**2. Applications of EMI suppressor sleeve cores**

The Magnetic Field (H) is associated with electrodynamic phenomena and appears whenever there are electric currents. The H field can produce effects capable of seriously disturbing the operation of an electronic circuit. Whenever current flows in a circuit, this current creates a magnetic field in that circuit, which will vary as the current varies. Consequently, in any circuit that carries an alternating current, variations of magnetic flux occur. According to Lenz's law, an electromotive force will be induced by the field variation. Therefore, if the current is constant, there will be no induced electromotive force.

Considering that the flux density (B) is proportional to the product of the permeability of the medium and the incident H field, B is the result of the action of H in a magnetic circuit, and its intensity will be higher or lower depending on the permeability of the matter (μr). For the shielding of conductors against EMI, the most common is to use ferromagnetic materials since they present a permeability much higher than that of vacuum (μ0).

When introducing the sample, the external field deforms considerably, being, at each point, the resultant of the initial magnetic field and the field created by the orientation of the magnetic domains. As shown in **Figure 3**, the material concentrates the field lines and regions outside and close to the material, reducing the emitted field.

As explained above, unexpected EMI sources in cables can appear in our system when connected to another device. One of the most used techniques for reducing cables' interferences is applying an EMI suppressor such as sleeve cores to them. This EMI suppressor provides selective attenuation of undesired interference components that the designer may wish to suppress and it does not affect the intended signal. Thereby, this component is widely used to filter EMI in power cables to reduce high-frequency oscillations generated by switching transients or parasitic resonances within a circuit, and EMI in peripheral cables of electronic devices such as multiconductor USB or video cables.

From the standpoint of the magnetic properties, a sleeve core is defined by the relative permeability since it is the main parameter that describes the performance of a specific magnetic material to concentrate the magnetic flux in the core. This parameter is generally expressed through its complex form represented by the real component (μr') that quantifies the real or inductive part and the imaginary or resistive component (μr") that is related to the material ability to absorb the electromagnetic interferences [6, 7].

The presence of noise current in a conductor generates an undesired magnetic field around it, resulting in EMI problems. The effectiveness of a sleeve core to reduce EMI in cables is defined by its capability to increase the flux density of a certain field strength created around a conductor. Thereby, noise current generates a magnetic field which is concentrated into magnetic flux inside the ferrite by the core's magnetic permeability (μr'). This magnetic field inside the ferrite is reduced by the ferrite's magnetic loss (μr"), converting it into heat energy. As a result of these two filtering mechanisms the flowing noise current in the conductors is reduced.

Currents that flow in cables (with two or more conductors) can be divided into differential mode (DM) and common mode (CM) depending on the directions of propagation. Although DM currents are usually significantly higher than CM currents, one of the most common EMI radiated problems is originated by CM currents

**71**

**Figure 5.**

*Diagram of an external power supply elements.*

**Figure 4.**

*return paths).*

*Characterization of Nanocrystalline Cores for EMI Suppression in Cables*

flowing through the cables of the system [8]. CM currents have a much greater interfering potential, despite not having a high value. This fact is due to only a few microamps are required to flow through a cable to fail radiated emission requirements [5, 9]. The use of sleeve cores is an efficient solution to filter the CM currents in cables because, if a pair of adjacent conductors is considered, when the cable ferrite is placed over both signal and ground wires, the CM noise is reduced. As shown in **Figure 4**, the CM currents in both wires flow in the same direction, so the two magnetic fluxes in the cable ferrite are added together, and the filtering action occurs in the sleeve core. The intended (DM) current is not affected by the presence of the cable ferrite because the DM current travels in opposite directions and is transmitted through the signal and returns. Thus, the current of the two conductors is opposing, meaning they cancel out and the cable ferrite has no effect [10, 11]. In the case of wanting to filter the DM currents, it would be necessary to use a sleeve

An external power supply (**Figure 5**) can be considered a specific example of the application of sleeve cores to reduce EMI in terms of both radiated and conducted emissions. Within the conducted emission range (150 kHz – 30 MHz), the conductors of the system are generally too short to be considered an EMI antenna source since the impedance of possible parasitic inductors is low, and the impedance of parasitic capacitors is typically high. Nevertheless, in the radiated emissions range (from 30 MHz), the parasitic associated with conductors and power line EMI filters can be significant if conductors are long enough to be considered an unintended antenna [12, 13]. External power supplies typically incorporate discrete inductors, capacitors in the AC input circuitry to implement common mode, and differential mode filters before the input bridge and the switching stage. This filtering stage's main objective is to attenuate the interferences that can be conducted out from the power supply to the AC input power lines. Accordingly, the internal PCB is designed to hold these filtering components in order to pass regulatory safety and EMC testing. When these techniques are considered, a power supply design may meet conducted and radiated emission requirements when tested in isolation. Nevertheless, when the power supply is added to a complete system, the system may fail emissions testing due to the interferences emitted from the system load to the

*Diagram of CM and DM currents passing through a cable ferrite with two adjacent conductors (signal and* 

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

core in each of the cable's conductors.

