Patent Description:
Artificial target devices of various sorts are used in military operations and training as well as in hunting and shooting practice to mimic a particular target. In target practice artificial targets may simply take the form of a dummy shaped and painted to resemble the target. Simple examples of such dummies include a plastic duck or a cardboard cut into the shape of an off-road vehicle. Dummies are also used to distract the enemy in combat by placing artificial targets in the field to steer offensive actions away from the actual troops.

Such artificial targets can be quite sophisticated in that they are constructed as actively transmitting devices for drawing attention to them. With modern combat increasingly involving machine-assisted vision, so too do artificial targets. Dummies have been developed to transmit infra-red signals to mimic the thermal signature of a military asset, such as a tank, so as to be detected by a heat-seeking missile, for example. Several different techniques have been developed for this purpose, including blowing hot air into an inflatable dummy.

Actively transmitting dummies have, however, traditionally only been able to produce a relatively coarse thermal signature. An improvement to the fidelity of thermal images is disclosed in <CIT>, wherein it is proposed to produce a thermal image with individually controlled active thermal elements disposed in an array to provide a reproduction of a pixelated image of the target. <CIT> discloses a target device comprising separately fabricated panels each comprising a metal coating on both sides of an electrically insulating panel to produce a heat signature of an imitated target. <CIT> discloses another artificial target device for producing a deceptive thermal signature of an object.

While such known systems are useful in producing relatively accurate thermal signatures, dummies must be very realistic to convince modern military vehicles equipped with advanced sensors aided by artificial intelligence. It is therefore an object of the present invention to improve the deceptive properties of known artificial targets or at least provide the public with a useful alternative.

According to a first aspect, there is proposed a novel multi-spectral artificial target device for producing a deceptive thermal and radar signature of an object. The device features a multi-layer structure with a substrate and a functional thermal signal layer, which is provided directly or indirectly on the substrate. The thermal signal layer includes electrically conductive material such arranged to form an array of independently controlled thermal elements for outputting a thermal signal, which is observable in the infra-red spectrum, upon exposure to a control voltage. The multi-layer structure further includes a functional radar signal layer, which is provided directly or indirectly onto the substrate. The radar signal layer outputs a radar response signal, which is observable in the radio frequency spectrum, upon exposure to an external radar stimulus or excitation.

According to a second aspect, there is proposed a method of producing a multi-spectral artificial target device for producing a deceptive thermal and radar signature of an object. The involves the following activity:.

Various embodiments of the first aspect may comprise at least one feature from the following itemized list:.

Considerable benefits may be gained with aid of the present proposition. The additional functional radar signal layer renders the artificial target device multi-spectral in the sense that it is able to produce not only the thermal signature of the portrayed target but also the radar signal as well. Accordingly, the device may be used to deceive advanced equipment scanning the surrounding in infra-red and radio frequency spectrums. By incorporating the functional layers in a single multi-layer structure means that a frame, which is constructed to resemble the 3D shape of the portrayed object, may be clad with the multi-layer structure to add the thermal and radar traces of the object to a realistic shape.

According to one embodiment the functional layers are constructed as separate physical layers, which provides the additional effect of gaining a degree of freedom to fine-tune the radar appearance properties and the thermal signature independently from one another. Indeed, a single artificial target device may include sections that provides weaker radar responses and sections that provide stronger radar responses to mimic objects with similar properties.

In the following certain exemplary embodiments are described in greater detail with reference to the accompanying drawings, in which:.

In the present context the expression "artificial target device" includes, but is not limited to, decoy devices for imitating objects, particularly military assets, and dummies for targeting practice.

In the present context the expression "array" includes, but is not limited to, an ordered series or arrangement.

