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Neodymium iron boron magnetic circuit design

2018-06-12
Neodymium iron boron magnetic circuit design

Design magnetic circuit to suit local conditions
     From the introduction of magnetic materials, we describe magnetic circuit design principles and magnetic circuit design methods. Because each application of Men Yangu has a special package of ○, plus 1 il of the magnetic circuit research is far inferior to the study of the circuit, so the design of the magnetic circuit is not as clear as the color road design, as accurate, and the design There are always Wr cases in the side. This leads to diversification of design methods and diversification of design results.
     With this in mind, only from the specific design, to explore the mystery of the magnetic circuit to set a deficit of ten. Due to the extensive application of magnetic circuits, the design of each type of product is very different, such as generators, motors, speakers, and measuring instruments. Therefore, we can only select relatively brighter, more researchers, and it is easier. A brief introduction to the accepted content.
     We have repeatedly stressed that the design of the magnetic circuit is complex, difficult, and the results are diverse and not precise. This is because:
     1) The relationship between the magnetic properties of the permanent magnets themselves is relatively complex, and the performance of the permanent magnets is only relevant to the special structures and dimensions of the magnets, and is also related to the operating characteristics.
     2) The magnetic induction and magnetic field strength inside the magnet are all very complicated. For this reason, many assumptions have been made in the design. In particular, there are many assumptions about the leakage flux distribution in the air.
     3) The accuracy of the parameter test of the magnet itself as a design basis is certain, while the test specimen and the magnetic circuit are used: the magnets are not the same.
     4) The practicality and diversity of the magnetic circuit design, coupled with the current methods can still cope with the commonly used design. So for researchers and scholars, the study of magnetic circuit design is not attractive.

Speaker magnetic circuit design

Design preparation
      The amount of magnets used for the binoculars is the first one for the total amount of magnets used. According to statistics in Japan, the amount of money it consumes accounts for 40% of the total amount. Although there is no complete statistics, the main users of hard magnetic magnetic materials are also speaker manufacturers, so E first analyzed and explained the design of speaker magnetic circuits.
      In addition to the speakers, there is a similar structure called a voice coil motor, also called a linear motor, which converts electrical energy into linear mechanical motion for use in disk storage in electronic computers.
      Permanent magnet voice coil motor structure, the figure in the magnet gap in the air gap to establish a constant magnetic field, the air gap to place a voice coil, when the voice coil current flow, under the magnetic field under the voice coil for linear motion.
      The speaker and voice coil motor are similar in structure, and the design method and magnetic circuit structure are also similar. In order to achieve a good design, the role of the magnetic circuit in the speaker must be clearly understood.

1. Structure of a cone (cone) speaker
      The general structure of the cone speaker. Paper cones are pressed from special pulp and most are conical. The central part of the cone is mechanically connected to the same moving coil. This variable coil is called a voice coil. The voice coil is located between the magnetic gaps of the magnetic circuit so that the magnetic lines of force are perpendicular to the conductors of the voice coil. One of the functions of the centering support is to limit and ensure that the voice coil and the cone are only judged second. Blindness, blindfolds, dust covers, paper cones, etc. constitute the speaker's vibration system. Another part of the cigarizer is a magnetic circuit system that includes a magnet and a magnetic system. The brackets, pressers, and the like are auxiliary systems of the loudspeaker, which play a role of connecting, supporting, and fixing each component.

2. Efficiency
       The efficiency can be expressed as the ratio of the speaker's radiated output sound power to the transmitted power applied to the speaker. The efficiency of the cone (cone) speaker is low, only a few percent, and the speaker's equivalent circuit.
       At this time, the efficiency can be reduced to C, which is the air gap flux density, unit T; l is the voice coil wire length inverse, rate meter Cm; rA force radiation resistance, mechanical Europe; XA is the borrowing force resistance, mechanical European IrE For the first ring throwing resistance, as early as fIl/IC blade diaphragm system resistance, mechanical Europe; rC diaphragm system resistance, mechanical Europe.
       From this we can see that the efficiency of the loudspeaker is proportional to the mine. Under the same conditions, increasing the value of B is very significant.

