To summarize this blog series upon its completion, electromagnetic interference (EMI) — which consists of a source, a path, and a victim — is a problem in electrical and electronic systems. Some systems emit noise, others are susceptible to noise, and some both emit and are affected by noise. However, a wide variety of components that can be used to effectively filter EMI in almost any application are readily available through several trusted suppliers.

General Filtering Solutions

Board level EMI filtering components, like ceramic feedthrough capacitors, offer a simple solution for filtering noise, as these components essentially replace three-component tee filters with a single SMT device. Tee filters consist of two inductors and a capacitor (Figure 1), and are often constructed using ferrite beads and a ceramic capacitor. Although effective, three-element tee filters take up a great deal more space than a single surface mount feedthrough ceramic capacitor, and can also be more costly than single component solutions. Alternately, although feedthrough capacitors also have three terminals — two of which help increase its series inductance to increase high frequency impedance, and a middle, third terminal that connects directly to ground and lowers parallel inductance to increase the filtering bandwidth — another benefit they provide, beyond size and cost, is that they don’t suffer from the hysteresis effects that plagues ferrite components.

Mission Critical Filtering Solutions

Mission critical applications require more sophisticated EMI filters than general filtering applications, as each of these applications typically has its own unique set of performance standards that have to be met, tested, and qualified to ensure that the devices operate optimally at all times. Box-level EMI filters are often used in such applications — and especially those with harsh environment operating conditions — due to their ability to effectively filter a broad range of electrical noise up to 50GHz while withstanding wide temperature variations and high vibration environments. Constructed using discoidal capacitors and inductive elements housed inside a metal sleeve, high reliability feedthrough filters are widely used for box-level EMI filtering in a range of mission critical applications, including: medical implantable, space, aerospace, down-hole, and military systems and equipment. Additionally, fully- and semi-hermetically sealed devices that are both airtight and resistant to moisture are also available and effective in many such applications.

Conclusion

Electromagnetic interference is an unavoidable problem in electrical and electronic systems. So, when designs aren’t working as they should, it is often useful to consider whether the issue could be a result of EMI. If it is, the source, path, and victim can be determined to appropriately address the problem; and, depending on the application’s requirements, any number of a vast range of components can be used to effectively filter the offending noise.