Hand held metal detectors

Like it or not, airport-security is only going to become more strict. Ever since the terrorist attacks of 9/11 exposed the weakness in our country’s airport-security, we’ve had to endure many increased-security measures–from more “random” searches to restricting any liquids brought through security. Many people consider these measures inconvenient, but agree that it’s better to be safe than sorry.

One procedure that has remained fairly unchanged, however, is detecting metal on passengers before boarding a plane–and almost everyone has had an awkward experience of being frisked by one of the hand held metal detectors.

These metal detectors, also known as security wands, allow fast and portable metal detection, as well as concentrated focus on specific regions. Wands are able to pinpoint exactly where a perpetrator would be hiding a dangerous weapon, whereas a walk-through metal detector can only determine the presence of such a weapon

There are many types of metal detection, but they all share various similarities. Hand held metal detectors (as well as all metal detectors) rely on a basic system called beat frequency oscillation (BFO). This system involves two coils of wire, which are connected to an oscillator that produces thousands of pulses per second. When the pulses travel the length of the wire, they create radio waves.

A tiny receiver located on the metal detector will pick up these radio waves and transmit them into an audible series of beeps–usually based on the difference between the frequencies. When the coils pass over a metal object, the current passing through the coils creates a magnetic field around the object. This newly-created field interferes with the frequency from the initial coils, thereby changing the frequency of oscillation in the metal detector. The resulting radio waves change the duration and tone of the beeps, and that’s why hand held metal detectors will beep more rapidly when passed over metal objects.

Although most metal detection is based off BFO, it’s very basic in the long run. Manufacturers of hand held metal detectors have been able to tweak the process to be more discriminatory in the materials they can detect. For example, White, one of the most prominent detector-manufacturing companies, boasts that its Matrix 100 model can detect an object as small as a hypodermic needle from 2 cm away. The sensitivity can also be reduced, so extraneous material in the perpetrator’s surroundings doesn’t set it off (for example, the metal floors shouldn’t set a detector off when scanning footwear).

Hand held metal detectors aren’t just for airport security, but wherever crowd protection is a priority: major sporting events, political rallies, and even (sadly) some schools require security wands on-hand.

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