3. Distortion
       In the sense that loudspeakers are in a sense, distortion is more important than efficiency improvement. Especially for high-fidelity speakers and monitor speakers, reducing distortion is the first task.
      Speaker output sound pressure distortion, nonlinear distortion, transient distortion, abnormal sound, etc., only explain the nonlinear vector true here.
      The cause of non-linear distortion comes from the vibration system and the drive system, the distortion caused by the suspension, the distortion caused by the basin, and the distortion caused by the driving force. The former is due to the non-linearity of the mechanical properties of the supporting parts such as the centering support, the folding ring and the paper cone diaphragm; the latter is due to the uneven magnetic flux distribution in the air gap where the voice coil is located and the nonlinearity of the magnetic material around the voice coil. caused.
      The distribution of the magnetic flux of the general speaker phosphorous field. In the central portion of the magnetic gap (with an air gap length of 70% to 80%), it is relatively even and falls on both sides, and the two parts are asymmetrical. Therefore, when the voice coil moves in both directions, the values are not the same, and the driving force generates nonlinear distortion.
      The resulting distortion in the voice coil current is due to the non-linearity of the yoke and the blade in equation (4-2). Since the magnetic material around the voice coil has a non-linear magnetization characteristic, B. is unevenly distributed as previously described, and is naturally influenced by the nonlinearity of the vibration system.
      The alkynes that are caused by the non-linearity of the magnetization characteristics are described in more detail here. The magnet near the voice coil has a working state.
      The permanent magnet generates a DC magnetic field, and the magnetizer and the magnetic gap of the magnetic plate and the like are magnetized by the same DC magnetic field, and the AC magnetic flux generated by the AC magnetic field in proportion to the current flowing through the voice coil passes through it. The trajectory described by the magnetic field to the AC magnetic field is not a straight line, and high harmonic waves appear. Therefore, when a voice coil is added with a sine voltage, the current flowing through the voice coil is distorted due to the presence of an alternating magnetic field.
      The distortion produced by the audio current flowing through the voice coil varies depending on where the magnetic flux passes. In the vicinity of the magnetic coil around the voice coil and the magnetically conductive plate, there are many distortions of ((A) three times, and when the magnetic flux (ΦB) of the magnet increases, the second harmonic distortion is generally more.
      The speaker requires, when certain, that the force of the voice coil is uniform, regardless of how the voice coil moves. In magnetic circuit design two, several measures can be taken to ensure that the force is independent of the position of the voice coil:
       1) Use a short voice coil to place the voice coil in a place where the magnetic flux is distributed evenly.
       2) Using long voice coils, the magnetic lines of force cut by the voice coils do not change. Just in front of the short voice coil, it can also reduce distortion.
       When the iphone is required, when it is fixed, no matter how the voice coil moves, it is hoped that its force can be evenly applied to the design of the magnetic cymbal if any measure is taken to ensure that the force is independent of the position of the voice coil:
       1) Use a short voice coil to place the voice coil in a place where the magnetic flux is distributed evenly.
       2) Using long voice coils, the magnetic lines of force cut by the voice coils do not change. Contrary to the previous short voice coil, distortion can also be reduced.
       3) Use a special magnetic circuit structure to ensure uniform air gap magnetic flux T-shaped magnetic circuit.
       With these three methods, speaker distortion can be reduced. However, using the first method, the voice coil is not short enough to utilize magnetic turbulence; in the second method, the voice coil length increases the weight of the voice coil. Both will reduce the speaker's efficiency, leading to a significant increase in cost, and there will be a conflict between cost and distortion.
       Of course, with a T-shaped magnetic circuit, no second harmonic generation occurs because of the symmetrical distribution of the magnetic flux. However, this method has no effect on reducing the third harmonic distortion, so it must be combined with other methods. The trick of design is to avoid entangling the lost state.
