**4. Characterization methods**

The evaluation of NC sleeve cores is carried out by analyzing the performance regarding two MnZn and NiZn ceramic cores. Therefore, the evaluation of the three different solutions in terms of EMI suppression from the standpoint of the magnetic

**75**

up to 200 MHz.

*Characterization of Nanocrystalline Cores for EMI Suppression in Cables*

properties, the impedance, and the insertion loss provided by different samples. One of the cores selected is based on MnZn, a material widely used to reduce EMI in the low-frequency region and the other selected core is made of NiZn that is generally employed to filter EMI from some tens of megahertz. Thus, it is important that the analyzed sleeve cores have a similar volume in order to conclude which solutions is more effective depending on the frequency range selected. Accordingly, different ceramic MnZn and NiZn sleeve core samples with similar dimensions to the NC samples have been selected to be characterized and evaluated, as shown in **Table 1**. Note that two sets of three different materials are analyzed. In the case of the small samples set (S1, S2, and S3), the ceramic samples are longer than the NC one, whereas in the large samples set (S4, S5, and S6), the three cores have similar dimensions.

**Outer diameter (OD) (mm)**

S1 NC 15.3 5.5 20.0 S2 MnZn 16.0 8.0 28.5 S3 NiZn 17.5 9.5 28.5 S4 NC 28.3 15.5 30.0 S5 MnZn 26.0 13.0 28.5 S6 NiZn 26.0 13.0 28.5

**Inner diameter (ID) (mm)**

**Height (H) (mm)**

The relative permeability (μr) is one of the most important parameters that define the material's ability to absorb electromagnetic interferences. The permeability relates the magnetic flux density of a specific magnetic field in a defined medium. When a sleeve core is placed around a certain cable, it concentrates the magnetic flux. The material's internal properties describe its ability to

focus the magnetic flux is represented through the permeability complex parameter. The effectiveness to attenuate EM interferences of a material can be quantified by separating μr into its complex form. The real component is related to the stored energy or inductive part (μ') and the imaginary component that provides the losses or resistive part (μ"). Thereby, the complex relative permeability is expressed by:

> µ

The magnitude of the NC material's relative permeability is represented together with MnZn and NiZn permeability traces in **Figure 10** to study the frequency region covered by each material. This graph shows the NC core provides higher permeability than the ceramic materials throughout almost the entire frequency range studied, despite being the material with higher initial permeability. MnZn has an initial permeability (μi) of 5000 and it is able to provide a permeability around 3000 up to the 2 MHz, providing a similar value to NC at this frequency point. NC demonstrates the best performance in the mid-frequency region, whereas the NiZn material (μi = 620) is more effective in the high-frequency region. The NC material has an initial permeability (μi) of 30000 and it provides a significant permeability

*<sup>r</sup>* ( *f fjf* ) = ′ ′′ ( ) − ( ) (1)

µµ

*DOI: http://dx.doi.org/10.5772/intechopen.96694*

**Magnetic material**

**Sample reference**

**Table 1.**

**4.1 Relative permeability**

*List of sleeve core samples analyzed.*


*Characterization of Nanocrystalline Cores for EMI Suppression in Cables DOI: http://dx.doi.org/10.5772/intechopen.96694*

#### **Table 1.**

*Materials at the Nanoscale*

**Figure 8.**

*Diagram of the manufacturing procedure of nanocrystalline cores..*

**74**

the tape [11, 18, 28].

**Figure 9.**

since it is in the order of nanometers.

*SEM photograph of a nanocrystalline core material.*

**4. Characterization methods**

process under the presence of transversal and/or longitudinal magnetic fields. This treatment modifies the magnetic properties and the amorphous structure forms ultrafine crystals with a typical size of 7–20 nm, obtaining the nanocrystalline material. The last stage of this procedure corresponds to applying a protective coating or a plastic housing that protects the obtained cores due to the brittle nature of

**Figure 9** shows a SEM photograph of a NC sample where it is possible to observe the difference in terms of the grain size if it is compared with the ceramic materials