<FIG> illustrates a schematic representation of a cross-section of an exemplary multi-layer structure <NUM> employed in an artificial target device according to one embodiment. The multi-layer structure <NUM> features a substrate <NUM> on which several layers are provided to produce a multi-spectral signature of a target. The substrate <NUM> may be made of a pliable material which can be bent around a frame to resemble the three-dimensional shape of the portrayed object. The substrate <NUM> may include a base material that is coated with another material or it may have a uniform structure. According to one embodiment the substrate <NUM> is made of a polymer material. According to another embodiment the substrate <NUM> includes a polymer coating. According to a particular embodiment the substrate <NUM> consists substantially of or has a coating made of polyethylene terephthalate (PET), Polyethylene naphthalate (PEN), polyethylene (PE), polypropylene (PP), Polyimide (PI). If a polymer-based substrate <NUM> is used, a suitable material thickness may be in the range of <NUM> to <NUM>, particularly <NUM> to <NUM>, especially <NUM>. Alternatively, the substrate <NUM> may include a fibrous base, such as Kevlar or glass-fiber or carbon-fiber base, with or without a polymer coating. If a fiber-based substrate <NUM> is used, a suitable basis weight may be <NUM> to <NUM>/m<NUM>, particularly <NUM> to <NUM>/m<NUM>, particularly <NUM> to <NUM>/m<NUM>, such as <NUM>/m<NUM>. Other examples include board, paper, or fabric. Generally speaking it is advantageous to construct the substrate <NUM> of a non-metallic material so as to prevent interference between other layers which will be discussed in the following. Alternatively the substrate may be made from a basic printed circuit board (PCB) or printed wiring board (PWB) material, such as laminated layers of fiber, such as fiberglass, cloth or paper, with thermoset resin. If the multi-layer structure is constructed from a relatively rigid material, it may form part of the frame. Conversely, the frame may perform some of the functions of the device, such as a supplement the radar response.

The substrate <NUM> is layered with a functional radar signal layer <NUM>. In this context a "functional radar signal layer" refers to a physical layer that has the capability of producing a radar response signal, when exposed to an incident radar wave. As will become apparent here after, several functional layers may be provided with several physical layers or a single physical layer. According to the embodiment of <FIG>, the radar signal layer <NUM> is provided for by a separate physical layer.

To be effective, the reflective radar emission produced by the radar signal layer <NUM> is observable in the radio frequency spectrum. The radar signal layer <NUM> is made of a metallic material that has enough thickness to produce a radar response. The radar signal layer <NUM> has a suitable thickness in the range of <NUM> to <NUM>, particularly <NUM> to <NUM>, more particularly <NUM> to <NUM>, especially <NUM>. With a thick enough layer, the radar signal layer <NUM> is set to provide for sufficient penetration depth (skin depth) for incident radar waves. For example, if the radar signal layer <NUM> is constructed from copper, or an alloy consisting predominantly of copper, a practical penetration depth would be about <NUM> for radar waves emitted at <NUM>. A comparable penetration depth for aluminium, or an alloy consisting predominantly of aluminium, would be about <NUM>. In particular, the radar signal layer <NUM> has radar reflectance which is different to that of the thermal signal layer <NUM> or substrate <NUM> or both the thermal signal layer <NUM> and the substrate <NUM>. The radar signal layer <NUM> has preferably radar reflectance which is greater than, that of the thermal signal layer <NUM> or substrate <NUM> or both the thermal signal layer <NUM> and the substrate <NUM>. In the present context the radar reflectance refers to the effectiveness of a layer in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at an interface. The reflectance is dependent on the wavelength of the incident radiation.

According to one embodiment the separate radar signal layer <NUM> is patterned such to match the shape and pattern of the thermal elements <NUM> on the thermal signal layer <NUM>. Accordingly, the radar signal layer comprises small gaps in the layer similarly to the small gaps between the thermal elements <NUM> shown in <FIG>. If the gap is made relatively small, for example <NUM>, the gaps will not be observed by a radar. The gaps prevent heat transfer between adjacent thermal elements, but the gaps even out the heat distribution within the thermal element <NUM>.

