You know the drill: hand luggage in the X-ray thingy, put coins-phone-keys-bracelets-watch-necklace in the tray and ready for the metal detector. How the eff does it know I forgot to take off my stupid belt?!
The basic principle behind a metal detector is electromagnetic induction (yup, the fancy stoves thing). The idea is that every electric current generates a magnetic field, and every change in a magnetic field generates a current.
As we step through the airport metal detector, three things happen:
- The metal detector generates a relatively strong magnetic field for a few hundredth of a second.
- With this pulse, the magnetic field around us goes rapidly from nothing to strong to nothing again. That generates a current on us and everything we’re carrying, which is stronger the more conductive the objects we have are. Basically, unless an object is metallic, this current is zero. But the belt buckle conducts enough to produce a moderate current, which in turn briefly generates its own magnetic field.
- Through the exact same process, this magnetic field generates a current in a coil inside the detector, which activates the circuit that sounds the annoying alarm.
In a way, the metal detector gives a magnetic “shriek” then “listens for an echo” from metallic objects. The actual machines are obviously more complicated, but that’s the working principle.
Once established that we have a metallic object, the security officer can approach us with another device, which works much the same way. The only difference is that this one generates a weaker magnetic field that changes all the time, rather than an intense impulse.
If you want more
- How much time have we collectively wasted taking off our shoes after getting metal detectors to beep?
- Do these strong magnetic fields put us at any danger? Not really (the radiation we’ll soak in during the flight is much worse, for example)
PhysicalLove 