First of all, we have to understand what is amorphous? During the preparation of the metal, if it is cooled with an ultra-fast cooling rate during its solidification process, the atoms are in a disorderly state at this time, and they will be instantly frozen before they can be rearranged. The structure formed at this time is Amorphous. Nanocrystalline is based on the amorphous state, through a special heat treatment, let it form crystal nuclei and grow. However, it is necessary to control the size of the crystal grains at the nanometer level, and do not form complete crystals. The structure formed at this time is nanocrystalline.
Compared with cobalt-based amorphous and ferrite, nanocrystalline has a high saturation magnetic inductance and can reduce the volume of magnetic devices. High magnetic permeability, small loss, and small coercive force can reduce the loss of magnetic devices. Therefore, nanocrystalline are the best soft magnetic materials in high-frequency power electronics applications.
3. Characteristics of nanocrystalline
The frequency of the current wireless charging "Qi standard" is between 100-200k. At this frequency, the magnetic permeability of the nanocrystalline is very close to that of the cobalt-based amorphous, which is significantly higher than that of the iron-based amorphous and ferrite . The loss is just the opposite, significantly lower than iron-based amorphous and ferrite.
Nanocrystalline also have advantages in temperature applications. Not only are nanocrystalline wider in application temperature than cobalt-based amorphous and ferrite, but in the range of -40℃-120℃, the stability of nanocrystalline is also significantly better than ferrite.
Nanocrystalline also have obvious advantages in the design of magnetic materials. Nanocrystalline can be oriented to control permeability and anti-saturation magnetic fields. The magnetic permeability of nanocrystalline can be adjusted freely within 1000-30000. The design of the magnetic material requires that the magnetic saturation should not be reached under a specific working current. Once the magnetic saturation is reached, it will stop working. The nanocrystalline adjustable anti-saturation magnetic field can reach 30~350A/m, making the application range of wireless charging more width.
Wireless charging has become popular in mobile phones, and there are many products in the wearable field. In the future, wireless charging will be popularized in homes, offices, public places, travel tools, and transportation.
Wireless power transmission (WPT): The structure of wireless charging for smart phones and smart wearables (small power) is similar to a transformer. It consists of a transmitter and a receiver. The transmitter and the receiver are both made of coils and magnetic materials. The magnetic materials are different. The choices are ferrite, amorphous, nanocrystalline, etc.
Magnetic shielding: Provide a low-impedance path for the magnetic flux, reduce the magnetic field lines radiating outward, reduce the impact on the surrounding metal objects, and prevent eddy currents and signal interference.
Permeability reduction: improve the coupling coefficient, improve the magnetoelectric conversion efficiency, use fewer turns to achieve a higher inductance coil, reduce the coil resistance, and reduce the efficiency reduction caused by heating (the more turns, the higher the resistance) .
Simulating real scenes, conducting comparative tests under the same conditions, using different thickness nanocrystalline magnetic sheets and ferrite with different permeability and thickness to compare the charging efficiency. As the thickness increases, the charging efficiency continues to increase, but the nanocrystalline is not as thick as possible, basically saturated by 0.1mm, therefore, when designing a wireless charging module, the nanocrystalline magnetic permeable sheet does not need to be too thick, it will Increase material cost. The law of ferrite is similar to that of nanocrystals. The higher the magnetic permeability, the higher the charging efficiency, the thicker the thickness, and the higher the charging efficiency. However, under the same charging efficiency, the thickness of the nanocrystalline magnetic sheet is only the ferrite. half.