The deceptiveness of the multi-layer structure <NUM> may be further increased by providing a visual deception layer <NUM> as the outermost layer. The visual deception layer <NUM> includes a simple coat of paint or it may comprise a projection screen for displaying a projected image of the portrayed object. The color and pattern of the paint is selected to imitate the portrayed object and may be applied with a brush, spray gun, printing, or laminating, for example. The visual deception layer <NUM> may additionally include letters and/or numbers to deceive character recognition software on a hostile craft. An examples of such an application is a license plate when portraying a vehicle. If a projection screen is provided, the material of the visual deception layer <NUM> is selected to provide enough gain for the image production. Suitable painting methods and projector screens are known per se. The visual deception layer <NUM> is optional especially if the outermost layer in the multi-layer structure <NUM>, which ever layer it may be, has an appearance which is close enough to the portrayed object.

<FIG> further shows a functional thermal signal layer <NUM> constructed as a separate physical layer on the substrate <NUM>. In this context a "functional thermal signal layer" refers to a physical layer that has the capability of outputting a thermal signal, which is observable in the infra-red spectrum. As will become apparent here after, several functional layers may be provided with several physical layers or a single physical layer. According to the embodiment of <FIG>, the thermal signal layer <NUM> is provided for by a separate physical layer. According to this particular embodiment the thermal signal layer <NUM> is provided on a side of the substrate <NUM> which is opposite to the radar signal layer <NUM>.

The thermal signal layer <NUM> may be constructed by a number of different configurations that are shown in <FIG>. Regardless of the configuration the thermal signal layer <NUM> may particularly be constructed of a relatively thin layer of conductive material deposited onto the substrate <NUM>. Suitable materials for the thermal signal layer <NUM> include carbon, metals, based on particles fibers, sheetlets or bulk metal. The material thickness may be in the range of from tens of nanometers to hundreds of micrometers depending on material used; thicker for materials having lower conductivity such as ink based metal layers or carbon based materials. To produce distinguishable temperature gradients in respect to the ambient, the attainable resistance for the layer or parts thereof is in the range of <NUM> to <NUM> ohm, whereby relatively low voltages may be used. The resistance of the layer is affected by the thickness, area, and material of the layer.

Several alternative methods are available for depositing the thermal signal layer <NUM> onto the substrate <NUM>. The deposition may be made on an atomic level through atomic layer deposition (ALD) or on a coarser lever, e.g. printing an ink containing material particles or by laminating the foil. Further alternatives include sputtering, chemical vapor deposition (CVD), pulsed laser deposition (PLD), and several other techniques aimed at producing very thin membranes. Relatively thick layers may be produced by painting with brush or spray application, for example. According to one embodiment the thermal signal layer <NUM> is printed onto the substrate <NUM>. Suitable printing methods include offset, flexo, gravure, screen printing, rotary screen printing, ink-jet-printing, dispensing. According to another embodiment the thermal signal layer <NUM> may be provided onto the substrate <NUM> by using various coating methods, such as slot-die coating, blade-coating, reverse offset coating, extrusion and lamination.

The material of the thermal signal layer <NUM> is patterned to provide for an array of independently controlled thermal elements <NUM>. The thermal elements <NUM> are used as thermal pixels or parts that, when controlled individually to emit a particular infrared signal, collectively make up the pursued thermal signature. The patterning may be achieved by subtracting parts of the deposited layer of conductive material or by adding the desired pattern during deposition. Suitable methods for subtractive patterning include wet-etching, dry-etching, kiss- and die cutting, laser processing.

