What are the characteristics of a shield and what circuits is it typically used in?
2022-03-02
First, let's talk about Shielding To define shielding, we must mention EMC control. We know that the three elements of electromagnetic compatibility are the interference source, the interference method, and the sensitive source. Therefore, the three treasures of controlling electromagnetic compatibility are filtering, grounding devices, and shielding. Shielding is a shielding method. Also, there is the phone's upper board. As the saying goes: Insufficient indoor space, shielding must be used, which means that the phone's upper board must have high-density shielding. Also, there are radio frequency signals. In this case, a series of shielding measures are used. The above mentions various shielding methods.
Next, let's look at the effectiveness of shielding: Simply put, there are two main effects: First, it avoids external radiation interference; second, it shields external radiation interference; More complexly, it is to avoid interference from external electrostatic fields, electromagnetic fields, or magnetic fields on internal mechanical equipment or to prevent damage to the external environment from the mechanical equipment's magnetic field. Place the mechanical equipment in a closed or similar closed alloy shell or metal mesh cover.
1. Did you use the correct shielding specifications?
Each microwave RF PCB needs to be installed in a shielding cavity, with a large number of series resonances. The resonance frequency is related to the specifications of the shielding cavity's mechanical equipment, as well as the PCB's layer structure and materials. When designing microwave RF PCBs, pay attention to series resonance. When the output power is close to series resonance, part of the kinetic energy is absorbed, resulting in peak loss, thus endangering the normal operation of the power supply circuit. Therefore, we should choose a suitable shielding cavity specification so that its series resonance does not fall within the intermediate frequency range of the patch antenna power supply circuit. The calculation method is left to the electronic engineers. PCB design engineers must pay attention to the following points when designing the scheme: Increase the height-to-width ratio of the shielding, try to reduce the application of square shielding, and add some high components to widen the relative height of the shield.
2. Did you use the correct shielding raw materials?
Common shielding materials are high-conductivity energy materials, such as copper coins, copper alloy plates, aluminum foil, thick steel plates, or metal plating, conductive plating, etc. Electrostatic shielding is suitable for avoiding the influence of electric fields. For example, for the interference safety protection of small and medium-sized instruments or components, a copper-aluminum density shell is used as a shield. For low-frequency magnetic induction interference, a shell made of iron or beryllium molybdenum aluminum alloy and other permanent magnetic materials is used. Superconducting shields are used to prevent interference caused by high-precision magnetic induction measurements at ultra-low temperatures.
3. The internal radiation stray of the power supply circuit itself is large.
If the internal radiation stray of the shielding is very large, after the shielding is covered, the radiation stray cannot radiate outward, but will be coupled into transmission stray. Therefore, when the RF circuit itself is not well done, the transmission stray without shielding is better than that with shielding.
Shielding The purpose is to protect. For power supply circuits that are very prone to mutual interference, consider protection:
1) For example, microwave RF modules and high-frequency modules, the low-frequency data signals of the receiving channel will cause great interference to the RF signals; on the other hand, the RF signals of the safety channel will also cause radiation interference to the high-frequency data signals.
2) For example, the local oscillator power supply circuit in the microwave RF area needs to be independently shielded. We know that the local oscillator pulse signal itself is relatively high and will cause relatively large radiation interference to other modules.
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