Development history and working principle of metal detector
The development history and working principles of metal detectors were published. In the early 1969, a monograph "electronic metal detector Handbook" was published in the United States, which systematically summarized the previous research and products on metal detection. But, because of the early age, its content seems to be a bit old. Later, there were many new developments, especially the application of amplitude phase method, inverse identification and sampling technology. The quality of the metal detector has increased a lot, and the application scope has also expanded greatly. Metal detectors are typical of several types: security doors, handheld portable metal detectors, underwater metal detectors, underground metal detectors, and so on.
Metal detectors are the earliest electronic devices for nondestructive detection of underground objects. They are usually used to detect pipes, cables, reinforcing bars or other metal objects in underground and buildings, or detect metal objects in any layered medium. The security and public security departments use it to check the knives, guns, or weapons hidden in the body and in the mail. In military applications, can detect mines, bombs, underwater, sinking underground. The pipeline of textile and food industry is used to check residual nails, wire and other metal fragments. It can also be used as an important equipment for underground cultural relics excavation, meteorite identification and medical examination.
In physics, metals can be divided into two major categories, ferromagnetic metals and non ferromagnetic metals. From the user requirement of detection on said metal objects to be detected can be divided into valuable metal targets, military targets or special target is a metal target, and nails, screws, nuts, cap and other debris in the case of special requirements, are generally regarded as the goal of useless garbage or worthless metal.
The basic principle of metal detectors are mainly using physical property of metal object magnetic effect is obvious, and remove background noise interference by various means, the target signal isextracted according to user needs to sound, light or (and) the form of electric signal or display the target object images. The magnetic effects of metal objects include the magnetostatic effect and the alternating electromagnetic effect. Magnetostatic effect refers to the reaction of ferromagnetic metal to a constant magnetic field, a constant magnetic field, a permanent magnet's magnetic field, a magnetic field and a geomagnetic field generated by a DC coil. Alternating electromagnetic effect refers to the ferromagnetic or non ferromagnetic metal magnetic field of the coil through the alternating current response is generally used to measure the coil inductance changes, for example, when the ferromagnetic metal objects close to the alternating current through the coil, because the permeability value increased, while increasing the coil inductance. When the non ferromagnetic metal object is near the coil passing through the alternating current, the real part of the coil impedance increases, that is, the loss increases and the imaginary part decreases, that is, the inductance of the coil decreases. The appropriate design of electronic circuits can change the inductance of the coil and display it in the form of alarm signal. A metal detector is a device that can detect the existence of a metal target with a magnetostatic effect or a nondestructive electromagnetic effect.
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