With the wider and wider application of metal detectors, more and more people begin to care about whether the metal detectors have radiation. So will metal detectors have adverse effects on our health?
We usually check luggage at stations and airports using low-frequency electromagnetic field, the power is very small, much less than the power of mobile phone calls. It just checks whether there are metal objects. In fact, many things that generate electricity or use electricity, such as power lines or household appliances, generate electromagnetic fields. It is safe for everyone to pass through such a low-level metal detector. In addition, the handheld metal detector used by security inspectors is the same. Many people mistakenly believe that these scanners use X-rays, but this is not the case. X-ray machines at stations and airports are only used to check luggage. Pregnant women try to stay away from luggage machines, but do not fear metal machines.
Another way of saying is that metal detector generates high frequency variable magnetic field through oscillator connected by the middle radiation coil. Once metal impurities enter the magnetic field area, the magnetic field will be disturbed and an alarm signal will be generated. Therefore, the metal detector is electromagnetic detection, there is no radiation. In the field of metal detectors, the old-fashioned security gate uses X-ray to detect, but now it uses electromagnetic field to detect metal objects.
The earliest application of metal detectors was during World War II, when it was commonly known as "mine detectors". By using the difference of the physical characteristics between the mine and the surrounding soil, the electromagnetic field radiated by the mine detectors was distorted, and the location of the mine was determined by detecting the signal of the distorted field. Modern equipment of this type plays a role in various fields, such as airport security doors and hand-held metal detection devices.
Nowadays, the metal detection machine used in industry is a kind of precise detection equipment for eliminating foreign metal contamination. Metal detection machine is used to detect metal foreign bodies mixed in food, medicine, textile, cosmetics and other production processes. The principle is a central transmitting coil and two equivalent receiving coils, which are mounted in a probe head. The oscillator emits a high frequency magnetic field through the middle radiation coil, which is connected with two receiving coils, but the polarity is opposite. When the magnetic field is not disturbed by the outside world, the voltage output signals generated by the oscillator cancel each other. Once metal impurities enter the magnetic field, this equilibrium will be destroyed, and metal detectors can detect the presence of metal.
Metal testing machines are widely used in food, pharmaceutical, daily chemical and other processing and packaging industries, to help manufacturers to control quality, to ensure that the final products into the market will not cause physical harm to consumers.
Metal detection machine was originally used for non-destructive detection of underground targets. It was usually used to detect cables, pipes, steel bars or other metal objects in underground and buildings. It could also be used to detect metal objects in any layered media. Security and public security departments use it to check for hidden weapons such as knives and guns in human bodies and mail. In military applications, it can detect mines, bombs, underwater mines, underground camouflage and so on. It can be used to inspect the remaining wire, nails and other metal fragments on the production line of textile and food industries. It can also be used as an important equipment for the excavation of underground cultural relics, meteorite identification and medical inspection.
In physics, metals can be divided into ferromagnetic metals and non-ferromagnetic metals. According to the requirements of user detection, the metal objects can be divided into valuable metal targets and non-valuable metal targets.
The basic principle of metal detector is to use the obvious physical characteristics of metal objects - magnetic effect, remove background and noise interference by various methods, extract the target signal separately, and then display the target signal or image in the form of sound, light or (and) electricity according to user's needs. The magnetic effects of metal objects include magnetostatic effects and alternating electromagnetic effects. Magnetostatic effect refers to the response of ferromagnetic metals to a constant magnetic field, which includes the magnetic field of permanent magnets, the magnetic field and the geomagnetic field generated by DC coils, etc. Alternating electromagnetic effect refers to the response of ferromagnetic or non-ferromagnetic metals to the magnetic field generated by coils passing alternating current, which is generally measured by the variation of inductance of coils. When the non-ferromagnetic metal object is close to 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. Appropriate design of electronic circuit can show the change of inductance of coil in the form of alarm signal. Metal detector is a device which can detect the existence of metal target nondestructively by magnetostatic effect or alternating electromagnetic effect.