, thus inducing no change in the design of the final product in which it is used. It also takes exactly the same principles of construction as conventional solutions, both in terms of materials and basic structures that tools. The extra cost it induces is therefore very minimal. Its much more open and airy configuration gives it not only a great ability to evacuate heat in a natural way, but also moisture desorption properties that diminish still warming up. The invention also has a lower weight depending on the extent of the recesses, advantage of importance if we consider applications in a field such as avionics for example.
  • FIGS. 1a and 1b respectively show a front view and a sectional view of an exemplary embodiment of a polarizer according to the invention.
  • FIG. 1a illustrates, by a front view, a plate 20 of a core material of the polyurethane foam type, for example, the plate having been recessed from one face to the other in several places.
  • the recesses 21 are for example cylindrical and all identical, they are uniformly distributed and draw for example a regular pattern forming equilateral triangles 22 and 23 over the entire surface of the plate 20.
  • the recess cylinders have a diameter of about 10 millimeters and the equilateral triangles 22 and 23 forming the pattern have a base of the order of about 20 millimeters. This corresponds to an approximate recess rate of 35%. But depending on the surface of the core material plate, the size of the recesses and the pattern they draw may be different.
  • a decrease in the volume of material by recess in a proportion of about one-third allows the core material to continue to play its role of framework of the composite structure. Beyond that, it could affect the mechanical strength of the whole.
  • the recesses will allow to limit the amount of heat dissipated when the structure is exposed to electromagnetic radiation.
  • Figure 1b shows the stack of five layers of the type of that of Figure 1a.
  • the plate 20 of core material is seen at the cutting axis 34 of Figure 1a, therefore, only three recesses are visible in Figure 1b.
  • the five layers of core material 20, 24, 25, 26 and 27, for example, have all been recessed identically. They thus each have three recesses.
  • the five layers of core material have been advantageously bonded to six layers of skin material 28, 29, 30, 31, 32 and 33 of epoxy glass of the printed circuit type for example having a non-powered copper pattern.
  • a layer of core material is interposed between two layers of skin material, which is where the multilayer sandwich structure lies, and then glued.
  • the assembly can be done by coating one side of the glue core material plate, then attaching a skin material plate, and repeating the operation on the other side. This procedure reduces the amount of glue used in the recesses and therefore also the amount of material traversed by the radiation. But it can also be envisaged to glue the skin material plates even with the recesses of the core material plate and then to assemble them to the core material plate.
  • At least one hole 35 is made in each layer of skin material at each recess of the core material.
  • three holes forming the vertices of a triangle are made at each recess, only one of which is visible in FIG. 1b.
  • they are circular holes with a diameter of the order of one millimeter. In any case, their diameter is much smaller than the smallest width of the recesses.
  • the holes in the skin material must not prevent it from playing its role of protection and structure. So do not make too many holes or make big holes.
  • piercing the skin material according to the recesses of the core material exactly would lead to a weakening of the final composite structure which would greatly impair its rigidity.
  • the holes of the different layers are aligned, which made it possible to pierce them indifferently before or after assembly.
  • the function of the holes is to promote the natural ventilation of the recesses of the core material and thus the evacuation to the outside of the dissipated heat.
  • FIG. 2a graphically illustrates the heating of a polarizer according to the prior art, that is to say having neither recess core materials nor piercing skin materials.
  • FIG. 2b graphically illustrates the heating of the polarizer of the example described above.
  • the two polarizer devices were used in the same electronic scanning antenna emitting a high power microwave signal directly on the composite structure.
  • the layers of skin material are printed epoxy glass circuit boards printed with non-powered copper patterns.
  • it is the same polymethacrylimide foam which constitutes the core material.
  • the two graphs are in an axis system where the x-axis represents the time in hours and the y-axis represents the temperature in degrees Celsius.
  • the curve 40 shows the evolution of the outer skin temperature, that is to say the layer in contact with the ambient air
  • the curve 41 shows the evolution of the core temperature of the structure, i.e. layers of core material. It can be seen that the outer skin temperature stabilizes only slightly above 60 ° C and that the core temperature rises to around 145 ° C.
  • curve 42 shows the evolution of the outer skin temperature, that is to say layers 28 and 33
  • curve 41 shows the evolution of the temperature of the core of the structure, that is to say the layers 20, 24, 25, 26 and 27.
  • the outer skin temperature stabilizes a little below 60 ° C and the temperature at the heart of the structure stabilizes at 100 ° C.
  • the composite structure according to the invention is therefore much more effective in limiting the heating.
  • Measuring complements also show that the temperature ratio between the core of the structure and the outer skin is decreased by about 50%.
  • the results obtained go beyond what could be expected of a structure having a recess rate of the order of 35% only. Indeed, the aeration produced by the holes directly facilitates heat exchanges with the outside.
  • the exemplary embodiment presented relates to a polarizer, but a multilayer composite structure stacked according to the invention can be implemented for other applications where conductive patterns are exposed to electromagnetic radiation, such as magnetic stripe structures. for example.

