What Are the Two Types of EMI?

Grant Phelps, Author at Captor Corporation

Author Archives: Grant Phelps

Types of EMI Filters
August 28, 2024 4:47 am Leave a Comment
EMI filters prevent the disruption of the proper performance of electronic circuits caused by electromagnetic interference (EMI). Additionally, filters provide protection against your system causing feedback on power lines and signal lines that may render your product non-compliant to MIL-STD-461 and DO-160 requirements. The right EMI filter depends on your specific design requirements and EMI filtering needs.

Established in 1965, Captor Corporation is a leading provider of high-performing EMI filters. Our custom solutions are often delivered faster and at a more competitive price point than standard off the shelf options provided by our competitors. Our capabilities allow us to deliver a wide variety of EMI filters tailored to the needs of our customers.

What Are the Two Types of EMI?

Electromagnetic interference occurs when two or more electrical circuits interfere with each other. EMI can be categorized into two types based on its coupling mechanism (the way electrical energy transfers from one circuit to another):
- Conducted EMI. This type of interference is passed along wires and cables from a source to a receiver. This process is engaged by switching currents within the device itself or from external sources like power lines or nearby equipment.
- Radiated EMI. This type of interference is the most common and is passed through the air as electromagnetic waves. These fields are generated by almost any electrical or electronic device. It can be emitted from your device or come from external sources like radio waves, electrical equipment, and natural occurrences such as lightning, electric storms, and sun flares.
Both types of EMI can disrupt the proper functioning of your electronic designs causing malfunctions ranging from mild to hazardous. Fortunately, different types of EMI filters work to address each kind of issue.

Passive EMI Filters

Passive filters work by absorbing unwanted energy and reducing emissions of a power electronic circuit. They rely on passive components like capacitors, inductors, and resistors to reduce EMI.

Passive EMI filters are generally more affordable than active filters. They have a simpler design that makes them easier to implement, requiring less expertise from the operator. Passive filters also offer the advantage of lower power consumption as they don’t require any additional power to operate.

Three types of passive EMI filters are available:
- Single-Stage Filters. Typically composed of a single capacitor and inductor (L-Circuit Filter) arranged in a specific configuration, these are the simplest EMI filters. Captor often utilizes feedthrough capacitors in our designs and brochure products to provide high frequency suppression.
- Multiple-Stage Filters. These filters achieve better noise suppression by using multiple stages of filtering components (Pi-Circuit, Double Pi-Circuit, T- Circuit, Double or Triple-L Circuit). Multiple components combined with our feedthrough capacitors offer performance lower in the frequency spectrum and then hold the filtering up into to the higher frequencies.
- Feed-Through Capacitors. By using a capacitive element built around a central conductor (C-Circuit Filter), these filters allow desired signals to pass while suppressing unwanted noise. The capacitance level determines which frequency the unit begins suppressing and then will hold out to the high frequencies.
Which Type of EMI Filter is Best for My Design?

Am I filtering a power supply with a certain switching frequency?

Am I filtering for a motor load?

Am I filtering for a condenser load?

Am I filtering for a radar load?

What is your load?

Do I need lightning protection?

Do I need transient pulse protection?

Do I need HEMP protection?

We need to pay special attention to the above. The question Which Type of EMI Filter is Best for My Design? is not answered.

Passive filters help control conducted emissions and are often the more cost-effective option. Passive filters can be used in appliances, electronic devices, power lines, and other applications battling, low to high-frequency electromagnetic noise.

Whatever your design requirements, proper EMI filtering is crucial for ensuring electromagnetic compatibility (EMC) and compliance with key regulations.

EMI Filters from Captor Corporation

Captor Corporation is a leader in the field of EMI filters. Our custom solutions are tailored to your needs and often cost less than off-the-shelf options. We can help you choose the filter that will achieve optimal performance and minimize interference in your electronic systems.

Request a quote to get an estimate for the EMI filters most likely to meet your needs and exceed your expectations.
Why Are EMI Filters Important?
August 6, 2020 2:22 pm Leave a Comment
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?
June 4, 2020 2:23 pm Leave a Comment

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.

EMI Filters

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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.
Captor Corporation Receives Raytheon IDS Supplier Excellence Award
March 20, 2020 6:10 pm Leave a Comment
Raytheon’s Integrated Defense Systems business established the annual Supplier Excellence Awards program to recognize suppliers who have provided outstanding service and partnership in exceeding customer requirements. Award candidates are judged on certain criteria, including overall quality and on-time delivery. Captor Corporation was one of 86 companies recognized by Raytheon’s Integrated Defense Systems business for 4-Star honors.