The evaluation of NC sleeve cores is carried out by analyzing the performance regarding two MnZn and NiZn ceramic cores. Therefore, the evaluation of the three different solutions in terms of EMI suppression from the standpoint of the magnetic *List of sleeve core samples analyzed.*

properties, the impedance, and the insertion loss provided by different samples. One of the cores selected is based on MnZn, a material widely used to reduce EMI in the low-frequency region and the other selected core is made of NiZn that is generally employed to filter EMI from some tens of megahertz. Thus, it is important that the analyzed sleeve cores have a similar volume in order to conclude which solutions is more effective depending on the frequency range selected. Accordingly, different ceramic MnZn and NiZn sleeve core samples with similar dimensions to the NC samples have been selected to be characterized and evaluated, as shown in **Table 1**. Note that two sets of three different materials are analyzed. In the case of the small samples set (S1, S2, and S3), the ceramic samples are longer than the NC one, whereas in the large samples set (S4, S5, and S6), the three cores have similar dimensions.

#### **4.1 Relative permeability**

The relative permeability (μr) is one of the most important parameters that define the material's ability to absorb electromagnetic interferences. The permeability relates the magnetic flux density of a specific magnetic field in a defined medium. When a sleeve core is placed around a certain cable, it concentrates the magnetic flux. The material's internal properties describe its ability to focus the magnetic flux is represented through the permeability complex parameter. The effectiveness to attenuate EM interferences of a material can be quantified by separating μr into its complex form. The real component is related to the stored energy or inductive part (μ') and the imaginary component that provides the losses or resistive part (μ"). Thereby, the complex relative permeability is expressed by:

$$
\mu\_r(f) = \mu'(f) - j\mu''(f) \tag{1}
$$

The magnitude of the NC material's relative permeability is represented together with MnZn and NiZn permeability traces in **Figure 10** to study the frequency region covered by each material. This graph shows the NC core provides higher permeability than the ceramic materials throughout almost the entire frequency range studied, despite being the material with higher initial permeability. MnZn has an initial permeability (μi) of 5000 and it is able to provide a permeability around 3000 up to the 2 MHz, providing a similar value to NC at this frequency point. NC demonstrates the best performance in the mid-frequency region, whereas the NiZn material (μi = 620) is more effective in the high-frequency region. The NC material has an initial permeability (μi) of 30000 and it provides a significant permeability up to 200 MHz.

**Figure 10.** *Relative permeability of NC core compared to MnZn and NiZn compositions.*

#### **4.2 Impedance parameter**

The permeability parameter is used to describe the core material's behavior; however, manufacturers of EMI Suppressors generally provide their customers the impedance that it introduces in the cable in which it is applied. Typically, the datasheets only specify the impedance at several frequency points or the graph of the magnitude of the impedance in the frequency range where it is more effective. The impedance of a certain sleeve core considers, besides the material permeability, other variables such as the self-inductance defined by the dimensions and the shape. Thereby, sleeve cores are usually defined and classified by specifying the magnitude of the impedance (ZF), which is obtained from the equivalent component parameters such as resistance (R) and the impedance of the inductive part (XL). The magnitude of the impedance is given by:

$$\left| \mathbf{Z}\_{\rm F} \right| = \sqrt{\mathbf{R}^2 + \left( \mathbf{X}\_{\rm L} \right)^2}. \tag{2}$$

**77**

**Figure 11.**

**Figure 12.**

*when introduced into a system.*

*Characterization of Nanocrystalline Cores for EMI Suppression in Cables*

problems. The impedance introduced by the sleeve core (ZF) in that system is introduced in the path that connects both systems. The equivalent circuit diagram employed to determine this impedance relation and analyze the effect of introduc-

*Schematic of source and load equivalents circuits used to determine the insertion loss parameter of a sleeve core* 

According to this diagram, when the system impedance is known, the insertion loss (A) in terms of decibels can be calculated through the Eq. (3) considering the

( ) AFB

ZZZ A 20log Z Z *dB* + + <sup>=</sup> <sup>+</sup>

The results presented in this section correspond to the analysis of the performance provided by NC samples compared to ceramic solutions. This comparison

A B

(3)

ing a sleeve core into a certain system is shown in **Figure 12** [29].

impedance of the sleeve core (ZF):

**5. Results and discussion**

*DOI: http://dx.doi.org/10.5772/intechopen.96694*

*Setup for measuring impedance of sleeve core samples.*

The measurement of the impedance carried out in this contribution has been performed by using the E5061B Vector Network Analyzer (Keysight) connected to the Terminal Adapter 16201A (Keysight) and the Spring Clip Fixture 16092A (Keysight), as shown in **Figure 11**. These fixtures are internally compensated by an impedance standard calibration method to consider the electrical length path and the impedance variations caused by parasitic elements.