**Figure 3.** *Management of H field through introducing a sleeve core.*

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

flowing through the cables of the system [8]. CM currents have a much greater interfering potential, despite not having a high value. This fact is due to only a few microamps are required to flow through a cable to fail radiated emission requirements [5, 9]. The use of sleeve cores is an efficient solution to filter the CM currents in cables because, if a pair of adjacent conductors is considered, when the cable ferrite is placed over both signal and ground wires, the CM noise is reduced. As shown in **Figure 4**, the CM currents in both wires flow in the same direction, so the two magnetic fluxes in the cable ferrite are added together, and the filtering action occurs in the sleeve core. The intended (DM) current is not affected by the presence of the cable ferrite because the DM current travels in opposite directions and is transmitted through the signal and returns. Thus, the current of the two conductors is opposing, meaning they cancel out and the cable ferrite has no effect [10, 11]. In the case of wanting to filter the DM currents, it would be necessary to use a sleeve core in each of the cable's conductors.

An external power supply (**Figure 5**) can be considered a specific example of the application of sleeve cores to reduce EMI in terms of both radiated and conducted emissions. Within the conducted emission range (150 kHz – 30 MHz), the conductors of the system are generally too short to be considered an EMI antenna source since the impedance of possible parasitic inductors is low, and the impedance of parasitic capacitors is typically high. Nevertheless, in the radiated emissions range (from 30 MHz), the parasitic associated with conductors and power line EMI filters can be significant if conductors are long enough to be considered an unintended antenna [12, 13]. External power supplies typically incorporate discrete inductors, capacitors in the AC input circuitry to implement common mode, and differential mode filters before the input bridge and the switching stage. This filtering stage's main objective is to attenuate the interferences that can be conducted out from the power supply to the AC input power lines. Accordingly, the internal PCB is designed to hold these filtering components in order to pass regulatory safety and EMC testing. When these techniques are considered, a power supply design may meet conducted and radiated emission requirements when tested in isolation. Nevertheless, when the power supply is added to a complete system, the system may fail emissions testing due to the interferences emitted from the system load to the

**Figure 4.**

*Materials at the Nanoscale*

emitted field.

electromotive force will be induced by the field variation. Therefore, if the current

Considering that the flux density (B) is proportional to the product of the permeability of the medium and the incident H field, B is the result of the action of H in a magnetic circuit, and its intensity will be higher or lower depending on the permeability of the matter (μr). For the shielding of conductors against EMI, the most common is to use ferromagnetic materials since they present a permeability

When introducing the sample, the external field deforms considerably, being, at each point, the resultant of the initial magnetic field and the field created by the orientation of the magnetic domains. As shown in **Figure 3**, the material concentrates the field lines and regions outside and close to the material, reducing the

As explained above, unexpected EMI sources in cables can appear in our system when connected to another device. One of the most used techniques for reducing cables' interferences is applying an EMI suppressor such as sleeve cores to them. This EMI suppressor provides selective attenuation of undesired interference components that the designer may wish to suppress and it does not affect the intended signal. Thereby, this component is widely used to filter EMI in power cables to reduce high-frequency oscillations generated by switching transients or parasitic resonances within a circuit, and EMI in peripheral cables of electronic devices such

From the standpoint of the magnetic properties, a sleeve core is defined by the relative permeability since it is the main parameter that describes the performance of a specific magnetic material to concentrate the magnetic flux in the core. This parameter is generally expressed through its complex form represented by the real component (μr') that quantifies the real or inductive part and the imaginary or resistive component (μr") that is related to the material ability to absorb the electro-

The presence of noise current in a conductor generates an undesired magnetic field around it, resulting in EMI problems. The effectiveness of a sleeve core to reduce EMI in cables is defined by its capability to increase the flux density of a certain field strength created around a conductor. Thereby, noise current generates a magnetic field which is concentrated into magnetic flux inside the ferrite by the core's magnetic permeability (μr'). This magnetic field inside the ferrite is reduced by the ferrite's magnetic loss (μr"), converting it into heat energy. As a result of these two filtering mechanisms the flowing noise current in the conductors is

Currents that flow in cables (with two or more conductors) can be divided into differential mode (DM) and common mode (CM) depending on the directions of propagation. Although DM currents are usually significantly higher than CM currents, one of the most common EMI radiated problems is originated by CM currents

is constant, there will be no induced electromotive force.

much higher than that of vacuum (μ0).

as multiconductor USB or video cables.

magnetic interferences [6, 7].

