Chinese military invents a new invisibility cloak for drones

Imagine a warplane shrouded by a “cloak” that can zip through the skies, reliably protected from enemies’ eyes and radars. Earlier this year, scientists at Zhejiang University in China announced that they had created just that: an “Aeroamphibious invisibility cloak” for aircraft which literally has a similar effect to what you might see on Star Trek with the Klingon cloaking shields! Now, the Chinese military wants to apply the new stealth technology to its growing drone fleet.

Aircraft are spotted when they reflect incoming waves from radar systems. But invisibility cloaks are crafted to trick radar systems with specially engineered tunable and digital metamaterials that bend these waves around the aircraft as if they were passing through a plane. The goal is to manipulate waves across the electromagnetic spectrum, including the portions that are visible and invisible to the human eye.

Militaries around the world have worked for decades to make weapons platforms like warplanes undetectable to radar systems. But such stealth tech is far from perfect, and these weapons can still be spotted with the right radar. Now, the Zhejiang University team says they can close the invisibility gap and render aircraft entirely imperceptible. But is it all too good to be true?

Before invisibility cloaks, stealth planes were the most cutting-edge option available. The exterior of these aircraft are built with special composite materials, which contain substances like graphene and carbon fiber, that can absorb certain types of radar waves rather than pinging them back. Stealth planes like America’s F-35, F-22 Raptor, and B-2 Spirit are also designed with flat surfaces to reflect as few radar waves as possible, and instead appear to be a bat or a bird traversing the sky. Similar designs on submarines make these steel beasts undetectable to sonar operators.

The US military took the initial lead on stealth planes. In the 1970s, the US Department of Defense began developing this technology, which wasn’t publicly announced until a Pentagon press conference in 1980. Then, the country’s first stealth plane was introduced into combat in 1989. From that moment on, US rivals and even some allies began developing countermeasures to detect and shoot down the Pentagon’s sly new aircraft.

These nations have developed countermeasures for detecting stealth planes, such as more sophisticated types of radar that can catch a broader spectrum of frequencies.

Today, Russia employs radar systems that operate on relatively low frequency bands, including the Nebo-M radar. This system sends out long wavelengths, which makes it more difficult for the stealth planes to avoid radar pulses. US stealth planes, for example, can be spotted by Nebo-M radar because they’re designed to escape shorter radar wavelengths.

China, meanwhile, claims to have developed a new radar system that uses the country’s BeiDou satellite constellations to detect slight refractions from passing stealth planes.

“Using a simple receiving antenna, the radar is cost-effective, can be deployed almost anywhere on Earth and does not emit signals that might reveal its location,” according to the South China Morning Post.

Combined with advancing radar systems, the new invisibility cloaking technology from Zhejiang University could offer China an unparalleled advantage over its rivals.

China has sought out true invisibility with the help of advanced metamaterials for over a decade. Liu Ruopeng, an entrepreneur dubbed “China’s Elon Musk”, has researched these engineered synthetic materials for nearly two decades.

By 2011, scientists at Guangqi Advanced Institute of Technology in China were already mass-producing specialized metamaterials for potential use in China’s ongoing fifth-generation warplane program - the J-35 and the J-20 “Mighty Dragon” are its two fifth-gen warplanes.

Two years later, scientists at the University of Texas, Austin, announced they too had created an invisibility cloak. But this was only designed to shield aircraft from microwave light. Then in 2016, scientists in the United Kingdom announced a “surface wave cloak” that could make curved surfaces appear flat when coming into contact with electromagnetic waves from multiple frequencies, preventing them from scattering and alerting radars.

A few years later, scientists from the US and Canada achieved a major breakthrough in metamaterial production: an innovative new type of metalens, which is a flat surface that uses nanostructures to manipulate light. Unlike past stealth designs, this metalens renders an object invisible by expertly bending waves from across the entire visible light spectrum. The surface is filled with titanium nano-fins that can deftly guide incoming lightwaves, regardless of wavelength, through metamaterials that bend the waves with surgical precision. And because the metalens is relatively thin, it’s easier to use and produce than past designs.

In the meantime, the Chinese military has worked to take invisibility cloaks out of the lab and into the clouds. As of 2018, the Guangqi Advanced Institute of Technology was allegedly producing more than 100,000 square feet of electromagnetic materials every year. These were created for China’s fifth-generation warplane, the Chengdu J-20 “Mighty Dragon,” according to defense analysts Jeffrey Lin and P.W. Singer.

The Zhejiang University research team designed their invisibility cloak for a fast-moving drone, so they had to ensure that it could conceal a large, moving object in any weather and any environment, be it air, water, or land.

The scientists had to overcome the significant obstacles faced by past invisibility cloak experiments. For one, the metamaterials used in previous designs struggled to bend electromagnetic waves consistently into a single spot to maintain invisibility. So, the researchers developed a new three-dimensional metamaterial to manipulate incoming waves and ensure that the cloak remains invisible in any context.

With the help of Artificial Intelligence (AI), the cloak adjusts to changing conditions like a chameleon: on-board sensors gauge factors like the frequency and angular velocity of incoming radar waves, then AI processes this information and directs the drone to manipulate tiny structures on the metamaterial’s surface to guide the waves. Unlike other cloak concepts, the researchers say the intelligent system could theoretically work in real time without human intervention.

In indoor tests simulating land, sea, and air environments, the cloaked drone’s electric field strength was, on average, about 90 percent similar to that of its background. This indicated that it tended to blend in significantly better than a drone without an invisibility cloak, which was only up to 45 percent similar in electric field strength relative to the background environment.

Zhejiang University’s new cloak technology has not been not applied to Chinese warplanes because it’s intended for use, at least initially, on China’s massive, growing fleet of drones. Cloaking a drone, or a swarm of hypersonic drones, with real invisibility would be a decisive advantage for China in any possible conflict with the United States or its allies in the Indo-Pacific region.