Abstract

The structure has a stack of layers (20, 24-27) intercalated between layers (28-33) comprising a conductor pattern with polarization rotation function. The layers (20, 24-27) are made of a core material such as polyurethane or polymethacrylimide foam, and the layers (28-33) are made of a skin material such as epoxy glass or copper. The layers (20, 24-27) have recesses (21) crossing both sides of the layers (20, 24-27), where the recesses of two attached layers are connected two-by-two through holes (35) in the layers (28-33).

Description

La présente invention concerne une structure composite à plusieurs couches empilées dont l'échauffement reste limité sous l'effet d'un rayonnement électromagnétique. Elle s'applique par exemple dans les domaines de la détection et des télécommunications.The present invention relates to a multilayer composite structure stacked whose heating remains limited under the effect of electromagnetic radiation. It applies for example in the fields of detection and telecommunications.

La portée sans cesse croissante des antennes impose des émissions d'ondes électromagnétiques toujours plus élevées en puissance. Et les fonctions sans cesse plus évoluées des antennes entraînent une complexité toujours plus grande. La gamme des matériaux utilisés pour assurer les diverses fonctions s'élargit, ces matériaux étant plus ou moins exposés au rayonnement selon leur agencement par rapport à l'émetteur de puissance. Or tous les matériaux présentent des propriétés d'échauffement lorsqu'ils sont traversés par un rayonnement électromagnétique, en fonction de leur facteur de perte, noté « tgδ ».The ever increasing range of antennas imposes emissions of electromagnetic waves always higher in power. And the increasingly advanced functions of the antennas lead to ever greater complexity. The range of materials used to perform the various functions expands, these materials being more or less exposed to radiation according to their arrangement with respect to the power transmitter. However, all the materials have heating properties when they are crossed by electromagnetic radiation, depending on their loss factor, denoted "tgδ".

Le facteur de perte tgδ d'un matériau traduit sa capacité à absorber une partie de la puissance d'un rayonnement auquel il est exposé, cette puissance étant restituée par le matériau par dissipation de chaleur. Ainsi, plus le facteur de perte tgδ d'un matériau est élevé, plus il s'échauffe lorsqu'il est exposé à un rayonnement électromagnétique. Dans l'ordre croissant du facteur de perte, peuvent être cités le vide qui est un milieu présentant un facteur de perte quasiment nul et l'air qui est un milieu présentant un facteur de perte encore extrêmement faible. En première approche, le facteur de perte augmente avec la densité du matériau, c'est pourquoi les matériaux solides présentent des facteurs de perte bien supérieurs au vide et à l'air.The loss factor tgδ of a material reflects its ability to absorb a portion of the power of radiation to which it is exposed, this power being restored by the material by heat dissipation. Thus, the higher the loss factor tgδ of a material, the more it heats up when exposed to electromagnetic radiation. In the ascending order of the loss factor, there can be mentioned the vacuum which is a medium with a loss factor of almost zero and the air which is a medium with a loss factor that is still extremely low. As a first approach, the loss factor increases with the density of the material, which is why solid materials have loss factors much higher than vacuum and air.

Dans les antennes émettrices à forte puissance, notamment pour leurs parties directement exposées à l'émetteur de puissance, il doit être tenu compte de ce phénomène. Cela n'est pas sans poser problème. Par exemple dans des antennes à balayage électronique, des matériaux sont utilisés pour jouer le simple rôle d'entretoise, c'est-à-dire que leur seule fonction est d'assurer un espacement déterminé entre deux éléments ayant eux-même des fonctions plus évoluées. La matière dont sont constituées les entretoises n'a en soi aucune importance, à ceci près que les entretoises doivent perturber le moins possible le fonctionnement de l'antenne, comme par exemple absorber le moins possible de sa puissance et ainsi chauffer le moins possible.In high-power transmitting antennas, especially for their parts directly exposed to the power transmitter, this phenomenon must be taken into account. This is not without problem. For example in electronic scanning antennas, materials are used to play the simple role of spacer, that is to say that their only function is to ensure a determined spacing between two elements having themselves more functions. advanced. The material of which the spacers are made has no importance in itself, except that the spacers must disturb as little as possible the operation of the antenna, as for example to absorb as little power as possible and thus heat as little as possible.

