How Exactly EMI/RFI Shielding Manages Interference
Electromagnetic interference (EMI), also called radio-frequency interference (RFI), is a disturbance produced by an outside source that affects an electrical circuit due to electromagnetic induction, coupling or conduction.
EMI/RFI shielding is designed to protect electronic devices from malfunction by blocking unwanted external electromagnetic waves or preventing internal electromagnetic waves from emitting and interfering with other circuits or devices.
From pacemakers to cockpit sensors to microwaves, these precise applications all rely on EMI/RFI shielding to properly function.
This shielding must be the appropriate property, material and form to successfully alter the path of undesired electromagnetic waves and block them from entering or exiting the equipment.
Types of Mechanism in EMI/RFI Shielding
The shielding alters the path by absorbing or reflecting electromagnetic waves through conductive or ferromagnetic materials.
Electromagnetic waves are made up of two components: an electric component and a magnetic component. Both components travel at the same frequency and cannot exist without the other. Because of this, it is sufficient to protect one component.
There are different mechanisms involved to filter out each.
Reflection
This reduces the effect of the electric component of EMI/RFI shielding. In order to efficiently reflect, the material must have mobile charge carriers. This means the material must be conductive. The incoming electromagnetic wave interacts with the mobile charge carriers in the conductive shield. This causes the charges to flow and redistribute along the conductor creating an opposing electromagnetic field. The electromagnetic field generated by the recirculation of charges cancels out the external magnetic field. In this mechanism, the higher the conductivity of the material, the better is the shielding characteristics.
Absorption
This acts on the magnetic component of EMI/RFI shielding. In order to effectively absorb, the material must have electric and magnetic dipoles (a pair of equal and oppositely charged poles separated by distance). These are materials with a high dielectric constant and high magnetic permeability. An enclosure with this makeup absorbs the magnetic field lines by creating a pathway within itself.
Multiple Reflections
This is observed in composite materials with large interfacial areas or surfaces with porous structures. Shielding is achieved by having multiple reflecting boundaries for reverberating electromagnetic waves. This results in the scattering of the electromagnetic waves.
Types of EMI/RFI Shielding Materials
The two main properties when it comes to EMI/RFI shielding are: electrical conductivity and magnetic permeability.
Different materials demonstrate these properties in different ways and are selected based on the relative strengths of the electric and magnetic components in a given electromagnetic wave.
Materials that are suitable for enclosure construction will provide shielding against electrical fields through reflection, while materials with high permeability will provide shielding against magnetic fields through absorption.
Aluminum
Strong strength-to-weight ratio and nearly 60% conductivity.
Copper
Higher rate of conductivity, but effectively reduces both magnetic and electrical waves.
Beryllium Copper
High tensile strength with a high deflection range for electrical conductivity.
Nickel Silver
Strong magnetic permeability of 1.
300 & 400 Stainless Steel
Well-suited for applications that do not require high attenuation.
Other options include:
- Kovar
- Cold-rolled steel
- Phosphor Bronze
- Cupro Nickel
- Invar
- Brass
Types of EMI/RFI Shielding
Depending on the application, EMI/RFI shielding can take on various forms.
Solid Enclosures
Metallic cases that provide structural support to the unit and prevent electromagnetic waves from entering or exiting a particular system. This includes board level EMI shielding, which are available in one-piece or two-piece designs to provide six-sided protection.
Wire Mesh and Screens
Similar to solid enclosures, wire mesh and screens prevent electromagnetic waves from entering or exiting a particular system. They can be easily adapted to fit complex shapes and size, while also offering translucency for see-through enclosures and displays.
Gaskets and O-Rings
Applied to enclosure covers, doors or other sensitive areas, gaskets and o-rings are packed with metallic or metal-coated particles that ensure electrical conductivity.
Cable Shielding
Tapes or wire braids that cover the insulated conductor of a power or instrument cable. When used in a power cable, this prevents the creation of electromagnetic waves that can affect nearby electronic components. When used in instrument cabling, the main function is to prevent external electromagnetic waves from distorting the signal that flows through the cable.
EMI/RFI shielding is essential to reducing the intensity of unwanted electromagnetic interference in sensitive electronic devices.
At Switzer, we know each application is unique and requires specific properties, materials and form to ensure the proper function of your critical systems. It’s why we are committed to being a partner, not just a part provider. Our solutions-based approach offers an exceptional degree of control that creates exceedingly precise, highly functional EMI/RFI shielding components.
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