Shielding box, also known as isolation box, shielding box and electromagnetic shielding box, can handle conduction and radiation, and provide an efficient isolation test environment for the production and manufacture of wireless communication products. The test content includes coupling test, RF function test, electromagnetic interference test and electromagnetic Compatibility testing. The shielding box is mostly designed with aluminum alloy material, the shielding material has strong barrier ability and good wave absorption function; the supporting test interface and anti-pressure sealing design are convenient for testing and good shielding effect; the data port and power signal use EMI filter; the internal space is large , suitable for a variety of product testing, such as circuit boards, mobile phones and PADs.
There are two functions of the shielding box, one is to shield external interference signals and prevent external electromagnetic radiation from entering the inner area of the shielding box; the other is to absorb internal interference signals, that is, to limit the electromagnetic radiation inside the equipment beyond the area of the shielding box. The shielding box realizes the shielding function mainly using two principles:
1) The principle of electromagnetic induction of the circuit: the metal material inside the shielding box has resistance, and the electromotive force on the induction surface forms an eddy current, and the magnetic field generated by the eddy current is opposite to the original magnetic field direction, which can offset the original At the same time, the eddy current can generate heat inside the metal material and consume part of the electromagnetic radiation, which also plays a shielding role.
2) The principle of electromagnetic field transmission: Due to the special metal material inside the shielding box, the impedance of the electromagnetic wave does not match, which will cause the electromagnetic wave to reflect; the electromagnetic wave will attenuate during the transmission process, which is currently the most used method of electromagnetic shielding boxes.
When it comes to shielding boxes, filters come to mind. What is a filter? Why should the shielding box be used together with the filter? A filter is a device that filters waves, allowing signals with frequencies to pass through and blocking signals without frequencies. There will be many input and output power lines and circuit board wires in the use of the shielding box. The electromagnetic waves radiated from the outside will interfere with the incoming equipment on the wiring harness. In order to prevent this phenomenon, a filter must be installed. The filter extracts the original signal information from the interfered signal to obtain a specific frequency, and all filters can achieve the effect of eliminating interference noise.
When designing the shielding of electronic equipment, we need to choose the appropriate shielding effectiveness index. The structural design of the shielding equipment should be simple, reduce additional gaps and holes, and no conductor cables can pass directly through the shielding equipment, so the shielding effectiveness will be greatly reduced. , The design of shielding equipment should ensure that it is a complete and continuous conductor, and ensure the surface finish and contact tightness of the product.
In addition to filters, we can also improve electromagnetic interference problems through ground wire design and circuit board design. A lot of electromagnetic interference is generated by the ground wire. If the design of the ground wire is insufficient, the potential will be unstable and cause circuit failure. Therefore, in the design of the ground wire, it is necessary to ensure the stability of the ground wire potential and eliminate interference; secondly, the circuit board is the core of the interference. In the circuit board design, it is necessary to reduce the radiation generated by the circuit board circuit and the sensitivity to external interference, and reduce the influence between circuits.
With the rapid development of electronic equipment, there are more and more scenarios where electromagnetic shielding boxes are used in the production test process. Various types of shielding boxes have appeared successively, including mobile phone tablet shielding boxes, WIFI Bluetooth shielding boxes, manual shielding boxes, and pneumatic fully automatic shielding boxes. The development of shielding boxes is also getting faster and faster, the performance indicators are gradually improving, and they are more intelligent and automated.