Par exemple, il peut être cité le cas des « Grilles de Rotation de Polarisation », que l'on appellera polariseur par la suite. Un polariseur est un dispositif classique dans les antennes à balayage électronique qui transforme les ondes à polarisation horizontale qui la traversent en ondes à polarisation verticale et vice-versa. Un polariseur comporte un support sur lequel est disposé une grille conductrice, comme une grille à méandre ou une grille de fils métalliques, la grille conductrice présentant des propriétés polarisantes. Les polariseurs actuels ont des fonctions très évoluées qui nécessitent l'utilisation de plusieurs grilles superposées et donc l'utilisation d'entretoises entre les grilles. Les solutions actuelles consistent à utiliser des entretoises en matériaux mousse et des supports de grille en verre époxydique, le tout assemblé en structure composite de type « sandwich ». Une structure composite de type sandwich est un assemblage d'au moins deux matériaux différents se présentant en plaques, l'un appelé « matériau d'âme » constituant l'ossature et assurant la tenue mécanique et l'autre appelé « matériau de peau » constituant la protection et assurant la structure. Les plaques des deux matériaux sont assemblées par collage. L'épaisseur des plaques de matériau d'âme est bien supérieure à celle des plaques de matériau de peau. Dans le cadre des polariseurs actuels, le matériau de peau est constitué par des circuits imprimés en verre époxy comportant un motif de cuivre non alimenté en courant électrique, ce motif jouant le rôle de grille polarisante. Le matériau d'âme est une mousse, les matériaux de type mousse étant des matériaux solides de densité faible présentant donc le double avantage d'avoir un poids léger et un facteur de perte assez faible. Mais dans des conditions d'utilisation extrêmes, à pleine puissance d'émission et à température extérieure très élevée de l'ordre de 80°C par exemple, il arrive encore fréquemment que ces matériaux s'échauffent, risquant de détériorer tout ou partie du polariseur et même de l'antenne.For example, the case of "Polarization Rotation Grids" can be cited, which will be called polarizer afterwards. A polarizer is a conventional device in electronic scanning antennas that transforms horizontally polarized waves that pass through it into vertically polarized waves and vice versa. A polarizer comprises a support on which is disposed a conductive grid, such as a meander grid or a grid of metal wires, the conductive grid having polarizing properties. Current polarizers have very advanced functions that require the use of several superimposed grids and therefore the use of spacers between the grids. Current solutions include the use of foamed spacers and epoxy glass grid supports, all of which are assembled into a sandwich composite structure. A sandwich type composite structure is an assembly of at least two different materials in the form of plates, one called "core material" constituting the framework and providing the mechanical strength and the other called "skin material" constituting the protection and ensuring the structure. The plates of the two materials are assembled by gluing. The thickness of the core material plates is much greater than that of the skin material plates. In the context of current polarizers, the skin material consists of epoxy glass printed circuits having a non-electric power copper pattern, this pattern acting as a polarizing gate. The core material is a foam, the foam type materials being low density solid materials thus having the double advantage of having a light weight and a low loss factor. But under extreme conditions of use, at full transmission power and very high outside temperature of the order of 80 ° C for example, it is still common for these materials to heat up, potentially damaging all or part of the polarizer and even the antenna.

Les solutions qui consistent à changer de matériau ne sont pas très efficaces, les mousses étant déjà les matériaux à facteur de perte le plus faible et les mousses entre elles ne présentant pas des facteurs de perte très différents. Cela ne permet pas de diminuer l'échauffement dans des proportions importantes. Seul un test en fin de cycle de production, consistant à échauffer les structures composites avant assemblage, permet de tester convenablement les réalisations et d'éliminer les réalisations défectueuses.Solutions that involve changing material are not very efficient, foams are already the weakest loss factor materials and foams between them do not exhibit very low loss factors. different. This does not reduce the heating in significant proportions. Only a test at the end of the production cycle, consisting in heating the composite structures before assembly, makes it possible to properly test the achievements and eliminate the defective implementations.

Il apparaît que selon la qualité de réalisation de la structure sandwich, la marge de sécurité par rapport aux matériaux utilisés peut être trop étroite. En premier lieu, et ceci même en condition d'utilisation normale, il conviendrait que les structures composites utilisées ne montent pas à des températures trop proches de la température de transition vitreuse du matériau de type mousse, température notée « Tg ». La température de transition vitreuse d'une mousse est la température à laquelle elle passe de l'état vitreux, c'est-à-dire de l'état solide auquel elle est capable d'assurer un rôle d'entretoise, à un état que l'on peut qualifier de caoutchoutique, qui est un état intermédiaire plu mou auquel elle n'est plus capable d'assurer un rôle d'entretoise.It appears that according to the quality of realization of the sandwich structure, the margin of safety with respect to the materials used may be too narrow. First, and this even under normal use conditions, the composite structures used should not rise to temperatures too close to the glass transition temperature of the foam-type material, temperature "Tg". The glass transition temperature of a foam is the temperature at which it goes from the vitreous state, that is to say from the solid state to which it is capable of acting as a spacer, to a state which can be described as rubbery, which is a softer intermediate state to which it is no longer capable of acting as a spacer.

