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Reducing EMI with Flex Suppressor Sheets

Our friend at Kemet - James C Lewis, the Technical Marketing Director is looking at how to reduce EMI with Flex Suppressor sheets.

Introduction: Radiated vs. Conducted Emission

When solving electromagnetic suppression issues, there are two approaches. One is to reduce the amount of energy radiated by the system or eliminate it from the conducting path. In cases where a design is complete and modifications can’t be made, damping radiated emissions may be the only option.

A very common example of radiated suppression involve the EMI Cores you find on power or USB cables. These help to reduce relatively low frequency EMI (kilohertz to hundreds of megahertz) typical to these applications.  As frequencies of signals increase to the gigahertz range and connections are only found as traces, not wires, the need for a highly responsive material becomes even more important. Flex Suppressors® are ideal for these higher performance applications.


Flex Suppressor Overview

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A Flex Suppressor sheet is composed of magnetic powder that is suspended in a flexible polymer material.  This magnetic powder is a proprietary mixture made primarily of iron and silicon. The iron flakes are so thin that eddy currents are not able to form on the skin, causing the electromagnetic field to collapse. Because the metallic flakes are separated from each, the overall sheet is non-conductive.  This means it can be placed directly on ICs without fear of causing shorts between pins or from nearby metal shields.

Depending on the amount of permeability needed, the material is available in several thicknesses. The thicker the material used, the higher the permeability. There is a non-linear relationship between thickness and permeability. If the thickness is decreased by 50%, the permeability of the material is increased by approximately four times. 

Because there are many factors involved in determining the material thickness needed, many customers choose trial and error to find the right amount. It is common to take the 1 mm sheet, measure EMI, and add additional layers if needed. This helps to determine the right thickness for your situation.

An adhesive backing is available to make it easier to attach to an IC, circuit board or enclosure. 

Flex Suppressor Series Comparison

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Figure 1: Permeability Graph


The graph in Figure 1 shows the inductance (µ`) and magnetic impedance (µ``) of the different types of Flex Suppressor material available. When trying to reduce noise in a certain frequency range, µ`` is the key parameter. The EFG Series has a relatively low permeability below 1 GHz. However, at 3 GHz, it provides the highest amount of suppression. With its peak around 3 GHz, the EFG is ideal for applications that need to desensitize components to a nearby WiFi and Bluetooth radio.

If your application requires the Flex Suppressor to be attached before the board goes through the reflow oven, consider the EFH Series. It can withstand reflow temperatures, but has mid-range noise suppression compared to the other series.

The EFF Series is the highest permeability material available and represents the latest developments in the Flex Suppressor product line.
All Flex Suppressor sheets available from KEMET are halogen and lead free.

 

Part Number Type Fixing Method Thickness Article no
EFA(003)-240X240T0800 EFA - Flame Retardant & Red Phosphorous Free Self-Adhesive 0.03mm 811-9149
EFA(005)-240X240T0800 EFA - Flame Retardant & Red Phosphorous Free Self-Adhesive 0.05mm 811-9143
EFA(01)-240X240T0800 EFA - Flame Retardant & Red Phosphorous Free Self-Adhesive 0.1mm 811-9152
EFA(02)-240X240T0800 EFA - Flame Retardant & Red Phosphorous Free Self-Adhesive 0.2mm 811-9159
EFA(03)-240X240T0800 EFA - Flame Retardant & Red Phosphorous Free Self-Adhesive 0.3mm 811-9161
EFF(007)-240X240T0800 EFF - Extra High Magnetic Permeability Self-Adhesive 0.07mm 811-9165
EFF(01)-240X240T0800 EFF - Extra High Magnetic Permeability Self-Adhesive 0.1mm 811-9174
EFF(02)-240X240T0800 EFF - Extra High Magnetic Permeability Self-Adhesive 0.2mm 811-9171
EFF(03)-240X240T0800 EFF - Extra High Magnetic Permeability Self-Adhesive 0.3mm 811-9183
EFG(005)-240X240T0800 EFG - High Frequency Self-Adhesive 0.05mm 811-9187
EFG(01)-240X240T0800 EFG - High Frequency Self-Adhesive 0.1mm 811-9196
EFG(02)-240X240T0800 EFG - High Frequency Self-Adhesive 0.2mm 811-9193
EFG(03)-240X240T0800 EFG - High Frequency Self-Adhesive 0.3mm 811-9206
EFH(005)-240x240T2200 EFH - High Temperature Self-Adhesive 0.05mm 811-9200
EFH(01)-240x240T2200 EFH - High Temperature Self-Adhesive 0.1mm 811-9219
EFR(005)-240X240T0800 EFR - Standard Specification Self-Adhesive 0.05mm 811-9212
EFR(01)-240X240T0800 EFR - Standard Specification Self-Adhesive 0.1mm 811-9216
EFR(02)-240X240T0800 EFR - Standard Specification Self-Adhesive 0.2mm 811-9228
EFR(03)-240X240T0800 EFR - Standard Specification Self-Adhesive 0.3mm 811-9231
EFR(05)-240X240T1500 EFR - Standard Specification Self-Adhesive 0.5mm 811-9238
EFR(10)-240X240T1500 EFR - Standard Specification Self-Adhesive 1mm 811-9240
EFX(005)-240X240T0800 EFX - High Magnetic Permeability Self-Adhesive 0.05mm 811-9244
EFX(01)-240X240T0800 EFX - High Magnetic Permeability Self-Adhesive 0.1mm 811-9253
EFX(02)-240X240T0800 EFX - High Magnetic Permeability Self-Adhesive 0.2mm 811-9250
EFX(03)-240X240T0800 EFX - High Magnetic Permeability Self-Adhesive 0.3mm 811-9262
EFX(05)-240X240T1500 EFX - High Magnetic Permeability Self-Adhesive 0.5mm 811-9275
EFA(02)-240X240 EFA - Flame Retardant & Red Phosphorous Free Tape 0.2mm 811-9155
EFA(03)-240X240 EFA - Flame Retardant & Red Phosphorous Free Tape 0.3mm 811-9168
EFF(02)-240X240 EFF - Extra High Magnetic Permeability Tape 0.2mm 811-9177
EFF(03)-240X240 EFF - Extra High Magnetic Permeability Tape 0.3mm 811-9180
EFG(02)-240X240 EFG - High Frequency Tape 0.2mm 811-9199
EFG(03)-240X240 EFG - High Frequency Tape 0.3mm 811-9203
EFR(02)-240X240 EFR - Standard Specification Tape 0.2mm 811-9225
EFR(03)-240X240 EFR - Standard Specification Tape 0.3mm 811-9222
EFR(05)-240X240 EFR - Standard Specification Tape 0.5mm 811-9234
EFR(10)-240X240 EFR - Standard Specification Tape 1mm 811-9247
EFX(02)-240X240 EFX - High Magnetic Permeability Tape 0.2mm 811-9256
EFX(03)-240X240 EFX - High Magnetic Permeability Tape 0.3mm 811-9269
EFX(05)-240X240 EFX - High Magnetic Permeability Tape 0.5mm 811-9266

Flex Suppressor® is a registered trademark of NEC TOKIN Corporation.

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27 Oct 2014, 14:28