Artistic representation of a future combat vehicle protected by an active camouflage system
Currently, infantry reconnaissance and infiltration operations are performed with a conventional camouflage designed to camouflage a soldier using two main elements: color and pattern (camouflage pattern). However, military operations in urban environments are becoming more prevalent, in which the optimal color and pattern can change continuously, even every minute. For example, a soldier wearing a green uniform will stand out clearly against a white wall. An active camouflage system could constantly update color and pattern, hiding the soldier in his current environment
Nature has been using actively adaptive camouflage "systems" for millions of years. Can you see the chameleon in this photo?
Simplified representation of the principle of operation of active-adaptive camouflage using the example of MBT
This article provides an overview of current and future active (adaptive) camouflage systems. While there are numerous applications for these systems or are in development, research focus is on systems that could be used in infantry operations. In addition, the purpose of these studies is to provide information used to assess the current applicability of active camouflage systems and to help design future ones.
Definitions and basic concepts
Active camouflage in the visible spectrum differs from conventional camouflage in two ways. First, it replaces the appearance of what is being masked with an appearance that not only resembles the environment (like traditional masking), but accurately represents what is behind the object being masked.
Second, active camouflage also does this in real time. Ideally, active camouflage could not only mimic nearby objects, but also distant ones, possibly as far as the horizon, creating a perfect visual camouflage. Visual active camouflage can be used to disable the ability of the human eye and optical sensors to recognize targets.
There are many examples of active camouflage systems in fiction, and developers often choose a name for a technology based on some terms and names from fiction. These generally refer to full active camouflage (i.e. complete invisibility) and do not refer to the capabilities of partial active camouflage, active camouflage for special operations, or any of the current real-world technological advances. However, complete invisibility will certainly be useful for infantry operations, such as reconnaissance and infiltration operations.
Camouflage is used not only in the visual spectrum, but also in acoustics (for example, sonar), the electromagnetic spectrum (for example, radar), thermal field (for example, infrared radiation) and for changing the shape of an object. Camouflage technologies, including some active camouflages, have been developed to a certain extent for all these types, especially for vehicles (land, sea and air). While this work relates primarily to visual camouflage for a dismounted infantryman, it is useful to briefly mention solutions in other areas, as some technological ideas can be carried over to the visible spectrum.
Visual camouflage. Visual camouflage consists of shape, surface, gloss, silhouette, shadow, position, and movement. An active camouflage system can contain all of these aspects. This article focuses on visual active camouflage, so these systems are detailed in the following subsections.
Acoustic camouflage (e.g. sonar). Since the 1940s, many countries have experimented with sound-absorbing surfaces to reduce the sonar reflections of submarines. Gun jamming technologies are a type of acoustic camouflage. In addition, active noise cancellation is a new trend that could potentially evolve into acoustic camouflage. Active noise canceling headphones are currently available to the consumer. The so-called Near-Field Active Noise Suppression systems are being developed, which are placed in the acoustic near field to actively minimize the tonal noise of the propellers in the first place. It is predicted that promising systems for long-range acoustic fields could be developed in order to mask the actions of the infantry.
Electromagnetic camouflage (such as radar). Radar camouflage nets combine special coatings and microfiber technology to provide broadband radar attenuation in excess of 12 dB. The use of optional thermal coatings extends infrared protection.
The BMS-ULCAS (Multispectral Ultra Lightweight Camouflage Screen) from Saab Barracuda uses a special material that is attached to the base material. The material reduces the detection of broadband radar, and also narrows the visible and infrared frequency ranges. Each screen is designed specifically for the equipment it protects.
Camouflage uniforms. In the future, active camouflage can determine the object to be cloaked in order to adapt it to the shape of the space. This technology is known as SAD (Shape Approximation Device) and has the potential to reduce shape detection capability. One of the most compelling examples of uniform camouflage is the octopus, which can blend in with its surroundings not only by changing color, but also by changing the shape and texture of its skin.
Thermal camouflage (e.g. infrared). A material is being developed that attenuates the heat signature of naked skin by diffusing heat emission using silvered hollow ceramic balls (senospheres), an average of 45 microns in diameter, embedded in a binder to create a pigment with low emission and diffusion properties. Microbeads work like a mirror, reflecting the surrounding space and each other, and thus distribute the thermal radiation from the skin.
