EMI is becoming a serious problem, just as it can appear anywhere in electronic circuits, and produce unpredictable and machine-damaged consequences. This situation is becoming more serious due to factors such as increased equipment frequency, high integration of electronic systems, higher power density, and reduced thickness and size of PCB boards.
The most common approach to electromagnetic noise is to shield the system with conductive materials, such as shielding cavities, tin foil tape, or conductive gaskets. However, this does not apply to all electronic devices. Most of them have components that work at high frequencies, causing complex EMI problems that cannot be removed with conductive shields.
In order to avoid such problems, flexible absorbers (polymers doped with ferrite powder) can be used to suppress unwanted high-frequency electromagnetic components.
The nature of flexible absorber
The best description of the material's ability to absorb direct and dissipated electromagnetic noise signals is the u'' part of the composite permeability. The magnetic permeability of a material is determined by the molecular composition and structure, and is expressed in plural.
The real part quantitatively describes the ability to store energy or induction, and the imaginary part quantitatively describes the ability to consume energy or absorb:
The performance of these parameters is determined by the material composition and frequency factors. Therefore, it is very important to know in which frequency band the noise level exceeds the standard.
With these data, it is possible to find a balance between reflection and magnetic loss according to the application and the characteristics of electromagnetic noise signals. The figure above shows the composite permeability curves of several flexible absorbers with different performance characteristics.
Since magnetic permeability changes with frequency, it is necessary to determine the frequency range in which noise needs to be suppressed when selecting the correct material. The standard material properties table often does not give this part of the information, but often just lists some general parameters, and does not include the part of absorption and reflection.
In any case, it may be difficult to predict the performance of the absorbing material because it is determined by multiple variables other than the permeability of the absorbing material. These variables include patch thickness, size, geometry, and the distance between the noise source and the absorbing material, and so on.
Therefore, for general systems, the attenuation of electromagnetic noise suppression materials cannot be predicted. However, in order to study the effects of materials in complex electronic systems, it is better to obtain real results through some experimental characterization methods.