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Written by Amy Brown
on March 31, 2022

Electromagnetic Interference (EMI) is an electromagnetic emission that interferes with another electronic device. EMI can be from intentional or unintentional sources, continuous or intermittent, and at a single frequency or across a broad range of frequencies. EMI encompasses the entire electromagnetic spectrum but is most applicable to modern electronic devices over the frequency range of 10 kHz to 10 GHz.

Sources of EMI

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Unintentional EMI sources include switch-mode power supplies (SMPS), digital devices, brushed DC motors, high-voltage ignition systems, and fluorescent lighting. SMPS is the most common unintentional EMI source; since they are now used almost exclusively in LED light bulbs, digital devices, and battery chargers for cell phones and laptops.

Intentional EMI sources are most commonly radio frequency transmitters, whose emissions we often refer to as radio frequency interference (RFI). This includes AM radio, FM radio, television, cell phones, Wi-Fi, Bluetooth, and many other fixed and mobile radio communication systems used by aviation, emergency services, police, and the military.

Intermittent EMI includes transients that can cause catastrophic damage to electronics, including electrostatic discharge, lightning, inductive kickback, and electromagnetic pulse events (EMP).

Finding the Problem

EMI-Filters-variety-webIntegral to finding an EMI filtering solution to an EMC problem is the ability to test for electromagnetic compatibility (EMC) compliance. A wide range of EMC and environmental tests can help identify potential problems and recommend design solutions.

APITech's extensive in-house EMC test capabilities allow for a faster turnaround of your complete EMI filtering design solution. Some benefits of in-house testing:

  • Ambient-free in-house shielded anechoic chamber
  • NARTE certified engineering staff
  • Highly accurate computer-controlled instrumentation accumulates and presents data in multiple formats
  • Testing to military and international commercial regulations

An in-house, fully equipped EMC laboratory offers customers a flexible resource to assist product development by identifying and correcting EMI susceptibility and emission problems. APITech will evaluate and fine-tune installed EMI filter performance to find a solution for your unique requirements.

APITech's experienced engineering staff solve demanding EMC challenges. We can test your equipment, determine the state of compliance, and work with you to develop a viable solution. It is not uncommon for our clients to leave our lab with an EMI solution prototype in hand.

What is an EMI filter?

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EMI filter products mitigate EMI/RFI in the most rugged environments and reduce high-frequency electronic noise that may interfere with other devices. An EMI filter can be embedded into circuit boards or used within a device, such as a connector, reducing the amount of real estate required within a product enclosure.

APITech offers one of the largest and most trusted selections of EMI filter components and assembly solutions for EMC compliance, energy efficiency, and power management, addressing both conducted and radiated EMI. EMI filter solutions are ideal for mission-critical radar, military defense, EW, communication, industrial, medical, and energy platforms.

Types of EMI Filters

1. Planar Array Ceramic Capacitors: EMI filters are designed and manufactured in the USA with the largest offering of EMI filter capacitor sizes and configurations (cylindrical and rectangular geometries). Solid wall and embedded technologies for commercial and high-performance EMI filter applications.

Successful use cases include:

  • Implantable medical devices: Custom mini-discoidal and planar ceramic capacitors help prevent malfunctioning because of EMI.
  • Missile surveillance: Custom planar capacitors designed for high-reliability filter out EMI.

2. EMI Filter Connectors: EMI filter compact shell connectors are an effective EMI filter device, reducing the amount of real estate required within a product enclosure. Planar-style EMI filter capacitor arrays in C and Pi circuits deliver protection up to 200nF in most configurations, including transient protection.

Successful use cases include:

  • Aerospace mid-flight lightning protection: Transient survival connector engineered into the aircraft maintains the critical electronic equipment on board, increasing safety, system capacity, and overall efficiency.
  • Military airborne radios: EMI filtered circular connectors in aluminum and we employ electroless nickel to keep the signal clear and accurate for the warfighters.

3. EMI Filter D-Sub Connectors: Improve performance, save board space and reduce costs by managing EMI filter needs at the signal and power I/O. There is a wide range of capacitance, selectively loaded designs, and EMI filter connectors in industrial, aerospace, wireless telecom, and 5G test applications.

EMI Filters MRI-webSuccessful use cases include:

  • UAV RF communications signal translators: Rugged constructed micro-D EMI filter connectors, designed and built to MIL-DTL-83513, used to filter low rate signal line for the engine and flight control system.
  • Medical imaging equipment, including MRI, X-ray, ultrasound, and CT machines: High-performance d-sub connectors are used to filter the signal lines that send data from the machine to the monitoring device.

4. Panel Mount EMI Filters: Bulkhead /panel-mount EMI filters provide superior high-frequency insertion loss, built in accordance with MIL-PRF-15733 or MIL-PRF-28861. APITech offers the most-available QPL designs in the industry and the largest selection of mechanical and electrical configurations for versatility and ease of design.

Successful use cases include:

  • Digital instruments, such as industrial flow meters: Resin-sealed EMI filters eliminate interference problems and enable a consistent line of efficient and accurate measurement solutions.
  • Traffic alert collision avoidance systems (TCAS): In these systems, wiring can inadvertently act as an antenna. Hermetically sealed EMI filters are used to eliminate this noise and filter it to ground to ensure the system functions properly.

5. EMI Filters, Transformers & Inductors: EMI filters for single-phase, 3-phase, or DC power applications filter the AC or DC power entering your system with designs to meet MILSTD-461 and HEMP requirement MIL-STD-188-125. Specializing in custom magnetic components, including current sense transformers, APITech produces high-quality magnetics to meet the industry’s most stringent requirements.

EMI Filters 12-MMB-webSuccessful use cases include:

  • Command-and-control systems: Hazardous transient conditions can affect these systems, including an electromagnetic pulse (EMP) and high-altitude electromagnetic effects (HEMP). APITech EMP/HEMP filters are used in the network enclosure assembly to protect the internal systems.
  • Power lines and industrial measuring instruments: Dual-stage power line EMI filters have excellent attenuation for high-voltage impulses to suppress conducted interference.

    If you need help with resolving your EMI challenges, please contact amy.brown@apitech.com

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