L'invention se propose donc notamment de maintenir les matériaux de type mousse à une température nettement inférieure à leur température de transition vitreuse, en diminuant la chaleur dissipée et en favorisant son évacuation par diminution du volume de matière traversé. A cet effet, l'invention a pour objet une structure composite à plusieurs couches empilées soumise à un rayonnement électromagnétique. Elle comporte un empilement de plaques d'un matériau d'âme, les plaques de matériau d'âme étant intercalées entre des plaques d'un matériau de peau comportant un motif conducteur. Chaque plaque de matériau d'âme comporte des évidements la traversant de part en part, les évidements de deux plaques mitoyennes de matériau d'âme étant reliés deux à deux par un trou dans la plaque de matériau de peau les séparant.The invention therefore proposes in particular to maintain the foam-type materials at a temperature well below their glass transition temperature, by reducing the heat dissipated and promoting its evacuation by reducing the volume of material passed through. For this purpose, the subject of the invention is a composite structure with several stacked layers subjected to electromagnetic radiation. It comprises a stack of plates of a core material, the core material plates being interposed between plates of a skin material having a conductive pattern. Each core material plate has recesses passing therethrough, the recesses of two adjacent core material plates being connected in pairs by a hole in the skin material plate separating them.

En effet, la quantité de chaleur dissipée est une fonction croissant avec le volume de matière traversé. Mais il s'agit surtout de ne perturber ni le fonctionnement de l'antenne, ni sa conception. Car l'épaisseur de la structure composite est souvent une caractéristique nécessaire au bon fonctionnement de l'antenne, par exemple elle peut être fonction de la longueur d'onde émise. Il ne peut donc être envisagé de la diminuer, sauf peut-être dans quelques cas particuliers. De plus, l'encombrement extérieur de la structure composite peut être une contrainte nécessaire à l'assemblage de l'ensemble. Par exemple la structure composite peut contribuer de manière décisive à la rigidité et la compacité de l'assemblage. D'après l'invention, une bonne manière de diminuer le volume de matière traversé sans modifier le volume extérieur de la structure composite est de l'évider, c'est à dire de procéder à des retraits de matière qui ne changent en rien son aspect extérieur. Par ailleurs, les évidements sont pratiqués de manière à optimiser l'évacuation de la chaleur dissipée vers l'extérieur de la structure composite par aération naturelle, afin de diminuer encore l'échauffement.Indeed, the amount of heat dissipated is an increasing function with the volume of material passed through. But it is mainly to disturb neither the operation of the antenna nor its design. Because the thickness of the composite structure is often a necessary feature for the proper functioning of the antenna, for example it may be a function of the wavelength issued. It can not be considered to reduce it, except perhaps in a few particular cases. In addition, the external dimensions of the composite structure may be a constraint necessary for assembling the assembly. For example the composite structure can contribute decisively to the rigidity and compactness of the assembly. According to the invention, a good way of reducing the volume of material passed through without modifying the external volume of the composite structure is to hollow out it, that is to say to make withdrawals of material which do not change its substance. external appearance. In addition, the recesses are made in such a way as to optimize the evacuation of the heat dissipated towards the outside of the composite structure by natural aeration, in order to further reduce the heating.

Avantageusement, les motifs conducteurs sur les plaques de matériau de peau peuvent avoir une fonction de rotation de polarisation du rayonnement électromagnétique.Advantageously, the conductive patterns on the skin material plates can have a polarization rotation function of the electromagnetic radiation.

Par exemple, les plaques de matériau de peau et les plaques de matériau d'âme peuvent être assemblées par collage.For example, the skin material plates and the core material plates can be assembled by gluing.

Par exemple encore, les plaques de matériau d'âme ont toutes le même motif d'évidement et par exemple chaque évidement peut être en forme de cylindres dont l'axe est normal au plan de la plaque.For example again, the core material plates all have the same recess pattern and for example each recess can be in the form of cylinders whose axis is normal to the plane of the plate.

Les plaques de matériau de peau peuvent être en verre époxy, les plaques de matériau d'âme peuvent être en mousse polyuréthane ou polyméthacrylimide et le motif conducteur sur les plaques de matériau de peau peut être en cuivre.The skin material plates may be epoxy glass, the core material plates may be polyurethane foam or polymethacrylimide and the conductive pattern on the skin material plates may be copper.

Dans un mode de réalisation, les trous des différentes plaques de matériau de peau peuvent être alignés.In one embodiment, the holes of the different skin material plates may be aligned.