<FIG> shows an exemplary array of nine thermal elements <NUM> arranged in a matrix-like pattern of three-by-three. Each thermal element <NUM> includes a first electrode <NUM> and a second electrode <NUM> with an electrically resistive element <NUM> there between. In the example of <FIG>, the elements <NUM>, <NUM>, <NUM> are all made of the same material that forms the thermal signal layer <NUM>. The electrically resistive element <NUM> is constructed by patterning the material of the thermal signal layer <NUM> into a "labyrinth" or angled or curved spiral shape that extends between two strips of the same material, namely the first and a second electrode <NUM>, <NUM>. In illustrated example the thermal elements <NUM> share the first electrode <NUM> which frames the elements. The second electrode <NUM>, however, is individual for each thermal element <NUM> at the center of the thereof. The thermal elements <NUM> further include strips of electrically non-conductive sections <NUM> between thermal elements <NUM> to minimize heat transfer between thermal elements <NUM>. The non-conductive sections <NUM> may simply be voids in the electrically conductive material that forms the thermal signal layer <NUM>, whereby the substrate or a coating thereof may be exposed at the non-conductive sections <NUM>.

<FIG> shows an alternative embodiment of the construction of <FIG>. The thermal signal layer <NUM> of <FIG> comprises separate electrically resistive elements <NUM> between sections of the electrically conductive material, i.e. connecting the first and a second electrode <NUM>, <NUM>. The electrically resistive elements <NUM> may take the form of a piece of material that has conductivity smaller than that of the surrounding electrode <NUM>, <NUM>. According to a particular embodiment the electric conductivity of the electrically resistive element <NUM> is smaller than <NUM>,<NUM>*<NUM>-<NUM> S/m. The electrically resistive elements <NUM> may be printed or otherwise overlaid onto the electrode(s) <NUM>, <NUM>. It is to be noted that the resistance over the electrically resistive elements <NUM> is greater than that across the first and/or second electrode <NUM>, <NUM>. The difference in resistance may be a decade or more, such as hundred times or more. In the illustrated embodiment the electrically resistive elements <NUM> are surrounded by non-conductive sections <NUM> to isolate the first and a second electrode <NUM>, <NUM> from each other.

<FIG> shows a variant of the embodiment of <FIG>. <FIG> is an illustration featuring a two-by-two configuration of a larger array of thermal elements <NUM>. Instead of a winding shape shown in <FIG>, the electrically resistive element <NUM> may be shaped to meander between the electrodes <NUM>, <NUM>. In the illustrated example, the adjacent thermal elements <NUM> in a given column share the second electrode <NUM>, whereas each thermal element <NUM> has an individual first electrode <NUM>.

Indeed, the thermal elements <NUM> may be patterned in several different ways. The thermal elements <NUM> may also be constructed in a host of different configurations, as illustrated by <FIG>.

According to the embodiment shown in <FIG>, which is the schematic cross-sectional illustration of <FIG>, the thermal signal layer <NUM> is deposited onto the substrate <NUM>. <FIG> shows the first electrode <NUM> occupying the periphery of the substrate <NUM>, the second electrode <NUM> in the middle, and the windings of the electrically resistive element <NUM> between the first and second electrode <NUM>, <NUM>. The thermal signal layer <NUM> is powered by a driving layer <NUM> on the opposite side of the substrate <NUM>. The driving layer <NUM> has an electrically conductive lead <NUM> for providing voltage to the thermal signal layer <NUM>. The lead <NUM> is connected to a voltage source (not illustrated) through a control circuit (not illustrated).

The lead <NUM> is connected to the thermal signal layer <NUM> though an electric connection, which may be provided in several different ways. According to the embodiment of <FIG> there is a conductor <NUM> devised into the substrate <NUM>. The conductor <NUM> may be constructed by first providing a hole through the substrate <NUM> and then introducing electrically conductive material into the hole to connect the lead <NUM> and the electrode <NUM>. The electrically conductive material may be a lead that is soldered or otherwise bonded between the lead <NUM> and the electrode <NUM> or it may be a crimp or pin. If the lead <NUM> printed onto the surface of the substrate <NUM>, the same printing technique may be used to fill the channel extending through the substrate to fill the channel.

