Disclosure of Invention
In order to solve the defects in the prior art, the application aims to provide a permanent magnet magnetizing control method and a magnetizing machine based on magnetic domain dynamics, and the method can improve the magnetizing precision and efficiency.
In a first aspect, the present application provides a permanent magnet magnetizing control method based on magnetic domain dynamics, the method comprising:
The method comprises the steps of obtaining a three-dimensional model of a permanent magnet to be magnetized, dividing the three-dimensional model into a plurality of cubic units, wherein each cubic unit is used as a magnetic domain unit;
Acquiring a dynamic equation of each magnetic domain unit, wherein the dynamic equation is used for calculating the instantaneous magnetic moment direction of the magnetic domain unit;
the magnetic moment directions of the magnetic domain units are randomly distributed when not magnetized so as to be used for simulating a state that the initial magnetization intensity is zero, the magnetic domain units do spin precession under the action of an effective magnetic field, and the magnetic moment directions of the magnetic domain units gradually approach to the effective magnetic field direction;
Solving the instantaneous magnetic moment direction of each magnetic domain unit at different moments based on a kinetic equation, and determining a change track of the magnetic moment direction of each magnetic domain unit from the initial magnetic moment direction according to the instantaneous magnetic moment direction of the magnetic domain unit at different moments for each magnetic domain unit;
And determining the degree of consistency of the magnetic moment directions of the magnetic domain units according to the magnetic moment direction change tracks of the magnetic domain units, and generating a relation map of magnetizing saturation, pulse magnetic field intensity and pulse duration, wherein the magnetizing machine can execute magnetizing control on the permanent magnet to be magnetized according to the target magnetic field intensity and target magnetizing time determined from the relation map.
In one embodiment, the dynamics equation introduces a spin precession equation of a damping term based on a magnetic moment dynamics principle, the damping term controlling a speed of the instantaneous magnetic moment direction approaching the effective magnetic field direction by a damping coefficient α.
In one embodiment, obtaining a kinetic equation for each magnetic domain unit includes:
The dynamic behavior of each magnetic domain cell is described by the LLG equation;
setting the magnetization intensity of each magnetic domain unit to be constant and the magnetic moment direction to be variable in the LLG equation to obtain a dynamic equation of each magnetic domain unit;
Wherein the dynamic equation of the magnetic domain unit comprises gyromagnetic ratio, damping coefficient alpha and effective magnetic field Heff.
In one embodiment, the kinetic equation for a magnetic domain unit is:
;
Wherein,Representing the instantaneous magnetic moment direction of the magnetic domain cell mi,Represents gyromagnetic ratio, alpha represents damping coefficient,Indicating the effective magnetic field.
In one embodiment, the effective magnetic field is calculated from the superposition of the following components:
An external magnetizing magnetic field component whose direction is aligned with the easy axis of magnetization of the permanent magnet to be magnetized;
an exchange field component between adjacent magnetic domains, which is an interaction between adjacent magnetic domain units;
the anisotropic field component of the material is determined by the structure of the permanent magnet to be magnetized;
the demagnetizing field component is calculated by the product of the magnetization and the demagnetizing tensor.
In one embodiment, solving the instantaneous magnetic moment direction of each magnetic domain cell at different moments based on the kinetic equation includes:
setting a time step delta t, and iteratively calculating the instantaneous magnetic moment direction according to the time step delta t;
Aiming at each time step delta t, solving a kinetic equation by adopting a Dragon-Gregory tower method, and updating the instantaneous magnetic moment direction;
and stopping iterative calculation of the instantaneous magnetic moment direction until the three-dimensional model of the permanent magnet to be magnetized reaches magnetizing saturation.
In one of the embodiments, the un-magnetized state of the permanent magnet to be magnetized is simulated by:
Randomly distributing magnetic moment directions for each magnetic domain unit, wherein the magnetic moment directions of the magnetic domain units are uniformly distributed in a three-dimensional space;
The magnetic moment directions of the magnetic domain units are different from each other when the magnetic domain units are not magnetized, the magnetic domain units are offset to present a scattered state, the initial magnetization saturation degree when the magnetic domain units are not magnetized is calculated through the average included angle between the magnetic moment directions and the easy magnetization axis, and the included angle ranges from 85 degrees to 95 degrees.