**70**

**Figure 3.**

*Management of H field through introducing a sleeve core.*

reduced.

*Diagram of CM and DM currents passing through a cable ferrite with two adjacent conductors (signal and return paths).*

**Figure 5.** *Diagram of an external power supply elements.*

designed power supply through the DC output cable back. One of the most common solutions to solve this EMI problem is integrating a sleeve core that reduces the undesired interferences without affecting the DC intended signal.

The advantage of using this EMI solution is that it does not involve redesign the electronics and, generally, the mechanical redesign. This is an important advantage because determining in the testing stage, which is the EMI source, may not be straightforward. However, the use of a sleeve core involves adding an extra component whose drawbacks result in increasing the product's size and weight besides the cost of the filtering component and its installation. Therefore, this is an effective solution to attenuate EMI emissions in cables when it is not possible to solve the problem through a system redesign, but it is essential to strike a balance between performance and other factors such as weight, dimensions, and cost [14].

Sleeve cores are manufactured with magnetic material that allows them to control interferences in a certain frequency range with a specific ratio. The values of these two parameters mainly depend on the EMI suppressor intrinsic composition and internal structure. The most used sleeve ferrite cores are based on ceramics or polycrystalline materials because they contain metal oxides, such as manganese or zinc oxide [15]. Thereby, MnZn and NiZn are the most popular EMI suppressor solution due to their heat resistant, hardness, and high resistance to pressure. One of the ceramics' main advantages is the possibility of manufacturing samples with many different shapes able to provide a significant performance [16, 17]. The starting material of ceramics is iron oxide Fe2O3 mixed with one or more divalent transition metals, such as manganese, zinc, nickel, cobalt, or magnesium [18]. Nanocrystalline sleeve core represents an innovative and increasingly used solution for EMI suppression in cables. This solution has demonstrated excellent suitability to reduce interferences from the low-frequency region to the mid-frequency range [19, 20]. In this sense, some researchers have investigated the use of NC structure compositions to make EMC components because this kind of core can reduce its volume by 50–80% and yield greater magnetic properties and insertion losses than conventional ceramic components [21–24].

Consequently, some NC novel samples are characterized and compare to MnZn and NiZn cores to determine this novel material's effectiveness compared to the conventional ceramic solutions by analyzing samples with different dimensions.

#### **3. Nanocrystalline core description**

The manufacturing procedure of ceramic materials (**Figure 6**) is based on, firstly, mixing raw materials into the desired proportions. Next, it is then precalcined to form the ferrite. The pre-sintered material is then milled to obtain a specific particle size. Subsequently, the granulated material is shaped by a pressing technique to obtain the final form. Finally, the resultant core is sintered, promoting any unreacted oxides to be formed into ferrite and protected with epoxy [25, 26]. The manufacturing procedure and the material mix are essential to define a ceramic core's magnetic properties. Thereby, MnZn materials can provide a significant performance for EMI suppression applications, covering the range of frequency from hundreds of kHz to some MHz. In contrast, NiZn materials are intended for a higher frequency operation than MnZn, covering from tens of MHz to several hundreds of MHz [16, 19, 20, 27].

**Figure 7** shows two micrographs of the samples obtained using scanning electron microscopy (SEM). In these photographs, it is possible to observe the internal structure and the grain size of MnZn (a) and NiZn (b) ceramic materials.

**73**

**Figure 6.**

**Figure 7.**

*Characterization of Nanocrystalline Cores for EMI Suppression in Cables*

The results presented in [19, 20] highlighted the great suitability of NC EMI suppressors to filter electromagnetic interference throughout the frequency band from 100 kHz to 100 MHz. Furthermore, data obtained from its magnetic properties indicate that this EMC solution could also provide good performance in terms of EMI suppression at higher frequencies. The advantages of iron-based nanocrystalline materials lie in the high values of relative permeability, the reduction of the magnetic components' volume, and the stable operation up to high-temperatures. These properties are mainly defined by the manufacturing procedure. The manufacturing procedure of NC samples (**Figure 8**) is quite different from the used for ceramic production since it is formed by a continuous laminar structure that is wound to form the final core. The material is a two-phase structure consisting of an ultra-fine grain phase of FeSi embedded in an amorphous ribbon of 7–25 micrometers in thickness. Firstly, the base material is molten by heating it at 1300 °C and depositing it on a water-cooled wheel that reduces the temperature of the material to 20 °C. Next, the resulting amorphous metal ribbon is exposed to an annealing

*SEM photographs of ceramics core materials: (a) MnZn material composition; (b) NiZn material composition.*

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

*Diagram of the manufacturing procedure of ceramic cores.*

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

**Figure 6.**

*Materials at the Nanoscale*

cost [14].

conventional ceramic components [21–24].