#### **4.3 Insertion loss parameter**

Another kind of EMC component datasheets, such as common-mode-chokes, show the attenuation ratio or insertion loss in terms of decibels (dB) that are able to provide. In the case of sleeve cores, it is also possible to determine the insertion loss that it introduces when applied in a cable. The insertion loss that a sleeve ferrite core is able to yield is strongly dependent on the impedance of the system in which it is placed, besides its impedance response depending on the frequency. Subsequently, these components are more effective against EMI when the source and load systems' impedance is low. The equivalent circuit approach to determine the insertion loss parameter of a specific sleeve core requires considering the source impedance (ZA) and the load impedance (ZB) of the system with electromagnetic interference

*Characterization of Nanocrystalline Cores for EMI Suppression in Cables DOI: http://dx.doi.org/10.5772/intechopen.96694*

**Figure 11.** *Setup for measuring impedance of sleeve core samples.*

**Figure 12.**

*Materials at the Nanoscale*

**4.2 Impedance parameter**

**Figure 10.**

magnitude of the impedance is given by:

**4.3 Insertion loss parameter**

the impedance variations caused by parasitic elements.

The permeability parameter is used to describe the core material's behavior; however, manufacturers of EMI Suppressors generally provide their customers the impedance that it introduces in the cable in which it is applied. Typically, the datasheets only specify the impedance at several frequency points or the graph of the magnitude of the impedance in the frequency range where it is more effective. The impedance of a certain sleeve core considers, besides the material permeability, other variables such as the self-inductance defined by the dimensions and the shape. Thereby, sleeve cores are usually defined and classified by specifying the magnitude of the impedance (ZF), which is obtained from the equivalent component parameters such as resistance (R) and the impedance of the inductive part (XL). The

*Relative permeability of NC core compared to MnZn and NiZn compositions.*

= + ( ) <sup>2</sup> <sup>2</sup>

The measurement of the impedance carried out in this contribution has been performed by using the E5061B Vector Network Analyzer (Keysight) connected to the Terminal Adapter 16201A (Keysight) and the Spring Clip Fixture 16092A (Keysight), as shown in **Figure 11**. These fixtures are internally compensated by an impedance standard calibration method to consider the electrical length path and

Another kind of EMC component datasheets, such as common-mode-chokes, show the attenuation ratio or insertion loss in terms of decibels (dB) that are able to provide. In the case of sleeve cores, it is also possible to determine the insertion loss that it introduces when applied in a cable. The insertion loss that a sleeve ferrite core is able to yield is strongly dependent on the impedance of the system in which it is placed, besides its impedance response depending on the frequency. Subsequently, these components are more effective against EMI when the source and load systems' impedance is low. The equivalent circuit approach to determine the insertion loss parameter of a specific sleeve core requires considering the source impedance (ZA) and the load impedance (ZB) of the system with electromagnetic interference

Z R X. F L (2)

**76**

*Schematic of source and load equivalents circuits used to determine the insertion loss parameter of a sleeve core when introduced into a system.*

problems. The impedance introduced by the sleeve core (ZF) in that system is introduced in the path that connects both systems. The equivalent circuit diagram employed to determine this impedance relation and analyze the effect of introducing a sleeve core into a certain system is shown in **Figure 12** [29].

According to this diagram, when the system impedance is known, the insertion loss (A) in terms of decibels can be calculated through the Eq. (3) considering the impedance of the sleeve core (ZF):

$$\mathbf{A}\left(dB\right) = 2\mathbf{0}\log\left(\frac{\mathbf{Z}\_{\text{A}} + \mathbf{Z}\_{\text{F}} + \mathbf{Z}\_{\text{B}}}{\mathbf{Z}\_{\text{A}} + \mathbf{Z}\_{\text{B}}}\right) \tag{3}$$

#### **5. Results and discussion**

The results presented in this section correspond to the analysis of the performance provided by NC samples compared to ceramic solutions. This comparison is carried out by evaluating both the impedance and insertion loss parameters described in the previous section. Two sets of three sleeve cores are analyzing to study the performance provided by samples intended for thin cables (samples S1, S2, and S3) and those with larger diameters (samples S4, S5, and S6). These results make it possible to observe the performance of each EMI suppression solution. It allows the system designer to select the best component to solve EMI problems depending on the frequency range where it is located.

