How Flexible Absorber Sheets Solve EMI Problems: Properties + Materials [Part 1 of 2]

Have you experienced electromagnetic interference (EMI) noise issues in your applications? Join the club.

EMI is a growing problem for engineers, and conductive materials don’t always work as shielding. Fortunately, flexible absorber sheets can be used to help solve unwanted EMI problems in a variety of applications.

In this two-part blog series, learn why and how to use flexible absorber sheets to reduce EMI noise in your design!

Why Use Flexible Absorber Sheets for EMI Issues?

Electromagnetic interference (EMI) has become a serious problem, as it can occur anywhere in electronic circuits with unpredictable and detrimental effects. And it’s only getting more serious, thanks to factors like increases in device frequency, high integration in electronic systems, higher power densities, and reductions in PCB thickness and size.

The most common solution for electromagnetic noise problems is shielding the system with conductive materials, such as shielded enclosures, foil tape, or conductive gaskets. But this doesn’t work for all electronic devices. Many of them have parts that operate at high frequencies, causing complex EMI problems that cannot be removed with conductive shielding.

In order to avoid these issues, flexible absorber sheets (like our WE-FAS series, which is made of a polymer filled with ferrite powder material) can be used to suppress unwanted high-frequency EM components.

Flexible Absorber Sheet Properties

One of the most important parameters that describes the material’s ability to absorb direct and dissipated electromagnetic noise is represented by the part µ’’ of the complex permeability (µ). A material’s permeability is the result of molecular composition and structure and is defined as the complex permeability.

The real part quantifies the stored energy or inductive component, while the imaginary part quantifies the absorbed energy or absorption component:

µ r = µr'- jµr"

The behavior of these parameters depends on the material composition and frequency. Thus, it is very important to know in which frequency range noise levels exceed maximum permitted limits.

With this data, it is possible to establish a balance between reflection and magnetic losses depending on the application and the kind of electromagnetic noise. Figure 2 shows the complex permeability of several flexible absorber sheets of the WE-FAS series with different performance characteristics.

As permeability is frequency dependent, the correct material needs to be selected according to the frequency range where noise levels need to be suppressed. Standard specifications don’t give this information, as they state only general parameters, not absorption and reflection components.

Nevertheless, it can be difficult to estimate the absorber material performance, as it is the result of many variables in addition to the absorber permeability. These variables include sheet thickness, size, geometry, and the distance between the noise source and absorber material.

Thus, in basic systems, the attenuation of a certain electromagnetic noise suppression material cannot be estimated. However, in order to study the effect in more complex electronic systems, it is often better to obtain real results through some experimental characterization techniques.

In our next post, we’ll go over those experimental characterization techniques in detail.

In the meantime, you can learn more about flexible absorber sheets by reading our ANP059 application note or by viewing our WE-FAS EMI Flexible Absorber Sheet product family!

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