How Things Work

Walking through an airport metal detector 10 years from now will be a different experience than it is today.

Most walk-through metal detectors today use pulse induction to pick up on metal objects located on or hidden underneath clothing.

Pulse induction is the process of sending out an electrical impulse in a wire coil. This electrical impulse creates a magnetic field, which disappears once the pulse ends. Another electric pulse (called the reflected pulse) is then sent through the wire.

This process is repeated hundreds of times per second.

In the presence of metal objects, the first electrical impulse creates a magnetic field around the object. Once the initial impulse disappears, however, the object’s magnetic field causes the reflected impulse to last longer than normal.

Measurements of the reflected signal are sent to an integrator, which is a mechanism that transforms signals into direct current. Direct current joins an audio circuit, and an alarm sounds if metal is present.

Though current airport metal detectors are an accurate way to determine the presence of metallic objects, they do not provide details for airport security guards to know what type of metallic object a person has with him or her. Aviation security companies are trying to address this problem.

Researchers for security device manufacturers are creating metal detectors that can separate the body into separate “zones” and see through clothing.

Unlike many older scanners, the most recently produced scanners can focus on each individual zone and detect the presence of metal.

One such detector is the Intelliscan, manufactured by OkRanger. This detector scans a person’s body in 18 zones. Six horizontal divisions cover a person’s head, shoulders, chest, waist, knees, and feet, and three vertical divisions cover the left, center, and right portions of the body.

Intelliscan detects the presence of multiple weapons and locates them in one of the 18 zones.
Multi-zone detectors may cut back on the number of false alarms caused by coins and belt buckles. A multiple-zone detector has a threshold for each zone, and these thresholds can be set so that the alarm is less likely to sound because of harmless metal objects.

In addition to detecting the location of weapons, the next step in security scanner technology involves the ability to detect plastics, drugs, and explosives.

X-ray technology, for instance, allows baggage screeners to “see” into luggage, detecting everything from handheld weapons to plastic toys. Researchers would similarly like to “see” into human clothes.
But there’s one problem: Radiation of this kind can harm people’s skin. But researchers are proposing a possible solution to the radiation problem: millimeter-wave technology.

Millimeter waves are a form of radiation with a frequency ranging from 20 to 100 gigahertz. Such radiation poses no health risk to humans, and it can detect all objects — drugs, explosives, and metals — hidden underneath clothing.

Millimeter-wave technology produces images based on differing levels of radiation given off by objects.
European research establishment Farran Technology is working on the Tadar Millimeter-Wave People Screening Camera.

This camera detects objects using millimeter-wave technology, making clothes transparent but other objects visible. The radiation emitted from guns and explosives, for instance, contrasts with the radiation emitted from one’s skin, leading to clear pictures of hidden objects.

If millimeter-wave scanners become present in airports all across the globe, passengers would no longer be asked to walk (and re-walk) through archway metal detectors.

Instead, they would stand in a temperature-controlled environment and receive whole-body scans before boarding their planes.

Presumably, such a procedure would eliminate the need for body searches. It could also make security lines shorter.

With fewer false alarms and more complete pictures of concealed objects, airport security is becoming not only safer but easier as well.