Cables are interfaces that connect two or more devices and transfer data, power, and so on. Hence, they form a crucial element of any network. Hence, cables must be insulated, of appropriate length and without any loose or open ends. However, sometimes EMI is produced by connected or nearby devices which may hamper cable functioning. This may also happen at board level, wherein two or more components on the PCB may produce EMI. Electromagnetic interference occurs when signals from internal circuit components or two nearby devices clash with each other and cause noise. EMI is something that all electronic devices and PCB manufacturers must control or mitigate at the design stage. EMI in cables disrupts data transmission and may altogether attenuate signals. Hence, cables must be shielded from EMI. This post discusses various ways to mitigate EMI in cables.
Ways in Which Cables May Be Affected by EMI
Cables sometimes act as sensors or antennas and either emit or absorb EMI in the surrounding environment. Here are some reasons why EMI affects the functioning of cables.
- In high-frequency applications, cables carrying these signals often radiate EMI which causes noise in nearby devices.
- If cables are placed near to noise-producing devices, that EMI is conducted within them as well as transmitted to other devices.
- Often HDMI cables are used for transmission or streaming of audio or video files. These cables have multiple conductors which cause crosstalk and deteriorate the signals.
EMI in cables can affect even the PCBs in the connected device which directly hampers its functioning. Hence, just as PCB shields are used to mitigate internal level EMI, it is crucial to use shielding solutions for cables to facilitate their seamless functioning. There are various ways in which you can mitigate EMI in cables. You need to choose the right one based on your application requirements.
Solutions to Mitigate EMI in Cables
Considering the increasing number of high-frequency applications across industries, the solutions to curb EMI in cables is important. Here are some pointers which if one implements may help prevent EMI in cables.
- Shielded cables: These cables are not only insulated from the outside by a non-conductive covering but also have built-in shielding. This additional layer of conductive material such as foil or braided wire surrounds the inner conductors. This layer acts as a barrier to block or absorb electromagnetic interference. This is an EMI elimination technique.
- Twisted pair configuration: The right configuration of twisted pairs in cables helps filter out EMI. So, this is an EMI filtration technique that is effective at reducing both common mode and differential mode EMI. Also, you can use EMI chokes at entry points of each cable as they filter noise.
- Grounding of cables: Grounding techniques are effective at shielding EMI, and they also increase safety. Devices and equipment connected to the cable must be properly grounded. This helps EMI signals to deviate or dissipate, which avoids their clashing and noise.
- Placement and routing: Position and route the cables well so that they are nowhere nearby high-power cables to avoid electromagnetic coupling. Properly route and separate cables to minimize the potential for electromagnetic coupling between them. Avoid running sensitive cables parallel to high-power or noisy cables.
- Using foil tape or ferrite cores: Attaching ferrite cores around the cable helps absorb electromagnetic signals. Also, you can wrap the cable with metallic foil tape or adhesive-backed conductive tape that blocks EMI by creating a conductive shield.
While shielding of cables is necessary to mitigate external EMI, PCBs must be protected from internal EMI to keep the device functional. PCB shields are widely used to control board level EMI. However, these shields must be designed based on the board shape and dimensions, and must be lightweight yet flexible. After all, the device must be protected from both external and internal EMI to get the best output. XGR Technologies offers SnapShot™ EMI shields made from a thin polyetherimide film on the interior and conductive tin on the exterior surfaces. These are flexible and lightweight shields that help reduce electromagnetic inference. If you need further information on these EMI shields, you can contact the XGR Technologies team via phone or email.
