MULTILAYER ULTRATHIN AND FLEXIBLE UNIT HEATER CELLS FOR INFRARED STEALTH

Description

Field of the Invention

[0001] The present invention relates to a multilayer, ultra-thin and flexible system of unit heater cells, obtained by printed electronic technology, for infrared (IR) stealth.

[0002] The invention could also be used in applications in fields like aeronautics or automotive industry, for providing customized heating parts regarding localized areas, such as for example in defrost applications.

Background and Prior Art

[0003] In the context of current military conflicts, and mainly asymmetric conflicts, the protection of troops and equipment is essential. Military strategies in mission theatres are also permanently in evolution, mainly due to the emergence of increasingly efficient and sophisticated technologies. This essential aspect of protection for the troops is now reinforced by calls for proposals of the European Defence Industrial Development Programme (EDIDP).

[0004] On the ground, the main objective in terms of protection and therefore stealth is, according to danger order :

• not to be seen at long distance (12-20 km) ;
• not to be recognized, with change of signature occurring at medium distance (4-12 km) ;
• not to be identified, with possible use of decoy system (<4 km).

[0005] Day or night, a widely used means of detection remains infrared thermography, which enables to perceive the thermal signature of a soldier, (armoured) vehicle, etc.

[0006] The idea at the basis of the present invention is therefore to be able to couple both camouflage in the visible while being stealthy in the infrared, either by blending into the environment (i.e. becoming "invisible") or by adjusting the thermal signature to dupe the enemy.

[0007] Document US 8,077,071 B2 (or US 2010/0288116 A1) discloses a number of systems and assemblies for simultaneous adaptive camouflage, concealment and deception. The assemblies that can be used in the systems include a vinyl substrate layer and a miniaturized thermoelectric device array secured to the vinyl substrate layer. The miniaturized thermoelectric device array is configured to provide an adaptive thermal signature to a side of the miniaturized thermoelectric device array that faces outward from the vinyl substrate layer. A flexible image display matrix can be secured on the vinyl substrate layer, said flexible image display matrix being configured to display visual images. A laminate layer can be secured over the vinyl substrate layer covering the flexible image display matrix and the miniaturized thermoelectric device array to provide protection and strengthen the assemblies. One or more nanomaterials can be disposed on the vinyl substrate layer or the laminate layer to provide thermal or radar suppression. This disclosure seems to be only a concept, a suggestion for combining a succession of new technologies not yet turned into practice, which would be expensive and lacking flexibility.

[0008] Document WO 2009/040823 A2 relates to a thermal vision countermeasure system to enable concealment of objects from identification by thermal imaging night vision systems, including a screen made of thermoelectric (Peltier effect) modules, disposed between the target object and an IR detector. The screen, formed of a number of thermoelectric units, is coupled to the target object, and the thermoelectric unit includes a thermoelectric cooler (TEC) module coupled to a plate formed of a material selected from aluminium, copper, or aluminium with copper, the plate being substantially larger than the TEC module. This technology allows full coverage with interchangeable and bee structure modules, providing IR cartography and radar stealth. However this solution is complex, expensive to develop, provides poor cartography resolution and does not allow visible dissimulation.

[0009] Document WO 2012/169958 A1 discloses a device for signature adaptation, comprising at least one surface element arranged to assume a determined thermal distribution, wherein said surface element comprises at least one temperature generating element arranged to generate a predetermined temperature gradient to a portion of said surface element. The surface element also comprises at least one radar suppressing element, wherein said radar suppressing element is arranged to suppress reflections of incident radio waves. The invention also concerns an object provided with a device for signature adaptation. A full coverage is obtained thanks to interchangeable and honeycomb-like hexagonal unitary panels structure, with good spatial resolution. However, this solution is complex, expensive to develop, not easy to attach on site and does not provide visible dissimulation (not embedded).

[0010] Document US 9,777,998 B1 discloses a device provided for camouflaging an object from an infrared detection apparatus. The device includes a cloak positionable between the object and the infrared detection apparatus. The cloak includes a layer of infrared absorptive material including a plurality of silicon nanowires. A flexible substrate has a first surface operatively connected to an inner surface of the layer. The substrate includes a heat dissipation arrangement for dissipating heat generated by the cloak during operation. An array of infrared emitters is operatively connected to a second surface of the substrate. The array of infrared emitters selectively radiates an infrared pattern to disguise the object to the infrared detection apparatus. The heat dissipation arrangement includes a channel formed in the flexible substrate and adapted for receiving a cooling fluid therein. The heat dissipation arrangement further includes a pump for recirculating the cooling fluid through the channel. Each IR emitter is electrically connected to a corresponding contact by a corresponding line, each contact is operatively connected to a processing unit, e.g. a controller. The controller is configured to selectively actuate each IR emitter such that each actuated IR emitter transmits an infrared signal that is visible to IR reader. This disclosure is very conceptual and poor in details.

[0011] Document FR 2 733 311 A1 discloses a fibre optics network having a grid of fibre optic cables with a section having the sleeve removed and fed from an input point. Different infrared bands are generated and radiated from one of the optical lines. The system measures the background radiance in the different infrared bands and sets the radiated levels to provide camouflage. The optical cables are embedded in a flexible outer section.

[0012] Document CN 110058428 A relates to a carbon material based double-sided active infrared emissivity adjustment thin film, in particular to a thin film material based on a carbon material (including graphene, carbon nanotubes, amorphous carbon, carbon black and the like) and ionic liquid. A flexible device with double-sided infrared radiation control can be realized through a voltage regulation mode, with low working voltage and power consumption, large emissivity adjusting amplitude and simple structure. The adjustment thin film is suitable for large-scale production, has good mechanical bending performance, can be widely applied to infrared camouflage or stealth on the surfaces of automobiles, ships, airplanes, satellites and the like, and can also be applied to the surfaces of batteries, micro-nano satellites and the like to realize temperature control.