Firstly, the impedance measured of the two sets of samples is shown in **Figures 13** and **14**. **Figure 13** shows the response of the three small samples and it can be observed that the MnZn sleeve core is able to provide the best performance in the low-frequency, achieving its maximum value at 1.5 MHz (132.08 Ω). NiZn sleeve core reaches the maximum impedance value at 50.1 MHz (145.63 Ω). This material represents an interesting solution to reduce EMI in the mid and high-frequency regions, whereas it does not provide a valuable impedance in the low-region. NC sample offers the highest impedance values in the mid-frequency region (from 4.1 MHz to 95.6 MHz), reaching the maximum impedance value at 34.9 MHz (162.04 Ω).

**Figure 13.** *Magnitude impedance of the NC (S1), MnZn (S2), and NiZn (S3) samples.*

**79**

**Figure 15.**

*Insertion loss of the NC (S1), MnZn (S2), and NiZn (S3) samples.*

*Characterization of Nanocrystalline Cores for EMI Suppression in Cables*

Nevertheless, in contrast to ceramic materials, NC sample is able to provide a significant response in both the low and high-frequency region. NC sleeve core shows a better performance than ceramics to reduce EMI emissions in a

**Figure 14** shows the performance of the large sleeve core samples in terms of the impedance response. It is possible to observe that the MnZn sample is the most effective solution to reduce interferences up to 1.2 MHz. From this frequency value, the NC sample is able to introduce a higher impedance value than the other two solutions, covering the range from 1.2 MHz to 77.7 MHz. NiZn sample provides larger impedance than NC in the high-frequency region. The maximum impedance value offered for the MnZn sample is located at 0.6 MHz (89.55 Ω). In the case of the NC sample, this value is achieved at 33.1 MHz (186.77 Ω), whereas the NiZn sample reaches the highest impedance value at 48.2 MHz (157.49 Ω). It is possible to observe that the frequency ranges where the large sleeve core is most effective are similar to the provided by the small samples. In **Figure 14**, the MnZn sample (S5) shows a less significant performance than the smaller sample response based on the same material (S2). The dimensional effect causes this shift in the resonance frequency (maximum impedance value). Thereby, MnZn material reduces its performance when it is used to manufacture large cores due to its internal structure and electrical features. Nevertheless, it is possible to observe that the dimensional effect does not affect the NC and NiZn material when used to manufacture large EMI suppressor cores. However, despite these aspects, the effectiveness in the different frequency regions is similar to the described for the

The insertion loss results have been obtained by considering a system with an input and output impedance of 50 Ω (ZA = ZB = 50 Ω). Thereby, the experimental results that are shown in **Figures 15** and **16** can be compared by considering Eq. (3) and the impedance provided by each sleeve core (ZF). The results obtained in terms of insertion loss correlate with the impedance responses shown previously since MnZn samples provide a higher attenuation ratio in the lowfrequency region. Specifically, the S2 sample provides up to −7.25 dB at 1.7 MHz and − 5.43 dB at 0.6 MHz in the case of S4. Thereby, MnZn material represents the best solution when the interferences are located below 4.2 MHz, considering the small sample set (see **Figure 15**). This frequency range is reduced when larger samples are analyzed since the MnZn S4 sample predominant frequency range

*DOI: http://dx.doi.org/10.5772/intechopen.96694*

wideband frequency range.

last set of samples.

