When mention metal detectors, people will immediately think of the "treasure" boy story. In fact, there are not only mineral exploration detectors and landmine detectors, but also various detectors such as food inspection and fiber foreign bodies that are widely active in the industry.
Sensors have different shapes due to different ways. The sensor is basically composed of a primary coil and a secondary coil, and is configured so that the magnetic fluxes generated by the primary coil just disappear when passing through the secondary coil. When approaching the metal body, the path of the magnetic flux changes slightly, the balance is broken, and a signal appears at the output.