Airport Security Sensors


When we are at the airport, our luggage have a x-ray check but we just go through a big senser. And if the senser sounds, we have to be checked by something like a scanner on our body. But I usually don't see any screen to display what is detected by the big senser and the scanner-like thing (but we can see clearly what is inside our luggage). So what are being emitted from the two devices used on human? How do they work?


The luggage is checked by relatively low energy x-rays. The display just shows the shadows of the objects inside, caused by the absorption of the x-rays. The more dense an object is the darker the image.

The people are checked by a metal detector. That doorway looking thing you walk through encloses transmitting and receiving antennae. Small pulses of magnetic fields are generated at the transmitter and if no conducting material is between the transmitter and receiver the received pulses look like the transmitted ones. If a conductor is carried through the portal, the received pulses are distorted. The electronic circuitry senses this change and sounds an alarm. The small wand is contains a coil of wire carrying an alternating current. Any conducting material near the coil will change its inductance enough to be detectable to the circuitry in the device. Since most weapons involve significant amounts of metal, which is a good conductor, this device is really a weapons detector. The only radiation associated with the metal detector is very low energy electro-magnetic radiation in the radio frequency range.