Almost all electronic devices produce electromagnetic waves — a common form of radiation that travels through the air. These waves play a critical role in helping devices communicate, such as cellphones and other devices that produce a wireless signal.
When the electromagnetic waves produced by one device interfere with the normal operation of another device, it’s referred to as electromagnetic interference (EMI).
A wide range of electronic devices can produce EMI, including intentional radiators (devices that are designed to emit radio frequency energy, such as phones or Wi-Fi routers) and unintentional radiators (devices that emit radio frequency energy as a byproduct of their operation).
To prevent EMI from affecting the function of devices, manufacturers use EMI shielding to block electromagnetic emissions from entering or exiting a device.
Shielding is made using a variety of materials, including metals such as steel, aluminum, copper and others. Some forms of shielding use non-metal materials, including silicone shielding, to cut emissions in devices that may not be able to house a typical metal enclosure.
Below, we’ve explained what electromagnetic interference is, as well as how shielding is used to reduce EMI and improve electromagnetic compatibility (EMC).
We’ve also discussed the most common materials used to create EMI shielding, along with key benefits of each material.
For more help with electromagnetic compatibility, including EMC lab testing and compliance for FCC Part 15 and other regulations, contact us online or call us at 866-540-5287.
What Causes EMI?
EMI is any type of interference or noise that affects an electronic device. It has several causes, ranging from emissions produced by phones, radios, Wi-Fi routers and other electronic devices to lightning, solar flares and other weather events.
The most common man-made causes of EMI are electronic devices, TV and radio signals, and power lines. These can produce electromagnetic fields, either unintentionally or for radio wave communication, that may affect other devices and cause interference.
Common natural sources of electromagnetic interference include lightning, which can produce conducted emissions and radiated emissions, and solar flares, which can produce a significant amount of electromagnetic radiation that may temporarily affect electronics.
Our full guide to the causes of electromagnetic interference goes into more detail about things that can cause EMI, including consumer devices, industrial equipment and weather.
How Does EMI Shielding Work?
Electromagnetic interference shielding is a technique that’s used to protect electronic devices from interference. The basic principle behind shielding is to create a barrier, like a real shield, that either reflects or absorbs electromagnetic waves before they can affect a device.
This barrier approach means that electromagnetic waves are blocked before they can affect a device’s sensitive internal components.
The most common form of EMI shielding is reflection. This process involves using a conductive material, such as certain types of metal, to cancel out and reflect electromagnetic energy just as it comes into contact with a device.
When an electromagnetic wave comes into contact with a conductive surface, the electrical field part of the wave can induce currents on the surface of the material.
These currents generate an electromagnetic field in the opposite direction to the incoming wave, effectively canceling it out and reflecting it away from the device.
Another method of EMI shielding is absorption. Some materials can absorb the electromagnetic waves produced by electronic devices. For example, some magnetic materials can absorb EMI and dissipate it as heat.
Absorption is typically used to provide protection against magnetic fields, which aren’t as easy to reflect as electric fields.
A third method of electromagnetic interference shielding is grounding. Grounding makes a path for any absorbed or reflected electromagnetic waves, allowing them to dissipate safely into the Earth and reducing the potential for interference within the device.
Common EMI Shielding Materials
A variety of materials are used for electromagnetic interference shielding. The most common shielding materials are metals, such as steel, aluminum and copper. Other materials used for shielding include silicone and carbon foam.
You can find more information about the most common materials for electromagnetic shielding below.
Pre-Tin Plated Steel
Pre-tin plated steel is a type of steel that’s coated with a thin layer of tin. This coating process increases the steel’s conductivity, allowing it to reflect and absorb electromagnetic waves from other devices. It also enhances the steel’s corrosion resistance.
Because of its conductivity, corrosion resistance and affordable cost, pre-tin plated steel is an economical form of shielding that’s widely used in electronic devices. You can find this type of steel in the housings of electronic devices that require a mix of durability and shielding.
