1. Magnetic field shielding
Most devices are not sensitive to magnetic field interference, but for some devices, such as electron microscopes, biological brain wave scanners, nuclear magnetic resonance imaging systems, mass spectrometers, magnetic field interference can be fatal to interference with these electronic systems. Magnetic fields can have an impact on these devices that use magnetic fields. If the electron beam in CTR is interfered with by the external magnetic field, the deflection of the electron beam will change, resulting in image distortion. When the changing frequency of the external magnetic field is the same as the scanning frequency of the field, the image will only be distorted. When the frequency of the external magnetic field is different from the field scanning frequency, the image will roll.
Wherever there is a change in current, there is a change in magnetic field. In our living space, magnetic field interference often occurs. For example, in the vicinity of electrified railways, elevators in high-rise buildings, electric welding equipment in workshops, electroplating tanks, electric arc furnaces and induction heating furnaces, etc., when they work, they are accompanied by large current changes, resulting in changes in magnetic fields. Because the frequency of these disturbances is very low (usually 50Hz or 60Hz power frequency AC, some even direct current), these problems are very tricky to deal with.
2, magnetic field shielding principle
For very low frequency or DC magnetic field shielding, the sensitive device can be surrounded by ferromagnetic materials. Using the low impedance and high permeability characteristics of ferromagnetic materials, the magnetic field can play a role in the external magnetic field, so that the magnetic field line around the sensitive device is concentrated into the shielding material, so that the magnetic field in the shielding body is greatly weakened, and the magnetic shielding effect is played on the sensitive device.