In the low frequency range, ferrite absorbing materials mainly come from the loss of hysteresis, eddy current and magnetic aftereffects, which cause the loss of electromagnetic waves by ferrite; in the high frequency range, the loss of electromagnetic waves by ferrite is mainly from natural sources. Resonance loss, domain wall resonance loss and dielectric loss. (Electrical loss mechanism) Dielectric loss is the main cause of electrical loss in microwave ferrites. Charges cannot pass through the dielectric in the electric field like a conductor, but the charge particles will shift each other under the action of the electric field, causing the positive and negative charge centers to separate , Forming many electric dipoles, this process is polarization. In the process of polarization, the part of the charge lost in the form of heat causes electrical loss.
It is generally believed that the polarization of polycrystalline electromagnetic media mainly comes from four mechanisms: electronic polarization, ion polarization, inherent electric dipole orientation polarization and interface polarization.
Lattice vacancies, the inhomogeneity of the dielectric body, and the existence of high conductivity are the main reasons for the dielectric loss caused by the inherent galvanic orientation polarization; the main reason for the dielectric loss caused by the interface polarization is the zero of the high conductivity Phase dispersion distribution. The dielectric loss of ferrite is basically due to the excess of electrons caused by the existence of two valence states of iron, that is, the sum of the electrons. The electrons will run from one iron ion to another iron ion, and some will be caused in the process. Conduction and dielectric loss.
(Magnetic loss mechanism) Magnetic loss is the energy loss produced by magnetic materials in an alternating magnetic field, which is mainly caused by hysteresis loss, eddy current loss and residual loss. (Hysteresis loss) Hysteresis loss refers to the loss of part of the energy supplied by the external magnetic field by overcoming various damping effects during the dynamic magnetization process of the irreversible jump.
The area of the hysteresis loop is numerically equal to the value of the hysteresis loss per magnetization cycle, that is: the method to reduce the hysteresis loss is to reduce the coercive force of the ferromagnetic material, and the reduction of the coercive force makes the hysteresis loop narrower , Its so-called area is reduced, thereby reducing hysteresis loss. (Eddy current loss) When a conductor is placed in a changing magnetic field, an induced current or eddy current will be generated inside the conductor. The eddy current cannot be transported out like the current in the wire, but will cause the magnetic core to heat up and cause energy loss, that is, eddy current loss.
In addition, frequency has little effect on ferrite eddy current loss. (Residual loss) Residual loss refers to all losses except eddy current loss and hysteresis loss, which come from the magnetization relaxation process. Different materials have different residual loss mechanisms in different frequency ranges due to different mechanisms of magnetization relaxation process.
In the low-frequency weak field, the residual loss is mainly the magnetic after-effect loss. In the case of high frequency, dimensional resonance loss, domain wall resonance loss and natural resonance loss all belong to the category of residual loss.
In summary, to obtain a high loss ferrite absorbent, the ways are: increase the saturation magnetization of the ferromagnetic body; increase the impedance coefficient; reduce the magnetocrystalline anisotropy field; due to the resonance frequency and the magnetocrystalline anisotropy The field of anisotropy is proportional, so the absorption band of the material can be controlled by changing the magnetocrystalline anisotropy field of the ferromagnet. In the actual preparation operation, it can be controlled by changing the composition of the material and the preparation process.
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