**Figure 14.** *Magnitude impedance of the NC (S4), MnZn (S5), and NiZn (S6) samples.*

*Materials at the Nanoscale*

is carried out by evaluating both the impedance and insertion loss parameters described in the previous section. Two sets of three sleeve cores are analyzing to study the performance provided by samples intended for thin cables (samples S1, S2, and S3) and those with larger diameters (samples S4, S5, and S6). These results make it possible to observe the performance of each EMI suppression solution. It allows the system designer to select the best component to solve EMI problems

Firstly, the impedance measured of the two sets of samples is shown in **Figures 13** and **14**. **Figure 13** shows the response of the three small samples and it can be observed that the MnZn sleeve core is able to provide the best performance in the low-frequency, achieving its maximum value at 1.5 MHz (132.08 Ω). NiZn sleeve core reaches the maximum impedance value at 50.1 MHz (145.63 Ω). This material represents an interesting solution to reduce EMI in the mid and high-frequency regions, whereas it does not provide a valuable impedance in the low-region. NC sample offers the highest impedance values in the mid-frequency region (from 4.1 MHz to 95.6 MHz), reaching the maximum impedance value at 34.9 MHz (162.04 Ω).

depending on the frequency range where it is located.

*Magnitude impedance of the NC (S1), MnZn (S2), and NiZn (S3) samples.*

*Magnitude impedance of the NC (S4), MnZn (S5), and NiZn (S6) samples.*

**78**

**Figure 14.**

**Figure 13.**

Nevertheless, in contrast to ceramic materials, NC sample is able to provide a significant response in both the low and high-frequency region. NC sleeve core shows a better performance than ceramics to reduce EMI emissions in a wideband frequency range.

**Figure 14** shows the performance of the large sleeve core samples in terms of the impedance response. It is possible to observe that the MnZn sample is the most effective solution to reduce interferences up to 1.2 MHz. From this frequency value, the NC sample is able to introduce a higher impedance value than the other two solutions, covering the range from 1.2 MHz to 77.7 MHz. NiZn sample provides larger impedance than NC in the high-frequency region. The maximum impedance value offered for the MnZn sample is located at 0.6 MHz (89.55 Ω). In the case of the NC sample, this value is achieved at 33.1 MHz (186.77 Ω), whereas the NiZn sample reaches the highest impedance value at 48.2 MHz (157.49 Ω). It is possible to observe that the frequency ranges where the large sleeve core is most effective are similar to the provided by the small samples. In **Figure 14**, the MnZn sample (S5) shows a less significant performance than the smaller sample response based on the same material (S2). The dimensional effect causes this shift in the resonance frequency (maximum impedance value). Thereby, MnZn material reduces its performance when it is used to manufacture large cores due to its internal structure and electrical features. Nevertheless, it is possible to observe that the dimensional effect does not affect the NC and NiZn material when used to manufacture large EMI suppressor cores. However, despite these aspects, the effectiveness in the different frequency regions is similar to the described for the last set of samples.

The insertion loss results have been obtained by considering a system with an input and output impedance of 50 Ω (ZA = ZB = 50 Ω). Thereby, the experimental results that are shown in **Figures 15** and **16** can be compared by considering Eq. (3) and the impedance provided by each sleeve core (ZF). The results obtained in terms of insertion loss correlate with the impedance responses shown previously since MnZn samples provide a higher attenuation ratio in the lowfrequency region. Specifically, the S2 sample provides up to −7.25 dB at 1.7 MHz and − 5.43 dB at 0.6 MHz in the case of S4. Thereby, MnZn material represents the best solution when the interferences are located below 4.2 MHz, considering the small sample set (see **Figure 15**). This frequency range is reduced when larger samples are analyzed since the MnZn S4 sample predominant frequency range

**Figure 15.** *Insertion loss of the NC (S1), MnZn (S2), and NiZn (S3) samples.*

**Figure 16.** *Insertion loss of the NC (S4), MnZn (S5), and NiZn (S6) samples.*

is shorter up to 1.3 MHz if compared to the NC S3 sample (see **Figure 16**). As a result of this, the effectiveness of MnZn material is reduced compared to NC material when the dimensions of the sample are increased, since the S4 sample's frequency range is shorted 3.9 MHz and the maximum attenuation has been reduced 1.82 dB. Considering this behavior of MnZn material when a large core is employed, NC represents an alternative solution to suppress EMI in the low-frequency region when a large sleeve core is needed due to it provides higher attenuation than NiZn in this range. Regarding the mid-frequency region, NC samples (S1 and S4) have a similar response, reaching the maximum values of insertion loss at 33.5 MHz (−8.33 dB) in the case of S1 and 28.2 MHz (−9.11 dB) for S4. NC S1 sample has the predominant response from 4.2 MHz to 60.4 MHz, considering the small sample set (see **Figure 15**) and from 1.3 MHz to 57.2 MHz in the case of the large samples (see **Figure 16**). NiZn S3 and S6 samples are able to offer the best performance in the high-frequency region since NC samples have a resonance frequency lower than the value shown by NiZn cores. This insertion loss difference between NC and NiZn in the high-frequency region is more significant when the large sample cores.

