Metal Detectors At Airports: Security Or Privacy Invasion?

Metal detectors are a common feature of airport security, used to screen individuals and prevent prohibited items from compromising safety. Almost all airport metal detectors use pulse induction, which sends out short bursts of current to generate a magnetic field. When a metal object enters the field, it disrupts the magnetic field and triggers an alarm. This technology can differentiate between harmless items like phones and potential threats like firearms. Metal detectors are an important part of a multi-layered security approach, which also includes X-ray machines, surveillance cameras, and full-body scanners. These security measures are designed to protect travellers and staff from external threats while minimising disruptions and maintaining a smooth flow of passengers.

Walk-through metal detectors

If a person walks through the metal detector carrying a metal object, the pulse creates an opposite magnetic field in the object. When the pulse's magnetic field collapses, the magnetic field of the object makes the reflected pulse take longer to disappear. This is detected by a sampling circuit in the metal detector, which compares the length of the reflected pulse to the expected length. If the decay of the reflected pulse takes longer than normal, the circuit determines that there is a metal object present.

The sampling circuit then sends the signals to an integrator, which amplifies and converts them to direct current (DC). The DC's voltage is connected to an audio circuit, which changes it into a tone that the metal detector uses to indicate that a target object has been found. If a metal object is detected, the person is asked to remove any metal objects and walk through the detector again. If the metal detector continues to indicate the presence of metal, an attendant will use a handheld detector to investigate further.

The latest walk-through metal detectors have multiple zones, with multiple transmit and receive coils at different heights. This allows them to detect multiple objects and pinpoint their location.

Hand-held metal detectors

The technology used in hand-held metal detectors is based on pulse induction (PI). They generate a magnetic field that can identify metal objects. When a metal object enters the detector's field, it disrupts the magnetic field and triggers an alarm or warning noise. This technology can differentiate between harmless items, such as cell phones or belt buckles, and potential threats like firearms or knives.

The SuperWand, for example, is a widely used hand-held metal detector in airports. It offers 360-degree detection power, ensuring thorough scanning and precise pinpointing of metal targets. This device seamlessly integrates with walk-through metal detectors, providing comprehensive security screening.

In conclusion, hand-held metal detectors play a crucial role in maintaining airport security by providing a secondary layer of protection. Their precision, portability, and versatility make them a valuable tool for security personnel to identify and address potential security risks effectively.

How metal detectors work

Metal detectors are used in airport security to ensure that no one is bringing a weapon onto a plane. They are also used to detect foreign bodies in food and in the construction industry to detect pipes and wires buried in walls and floors.

Metal detectors work by using magnetic fields to identify metal objects. They create a magnetic field by using a brief pulse of electrical current. If there is a metal object present, the magnetic field will be reflected back to the machine, and the machine will make a beeping noise to alert the security agent. The magnetic field is created by the flow of current through wires or electrical devices.

Most metal detectors consist of a control box, an adjustable shaft, and a variable-shaped pickup coil. When the coil nears metal, the control box signals its presence with a tone, light, or needle movement. Signal intensity typically increases with proximity to the metal object.

Metal detectors use one of three technologies: very low frequency (VLF), pulse induction (PI), or beat-frequency oscillation (BFO). VLF technology uses two coils to make an electromagnetic field. When the field finds an object that conducts electricity, the object's own magnetic field is detected, and the detector alerts that it has found metal.

PI technology sends powerful, short bursts of current through a coil of wire. Each pulse generates a brief magnetic field. When the pulse ends, the magnetic field reverses polarity and collapses, resulting in a sharp electrical spike. This spike lasts a few microseconds and causes another current to run through the coil. This current is called the reflected pulse and lasts about 30 microseconds. Another pulse is then sent, and the process repeats. If there is a metal object present, it creates an opposite magnetic field, which makes it take longer for the reflected pulse to disappear.

BFO technology uses two coils of wire, one in the search head and a smaller one in the control box. Each coil is connected to an oscillator that generates thousands of pulses of current per second. The frequency of these pulses is slightly offset between the two coils. As the pulses travel through each coil, they generate radio waves. When the coil in the search head passes over a metal object, the magnetic field created causes the frequency of the radio waves to deviate from the frequency of the coil in the control box, and the audible beats change in duration and tone.

Other security measures

In addition to metal detectors, airports employ a variety of security measures to ensure the safety of travellers. Here are some of the key components of airport security, aside from metal detectors:

X-ray Machines:

Airport security uses X-ray machines to screen carry-on items and checked luggage. These machines help identify potential threats, such as weapons, explosives, and other prohibited items. X-ray technology plays a crucial role in ensuring that no unauthorised items are brought on board an aircraft.

Surveillance Cameras:

Surveillance cameras are installed throughout airports to monitor passengers and detect suspicious activities. They help security personnel keep a close eye on the premises, allowing them to identify and respond to potential security risks promptly.

Millimetre Wave Scanners:

Millimetre wave scanners are another essential tool in airport security. These machines use non-ionizing radiofrequency waves to detect hidden threats, such as guns and knives, on a person's body. They emit very low levels of radiation, even less than a cell phone, and are considered safe for travellers.

Backscatter X-ray Machines:

Backscatter X-ray machines are used to detect threats such as weapons or explosives that may be concealed under clothing. These machines use very low-energy X-rays that are reflected back to the machine itself. The amount of radiation exposure from these scanners is equivalent to the cosmic radiation received during two minutes of flight, posing a very low risk to individuals.

Hand-held Metal Detectors:

In addition to walk-through metal detectors, security personnel also use hand-held metal detectors for more targeted examinations. These devices are employed for secondary searches when a more detailed inspection is required after an initial alert from a walk-through detector.

Trained Security Personnel:

Technology alone cannot ensure airport security. Trained security professionals, such as Transportation Security Administration (TSA) officers, play a crucial role in interpreting signals from metal detectors and other equipment, making quick decisions, and ensuring efficient handling of security threats. Their expertise helps maintain a balance between thorough searching and a smooth flow of passengers.

Items that set off metal detectors

Metal detectors are a common feature of airport security, with all passengers required to walk through one before boarding their flight. These metal detectors rely on pulse induction (PI) technology to identify metal objects on a person's body. While some items are obvious security threats, such as guns, knives, and other weapons, there are other everyday items that can also set off a metal detector.

One of the most common items that can cause an issue is coins. It is easy to forget that you have loose change in your pocket, and coins are often made of metals that are easily detected. Similarly, other small metal items like hair accessories, belt buckles, and watches can also set off the alarm. Even a simple piece of gum packaging can be a problem, as many wrappers are made of aluminum foil, which is a non-ferrous metal that can be detected by some machines.

In addition, certain items of clothing can contain enough metal to trigger the alarm. For example, women's bras with underwire have been known to set off metal detectors, although newer technology has made this less likely. It is also worth noting that some metals are harder to detect than others. Stainless steel, for instance, has low magnetic permeability, making it more difficult for metal detectors to pick up.

To avoid any delays or complications, it is advisable to remove all metal items before passing through a metal detector. This includes emptying your pockets of any small items like coins, gum wrappers, or keys, and removing any unnecessary jewelry or metal accessories.

Frequently asked questions