EMI Shielding Materials in Electronics

Key Takeaways

• EMI shielding prevents unwanted electromagnetic waves from reaching electronic devices.

• The factors affecting the shielding effectiveness of metalized plastics are foil material, foil thickness, and grounding arrangement.

• EMI shielding foams are popular due to their light weight, reduced density, and high shielding effectiveness. 

EMI shielding materials either absorb or reflect EMI radiations

Electromagnetic interference (EMI) refers to the electromagnetic waves emitted by an electronic device that interfere with the device’s operation as well as disturb the workings of nearby devices. If not taken care of, EMI leads to device malfunction. To protect electronics from EMI, EMI shielding is commonly used.

In EMI shielding, electronic devices are guarded by enclosing them inside metal boxes. EMI shielding materials either absorb or reflect EMI radiations, ensuring the device is immune to EMI. EMI shielding also prevents emissions from devices. 

The Basic Principles of EMI Shielding

EMI shielding relies on the reflection and absorption of EMI radiation. This reflection results in EMI radiation bouncing off the surface of EMI shielding materials. However, sometimes this is not enough; reflections can be extremely harmful to humans, and in some cases, lead to death. Therefore, absorption of EMI radiation is much safer. To ensure safety, it is important to select the appropriate EMI shield—there are a variety of shielding materials, each with unique properties. 

EMI Shielding Materials

EMI shielding materials include metals, metalized plastics, foams, carbons, conductive polymers, ceramics, concrete, and some composite materials. Usually, EMI shielding materials are selected so that they can either reflect or absorb electromagnetic radiation. Manufacturability, availability, shielding effectiveness, absorption, and reflection properties are the main factors that determine which EMI shielding material is best for specific applications.

Next, we will take a look at three common EMI shielding materials. 

Metals

EMI shields made from metals can reflect, absorb, and transmit electromagnetic interference. The physical properties of thermal conductivity and electrical conductivity make metals the best candidate for EMI shielding material. Meal casings are used to protect electrical equipment from electrostatic charges. Grounded metal covers are used in electrical machines, as they dissipate heat and transfer the static charges to the ground. Metal enclosures also prevent EMI from escaping the shield and protect the device inside it from stray radiations.

The list  below gives commonly used EMI shielding metals:

Plastic Materials

Metalized plastic is a new trend for EMI shielding. The embedded thin metal foils of aluminum, copper, or silver used with polymers can be connected to the ground. The factors affecting the shielding effectiveness of metalized plastics are foil material, foil thickness, and grounding arrangement. The electrical conductivity of the plastic in EMI shielding can be increased with the following: 

1. Conductive fillers
2. Intrinsically conductive polymers
3. Conductive coating on plastics

EMI Shielding Foams

EMI shielding foams are popular due to their light weight, reduced density, and high shielding effectiveness. There are various types of foams available, such as polymer-based composite foams, carbon foams, syntactic foams, and carbon nanotubes (CNTs)/graphene foams.

The design of EMI shielding is complex due to factors such as geometry, clearance requirement, and obstacles. Luckily, Cadence software offers 3D tools that aid in the design of EMI shields. 

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