In order to study the attenuation performance of certain EMI noise suppression materials in complex electronic systems, the best way is through some actual measurement and characterization methods. It is very meaningful to evaluate absorbing patches with different electromagnetic performances by measuring the absorption capacity of materials through experimental settings.
In this article, we will introduce several test methods used to characterize the internal and external characteristics of absorbing materials. These characterization methods focus on the problems of transmission line, cavity resonance and magnetic decoupling. We will show the readers these test settings and test results to assist you in deciding which materials can provide the best performance in actual applications.
The first introduction is the microstrip transmission line method.
This technology is used to measure the performance of flexible absorbers when transmission lines are involved in the system. In this way, patches of different material composition or thickness will be measured to obtain the maximum transmission attenuation in a specific application.
These problems will appear in high-frequency data lines, where the digital signal switching from MHz to GHz will generate conducted noise on the data line. An interesting way to solve this problem is to place a piece of absorbing material above the data line, as shown in Figure 3. This will form a low-pass filter to absorb or attenuate high-frequency conducted noise.
A test device built on a microstrip line is used to measure the attenuation of conducted noise after the introduction of absorbing materials into the PCB or noise path. This microstrip line method is used as a section of transmission line, and the measured noise signal will be used to measure the absorption capacity of the sample. This set of test equipment simulates the noise source inside the electronic circuit, so the absorption of the transmitted signal can be determined.
The fabricated microstrip line includes a PCB board and a microstrip etched on it, with SMA interfaces connected at both ends. The base material of the microstrip line is PTFE (length 100mm, width 50mm, thickness 1.6mm), the circuit is copper conductor (length 54.4mm, width 4.4mm, thickness 0.018mm), and the bottom copper floor (length 100mm, width 50mm, Thickness 0.018mm). Two SMA connectors are respectively connected to the microstrip line through through holes at both ends.
By comparing the power of the transmission line before and after placing the absorbing material on the device, we can get the absorption rate of the material. In order to carry out this experiment, the coaxial cable connected to the vector network was connected to each SMA interface separately. Set the two ends as signal source and signal receiver respectively, and start the test test by measuring the S21 parameters.
The coaxial test method provides a means to study the problem of suppressing EMI noise in a resonant cavity. When electronic circuits are placed in metal enclosed spaces, cavity resonance problems are usually encountered. A noisy circuit will resonate in a confined space, causing interference and even system failure.
After measuring the absorbing materials of different compositions and thicknesses, we can further select the patch that can filter the cavity resonance frequency best. In this type of application, the patch is placed under the metal cover to absorb electromagnetic noise, as shown in Figure 6. The usual way to reduce this type of noise is to place the absorbing material inside the enclosed space to reduce internal reflections.
In order to characterize the absorptive capacity of absorbing materials of different materials or thicknesses, we need to repeatedly attach different absorbing materials to the reflecting surface and compare the results. The evaluation of the material in this setting is obtained by measuring the reflection coefficient (S11) and comparing it with the case when the absorbing material is not included.
Summary of Using Absorbing Materials to Reduce EMI Noise
Flexible absorbing patches can solve a variety of EMI problems in different applications. By characterizing the performance of absorbing patches, these patches can be used to reduce the conduction noise interference of data lines, the failure of electronic circuit boards due to cavity resonance in metal enclosed areas, and the same line or similar lines EMI problems between components, etc.
Absorbent materials have many advantages in controlling EMI problems, and they have been proved by comparative absorption in experiments. For this reason, such materials can provide innovative and straightforward solutions without the need to redesign the circuit.