Multispectral camouflage. Some camouflage systems are multispectral, meaning they work for more than one camouflage type. For example, Saab Barracuda has developed a High Mobility on-Board System (HMBS) multispectral camouflage product that protects artillery pieces during firing and redeployment. Signature reductions of up to 90% are possible, and thermal radiation suppression allows engines and generators to idle for quick start-up. Some systems have double-sided coating, which allows soldiers to wear double-sided camouflage for use on different types of terrain.
In late 2006, BAE Systems announced what was described as "a leap forward in camouflage technology," at its center of advanced technology invented "a new form of active stealth … At the push of a button, objects become virtually invisible, blending into their background." According to BAE Systems, the development "gave the company a decade of leadership in stealth technology and could redefine the world of 'stealth' engineering." New concepts were implemented based on new materials, which allows not only changing their colors, but also shifting the infrared, microwave and radar profile and merging objects with the background, which makes them almost invisible. This technology is built into the structure itself rather than based on the use of additional material, such as paint or an adhesive layer. This work has already led to the registration of 9 patents and may still provide unique solutions to signature management problems.
Active camouflage system based on RPT technology with projection onto a reflective raincoat
The next frontier: transformation optics
The active / adaptive camouflage systems described in this article and based on scene projection are quite similar to science fiction in themselves (and indeed this was the basis of the movie "Predator"), but they are not part of the most advanced technology researched in the search " shroud of invisibility. " Indeed, other solutions are already outlined, which will be much more effective and practical in comparison with active camouflage. They are based on a phenomenon known as transformation optics. That is, some wavelengths, including visible light, can be "bent" and flow around an object like water enveloping a stone. As a result, objects behind the object become visible, as if light passed through empty space, while the object itself disappears from view. In theory, transformation optics can not only mask objects, but also make them visible where they are not.
Schematic representation of the principle of invisibility by means of transformation optics
Artistic representation of the structure of a metamaterial
However, for this to happen, the object or area must be masked using a cloaking agent, which must itself be undetectable to electromagnetic waves. These tools, called metamaterials, use cellular structures to create a combination of material characteristics that are not available in nature. These structures can direct electromagnetic waves around an object and cause them to appear on the other side.
The general idea behind such metamaterials is negative refraction. In contrast, all natural materials have a positive refractive index, an indicator of how much electromagnetic waves are bent as they move from one medium to another. A classic illustration of how refraction works: a part of a stick immersed in water appears to be bent beneath the surface of the water. If the water had negative refraction, the submerged part of the stick, on the contrary, would protrude from the surface of the water. Or, for another example, a fish swimming underwater would appear to be moving in the air above the surface of the water.
New masking metamaterial revealed by Duke University in January 2009
An electron microscope image of a finished 3D metamaterial. Split gold nanorings resonators are arranged in even rows
Schematic and electron microscope view of a metamaterial (top and side) developed by researchers at the University of California, Berkeley. The material is formed from parallel nanowires embedded inside porous alumina. When visible light passes through a material according to the phenomenon of negative refraction, it is deflected in the opposite direction.
In order for a metamaterial to have a negative refractive index, its structural matrix must be less than the length of the electromagnetic wave used. In addition, the values of dielectric constant (the ability to transmit an electric field) and magnetic permeability (how it reacts to a magnetic field) must be negative. Mathematics is integral to designing the parameters needed to create metamaterials and demonstrate that the material guarantees invisibility. Unsurprisingly, more success has been achieved when working with wavelengths in the wider microwave range, which ranges from 1 mm to 30 cm. People see the world in a narrow range of electromagnetic radiation, known as visible light, with wavelengths from 400 nanometers (violet and magenta light) to 700 nanometers (dark red light).
Following the first demonstration of the feasibility of the metamaterial in 2006, when the first prototype was built, a team of engineers at Duke University announced in January 2009 a new type of cloaking device, much more advanced in cloaking across a wide spectrum of frequencies. The latest advances in this area are due to the development of a new group of complex algorithms for the creation and production of metamaterials. In recent laboratory experiments, a beam of microwaves directed through a masking means to a "bulge" on a flat mirror surface was reflected from the surface at the same angle as if there were no bulge. In addition, the cloaking agent prevented the formation of scattered beams, usually accompanying such transformations. The phenomenon underlying the camouflage resembles a mirage seen on a hot day ahead of the road.