[0013] Lin Xiao et al., in Fast Adaptive Thermal Camouflage Based on Flexible VO2/Graphene/ CNT Thin Films, Nano Lett. 2015, 15, 8365-8370 (Am. Chem. Soc.), demonstrate an active cloaking device capable of efficient thermal radiance control, which consists of a vanadium dioxide (VO₂) layer, with a negative differential thermal emissivity, coated on a graphene/carbon nanotube (CNT) thin film. A slight joule heating drastically changes the emissivity of the device, achieving rapid switchable thermal camouflage with a low power consumption and excellent reliability. This device is intended to find wide applications not only in artificial systems for infrared camouflage or cloaking but also in energy-saving smart windows and thermo-optical modulators.

[0014] Prior art IR stealth solutions generally present the following drawbacks:

• they are expensive ;
• they have a lack of flexibility in respect of on-site fixing or repair;
• they do not satisfy existing visible and aesthetic constraints ;
• they usually have a heavy and/or cumbersome design.

Aims of the Invention

[0015] The present invention aims to provide an efficient active IR stealth system, which is inexpensive, light and not bulky as well.

[0016] Another goal of the invention is to provide a flexible, easy-to-attach, embedded, customizable in terms of shape and/or pattern and object-matching solution.

[0017] Furthermore, the invention is intended to provide a spatial IR mapping with suitable resolution.

Summary of the Invention

[0018] The above aims of the invention are solved by an ultrathin, multilayer and encapsulated surface element according to claim 1 as well as the use of one or more surface elements according to claim 18.

[0019] A first aspect of the present invention relates to an ultrathin multilayer and encapsulated surface element for providing thermal signature adaptation with the purpose of infrared stealthing, and being also suited for camouflage in the visible, the element being flexible and comprising :

• a lower layer made of an insulation substrate ;
• an intermediate layer comprising a plurality of conductive tracks connectable to a power supply ;
• a plurality of active heat dissipation elements connected to the conductive tracks in the intermediate layer and capable to irreversibly provide a temperature increase by Joule effect in a given time interval when a current is fed into said heat dissipation elements, wherein each dissipation element comprises an electric conductive path extending between a first connexion and a second connection connecting respectively said dissipation element to least two of the conductive tracks, said dissipation element being capable of providing the temperature increase throughout said path from the first connection to the second connection when the current is fed, the heat dissipation elements and the conductive tracks being printed on the insulation substrate ;
• an upper layer made of a protective layer;

the heat dissipation elements having a size and being organized according to a spatial arrangement so as to provide a predetermined infrared spatial resolution, when a current is fed into said dissipation elements.

[0020] According to preferred embodiments, the surface element additionally comprises one or a suitable combination of the following features :

• the spatial arrangement is a two-dimensional array of cells or pixels comprising heat dissipation elements regularly spaced in two orthogonal directions, each cell or pixel being independently connectable to the power supply via the conductive tracks ;
• the spatial arrangement is a two-dimensional array of cells or pixels comprising heat dissipation elements regularly spaced in two orthogonal directions, each cell or pixel being connectable in a multiplexed manner to the power supply via the conductive tracks ;
• the heat dissipation elements are made of carbon containing material, PTC ferroelectric material or any resistive material having a resistance higher than the resistance of the conductive tracks ;
• the carbon-containing heat dissipation elements are made of carbon black, amorphous carbon, graphite, graphene nanoplatelets or carbon nanotubes ;
• the resistive material having a resistance higher than the conductive tracks is made of tungsten, a metallic alloy such as nichrome (NiCr), a transparent conducting oxide (TCO) film material such as aluminium-doped zinc oxide (AZO) or indium tin oxide (ITO), or a transparent conducting polymer such as Poly(3,4-ethylenedioxythiophene) PEDOT: poly(styrene sulfonate) PSS ;
• the conductive tracks are made of silver, gold, copper, aluminium or zinc ;
• the heat dissipation elements and the conductive tracks attachment to the substrate is obtained by inkjet, screen printing or serigraphy, flexography or sintering or other printing electronic deposition methods, possibly combined with heating or radiation such as oven, IPL, IR, UV, laser, and in particular 3D printing electronic deposition methods, such as spray with stencil, micro spray, 3D inkjet or ink dispensing ;
• the insulation substrate is made of a glass plate or of a polyimide film ;
• each cell comprises a module of conductive tracks having an input electrode and an output electrode, said input electrode and said output electrode having the form of interdigitated combs, and comprising an array of heat dissipation elements having the form of studs connected between the respective teeth of the interdigitated combs ;
• each cell or pixel is obtained by firstly printing the module of conductive tracks on the insulation substrate and secondly printing the array of heat dissipation elements onto both insulation substrate and module of conductive tracks, so that the heat dissipation elements are brought into close electrical contact with the module of conductive tracks ;
• each heat dissipation element has an essentially squared shape with an upper surface and a lower surface, said lower surface being provided with a side recess on two parallel edges, so that the heat dissipation element can be inserted between adjacent teeth of the first electrode and the second electrode respectively ;
• each cell or pixel has an independent input connection, respectively an independent output connection with the power supply ;
• each cell or pixel has a multiplexed connection with the power supply, it means that each cell or pixel of the two-dimensional array is powered by selecting respective row and column powering tracks corresponding to the (X, Y) position of the cell in the two-dimensional array ;
• row and column powering tracks overlap with insulation in the array thanks to positioning dielectric elements preventing unwanted electric contacts at the crossover points of the row and column powering tracks ;
• a flat or surface-mounted (SMD) diode is mounted on each pixel output, so that no leakage current could pass to an adjacent pixel and improperly lighten in whole or in part the corresponding row and column ;
• the protective layer is an encapsulating insulating layer obtained by serigraphy or spray and made of dielectric material such as an oxide, a polymer or a ceramic material.

