13.56MHZ antenna ferrite sheet/film is a kind of iron oxide material sintered at high temperature. In handheld devices such as NFC (Near Field Communication) payment mobile phones, the main function of electronic tags is to reduce the absorption of signal magnetic field by metal materials. At the same time, the ferrite film itself is a kind of ferrite material sintered at high temperature, which can effectively increase the induction distance by increasing the magnetic field intensity. The payment method of NFC mobile phone is realized by 13.56MHz RFID radio frequency identification system. The RFID smart tag of this application is attached to the back cover of the mobile phone, which can save space to the greatest extent. In a handheld electronic device such as a mobile phone, if an electronic tag is to be integrated or attached to the electronic device and used as a component of the device, due to the limited space, it is inevitable to attach an RFID tag (usually passive) to the surface of a conductive object such as metal or a place near the metal device. In this way, the alternating electromagnetic field excited by the tag under the signal sent by the card reader is easily attenuated by the eddy current of the metal, which greatly weakens the signal intensity and leads to the failure of the reading process. Therefore, in order to better apply card reading to products, it is necessary to add wave absorbing materials to products. Ferrite sheets have been widely used in micro-payment mobile phones and radio frequency fields.

ferrite

Ferrite is a ferromagnetic metal oxide. Generally, it can be divided into three types: permanent ferrite, soft ferrite and gyromagnetic ferrite. As far as electrical properties are concerned, the resistivity of ferrite is much higher than that of metal and alloy magnetic materials, and it also has higher dielectric properties. The magnetism of ferrite also shows high permeability at high frequency. Therefore, ferrite has become a non-metallic magnetic material widely used in the field of high frequency and weak current. Because the magnetic energy per unit volume stored in ferrite is low, the saturation magnetization is also low (usually only pure iron 1/3 ~ 1/5), which limits its application in low frequency, high voltage and high power fields that require high magnetic energy density.

Basic introduction/ferrite

Ferrite is sintered from iron oxide and other components. Generally, it can be divided into three types: permanent ferrite, soft ferrite and gyromagnetic ferrite.

Permanent magnet ferrite is also called ferrite magnetic steel, which is the small black magnet we usually see. Its raw materials mainly include iron oxide, barium carbonate or strontium carbonate. After magnetization, the residual magnetic field is very strong and can last for a long time. Usually used as a permanent magnet material. For example: speaker magnet.

Soft ferrite is made of iron oxide and one or more other metal oxides (such as nickel oxide, zinc oxide, manganese oxide, magnesium oxide, barium oxide, strontium oxide, etc.). ) and sintered. It is called soft magnetic because when the magnetized magnetic field disappears, the residual magnetic field is very small or almost non-existent. Usually used as choke coil, or magnetic core of intermediate frequency transformer. This is completely different from permanent magnet ferrite.

Gyromagnetic ferrite refers to ferrite material with gyromagnetic characteristics. The gyromagnetic characteristics of magnetic materials refer to the phenomenon that plane polarized electromagnetic waves will rotate around the propagation direction when propagating in a certain direction in the material under the action of two vertical DC magnetic fields and electromagnetic fields.

. Gyro ferrite is widely used in microwave communication field. According to crystal types, gyromagnetic ferrites can be divided into spinel type, garnet type and magnesite type (hexagonal type) ferrites.

The development of history

China first came into contact with natural ferrite, namely magnetite (Fe3O4), which was discovered in the 4th century BC. The compass invented by China is made of this natural magnetite. With the development of radio technology in 1930s, ferromagnetic materials with low high frequency loss are urgently needed. But the resistivity of ferroferric oxide is too low to meet this requirement. 1933, tokyo institute of technology first manufactured a permanent magnet material containing cobalt ferrite, which was then called OP magnet. From 1930s to 1940s, France, Japan, Germany, the Netherlands and other countries successively carried out research work on ferrite. Among them, J.L. Snooker, a physicist at Philips Laboratories in the Netherlands, developed various zinc-containing soft ferrite with excellent spinel structure in 1935, and realized industrial production in 1946. 1952, a permanent magnet ferrite with BaFe 12O 19 as the main component was developed by J.J. Venter and others in our laboratory. This kind of ferrite has similar hexagonal structure to the four kinds of VHF magnetic ferrites studied by G.H. Yonker et al. in 1956. In 1956, E.F. Bertau and F. Rafe also reported the research results that Y3Fe5O 12 has ferromagnetism. Among them, the substitution ion Y includes rare earth ions, such as Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Because the crystal structure of this magnetic compound is the same as the natural mineral garnet, it is called garnet ferrite. Up to now, except for the amorphous ferrite material prepared by Hiroo Sugimoto in 198 1 year, from the perspective of crystallization chemistry, it has not exceeded the above three types of crystal structures. Most of the work done is to carry out modification and in-depth research to adapt to new uses.