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EMI Shielding Materials – An Overview
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EMI shielding materials protect against electromagnetic interference. Available in different types and forms, they range from conductive plastics to foils and fabrics. The key to selecting the best EMI shielding material is by understanding how each is used, which is what this article will discuss. Get to know the types of materials available and what they mean when it comes to EMI shielding.
What is EMI Shielding?
EMI shielding means the protection of sensitive electronic equipment from unwanted electromagnetic interference, usually by the use of a shield made from a conductive material. EM means electromagnetic and describes the fields electrical energy sources generate.
Interference is the unwanted signal that arises from these fields, and that can degrade electrical or electronic systems and devices, normally by introducing noise into the signals. An EMI shield is the physical barrier that blocks — or reduces — the effects of electromagnetic interference.
Electromagnetic interference shielding involves the use of different materials to reflect, absorb, or dissipate the electromagnetic waves that may be present in an environment. These include EM waves from sources such as electric motors, cell phones, computers, and radio transmitters.
Read more about these EMI shielding materials in the next section. In addition, we’ll also be discussing material selection based on type of application and usage environment.
EMI Shielding Materials
EMI shielding materials are conductive and/or magnetic materials that reduce the electric or magnetic fields that can cause interference. The most common types of materials are metals, conductive plastics, and metal-embedded fabrics.
Often times, an EMI shield is a metal enclosure made silver (mostly as coatings or alloy components), copper, aluminum, or various types of steel. Iron nickel alloys are the most used EMI shielding materials. These include perm-alloy and mu-metal.
Often times, carbon fillers (carbon fibers, graphene, graphite) are used to produce electromagnetic interference shields, and commonly embedded in cement, ceramic, and plastic shields. The different types of materials for electromagnetic interference shielding are discussed below.
EMI Shielding Foil
EMI shielding tape or foil is made from thin layers of metal. This type of EMI shielding material offers several advantages: you can install it on any surface, plus it’s lightweight and flexible. Most importantly, you can use it to cover different device sizes, as it can be cut to shape.
EMI shielding materials for foil or tape include aluminum, copper, and silver. Silver offers the best shielding performance. However, it’s also the most expensive one. Copper and aluminum are great options when budget is a factor to consider.
EMI copper foil shielding tape provides better electrical conductivity than aluminum but costs more. On the other hand, aluminum foil EMI shielding offers the advantage of being lightweight and easy to use.
EMI Shielding Coating
An EMI shielding coating is a thin, protective layer that adheres to a device or component. These are also typically applied to plastic enclosures that do not have the necessary conductivity to provide a shield against electromagnetic interference.
The most commonly used materials for EMI shielding coatings are aluminum, copper and silver. Each of these provides different levels of EMI protection, so it’s important to choose the right one for your application.
EMI Shielding Plastics
Intrinsically conductive plastics are another popular choice for EMI shielding materials. These are plastics that have built-in conductivity, so they don’t need to be coated with metal in order to create an effective shield. They offer an alternative that is lightweight and cost-effective.
EMI shielding plastics sometimes have their properties modified, usually by doping, to increase their conductivity. These materials have good mechanical properties and can be used in a variety of applications including cables and enclosures.
EMI Shielding Silicone
Silicone is a non-conductive material that can be used as an EMI shielding material. However, for it to become conductive, it must be combined with metal particles. The combination of these two materials forms a composite that can provide an effective shield against EMI.
The advantage of EMI shielding silicone is that, in addition to being flexible, the material also offers a good level of waterproofing. This makes it great for use in outdoor applications or areas where moisture is present.
Silicone EMI shields are also tolerant to temperature fluctuations, and ideal for medical and aerospace applications.
EMI Shielding Foam
The range of EMI shielding materials also includes foam. This is typically carbon foam, which can either be graphite or non-graphite. This type of foam is lightweight, can be compressed and re-expanded, and offers good thermal insulation.
Foam EMI shields perform well in tough environmental conditions, as it does not corrode even in high humidity or other corrosive atmospheres. Also, foam is an ecologically friendly solution, as it contains no heavy metals.
EMI Shielding Fabric
Fabric shields are another popular EMI shielding material. Made from metal-woven fabrics or textiles, these are available as nylon and polyester. When used to cover a device, they offer the advantage of flexibility, as they can be tailored to fit different shapes and sizes.
EMI shielding fabrics do not offer one of the most effective shields, as the metal wire in the fabric can be stretched and loosened. This means that there will always be some gap between the shield and device, allowing EMI to pass through. Still, fabric shielding is useful when only a low-level protection is needed.
Best EMI Shielding Material
The best EMI shielding material must satisfy these three key criteria: it must be effective, economical for the application, and easy to install or use. For some applications such as cable protection, EMI shielding foil will work well.
For most applications that require a metal enclosure copper, iron-nickel alloy, and aluminum EMI shielding will work best, given the materials’ good conductivity and cost effectiveness when compared to silver.
For more demanding applications, such as those that require lightweight materials and waterproofing or need to operate in extreme conditions, silicone EMI shielding or foam may be better suited.
Whatever the application is, material selection should always be based on the environment in which your device will operate. This will help determine the requirements for material characteristics, and the most appropriate type of EMI shielding material for the job.
Conclusion
These are some of the most popular EMI shielding materials in use today. Some offer better shielding characteristics than others, while some are used for their other properties such as flexibility and/or light weight. When choosing the right EMI shielding material for a particular application, you will need to consider factors such as cost, performance, and environmental conditions.