[0021] A second aspect of the present invention relates to the use of one or more surface elements as described above, for providing an object or a person with a cover, sheet, blanket, casing or roofing capable of adapting the thermal signature of said object or person with the purpose of infrared stealthing, deception, camouflage, decoying or concealment.

[0022] Preferably, the plurality of heat dissipation elements selectively radiate a surface infrared pattern allowing to avoid the person or the object covered by said one or more surface elements to be detected by an infrared detection device.

Brief Description of the Drawings

[0023] 

FIG. 1 schematically represents the principle of an active system of heating resistors printed on a thermally and electrically resistive substrate, according to the present invention.

FIG. 2A and FIG. 2B schematically represent architectures for an active system according to the present invention, under the form of 3X3 independent heater modules, respectively of 10x10 multiplexed modules.

FIG. 3A and FIG. 3B schematically represent embodiments according to FIG. 1, wherein the thermally and electrically resistive substrate is a metal substrate covered with a dielectric layer, respectively a glass substrate.

FIG. 4A schematically represents an embodiment according to FIG. 1, wherein the active material is a ferroelectric positive temperature coefficient (PTC) material. FIG. 4B schematically represents a module comprising the active material of FIG. 4A, wherein the module is obtained by the superposition of a conductive layout and a T-dependent resistive layout.

FIG. 5A schematically represents an embodiment according to FIG. 4A, wherein the substrate is made of glass. FIG. 5B is a picture of a demonstrator according to FIG. 5A, with 3x3 independent heater modules.

FIG. 6A schematically represent an embodiment especially designed to be used in the case of multiplexed modules and wherein the substrate is made of a polyimide layer (Kapton^®). FIG. 6B represents a detail view showing the dielectric elements provided for track separation in the embodiment of FIG. 6A.

FIG. 7 shows a video excerpt of a IR pattern radiated using a 3x3 independent cells demonstrator according to an embodiment of the invention, said pattern being visualized with a computer equipped with a IR camera.

FIG. 8 shows a multiplexed cells demonstrator in which the activation of a pixel induces leakage current and residual lightning in the row and the column corresponding to this pixel.

FIG. 9 is a picture of a demonstrator corresponding to the configuration of FIG. 8, in which a SMD diode has been inserted at the output of each pixel in order to solve the above-mentioned leakage issue.

FIG. 10 shows an example of IR pattern radiated using a multiplexed cells demonstrator according to an embodiment of the invention, said pattern being visualized with a tablet computer equipped with a thermal camera (FLIR Systems, Inc.).

Detailed Description of the Invention

[0024] The present invention is based on an active (i.e. controllable) system 1 of heating resistors 2 printed on a thermally and electrically resistive substrate 3, as shown in FIG. 1. For example the resistive heating layer 2 printed on the resistive substrate 3 can be made of metal itself (e.g. silver conductive paste) or of a carbon-based material with power feeds under the form of a conductive layer 4 made of silver (or copper, aluminium, etc.). The underlying principle is that the heating element 2 is based on different resistivity between carbon and silver. Useful printing techniques are for example serigraphy (also called screen printing or silkscreen), inkjet, flexography, sintering and other printing electronic deposition methods, possibly combined with heating or radiation (oven, IPL, IR, UV, laser, etc.). In addition, other new 3D printing electronic deposition methods can also be used, such as spray (with stencil), micro spray, 3D inkjet , ink dispensing, etc. In this case, direct printing can be performed on 3D objects.

[0025] The whole multilayer system is finally encapsulated by an insulating protective layer 5 obtained for example by serigraphy or spraying and made of off-the-shelf dielectric components such as oxides (e.g. Al₂O₃, ZnO, TiO₂, etc.), polymers (polycarbonate, polyimide, PE, PP, PET, PVC, etc.) or ceramic-based materials.

[0026] The IR stealth technology according to the invention is intended to provide two functions :

• firstly, using active material in which temperature variation is a function of a controlled applied voltage and current;
• secondly, achieving an IR mapping having a given resolution by using a matrix of IR printed unit modules globally radiating IR pattern.

[0027] The following examples provide matrix/2D architectures that illustrate the general idea of the present invention. A first example (FIG. 2A) shows 3x3 independent modules 10 (from the point of view of power feeding) and a second example (FIG. 2B) shows 10x10 multiplexed modules 100. The independent modules 10 have each an independent power feed while in the multiplexed module 100, a specific module is chosen by power feeding a specific line and a specific column (matrix power feed).

[0028] Further, considering a multiplexed configuration of functionally independent modules/cells, one module 10 equals one pixel (FIG. 2A). The resistive elements 2 (e.g. made of carbon containing material) are under the form of a regularly spaced studs layout embedded in conductive tracks 4 (e.g. made of silver) under the form of combs (see detailed description below). In this array configuration, each cell or pixel 10 can be activated independently.

[0029] In another example of multiplexed modules configuration (FIG. 2B), each module may comprise 4 pixels. A power supply distributes the current to the pixels either sequentially or by selecting/programming a specific pixel to heat in a matrix way (selection of a row and a column). Each cell or pixel has a multiplexed connection with the power supply, it means that each cell or pixel of the two-dimensional array is connected to a "column" input electrode and to a "row" output electrode (or vice versa) so that a determined pixel in position (X, Y) is powered by selecting respective row and column powering tracks in the two-dimensional array. Row and column powering tracks suitably overlap in the array thanks to positioning dielectric elements 7 preventing electric contacts at the crossover points of the row and column powering tracks (see below).

Description of Preferred Embodiments of the Invention

[0030] In a first embodiment (FIG. 3A), the inventors used a metallic support 3 as a substrate covered with an insulating layer (dielectric) 6. The dielectric layer 6 was a PVC material layer having a thickness up to 200µm. Conductive tracks 4 were obtained by screen printing of silver-based microparticles. The layout (architecture) was made of linear simple tracks. Simulations showed an important heat dissipation through the underlying metal substrate and a non-uniform increase of temperature in a hexagonal full silver motif/heater module was observed (not shown).

