What is special about the discovery is that the coating material rendering them invisible to radar systems is in theory thin enough to be applied to stealth aircraft for the first time.


 
 
A team of Chinese researchers have made a breakthrough in stealth plane technology that could be so significant even local military sources say it should be kept out of the public realm.
The team released the technical and design details of an “invisibility circuit” they claim has the potential to help aircraft trick the best early warning systems in use today.
The researchers are affiliated with the Huazhong University of Science and Technology in Wuhan in central China’s Hubei province.
They published their paper in last month’s Journal of Applied Physics, run by the American Institute of Physics.

“It sounds like something that should be kept in the drawer,” said Professor Huang Jun, a military stealth technology researcher at the School of Aeronautic Science and Engineering at Beihang University. Huang was not involved in the research.
“This will be a breakthrough if it works as they claim,” he said.

That will be really bad news for early warning radars,” he added.
The researchers, led by Professor Jiang Jianjun at the Wuhan institute’s department of electronic science and technology, could not immediately be reached for comment.
According to their paper, they have created a multi-layer electrical circuit that can “trap” microwaves at ultra-high frequencies, thus confusing radar systems and enabling aircraft to sneak past them.

All radars work by detecting “echoes” of radiowaves, which are bounced off a target. If the waves are absorbed by the new circuit, the target - in this case an aeroplane - would disappear from radar screens.
What is unique about the latest finding is that the material used to create the circuit would be almost impossibly thin. At under one centimetre, it is just a tenth the size of similar products developed by overseas competitors. This means it could be used to coat planes for the first time, pundits say.
Stealth planes including the F-22 and F-35 used by the US military are not quite as evasive as they sound, according to Huang, who said they can be spotted by advanced radar systems even from a considerable distance.

Such radars typically use microwaves at strengths of 2 gigahertz or lower to identify and track stealth aircraft. This is because the currently available coating materials can only absorb electromagnetic waves at high frequencies.
Jiang’s team said the new circuits hit the military’s sweet spot as they can absorb waves ranging from 0.7Ghz to 1.9Ghz.
Many similar projects are kept under wraps because of their implications for national security and national defence. Some are supported by military funding, which prohibits their public disclosure.
But in this case the team was free to act on its own discretion as it relied solely on public funds.
Meanwhile, other sources said the new technology could be coupled with traditional paint materials to reach an unprecedented level of “invisibility” for military and other aircraft.
 
Yet the new circuit is not without problems.
First, it is unable to absorb microwaves generated at frequencies of 2Ghz or above, meaning that it could still be spotted by advanced radar systems, some of which can operate at over 40 Ghz.
As such, it could take years before it is used on an actual aircraft, Huang said.
It may initially be applied as an undercoat beneath other cutting-edge paints that are already used on stealth planes, he added.
“It will take countless field tests to prove the circuits can survive the cruel environment of battle,” he said.

Jiao Yongchang, a professor of radar technology at Xidian University in Xi’an, Shaanxi province, was more sceptical.
“The advent of the [invisibility circuit] generated some interest a few years ago, but now the hype is cooling down because of all the technical limitations,” Jiao said.
“The idea of it having any military application right now is the stuff of daydreams,” he added.
China has been developing “invisibility cloaks” for several years - some for radars, and others designed to trick the naked eye.
In 2013, a research team from Zhejiang University managed to hide cats and fish in broad daylight using specially designed glass prisms.


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