Strong ferrite is a kind of non-metallic magnetic material, also known as ferrite.
Ferrites is a kind of non-metallic magnetic material, also known as ferrite. It is made of Fe2O3 and one or several other metal oxides (such as nickel oxide, zinc oxide, manganese oxide, magnesium oxide, barium oxide, strontium oxide, etc.). Its relative permeability can be as high as several thousand, its resistivity is 1011 times that of metal, and its eddy current loss is small. There are five types of Ferrite: hard magnetic, soft magnetic, rectangular magnetic, gyromagnetic and piezomagnetic Formerly known as ferromagnetic or ferromagnetic, its production process and appearance are similar to ceramics, so it is also known as magnetic ceramics. Ferrite is a compound oxide of iron and one or more appropriate metal elements. Properties belong to semiconductors, usually used as magnetic media. The most important difference between ferrite magnetic materials and metal or alloy magnetic materials is conductivity. Generally, the resistivity of the former is 102-108 Ω· cm, while that of the latter is only 10-6-10-4 Ω· cm.
After the hard magnetic material is magnetized, there is remanence. The strength and direction of remanence depend on the strength and direction of magnetization. Recording tape is composed of tape base, adhesive and magnetic powder layer. The belt base is generally made of polycarbonate or vinyl chloride. The strong magnetic powder is made of r-Fe2O3 or CrO2 fine powder with strong remanence. When recording, the current corresponding to the sound change is amplified and sent to the coil of the recording head to generate a concentrated magnetic field in the gap of the head core. With the change of coil current, the direction and intensity of magnetic field change correspondingly. When the tape passes through the head gap at a constant speed, the magnetic field passes through the tape and magnetizes it. Since the tape leaves the head with corresponding remanence, its polarity and intensity correspond to the original sound. As the tape moves, so does the sound.
During playback, the recorded tape is pressed against the gap of the playback head at the same speed as the recording. The iron core of the strong magnet head is made of the soft magnetic material of the high conducting ferrite, which has little resistance to the magnetic flux. Therefore, the audio remanence flux recorded on the tape is easy to form a loop through the head core. The residual flux on the tape induces an induced electromotive force on the coil of the playback head which is the same as the variation rule of the residual flux. After amplified by the playback amplifier, it is sent to push the speaker, and the audio signal recorded on the tape will be restored to the original sound.
Guan Tao, deputy director of the balance of payments Department of the State Administration of foreign exchange, said at the meeting that, affected by the financial crisis, the goal of promoting China's balance of payments in the past few years is being achieved. At present, China's foreign trade surplus has decreased, its debt structure has improved, and its balance of payments is healthier. Although the balance of foreign exchange reserves has declined in some months, foreign exchange funds are still flowing in net at present, and the basis of China's balance of payments is stable.
At the same time, he believes that there are two main reasons for the low risk of the current reversal of China's balance of payments: first, although China's economy still faces many difficulties, it is still relatively good in the world economy. Secondly, at present, the RMB is relatively stable, and it is relatively safe to hold RMB assets, so there will be no panic flight of funds.
In view of the current situation, Guan Tao believes that we should further do a good job in foreign exchange management in accordance with the overall idea of "ensuring growth, preventing risks and promoting balance". He suggested liberalizing the restrictive measures of foreign exchange collection and settlement, and carefully using the policy of frequent adjustment of export promotion rate. He also believes that despite the recent good signs in global financial markets, it is not certain that it has improved.
Edge technologies of the United States began to produce rare earth giant magnetostrictive materials in 1989, with the trade name of Terfenol-D, and then ferredyn ab of Sweden also produced and sold rare earth giant magnetostrictive materials, with the product name of maggeg 86. In recent 10 years, Japan, Russia, the United Kingdom and Australia have also researched and developed tbdyfe2 magnetostrictive materials A small number of products are sold. Rare earth magnetostrictive materials are mainly used to make high-power sonar, the latter is widely used in underwater communication, guidance, fishing, oil well and geological exploration. Other applications include valve control, precision lathes, robots, peristaltic motors, damping, retarders and sensors. The development and application of rare earth magnetostrictive materials have been paid more and more attention. The output and market consumption are increasing rapidly. According to the statistics of American advanced technology company, the output of Terfenol-D alloy in the world was only 100kg in 1989, about 1000kg in 1993, 10 tons in 1995 and 70 tons in 1997. The value of Terfenol-D material used in sonar and other devices in the United States is about US $10 million to US $10 million per year. The market value of sonar, hydraulic press, robot and other devices is about US $600 million per year. In the last five years, the market growth rate of Terfenol-D is 99.99% per year.
Ferrite magnetic steel is the most widely used permanent magnetic material. It is made by powder metallurgy. It is mainly divided into barium material (BA) and strontium material (SR). It is a kind of permanent magnetic material that is not easy to demagnetize and not easy to corrode. The high working temperature of strong magnet can reach 250 ℃, which is hard and brittle. It can be cut and processed with diamond sand and other tools, and processed with alloy One time molding. These products are widely used in the fields of permanent magnet motor and speaker.
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