[0031] In a second embodiment (FIG. 3B), the metallic substrate covered with a dielectric insulating layer was replaced with a glass substrate 3, which is a good thermal and electric insulator. The conductive tracks 4 and architecture layout were unchanged.

[0032] The use of a substrate material having a drastically reduced thermal conductivity led to a much better spatial IR resolution (but with some local increase of temperature). Silver based heater tracks gave high ΔT but also gave uniform T mapping and further good IR spatial resolution. Different motifs/heater modules were investigated (hexagonal Ag/C, spiral Ag, ...) with the occurrence of non-uniform temperature and current distribution (not shown). This showed the need of further increasing IR spatial resolution.

[0033] In a third embodiment, while still utilizing a glass substrate 3 as a thermal insulator, an active material 20, under the form of a ferroelectric positive temperature coefficient (PTC) material, was used as carbon resistive material, in combination with conductive silver tracks 4, as described above (FIG. 4A). Each cell belongs to an array making a heat dissipation element and is obtained by the superposition of a silver layout 4 on a carbon layout 20 (FIG. 4B), which will be described with more details here below.

[0034] Each cell 10, 100 comprises a module of conductive tracks 4 having an input electrode 11, 101 and an output electrode 12, 102, having the form of two interdigitated combs, and comprising an array of heat dissipation elements 20 connected between the respective teethes 13, 103 of the interdigitated combs. Note that respective 10, 11, 12, etc. and 100, 101, 102, etc. reference signs refer to the embodiments with 3X3 independent heater modules and 10x10 multiplexed heater modules. The "cell" element can also be referred to as a "pixel" with reference to the IR spatial resolution of the device.

[0035] Preferably, each cell or pixel 10, 100 is obtained by firstly printing, for example by screen printing, the module of conductive tracks 4 on the insulating substrate 3, 30 and secondly printing the array of heat dissipation elements 20 onto both insulation substrate 3, 30 and module of conductive tracks 4, so that the heat dissipation elements are brought into close electrical contact with the module of conductive tracks 4. Each heat dissipation element has preferably a squared shape with an upper surface and a lower surface, said lower surface being provided with a side recess 21 on two edges, so that the heat dissipation element can be inserted between adjacent teethes 13, 103 of the first electrode 11, 101 and the second electrode 12, 102 respectively (see FIG. 4A).

EXAMPLE 1

[0036] The non-multiplexed heater motif size is: 4x4 cm² (see FIG. 5A and FIG. 5B). The material is composed of silver tracks having outside input/output electrode width of 10mm and interdigitated width of 0.4mm. The PTC carbon resistor is made of 100 small square units (2×2mm²). A temperature of about 50°C was obtained after 30s with a current of 210mA. A high spatial resolution is obtained with self-regulation, low current, homogeneity. The drawbacks are wide current feeds and a non-flexible substrate (glass).

[0037] In a fourth embodiment, Kapton^® (polyimide film, DuPont^™) has been used as a thermal insulator and flexible substrate 30 (FIG. 5A). The active material is again PTC (ferroelectrics) material 20 combined with conductive silver tracks 4.

[0038] The coupling of track width reduction with a PTC effect allows to perfectly localize the increase of temperature and thus provides high spatial resolution, with good time response (ΔT/Δt high, low current) and self-regulation (I~40mA, V~24V). The tracks were initially chosen very large (10 mm) outside the patch but their width could be reduced/optimized later on up to 10 times (not shown). As an additional advantage, the device is flexible.

EXAMPLE 2

[0039] In an example demonstrator with 3x3 independent cells (not shown), a heater motif of 4×4cm² is provided with 9 stealth cells with Ag tracks of 10mm width, Ag interdigitated tracks of 0.4 mm width and 100 units PTC-C resistors pixels of 2×2mm². The substrate is Kapton^®.

[0040] The (T, I, V) characteristics are the following :

• ΔT ~50°C after 30s ;
• 1=210mA.

[0041] An example of obtainable IR pattern is shown on FIG. 7.

[0042] In an alternative embodiment (FIG. 6A), the architecture is a 10x10 multiplexed configuration. The multiplexed solution has a number of advantages : save space, reduce the number of connectors needed to power the device (for 10x10 multiplexed, 20 connectors instead of 200 connectors for 10x10 independent cells and no space available in the center), easier control of IR cartography. Further, in this embodiment, a dielectric layer 7 (e.g. Al₂O₃) is provided for electrode separation (FIG. 6B).

EXAMPLE 3

[0043] In an example demonstrator with 10x10 multiplexed cells (not shown), the stealth cells are provided with Ag tracks of 1mm width, Ag interdigitated of 0.4 mm width and 9 units PTC-C resistors pixels of 2×2mm². The substrate is Kapton^®. The heater motif unit is 1.2×1.2cm².

[0044] The (T, I, V) characteristics are the following :

• ΔT 20-30°C after 30s ;
• I=100mA@60V.

[0045] In this last configuration, leakage current was observed, leading to some residual lightning 9 of the row and the column corresponding to the selected unit cell 8 (see FIG. 8). The problem was solved by inserting a flat or surface-mounted (SMD) diode 80 on each pixel output, so that the current could not pass to an adjacent pixel (FIG. 9). The insertion is performed, as known in the art, by a "pick & place" method using a conductive glue in order to ensure proper electric connection. Advantageously the SMD diode characteristics are 100V/1A (100 diodes for a 10 by 10 multiplexed device).

