1. The working principle of ferrite absorbing materials
Ferrite absorbing materials are both a magnetic medium with magnetic absorption and a dielectric with electric absorption. They are a class of absorbing materials with excellent performance.
In the low frequency range, the loss of ferrite to electromagnetic waves is mainly caused by the loss of hysteresis effect, eddy current effect and magnetic aftereffect; in the high frequency range, the loss of electromagnetic wave by ferrite mainly comes from natural resonance loss and domain wall resonance. Loss and dielectric loss.
In different frequency ranges, the mechanism of the residual loss of the absorbing material is different due to the different mechanism of the 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.
Second, the application of ferrite sheet
In handheld devices such as payment mobile phones, the main function of the electronic tag is to reduce the absorption of the signal magnetic field by the metal material, and increase the magnetic field strength to effectively increase the sensing distance. The payment method of the payment mobile phone (NFC) is through 13.56MHz; RFID radio frequency Realized by the recognition system. The RFID smart label of this application is affixed to the back cover of the mobile phone, which can save space to a certain extent. In handheld electronic devices such as mobile phones, electronic tags need to be integrated or attached to the electronic device to function as a component of the device. Often due to limited space, it is inevitable to attach RFID tags (usually passive) to metal, etc. The surface of the conductive object or the place where there are metal devices nearby. In this way, the alternating electromagnetic field induced by the tag under the action of the signal sent by the card reader is easily attenuated by the metal eddy current, which greatly weakens the signal strength, leading to the failure of the reading process. Therefore, in order for the product to be able to better use the card reader, it is necessary to add a microwave absorbing material to the product. Ferrite sheets have begun to be widely used in small payment mobile phones and radio frequency fields.
The shielding box also needs to use ferrite as a shielding material in some low frequency bands, and the overall application of ferrite is still very extensive.