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China tests stealth ‘invisibility cloaks’ on regular fighter jets


Jul 2, 2014
Military experiments with metamaterials designed to fool radars with wave-bending powers but observers say there’s still a long way to go before the technology is ready for the battlefield

China is testing an “invisibility cloak” on non-stealth military jets to help them evade radar detection, according to scientists involved in the project.

If successful, the technology could quickly boost the combat strength of the jets, the researchers say.

But others say the technology was difficult to mass produce, limited to a small range of radar bandwidths and would need to be combined with other devices to be truly effective.

The technology involves the use of a “metamaterial”, a fabricated layer comprising microscopic structures similar to integrated circuits. The metamaterial can alter the way radio waves bounce off its surface to create a ghost image or minimise echo on a radar, helping hide the aircraft in flight with greater efficiency.

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The metamaterial was developed by a research team at the State Key Laboratory of Millimetre Waves in Southeast University in Nanjing, Jiangsu province. It was being tested on aircraft at a major military aircraft production base in Shenyang, Liaoning province, a researcher in the laboratory confirmed.

The researcher declined to name the test site or the aircraft but Shenyang Aircraft Corporation, a subsidiary of the Aviation Industry Corporation of China, builds non-stealth fighter jets, including the J-11 and the J-15.

Other countries, especially the United States, have also been heavily engaged in the research and development of similar technology to cloak military jets in recent years.

Within China, the government has funded dozens of research teams over the years to develop the technology to hide objects from view and make them “disappear”. But there has so far been no public reports on the mass application of metamaterials.

“This is the beginning. More [applications] are on the way,” the researcher said, without elaborating.

The laboratory is China’s leading institute on metamaterials research and its defence applications.

A team led by Professor Cui Tiejun developed the world’s first programmable metamaterials that could change their physical properties in response to electric currents.

In theory, a fighter jet coated in the metamaterial could “transform” mid-flight to avoid radar detection.

In 2011, the team said it had developed a radio wave-absorbing device that could make a target invisible to the three most common radio bandwidths used by military radars.

Two years later, the team said it had created a “ghost illusion device” that could allow a plane to leave almost no radar signature. The device could make parts of the plane appear on radar as plastic, instead of metal, or show three planes instead of one, according to the team.

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It was unclear which type of device was being used in Shenyang or how close the technology was to practical deployment.

China has about 20 J-20 stealth fighters and roughly 1,500 other kinds of combat aircraft in service, according to some overseas estimates. Upgrading the existing non-stealth aircraft with new metamaterial could greatly improve their combat strength.

But Han Yiping, director of applied physics at Xidian University, formerly a military engineering institute, said metamaterials alone could not hide an aircraft from radar.

Stealth aircraft relied on a range of tactics, including low-reflection aerodynamic design and cloaks of ionised particles, to fly undetected, Han said.

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She said metamaterials were also extremely difficult to mass produce, and the technology would have to withstand the heat and shock of battle, meaning some performance would have to be sacrificed for reliability.

And at present, the technology was effective within only certain radio bandwidths, Han added.

Early this year, Shenzhen-based technology company Kuang-Chi said it had started mass production of a thin, metallic membrane that it claimed was a metamaterial.

“This is the first metamaterial production line in the world,” a company executive said in a documentary aired on China Central Television in March.

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Kuang-Chi president Liu Ruopeng, who used to work at the Nanjing laboratory, told Chinese news website Ifeng.com that China was well ahead of other countries in applying metamaterials to aircraft. Liu could not be reached for comment.
But there is debate in the research community about the value of Kuang-Chi’s product.

“There is not a clear-cut definition of a metamaterial, so not everyone in the research community agrees with their claim,” a researcher with the Chinese Academy of Sciences said.

“The consensus is that their product still has a lot of room for improvement.”

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