List of reference symbols

[0046] 

1

system of unit heater cells

2

resistive heating layer

3

insulating substrate

4

conductive layer

5

protective layer (encapsulation)

6

dielectric layer

7

dielectric layer element for electrode separation

8

selected pixel

9

pixels with leakage current

10

independent module

11

input electrode

12

output electrode

13

electrode tooth

20

layer of PTC ferroelectrics material

21

recess

30

layer of polyimide substrate (Kapton^®)

80

SMD diode

100

multiplexed modules

101

input electrode

102

output electrode

103

electrode tooth

Claims

1. An ultrathin, multilayer and encapsulated surface element (1) for providing thermal signature adaptation with the purpose of infrared stealthing, and being also suited for camouflage in the visible, the element being flexible and comprising :

- a lower layer made of an insulation substrate (3, 30) ;

- an intermediate layer comprising a plurality of conductive tracks (4) connectable to a power supply ;

- a plurality of active heat dissipation elements (2, 20) connected to the conductive tracks (4) in the intermediate layer and capable to irreversibly provide a temperature increase by Joule effect in a given time interval when a current is fed into said heat dissipation elements, wherein each dissipation element (2, 20) comprises an electric conductive path extending between a first connexion and a second connection connecting respectively said dissipation element (2, 20) to least two of the conductive tracks (4), said dissipation element (2, 20) being capable of providing the temperature increase throughout said path from the first connection to the second connection when the current is fed, the heat dissipation elements (2, 20) and the conductive tracks (4) being printed on the insulation substrate (3, 30) ;

- an upper layer made of a protective layer (5) ;

the heat dissipation elements (2) having a size and being organized according to a spatial arrangement so as to provide a predetermined infrared spatial resolution, when a current is fed into said dissipation elements.

2. The surface element according to Claim 1, wherein the spatial arrangement is a two-dimensional array of cells or pixels (10) comprising heat dissipation elements (2, 20) regularly spaced in two orthogonal directions, each cell or pixel (10) being independently connectable to the power supply via the conductive tracks (4).

3. The surface element according to Claim 1, wherein the spatial arrangement is a two-dimensional array of cells or pixels (100) comprising heat dissipation elements (2, 20) regularly spaced in two orthogonal directions, each cell or pixel (100) being connectable in a multiplexed manner to the power supply via the conductive tracks (4).

4. The surface element according to Claim 1, wherein the heat dissipation elements (2, 20) are made of carbon containing material, PTC ferroelectric material or any resistive material having a resistance higher than the resistance of the conductive tracks (4).

5. The surface element according to claim 4, wherein the carbon-containing heat dissipation elements (2, 20) are made of carbon black, amorphous carbon, graphite, graphene nanoplatelets or carbon nanotubes.

6. The surface element according to claim 4, wherein the resistive material having a resistance higher than the conductive tracks (4) is made of tungsten, a metallic alloy such as nichrome (NiCr), a transparent conducting oxide (TCO) film material such as aluminium-doped zinc oxide (AZO) or indium tin oxide (ITO), or a transparent conducting polymer such as Poly(3,4-ethylenedioxythiophene) PEDOT: poly(styrene sulfonate) PSS.

7. The surface element according to claim 1, wherein the conductive tracks (4) are made of silver, gold, copper, aluminium or zinc.

8. The surface element according to claim 1, wherein the heat dissipation elements (2, 20) and the conductive tracks (4) attachment to the substrate (3, 30) is obtained by inkjet, screen printing or serigraphy, flexography, sintering or other printing electronic deposition methods, possibly combined with heating or radiation such as oven, IPL, IR, UV, laser, and in particular 3D printing electronic deposition methods, such as spray with stencil, micro spray, 3D inkjet or ink dispensing.

9. The surface element according to claim 1, wherein the insulation substrate (3, 30) is made of a glass plate or of a polyimide film.

10. The surface element according to claim 2 or 3, wherein each cell (10, 100) comprises a module of conductive tracks (4) having an input electrode (11, 101) and an output electrode (12, 102), said input electrode (11, 101) and said output electrode (12, 102) having the form of interdigitated combs, and comprising an array of heat dissipation elements (2, 20) having the form of studs connected between the respective teeth of the interdigitated combs.

11. The surface element according to claim 10, wherein each cell or pixel (10, 100) is obtained by firstly printing the module of conductive tracks (4) on the insulation substrate (3, 30) and secondly printing the array of heat dissipation elements (2, 20) onto both insulation substrate (3, 30) and module of conductive tracks (4), so that the heat dissipation elements are brought into close electrical contact with the module of conductive tracks (4).

12. The surface element according to claim 11, wherein each heat dissipation element has an essentially squared shape with an upper surface and a lower surface, said lower surface being provided with a side recess (21) on two parallel edges, so that the heat dissipation element can be inserted between adjacent teeth of the first electrode and the second electrode respectively.

13. The surface element according to claim 2, wherein each cell or pixel (10) has an independent input connection, respectively an independent output connection with the power supply.

14. The surface element according to claim 3, wherein each cell or pixel (100) has a multiplexed connection with the power supply, it means that each cell or pixel (100) of the two-dimensional array is powered by selecting respective row and column powering tracks corresponding to the (X, Y) position of the cell (100) in the two-dimensional array.

15. The surface element according to claim 14, wherein row and column powering tracks overlap insulated in the array thanks to positioning dielectric elements (7) preventing unwanted electric contacts at the crossover points of the row and column powering tracks.

16. The surface element according to claim 14, wherein a flat or surface-mounted (SMD) diode (80) is mounted on each pixel (100) output, so that no leakage current could pass to an adjacent pixel and improperly lighten in whole or in part the corresponding row and column.

17. The surface element according to claim 1, wherein the protective layer (5) is an encapsulating insulating layer obtained by serigraphy or spraying and made of dielectric material such as an oxide, a polymer or a ceramic-based material.

18. The use of one or more surface elements (1) according to anyone of the preceding claims, for providing an object or a person with a cover, sheet, blanket, casing or roofing capable of adapting the thermal signature of said object or person with the purpose of infrared stealthing, deception, camouflage, decoying or concealment.

19. The use of one or more surface elements (1) according to claim 18, wherein the plurality of heat dissipation elements (2, 20) selectively radiate a surface infrared pattern allowing to avoid the person or the object covered by said one or more surface elements (1) to be detected by an infrared detection device.

