Elastomerics Blog

EMI/RFI shielding prevents unwanted electromagnetic energy from interfering with electronics, electro-mechanical devices, and electrical equipment. Electromagnetic interference (EMI) spans the entire electromagnetic spectrum while radio frequency interference (RFI) is a subset of EMI that refers to interference in the radio frequency (RF) band. EMI and RFI shielding gaskets prevent unwanted energy from entering an enclosure, but they also contain internal emissions.

Stockwell Elastomerics supplies enclosure-level EMI/RFI shielding that also provides environmental sealing. These EMI gaskets fabricate consist of solid silicones that contain metal or metal-coated particles, or cellular silicones that are bonded to Monel wire. Silicone elastomers are inherently electrically insulating, but adding metal particles or wires makes them electrically conductive instead. Either silicone or fluorosilicone can be used as the base elastomer.

How Shielding Works and Why It Matters

EMI/RFI shielding works by blocking, absorbing, or redirecting electromagnetic energy, which travels in the form of waves. The effectiveness of an EMI/RFI shield depends on its electrical conductivity, magnetic permeability, material thickness, frequency range, and shield geometry. A shield must create a continuous conductive path around protected electronics because any seams, joints, or gaps could become leakage points.

EMI/RFI shielding is essential for maintaining electromagnetic compatibility (EMC), the ability to operate in an electromagnetic environment without causing or experiencing unacceptable levels of interference. Without proper shielding, systems may fail EMC testing, experience field failures, or interfere with other devices and equipment. Shielding keeps out external interference, but it also prevents internal circuitry from radiating electronic noise into the environment.

Electromagnetic Interference (EMI) vs. Radio Frequency Interference (RFI)

EMI interrupts, obstructs, degrades, or otherwise limits the effective performance of circuits. The “electromagnetic” refers to how electric current has electrical and magnetic forces and effects. The “interference” refers to how when an electromagnetic signal is transmitted, or propagated, that signal can be received by a circuit that is not the intended recipient. The sources of EMI are many and include, switching transients, and magnetic fields from motors.

Like EMI, RFI limits the effective performance of circuits and is propagated through conduction or radiation. However, RFI refers to interference in the RF band, typically 20 kHZ to 300 GHz. The sources of RFI include Wi-Fi, Bluetooth radios, radar systems, RF transmitters, switching power supplies that generate high-frequency harmonics, and digital electronics with fast edge rates. Like EMI, RFI can enter or exit tiny gaps in enclosures, such as between the sides and cover.

Conductive Silicones vs. Other EMI/RFI Shielding Materials

Electrically conductive silicones are not the only type of EMI/RFI shielding material. Other types of elastomers, such as EPDM, can be filled with metal or metal-coated particles; however, silicone has a wider temperature range and provides superior resistance to sunlight and ozone. Metal foils, metallized fabrics, metal alloys, and rigid shields are also used for EMI/RFI shielding. Metals have higher conductivity and reflectivity, but conductive silicones offer important advantages.

For example, conductive silicones are multi-functional materials that block EMI/RFI and keep out environmental contaminants such as dust and moisture. Unlike rigid metals, conductive silicones are also soft and elastic. This allows them to conform to uneven surfaces, fill gaps, and maintain a consistent seal even when there are tolerance variations between surfaces. Conductive silicone gaskets also require less pressure, or a lower clamping force, to create an effective seal.

Request a Free Silicone EMI Gasket Materials Touch Brochure 

Stockwell Elastomerics cuts and molds gaskets from EMI/RFI shielding materials that are sourced from supplier partners and are kept in stock or ordered on-demand. Request a free silicone EMI gasket materials touch brochure for samples, and contact Stockwell Elastomerics for help with material selection and gasket design assistance.