EMI Filters from Captor Corporation

EMI filters exist as separate or integrated devices in electrical and electronic equipment. In simplest terms, within such equipment, they act as low-pass filters for unwanted—generally high-frequency—current. They consist of passive electrical components—including inductors and capacitors—that, when assembled together, form a complete LC circuit. The inductor component allows low-frequency and DC currents to pass through uninhibited and blocks high-frequency current (i.e., the noise). Once blocked, the low impedance path provided by the capacitor component directs the noise back into the power supply or a grounded connection.

Since EMI filters are only capable of diverting conducted interference, the devices are often combined with shielding and insulation components to block radiated noise that travels through the air. Radiated interference is especially a concern when there is a significant length of conductor between the filter and the interference source. If there is only a short length of wire between the filter and the noise source, the EMI filter alone may suffice.

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?

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.

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.

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.

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.

EMI vs. EMC