EMI (Electro Magnetic Interference), refers to the phenomenon that electronic equipment (interference source) interferes with other electronic equipment through electromagnetic waves. For example, when we watch TV, someone uses a hair dryer or electric razor, the image on the TV screen will be distorted; when there is an incoming call on the mobile phone, there will be noise in the speaker next to them... these are common electromagnetic Interference phenomenon. Even more serious is that if the electromagnetic interference signal hinders the flying aircraft, it will cause unimaginable consequences. Judging from these examples, it seems that electronic equipment has an invisible "attack", causing disruption and destruction to the normal operation of other electronic equipment
From the "attack" form, there are two main types of EMI: conducted interference and radiated interference. Electromagnetic conduction interference means that the interference source conducts the signal on its own electrical network to another electrical network through a conductive medium (such as a wire). For example, when we turn on the air conditioner, the electric lights at home may be dimmed for a while; radiated interference refers to the interference of other electronic devices in the form of radio waves.
When there is a spear, there is a shield, and when there is electromagnetic interference, it is anti-electromagnetic interference. The following introduces our second protagonist-EMS (Electro Magnetic Susceptibility), which refers to the easiness of the performance degradation of electronic equipment due to external electromagnetic interference. For example, it is also disturbed by a hair dryer or an electric shaver. Some TV screen images will be distorted, while others will not. This shows that under the "attack" of electromagnetic interference, the former has higher electromagnetic sensitivity and is more likely to be injured, that is, the "defense" is lower; while the latter has lower electromagnetic sensitivity and is not easily injured, that is "defense" Higher
EMC-Comprehensive offensive and defensive capabilities
With a spear and a shield, finally use them to arm our third protagonist--EMC
EMC (Electro Magnetic Compatibility) refers to the ability of electromagnetic energy generated by electronic equipment to neither interfere with other electromagnetic equipment nor be interfered by other electronic equipment. Therefore, EMC includes both EMI and EMS: on the one hand, the electromagnetic interference generated by electronic equipment in the environment during normal operation cannot exceed a certain limit, that isEMI; on the other hand, electronic equipment is required to The existing electromagnetic interference has a certain degree of anti-interference ability, that is EMS
Therefore, when we test the EMC of an electronic equipment, the relevant standards stipulate the maximum value of EMI and the minimum value of EMS, that is “low attack" and “high defense”. It’s like a shepherd dog, gently driving its own sheep, but when facing a wolf, it can beat and drive it away
For USB cables, this requires a good shielding of the cable, on the one hand, it does not allow electromagnetic waves to radiate to the external space (low attack), on the other hand, it is not affected by other electromagnetic wave radiation. This puts a high requirement on the design and production of cable and connectors. Most of USB cables on the market do not meet the requirements of EMC