How Do EMI/RFI Shielding Materials Work?
In a world filled with electronic devices, the impact of electromagnetic interference (EMI) and radio frequency interference (RFI) is a large concern. EMI and RFI can, at best, only cause some products to malfunction, disrupting signals and impacting performance. At worst, the interference can cause damage to sensitive electronic components, causing complete failure in functionality.
To protect against the issues caused by EMI and RFI, manufacturers have turned to electrical insulation materials—from films and papers to EMI/RFI shielding tape. How do these materials work? Are they right for your application? From the basics of EMI and RFI to the specific types of materials available to you, we’ll cover everything you need to know about electrical insulation solutions in this post.
What is EMI/RFI?
Electromagnetic interference and radio frequency interference occur when a signal generated by an external source disrupts the signal of another. While the two terms are often used as synonyms, they actually refer to two different types of disruptions. EMI is generally a blanket term that refers to any interference caused by conducted currents or radiated electromagnetic fields, while RFI is a specific subset of EMI that generally refers to radiated signals. Essentially, all RFI disruptions are also EMI disruptions, but not all EMI disruptions can be considered RFI disruptions.
There are three components to EMI/RFI disruption: the source, the path, and the receiving device. All EMI and RFI disruptions are caused by a source (generally a circuit) that either conducts or radiates electromagnetic energy. This energy travels along paths. If that path leads the energy to another circuit or electrical component that is susceptible to electromagnetic energy (the receiving device), interference can occur.
EMI and RFI interference can have many negative effects on the device, including:
A jamming or distortion of signals received by communication devices
Power outages and fluctuations
Electrical fast transitions (EFT)
Complete failure of the electronic circuit
Damage to electronic systems
Shorter lifespans of electronics
Hindered performance of electronics
Electric shock and burns to the device or users
The potential for ignition of the source
How EMI/RFI Shielding Works
Since there really isn’t a good way to prevent a source from giving off conducted currents or radiated electromagnetic fields, the best way to prevent EMI/RFI interference from occurring is to block the pathway between the source and the receiving device.
This is known as EMI/RFI shielding.
EMI/RFI shielding materials act as a barrier that covers electronics to prevent electromagnetic interference. The materials act as a conductor, absorbing or reflecting EMI/RFI interference to protect whatever it’s surrounding. They shield components and circuits from electrical surges, preventing the components from arcing while also acting as an electrical and thermal barrier. The materials, when designed and implemented effectively, create protection similar to a faraday cage, which attracts positive charges and redistributes the electrons along the conductive materials.
Creating a Strong EMI/RFI Shield
Effective EMI/RFI shielding comes down to three major components:
The attenuation of the shield
The testing standards it passes
The materials used
Attenuation in EMI/RFI Shielding
EMI/RFI shielding is measured in attenuation, which calculates the loss of signal strength in networking cables or connections. Typically measured in decibels (dB), attenuation takes the measurement of how strong the interfering signal is before it comes into contact with the EMI/RFI shielding materials and its strength afterwards. A highly effective shield would attenuate up to 90 to 120 dB.
As a measurement, you can say that 10 dB of electromagnetic shielding provided by a material will reduce the strength of the signal wave by a factor of 10; 20 dB will reduce it by a factor of 100; 30 dB by 1000, and so on.
When designing an EMI/RFI shield for your application, consider the attenuation the material provides based on how strong the expected interference will be.
Testing Standards for EMI/RFI Shielding
Since EMI/RFI shielding is commonly used in medical, military, and aerospace applications, there are many standards that products must meet. These include:
ASTM D4935: used to measure the “Standard Test Method for Measuring the Electromagnetic Shielding Effectiveness of Planar Materials.”
MIL-DTL-83528: used by the U.S. Department of Defense (U.S. DoD) to measure “Detail Specification: Gasketing Material, Conductive, Shielding Gasket, Electronic, Elastomer, EMI/RFI General Specification.”
MIL-STD-461: another U.S. DoD standard targeted towards “Electromagnetic Interference/Electromagnetic Compatibility.”
MIL-STD-285: used to measure the “Attenuation Measurements for Enclosures, Electromagnetic Shielding, For Electronic Test Purposes.”
IEEE 299-2006: a more general standard used in “determining the effectiveness of electromagnetic shielding enclosures at frequencies from 9 kHz to 18 GHz (extendable to 50 Hz and 100 GHz, respectively) for enclosures having all dimension greater than or equal to 2.0 m.”
The Types of EMI/RFI Materials
At Engineered Materials, we work with a range of electrical insulation materials that are easy to die cut, fold, bend, and score to meet the exact needs of your application. Our materials also provide varying levels of heat and flame protection, durability, and other capabilities. Our material selection includes:
Fish Paper and Alternatives: also known as electrical grade vulcanized fiber. This material is a fibrous dielectric paper that is lightweight and easy to fabricate into shapes. It has a wide range of operating temperatures—it will not become brittle in low temps nor soften at high temps. It also has excellent tear resistance and strength. As an alternative, you can also use multi-ply, unbleached kraft pulp paper, which offers a greater tear strength, but lower tensile strength. Both materials have a high arc resistance and excellent dielectric properties.
Nomex: Aramid Fiber Paper: aramid paper is known for its inherent dielectric strength and its very high level of chemical and flame resistance (UL 94 VTM-0 and V0 flammability rating). This is one of the highest-level materials you can get for electrical insulation and thermal stability. With operating temperatures as high as 200°C, as well as tear and abrasion resistance, this is the material of choice for many industries.
Formex: this flame-retardant electrical insulation material is made from FR polypropylene, which gives it a high level of flame retardancy (UL 94V-0 flame class rating) and very low moisture absorption (<0.6%) capabilities. The material is also highly malleable, allowing it to be folded, bent, and scored without cracking during fabrication. There are multiple difference Formex materials to choose from, each offering their own benefits at varying gauges.
Electrical Insulation Films: from Mylar® to Kapton® and Teflon™, there are a variety of different electrical insulation films at your disposal, depending on the specific needs of your application. Mylar is a Polyethylene Terephthalate (PET) Film that offers a balance of chemical/thermal resistance and electrical resistance; Kapton is a Polyimide Film that is known for its performance across a wide range of temperatures; Teflon films are highly regarded for their thermal properties and their chemical and environmental resistance.
Copper Foil Tapes: on top of the EMI/RFI shielding, these tapes provide superior energy reflection and dissipation, sealing, and sound damping. They are highly suitable for high heat applications because of their excellent temperature resistance. They also offer high protection when used as a moisture barrier. These materials are common in the electronics industry and are often used for static charge draining, seaming shielded rooms, cable wrapping, and surface contact to non-solderable materials.