There are various types of EMI, out of which radiation EMI signals travel freely in air. Radiated emissions or electromagnetic waves of varied frequencies from a printed circuit board may accidentally clash with the waves in a peripheral device or surroundings. This results in noise which is referred to as EMI or electromagnetic interference. This also causes coupling with PCB traces, board components, and so on. This needs to be prevented at all costs because it directly hampers the functionality of the printed circuit board as well as the concerned device. Such boards make the device dysfunctional in the presence of EMI and hence may not clear the electromagnetic compatibility (EMC) test required to meet certain industry standards. Also, the final products need to clear certain tests such as FCC and CISPR EMC. This post talks about sources of radiated EMI, ways to control it, and more.
What Are the Sources of Radiated EMI?
Radiated EMI travels in air for long distances. Depending on the frequency at which it is radiated and physical distance from a device, this EMI can impact its functioning. Here are some common sources of radiated EMI though PCBs.
- Amplified noise through radio signals, electrical motors, telecom equipment, radar systems, and so on.
- Switching noise that occurs due to switch-mode power supplies, regulators, AC/DC converters, and so on.
- Cavities in the board that are there due to the way stackups and planes are arranged create electromagnetic resonance.
- Waves on signal receiving antennas and unterminated transmission lines with varied frequencies of analog as well as digital signals.
- Burst of current created on a power bus that creates an electromagnetic pulse and may get transferred to ICs.
- Spurious harmonics from non-linear components on the board.
Ways to Mitigate Radiated EMI
Here are some pointers on how to mitigate radiated EMI.
- Implementing and maintaining signal integrity: Implementing good signal integrity practices, such as signal termination and routing techniques, controlled impedance, and so on help control electromagnetic radiation.
- Component placement: The way components are mounted on the board and their positioning can affect EMI generation. Hence, it is crucial to separate high-speed digital circuits from sensitive analog circuits, minimize trace lengths, and placing components with strong emissions away from sensitive components to control EMI generation.
- PCB trace routing: PCB traces must be routed considering signal paths and by reducing loop areas. This helps mitigate radiated EMI. Also, there must be appropriate spacing designed between traces, while avoiding sharp corners.
- PCB materials used: PCBs used in high-heat applications must have good electromagnetic compatibility (EMC) and mostly made of high-frequency laminates or materials that help reduce radiated EMI.
- EMI filters: Incorporating EMI filters and suppression components, such as ferrite beads, capacitors, and inductors help attenuate electromagnetic signals at varied frequencies which help reduce radiated EMI.
- Grounding and shielding techniques: This is an important aspect comprising the right signal return routes, ground plane placement, and the use of PCB EMI shields. Shields chosen must be flexible and perfectly fit the board based on its dimensions. Shields made of plasticized metal such as polyetherimide may be a perfect fitment. Also, check for custom options for the shields to get the best output.
If you are an OEM manufacturing electronic or electromechanical products, you would require PCBA that is EMC enabled. You may want to source for PCBs with EMI-inhibiting shields to prevent noise and increase the efficiency of your products. In fact, PCB manufacturers may also prefer to use EMI PCB shields to increase their efficiency and credibility. Ensure you source these shields from reliable and certified players that also offer custom options. XGR Technologies offers SnapShot® EMI shields with isolation for a wide frequency range from below 1 GHz to 12 GHz. These EMI shields are lightweight, flexible, as they are made of plasticized metal. While they stay firmly in place, these shields can be easily removed and reinstalled in case you need to make any changes to the board. You can contact XGR Technologies team today to know more about these EMI shields or share your requirements.
