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

In our previous post, we introduced flexible absorber sheets as an effective solution for reducing electromagnetic interference (EMI) noise. Ready to learn more? Great — let’s dive deeper.

In order to study the attenuation of a certain EMI noise suppression material in more complex electronic systems, it’s usually better to obtain real results through some experimental characterization techniques. It is more interesting to measure the absorbing capacity through experimental setups that make it possible to evaluate the material performance of several sheets that demonstrate different behavior.

In this post, we’ll describe several experimental tests that can be used to characterize absorber materials based upon internal and external properties.

The characterization techniques described simulate specific problems focused on transmission lines, cavity resonance, and magnetic decoupling. We’ll show you these setups and experimental results to help you determine which material provides the best performance for reducing electromagnetic noise problems depending on your application.

Microstrip Line Method

First up: the microstrip line method.

This technique makes it possible to evaluate the performance of the flexible absorber sheets in systems with transmission line issues through an experimental procedure. In this way, several sheets with different composition or thickness can be tested in order to obtain the maximum transmission attenuation power ratio in a specific application.

These problems can appear in high-frequency data buses where digital signals switch in the frequency range of MHz or GHz that can produce conducted noise on the data lines. An interesting solution in this sort of application is to place an absorber sheet on the data bus, as shown in Figure 3. This acts as a low-pass filter absorbing or attenuating high-frequency conducted noise.

A method based on a microstrip line (MSL) test fixture is used to evaluate the attenuation of conducting current noise in a PCB or noise path when the noise suppression sheet is in place. Thus, the MSL is employed as a transmission line, whereby a noise signal will be measured to know the sample absorption ability. This test fixture simulates a noise source inside an electronic circuit, making it possible to determine the transmission absorption.

The manufactured MSL employed in this procedure consists of a PCB where the strip conductor is printed and two SMA type connectors are connected in both ends. The MSL is composed of polytetrafluoroethylene (PTFE) dielectric PCB material (length = 100 mm, width = 50 mm, thickness = 1.6 mm), a copper strip conductor (length = 54.4 mm, width = 4.4 mm, thickness = 0.018 mm), and a copper ground plane located in the bottom (length = 100 mm, width = 50 mm, thickness = 0.018 mm). The SMA connectors are installed on the opposite side of the MSL and are connected with the end of the MSL through two vias.

You can obtain the absorbing ratio by comparing the transmission line power ratio before and after installing the absorbing sheet on the test fixture. In order to carry out the measurements, each end of a network analyzer coaxial cable is connected to each SMA test fixture portsThe network analyzer has to be configured to operate as signal source and signal receiver through measuring the S21 parameters to start the measurement procedure.

In Appendix I of the ANP059 application note, you can find further data acquired of different materials with different thickness of the WE-FAS range. With this info, you’ll be able to evaluate the absorber materials performance according to their composition and thickness.

Coaxial Line Method

Coaxial line experimental method provides a means of studying the noise suppression capabilities of the material to solve resonant cavity EMI issues. Cavity resonance is a problem that can appear when an electronic circuit is placed inside a metal enclosure. Noisy circuits usually cause the resonance inside the enclosure, which may cause interference problems or even generate a system malfunction.

Considering this, after evaluating some absorber materials with several compositions and sheet thickness, it is possible to choose the sheet with the best performance to filter the resonant frequency. In this kind of application, a sheet is placed under the cover of the metal enclosure to absorb the electromagnetic noise as illustrated in Figure 6. A means of reducing these issues is to place an absorber sheet inside the enclosure to attenuate or suppress the resonance by reducing the internal reflections.

To evaluate this material in this kind of application, you can use an experimental measurement system based on a coaxial line. In this procedure, one terminal of the coaxial line is shorted with a metallic surface, and the reflected energy inside it is measured with a network analyzer.

In order to characterize the absorption capacity of different compositions and/or thicknesses, you must repeat the process of setting the absorber material attached over the reflector and compare the results. The evaluation of absorber materials in this experiment is carried out by measuring the reflection parameter (S11) with the reference value set as the coaxial line without the absorber material.

Next, the sample is placed between the reflection material and a reflective material before the measurement is made. By comparing reference and measured data, it is possible to study the performance of each sheet. The reflection attenuation measured with the experimental coaxial line method with 0.3 mm thickness.

Again, several WE-FAS with different materials and thicknesses have been tested in Appendix II of the ANP059 application note in order to evaluate the attenuation ability in each case.

Summary of Using Flexible Absorber Sheets to Reduce EMI

Taking everything into consideration, WE-FAS flexible absorber sheets can solve a variety of EMI problems in different kinds of applications. Absorber materials have been characterized in order to be employed in applications with data buses affected by conducted problems, electronic circuits located inside an enclosure with malfunctions due to cavity resonance and EMI between components placed in the same circuit or in close proximity to it.

Absorber sheets can provide several advantages in controlling EMI. This is confirmed with experimental techniques, which provide results in terms of attenuation ratio depending on the kind of problem — thus demonstrating the best option to use when solving a specific EMI problem. Furthermore, several thicknesses have been evaluated to demonstrate the performance of different products depending on the device space limits.

Because of this, these materials can provide an innovative, straightforward solution without the need to modify or redesign your electronic circuit or product.

We hope you learned more about flexible absorber sheets and how they can help reduce EMI in your design. For more information, check out our ANP059 application note.

Ready to see the benefits for yourself? View our WE-FAS EMI Flexible Absorber Sheet product family, and contact us for your free samples!

The overall wireless power transmission market is expected to be valued at USD 11.27 Billion by 2022, growing at a CAGR of 23.15%


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