Category Archive: EMI Filters

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.

Why Are EMI Filters Important?

EMI, or electromagnetic interference, is any electrical or magnetic force that impedes signal flow. This interference can degrade the quality of communications transmissions, hinder the flow of electricity, and even damage the affected equipment. Both narrowband interference, which is caused by human activity, and broadband emissions, which can be either human or naturally caused, are forms of EMI.

EMI filters are devices and modules that directly counter the effects of interference to stabilize the electrical flow or signal transmission, thus protecting the integrity of the system or device.

Dangers of EMI

Uncontrolled EMI presents many dangers to both the electrical devices being impacted by the interference and the signal itself. Damage can be either temporary or permanent, but even temporary effects can be catastrophic if it interferes with critical components to everyday life, such as medical equipment or military communications. EMI can:

  • Cause damage to electronics: Specifically, residential and commercial electronics, such as microwaves, refrigerators, and television systems, are vulnerable to damage from EMI. Temporary interference may cause systems to malfunction and over- or under-power devices, which can degrade the machinery’s mechanical components.
  • Cause equipment to fail: When EMI blocks communication signal transmissions, it can make cell phones and other mobile devices fail. While this may be simply inconvenient in many residential contexts, it can be costly for employees and businesses and outright dire for hospitals, municipal facilities, and military installations. Some medical devices potentially vulnerable to EMI include pacemakers, hearing aids, and life support sensors.
  • Disrupt wireless communication: EMI can interfere with large-scale radio and television transmissions by inhibiting satellites. Commercial telecommunications systems may also suffer from unreliability, poor sound quality, and slow performance.
  • Interrupt power supply: EMI can be powerful enough to interfere with the power grid and localized electricity stations. It also can cause power failures for independent systems, such as military installations, mobile and remote sites.
  • Result in data loss and electronics malfunctions: When computers and cloud-based interactions are impeded, even for just a second, data can become lost and unrecoverable.

Each of these problems can have great consequences for the systems to which they are a part.

What Is an EMI Filter?

Where Does EMI Come From?

Like we briefly discussed earlier, there are two main sources, or types, of EMI: narrowband and broadband. Another way to categorize EMI is into human-made and natural sources of interference.

Man-Made EMI

In complex electronic systems or systems in crowded environments, such as hospitals or cities, technology can interfere with itself, resulting in man-made EMI. For example, some components within a computer may cause EMI, which interferes with more vulnerable components in the same computer. Alternatively, actively working medical equipment can interfere with sensors in a hospital room. Interference from other electronics in a shared space can be common.

Other man-made sources of EMI include more industrial ones, such as powerlines, generators, television, radio and satellite transmission, and operating systems for railroads and mass transit.

Natural EMI

Natural sources of EMI come from weather and cosmic effects. Common origins of EMI include lightning strikes, heavy storms, and cosmic noise. Even static electricity can cause natural EMI.

<Explore the difference between EMI and EMC.>

Choose Captor Corporation for EMI Filters

EMI filters can reduce or eliminate this issue. At Captor Corporation, we specialize in creating standard and custom EMI filters for a range of electronic devices, including aerospace and military EMI filters. Each of our products is designed to keep critical systems performing in optimal and consistent condition. Browse our EMI filters portfolio page to learn more about our custom EMI filter experience.

EMI vs. EMC: What’s the Difference?

EMI filter

Electromagnetic interference (EMI) and electromagnetic compatibility (EMC) are both important considerations when working with electronic components. EMI is caused by electromagnetic emissions that can disrupt the function of electronic devices and radio frequency (RF) systems. These devices and systems must be properly shielded from electromagnetic radiation for them to work well. EMC measures how well these devices and systems can work in the presence of disruptive electromagnetic interference.

What is EMI?

Electromagnetic interference often manifests as undesirable noise. It may also lead to erratic or disrupted function of electrical, electronic, and RF systems. There are four types of EMI:

  • Conducted EMI EMI that flows through wires and is caused by physical contact with the source of EMI.
  • Common Mode EMI – A high-frequency EMI that flows in the same direction through one or more conductors.
  • Differential Mode EMI A low-frequency EMI that flows in an opposite direction though adjacent wires.
  • Radiated EMI The most common type of EMI, caused by radiating electromagnetic fields. Common manifestations of radiated EMI include static noise on AM/FM radio receivers and “snow” on TV monitors.

Here are some of the most common sources of EMI:

  • Power generating equipment and peripherals, such as generators, power supplies, voltage regulators, switches and relays, battery chargers, and high voltage electrical transmission lines.
  • Devices operating at high frequencies, like oscillators, computing devices, radios, radar, and sonar equipment.
  • Machines that use both high voltage and high frequencies, including motors and ignition systems.

What is EMC?

Electromagnetic compatibility of an electrical, electronic, or RF device has two facets:

  • The ability to work properly in the presence of electromagnetic radiation.
  • The ability to not generate additional EMI that affects the operation of other devices in its vicinity.

The EMC of a device can be improved through good design, shielding, and EMI filtering. A device’s EMC can be measured through compliance testing using dedicated test systems that consist of antennas, near field probes, and spectrum analyzers. Even though EMC testing can be expensive, it is essential to ensure that a design will function properly and won’t generate disruptive electromagnetic interference.

<Learn why EMI filters are critical in electric devices.>

EMI and EMC Compliance

EMI and EMC compliance standards are not uniform around the world. Different regulatory bodies each have their own specific standards. For example, the compliance standards in the European Union are different from those in the United States. To further complicate matters, the U.S. military uses stricter standards than commercial industries. Even commercial compliance standards often vary depending on the specific industry and the end use of the device.

For reference, here are some of the most common compliance standards that must be met:

  • FCC Part 15 specifies U.S. EMC testing standards for consumer devices.
  • Military EMC testing standards can be found in MIL-STD 461 and MIL-STD 464.
  • In the EU, specifications by the ISO, IEC, CISPR, and other similar agencies govern EMI and EMC compliance.

Testing for compliance has to cover both immunity and emissions:

  • Immunity testing covers the susceptibility of the device to EMI, and whether it functions as designed in the presence of EMI of specified intensities, both continuously and intermittently.
  • Emissions testing ensures that any EMI emanating from a device remains within specified limits so that it won’t cause ancillary devices to function incorrectly. Since EMI may occur through both conduction and radiation, a comprehensive emissions testing scenario must cover conducted EMI as well as radiated EMI.

What Is an EMI Filter?

EMI Solutions from Captor Corporation

Captor Corporation has been a leading supplier of electronic filters for aerospace, military, and other applications for more than 55 years. Our team of expert engineers and technicians specialize in all aspects of electronic filter design and manufacturing, including reverse engineering of electrical and electronic circuits. We frequently custom design filters to fix products that fail EMI and EMC compliance tests.

You can learn more about Captor’s capabilities for designing standard and custom EMI filters from these links:

For more information about EMI and EMC and appropriate filter solutions from Captor Corporation, please request a quote today.