In a parallel and truly competing program, the University of California scientists announced in mid-2008 that they had pioneered 3-D materials that could change the normal direction of light in the visible and near infrared spectra. The researchers followed two distinct approaches. In the first experiment, they stacked several alternating layers of silver and non-conductive magnesium fluoride and cut the so-called nanometric "mesh" patterns into layers in order to create a bulk optical metamaterial. Negative refraction was measured at wavelengths of 1500 nanometers. The second metamaterial consisted of silver nanowires stretched inside porous alumina; it had negative refraction at wavelengths of 660 nanometers in the red region of the spectrum.
Both materials achieved negative refraction, with the amount of absorbed or "lost" energy as light passed through them was minimal.
Left is a schematic representation of the first 3-D "mesh" metamaterial developed at the University of California that can achieve negative refractive index in the visible spectrum. On the right is the image of the finished structure from a scanning electron microscope. Intermittent layers form small outlines that can deflect light back
Also in January 2012, researchers at the University of Stuttgart announced that they had made progress in the fabrication of a multi-layer cut-ring metamaterial for optical wavelengths. This layer-by-layer procedure, which can be repeated as many times as desired, is capable of creating well-aligned three-dimensional structures from metamaterials. The key to this success was a planarization (leveling) method for a rough nanolithographic surface combined with durable fiducials that withstand dry etching processes during nano-manufacturing. The result was perfect alignment along with absolutely flat layers. This method is also suitable for the production of freeform shapes in each layer. Thus, it is possible to create more complex structures.
Certainly, much more research may be required before metamaterials can be created that can work in the visible spectrum, in which the human eye can see, and then practical materials suitable, for example, for clothing. But even cloaking materials operating at just a few fundamental wavelengths could offer tremendous benefits. They can make night vision systems ineffective and objects invisible, for example, to laser beams used to guide weapons.
Working concept
Lightweight optoelectronic systems have been proposed based on modern imaging devices and displays that make selected objects almost transparent and thus virtually invisible. These systems are called active or adaptive camouflage systems due to the fact that, unlike traditional camouflage, they generate images that can change in response to changes in scenes and lighting conditions.
The main function of the adaptive camouflage system is to project the scene (background) behind the object onto the surface of the object closest to the viewer. In other words, the scene (background) behind the subject is transported and displayed in panels in front of the subject.
A typical active camouflage system will most likely be a network of flexible flat panel displays arranged in the form of some kind of blanket that will cover all visible surfaces of the object that need to be camouflaged. Each display panel will contain an active pixel sensor (APS), or possibly another advanced imager, which will be directed forward from the panel and will take up a small portion of the panel area. The "coverlet" will also contain a wire frame that supports a network of cross-linked optical fibers through which the image from each APS will be transmitted to an additional display panel on the opposite side of the cloaked object.
The position and orientation of all imaging devices will be synchronized with the position and orientation of one sensor, which will be determined by the main imager (sensor). The orientation will be determined by a leveling tool controlled by the main image sensor. A central controller connected to an external light meter will automatically adjust the brightness levels of all display panels to match the ambient light conditions. The underside of the masked object will be artificially illuminated so that the image of the masked object from above shows the ground as if it were naturally lit; if this is not achieved, then the obvious heterogeneity and discreteness of the shadows will be visible to the observer looking from top to bottom.
Display panels can be resized and configured so that a total of these panels can be used to mask various objects without having to modify the objects themselves. The size and mass of typical systems and subsystems of adaptive camouflage was estimated: the volume of a typical image sensor will be less than 15 cm3, while a system that cloaks an object 10 m long, 3 m high and 5 m wide will have a mass of less than 45 kg. If the object to be cloaked is a vehicle, then the adaptive camouflage system can be easily activated by the vehicle's electrical system without any negative impact on its operation.
An interesting solution to adaptive camouflage of military equipment Adaptive from BAE Systems
