First of all, let’s first understand what constitutes a high-permeability absorbing material: a high-permeability absorbing material refers to a type of absorbing material that has a high magnetic permeability real part u′ (generally ≥50) around 10MHz. material.
High permeability absorbing materials can be divided into the following two categories according to their application fields:
1. High permeability absorbing materials used to provide EMC/EMI solutions
This kind of absorbing material not only needs a higher real part u′ of permeability, but also a higher imaginary part u” (commonly known as “high magnetic loss”) of permeability.
Main principle analysis:
The higher the real part of the magnetic permeability can increase the magnetic flux of the interference source, and the higher the imaginary part of the magnetic permeability can effectively convert the concentrated magnetic flux into latent heat and consume it, thereby reducing or eliminating the electromagnetic radiation interference hazard of the interference source. .
2. Used to provide RFID/NFC anti-metal interference at 13.56MHz and below
While this kind of absorbing material requires a higher real part u′ of permeability, it also hopes to have a lower imaginary part u” (commonly known as “low magnetic loss”), that is, a higher quality factor ( u′/u″).
Analysis of the main principle: The higher the real part of the magnetic permeability can more bundle the magnetic flux of the communication antenna signal, thereby effectively reducing or eliminating the "metal eddy current" phenomenon generated when the antenna is close to the metal, and at the same time, the lower magnetic permeability is false. The part u" does not excessively lose the energy of the communication signal passed through, and ensures the response of communication recognition and the effective recognition distance.
At present, in the application of RFID/NFC anti-metal interference, absorbing materials can only provide solutions for RFID/NFC with frequencies of 13.56MHz and below. The reason: when the magnetic permeability of general absorbing materials is more than 10 MHz, its The real part of permeability u'will rapidly decay, while the imaginary part of permeability u″ will rise quickly. The absorber with the characteristics of high permeability real part u′ and low permeability imaginary part u″ is 13.56MHz While providing solutions for RFID/NFC anti-metal interference at frequencies below and below, the insertion of absorbing materials changes the line capacitance and impedance of the antenna and the distance (increase) and dielectric constant between the antenna and the metal base plate. It may cause the resonant frequency of the card reader or tag antenna to shift and affect the actual communication effect. Therefore, the company’s technicians must understand the relevant characteristics of their own wave-absorbing material system to guide customers to adjust the antenna resonant frequency correctly to achieve the best Communication effect. It can be seen that the application of absorbing materials, whether in EMC/EMI or RFID/NFC, will have more or less other effects on the entire system of the application object. In order to improve market competitiveness, in addition to the quality of the product itself, It is also necessary to strengthen relevant application research and provide customers with "personal" services.
In addition, in the application of WPC (Wireless Power Consortium) using Qi standard electromagnetic induction wireless charger, its requirements and principles for absorbing materials are similar to the above.
At present, there are two main types of absorbing materials in this application field:
1) Rigid ferrite absorbing material
The ferrite hard plate absorbing material has a relatively higher real part of permeability u'(up to about 200), a smaller imaginary part of permeability u”, and superior application performance. At present, it can only be prepared by a sintering process. To achieve superior permeability performance, and in order to reduce the negative impact of the process on its mechanical properties, the product size is limited (generally no more than 125mm × 125mm), so the loss of processing products is large. At the same time, because of its high brittleness, The equipment required for processing and preparation is high, and the scrap rate is also high. In addition, the products or products are prone to cracks during processing, storage and transportation, causing magnetic flux leakage, and the actual performance is also affected. Therefore, the market acceptance is not very high.
2) Soft magnetic alloy flexible absorbing material
The permeability performance of soft magnetic alloy flexible absorbing material is weaker than ferrite hard piece, but its flexible size can meet the low loss of product processing, and good product processing performance can reduce the scrap rate and processing cost, so the market The demand is not low.