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Current scanners – like those used in airports and other major transport hubs – slow down the flow of people and often miss illegal and dangerous concealed objects.
But better security checkpoints must balance tackling the threat of terrorism with civil liberty. As well as being safe, body-imaging systems cannot interfere with individual privacy.
The SPIDERS project, funded by the EU’s H2020 SME Instrument, took on this challenge by developing an innovative, high-resolution body scanner that can safely and effectively scan people moving around in real time.
‘When moving people are scanned, the operator has a small window of time to analyse the radiometric images, and in some cases might not see a potential threat,’ says project coordinator Nicolas Vellas of MC2 Technologies in France. ‘So, we’ve created innovative software which automatically detects hidden objects. Moreover, law requires that radiometric images cannot be displayed, to avoid any ethical issues. Thanks to automatic detection, the software can be configured so that operators cannot see the imagery.’
Safe, ethical scanning
The company’s original MM-Imager did not work in real time and could only scan one image per second at best – not enough to track moving people. However, over the course of the project, the team upgraded the technology so it could work in real time, with a greater field of view.
The final product is capable of scanning several people at a time, at a distance of one to ten metres. It can detect liquids, powders, metallic and non-metallic solids through thick clothes and even leather. The new scanner is also smaller, lighter and very energy-efficient, making it more suitable for use in crowded public locations. Furthermore, it does not emit any radiation, meaning there is no risk of harm to operators or the public.
The MM-Imager is a passive technology based on measuring the natural radiation given out by the human body at microwave frequencies – terahertz waves. The principle is similar to an infrared camera that measures infrared waves emitted by the body and processes that send signals to construct radiometric images. Terahertz waves can travel through materials such as fabrics, papers, plastics, wood, and even through walls, while infrared waves cannot even cross something as thin as a cigarette paper.
However, the terahertz signal needs to be amplified because it is so small – five times smaller in amplitude than infrared. So, the team had to create ultra-sensitive and stable millimetre wave sensors, which also take into account changes in temperature in the scanner’s environment.
For these sensors to scan a scene in real time would require a vast amount of complex and expensive electrical circuitry, so the solution is an innovative mechanical one, the details of which remain confidential. It also allows for easier calibration of the sensors and greater sensitivity, which means the scanner can achieve a field of view twice as large as would otherwise be possible.
A promising future
Recent demonstrations of the technology in France and China have attracted interest from potential customers. ‘Paris will organise the 2024 Olympic Games and our technology will be used to secure the sporting event,’ says Vellas. ‘The Chinese authorities are also looking for such technology to secure metro and train stations, airport terminals, police checkpoints and public areas such as stadiums. Experimental set-ups of the scanner have recently been launched in major towns, including Beijing, Shanghai and Chengdu.’