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Electromagnetic interference (EMI), filter kits provide a valuable protection against transient interference or electromagnetic noise. Different types of filter technologies are available to choose from but understanding their respective working principles and application fields is vital for successful implementation. This article is a comprehensive guide for manufacturers and engineers on the workings behind EMI filter kits and provides useful guidance on their appropriate use across various applications.

What Are EMI Filters?

EMI filters are an important type of device used to protect equipment from damages caused by electro-magnetic noise in specific application fields. These filters come with two main categories – – conducted noise filters and radiated noise filters. Both types of filters can provide similar levels of protection from electromagnetic interference. Though they have different methods of implementation and purpose, they essentially work together to provide protection.

Conductive Noise Filters

Conductive noise filters are used to protect against interference from conducted electromagnetic noise. These filters are typically placed between the device and the source of electromagnetic noise, such as a power line or signal line. The filter may be placed on the shield of a coaxial line, or at the device connection point, such as at ground. The filter will block conducted noise signals from entering the device, while allowing beneficial signals to pass through without interference.

Radiative Noise Filters

Radiated noise filters are used to protect against interference from electromagnetic radiation, such as radio frequency (RF) signals. These filters are typically placed between the device and the source of electromagnetic noise, such as a tower, antenna, or other type of broadcast radiator. The filter will block radiative noise signals from entering the device, while allowing beneficial signals to pass through without interference.

Common Application Fields

EMI filters are commonly used in the following application fields: aerospace, automotive, marine, medical, telecommunications, and consumer electronics. In these industries, EMI filters can be used to reduce or eliminate interference from a variety of sources. These sources can include power line and signal line conducted noise, radio frequency radiation, and power supply harmonics.

Working Principle

EMI filters work by blocking the unwanted electromagnetic noise while still allowing the desired signals to pass through the filter. The filter works by blocking a specific frequency or range of frequencies that cause an interference issue. This is done by redirecting the energy from the unwanted frequency to a ground point, where it is dissipated in the form of heat.

The filter is designed with multiple parallel paths which each incorporate a low-pass filter. The low-pass filter works by storing the energy from the unwanted frequency, and redirecting it through an inductor or choke coil to a ground point. This process blocks the unwanted frequencies while allowing the higher frequencies to continue to pass through the filter.

Conclusion

EMI filters are an important and essential device used to protect equipment from electro-magnetic noise in specific application fields. These filters come with two main categories, conducted noise filters and radiated noise filters, which work independently and together to provide protection from the various sources of interference. Understanding the working principles and applications of EMI filters is essential to ensure successful implementation and usage in various industry fields and commercial products.

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