EMI Filters 101

EMI filter exampleElectromagnetic interference (EMI) refers to unwanted currents or “electromagnetic noise” that interrupts the currents that electronic devices are intended to receive. EMI is typically generated by the components within a device or from external sources. The interference disrupts electronic devices, causing operations to function abnormally. It can also result in permanent damage, signal degradation, or temporary malfunction, depending on the severity of the disruption.

To combat the challenges posed by EMI, it is important to incorporate EMI filters in electrical and electronic equipment. At Captor Corporation, we offer a broad selection of industry-leading EMI filters suitable for use in various industries and applications. Our EMI filters enhance system performance by mitigating the effect of electromagnetic noise generated by devices such as microprocessors, motors, and power supplies.

This page will expand on some important questions regarding EMI filters to provide a better understanding of how they work and why they are important.

How Does an EMI Filter Work?

Most electronic devices rely on EMI filters to prevent electrical interference caused by high-frequency electronic noise. EMI filters for power supplies typically contain passive components, such as inductors and capacitors, to create LC circuits. An inductor prevents the passing of harmful and unwanted high-frequency currents but permits DC and low-frequency currents to pass through. Capacitors provide a low impedance path to divert high-frequency noise into the ground connection or back into the power supply, away from the filter input.

Dangers of EMI

The consequences of EMI have a significant impact on many industries, causing various issues such as data loss, downtime, and permanent damage. When electronic systems do not have adequate noise reduction, there is an increased risk for interference, which can cause hazardous interruptions in vulnerable devices such as mission-critical military equipment, life-sustaining medical equipment, and more.

In the military and defense sector, EMI filtration is vital. Ambient noise can interrupt military equipment that is essential to operations. There is also a risk of the weaponization of EMI, known as high altitude electromagnetic pulses (HEMP). EMI sources and HEMP threats can lead to sensitive data loss and the disruption of military operations or communications.

Why Are EMI Filters Important?

Where Does EMI Come From?

A variety of sources produce EMI, and the presence of EMI grows as the use of various technologies increases. As more electronics power on, electrical noise becomes more prevalent. There are three types of EMI sources, and they include:

  • Electronic. High-frequency noise is an unavoidable by-product of electronic technology. Equipment such as transmitters, igniters, power lines, electrical collectors, and generators produce a significant amount of EMI, which can degrade device operations.
  • Inherent. Thermal agitation, which refers to electrons moving through a circuit resistor, produces EMI within electronic devices.
  • Natural. Natural EMI results from natural events such as electrical storms, solar radiation, rainstorms, and snowstorms. Modern electronics are resilient to natural EMI, but older RF communications equipment may experience interference. This type of interference is often known as atmospheric noise.

EMI is caused by both residential and industrial sectors. Residential EMI typically disrupts or degrades signal without causing permanent damage to electronics. Appliances and wireless devices used by the typical consumer generate this type of interference. Some residential sources of EMI include cellular phones, microwaves, electric blankets, laptops, and more.

Industrial EMI can cause lasting and significant interference in essential electronics and may result in large-scale impacts. Industrial EMI produces ambient electromagnetic energy, which can interfere with local power grids, medical devices, and military operations. Common causes include television transmissions, electric motors and generators, radio and satellite, and more.

What Are the Applications of an EMI Filter?

A variety of applications depend on EMI filters for uninterrupted function. It is essential to consider the application when choosing the correct EMI filter to prevent interference and produce the expected results. Common types of EMI filters include:

  • Consumer Electronics. EMI filters for consumer electronics subdue electromagnetic noise for numerous household devices, such as washing machines, treadmills, and other appliances. These filters protect against EMI damage while ensuring that consumer electronics meet electromagnetic compatibility standards.
  • Single-phase. Small industrial and residential equipment rely on single-phase EMI filters to prevent noise. Common applications include small electronics and appliances, food service equipment, and more.
  • Three-phase. Industrial equipment, motors, medical devices, and test equipment rely on three-phase EMI filters for robust noise suppression in industrial applications. These filters have a three-stage filtering system for optimal EMI filtration.
  • Military EMI Filters. Aerospace and military communication systems rely on military EMI filters to protect against damage caused by high-frequency noise and HEMP interference. These filters must meet strict standards and comply with military regulations.

Where Should an EMI Filter Be Placed?

Placing the EMI filter where it is most beneficial to the application is key to getting the best protection. The most advantageous location for a mains or power line EMI filter is typically at the power entry point of the newly installed equipment. This location prevents high-frequency noise from entering or exiting the equipment.

What Is the Difference Between EMC and EMI?

It is critical to consider not only EMI but also electromagnetic compatibility (EMC) when installing electronics. As mentioned above, EMI refers to electromagnetic noise that can disrupt the operations of RF systems and electronic devices. Types of EMI include conducted, common mode, radiated, and differential mode.

EMC is an electrical component’s ability to withstand electromagnetic interference while operating, as well as its ability to not generate additional EMI that could interfere with nearby devices. Incorporating EMI prevention can enhance a product’s EMC, along with shielding and EMI filtering.

Industries and regulatory groups worldwide provide standards for EMC and EMI compliance. Military standards require rigorous testing for compliance under MIL-STD 464 and MIL-STD 461. Industry regulators make standards for industry-specific applications, and governing bodies like ISO provide standards and testing criteria. Testing for compliance must include both emissions and immunity to cover the device’s susceptibility to EMI and ensure EMI emanating from the device stays within specific limits.

To learn more about the differences between EMC and EMI, please visit our blog.


Captor Corporation Is Your Partner in EMI Filter Solutions

EMI is electrical noise generated by natural phenomena and human technology, which can lead to disruptions in electrical devices, permanent damage, degraded signals, and operation downtime. EMI filters prevent unwanted noise from entering and exiting the equipment to ensure proper device function, improve EMC, and limit interruptions.

At Captor Corporation, we have over half a decade of experience as an industry-leading EMI filter supplier. Our experts have worked with commercial industries and the military sector to deliver over 10,000 custom solutions in noise filtration. Our EMI filter supplying capabilities include standard, custom, MIL-COTS, TEMPEST, and HEMP filters.

Our team can handle everything from prototyping to large-scale production runs, and we offer custom EMI filter designs with current ratings from signal to 2000 A, DC voltage ratings up to and above1000 VDC, and AC voltage up to and above 750 VAC with frequencies of 50-60 Hz and 400 Hz. At Captor Corporation, we ensure optimal quality and performance by being certified to strict industry standards, including:

  • AS9100 Rev D
  • J-STD-001
  • IPC 610
  • IPC 620
  • ISO 9001:2015

Rely on Captor Corporation for quick turnaround times, testing, and inspection of products made to your exact specifications. To learn more about our EMI filter capabilities, or to get started on your EMI filter solution, contact us to speak with our specialists or request a quote today.

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