X-Ray Scanners: Magnet-Free Airport Security

Airport security systems use a variety of technologies to ensure the safety of passengers, including metal detectors, backscatter X-ray machines, millimeter wave scanners, and cabinet X-ray machines. While metal detectors rely on magnetic fields to detect metal objects, X-ray machines use electromagnetic waves to penetrate and examine the contents of luggage and carry-on items. These X-ray machines are designed to identify suspicious items, such as weapons, explosives, or components that could be used in an improvised explosive device (IED). Therefore, the primary function of airport X-ray machines is to utilize electromagnetic waves, rather than magnets, to detect prohibited items and ensure the security of passengers and staff.

X-ray machines are used to scan carry-on items and checked luggage

The X-ray system uses a conveyor belt to carry each item past the X-ray machine. These X-rays are more energetic than light, allowing them to penetrate many materials. The dual-energy X-ray system has a single X-ray source, sending out X-rays in the range of 140 to 160 kilovolt peak (KVP). The higher the KVP, the further the X-ray penetrates. After passing through the item, the X-rays are picked up by a detector, which passes them through a filter to block out lower-energy X-rays. The remaining high-energy X-rays hit a second detector. This process allows the machine to better represent low-energy objects, such as organic materials, which are typically coloured orange on the display monitor.

The Transportation Security Administration (TSA) in the United States ensures that X-ray equipment meets the Food and Drug Administration (FDA) requirements to limit radiation exposure for passengers and workers. The FDA's Center for Devices and Radiological Health (CDRH) mandates that all X-ray systems are built to use radiation safely and are correctly calibrated and maintained.

It is important to note that X-ray machines used in airports do not use magnets. Metal detectors, on the other hand, do use magnetic fields to identify metal objects.

Metal detectors use magnetic fields to detect metal objects

Metal detectors are an essential part of airport security, helping to keep people safe while travelling. They are used to detect metal objects, such as handguns, knives, and explosives, that are prohibited on flights. Metal detectors use magnetic fields to identify metal objects. This is achieved through the use of electromagnetic technology, which creates a magnetic field by passing an electric current through a coil of wire. When the detector is swept over a metal object, the magnetic field interacts with the atoms in the metal, inducing an electric current and creating another magnetic field around the object. This second magnetic field is then detected by the metal detector, which alerts the operator through a beeping noise or other signals.

Metal detectors come in various types, including walk-through detectors and handheld scanners. The simplest form of a metal detector consists of an oscillator that produces an alternating current, which passes through a coil and generates an alternating magnetic field. More advanced metal detectors may use multiple coils and different technologies, such as very low frequency (VLF), pulse induction (PI), or beat-frequency oscillation (BFO), to improve detection capabilities and discrimination between different types of metals.

While metal detectors are commonly used at airports, they also have a wide range of applications beyond security. They are used in building security, event security, archaeology, treasure hunting, and geological research, among other fields. Metal detectors have become an integral tool for ensuring safety, uncovering historical artefacts, and discovering valuable treasures.

Millimeter wave machines use non-ionizing radiofrequency waves to detect threats

Millimeter wave machines are considered non-invasive and emit far less energy than a cell phone. They are also incapable of causing cancers, as the radiation is non-ionizing and does not have enough energy to remove electrons from atoms.

The Transportation Security Administration (TSA) has introduced millimeter wave machines, along with other full-body scanners, at airports across the United States. These machines are used to detect hidden threats such as guns and knives, as well as other dangerous items that are not approved for air travel.

The use of millimeter wave machines in airport security has raised some concerns about privacy and health risks. To address privacy concerns, the TSA has implemented measures such as using automated target recognition software to create generic body outlines and ensuring that images are not stored.

Regarding health risks, several studies have determined that millimeter wave scanners pose little risk to passengers, pilots, or TSA agents. The waves produced by these scanners are much larger than X-rays and do not alter biological molecules. However, there have been questions about the efficacy of these scanners in detecting threatening objects, with some studies suggesting a high rate of false positives.

Backscatter machines use low-level X-rays to create a two-dimensional body image

Backscatter machines are one of the two types of whole-body imaging technologies used to perform full-body scans of airline passengers to detect hidden weapons, tools, liquids, narcotics, currency, and other contraband. They use low-energy X-rays to create a two-dimensional image of the body.

The X-rays penetrate clothing and about an inch into the body, where tissues scatter and ricochet the rays back toward the sensor, which records those scattered rays to create an image. The backscatter pattern depends on the material property and is good for imaging organic material.

Backscatter machines are more sophisticated than medical X-ray and dual-energy X-ray systems. The imaging sensor is placed on the same side of the body as the X-ray tube, as opposed to being on the other side as in traditional X-ray machines. The radiation dose is around 0.02 to 0.03 microsieverts, or about the same as one hour of exposure to natural environmental radiation.

The scanners use the energy signatures of ions and slower-moving photons created by the X-rays to produce images that identify organic material or non-organic objects. The differences are often easy to see, even to the untrained eye.

Backscatter machines are expensive, costing over $100,000 per unit, and have raised concerns about privacy and health risks. In the US, the TSA has installed about 500 backscatter scanners in close to 100 airports, and is planning to deploy at least 1,000 total scanners.

Puffer machines use air to dislodge trace amounts of explosives from passengers

Metal detectors are the most commonly used form of airport security. They use electromagnetic fields to detect metal objects, such as handguns. However, they cannot detect ceramic or plastic weapons.

Full-body imaging machines are another technology used at airports. These include passive millimeter wave (MWM) detection scanners, which can see through clothing to reveal metallic and non-metallic objects. They cannot, however, identify explosives by their chemical signatures.

Puffer machines, also known as explosive trace portal machines, are security devices that detect explosives and illegal drugs at airports. They were once thought to be a good solution for airport security. These machines use air to dislodge trace amounts of explosives from passengers' hair, bodies, clothing, and shoes. Aided by gravity, these particles are then directed into a scanner for analysis. The scanner examines the weight of the various molecules to look for specific substances.

The process of analysis is called ion mobility spectrometry (IMS). Puffer machines can detect explosives such as RDX, PETN, TNT, and nitroglycerin, as well as controlled substances like marijuana, cocaine, and heroin.

While puffer machines were once considered a viable option for airport security, they have since been abandoned by the TSA due to maintenance issues and the availability of more effective screening technologies.

Frequently asked questions