In one embodiment, for a permanent magnet to be magnetized, the effective magnetic field has an effective time less than the target magnetizing time and/or the effective magnetic field has a strength less than the target magnetic field strength, the magnetic moment direction of the magnetic domain unit does not completely coincide with the effective magnetic field direction, and/or
For a permanent magnet to be magnetized, the acting time of the effective magnetic field is smaller than the target magnetizing time and/or the strength of the effective magnetic field is smaller than the target magnetic field strength, and the magnetic moment direction of the magnetic domain unit is not completely inverted relative to the initial magnetic moment direction.
In one embodiment, the relationship of magnetizing saturation to pulse magnetic field strength and pulse duration comprises:
When the pulse magnetic field strength does not reach the target pulse magnetic field strength, the magnetizing saturation is increased along with the increase of the pulse magnetic field strength and the pulse duration;
increasing the pulse duration at a constant pulsed magnetic field strength stabilizes the magnetizing saturation at a certain value, rather than increasing it indefinitely;
Under the target pulse magnetic field intensity, if the pulse duration reaches the target magnetizing time, the permanent magnet to be magnetized can be saturated and magnetized, and if the pulse duration is smaller than the target magnetizing time, the permanent magnet to be magnetized cannot reach the saturated and magnetized.
In a second aspect, the present application also provides a magnetizing apparatus, comprising:
the magnetizing circuit is used for magnetizing the permanent magnet to be magnetized;
And the controller comprises a memory and a processor, wherein the memory stores a computer program, and the processor realizes the permanent magnet magnetizing control method based on magnetic domain dynamics in the first aspect when executing the computer program.
The method comprises the steps of dividing a three-dimensional model of a permanent magnet to be magnetized into a plurality of magnetic domain units, obtaining a kinetic equation of each magnetic domain unit, determining an initial magnetic moment direction of each magnetic domain unit to simulate a scattered state when the permanent magnet is not magnetized, solving an instantaneous magnetic moment direction of each magnetic domain unit at different moments based on the kinetic equation, determining a change track of the magnetic moment direction, determining the consistency degree of the magnetic moment direction according to the change track of the magnetic moment direction, generating a relation map of magnetizing saturation, pulse magnetic field intensity and duration, and further providing accurate control parameters for a magnetizer to ensure that the permanent magnet achieves an optimal magnetizing effect. According to the method, the intensity of the pulse magnetic field and the pulse duration are included in the influence factor of the magnetizing saturation, and the space distribution of the permanent magnet is also included in the influence of the magnetizing saturation by dividing the three-dimensional model of the permanent magnet to be magnetized into a plurality of magnetic domain units, so that the magnetizing precision and efficiency can be improved.
Detailed Description
The present application will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present application more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application. Unless defined otherwise, technical or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
In one embodiment, as shown in fig. 1, there is provided a permanent magnet magnetizing control method based on magnetic domain dynamics, the method comprising the steps of:
step 101, acquiring a three-dimensional model of a permanent magnet to be magnetized, dividing the three-dimensional model into a plurality of cubic units, wherein each cubic unit is used as a magnetic domain unit;
a three-dimensional model of the permanent magnet to be magnetized is obtained, which can describe the geometry and dimensions of the permanent magnet to be magnetized. Further, the three-dimensional model may be divided into a plurality of cubic units, each of which may be an independent magnetic domain unit, the size of which is determined according to the calculation accuracy, and the volume of the conventionally selected unit is about 1mm3 so as to accurately simulate the magnetization behavior of the magnetic domain. Wherein each magnetic domain unit has an independent magnetic moment vector whose initial direction is determined by the generated random number to reflect the random distribution of magnetic domain magnetic moment in the non-magnetized state.
