Traveling on airplanes is routine for millions of people. Yet most travelers never think about the security precautions that are taken at airports. When people check in at airports, their luggage and carry-on bags have to go through an elaborate screening process. The machines that perform this duty are typically metal detectors or X-ray scanners.
Metal Detectors
The principle of a metal detector is quite simple. Inside the machine are wire coils. A transmitter sends an electronic current through the coils. The current flow goes from clockwise to counterclockwise and back to clockwise again. This current creates an electromagnetic field. The direction of the current flow is reversed several thousand times every second. After a few seconds, this current or pulse slows down and disperses. Any metallic object like keys, coins, a knife or even a cell phone which happens to enter this electromagnetic field will influence the speed of the current. If the pulse hits a metallic object, it will take a few milliseconds longer for the magnetic pulse to go away. This delay sets off an alarm.
CT Baggage Scanners
When a passenger puts their bags through an X-ray machine, they go through a type of electromagnetic energy. Unlike visible light, humans cannot see X-rays. In hospitals, these X-ray energy beams can see through skin tissue to detect broken bones, tumors or other injuries. In an airport, X-ray technology is used in CT (computer tomography) scanners. Suitcases from passengers ride along a conveyor belt and pass through the hollow CT scanning machines. The X-rays bounce off the objects inside the suitcases, measuring the density and mass of each object. All that data is immediately entered into a computer. CT scanners are more complex than metal detectors and can analyze chemical components in addition to metallic objects. If the density and mass of items in the suitcase matches items that are known to be dangerous, the objects are removed from the suitcase.
High-tech Scanners
One limitation of CT scanning technology is that bags are scanned too slowly. This means only bags from suspicious passengers are scanned. Since this is not that effective, newer high-tech systems have been developed that are capable of detecting chemical components in individual items. The X-ray scanners most people see in airports are for screening carry-on bags. But these scanners are too small to scan all the luggage that goes into the cargo section of the plane. In busy airports, large trucks with built-in X-ray scanners (up to 5—7 meters long) are used. These trucks pull up beside containers that hold the suitcases, bags and other cargo. The entire container is scanned at once.
Traveling on airplanes is routine for millions of people. Yet most travelers never think about the security precautions that are taken at airports. When people check in at airports, their luggage and carry-on bags have to go through an elaborate screening process. The machines that perform this duty are typically metal detectors or X-ray scanners.Metal DetectorsThe principle of a metal detector is quite simple. Inside the machine are wire coils. A transmitter sends an electronic current through the coils. The current flow goes from clockwise to counterclockwise and back to clockwise again. This current creates an electromagnetic field. The direction of the current flow is reversed several thousand times every second. After a few seconds, this current or pulse slows down and disperses. Any metallic object like keys, coins, a knife or even a cell phone which happens to enter this electromagnetic field will influence the speed of the current. If the pulse hits a metallic object, it will take a few milliseconds longer for the magnetic pulse to go away. This delay sets off an alarm.CT Baggage ScannersWhen a passenger puts their bags through an X-ray machine, they go through a type of electromagnetic energy. Unlike visible light, humans cannot see X-rays. In hospitals, these X-ray energy beams can see through skin tissue to detect broken bones, tumors or other injuries. In an airport, X-ray technology is used in CT (computer tomography) scanners. Suitcases from passengers ride along a conveyor belt and pass through the hollow CT scanning machines. The X-rays bounce off the objects inside the suitcases, measuring the density and mass of each object. All that data is immediately entered into a computer. CT scanners are more complex than metal detectors and can analyze chemical components in addition to metallic objects. If the density and mass of items in the suitcase matches items that are known to be dangerous, the objects are removed from the suitcase.High-tech ScannersOne limitation of CT scanning technology is that bags are scanned too slowly. This means only bags from suspicious passengers are scanned. Since this is not that effective, newer high-tech systems have been developed that are capable of detecting chemical components in individual items. The X-ray scanners most people see in airports are for screening carry-on bags. But these scanners are too small to scan all the luggage that goes into the cargo section of the plane. In busy airports, large trucks with built-in X-ray scanners (up to 5—7 meters long) are used. These trucks pull up beside containers that hold the suitcases, bags and other cargo. The entire container is scanned at once.
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