L'invention a encore pour principaux avantages qu'elle ne modifie pas l'encombrement extérieur de la structure à laquelle elle est appliquée, n'induisant ainsi aucun changement de conception du produit final dans lequel elle est utilisée. Elle reprend aussi exactement les mêmes principes de construction que les solutions classiques, autant en terme de matériaux et structures de base que d'outillage. Le surcoût qu'elle induit est donc tout à fait minime. Sa configuration beaucoup plus ouverte et aérée lui confère non seulement une grande capacité à évacuer la chaleur de manière naturelle, mais également des propriétés de désorption de l'humidité qui diminuent encore son échauffement. L'invention présente aussi un poids moins élevé en fonction de l'ampleur des évidements, avantage d'importance si l'on considère des applications dans un domaine comme l'avionique par exemple.The main advantages of the invention are that it does not modify the external dimensions of the structure to which it is applied, thus inducing no change in the design of the final product in which it is used. It also takes exactly the same principles of construction as conventional solutions, both in terms of materials and basic structures that tools. The extra cost it induces is therefore very minimal. Its much more open and airy configuration gives it not only a great ability to evacuate heat in a natural way, but also moisture desorption properties that diminish still warming up. The invention also has a lower weight depending on the extent of the recesses, advantage of importance if we consider applications in a field such as avionics for example.

D'autres caractéristiques et avantages de l'invention apparaîtront à l'aide de la description qui suit faite en regard de dessins annexés qui représentent :

  • les figures 1a et 1b, un exemple de réalisation d'un dispositif de polariseur selon l'invention par deux vues en coupe,
  • les figures 2a et 2b, par deux graphiques l'échauffement d'un dispositif de polariseur selon l'art antérieur et l'échauffement d'un dispositif de polariseur selon l'invention.
Other characteristics and advantages of the invention will become apparent with the aid of the following description made with reference to appended drawings which represent:
  • FIGS. 1a and 1b, an exemplary embodiment of a polarizer device according to the invention with two sectional views,
  • FIGS. 2a and 2b, by two graphs, the heating of a polarizer device according to the prior art and the heating of a polarizer device according to the invention.

Les figures 1a et 1b illustrent respectivement par une vue de face et une vue en coupe un exemple de réalisation d'un polariseur selon l'invention.FIGS. 1a and 1b respectively show a front view and a sectional view of an exemplary embodiment of a polarizer according to the invention.

La figure 1a illustre par une vue de face une plaque 20 d'un matériau d'âme du type mousse polyuréthane par exemple, la plaque ayant été évidée d'une face à l'autre en plusieurs endroits 21. Avantageusement, les évidements 21 sont par exemple cylindriques et tous identiques, ils sont uniformément répartis et dessinent par exemple un motif régulier formant des triangles équilatéraux 22 et 23 sur toute la surface de la plaque 20. Dans l'exemple de réalisation, les cylindres d'évidement ont un diamètre de l'ordre de 10 millimètres environ et les triangles équilatéraux 22 et 23 formant le motif ont une base de l'ordre de 20 millimètres environ. Cela correspond à un taux d'évidement approximatif de 35%. Mais selon la surface de la plaque de matériau d'âme, la taille des évidements et le motif qu'ils dessinent peuvent être différents. En tous cas, une diminution du volume de matière par évidement dans une proportion de l'ordre d'un tiers permet au matériau d'âme de continuer à jouer son rôle d'ossature de la structure composite. Au-delà, cela pourrait nuire à la tenue mécanique de l'ensemble. De plus, il est préférable d'éviter d'évider la plaque au niveau des bords, car cela permet de ne pas modifier l'encombrement extérieur de la structure et donc de ne pas perturber son implantation dans le produit final qui l'utilise. Par diminution du volume de matière traversé, les évidements vont permettre de limiter la quantité de chaleur dissipée lorsque la structure est exposée à un rayonnement électromagnétique.FIG. 1a illustrates, by a front view, a plate 20 of a core material of the polyurethane foam type, for example, the plate having been recessed from one face to the other in several places. Advantageously, the recesses 21 are for example cylindrical and all identical, they are uniformly distributed and draw for example a regular pattern forming equilateral triangles 22 and 23 over the entire surface of the plate 20. In the embodiment, the recess cylinders have a diameter of about 10 millimeters and the equilateral triangles 22 and 23 forming the pattern have a base of the order of about 20 millimeters. This corresponds to an approximate recess rate of 35%. But depending on the surface of the core material plate, the size of the recesses and the pattern they draw may be different. In any case, a decrease in the volume of material by recess in a proportion of about one-third allows the core material to continue to play its role of framework of the composite structure. Beyond that, it could affect the mechanical strength of the whole. In addition, it is preferable to avoid hollowing out the plate at the edges, since this makes it possible not to modify the external dimensions of the structure and thus not to disturb its implantation in the final product that uses it. By decreasing volume of material traversed, the recesses will allow to limit the amount of heat dissipated when the structure is exposed to electromagnetic radiation.

