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How to compare the performance test of EMI and RF absorbing materials

Author:admin   AddTime:2021-05-14

With the increasing number of radiated electromagnetic interference (EMI) specifications that engineers need to follow, various types of EMI absorbing materials have begun to appear on the market. Generally speaking, these absorbing materials provided on the market are very thin and have good shape flexibility. Coupled with the design of the adhesive on the back, we can easily apply these absorbing materials. Go to the surface of some products that do not comply with the relevant specifications of electromagnetic interference and radio frequency interference (EMI/RFI). Therefore, the selection of appropriate absorbing materials has become a key factor in compliance with EMI/RFI related specifications and maintaining the integrity of the system. In the frequency range of 10MHz to 3000MHz, most absorbing materials will use lossy magnetic materials (for example, carbonyl iron or ferrite powder, etc.) to weaken their surface current. These surface currents originate from the interaction of harmful EMI and conductors, and their appearance can also cause secondary radiation of electromagnetic fields. Therefore, in order to ensure that products comply with relevant regulations, attempts are usually made to reduce the surface currents. In addition, these surface currents may also cause interference to other circuits and hinder the 



normal operation of the system. It takes a lot of money and time to compare the performance of absorbing materials provided by different manufacturers. Considering the cost of several thousand dollars a day in the EMI test laboratory, the number of trial and error testing must be limited to a minimum. Therefore, the method of carrying several kinds of absorbing materials that may be used to the EMI laboratory for testing to determine the best effect has proved to be a very expensive solution. The simple surface current reduction test device (SCRF) introduced in this article allows us to quickly and simply compare the performance of various absorbing material samples, thereby narrowing the selection range of absorbing materials and determining a certain frequency range One or two absorbing materials with the best performance required for specific EMI problems. The SCRF device is mainly composed of two magnetic field loop antennas that are electrostatically shielded, and by carefully placing them in a perpendicular position, an isolation of 70dB or even higher can be obtained in the relevant frequency range. One loop antenna in the SCRF is connected to a radio frequency (RF) sweep source, and the other loop antenna is connected to an RF sweep receiver. If a conductor plate similar to the product shell is placed in a fixed position close to the two loop antennas, a current will be generated on the surface of the conductor, and the secondary radiation generated by the surface current will be received by the loop antenna. The typical value of the increase in the signal received by the antenna is about 20dB to 30dB. On this basis, if a sample of a certain EMI absorbing material is covered on the conductor plate and the above test process is repeated, the reduction in the secondary radiation of the electromagnetic field can be measured. We can use this reduction in secondary radiation to compare the absorbing performance of different absorbing materials.

Absorbing Material:https://www.goodsmaterial.com/

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