Overview: High Frequency Electro-Magnetic Interference (EMI)

What is Electro-Magnetic Interference (EMI) Noise?

The number of electrical/electronic devices are growing continuously in every home / industrial environment. Electromagnetic disturbances emanating from one device may cause interference/malfunction to another electronic device in the same environment. These disturbances are commonly known as Electro- Magnetic Interference (EMI).


EMI can cause service interruption, data loss, permanent damage to equipment and failure when left uncontrolled. The stakes are even higher with medical and defence equipment.

What are the types of EMI Noise?

There are two main types of emissions — conducted EMI and radiated EMI. Conducted EMI passes through conductors such as wires or power lines. Radiated EMI travels through the air and does not require a conductor. However, both are equally damaging.

To meet legislation such as the EU Directive on EMC, in addition to other international regulations such as FCC, EMI filtering is now an essential element of equipment design.

The first and most effective option is to eliminate or minimise interference at the source itself. So that no external solutions need to be deployed. Reduce emission levels to acceptable limits. Alter the path of the emission from the identified source towards your equipment.

However, external solutions such as filters, shields, grounding are often deployed to minimise the impact of EMI on sensitive equipment.

What is Radio Frequency Interference (RFI)?

RFI refers to noise that falls in the Radio Frequency range within the entire electromagnetic frequency spectrum. Whereas EMI can refer to any frequency of electromagnetic noise. RFI is a subset of EMI and includes only electromagnetic currents with a frequency between 3 KHz and 300 GHz. RFI can also be conducted or radiated and can cause a variety of problems with electronic devices, just like any other EMI. Conducted RFI is most often found in the low frequency range of 3 kHz to 30MHz and radiated RFI in higher frequency ranges.

What are the causes of EMI?

  • Natural phenomenon : Lightning strikes, Solar flares and magnetic storms, Cosmic noise, Static electricity, Atmospheric electrical storms, Dust storms
  • Home environment : Cell phones, Laptops, Wi-Fi devices, Bluetooth devices, Microwave ovens, Home appliances
  • Industrial environment : Electric motors and generators, Telecom networks, TV transmission, Radio and Satellite, Power Grids, Medical Equipment, Defence installations

What are the Effects of EMI?

Annoying Effects: Momentary disturbance in Radio/TV transmission when the mixer or microwave is switched on.

Disturbing Effects: Unwanted reset in computers / digital equipment, Changes in status / settings, Excessive energy consumption.

Catastrophic Effects: Loss of data, Burnout of electronic components, Change of threshold settings, Improper / Unwarranted operations, Biological hazards and undesired output.

Differential Mode noise: EMI that appears on the two signal lines of a closed loop, but current flow is in opposite directions. High impedance EMI choke coils help to capture this unwanted noise and prevent it from being transmitted.

Common Mode noise: EMI that appears on the two signal lines simultaneously in the same direction and phase. The signal on each line returns through a common ground. Common mode EMI chokes help to capture this unwanted noise and prevent it from being transmitted and coupling back to ground.

How to Eliminate EMI?

  • Prevent EMI from the source equipment
  • Eliminate conducted emission using EMI filters
  • Block radiated emissions using shields and filters
  • Increase equipment immunity with layout changes and EMI filters
  • Apply grounding to divert the EMI to an alternate low impedance path
  • Minimise Harmonic distortion with harmonic filters

What EMISINDIA Offers?

EMISINDIA is a market leader and pioneer in EMI/EMC products and solutions . Apart from EMI filters and accompanying solutions from the EMISINDIA product catalog, Customer Specific EMI solutions are also delivered on request. High reliability, industry and military grade solutions provide compact and flexible solutions. Widely ranging interconnect options are supported for ease of integration into existing systems. Comprehensive Testing and consultancy services can also be availed to meet various industry and military standards.

EMI Filters for High Frequency Electromagnetic noise