La figure 1b présente l'empilement de cinq couches du type de celle de la figure 1a. La plaque 20 de matériau d'âme est vue au niveau de l'axe de coupe 34 de la figure 1a, c'est pourquoi trois évidements seulement sont visibles sur la figure 1b. Les cinq couches de matériau d'âme 20, 24, 25, 26 et 27, ont par exemple toutes été évidées de manière identique. Elles présentent ainsi chacune trois évidements. Les cinq couches de matériau d'âme ont été avantageusement collées à six couches de matériau de peau 28, 29, 30, 31, 32 et 33 en verre époxy du type circuit imprimé par exemple comportant un motif de cuivre non alimenté. Une couche de matériau d'âme est intercalée entre deux couches de matériau de peau, c'est là que réside la structure sandwich multicouche, puis collée. L'assemblage peut se faire en enduisant une face de la plaque de matériau d'âme de colle, puis en lui adjoignant une plaque de matériau de peau, enfin en répétant l'opération sur l'autre face. Ce mode opératoire permet de réduire la quantité de colle utilisée au niveau des évidements et donc également la quantité de matière traversée par le rayonnement. Mais il peut également être envisagé d'enduire de colle les plaques de matériau de peau, même au niveau des évidements de la plaque de matériau d'âme, puis de les assembler à la plaque de matériau d'âme.Figure 1b shows the stack of five layers of the type of that of Figure 1a. The plate 20 of core material is seen at the cutting axis 34 of Figure 1a, therefore, only three recesses are visible in Figure 1b. The five layers of core material 20, 24, 25, 26 and 27, for example, have all been recessed identically. They thus each have three recesses. The five layers of core material have been advantageously bonded to six layers of skin material 28, 29, 30, 31, 32 and 33 of epoxy glass of the printed circuit type for example having a non-powered copper pattern. A layer of core material is interposed between two layers of skin material, which is where the multilayer sandwich structure lies, and then glued. The assembly can be done by coating one side of the glue core material plate, then attaching a skin material plate, and repeating the operation on the other side. This procedure reduces the amount of glue used in the recesses and therefore also the amount of material traversed by the radiation. But it can also be envisaged to glue the skin material plates even with the recesses of the core material plate and then to assemble them to the core material plate.

Au moins un trou 35 est réalisé dans chaque couche de matériau de peau au niveau de chaque évidement du matériau d'âme. Par exemple, trois trous formant les sommets d'un triangle sont réalisés au niveau de chaque évidement, dont un seul est visible sur la figure 1b. Par exemple, ce sont des trous circulaires d'un diamètre de l'ordre d'un millimètre. En tous cas, leur diamètre est nettement inférieur à la plus petite largeur des évidements. En effet, les trous dans le matériau de peau ne doivent pas empêcher celui-ci de jouer son rôle de protection et de structure. Ainsi il ne faut pas faire trop de trous ou faire de trop gros trous. En particulier, percer le matériau de peau selon les évidements du matériau d'âme exactement amènerait à un affaiblissement de la structure composite finale qui nuirait grandement à sa rigidité. Dans cet exemple de réalisation, les trous des différentes couches sont alignés, ce qui a permis de les percer indifféremment avant ou après l'assemblage. La fonction des trous est de favoriser l'aération naturelle des évidements du matériau d'âme et ainsi l'évacuation vers l'extérieur de la chaleur dissipée.At least one hole 35 is made in each layer of skin material at each recess of the core material. For example, three holes forming the vertices of a triangle are made at each recess, only one of which is visible in FIG. 1b. For example, they are circular holes with a diameter of the order of one millimeter. In any case, their diameter is much smaller than the smallest width of the recesses. Indeed, the holes in the skin material must not prevent it from playing its role of protection and structure. So do not make too many holes or make big holes. In particular, piercing the skin material according to the recesses of the core material exactly would lead to a weakening of the final composite structure which would greatly impair its rigidity. In this embodiment, the holes of the different layers are aligned, which made it possible to pierce them indifferently before or after assembly. The function of the holes is to promote the natural ventilation of the recesses of the core material and thus the evacuation to the outside of the dissipated heat.