Step 102, acquiring a dynamic equation of each magnetic domain unit, wherein the dynamic equation is used for calculating the instantaneous magnetic moment direction of the magnetic domain unit;
For each magnetic domain unit, a kinetic equation for each magnetic domain unit is obtained. The dynamics equation corresponding to each magnetic domain unit is Landau-Lifshitz-Gilbert (LLG) equation, and the dynamics equation is used for calculating the instantaneous magnetic moment direction of the magnetic domain unit under the action of a pulse magnetic field.
It should be noted that, the dynamic equation of the magnetic domain unit may consider the spin precession of the magnetic moment, the damping effect, and the influence of the external magnetic field on the magnetic moment direction, and by solving the dynamic equation of the magnetic domain unit, the change condition of the magnetic moment vector direction of each magnetic domain unit with time may be obtained, so as to accurately simulate the magnetizing process of the permanent magnet. The method for solving the dynamic equation of the magnetic domain unit is a fourth-order Dragon-Gregorian tower method so as to ensure the accuracy and stability of calculation.
Step 103, determining an initial magnetic moment direction of each magnetic domain unit, wherein the magnetic moment directions of the magnetic domain units are randomly distributed when not magnetized so as to simulate a state that the initial magnetization intensity is zero, and the magnetic moment directions of the magnetic domain units gradually approach to the effective magnetic field direction under the action of the effective magnetic field;
the magnetic moment directions of the magnetic domain units are randomly distributed differently when not magnetized, which cancel each other out. The purpose of this is to simulate a state where the initial magnetization is zero. Further, under the action of the effective magnetic field, each magnetic domain unit starts to perform spin precession, and the magnetic moment direction of each magnetic domain unit can gradually approach to the direction of the effective magnetic field.
Specifically, initially, the magnetic moment vector direction of each magnetic domain unit is set by a random number generator to ensure that the magnetic moment vector direction has different orientations in a three-dimensional space, so as to reflect the scattered distribution of magnetic moment in an un-magnetized state. When an effective magnetic field is applied, the magnetic moment vector of each magnetic domain unit can conduct spin precession according to a dynamic equation, and the magnetic moment vector is gradually guided by the effective magnetic field in the spin precession process, and the direction of the magnetic moment vector is gradually closed to the direction of the effective magnetic field.
104, Solving the instantaneous magnetic moment direction of each magnetic domain unit at different moments based on a dynamics equation, and determining a change track of the magnetic moment direction of each magnetic domain unit from an initial magnetic moment direction according to the instantaneous magnetic moment direction of the magnetic domain unit at different moments;
Specifically, the magnetic moment direction of the magnetic domain unit is random at the beginning, which represents the random distribution of magnetic moment in the non-magnetized state. With the application of an external effective magnetic field, the magnetic moment begins to change according to the law described by the kinetic equation, typically gradually tending from an initial random direction toward the direction of the effective magnetic field.
Recording the magnetic moment direction of each magnetic domain unit under each time step can draw a track of the change of the magnetic moment direction along with time, and the change track of the magnetic moment direction of the magnetic domain unit from the initial magnetic moment direction can show the whole evolution process of the magnetic moment from the initial state to the stable state. It should be noted that, for each magnetic domain unit, the kinetic equation may be solved by a numerical method, for example, a langugan method, so as to obtain the instant direction of the magnetic moment at each time step.
And 105, determining the degree of consistency of the magnetic moment directions of the magnetic domain units according to the magnetic moment direction change tracks of the magnetic domain units, and generating a relation map of magnetizing saturation, pulse magnetic field intensity and pulse duration, wherein the magnetizing machine can execute magnetizing control on the permanent magnet to be magnetized according to the target magnetic field intensity and target magnetizing time determined from the relation map.
And calculating the consistency degree of the magnetic moment directions of the magnetic domain units and the effective magnetic field directions under different pulse magnetic field intensities and durations by analyzing the magnetic moment direction change tracks of all the magnetic domain units, so as to obtain the magnetizing saturation. The magnetizing saturation can reflect the magnetization degree of the permanent magnet under different magnetizing conditions. The relation map can intuitively display the relation among the three visual elements with the intensity of the pulse magnetic field and the pulse duration as the horizontal axis and the vertical axis and the magnetizing saturation as the color or the height.
