Metal Detector 101: Please empty your pockets

By Dinesh Kandanchatha.

The instruction to “empty your pockets” is sadly something anyone who has boarded a plane, has heard. The reality is that metal detectors and the intrusion they bring to our every day lives has become accepted. We simply have no choice but to comply when we board a plane or go to that sporting event. Given the ubiquity of these devices I thought it might make sense to explain how these devices and their sister devices the millimeter wave scanner work.

So how do these devices work? Metal detectors operate on a principle that current when passed through a coil will generate a magnetic field. Most simple metal detectors are created by using two pieces of coiled wire (one called a transmitter coil, through which the electricity that powers the machine flows, and the other called a receiver coil, which is attached to a sound system) to create a magnetic field. When a piece of metal enters through the magnetic field, the electricity powering the magnetic field runs through the metal object, creating a second magnetic field around the object. This metal field then reacts with the receiver coil, which, in turn, then triggers the sound system. Basically the presence of a metallic item disrupts the field and triggers the alarm.  It is important to note that any metallic item would create this second field.

One of the big challenges in weapons detection is that you have to do so safely- ie. Without “cooking” the general public. So given that metal detectors detect metal with nonionizing energy that is safe for humans even with repeated exposure this was a good solution..in 1931 when the first patents were issued.

What about millimeter wave technologies? Millimeter wave technologies were invented in the 2000’s to try to deal with the drawbacks of metal detectors ie. The inability to detect non metal.

Millimeter wave sensors are passive and rely on detecting energy emitted by objects. The machines work by bouncing electromagnetic waves off a person’s skin to create an image of the person’s body and any objects on it, which can be detected because the energy the sensors look for emitted by all matter. Human bodies radiate the energy at a rate higher than metal, plastic or composite materials, so those objects can be spotted under clothing, in silhouette. The challenge with these devices is that similar to metal detectors they are unable to identify exactly what the item is only its location. This device also requires you to empty your pockets so as to not set up false positives. Also it generates an image of you, which is not acceptable to many members of the public.

What is next in metal and weapons detection? Well, the work we are doing at Patriot 1 is to create a smart detector that would be able to detect different types of items so you could go about your day without emptying your pockets at all. Our technology based on wide band radar is safe, and is able to differentiate between different types of objects based on their resonant signature. We are excited about the possibilities of this technology for all kinds of item detection from weapons, to laptops and usb sticks.

While we go through our research though we will all have to get used to keeping our pockets clean, and empty.

References:

https://creativitytoday.wordpress.com/2013/06/03/the-physics-of-airport-metal-detectors/

Author: Dinesh Kandanchatha, Regular Contributor and CTO, Patriot One Technologies

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