Roberta Aguirre
Metal detectors and body scanners are a common feature of airport security. They are used to keep people safe while travelling, by identifying metal objects on passengers and in their luggage. Most metal detectors use pulse induction (PI) technology, which sends short bursts of current through a coil of wire, creating a magnetic field. If a metal object is detected, the pulse creates an opposite magnetic field, and the reflected pulse takes longer to disappear. This triggers an audio alert, and the passenger may be asked to remove metal objects or undergo a pat-down. While some small metal items, like buttons or earrings, may be ignored, larger metal objects like belt buckles or jewellery can trigger the alarm. It is important to note that the final decision on whether an item is allowed through security rests with the TSA officer.
| Characteristics | Values |
|---|---|
| Metal detectors at airport security | Use pulse induction (PI) technology |
| Use magnetic fields to identify metal objects | |
| Ignore very small amounts of metal | |
| Items that may trigger metal detectors | Metal studs or rivets on clothing |
| Metal buckles | |
| Watches made from cheap metals or large and chunky watches | |
| Items that typically do not trigger metal detectors | Underwire bras |
| Smartwatches | |
| Wigs | |
| Regular glasses | |
| Jeans |
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What You'll Learn
- Metal detectors at airport security use pulse induction technology
- Metal objects create an opposite magnetic field when passing through
- Metal detectors use non-ionizing radiation to scan for hidden items
- Metal detectors ignore small amounts of metal, like jean buttons or earrings
- Other screening equipment includes X-ray machines and millimeter wave scanners
Metal detectors at airport security use pulse induction technology
Metal detectors are a common feature of airport security. They are used to channel all public access to an airport through the terminal, ensuring that every person and item is scanned for security. While some items of clothing, such as jeans, jackets, and underwire bras, may be worn through metal detectors, other items, such as belts, hats, and heavily embellished clothing, will need to be removed.
Metal detectors at airport security use pulse induction (PI) technology. PI systems use a coil of wire on one side of the arch as both the transmitter and receiver. This coil emits powerful, short bursts (pulses) of electric current, which generate a brief magnetic field. When the pulse ends, the magnetic field collapses and reverses polarity, resulting in a sharp electrical spike. This spike causes another current, known as the reflected pulse, to run through the coil.
If a metal object passes through the metal detector, the pulse creates an opposite magnetic field in the object. This magnetic field makes the reflected pulse take longer to disappear. The sampling circuit in the metal detector monitors the length of the reflected pulse and compares it to the expected length. If the decay of the reflected pulse takes longer than normal, there is likely a metal object interfering with it.
The sampling circuit then sends weak signals to a device called an integrator, which amplifies and converts these signals to direct current (DC). The DC voltage is connected to an audio circuit, which changes the signals into a tone that the metal detector uses to indicate that a metal object has been found. Handheld metal detectors used by security attendants are also based on PI technology.
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Metal objects create an opposite magnetic field when passing through
Metal detectors at airports rely on pulse induction. When a person or item passes through the metal detector, a pulse is sent through a coil of wire, generating a magnetic field. When the pulse ends, the magnetic field reverses polarity and collapses. If a metal object is passing through the metal detector, the pulse creates an opposite magnetic field in the object. This causes the reflected pulse to take longer to disappear. This phenomenon is similar to echoes. The sampling circuit in the metal detector can determine if another magnetic field has caused the delay by comparing the length of the reflected pulse to the expected length.
If the decay of the reflected pulse takes longer than usual, it indicates the presence of a metal object. The sampling circuit then sends weak signals to a device called an integrator, which amplifies and converts these signals to direct current (DC). The DC voltage is connected to an audio circuit, which changes the signals into a tone that the metal detector uses to indicate that a target object has been found.
Many newer metal detectors are multi-zone, meaning they have multiple transmit and receive coils at different heights, allowing for more accurate detection. This technology is based on the fundamental properties of magnets and magnetic fields. Metals such as iron, nickel, and cobalt are attracted to magnets due to their magnetic properties. When a magnet is suspended freely, one pole always turns toward the north, with the opposite pole facing south. This is the basis for the creation of a compass.
At airport security, individuals are required to pass through metal detectors, and all items must go through an X-ray machine. While some metal objects, such as underwire bras, small metal buttons, and zips on jeans, may not trigger the metal detectors, other items like metal buckles and large, chunky jewellery are more likely to set off the alarms. It is always advisable to check with the airline and airport authorities for specific guidelines and restrictions regarding metal detectors and prohibited items.
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Metal detectors use non-ionizing radiation to scan for hidden items
When passing through airport security, you will be required to walk through a metal detector and place your items through an X-ray machine. While metal detectors were once the main security devices used at airports, new technologies such as backscatter and millimetre wave scanners have been introduced to detect hidden items and determine if passengers are carrying weapons or explosives.