According to the embodiment shown in <FIG>, which is the schematic cross-sectional illustration of <FIG>, the electrically resistive element <NUM> connects the electrodes <NUM>, <NUM> along the substrate <NUM>. The thermal signal layer <NUM> is powered similarly to the embodiment of <FIG>. The electrically resistive element <NUM> may be printed or coated or painted. The electrically resistive element <NUM> may have electrical resistivity higher than that of the electrical connectors. The electrically resistive element <NUM> may be produced in various shapes and thicknesses, wherein the cross-section determines the resistivity level. The electrically resistive element <NUM> may be made of temperature self-regulating material, wherein the material changes as a function of temperature, thus making the element a self-regulating heater element.

<FIG> shows an alternative to powering the thermal signal layer <NUM>, wherein the substrate <NUM> is made of or doped with conductive material. It follows that the lead <NUM> is electrically connected to the thermal signal layer <NUM> on areas which are not isolated. To isolate the thermal elements from each other, electric isolators <NUM> are provided between the lead <NUM> and the substrate <NUM>. Accordingly, the electric isolators <NUM> are provided in a pattern which forms the pattern of the array of thermal elements, whereby the pattern of the thermal elements may be formed without patterning the thermal signal layer <NUM> because only some sections of the thermal signal layer will be provided with a control voltage. Accordingly, the thermal signal layer <NUM> may include a solitary electrode <NUM>. The electric isolators <NUM> may be provided by provision of an air gap between the lead <NUM> and the substrate <NUM> or printed layer of dielectric material or a laminated membrane, for example.

<FIG> shows yet an alternative to powering the thermal signal layer <NUM>, wherein the electrically non-conductive substrate <NUM> is provided with channels that extend through the substrate and which have been filled with or provided with conductive material. Such channels may be produced by punching, drilling, laser, or etching, such as dry etching, for example. By providing the conductive channels in a particular pattern, the pattern of the thermal elements may be formed without patterning the thermal signal layer <NUM> because only some sections of the thermal signal layer will be provided with a control voltage. Alternatively metallic or other conductive particles may be pressed locally inside the otherwise non-conductive substrate <NUM> to establish conductive passages through the substrate.

In the example of <FIG> the functional thermal signal layer <NUM> and the functional radar signal layer <NUM> as physically separate layers on opposing sides of the substrate <NUM>. According to alternative embodiment, however, the functional thermal signal layer <NUM> and the functional radar signal layer <NUM> are provided in a single physical layer of a metallic film. Should the thermal and radar response be provided with a single layer, it is advantageous to maximize the coverage of the multi-layer structure <NUM> with the material making up the layer to maximize the radar response. For that purpose, the coverage of the layer is <NUM> per cent or more, particularly <NUM> or more, preferably in the range of <NUM> to <NUM> per cent. The single layer embodiment may be constructed, for example, according to any one of the examples shown in <FIG> provided that the material making up the thermal signal layer <NUM> is thick and conductive enough to produce the required radar response.

According to another embodiment, the multi-layer structure comprises a separate physical radar signal layer or several physical radar signal layers, wherein the artificial target device includes one or several sections that provide(s) (a) weaker radar response(s) and one or several section(s) that provide(s) (a) stronger radar responses to mimic objects with comparable properties. Examples of such objects include bunkers, anti-aircraft pits, etc..

The manufacturing of the multi-layer structure <NUM> may be achieved by employing techniques used for printed electronics to achieve relatively large areas for the functional thermal signal layer <NUM> and radar signal layer <NUM>. According to one embodiment a substrate <NUM> is unrolled from a roll of raw material and printed with conductive ink on one side of the substrate <NUM> to produce the thermal signal layer <NUM>. The conductive ink may be carbon ink or silver ink, or more specifically particulate or nano-particulate metal or carbon ink or with ink containing carbon or metal fibers or flakelets. The printing enables a relatively accurate and sharp pattern of the thermal elements <NUM>. Alternatively, the thermal signal layer <NUM> is printed as a blank layer of material which is then patterned through subtraction, such as mechanical or chemical subtraction. The patterning may also produce the electrically resistive element <NUM> or they may be added in a separate step by printing, such as offset, flexo, gravure, screen printing, rotary screen printing, ink-jet-printing, or by dispensing.