Consequently, MnZn samples are significantly effective in the low-frequency region, but their performance is strongly reduced in the high-frequency region. Contrary to this behavior, NiZn samples show great insertion loss in the highfrequency region, whereas it provides a poor performance in the low-region. However, NC samples show the best performance in the mid-frequency region at the same time that it provides a significant insertion loss in the low-frequency region and a comparable response than the offered by the NiZn samples in the high-frequency region.

Note that these results are related to the impedance of both systems where the cable in which the sleeve core is applied. Therefore, the insertion loss values obtained can be considered when the EMI suppression solution is applied to data or video cables. According to Eq. (3), if these samples were installed in power cables, it could be possible to obtain higher attenuation ratios. For instance, if the sleeve core is installed in a system where ZA = ZB = 5 Ω, the ZF provided by the sample is more significant than the system impedance. Thereby, if the maximum impedance provided by S1 is considered (ZF = 145.63 Ω) it can be able to introduce an insertion loss of −23.84 dB instead of the −8.33 dB obtained for ZA = ZB = 50 Ω.

**81**

**Author details**

frequency range.

and Julio Martos

Adrian Suarez\*, Jorge Victoria, Jose Torres, Pedro A. Martinez, Andrea Amaro

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Consequently, if the EMI disturbances are specifically located in the low or high-frequency region, a ceramic core is able to provide significant effectiveness to reduce them. If the interferences are detected in the mid-region (from 5 MHz to 100 MHz), NiZn material is able to provide better performance than MnZn if only ceramic cores are considered. NC structures usually represent a higher cost than ceramic, so that this solution may not always be considered to solve an EMI problem located in a specific frequency region. This is the reason why a designer could select a ceramic core instead of a NC core to reduce an EMI problem despite the ceramic core could not be the most effective solution. Nevertheless, when the EMI disturbances are distributed in different frequency regions, NC sleeve core shows a better performance than ceramics to reduce EMI emissions in a wideband

School of Engineering of the University of Valencia, Valencia, Spain

\*Address all correspondence to: adrian.suarez@uv.es

provided the original work is properly cited.

effective against high-frequency interferences.

*Characterization of Nanocrystalline Cores for EMI Suppression in Cables*

The performance of NC samples has been compared with the effectiveness provided by ceramic cores. Thereby, it has been analyzed the performance of each EMI suppression solution from the standpoint of the magnetic properties, imped-

Considering the results presented, it is possible to identify the frequency regions where each material solution is effective to reduce EMI when applied in a certain cable. According to the relative permeability data, the MnZn material analyzed is suitable when the interferences are located in the low-frequency region (from hundreds of kilohertz up to some megahertz). In contrast, NiZn solution is not effective in this frequency region. NiZn samples show an interesting solution to reduce EMI in the mid and high-frequency region since it shows a better response than MnZn up to about 5 MHz. The relative permeability data shows that NC material is able to provide a wideband solution due to it is able to offer a comparable response to MnZn material in the low-frequency region and NiZn material in the high-frequency region. Furthermore, NC shows the highest permeability in the mid-frequency region. The excellent magnetic properties shown by the NC material have been verified from the standpoint of the impedance and the insertion loss that the NC samples can introduce in a certain cable with electromagnetic disturbances. Therefore, MnZn samples show a significant performance to reduce EMI in the low-frequency region in terms of impedance and insertion loss, whereas NiZn is

*DOI: http://dx.doi.org/10.5772/intechopen.96694*

**6. Conclusions**

ance, and insertion loss.

*Characterization of Nanocrystalline Cores for EMI Suppression in Cables DOI: http://dx.doi.org/10.5772/intechopen.96694*
