F


or many years now, the aviation industry has had to respond to and attempt to


counter the threat of terrorism and other criminal acts. Civil aviation and airports continue to be attractive, high profile, targets and the industry is, and has to remain, open to new and evolving technology that may speed up and simplify the task of screening passengers both rapidly and accurately. It is undoubtedly the case that the most effective method of detecting prohibited articles secreted on the person is the hand search. When well- performed, this allows for the discovery of both metallic and non-metallic items, an important consideration as the technology employed by terrorists becomes ever more sophisticated.


Nevertheless, it is an unfortunate truism that, in today’s busy airports,


seeking to carry out a full body


search of all passengers would prove too time- consuming. Accepting that reality, the widespread deployment of metal detectors has proved to be an answer to the need both for speed in the screening of passengers and for a reliable aid in focusing the need for individual searches.


That said,


their limitations must never be overlooked in the overall task of providing a safe environment for the travelling public.


As one of the many who June 2010 Aviationsecurityinternational


has passed through numerous walk through metal detectors en-route to holidays or business trips, I have previously given little thought to their history and the technology behind them bar a basic understanding of their purpose and the simplified explanation of their capabilities, needed to coach aviation security officers through their training.


So now for the science... The simplest form of metal detector contains a coil producing an alternating current which, in turn, produces an alternating magnetic field. If a piece of metal is close to that coil, eddy currents will be created, which produce an alternating magnetic field. Put more simply, the magnetic field coming from the detector causes another magnetic field to appear in the metal object itself. That produces a change in the detector’s magnetic field due to the presence of another, opposite, field whereby the object that produces that change can be detected. The disruption in the detector’s field can be harnessed to something which will receive and interpret the information and relay it by causing, for example, the making of a sound, the switching on of a light or both, thereby alerting security officers to the need to conduct further screening.


But it wasn’t always so... Metal ‘detection’ began to be explored over a hundred years ago and was developed in earnest during the Second World War for mine detection – by a Polish signals officer, Lt Józef Stanisław Kosacki, serving with the 1st Polish Army Corps which was stationed in Scotland following the German defeat of Poland in 1939. The first industrial metal detectors were developed in the 1960s and were used in fields such as mining and the construction industry.


It


was a Finnish company that first developed metal detectors for use in aviation security in response to a series of aircraft hijackings, but these did not resemble what we might today recognise as the ‘traditional’ archway metal detectors used in airports.


In the airport


All travellers will readily recognise the ‘traditional’ walk through archways deployed in airports throughout the world. A convenient screening device, the Walk Through Metal Detector (WTMD) allows the operator to watch each person pass through. If the system detects metal it will sound an audible alarm, ensuring that the individual is selected for further screening.


Modern WTMDs


break their detection capability into zones, allowing security officers to note in which area of the body the metallic object has produced the change in the detector’s magnetic field by way of lighting up in the relevant ‘zone’.


for a more focused search and cuts down on overall screening times – not only good for airports with their need to rapidly process large numbers, but also for passengers keen to cut down on their time spent in the security screening area. In these days of quotas for random searches, the WTMDs can also be programmed to alarm ‘randomly’ at appropriate intervals to ensure that ratios are met and kept to.


The next layer of metal detection screening involves the use of the smaller handheld metal detectors (HHMDs) which are used to locate a metal object on a person more precisely.


These ‘wands’


are battery-operated and, depending on the model, can alert with a light, audible alarm or vibration. They are also used in smaller airports where the cost of WTMDs is prohibitive.


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This allows


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