In fact, the use of magnetic barriers of absorbing materials in daily life is already very common. Our mobile phone cases, mobile phone holsters, including anti-metal interference products and wireless charging products, are even more difficult to detect by us. The material magnetic isolation sheet solves the problem of electromagnetic interference, so what is the principle of wave absorption of the electromagnetic isolation sheet?
The principle of wave absorbing material and magnetic isolation sheet
The magnetic isolation sheet of the absorbing material is not only a magnetic medium with magnetic absorption, but also a dielectric medium with electric absorption. In the low frequency range, the magnetic isolation sheet of the absorbing material mainly relies on the loss of the hysteresis effect, the eddy current effect and the magnetic aftereffect to cause the loss of the ferrite to the electromagnetic wave; in the high frequency range, it mainly comes from the natural resonance loss and the domain wall resonance loss And dielectric loss.
The principle of wave absorbing material and magnetic isolation sheet is the electric loss mechanism:
Dielectric loss is the main reason for the electrical loss in the magnetic isolation sheet of the absorbing material. The charge 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 a lot of Electric dipole, 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.
The second principle of absorbing material and magnetic isolation sheet is the mechanism of magnetic loss:
Magnetic loss is the energy loss produced by the magnetic isolation sheet of the absorbing material in the alternating magnetic field, which is mainly caused by hysteresis loss, eddy current loss, remanence effect and magnetic resonance.
(1) Hysteresis loss: In the dynamic magnetization process of irreversible jump, a part of the energy supplied by the external magnetic field is lost by overcoming various damping effects. The area of the hysteresis loop is numerically equal to the value of the hysteresis loss per magnetization cycle.
(2) Eddy current loss: When the magnetic flux passing through the conductor changes with time, an induced current or eddy current will be generated inside the ferrite. 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, namely Eddy current loss.
(3) Remanence effect: The change of magnetic flux density in the magnet lags behind the applied magnetic field by a phase angle. The change of the applied magnetic field is zero, but the magnetic flux density in the magnet is not zero, resulting in remanence. To make the magnetic flux density zero, a reverse magnetic field must be applied. This process of eliminating the remanence will consume the energy of the magnetic field.
(4) Magnetic resonance: The magnetic dipole in the magnet vibrates at its natural frequency. If the external magnetic field is the same as its frequency, it will cause magnetic resonance, which will lead to strong absorption of electromagnetic waves by the material.