What exactly is EMI Shielding?
Any method used to protect a sensitive signal from external electromagnetic signals, or to prevent a stronger signal from leaking out and interfering with surrounding electronics, is referred to as EMI shielding. It can refer to PCB elements such as IC chips and active components, as well as connectors and cables that connect PCBs.
EMI is an abbreviation for ElectroMagnetic Interference, which means that a circuit has been designed to prevent disruption through shielding. Electromagnetic frequencies can affect many sensitive electronics, causing everything from a simple hiss on a communication line to the complete disruption of a safety-critical signal. As a result, it has an impact on a wide range of industries, including all consumer and industrial electronics, as well as critical systems for military and emergency services.
In a nutshell, here’s everything you need to know about EMI Shielding.
How does EMI Shielding function?
The primary goal of effective EMI shielding is to keep electromagnetic interference (EMI) or radio frequency interference (RFI) away from sensitive electronics. This is accomplished by employing a metallic screen to absorb electromagnetic interference transmitted through the air. The shielding effect is similar to that of a Faraday cage in that the metallic screen completely surrounds either the sensitive or transmitting electronics. The screen absorbs the transmitted signals and generates a current within the screen’s body. A ground connection, or virtual ground plane, absorbs this current.
The protected signal is kept clean of electromagnetic interference by absorbing these transmitted signals before they reach the sensitive circuitry, maximizing shielding effectiveness.
What materials are suitable for EMI shielding?
EMI shielding can be accomplished using a variety of techniques and materials, with the materials chosen depending on the type of electronics and frequencies involved. This is due to the fact that the amount of signal reduction/blocking depends on the material used, the size of the shielded volume, and the material thickness, all of which affect the range and strength of frequencies that can be absorbed by the shielding.
Here are a few examples:
- Shielding on PCBs typically consists of a PCB with a built-in ground plane and a metal box placed over the sensitive or transmitting elements. A Faraday cage arrangement is then used to completely encircle the components.
- An inner metallic casing would be used in devices such as audio speakers to successfully block EMI produced by nearby transmitting devices.
- Conductive paints and magnetic materials can also be used in environments with magnetic fields below 100 kHz. Sheet metal, metal foam, conductive plastics, and mesh metal screening are some other options.
Depending on the frequency, the shielding does not have to be a solid screen, but can simply be wire fencing with regular holes. It is therefore critical to understand which parts of the electromagnetic frequency spectrum must be avoided in any given application.
Examples of EMI Shielding Applications
Here are some examples of how EMI Shielding is used in a variety of applications.
EMI shielding is used to protect medical and laboratory equipment from signal interference, which is critical and potentially life-saving. AM/FM emergency service transmission and other telecommunications, data communications, theatre and ward patient monitoring equipment, and even in-body medical devices such as pacemakers are all examples of medical devices.
Data stored on RFID chips or embedded in other devices can be protected by EMI shielding.
EMI Shielding can be used in conjunction with air-gapped systems to supplement and increase existing security measures used in military, government, and financial systems.
Finally, shielding is required when any sensitive electronic element needs to be isolated from the surrounding electromagnetic fields, or when a specific element is transmitting unwanted additional signals. Every item must be considered for EMI/RFI protection in today’s technologically dependent environment.