Exports of Chinese electronic products are often restricted due to electromagnetic compatibility (EMC) issues. This article focuses on EMI suppression methods for product designers and sources of electromagnetic interference (EMI).
EMC refers to the ability of a device, apparatus, or system to operate in its intended environment without causing significant electromagnetic interference to other devices (IEEE C63.12 1987). Although EMC performance for wireless transceivers can be achieved by using discontinuous portions of the spectrum, in some cases, such as interference between cell phone signal jammers and medical devices, EMC is not sufficient.
During the operation of electrical and electronic equipment, voltage and current change intermittently or continuously, sometimes rapidly. This generates electromagnetic energy of various frequencies or bands, which is emitted by the corresponding circuits to the surrounding area.
EMI can enter or leave a circuit in two ways: radiation and conduction. Radiated EMI leaves through gaps, slots, openings, or other spaces in the device enclosure. Conducted EMI occurs when a signal line leaves the enclosure and couples with power lines, other signal lines, or control lines. The free radiation of these lines causes interference, but the interference is in a different frequency band than that emitted by the jammer.
Effective EMI suppression is achieved through a combination of shielding the equipment enclosure and employing slot shielding. In most cases, the following principles help achieve EMI shielding: reducing interference sources, using shielding, filtering, or grounding to isolate and improve circuit immunity to noise and EMI, and ensuring low sensitivity of sensitive circuits to interference. These goals should be prioritized by circuit designers and addressed early in the design phase. The most popular and useful cell phone jammer.
Designers have found that the use of shielding materials is very effective in reducing EMI. Today, a variety of shielding materials are widely used, including metal cans, thin sheets, aluminum foil tapes, and coatings applied to fabric or conductive tapes (such as conductive paint and zinc spray). Both metal and plastic coatings can have conductive layers. Once the designer has determined the enclosure material, it is time to start selecting gaskets.
