EMI Shielding and Effective Filtering

EMI RFI shielding is only effective when constructed properly. As a result, each time engineers need shielding, it is best to fully understand application needs and design requirements so you can create effective filtering. Below, we highlight some of the most important factors for creating strong and reliable EMI filtering.

What is the most effective location for a filter?
Ideally, engineers will filter at the connector interference because it offers the most robust line of defense against problems associated with RFI/EMI. Although this is the best spot, it should not be the only shielding option you utilize. Certain applications greatly benefit from multiple shielding options.

How do you measure EMI Shielding?
To properly measure EMI shield effectiveness, attenuation is one of the primary indicators. Attenuation refers to the difference between EM signals before and after shielding. A signal decrease in intensity or amplitude exponentially as the distance grows. Attention is measure in dB (decibels), and the rating is the field of strength measured with and without a protective medium. When testing the effectiveness of shielding, keep in mind the below ratings:

• 0   – 10 dB – Little to no effective shielding
• 11 – 30 dB – Low levels of shielding
• 31 – 50 dB – Medium levels of shielding
• 51 – 90 dB – High levels of shielding
• 91 – 120 dB – Exceptional levels of shielding

What tests can you use to test attenuation?
The way to calculate effectiveness is often complex, and the method used to retrieve these numbers does change depending on the shielding application. The four most common testing methods include:

• Open Field Testing
• Coaxial Transmission Line Test
• Shielded Box Test
• Shielded Room Test

Related Reading

• Three Most Common Questions about EMI Shielding
• Where Does Electric Magnetic Interference Come From?
• Creating Fast & Small Electronics with RFI Shielding