Keeping the initiative with plastics

The battlefield is a jungle where those who can stay invisible have the upper hand! Combining offensive effectiveness with defensive safety, the art of camouflage has become one of the most advanced fields of military research. However, more than simply striving for mimicry, it is now aimed at achieving stealth for vehicles and soldiers in order to thwart the enemy's detection capabilities. In order to achieve this, they must be address a range of issues such as reducing the electromagnetic signature of radar echo, the infrared footprint of heat sources and, at sea, the acoustic phenomena picked up by the sonar. These three issues that make motorised and metal-covered military equipment vulnerable, have opened up the way for non-conductive and insulating materials such as plastic resins.

Composites play the field

Almost transparent to radar and sonar waves, polymer matrix composites are the ideal materials for constructing the domes that cover detection equipment. Their lightness has also been a valuable asset for military aircraft.
However, lightweight and wave-permeable materials also have properties that are very useful for achieving stealth. Their intrinsic damping properties enable them to reduce the vibrations and noises of moving ships and make them less apparent on sonar screens.

This potential for absorption was also used to develop RAM materials (Radar Absorbent Materials) that can reduce radar echo and infrared signatures. In order to achieve this, carbon-, silicone- or polyurethane-based composites are coated in conductive polymers such as polyaniline, charged with ferrite particles that trap the waves not absorbed by the lower layers.
No less important is the role of paints and finishes applied to new equipment or during maintenance operations, which are unfortunately quite frequent with these fragile pieces of equipment. Some vehicles get around twenty successive coats aimed at improving stealth through their insulating, reflective, electromagnetic or anti-vibration properties. Others, like the Rafale, are coated with a stealth-improving paint for certain missions.

The Tiger hides its tracks

No single material is effective in all aspects of stealth which must, in addition, protect the equipment's vulnerable parts. This is why the goal of multi-spectral stealth (radar, infrared and acoustic) can only be achieved by combining several solutions such as those developed for the Franco-German Tiger helicopter.
In addition to the vehicle's geometric design, its low radar signature is due to innovations linked to the chemistry of polymers such as the structure made from 80% composite materials - mainly Kevlar and carbon fibres, and the use of absorbent paints.
As for infrared, the turbine thermal emission reducer is much sought after, not counting the very advanced research carried out on the polymer foam of the blades and their geometry, which provided a major contribution to the vehicle's stealth.

Nanos take the lead after the war in Kosovo

Certain air defence systems, not always the most sophisticated, are able to thwart the most effective RAM materials (Radar Absorbent Materials). So-called "passive" radars, which are in fact simple receivers that can capture the echo of relay antennas on aircraft, are capable of this. NATO, which came up against such radars on 27 March 1999 in Kosovo, suspects that the Serbian forces used this type of radar to shoot down the American F-117 Night Hawk stealth bomber.
While the Russians were examining the intact wing offered by their Serbian allies, and the Chinese were roaming the countryside looking for debris, the US Air Force applied itself to finding a way to thwart such radars.

Its engineers finally recommended adding a resin charged with absorbent nanoparticles to the sections of the aircraft that are most exposed to radar signals.
Although necessary, this solution was probably not sufficient. The formidable Night Hawk bowed out in 2008, 10 years ahead of schedule. Its fall nevertheless paved the way for nanoparticles in the field of stealth.

Metamaterials, the Holy Grail of stealth!

The defence industry is already preparing a new generation of active, rather than passive, stealth technologies. To achieve this, engineers are working on the development of nanostructured composites or metamaterials, often with a polymer matrix, which are structured in such a way as to stop or deflect the propagation of optical, acoustic or electromagnetic waves in the material.
The goal: manufacturing new coatings that can erase or disguise the radar or infrared signatures of vehicles in order to fool detection systems.

Certain flexible coatings can reduce the radar echo of a vehicle and also increase or reduce the apparent surface temperature of a vehicle to align it with the surrounding atmosphere. It then becomes almost undetectable.
This was achieved with the BZ 200 tarp adopted by the members of the Hubert commando unit. Tested with the French national Navy's most sophisticated detection systems, it was able to completely hide their light sea craft up to one nautical mile from the device.

The art of the chameleon resurfaces

Traditional camouflage is time-consuming and expensive. The paints quickly get damaged and it is impossible to have the right pattern for each theatre of operations on hand at any given time. The ideal scenario, therefore, would be to change skins like a chameleon.
This is now possible thanks to the dynamic electronic camouflage bearing the creature's name, unveiled at the 2014 Eurosatory trade fair in France. This system uses a multispectral active skin that covers the light spectrum from visible to infrared, in order to thwart both "normal" and "thermal" vision.
Six cutting-edge technologies were used to develop the camouflage, among which are liquid crystals that can selectively reflect light and organic light emitting diodes (OLED) which are essential for manufacturing flexible plastic screens.

DisaSolar, a French start-up specialising in the field of photovoltaics, opted for an even more original approach by developing flexible mimetic solar panels based on its ink-jet printing technology. These panels aim to provide greater autonomy to the electronic equipment of operational units while hiding their presence by matching the shape and colour of their immediate surroundings.