China is testing fighter jets equipped with 'invisibility cloaks' that make would make them impossible to detect on radar.

Researchers involved with the project say the technology will rapidly boost the combat power of the non-stealth military jets, the South China Morning Post reports.

However, critics say the technology is difficult to mass produce and are limited to a small range of radar bandwidths.

It involves the use of a 'metamaterial' that can change the way radio waves bounce off the surface to limit the echo on a radar in order to make aircraft harder to detect.

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China is testing fighter jets equipped with 'invisibility cloaks' that make would make them impossible to detect on radar. Pictured, a J-15 fighter jet

Researchers involved with the project say the technology will rapidly boost the combat power of the non-stealth military jets

The metamaterial was developed by a team at the State Key Laboratory of Millimetre Waves in Southeast University in Nanjing, according to the Post.

A researcher said it was being tested on aircraft at the military aircraft production base in Shenyang in the Liaoning province.

Although it wasn't revealed which aircraft the metamaterial was being tested on, the Shenyang Aircraft Corporation builds fighter jets including the J-11 and the J-15.

It comes after the Chinese state broadcaster revealed China has built an assembly line to mass produce cutting-edge 'super materials' that can perform the previously impossible.

WHAT ARE METAMATERIALS? Metamaterials are a new class of surfaces which have been engineered on the nanoscale, as small as a billionth of a metre wide. The materials used to construct them are arranged in certain patterns or shapes, designed to perform specific tasks. Most are created on computers and 3D-printed as plastic blocks or slabs, although metals and other materials can also be used. One such task is to bend electromagnetic radiation around an object. The first examples only worked with long-wavelength radiation, such as microwaves, while others altered the path of near-infrared radiation. Some can bend sound waves to focus them for medical purposes or to create speakers which direct sound to a specific spot. Some scientists have claimed there is nothing stopping them from scaling their inventions up to hide objects from visible light. So far, however, this has proved more of a challenge. When light is shone upon an object it is either reflected or absorbed, dictating how it appears to a human eye. Using metamaterials, the interaction of particles with light can be changed so that the object appears invisible, or as something completely different. Advertisement

So far, the assembly line located in a lab in Shenzhen has manufactured different types of materials, including one that renders objects invisible, China Central Television Station reported in a documentary released last month.

Although the station didn't explain what the invisibility cloak 'metamaterial' would be used for, according to Chinese news portal Sina, it is likely to be used on the country's warplanes, particularly the J-20.

What the broadcaster referred to as 'super materials' are generally known as metamaterials - a new class of finely-engineered surfaces that could have properties unachievable with conventional materials.

Some metamaterials can bend infrared radiation such as visible light, which means they could be used to create invisibility cloaks.

And according to the Chinese Central Television Station, the Chinese scientists have managed to make such invisibility materials in bulk.

China's J-20 has been compared to America's F-22 Raptor in terms of combat capabilities

CHINA'S J-20 Top speed: 1,305 mph Range: 2,113 mi Length: 67′ Wingspan: 42′ 0″ Weight: 43,000 lbs Engine Type: Xian WS-15 turbofan engines Cost: $110m Manufacturer: Chengdu Aircraft Industry Group Advertisement

AMERICA'S F-22 Top speed: 1,498 mph Range: 1,839 mi Length: 62′ Wingspan: 44′ 0″ Weight: 43,430 lbs Engine type: Pratt & Whitney F119 Cost: $130m Manufacturers: Boeing Defense, Space & Security, Lockheed Martin Aeronautics Advertisement

The report took the viewers inside the mysterious lab where Jin Xi, a doctor of Materials Science, and his team were busy feeding pieces of material from one machine to another.

Each piece, 80cm long and 60cm wide, is said to be the plated with bronze and would be used as the base material for the Chinese 'super material'.

A layer of special film, which could show some 20,000 patterns once exposed to light, will be added to this base material.

The patterns, as tiny as 0.2 square millimetres, are said to contain thousands of micro-structures invisible to the human eye.

These micro-structures are used to control the properties of metamaterials.

The report didn't mention what type of 'super material' the workers were making, but it claimed that Chinese scientists have developed metamaterials to help develop the country's aviation industry.

The programme, aired on China Central Television Station, shows workers making the base material (pictured) for different metamaterials, which the Chinese call 'super materials'

A report from Sina, one of China's largest news portals, claimed on March 11 that the lab in question is the State Key Laboratory of Metamaterial Electromagnetic Modulation Technology in Shenzhen, a state-funded lab established in 2011.

The Sina report also suggested that the metamaterials would be used for military purposes.

It also indicated that the invisibility material is likely to be used on J-20 fighter jets because the jet's chief engineer Yang Wei is also a member on the laboratory's academic board.

China's latest J-20 stealth fighter jets were commissioned into military service last year and are operated by the Chinese Air Force.

China's fourth-generation fighter jet, the J-20 made its maiden flight in 2011.

According to a 2017 report from China Central Television Station, the J-20 is capable of carrying multiple types of air-to-air missiles.

It's said to be powered by a made-in-China engine and has similar combat capabilities to those of America's F-22 Raptor.