Ansprüche

1. Ultradünnes, mehrschichtiges und eingekapseltes Oberflächenelement (1) zum Bereitstellen von Wärmesignaturanpassung zum Zweck von Infrarottarnung, das auch zur Camouflage im sichtbaren Bereich geeignet ist, wobei das Element flexibel ist und Folgendes umfasst:

- eine untere Schicht, die aus einem Isoliersubstrat (3, 30) gefertigt ist;

- eine Zwischenschicht, umfassend eine Vielzahl von Leiterbahnen (4), die mit einer Stromversorgung verbindbar sind;

- eine Vielzahl von aktiven Wärmeableitelementen (2, 20), die mit den Leiterbahnen (4) in der Zwischenschicht verbunden sind und in der Lage sind, in einem gegebenen Zeitintervall einen irreversiblen Temperaturanstieg durch den Joule-Effekt zu bewirken, wenn den Wärmeableitelementen ein Strom zugeführt wird, wobei jedes Ableitelement (2, 20) eine elektrische Leiterbahn umfasst, die sich zwischen einer ersten Verbindung und einer zweiten Verbindung erstreckt, die jeweils das Ableitelement (2, 20) mit mindestens zwei der Leiterbahnen (4) verbindet, wobei das Wärmeableitelement (2, 20) in der Lage ist, den Temperaturanstieg auf dem gesamten Weg von der ersten Verbindung zu der zweiten Verbindung zu gewährleisten, wenn der Strom eingespeist wird, wobei die Wärmeableitelemente (2, 20) und die Leiterbahnen (4) auf das Isoliersubstrat (3, 30) gedruckt sind;

- eine obere Schicht, die aus einer Schutzschicht (5) gefertigt ist;

wobei die Wärmeableitelemente (2) eine Größe aufweisen und gemäß einer räumlichen Anordnung organisiert sind, um eine vorbestimmte räumliche Infrarotauflösung bereitzustellen, wenn ein Strom in die Ableitelemente eingespeist wird.

2. Oberflächenelement nach Anspruch 1, wobei die räumliche Anordnung eine zweidimensionale Anordnung von Zellen oder Pixeln (10) ist, umfassend Wärmeableitelemente (2, 20), die regelmäßig in zwei orthogonalen Richtungen beabstandet sind, wobei jede Zelle oder jedes Pixel (10) unabhängig über die Leiterbahnen (4) mit der Energieversorgung verbindbar ist.

3. Oberflächenelement nach Anspruch 1, wobei die räumliche Anordnung eine zweidimensionale Anordnung von Zellen oder Pixeln (100) ist, umfassend Wärmeableitelemente (2, 20), die regelmäßig in zwei orthogonalen Richtungen beabstandet sind, wobei jede Zelle oder jedes Pixel (100) über die Leiterbahnen (4) auf gemultiplexte Weise mit der Stromversorgung verbindbar ist.

4. Oberflächenelement nach Anspruch 1, wobei die Wärmeableitelemente (2, 20) aus kohlenstoffhaltigem Material, PTC-ferroelektrischem Material oder einem beliebigen Widerstandsmaterial gefertigt sind, die einen höheren Widerstand als der der Leiterbahnen (4) aufweisen.

5. Oberflächenelement nach Anspruch 4, wobei die kohlenstoffhaltigen Wärmeableitelemente (2, 20) aus Ruß, amorphem Kohlenstoff, Graphit, Graphen-Nanoplättchen oder Kohlenstoff-Nanoröhren gefertigt sind.

6. Oberflächenelement nach Anspruch 4, wobei das Widerstandsmaterial, das einen höheren Widerstand als die Leiterbahnen (4) aufweist, aus Wolfram, einer metallischen Legierung wie Nickelchrom (NiCr), einem transparenten leitenden Oxid (TCO)-Filmmaterial, wie beispielsweise aluminiumdotiertem Zinkoxid (AZO) oder Indiumzinnoxid (ITO) oder einem transparenten leitenden Polymer, wie beispielsweise Poly(3,4-ethylendioxythiophen) PEDOT: Poly(styrolsultanat) PSS gefertigt ist.

7. Oberflächenelement nach Anspruch 1, wobei die Leiterbahnen (4) aus Silber, Gold, Kupfer, Aluminium oder Zink gefertigt sind.

8. Oberflächenelement nach Anspruch 1, wobei die Wärmeableitelemente (2, 20) und das Anbringen der Leiterbahnen (4) auf dem Substrat (3, 30) durch Tintenstrahl, Siebdruck oder Serigraphie, Flexodruck, Sintern oder andere elektronische Druckverfahren, möglicherweise in Kombination mit Heizung oder Strahlung, wie beispielsweise Ofen, IPL, IR, UV, Laser, und insbesondere durch elektronische 3D-Druckverfahren, wie beispielsweise Sprühen mit Schablone, Mikrosprühen, 3D-Tintenstrahl oder Tintenauftrag, erlangt wird.

9. Oberflächenelement nach Anspruch 1, wobei das Isolationssubstrat (3, 30) aus einer Glasplatte oder aus einer Polyimidfolie gefertigt ist.

10. Oberflächenelement nach Anspruch 2 oder 3, wobei jede Zelle (10, 100) ein Modul von Leiterbahnen (4) umfasst, die eine Eingangselektrode (11, 101) und eine Ausgangselektrode (12, 102) aufweisen, wobei die Eingangselektrode (11, 101) und die Ausgangselektrode (12, 102) die Form von ineinandergreifenden Kämmen aufweisen und eine Anordnung von Wärmeableitelementen (2, 20) umfassen, die die Form von Stiften aufweisen, die zwischen den jeweiligen Zähnen der ineinandergreifenden Kämme verbunden sind.

