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Posted on 26 May 2019

High Permeability, High Impedance Mn-Zn Ferrite Material for Wide Frequency EMI Applications

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High permeability Mn-Zn ferrite materials are widely used in the field of solving electromagnetic interference (EMI) problems, such as the filters of electronic equipments, the line filters of switch power supply and the common mode chokes of commercial power. The impedance of high permeability Mn-Zn ferrite materials plays an extremely important role reducing EMI. This paper introduces DMEGC’s new R10KZ material with high permeability and high impedance over a wide frequency range.

By Chao-Ming Wang, Xin Jin, Yang-Zhong Du and Su-Ping Wang; Hengdian Group DMEGC Magnetics CO., LTD, Hengdian, Zhejiang 322118, China

The electronic equipments are widely used in the real life and the electro-magnetic interference (EMI) becomes more obvious, what often causes problems fulfilling electromagnetic compatibility (EMC) requests. Therefore, the developed countries and regions paid more attention to the control of EMI which has been brought into the category of management of the state’s legal system and environmental protection. All the councils subjected to IEC are designated corresponding standards. Filtering is a technology to deal with electromagnetic noise in a certain frequency range, which can filter out the part of signal that we don’t need. However, Mn-Zn ferrites with high permeability are regarded as one of key materials meeting requested EMC standards. Thus, the research on the impedance characteristics at various frequency ranges is highly demanded.

The ferrite impedance can be divided into two parts, inductance and resistance contributions. In the low frequency range, ferrite impedance are mainly dominated by inductance. It can be expressed as follows:

\begin{equation} Z=K\cdot jwL\end{equation}

Where K is the constant related with cores and L is the inductance. While operated at intermediate frequency range, both inductance and resistance contribute to the impedance due to the increasing resistance. And the impedance can be expressed as follows:

\begin{equation}Z=K\cdot \bigg(\frac{1}{R}+\frac{1}{jwL}+jwC\bigg)^{-1}\end{equation}

Where R is the resistance component and C is capacitor component. In the high frequency range, the ferrite impedance is mainly attributed to the resistance contribution for the decreasing inductance and increasing resistance. Therefore, it is necessary to adjust the ferrite compositions and sintering processing in order to satisfy applications’ various demands in impedance at different frequency ranges.

Sample preparation and property measurements The Mn-Zn ferrites, applied in EMI Applications, must have high permeability and high impedance over a wide frequency range. Thus it can eliminate the noise in the circuit. According this request, we optimized the composition and additions of the materials by making series experiments, and improved the sintering technology.

The initial permeability (μi) and Curie temperature (Tc) were measured by HP4284A, the impedance by HP4291B impedance analyzer and the saturation magnetic flux density (Bs) using SY8258. The elemental properties of R10KZ are listed in Table 1.

The initial permeability, saturation magnetic flux density and Curie temperature of R10KZ

The relationship between the initial permeability and frequency of R10KZ is shown in Figure 1.

Initial permeability vs. frequency of R10KZ

It shows almost stable permeability of R10KZ below 200 KHz, indicating an excellent frequency characteristic. Figure 2 shows the impedance of standard R10K and newly developed R10KZ material from 10 kHz to 1MHz.

Impedance of standard R10K and R10KZ material

The impedance of R10KZ is remarkable higher than R10K impedance in 200 kHz to 1MHz frequency range. The Zmax of R10KZ material increased by 25% compared to R10K material.

Figure 1 and figure 2 exhibit the frequency characteristics of permeability and impedance of R10KZ material of H25*15*12 core. Furthermore, we can also provide other shapes or sizes of high impedance materials, which can meet different needs of customers.

Impedance versus number of turns

Figure 3 shows the impedance versus number of turns for H25*15*12 R10KZ core, and Figure 4 shows the permeability of different size core for R10KZ material.

Permeability versus different core size

Conclusion

Ferrite material R10KZ means remarkable improvement of weaknesses of high permeability materials and offers opportunity to further technical improvement and cost reduction of various applications.

 

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