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Factors Affecting the Filtering Effect of Magnetic Rings

1.1 Factors Affecting the Filtering Effect of Magnetic Rings

The specification sheet of a general magnetic ring usually provides the frequency impedance curve of different winding turns, as shown in the following figure:

It can be seen from the figure that the impedance difference is very large when the same magnetic ring has different winding turns. If the specification sheet of the magnetic ring does not provide the curve, the following formula can be used for a simple calculation:

Here, N represents the number of turns of the winding, µr is the permeability of the magnetic ring, µ0 is the initial permeability, A is the cross-sectional area of the magnetic ring, and r is the radius from the outer circle to the center.

1.2 Magnetic Permeability

【Key Points】: When selecting magnetic rings, one should choose the one with a higher magnetic permeability based on the specific frequency points of the noise interference that needs to be suppressed.

1.3 Curie Temperature Curve

The Curie temperature is the temperature at which the magnetic domains within the magnetic ring disintegrate. As can be seen from the above figure, the magnetic permeability gradually reaches a peak as the temperature increases. When the temperature rises further, the magnetic permeability begins to drop sharply. When it drops to the point where the magnetic permeability becomes 1, the magnetic ring loses its magnetism. Different magnetic rings have different Curie temperature points. Especially for magnetic rings used in high-temperature environments, the influence of the Curie temperature must be paid attention to to ensure the good filtering performance of the magnetic ring.

1.4 Flow Capacity

The distribution of magnetic domains inside the magnetic ring is such that when the magnetic ring is not subjected to a magnetic field, the distribution of the magnetic domains is in a disordered state. However, when a magnetic field is applied, the magnetic domains become in an ordered state. As the current increases, the magnetic field strength also increases, causing the arrangement of the magnetic domains to become more compact and resulting in a greater number of ordered magnetic domains. The magnetic flux lines passing through become denser, and the impedance of the magnetic ring increases accordingly.

1.5 Air Gap

Frequency characteristic impedance curve

As can be seen from the figure, the impedance of the clamp-type magnetic ring increases almost linearly as the frequency increases. Above 1GHz, the impedance continues to increase. However, the Micro flat magnetic ring reaches a peak when the frequency increases. When the frequency further increases, the impedance decreases, especially above 1GHz. Therefore, if you want to suppress high-frequency noise, the clamp-type magnetic ring should be selected.

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