Illusion ‘cloak’ makes you see what's not there

Illusion ‘cloak’ makes you see what's not there

TECHNOLOGY Augmented reality helps track police suspects on an iPhone shows the location of officers on control-room screens using GPS signals sent b...

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TECHNOLOGY

Augmented reality helps track police suspects on an iPhone shows the location of officers on control-room screens using GPS signals sent by their radios. If a suspect has a cellphone that police have a fix on, or they are being closely followed by a covert officer, they too can be tracked. Officers can also use their phone to “tag” the location of a suspect

Illusion ‘cloak’ makes you see what isn’t there NOW you see it, now it looks like something else. Radar images might never be the same again, thanks to an illusion device that can change an object’s appearance. The technology could ultimately be used to hide military aircraft. The device is part of a growing family of metamaterials – structures designed to steer light along curved paths. They have already been used to make objects appear invisible and to disguise a gap between two objects. Wei Xiang Jiang and Tie Jun Cui’s team at Southeast University in Nanjing, China, have created a structure that changes the way radio waves interact with a copper cylinder 26 | NewScientist | 19 February 2011

Sloggett, a security researcher at the University of Reading, UK. “Terrorists have been very good at turning our own technology against us. The Mumbai attacks [in India in 2008] were meticulously planned on Google Earth, for instance. If terrorists get hold of police location data on mobile phones it could be disastrous.” Stopping criminals hijacking AR data will require strongly encrypted data links. While the Frequentis demonstration system used a regular 3G network, van Loo says that by the time it is commercialised it could be using an encrypted emergency-servicesonly 4G network – known as LTE for Public Safety. The UK Home Office is funding 12 months of tests on a range of AR systems, including iAPLS, at the University of Nottingham. These include motion-tracking visors that overlay data on to an officer’s field of view, systems that overlay contoured street maps on live helicopter video in real time to help police, and a system that tracks troops as they scout for landmines to ensure their search pattern covers all –No safety in numbers– the ground. Paul Marks n FREQUENTIS AG

PICTURE the scene: armed police officers are warned on their radios that a suspect male terrorist has been tracked to a crowded football stadium. Even with a full description, it’s all but impossible to pick him out amid the matchday melee. Perhaps smartphones fed augmented reality (AR) data by the police control centre could help focus the search. After booting up an iPhone app, an officer would train the phone’s camera on the crowd. The suspect’s position, after he had been tracked by covert police, would be highlighted by an icon overlaid on the image. Similarly, other icons could pinpoint the positions and range of other officers (see picture), including those operating undercover. The system, called iAPLS, has been developed by engineers at Frequentis, a surveillancesystems company based in Vienna, Austria. It is a mobile extension of the firm’s Automatic Personal Location System, which

package to make it visible to fellow law enforcers. What Frequentis engineer Reinard van Loo and his colleagues have done is package APLS data so that it can be sent via a regular 3G link to a standard iPhone, making location information available to all officers on duty, not just those in the control room. The extra data that this kind of AR app will provide could be a double-edged sword, warns David

so that it appears to be composed of another material altogether. Copper conducts electricity well and reflects incoming radio waves, giving it a bright radar signature. To alter this behaviour, the team built a device made of 11 concentric rings of circuit boards etched with small metal-lined channels that prevent electromagnetic waves reflecting away. Instead, they guide the waves in a direction that the researchers choose specifically to make the hidden object appear to have different electrical properties. Placed around a copper cylinder, the arrangement created the illusion that the cylinder was made of a dielectric, a class of materials

including porcelain and glass that do not conduct electricity and are more transparent to radio waves. The illusion only worked when the cylinder was viewed from the side; what’s more, the imaginary object it generated was the same size as the original. Future designs would have to account for all three dimensions, and might produce an

“Similar devices could be used to convert the radar image of an aircraft into a flying bird” illusion quite different from the object they disguise. “In principle, this technology could be used to make an illusion of an arbitrary shape and size,” says Cui, whose team created an electromagnetic “black hole” for

light in 2009. Similar illusion devices could eventually be used for stealth technology: for example, to “convert the radar image of an aircraft into a flying bird”, Cui says. The work, which will be published in Physical Review E, is still at an early stage, however. At 45 millimetres, the team’s illusion device is three times as wide as the cylinder it disguised. “Their device is still fairly bulky relative to the original object, so further work needs to be done before a real device can be deployed,” says John Pendry of Imperial College London. Although invisibility devices were invented first, the illusion technology might win the race to be put to practical use. “It is easier to falsify something than to hide it,” Pendry says. The team next plans to explore ways to design devices with more complex shapes. Rachel Courtland n