A PCB is a core to any electronic device. It is usually designed for electromagnetic field interactions. At times, these electromagnetic interactions may interfere with the working of other circuits or devices close by the PCB. To avoid this, the PCB must be designed with electromagnetic compatibility. PCB designers have been following design guidelines to minimize EMI. However, that becomes insufficient at times. This is when EMI shielding comes into picture. The EMI shields are generally made of metals or plasticized metals, and are used to protect PCBs from EMI and RF. These shields isolate the sensitive components in the board from the rest of the board, without affecting their performance or connectivity with other components on the board. Although designed for effective EMI shielding, these enclosures may not be perfect. They may not work as expected due to reasons ranging from geometrical inaccuracies to surface irregularities. Hence, the effectiveness of these shields needs to be tested employing various tests and techniques. This post offers insights on various popular EMI shielding effectiveness tests, techniques, and more.
An Overview of EMI Shielding Effectiveness
The primary purpose of the EMI shield is to prevent electromagnetic radiation from interfering with the PCB performance. The amount of attenuation achieved by the EMI shield is used to determine its effectiveness. This shows the immunity of the PCB or the device from external EMI sources. Attenuation is generally measured in decibels (dB) and indicates the intensity or strength of electromagnetic signal before and after shielding. The shield of high effectiveness may possess an attenuation of 90dB to 120dB. The shield of low effectiveness would have attenuation from 10 to 30dB. The effectiveness of EMI shield would be high if the signal losses its intensity after hitting it.
Common EMI Shielding Effectiveness Standards
With increasing use of electronic devices in all spheres of our lives, the world governments have erected strict regulations to ensure the minimum EMI effectiveness of the device. Many industries such as military and defense, aerospace, medical, and automotive have established strict regulations and standards to ensure EMI shielding effectiveness of electronic equipment. The manufacturers often test their devices against testing standards developed by the IEC, ASTM, IEEE, and MIL to ensure standards of EMI shielding effectiveness.
- For instance, to check the shielding effectiveness of planar materials, ASTM D4935-10 EMC testing is performed.
- IEC 61000-5-7 testing standard is applicable for testing EMI shielding effectiveness of empty enclosures.
- IEEE Standard 299 is applicable for EMI shielding in a wide and extensible range of frequencies between 9kHz and 18GHz, which may be extended to even 100 GHz.
- MIL-STD-285 testing is performed for checking EMI attenuation by shielding enclosures used in mission critical equipment in the military sector.
Types of EMI Shielding Effectiveness Tests
The EMI shielding effectiveness is evaluated by measuring the EMI and RF signal attenuation on a shield under different conditions. The following are some common types of EMI shielding effectiveness tests performed.
- Open field test: This testing is performed by creating a simulated environment close to that in electronics manufacturing. Conductive emissions are tested by positioning sensors or antenna at specific distances from the device. A noise level meter is used to determine the EMI level.
- Shielded box test: This testing is done in a sealed box with a conductive shielding unit placed at an open portion. The incoming and outgoing electromagnetic signals are recorded and analyzed.
- Shielded room test: Here two shielded rooms are used, wherein one room has sensors, while the other has the device and testing tools with a wall between both the rooms.
If you are a manufacturer of electronic, electrical, or electromechanical devices, especially devices that are sensitive to EMI or noise, ensure to source shields that are tested to standards of industry you work for. XGR Technologies offers SnapShot EMI shields that outperforms competitor products in shielding effectiveness from below 1 GHz to 12 GHz. It offers extremely consistent isolation across a wide frequency range. The shield features non-conductive interior surface which reduces electromagnetic coupling with traces of the circuit, reduces the overall shield volume, and eliminates any threats of shorting. You can get in touch with our team today to discuss your specific application requirements.