Further, the magnetizing machine can execute magnetizing control on the permanent magnet to be magnetized according to the target magnetic field intensity and the target magnetizing time determined from the relation map, namely, according to the required magnetizing saturation, the corresponding pulse magnetic field intensity and duration are found in the relation map, so that the magnetizing process is accurately controlled, and the permanent magnet is ensured to achieve the expected magnetizing effect.
In the embodiment, a three-dimensional model of a permanent magnet to be magnetized is divided into a plurality of magnetic domain units, a kinetic equation of each magnetic domain unit is obtained, an initial magnetic moment direction of each magnetic domain unit is determined to simulate a scattered state when the permanent magnet is not magnetized, instantaneous magnetic moment directions of each magnetic domain unit at different moments are solved based on the kinetic equation, a change track of the magnetic moment directions is determined, the consistency degree of the magnetic moment directions is determined according to the change track of the magnetic moment directions, a relation map of magnetizing saturation, pulse magnetic field intensity and duration is generated, accurate control parameters are provided for the magnetizer, and optimal magnetizing effect of the permanent magnet is ensured. According to the method, the intensity of the pulse magnetic field and the pulse duration are included in the influence factor of the magnetizing saturation, and the space distribution of the permanent magnet is also included in the influence of the magnetizing saturation by dividing the three-dimensional model of the permanent magnet to be magnetized into a plurality of magnetic domain units, so that the magnetizing precision and efficiency can be improved.
In one embodiment, the dynamics equation introduces a spin precession equation of a damping term based on a magnetic moment dynamics principle, the damping term controlling a speed of the instantaneous magnetic moment direction approaching the effective magnetic field direction by a damping coefficient α.
The dynamics equation can describe magnetic moment dynamics from a microscopic mechanism, and can reflect the influence of magnetizing field intensity, field duration, ferromagnetic materials and the like on magnetic moment direction change.
In micromagnetism, the relationship between magnetization M and angular momentum L is:
;
wherein, gamma is gyromagnetic ratio, and the size isUnder the action of the effective field Heff, the moment T of force applied by the magnetization intensity is:
。
Wherein mu0 is vacuum magnetic permeability, M is magnetization intensity, and Heff is effective field.
The effective field Heff is expressed as:
。
Wherein mus is magnetic permeability, which represents the response capability of the material to a magnetic field in a certain direction,The Hamiltonian amount is the Hamiltonian amount of the magnetic system and comprises exchange energy, anisotropic energy, interaction energy, zeeman energy and the like of the magnetic system.
The expression of hamiltonian is:
。
Wherein,For the exchange energy of the magnetic system,In order for the energy of the anisotropy to be that of,In order for the energy of the interaction to be that of the interaction,Is the externally applied magnetic field energy.
According to the theorem of angular momentum,。
The relation between the magnetization intensity M and the angular momentum L and the magnetization intensity moment expression are brought into the angular momentum theorem to obtain:
。
The equation may represent the precession form of the spin magnetization vector in the external magnetic field, but damping dissipation is not considered, and the damping term TD is derived from the lagrangian equation as follows:
;
Where α is the damping constant and MS is the saturation magnetization, therefore the magnetization dynamics equation taking into account the damping dissipation is:
。
And (3) M multiplied by two sides simultaneously to obtain:
。
The formula is arranged, and the magnetizing dynamics equation is as follows:
。
Wherein, put the differential term on the left side of the equation uniformly, it is more favorable to carry on the numerical simulation. Macroscopically, the magnetization is a function of time and position, its value being the vector sum of all the magnetic moments,
In the embodiment, the dynamic equation controls the speed of the instantaneous magnetic moment direction approaching to the effective magnetic field direction by introducing a damping term and utilizing the damping coefficient alpha, so that the dynamic change of the magnetic moment under the action of an external field can be accurately simulated, and the accuracy and the reliability of magnetization simulation are improved.