11. Oberflächenelement nach Anspruch 10, wobei jede Zelle oder jedes Pixel (10, 100) dadurch erlangt wird, dass erstens das Modul von Leiterbahnen (4) auf das Isoliersubstrat (3, 30) gedruckt wird und zweitens die Anordnung von Wärmeableitelementen (2, 20) sowohl auf das Isoliersubstrat (3, 30) als auch auf das Modul von Leiterbahnen (4) gedruckt wird, sodass die Wärmeableitelemente in engen elektrischen Kontakt mit dem Modul von Leiterbahnen (4) gebracht werden.

12. Oberflächenelement nach Anspruch 11, wobei jedes Wärmeableitelement eine im Wesentlichen quadratische Form mit einer oberen Oberfläche und einer unteren Oberfläche aufweist, wobei die untere Oberfläche an zwei parallelen Rändern mit einer seitlichen Aussparung (21) versehen ist, sodass das Wärmeableitelement zwischen benachbarte Zähne der ersten Elektrode bzw. der zweiten Elektrode eingesetzt werden kann.

13. Oberflächenelement nach Anspruch 2, wobei jede Zelle oder jedes Pixel (10) eine unabhängige Eingangsverbindung bzw. eine unabhängige Ausgangsverbindung mit der Stromversorgung aufweist.

14. Oberflächenelement nach Anspruch 3, wobei jede Zelle oder jedes Pixel (100) eine gemultiplexte Verbindung mit der Stromversorgung aufweist, was bedeutet, dass jede Zelle oder jedes Pixel (100) der zweidimensionalen Anordnung durch Auswählen der jeweiligen Zeilen- und Spaltenstromversorgungsspuren entsprechend der (X, Y)-Position der Zelle (100) in der zweidimensionalen Anordnung mit Strom versorgt wird.

15. Oberflächenelement nach Anspruch 14, wobei sich Zeilen- und Spaltenversorgungsspuren in der Anordnung dank eines Positionierens dielektrischer Elemente (7), die unerwünschte elektrische Kontakte an den Kreuzungspunkten der Zeilen- und Spaltenversorgungsspuren verhindern, isoliert überlappen.

16. Oberflächenelement nach Anspruch 14, wobei eine flache oder oberflächenmontierte (SMD) Diode (80) an jedem Pixel (100) montiert ist, sodass kein Leckstrom zu einem benachbarten Pixel fließen und die entsprechende Zeile und Spalte ganz oder teilweise unzulässig aufhellen kann

17. Oberflächenelement nach Anspruch 1, wobei die Schutzschicht (5) eine einkapselnde Isolierschicht ist, die durch Serigraphie oder Sprühen erlangt wird und aus dielektrischem Material wie einem Oxid, einem Polymer oder einem Material auf Keramikbasis gefertigt ist.

18. Verwendung eines oder mehrerer Oberflächenelemente (1) nach einem der vorherigen Ansprüche, um ein Objekt oder eine Person mit einer Abdeckung, Folie, Decke, Hülle oder Bedachung zu versehen, die in der Lage ist, die Wärmesignatur des Objekts oder der Person zum Zweck von Infrarottarnung, Täuschung, Camouflage, Ablenkung oder Verschleierung anzupassen.

19. Verwendung eines oder mehrerer Oberflächenelemente (1) nach Anspruch 18, wobei die Vielzahl von Wärmeableitelementen (2, 20) selektiv ein Oberflächeninfrarotmuster ausstrahlen, das es ermöglicht, zu vermeiden, dass die Person oder das Objekt, das von dem einen oder den mehreren Oberflächenelementen (1) abgedeckt wird, von einer Infraroterfassungsvorrichtung erfasst wird.

Revendications

1. Élément de surface (1) ultramince, multicouche et encapsulé destiné à fournir une adaptation de signature thermique à des fins de furtivité infrarouge, et étant également adapté à des fins de camouflage dans le visible, l'élément étant flexible et comprenant :

- une couche inférieure constituée d'un substrat isolant (3, 30) ;

- une couche intermédiaire comprenant une pluralité de pistes conductrices (4) qui peuvent être connectées à une alimentation électrique ;

- une pluralité d'éléments actifs de dissipation thermique (2, 20) connectés aux pistes conductrices (4) dans la couche intermédiaire et capables de produire de manière irréversible une augmentation de température par effet Joule dans un intervalle de temps donné lorsqu'un courant est fourni dans lesdits éléments de dissipation thermique, caractérisé en ce que chaque élément de dissipation (2, 20) comprend un chemin conducteur électrique s'étendant entre une première connexion et une deuxième connexion qui relient respectivement ledit élément de dissipation (2, 20) à au moins deux des pistes conductrices (4), ledit élément de dissipation (2, 20) étant capable de produire l'augmentation de température tout au long dudit chemin de la première connexion à la deuxième connexion lorsque le courant est fourni, les éléments de dissipation thermique (2, 20) et les pistes conductrices (4) étant imprimés sur le substrat isolant (3, 30) ;

- une couche supérieure constituée d'une couche protectrice (5) ;

les éléments de dissipation thermique (2) ayant une taille et étant organisés selon une disposition spatiale telle qu'ils produisent une résolution spatiale infrarouge prédéterminée, lorsqu'un courant est fourni dans lesdits éléments de dissipation.

2. Élément de surface selon la revendication 1, caractérise en ce que l'agencement spatial est un réseau bidimensionnel de cellules ou pixels (10) comprenant des éléments de dissipation thermique (2, 20) régulièrement espacés dans deux directions orthogonales, chaque cellule ou pixel (10) pouvant être connecté indépendamment à l'alimentation électrique via les pistes conductrices (4).

3. Élément de surface selon la revendication 1, caractérisé en ce que l'agencement spatial est un réseau bidimensionnel de cellules ou pixels (100) comprenant des éléments de dissipation thermique (2, 20) régulièrement espacés dans deux directions orthogonales, chaque cellule ou pixel (100) pouvant être connecté de façon multiplexée à l'alimentation électrique via les pistes conductrices (4).