La figure 2a illustre par un graphique l'échauffement d'un polariseur selon l'art antérieur, c'est-à-dire ne comportant ni évidement des matériaux d'âme ni percement des matériaux de peau. La figure 2b illustre par un graphique l'échauffement du polariseur de l'exemple décrit précédemment. Les deux dispositifs de polariseur ont été utilisés dans une même antenne à balayage électronique émettant un signal hyperfréquence de forte puissance directement sur la structure composite. Dans les deux dispositifs, les couches de matériau de peau sont des circuits imprimés en verre époxy sur lesquelles sont imprimés des motifs de cuivre non alimentés. Dans les deux dispositifs, c'est une même mousse polyméthacrylimide qui constitue le matériau d'âme. Les deux graphiques sont dans un système d'axe où l'axe des abscisses représente le temps en heures et l'axe des ordonnées représente la température en degrés celsius.FIG. 2a graphically illustrates the heating of a polarizer according to the prior art, that is to say having neither recess core materials nor piercing skin materials. FIG. 2b graphically illustrates the heating of the polarizer of the example described above. The two polarizer devices were used in the same electronic scanning antenna emitting a high power microwave signal directly on the composite structure. In both devices, the layers of skin material are printed epoxy glass circuit boards printed with non-powered copper patterns. In both devices, it is the same polymethacrylimide foam which constitutes the core material. The two graphs are in an axis system where the x-axis represents the time in hours and the y-axis represents the temperature in degrees Celsius.

Pour le dispositif selon l'art antérieur, la courbe 40 montre l'évolution de la température de peau externe, c'est-à-dire de la couche au contact de l'air ambiant, et la courbe 41 montre l'évolution de la température du coeur de la structure, c'est-à-dire des couches de matériau d'âme. Il peut être constaté que la température de peau externe ne se stabilise qu'un peu au-dessus de 60°C et que la température au coeur de la structure grimpe jusqu'aux alentours de 145°C.For the device according to the prior art, the curve 40 shows the evolution of the outer skin temperature, that is to say the layer in contact with the ambient air, and the curve 41 shows the evolution of the core temperature of the structure, i.e. layers of core material. It can be seen that the outer skin temperature stabilizes only slightly above 60 ° C and that the core temperature rises to around 145 ° C.

De manière similaire pour le dispositif de l'exemple de réalisation précédent, la courbe 42 montre l'évolution de la température de peau externe, c'est-à-dire des couches 28 et 33, et la courbe 41 montre l'évolution de la température du coeur de la structure, c'est-à-dire des couches 20, 24, 25, 26 et 27. La température de peau externe se stabilise un peu en dessous de 60°C et la température au coeur de la structure se stabilise dès 100°C.Similarly for the device of the previous embodiment, curve 42 shows the evolution of the outer skin temperature, that is to say layers 28 and 33, and curve 41 shows the evolution of the temperature of the core of the structure, that is to say the layers 20, 24, 25, 26 and 27. The outer skin temperature stabilizes a little below 60 ° C and the temperature at the heart of the structure stabilizes at 100 ° C.

Avec des matériaux strictement identiques et pour une application identique, la structure composite selon l'invention se montre donc bien plus efficace à limiter l'échauffement. Des compléments de mesure montrent également que le rapport de température entre le coeur de la structure et la peau externe est diminué d'environ 50%. Ainsi, les résultats obtenus vont au-delà de ce qui pourrait être attendu d'une structure présentant un taux d'évidement de l'ordre de 35% seulement. En effet, l'aération produite par les trous facilite directement les échanges thermiques avec l'extérieur.With strictly identical materials and for an identical application, the composite structure according to the invention is therefore much more effective in limiting the heating. Measuring complements also show that the temperature ratio between the core of the structure and the outer skin is decreased by about 50%. Thus, the results obtained go beyond what could be expected of a structure having a recess rate of the order of 35% only. Indeed, the aeration produced by the holes directly facilitates heat exchanges with the outside.

L'exemple de réalisation présenté concerne un polariseur, mais une structure composite à plusieurs couches empilées selon l'invention peut être mise en oeuvre pour d'autres applications où des motifs conducteurs sont exposés à un rayonnement électromagnétique, comme les structures à bande magnétique interdite par exemple.The exemplary embodiment presented relates to a polarizer, but a multilayer composite structure stacked according to the invention can be implemented for other applications where conductive patterns are exposed to electromagnetic radiation, such as magnetic stripe structures. for example.

Claims (10)

