Security screening is likely to be a very large market for millimetre wave technology. This is because over the last few decades the demand for individuals to be screened for concealed illegal or forbidden items has risen dramatically, with little sign of the demand abating.
The capability for screening individuals for items concealed under clothing is enabled by the almost complete transparency of clothing to millimetre waves. Millimetric sensors are capable of detecting both metal and non-metallic objects. Deployment scenarios for these systems fall naturally into two categories, full-body and stand-off:
1) Full-body (surround imaging) scanners closely scrutinise all surfaces of the human bodywith millimetre scale resolution. At airport departure lounge entrances, the market requirement is to do this within about one second in a walk-through system, with a high probability of detection and low false alarm rate. At entrances to other areas (public transport networks, arenas and buildings) the requirements have slightly lower specifications.
2) Stand-off screening systems provide an initial first layer of screening of individuals for larger threats, at ranges out to tens of metres. Typical scenarios here are the approach to checkpoints and in public places where numbers of people congregate.
Clothing penetration of millimetre waves varies considerably over the band and this dictates the screening capabilities. Greater penetration at lower frequencies enables screening through thicker clothing and greater numbers of layers, whilst at the high frequencies screening is guaranteed only through thinner clothing.
Penetration of millimetre waves into the human body is only a fraction of a millimetre into the skin, with 10% to 40% of this radiation being reflected from the body.
Security screening of fibre glass and soft canvas sided vehicles for stowaways is an application where millimetre wave sensors are used to combat human trafficking.