4. Élément de surface selon la revendication 1, caractérisé en ce que les éléments de dissipation thermique (2, 20) sont constitués d'un matériau contenant du carbone, d'un matériau ferroélectrique PTC ou d'un matériau résistif quelconque ayant une résistance supérieure à la résistance des pistes conductrices (4).

5. Élément de surface selon la revendication 4, caractérisé en ce que les éléments de dissipation thermique contenant du carbone (2, 20) sont constitués de noir de carbone, de carbone amorphe, de graphite, de nanoplaquettes de graphène ou de nanotubes de carbone.

6. Élément de surface selon la revendication 4, caractérisé en ce que le matériau résistif ayant une résistance supérieure à celle des pistes conductrices (4) est constitué de tungstène, d'un alliage métallique tel que le nichrome (NiCr), d'un matériau de film d'oxyde conducteur transparent (TCO) tel que l'oxyde de zinc dopé à l'aluminium (AZO) ou l'oxyde d'indium-étain (ITO), ou d'un polymère conducteur transparent tel que le poly(3,4-éthylènedioxythiophène) PEDOT : poly(sulfonate de styrène) PSS.

7. Élément de surface selon la revendication 1, caractérisé en ce que les pistes conductrices (4) sont en argent, en or, en cuivre, en aluminium ou en zinc.

8. Élément de surface selon la revendication 1, caractérisé en ce que la fixation des éléments de dissipation thermique (2, 20) et des pistes conductrices (4) au substrat (3, 30) est obtenue par jet d'encre, par impression au cadre ou sérigraphie, par flexographie, par frittage ou par d'autres procédés de dépôt électronique par impression, éventuellement combinés à un chauffage ou à un rayonnement tels que four, IPL, IR, UV, laser, et notamment des procédés de dépôt électronique par impression 3D, tels que la pulvérisation avec pochoir, la micropulvérisation, le jet d'encre ou la distribution d'encre 3D.

9. Élément de surface selon la revendication 1, caractérisé en ce que le substrat isolant (3, 30) est constitué d'une plaque de verre ou d'un film de polyimide.

10. Élément de surface selon la revendication 2 ou 3, caractérisé en ce que chaque cellule (10, 100) comprend un module de pistes conductrices (4) comportant une électrode d'entrée (11, 101) et une électrode de sortie (12, 102), ladite électrode d'entrée (11, 101) et ladite électrode de sortie (12, 102) ayant la forme de peignes interdigités, et comprenant un réseau d'éléments de dissipation thermique (2, 20) ayant la forme de plots connectés entre les dents respectives des peignes interdigités.

11. Élément de surface selon la revendication 10, caractérisé en ce que chaque cellule ou pixel (10, 100) est obtenu premièrement en imprimant le module de pistes conductrices (4) sur le substrat isolant (3, 30) et deuxièmement en imprimant le réseau d'éléments de dissipation thermique (2, 20) à la fois sur le substrat isolant (3, 30) et sur le module de pistes conductrices (4), de sorte que les éléments de dissipation thermique sont mis en contact électrique étroit avec le module de pistes conductrices (4).

12. Élément de surface selon la revendication 11, caractérisé en ce que chaque élément de dissipation thermique a une forme essentiellement carrée avec une surface supérieure et une surface inférieure, ladite surface inférieure étant pourvue d'un évidement latéral (21) sur deux bords parallèles, de sorte que l'élément de dissipation thermique peut être inséré entre les dents adjacentes de la première électrode et de la deuxième électrode respectivement.

13. Élément de surface selon la revendication 2, caractérisé en ce que chaque cellule ou pixel (10) a une connexion d'entrée indépendante, respectivement une connexion de sortie indépendante avec l'alimentation électrique.

14. Élément de surface selon la revendication 3, caractérisé en ce que chaque cellule ou pixel (100) a une connexion multiplexée avec l'alimentation électrique, ce qui signifie que chaque cellule ou pixel (100) du réseau bidimensionnel est alimenté en sélectionnant des pistes d'alimentation de ligne et de colonne respectives correspondant à la position (X, Y) de la cellule (100) dans le réseau bidimensionnel.

15. Élément de surface selon la revendication 14, caractérisé en ce que les pistes d'alimentation de rangée et de colonne se chevauchent et sont isolées dans le réseau grâce au positionnement d'éléments diélectriques (7) empêchant les contacts électriques indésirables aux points de croisement des pistes d'alimentation de ligne et de colonne.

16. Élément de surface selon la revendication 14, caractérisé en ce que une diode plate ou montée en surface (SMD) (80) est montée sur chaque sortie de pixel (100), de sorte qu'aucun courant de fuite ne peut se propager à un pixel adjacent et éclairer de manière indésirable, en totalité ou en partie, la ligne et la colonne correspondantes.

17. Élément de surface selon la revendication 1, caractérisé en ce que la couche protectrice (5) est une couche isolante encapsulante obtenue par sérigraphie ou par pulvérisation et constituée d'un matériau diélectrique tel qu'un oxyde, un polymère ou un matériau à base de céramique.

18. Utilisation d'un ou plusieurs éléments de surface (1) selon l'une quelconque des revendications précédentes, pour doter un objet ou une personne d'un recouvrement, d'une feuille, d'une couverture, d'une enveloppe ou d'une toiture capable d'adapter la signature thermique dudit objet ou de ladite personne à des fins de furtivité, de tromperie, de camouflage, de leurrage ou de dissimulation infrarouge.

19. Utilisation d'un ou plusieurs éléments de surface (1) selon la revendication 18, caractérisée en ce que la pluralité d'éléments de dissipation thermique (2, 20) rayonne sélectivement un motif infrarouge de surface qui permet d'éviter que la personne ou l'objet recouvert par lesdits un ou plusieurs éléments de surface (1) ne soient détectés par un dispositif de détection infrarouge.

Drawing