Aluminum
Aluminum is a lightweight, highly conductive material. As such, it’s one of the most widely used metals for EMI shielding. It’s particularly effective for shielding as it can both reflect and absorb electromagnetic waves, allowing it to provide significant protection.
Because of its high conductivity-to-weight ratio and the ease at which it can be manufactured in complex shapes, aluminum is frequently used as a shielding metal in consumer electronics and aerospace applications.
Copper
Copper has the second-highest level of electrical conductivity of any metal, behind silver. Due to its conductivity, it’s often used in the form of sheets, foils and meshes to absorb electromagnetic waves and convert them to heat, reducing the effects of emissions on a device.
Despite its advantages, copper is more expensive than other shielding materials, such as pre-tin plated steel and aluminum. This cost factor means designers and engineers may consider other materials before using copper for internal shielding.
Copper Alloy 770
Copper alloy 770, or nickel silver, is a copper alloy with nickel and zinc. This metal offers a mix of conductivity and corrosion resistance. It’s less conductive than pure copper, but provides an adequate level of shielding against EMI due to its absorption and reflection qualities.
Due to its nickel content, copper alloy 770 has a silver-like appearance that makes it useful for visible components that need an aesthetic appeal in addition to EMI shielding. This material is often used for connectors, enclosures and other visible components.
Film, Tape & Foil Shielding
Film, tape and foil shielding materials are typically used in applications where space constraints and flexibility are critical. These materials, which are usually made from metals like aluminum or copper, are applied as thin layers to surfaces or components that require EMI shielding.
The metallic nature of film, tape and foil shielding allows it to reflect and absorb electromagnetic waves, effectively preventing interference. Furthermore, because these materials are light, they can be used to wrap cables, irregular shaped components and other surfaces without adding a significant amount of weight to a device.
Silicone Shielding
Silicone is not a conductive material. However, its flexibility means it can be molded into a wide range of shapes. When silicone is embedded with conductive metals, it offers good shielding in an inexpensive, durable form that’s suitable for a wide range of devices.
Silicone shielding is typically used in devices that require both electromagnetic shielding and a high degree of environmental sealing. For example, silicone’s ability to tolerate a wide range of temperatures makes it an ideal shielding material for use in aerospace applications.
Carbon Foam Shielding
Carbon foam is a lightweight foam that’s infused with carbon. It has a low density and a large surface area, making it effective for both thermal management and reducing electromagnetic interference.
This type of foam is available in graphitic and non-graphitic forms. One of the key advantages offered by foam is its flexibility. Thanks to its light weight, its flexibility and its resistance to rust and corrosion, foam is often used in panels, inserts and a wide range of electronic devices.
EMI Shielding Fabric
Finally, some devices use fabric for electromagnetic shielding. EMI shielding fabric is typically made from polyester or nylon, with small amounts of conductive metal interwoven in the fabric to provide optimal protection from interference.
Fabric only offers a mild degree of shielding against electromagnetic interference, but is often enough to provide adequate protection for electronic devices. Due to the metal content of this type of shielding material, it may suffer from corrosion over time.
Contact Us About EMC Testing & Compliance
A wide range of materials are used for electromagnetic interference shielding, from common metals like aluminum, pre-tin plated steel and copper to alternative materials such as silicone and carbon foam.
If your device exceeds the emissions limits stated in FCC Part 15 or similar regulations, or is strongly affected by emissions from other devices, adding shielding can help you bring it to a compliant level and successfully complete lab testing.
As an ANSI-accredited testing lab, our team can test your device and help you achieve FCC, CE and other forms of regulatory compliance. We can also help you accurately assess your device’s performance and, if needed, take steps to improve its EMI shielding.
To request a free quote for testing and compliance for your device, or to ask our engineering team your questions about electromagnetic compatibility, contact us online or call us at 866-540-5287.
