The New Wave

Metal detectors have been a familiar sight in airports since the 1970s. However, they could seen be replaced by new screening machines that use milimetre wave technology.

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By  Neil Denslow Published  November 4, 2004

|~|mmw_m2.jpg|~||~|Since 9/11 especially, the aviation industry has heavily invested in improving airport security and in ways to stop people carrying potential weapons and contraband onto aircraft. However, while there have been many developments in baggage screening over recent years, the method and technology used for screening passengers has largely remained unchanged for nearly 30 years. The reign of the metal detector may soon be coming to end though, as a number of companies are now investing in millimetre wave imaging technology, which promises to offer a faster, cheaper and more effective alternative. Walkthrough metal detectors or magnetometers were first introduced into airports to screen passengers in the 1970s following a wave of aircraft hijackings. They clearly allow security personnel to check passengers and carry-on bags for metal objects, predominately guns and knives, without the need to psychically search people. However, in recent years, government legislation and incidents like the shoe bomber and last year’s attempt to hijack a Qantas jet with a wooden stake have created a need to detect non-metallic objects, which magnetometers are clearly unable to do.“What we have seen recently is a requirement to detect explosives on the body and other types of threats, such as ceramics and plastics,” comments Michael Burns, director, aviation markets, QinetiQ. “These are all things that you can get through a magnetometer with little difficulty.” A further difficulty is caused by the low throughput achieved by magnometers; in the US, for instance, the average is only around 120 people per metal detector per hour. This throughput figure is primarily limited by the large number of false alarms generated by metal detectors. Each alarm forces the whole process to be stopped so that the person can be re-scanned or hand searched. This ensures there are no security breaches, but it quickly translates into long queues of disgruntled passengers. The only way to speed up passenger throughput at a checkpoint using existing technologies is to install more machines and more people to man them. However, this clearly has a cost implication, which makes it an impractical option for most airports. “Obviously, the less capacity you can push through a checkpoint, the more checkpoints you must have and the greater the costs,” says Burns. Given these issues, the hunt is on for new technologies that can screen passengers more quickly and cheaply, as well as being able to spot non-metallic threats, such as explosives and ceramics. The leading technology at the moment is explosive trace detection machines that can sniff out the residue of explosive materials on passengers or their bags. Most countries are heading towards screening all bags in this way, and trials are now being carried out in the US using this technology to screen passengers. However, these systems still have a number of shortcomings. For instance, while the false alarm rates are low, if there is an alarm, the presumption has to be that the passenger is carrying explosives, which has a clear impact on the operations of the airports. Also, these systems just detect explosives, which means that they must be used in tandem with a metal detector. “However, as soon as you do this you multiply the problems of throughput and of false alarms,” notes Burns. “Thus while trace seems to be one of the better ways of detecting explosives, operationally it is very difficult.”||**|||~||~||~|Another possible replacement for metal detectors are backscatter x-ray machines, which can crate a clear image of everything under the person’s clothes. X-ray and CAT scans are now widely used for baggage screening, but using this technology on people creates a host of difficulties. For instance, x-ray machines generate a clear and recognisable image of the person being photographed, which creates privacy issues. The technology is also slow to use, as multiple photographs need to be taken of the person, which translates into long queues at checkpoints. Furthermore, there are also health concerns over frequent exposure to x-rays. “Even at very low dosages there is an issue for how many times people will go through this,” comments Burns. “If you are a frequent traveller, you are going to go through these machines on a very regular basis.” Given these difficulties, QinetiQ and a number of other companies, including L-3 Communications, are investing in millimetre wave technology instead. Millimetre waves are essentially a frequency of light, which can penetrate any material. However, the waves are absorbed or reflected at different rates, and measuring these differences means that different materials can be seen. “Millimetre wave is the use of a thermal imaging technique that works by detecting the radiation naturally emitted from objects, not unlike conventional infra-red thermal imaging,” explains Brian Howe, vice president, EMEA, security & detection systems, L-3 Communications. “When deployed in an airport security system, millimetre wave is able to detect not just metal, but also… ceramic weapons, plastic explosives, drugs and other contraband,” he adds. The technology has been widely used in military applications, such as allowing helicopter pilots to see through smoke, for a number of years. This experience has proven the technology and also encouraged manufacturers to develop low powered systems that generate little radiation, which means that the systems pose no health risk when used on people. “The total energy output is a millionth of what you get from even a mobile phone,” says Burns. The systems, which are scheduled to be trialled within the next 12 months, also promise to be quicker to use than traditional technologies, as they capture realtime video images. As such, people just need to walk through the portal and turn around and everything on their body will be clearly seen by the machine. This quicker speed of operation, and lower false alarm rate, means that there will be greater throughput and, hence fewer machines will be required. Therefore, even though the units will probably cost around $250,000 each when they come onto the market, they will be more cost effective than magnometers. “You would increase the technology spend, but massively reduce the manpower spend,” says Burns. “For a lot airports you would need half the number of checkpoints that you have at the moment… and you are gaining that with much better detection, as you are seeing things you cannot detect at present.” The technology has raised privacy issues, as it can essentially see through people’s clothing. However, there are ways of overcoming this issue. For instance, because the reflective properties of the human body are known, these waves can be blocked out on screen by the software, so that security guards cannot see it. Alternatively, the queues could be divided between male and female, or the screening even be done automatically without any human interaction. Instead, the computer would raise an alarm if something metallic or explosives, for instance, were detected. Which method a country adopts will largely depend on their own internal priorities. “The Americans are very interested in automatic detection as they are interested in high throughput,” notes Burns “The EU, however, is much more interested in having people look it, as they do not want to rely on a just machine.” Furthermore, passengers’ privacy concerns are usually countered by their desire to get through the airport as quickly as possible. This explains why biometric systems for frequent travellers have proven so popular. QinetiQ found similar results when it trialled a millimetre wave portal in London Gatwick, with people preferring to be screened than having to queue up and be checked by hand. “People found the privacy issues of being physically searched far greater than the privacy issues of being screened,” comments Burns.||**||

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