Structure composite à plusieurs couches empilées soumise à un rayonnement électromagnétique, caractérisée en ce qu'elle comporte un empilement de plaques d'un matériau d'âme (20, 24, 25, 26, 27), les plaques de matériau d'âme étant intercalées entre des plaques d'un matériau de peau (28, 29, 30, 31, 32, 33) comportant un motif conducteur, chaque plaque de matériau d'âme comportant des évidements (21) la traversant de part en part, les évidements de deux plaques mitoyennes de matériau d'âme étant reliés deux à deux par un trou (35) dans la plaque de matériau de peau les séparant, chacune des deux plaques externes de matériau de peau comportant un trou au niveau de chaque évidemment de la plaque de matériau d'âme qui lui est adjacente.Multilayered composite structure subjected to electromagnetic radiation, characterized in that it comprises a stack of plates of a core material (20, 24, 25, 26, 27), the core material plates being interposed between plates of a skin material (28, 29, 30, 31, 32, 33) having a conductive pattern, each core material plate having recesses (21) passing therethrough, the recesses of two adjacent sheets of core material being connected in pairs by a hole (35) in the skin material plate separating them, each of the two outer plates of skin material having a hole at each of the evident portions of the plate of soul material that is adjacent to it. Structure composite à plusieurs couches empilées soumise à un rayonnement électromagnétique selon la revendication 1, caractérisée en ce que les motifs conducteurs sur les plaques de matériau de peau (28, 29, 30, 31, 32, 33) ont une fonction de rotation de polarisation du rayonnement électromagnétique.Multilayer composite multilayer structure subjected to electromagnetic radiation according to claim 1, characterized in that the conductive patterns on the skin material plates (28, 29, 30, 31, 32, 33) have a polarization rotation function electromagnetic radiation. Structure composite à plusieurs couches empilées soumise à un rayonnement électromagnétique selon la revendication 1 ou 2, caractérisée en ce que les plaques de matériau de peau (28, 29, 30, 31, 32, 33) et les plaques de matériau d'âme (20, 24, 25, 26, 27) sont collées.An electromagnetic radiation stacked multilayer composite structure according to claim 1 or 2, characterized in that the skin material plates (28, 29, 30, 31, 32, 33) and the core material plates ( 20, 24, 25, 26, 27) are glued. Structure composite à plusieurs couches empilées soumise à un rayonnement électromagnétique selon la revendication 1, 2 ou 3, caractérisée en ce que les plaques de matériau d'âme (20, 24, 25, 26, 27) ont toutes le même motif d'évidement.An electromagnetic radiation stacked multilayer composite structure according to claim 1, 2 or 3, characterized in that the core material plates (20, 24, 25, 26, 27) all have the same recess pattern . Structure composite à plusieurs couches empilées soumise à un rayonnement électromagnétique selon la revendication 1, 2, 3 ou 4, caractérisée en ce que les évidements (21) des plaques de matériau d'âme (20, 24, 25, 26, 27) sont en forme de cylindres dont les axes sont normaux au plan de la plaque.A multilayer composite structure subjected to electromagnetic radiation according to claim 1, 2, 3 or 4, characterized in that the recesses (21) of the material plates webs (20, 24, 25, 26, 27) are cylinder-shaped whose axes are normal to the plane of the plate. Structure composite à plusieurs couches empilées soumise à un rayonnement électromagnétique selon la revendication 1, 2, 3, 4 ou 5, caractérisée en ce que les plaques de matériau de peau (28, 29, 30, 31, 32, 33) sont en verre époxydique.Multilayer composite multilayer structure subjected to electromagnetic radiation according to claim 1, 2, 3, 4 or 5, characterized in that the skin material plates (28, 29, 30, 31, 32, 33) are made of glass epoxy. Structure composite à plusieurs couches empilées soumise à un rayonnement électromagnétique selon la revendication 1, 2, 3, 4, 5 ou 6, caractérisée en ce que les plaques de matériau d'âme (20, 24, 25, 26, 27) sont en mousse polyuréthane.An electromagnetic radiation stacked multilayer composite structure according to claim 1, 2, 3, 4, 5 or 6, characterized in that the core material plates (20, 24, 25, 26, 27) are polyurethan foam. Structure composite à plusieurs couches empilées soumise à un rayonnement électromagnétique selon la revendication 1, 2, 3, 4, 5 ou 6, caractérisée en ce que les plaques de matériau d'âme (20, 24, 25, 26, 27) sont en mousse polyméthacrylimide.An electromagnetic radiation stacked multilayer composite structure according to claim 1, 2, 3, 4, 5 or 6, characterized in that the core material plates (20, 24, 25, 26, 27) are polymethacrylimide foam. Structure composite à plusieurs couches empilées soumise à un rayonnement électromagnétique selon la revendication 1, 2, 3, 4, 5, 6 ou 7, caractérisée en ce que le motif conducteur sur les plaques de matériau de peau (28, 29, 30, 31, 32, 33) est en cuivre.Multilayer composite multilayer structure subjected to electromagnetic radiation according to claim 1, 2, 3, 4, 5, 6 or 7, characterized in that the conductive pattern on the skin material plates (28, 29, 30, 31 , 32, 33) is made of copper. Structure composite à plusieurs couches empilées soumise à un rayonnement électromagnétique selon la revendication 1, 2, 3, 4, 5, 6, 7 ou 8, caractérisée en ce que les trous des différentes plaques de matériau de peau (35) sont alignés.An electromagnetic radiation stacked multilayer composite structure according to claim 1, 2, 3, 4, 5, 6, 7 or 8, characterized in that the holes of the different skin material plates (35) are aligned.
EP06126432A 2006-01-03 2006-12-18 Composite structure with several stacked layers subjected to electromagnetic radiation Withdrawn EP1804336A1 (en)

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