**3. Nanocrystalline core description**

designed power supply through the DC output cable back. One of the most common solutions to solve this EMI problem is integrating a sleeve core that reduces the

Sleeve cores are manufactured with magnetic material that allows them to control interferences in a certain frequency range with a specific ratio. The values of these two parameters mainly depend on the EMI suppressor intrinsic composition and internal structure. The most used sleeve ferrite cores are based on ceramics or polycrystalline materials because they contain metal oxides, such as manganese or zinc oxide [15]. Thereby, MnZn and NiZn are the most popular EMI suppressor solution due to their heat resistant, hardness, and high resistance to pressure. One of the ceramics' main advantages is the possibility of manufacturing samples with many different shapes able to provide a significant performance [16, 17]. The starting material of ceramics is iron oxide Fe2O3 mixed with one or more divalent transition metals, such as manganese, zinc, nickel, cobalt, or magnesium [18]. Nanocrystalline sleeve core represents an innovative and increasingly used solution for EMI suppression in cables. This solution has demonstrated excellent suitability to reduce interferences from the low-frequency region to the mid-frequency range [19, 20]. In this sense, some researchers have investigated the use of NC structure compositions to make EMC components because this kind of core can reduce its volume by 50–80% and yield greater magnetic properties and insertion losses than

Consequently, some NC novel samples are characterized and compare to MnZn and NiZn cores to determine this novel material's effectiveness compared to the conventional ceramic solutions by analyzing samples with different dimensions.

The manufacturing procedure of ceramic materials (**Figure 6**) is based on, firstly, mixing raw materials into the desired proportions. Next, it is then precalcined to form the ferrite. The pre-sintered material is then milled to obtain a specific particle size. Subsequently, the granulated material is shaped by a pressing technique to obtain the final form. Finally, the resultant core is sintered, promoting any unreacted oxides to be formed into ferrite and protected with epoxy [25, 26]. The manufacturing procedure and the material mix are essential to define a ceramic core's magnetic properties. Thereby, MnZn materials can provide a significant performance for EMI suppression applications, covering the range of frequency from hundreds of kHz to some MHz. In contrast, NiZn materials are intended for a higher frequency operation than MnZn, covering from tens of MHz to several hundreds of

**Figure 7** shows two micrographs of the samples obtained using scanning electron microscopy (SEM). In these photographs, it is possible to observe the internal

structure and the grain size of MnZn (a) and NiZn (b) ceramic materials.

The advantage of using this EMI solution is that it does not involve redesign the electronics and, generally, the mechanical redesign. This is an important advantage because determining in the testing stage, which is the EMI source, may not be straightforward. However, the use of a sleeve core involves adding an extra component whose drawbacks result in increasing the product's size and weight besides the cost of the filtering component and its installation. Therefore, this is an effective solution to attenuate EMI emissions in cables when it is not possible to solve the problem through a system redesign, but it is essential to strike a balance between performance and other factors such as weight, dimensions, and

undesired interferences without affecting the DC intended signal.

**72**

MHz [16, 19, 20, 27].

*Diagram of the manufacturing procedure of ceramic cores.*

**Figure 7.** *SEM photographs of ceramics core materials: (a) MnZn material composition; (b) NiZn material composition.*

The results presented in [19, 20] highlighted the great suitability of NC EMI suppressors to filter electromagnetic interference throughout the frequency band from 100 kHz to 100 MHz. Furthermore, data obtained from its magnetic properties indicate that this EMC solution could also provide good performance in terms of EMI suppression at higher frequencies. The advantages of iron-based nanocrystalline materials lie in the high values of relative permeability, the reduction of the magnetic components' volume, and the stable operation up to high-temperatures. These properties are mainly defined by the manufacturing procedure. The manufacturing procedure of NC samples (**Figure 8**) is quite different from the used for ceramic production since it is formed by a continuous laminar structure that is wound to form the final core. The material is a two-phase structure consisting of an ultra-fine grain phase of FeSi embedded in an amorphous ribbon of 7–25 micrometers in thickness. Firstly, the base material is molten by heating it at 1300 °C and depositing it on a water-cooled wheel that reduces the temperature of the material to 20 °C. Next, the resulting amorphous metal ribbon is exposed to an annealing

**Figure 8.**

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

#### **Figure 9.**

*SEM photograph of a nanocrystalline core material.*

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 the tape [11, 18, 28].

**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 since it is in the order of nanometers.
