Camouflage
Camouflage occurs when objects are disguised so they can’t be seen easily. In their natural environment, animals have developed colours that enable them to blend into their environment, for example, a tiger’s stripes. This is mostly so they can’t be seen by other animals that might prey on and eat them.
Do invisibility cloaks exist?
A scanning electron microscope image of a fabricated metamaterial developed by UC Berkeley researchers. The alternating layers form small circuits that can bend light backwards.
The military uses camouflage to prevent other people seeing their operations. With new technologies using infrared, radar and radio signals enabling greater ability in sensing objects, military operators have to develop new camouflage methods to avoid being detected. They have developed anti-sense strategies and methods, often using camouflage coatings or covers.
Many different ways of disguising or camouflaging metal objects include stealth technology (such as plasma clouds, radioactive paints and light-bending cloth) to hide objects so they cannot be sensed and therefore make them invisible to sensors used by the enemy. Mostly these technologies bend light or deflect other electromagnetic waves.
The following examples show the use of the properties of waves such as absorption, scattering and refraction in camouflage.
On the ground
The position of military equipment can be highly secretive. Military surveillance satellites seek out these positions. Camouflage nets and other means are used to prevent detection of the equipment.
MULE (Multifunctional Utility Logistics Equipment)
Different types of MULE are used to carry equipment, detect mines or use machine guns. They are very visible during the day so they are mostly used at night.
The US Army are using Multifunctional Utility Logistics Equipment (MULEs) – unmanned remote-controlled vehicles up to 15m long and 2m wide. To make them invisible at night, they’re covered with paint that absorbs infrared waves so they can’t be seen with night goggles or other infrared sensors.
A different kind of paint is also being tested to see how it changes the wavelength of sensor signals used by the enemy. When the enemy sensors send out a signal, its wavelength can be changed and it can be absorbed by moisture in the air – making the target objects appear ‘invisible’.
Metamaterials are also being developed for making soldiers’ clothing. These materials bend light and any other form of electromagnetic radiation around whatever object it covers. Helmets may soon be equipped with lights that would blank out the soldier beneath it by electronically reading, analysing and mimicking the characteristics of the light surrounding the soldier – the soldier would be invisible.
In the air
Aircraft engineers tried to design planes that have minimal silhouettes against the daytime sky. They realised it was the shadow under the plane, not the colour of the underside of the plane, that made it visible during the day. They attached fluorescent lights under the fuselage and wings that pilots could dim or brighten to match the brightness of the day, thus rendering them invisible.
F-22 Raptor
The F-22 Raptor only appears as a very small blip on a radar screen. Anti-sensing design features include super-cooled engines, thrust vectoring nozzles and electromagnetic-emitting sensors.
The idea of making planes invisible was boosted by observations made during the US space programme. They observed that a spacecraft was not sensed by radar or radio waves upon re-entering the atmosphere because a lot of friction on the surface caused it to heat up, creating a plasma ‘bubble’ around the craft that made it unable to be sensed by radar detectors.
A concept called plasma aerodynamics uses the shape of the plane and other features to ‘cloak’ or hide the plane from detection. One way of doing this could be to have an onboard device that zaps the atmosphere just in front of the aircraft, providing a cloud of plasma to fly into.
Another idea suggests using an onboard device that surrounds the craft in a plasma cloud that can absorb radar.
A third idea is to paint planes with radioisotopes that ionise the atmosphere surrounding the plane, placing it in a plasma sheath or glove. Electromagnetic radiation behaves differently in plasma and thus can’t be used to detect the plane.
The advantage of flying a plane in a plasma cloud is that it can reduce drag by 2%, making the plane fly more quickly and efficiently. A disadvantage of painting planes with radioactive material is that they can glow in the dark!
Plasma ball.
Scientists are investigating different ways of using plasma to hide military equipment.
In the sea
The Swedish Navy has a Visby class of warships that are made from the same ultra-hard carbon-fibre material used in Formula One racing cars. This makes them very light and quick and reduces fuel consumption. These vessels have layered and textured carbon-fibre cover that absorbs radar rather than reflecting it back.
A Russian submarine uses a double-layered hull coated with rubber anti-sonar tiles to reduce the amount of sound it produces when travelling through the water.
Computer systems are also being developed to continually vary the frequency of vibrations given off by submarine engines so they can avoid sonar lock-ons and thus avoid being located.
Useful links
Watch this You Tube clip on stealth technology.
This National Geographic article How to be invisible looks at what we can learn from the way various species use different forms of disguise to hide from those who want to eat them – or to better ambush their prey
