Since Alexander Graham Bell invented the first metal detector in 1881. Metal detectors are developing together with science and technology. So far, many different types of detectors have been developed for different purposes.
For example, the working principle of underground metal detector is simple. When the detector is switched on, the coil will emit electromagnetic waves. When the metal objects are touched, the signals will be displayed on the detector's head. We can see the types of metal detected through the head of the detector. This type of underground metal detector is the most popular treasure hunter, they can find underground treasure through the detector. Many metal detection enthusiasts use different types of underground metal detectors to search for the remains of ancient tombs.
Handheld metal detectors are widely used in our daily life. This type of metal detectors are generally used by security guards, subway and airport staff, as well as in large and important occasions to carry out safety testing for people entering the airport, to prevent some non-legal personnel from carrying some dangerous goods which threaten people's lives and property. It is also often seen that this type of metal detectors are used in school exams to prevent candidates from cheating on electronic products. The working principle of this type of metal detectors is to send a short pulse, and then a strong current is emitted through a coil to send a signal when it touches a metal object. When the detector receives a signal, it will send out a signal. Lighting and buzzing. But this metal detector can't distinguish the kinds of metals. It only detects metals singly.