In one embodiment, as shown in fig. 2, the dynamic equation for each magnetic domain unit is obtained, comprising the steps of:
the dynamic behavior of each magnetic domain unit is described by the LLG equation, wherein the dynamic equation of the magnetic domain unit includes gyromagnetic ratio, damping coefficient α, and effective magnetic field Heff.
The dynamic behavior of each magnetic domain unit can be described by an LLG equation, wherein the LLG equation integrates the precession and damping effects of magnetic moment, and can accurately simulate the dynamic change of magnetic moment under the action of external field.
The gyromagnetic ratio gamma is a constant related to the material characteristics, and can reflect the precession speed of magnetic moment under the action of unit magnetic field, and the magnitude of the gyromagnetic ratio gamma is 2.21 multiplied by 105 m/(As). The damping coefficient alpha can control the speed of the magnetic moment direction approaching to the effective magnetic field direction, a larger alpha value means that the magnetic moment direction changes faster, the magnetic moment direction can be aligned to the effective field direction more rapidly, a smaller alpha value means that the magnetic moment direction changes slower, and the duration of the precession process is longer. The effective magnetic field Heff is the total magnetic field in which the magnetic moment is located, and may include not only the externally applied magnetizing field, but also an anisotropic field, an exchange field, etc. inside the material, and the direction and the size of Heff jointly determine the precession track and the final stabilizing direction of the magnetic moment.
And 202, setting the magnetization intensity of each magnetic domain unit to be constant and the magnetic moment direction to be variable in the LLG equation to obtain a dynamics equation of each magnetic domain unit.
To simplify the calculation and focus on the change in magnetic moment direction, the magnetization of each magnetic domain cell is set to be constant in the LLG equation, allowing only the magnetic moment direction to be changed, resulting in a kinetic equation for each magnetic domain cell suitable for magnetization analysis.
Illustratively, assuming that the magnetization of each magnetic domain unit is of a constant magnitude, the effective magnetic field acts only on its direction. Assuming that the magnetization of each magnetic domain unit is 1, the saturation magnetization is taken as a reference value, that is:
。
wherein x, y, z are x-axis direction, y-axis direction and z-axis direction in space, and mi is magnetization vector after normalization processing of the ith magnetic domain unit.
In one embodiment, the kinetic equation for a magnetic domain unit is:
;
Wherein,Representing the instantaneous magnetic moment direction of the magnetic domain cell mi,Representing gyromagnetic ratio, α representing damping coefficient, and Heff representing effective magnetic field.
Specifically, mi is a normalized magnetization vector of an ith magnetic domain unit, the mode length of the normalized magnetization vector is kept to be 1, only the direction of the normalized magnetization vector changes, gamma is gyromagnetic ratio, is a constant related to material characteristics and reflects the precession speed of magnetic moment under the action of a unit magnetic field, Heff is an effective field comprising an externally applied magnetic field, an anisotropic field, an exchange field and the like in the material, and alpha is a damping coefficient and controls the change rate of the direction of the magnetic moment.
In this embodiment, by the dynamic equation of the magnetic domain unit, the dynamic evolution process of the magnetic moment direction under the action of the external field can be focused on without considering the change of the magnetization intensity, so that the magnetizing behavior of the permanent magnet can be more efficiently analyzed and predicted.
In one embodiment, for the cell domains, m0 is the initial magnetic moment, and the magnetic moment vector is subject to spin precession under the effect of the effective field, gradually approaching the effective field direction. When the effective field has too short acting time or insufficient intensity, the magnetic moment direction is not completely consistent with the effective field direction finally according to a magnetic moment dynamics equation, but stays at a certain position in the precession motion, as shown in fig. 3 (a), namely, incomplete inversion of magnetic domains and microcosmic manifestations of incomplete magnetization. When the effective field strength and time are sufficient, the direction of the end-of-action magnetic moment vector is substantially coincident with the effective field direction, as shown in FIG. 3 (b), and the domain is flipped and the magnetic moment vector is coincident with the effective field direction.
