announcement

Share facts or photos of intriguing scientific phenomena.

Walk-through Metal Detectors

Walk-through Metal Detectors

Understand the purpose and functioning of walk-through metal detectors, by means of the information presented in this article.
Puja Lalwani
Walk through Metal Detectors
With increasing instances of terror and violence, security measures have been beefed up at all public places. It is common for those with intentions of spreading terror, to attack extremely crowded places, which is why the security level at all such places, like airports, malls, movie theaters, and events such as exhibitions, is extremely high. One of the ways in which tight security is maintained at such spots, is with the use of walk-through metal detectors. When monitored by effective security persons, their function has proven useful in detecting the presence of any dangerous metallic objects such as guns, knives, etc. Along with these, hand-held detectors are also used, to enhance the effectiveness of the security measures used. Now, even small business and store owners are aiming to use these security devices, just for the purpose of basic safety.

How do they Work?

As compact as the machine itself is, a lot goes into the history of metal detectors and their functioning. Walk-through metal detectors are based on a system known as Pulse Induction or PI. Based on this system, a coil of wire is placed on any one side, at the top of the device. This coil of wire is considered as the transmitter and receiver of magnetic fields. From this wire, short pulses of electricity are generated. The magnetic field reverses the polarity, when these bursts of pulses end, and there is a sharp boost of electricity, which lasts for a couple of microseconds. Due to this boost, another current, or the reflected pulse, runs through the coil for about 30 microseconds. Every second, almost a hundred such pulses are sent. However, the effectiveness of these pulses and the numbers that are sent, differ on the basis of the model that you are using. The minimum number of pulses ranges from about 25 per second, to over a thousand pulses per second.

The electromagnetic field that is generated due to the passing of a metal object through the detector, causes a reflected pulse, which takes longer than usual to vanish. As mentioned earlier, while a reflected pulse generally lasts only for about 30 microseconds, when a metal object disturbs the flow of the pulse, the pulse will linger for a longer time period, say a fraction longer. The length of the pulse that has been obstructed, is measured by a sampling circuit. The extended length is then compared to the length that the pulse is expected to last for, to check for the presence of a metallic object. If such a presence is detected, the sampling circuit sends signals to the integrator, that converts these signals to direct current (DC), which in turn is connected to an audio device, that beeps when such a signal is sent to it. This is the beep that you would commonly hear when passing through detectors, indicating the presence of metallic objects with, on, or around you.

To eliminate the possibility of a beep due to loose change, keys, cell phones, etc., you are usually asked to keep these items aside and go through a metal detector, especially when it comes to airport security. In spite of doing so, if the machine continues to beep, you are asked to step aside where you are checked with a hand held device to detect the cause of the continuous beeping.

Thus, keeping a hand-held metal detector, in spite of the presence of walk-through one, will help enhance the security cover. The varieties that are available in the market have a system where the sensitivity of detection can vary. However, when it is set to a high sensitivity, it is going to start beeping even in the presence of loose change in your pocket, or the piercings on your body. While in high security zones this is essential, in public places such as a mall or a movie theater, having the machine go off constantly may cause a nuisance, making the task of identifying the presence of dangerous objects further challenging. In any case, whatever the sensitivity level, a walk-through detector is designed to detect the presence of dangerous objects.

Usually, portable walk-through metal detectors are used in public settings, for events that are temporary, such as exhibitions. However, we have seen these even in hotels and malls. If you are a store owner, or are organizing an event that has the need to keep such a security device at hand, you may avail of used varieties (in good condition), that you can find for sale over the Internet. Such machines are also available on rental, for temporary functions and events. Ensure you have someone to man the devices, and identify any suspicious persons or objects. Depending on your requirements, you can opt for either, and have a grand, enjoyable, and safe event, or simply maintain the security of your premises.