Figure: EMI Suppression SheetElectromagnetic interference (EMI) is the electromagnetic noise signals that can be emitted from electrical and electronic devices during their normal operation and can interfere with the operation of other nearby devices. 

EMI suppression sheets are thin, flexible electromagnetic wave absorber sheets designed to reduce or suppress EMI or radiated noise in electronic devices and circuits. These sheets can be directly applied to parts/components (e.g., ICs, processors, traces, or cables) that act as sources of EMI.  

By suppressing electromagnetic noise in electronic devices, EMI suppression sheets improve the device's electromagnetic compatibility (EMC) performance and help manufacturers comply with EMC standard requirements. In addition to EMI suppression, they are used in various other applications, such as blocking undesired magnetic coupling in wireless power chargers, avoiding cavity resonances, preventing electrostatic discharge (ESD), and more.

Figure2: EMI Suppression Sheet ApplicationsEMI suppression sheets can be made of different materials and constructions. These sheets are typically composed of a polymer matrix filled with magnetic materials, e.g., polymers infused with ferrite powder, polymeric resin mixed with magnetic metal flake fillers, or synthetic rubber blended with magnetic metal flake fillers. The sheet may utilize other construction designs, including:

• Nanocrystalline EMI Suppressor Sheet (consists of high-performance nanocrystalline soft magnetic material)
• Flexible sintered ferrite sheet (consists of pre-cracked thin ferrite plates placed between a layer of adhesive tape and a PET cover layer).

 These sheets reduce or suppress EMI by absorbing incident electromagnetic wave energy and converting it into heat through magnetic losses in the material. They are supplied with an adhesive film for easy application and are available in the form of sheets or rolls. The sheets can be conveniently cut to size using scissors to fit specific components or areas.

Key features and advantages of EMI suppression sheets:       

• Flexible and easy to handle
• High Permeability
• Provide effective EMI suppression over the wide frequency range, e.g., 1MHz up to 6GHz, 1 MHz to 18 GHz
• Help to change the magnetic flux path to avoid interference with surrounding cables or other components
• Help to reduce the eddy current when the magnetic flux is close to the metal
• High surface resistance 
• Prevents resonance effectively
• The sheets can be customizable in any shape, size, and/or thickness.

EMI suppression sheets Applications:

Figure: EMI suppression sheets application in wireless power chargers

• Can be attached on ICs, processors, controllers, databus, and cables to reduce EMI
• Blocks undesired magnetic coupling in wireless power chargers
• Suppresses cross-talk between substrates
• SAR reduction
• EMC shielding
• Prevents cavity resonances
• Prevents Electro Static Discharge (ESD)
• Suppresses radiated noise in mobile phones, notebook PCs, wireless LANs, wearable devices, set-top boxes, car audio and video systems, Optical reception modules, Scanners, HDDs, and many more.
• Enhances Near-field communication (NFC) performance
• Can be used to change the magnetic flux path,   preventing the magnetic flux from affecting other components.
• EMI-shielding box / black box
• Between printed circuit boards.