MC Explains | How do full-body scanners at Delhi and Mumbai airport work?

Delhi’s Indira Gandhi International Airport and Mumbai’s Chhatrapati Shivaji Maharaj International Airport have once again started trials for full-body scanners.

The development followed a directive issued by the Bureau of Civil Aviation Security way back in 2019. The adoption of the new technology was delayed because of the Covid-19 pandemic.

The Airports Authority of India had in 2020 issued a tender to procure 198 body scanners for 63 airports after the circular, but the civil aviation ministry approved the purchase of only 98.

A full-body scanner is used to detect objects without physical contact with or breaching the privacy of passengers.

“Walk-through metal detectors and hand-held metal detectors cannot detect non-metallic weapons and explosives. But the new full-body scanners detect both metallic and non-metallic items concealed in the body,” an official of the BCAS said.

The full body scanners, made by US-based Leidos Aviation, are expected to cost around Rs 4 crore, including annual maintenance. Trials will be carried out for 45 to 60 days at the two airports.

How the scanners work

According to officials from Delhi International Airport, the full-body scanners have a complete glass frame with two antennae that transmit waves simultaneously as the frame of the machine rotates around the passenger.

"Passengers enter the glass frame and raise their arms and the scanners detect any object and display it on a screen," DIAL officials said.

According to DIAL, the scanners will be able to detect non-metallic objects such as narcotics, plastic explosives, and prohibited or illegal objects made of substances such as rubber that cannot be detected by metal detectors.

“At present, passengers have to remove their jewellery, shoes, belt, phones, devices, and any other objects that can trigger the metal detector. In the case of the new millimetre wave scanners, they can walk into the machine without having to remove anything. Once the machines are in place, there will be no need for physical frisking or passengers having to take off items of clothing. The scanners will speed up security checks,” a DIAL official said.

The machines scan around 200-300 people every hour and detect the size, shape, and location of objects concealed in body cavities or organs as well.

The scanners do not use X-rays. They use harmless radio waves or millimetre waves, which travel through most clothing and bounce off the outermost layer of the skin, the epidermis.

Those radio waves are then reflected back and analysed by software specially designed to detect potential threats.

Millimetre waves are electromagnetic waves at the higher end of the microwave band, lying in the extremely high frequency (EHF) range of 30-300 GHz.

Millimetre waves easily pass through common clothing materials and reflect off any concealed objects. An imaging system uses the reflected wave fronts to construct a three-dimensional image on a monitor, revealing the size, shape, and orientation of the concealed object.

As per Leidos, signals from the machine are 1,000 times less powerful than those from cell phones and other wireless handsets. It has been approved by the Transport Security Administration (TSA), and is deployed at airports across the US.

The new body scanner will be a safer alternative for passengers as it doesn’t use X-rays or ionising radiation, officials said. BCAS has noted that millimetre-wave technology should be used in order to avoid harmful X-ray radiation.

“There are no known safety worries if you have implanted medical devices like pacemakers or defibrillators. That’s because the power levels and peak electrical field levels used in the scanner are significantly lower than what you might experience from a mobile phone. Also, pacemakers and defibrillators are under the skin and the radio waves used by the scanners don’t get that far,” Leidos said in a statement.