The components of the mobile phone shielding box generally include: the host, the antenna, and the power adapter. When installing the mobile phone jammer, because there is a strong signal magnetic field within a certain distance between the host and the antenna (usually 20-30 cm), and there is also magnetic field interference around the 220V power line (strong current) (usually 5-10 cm), so , How to install each component well is very important. Incorrect placement may cause interference to the shielding signal transmission, thereby affecting the shielding effect.
According to the Penal-Lenz law, the eddy current always prevents the change of the electromagnetic field, that is, consumes the energy of the electromagnetic field. The higher the frequency of electromagnetic field changes, the better the conductivity of the metal and the better the shielding effect. For low frequency electromagnetic field changes (such as power frequency 50Hz), ferromagnetic materials must be used for shielding, like the shielding of power transformers, iron with good permeability must be used for shielding.
In order to reduce the coupling interference voltage of the alternating electric field to the sensitive circuit, the mobile phone shielding box can be provided with a metal shielding body with good conductivity between the interference source and the sensitive circuit, and the metal shielding body can be grounded. The coupling interference voltage of the alternating electric field to the sensitive circuit depends on the product of the alternating electric field voltage, the coupling capacitance and the ground resistance of the metal shield. As long as the metal shield is well grounded, the coupling interference voltage of the alternating electric field to the sensitive circuit can be reduced. The electric field shielding is mainly based on reflection, so the thickness of the shielding body does not need to be too large, and the structural strength is the main consideration.
Generally, a high-conductivity material is used as the shield, and the shield is grounded. It uses the shield body to generate the eddy current magnetic field in the opposite direction under the action of the high-frequency magnetic field and the original magnetic field to offset the original magnetic field to weaken the interference of the high-frequency magnetic field, and realize the electric field shielding due to the grounding of the shield body. The thickness of the shield does not need to be too large, and the skin depth and structural strength are the main considerations.