安检入口使用的金属探测器，在探测环的一面是“发射”线圈，另一面则是“接收”线圈。当乘客或行李经过探测环时，发射线圈短时间接通，在乘客周围产生一个磁场。
The metal detector used at the entrance of the security inspection is a "transmitting" coil on one side of the detection ring and a "receiving" coil on the other. When a passenger or luggage passes through the detection ring, the transmitting coil communicates indirectly for a short time, creating a magnetic field around the passenger.
如果你携带有金属物件，如说几个硬币，磁场就在金属物件中诱生出电流，这个电流又产生一个围绕着金属物件的磁场，这个磁场反过来又在接受线圈中感应出电流。
If you carry a metal object, say a few coins, the magnetic field induces an electric current in the metal object, which in turn generates a magnetic field around the metal object, which in turn induces an electric current in the receiving coil.