       The non-linear relationship of the magnetization characteristics, if the AC magnetic flux passing through the magnet decreases, and the local hysteresis loop linearizes, resulting in a decrease in distortion.
       The magnetic circuit designed according to this idea is a multi-layer core magnetic circuit, and the use of a material having a smaller hysteresis characteristic in the vicinity of the magnetic gaps of the magnetic column and the magnetic plate can reduce the third harmonic distortion.
       With the addition of steel straws and copper rings, the so-called short-circuit ring method is used. A copper and aluminum short-circuit ring is fitted over the outer diameter of the magnetic column and the diameter of the magnet spoon to act as a secondary coil for the voice coil. The short circuit ring can be added to the upper or lower part of the magnetic column. As a result of the short circuit, the voice coil inductance is close to zero. The short-circuit ring makes the magnetic material non-linear package change in the amount of small, but also to reduce the distortion. The magnetic column short-circuit ring is advantageous for reducing the third harmonic distortion. The magnet internal diameter short-circuit ring is advantageous for reducing the third harmonic distortion.
       In addition, the saturation flux density material can be added to the magnetic circuit to linearize the local magnetic hysteresis loop. The 78% Ni NiFe alloy (Permalloy) is the low saturation flux density material. Can also be from the structure of ideas, magnetic gap near the magnetic material to remove a part of it, so that saturation, which reduces the magnetic permeability of the nonlinear, reducing the third harmonic distortion.
       The above method linearizes the local hysteresis loop and thus reduces the distortion, but it is accompanied by a decrease in the magnetic flux density in the air gap.
        As mentioned earlier, if the local hysteresis loop can be linearized, distortion is reduced, as discussed further below. f is divided into several minimum unit magnetic domains. When an external magnetic field is present, the proportion of magnetic domains in the same direction as the external magnetic field increases. This change is manifested as a change in the magnetic flux density, but due to the internal stress and impurities of the magnet, this change is not linear, and local Hysteresis loop, in the larger magnetic domain and magnetic domain interaction, when the magnetic domain of a magnetic domain changes the other magnetic domains to each other, the local hysteresis loop is rectangular, the distortion increases dramatically.
        On the contrary, if the magnetic domain is small, the direction of a magnetic domain is changed, but the magnetization direction of the magnetic domain gradually changes, and the local magnetic hysteresis loop can be linear.
        Using iron-nickel ring magnetic domains can effectively reduce distortion. . The so-called iron-nickel ring is an alloy of iron and a nickel table, and the crystal grains of the alloy are usually large, and the crystal grains are refined by proper processing such as bending and pulling. As the crystal grains are refined, fewer magnetic domains are selected and the distortion is further reduced. In order to improve the magnetization characteristic with an iron-nickel ring in particular, a special sintering heat treatment is performed. Since the magnetization characteristics of the iron-nickel alloys are deteriorated due to the processing, the heat treatment also improves the magnetization characteristics. As a result, the disadvantage of lowering the air gap flux density due to the low B ferro nickel ring no longer exists.
        Loudspeaker distortion produced by this method will be greatly reduced.
        Since the cross-sectional area of the magnetic flux is reduced near the center of the magnetic plate, the thickness is increased at the center portion for this purpose, and there is a magnetic circuit composed of an additional taper magnetic plate.
        Because the amplitude of the voice coil of the tweeter magnetic circuit is small, the magnetic gap can be made wider and smaller, and the dike can be used to prepare the magnetic circuit.
        Some horn loudspeakers have magnetic poles that are hollow and serve as sound waves. At this time, to prevent saturation of the magnetic column, the root of the magnetic column can be thickened.
4. Transient characteristics
         The transient characteristics of a loudspeaker refer to the ability of the loudspeaker to respond to rapidly changing input signals. It asks that the magnetic circuits are closely linked. This kind of connection is reflected by the loudspeaker quality factor and the magnetic air gap coordinate density.