The driving layer <NUM> is produced by printing, or by patterning of metal foil using laser, cutting or wet- or dry-etching or laminated in a form of pre-patterned foil.

If the functional thermal signal layer <NUM> and radar signal layer <NUM> are produced as separate physical layers, the radar signal layer <NUM> is added onto the substrate <NUM> or pre-produced physical thermal signal layer <NUM>. If the radar signal layer <NUM> is layered onto the pre-produced physical thermal signal layer <NUM>, an intermediate step of providing an electric isolator film there between is conceivable. In the provision of the radar signal layer <NUM> there are several alternatives to consider. A metallic film is provided. A layer of adhesive, such in the form of a sprayed, rolled, or transplantable film, is applied onto the metallic film, onto the substrate <NUM>, or onto the thermal signal layer <NUM>, in which case the layer of adhesive forms the isolating intermediate electric isolator film. The metallic film is then laminated onto the substrate <NUM> or onto the thermal signal layer <NUM> through the layer of adhesive. Alternatively the metallic film may be evaporated, coated, printed, or mechanically affixed, such as stapled, onto the the substrate or onto the thermal signal layer.

The multi-layer structure <NUM> may be provided with a visual deception layer <NUM>. The visual deception layer <NUM> may be applied to the thermal signal layer <NUM> or radar signal layer <NUM> by painting, laminating, applying a textured wrap or foil, or any detailed mask observable with the human eye.

With the multi-layer structure <NUM> ready, it is attached to a frame which is constructed to resemble the 3D shape of the portrayed object. The multi-layer structure <NUM> is preferably made from pliable materials that can withstand deformation enough to facilitate bending so as to conform to the shape of the frame. It is particularly useful to be able to wrap the frame with a sheet-like multi-layer structure <NUM>. Finally, the artificial target device is provided with an electric power source and control processor with the required data transfer interfaces, such as wired or wireless remote connection data interface, to control the temperature of the thermal elements <NUM> according to a set of computer readable instructions accessed by the control processor. The processor may be connected to a power output stage. A human-machine interface may also be included to control device.

The use of the decoy device is relatively straight-forward. First, an infra-red image of the object is acquiring for processing. The infra-red image is converted into a digital image which comprises pixels. The pixels are then converted into machine readable control instructions for controlling the thermal signal layer <NUM> to reproduce or mimic the thermal signature of the object. Said control instructions are stored to a local memory comprised by the artificial target device or to a memory that is external to and retrieved by the artificial target device through a wired or wireless interface. A processor comprised by the device reads said control instructions and controls the artificial target device to provide a different voltage, current, or duty cycle to at least two individual thermal elements <NUM> in the array to form the desired thermal signature.

Claim 1:
A multi-spectral artificial target device for producing a deceptive thermal and radar signature of an object, comprising a multi-layer structure (<NUM>) which comprises:
- a substrate (<NUM>);
- a functional radar signal layer (<NUM>) which is provided directly or indirectly onto the substrate (<NUM>), which radar signal layer (<NUM>) is configured to output a radar response signal, which is observable in the radio frequency spectrum, upon exposure to an external radar stimulus or excitation, characterized by
- a functional thermal signal layer (<NUM>), which is provided directly or indirectly on the substrate (<NUM>) and which comprises electrically conductive material arranged to form an array of independently controlled thermal elements (<NUM>), which thermal signal layer (<NUM>) comprises electrically non-conductive sections (<NUM>) between thermal elements (<NUM>), wherein each thermal element (<NUM>) is configured to output a thermal signal, which is observable in the infra-red spectrum, upon exposure to a control voltage.