In addition to metal detectors, millimetre wave machines are commonly used at airport security to detect hidden items. These machines use non-ionizing radiofrequency waves, which are reflected off the body and back to the machine. The waves can pass through clothing and bounce off the skin and any hidden objects, creating a 3D image that can be analysed for concealed items. Unlike X-ray machines, millimetre wave scanners emit very low levels of radiation, even less than a cell phone, and are considered safe.
It is important to note that some screening equipment, such as backscatter scanners, use ionizing radiation, which has higher energy levels and can knock electrons out of atoms. While the amount of radiation from backscatter machines is generally considered low, there are concerns about potential health risks, particularly the possibility of increasing the risk of cancer. However, opinions vary among scientists, and the TSA states that estimating the potential effects of backscatter scans is challenging due to the low doses of radiation involved.
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Metal detectors ignore small amounts of metal, like jean buttons or earrings
Metal detectors at airports rely on pulse induction (PI) technology. PI systems use a coil of wire on one side of the arch as the transmitter and receiver. This technology sends powerful, short bursts (pulses) of current through the coil of wire. When the pulse ends, the magnetic field reverses polarity and collapses very suddenly, resulting in a sharp electrical spike. This spike lasts a few microseconds and causes another current, called the reflected pulse, to run through the coil.
If a metal object passes through the metal detector, the pulse creates an opposite magnetic field in the object. When the pulse's magnetic field collapses, the magnetic field of the object makes it take longer for the reflected pulse to completely disappear. This process works like echoes. The sampling circuit in the metal detector is set to monitor the length of the reflected pulse. By comparing it to the expected length, the circuit can determine if another magnetic field has caused the delay.
If the decay of the reflected pulse takes more than a few microseconds longer than normal, there is probably a metal object interfering with it. 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, where it is changed into a tone that the metal detector uses to indicate that a target object has been found.
Despite the common belief that metal detectors can detect all metals, some metals are challenging or nearly impossible for standard metal detectors to recognize. Metal detectors struggle with stainless steel, especially when it is smaller in size, due to its low magnetic permeability. Non-ferrous metals like gold, copper, and aluminum can be detected but are not as easily discernible as ferrous metals, which contain iron. The detection capability depends on the metal detector's frequency, calibration, and the metal's size and shape.
Metal detectors are also designed to ignore small amounts of metal. For example, underwire bras rarely cause issues at airport security. Similarly, smartwatches like Apple Watches or FitBits usually don't set off alarms. Metal buttons and zips on jeans are so small that they are unlikely to be picked up by metal detectors. However, styles with metal studs or rivets may sometimes set off scanners, so you may be asked to undergo a pat-down.
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Other screening equipment includes X-ray machines and millimeter wave scanners
Metal detectors, X-ray machines, and millimeter wave scanners are all used to screen passengers and their belongings at airports. While metal detectors can only detect metal objects, full-body scanners can detect both metal and non-metal objects, including those hidden in body cavities.
X-ray machines are used to screen carry-on items and checked luggage for items that are not approved for air travel. They emit ionizing radiation, which has enough energy to knock electrons out of atoms. Backscatter X-ray machines, previously used by the Transportation Security Administration (TSA), used very low-energy X-rays that were reflected back to the machine itself. However, due to concerns about radiation exposure, these machines were replaced with millimeter-wave scanners by May 2013.
Millimeter-wave scanners use non-ionizing radiation in the form of low-level radio waves to scan a person's body. They operate in the millimeter or sub-terahertz band, using electromagnetic radiation similar to that used by wireless data transmitters. The scanner constructs a 3D image that is sent to a remote monitor. The United States Food and Drug Administration (FDA) has the authority to set standards for machines that produce radiation, including millimeter-wave security screening systems. While the health risks of millimeter wave scanners are still being studied, they do not generate ionizing radiation, and the amount of radiation exposure is comparable to the cosmic radiation received during two minutes of flight.
Passengers who are concerned about radiation exposure from X-ray or millimeter wave scanners can opt for a pat-down search instead. Additionally, certain populations, such as pregnant women, babies, children, and people with disabilities, may be subjected to alternate screening methods as recommended by radiation authorities.
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Frequently asked questions
Yes, you can take your metal detector through airport security. However, it will need to be screened separately, just like any other electronic device. Make sure to inform yourself about the specific policies of the airport and the airline you are flying with.
Metal detectors at airports are generally sensitive enough to detect even the smallest amounts of metal. However, the metal in your detector is unlikely to set off the alarm, as the machines are designed to ignore very small amounts of metal, such as the buttons on your jeans or small earrings.
If your metal detector sets off the alarm, you will be asked to step back and go through the metal detector again. If the alarm persists, a security officer will use a handheld detector to identify the cause of the issue.