In one embodiment, the effective magnetic field is calculated from the superposition of the following components:
An external magnetizing magnetic field component whose direction is aligned with the easy axis of magnetization of the permanent magnet to be magnetized;
an exchange field component between adjacent magnetic domains, which is an interaction between adjacent magnetic domain units;
the anisotropic field component of the material is determined by the structure of the permanent magnet to be magnetized;
the demagnetizing field component is calculated by the product of the magnetization and the demagnetizing tensor.
In modeling of the permanent magnet magnetizing process, the effective magnetic field Heff is calculated by superposition of a plurality of components including an external magnetizing field component, an exchange field component between adjacent magnetic domains, a material anisotropy field component, and a demagnetizing field component.
Wherein the external magnetizing field component, whose direction is aligned with the easy axis of the permanent magnet to be magnetized, is the main driving force in the magnetizing process, determining the basic orientation of the magnetic moment, the exchange action field component between adjacent magnetic domains is derived from the interaction between adjacent magnetic domain units, which tends to make the adjacent magnetic moment direction consistent, the material anisotropy field component is determined by the structure of the permanent magnet to be magnetized, such as crystal anisotropy or shape anisotropy, so that the magnetic moment is more stable in certain directions, and the demagnetizing field component reflects the reverse magnetic field generated by the magnetic moment itself by the product of magnetization and demagnetizing tensor, whose size and direction depend on the distribution of magnetization and the shape of the permanent magnet.
In this embodiment, the components act together to determine the dynamic behavior of the magnetic moment during magnetization and the resulting magnetization state.
In one embodiment, as shown in FIG. 4, solving the instantaneous magnetic moment direction of each magnetic domain cell at different moments based on the kinetic equation includes the steps of:
step 401, setting a time step delta t, and iteratively calculating an instantaneous magnetic moment direction according to the time step delta t;
step 402, solving a kinetic equation by adopting a Dragon-Greek tower method aiming at each time step deltat, and updating the instantaneous magnetic moment direction;
A time step deltat is set as a basic unit of time advancement in the calculation process. The size of this time step Δt can be determined according to the required computational accuracy and efficiency, typically on the order of nanoseconds to microseconds. If Δt is set, iterative calculation is performed according to the time step Δt to gradually find the instantaneous magnetic moment direction of each magnetic domain unit.
For each time step Δt, a dynamic equation can be solved by a Dragon-Gerdostat method, and the instantaneous magnetic moment direction is updated. The Dragon-Gregory tower method is a commonly used numerical method for solving a normal differential equation, and the value of the next time step is estimated by calculating a plurality of intermediate slopes in each time step, so that the solving accuracy is improved.
It should be noted that, within each time step Δt, four phases of the Dragon-Gerdostat method are used to calculate the change of the magnetic moment direction, namely, calculate the slope k1 of the current time step, based on the current magnetic moment direction and the effective field;
The intermediate state is estimated using k1, the slope k2 is calculated, the other intermediate state is estimated again using k2, the slope k3 is calculated, and finally the final slope k4 is calculated using k 3. By calculating the four slopes, a more accurate magnetic moment direction update formula can be obtained, so that the magnetic moment direction can be accurately updated in each time step deltat.
And 403, stopping iterative calculation of the instantaneous magnetic moment direction until the three-dimensional model of the permanent magnet to be magnetized reaches the magnetizing saturation.
And in each time step, solving a kinetic equation by adopting a Dragon-Greek-Tata method, and updating the instantaneous magnetic moment direction. The process is continued until the three-dimensional model of the permanent magnet to be magnetized reaches a magnetizing saturation, i.e. the magnetic moment direction of most magnetic domain units is basically consistent with the effective field direction, and the magnetizing saturation reaches an expected value, and at this time, the iterative calculation of the instantaneous magnetic moment direction is stopped. For example, the determination of the magnetizing saturation may be determined by calculating the degree of deviation of the magnetic moment directions of all the magnetic domain units from the effective field direction, and when the degree of deviation is smaller than a certain preset threshold value, the permanent magnet is considered to have reached the magnetizing saturation state.
In the embodiment, the change of the magnetic moment direction along with time can be accurately simulated by setting a proper time step delta t and solving a kinetic equation by adopting a Dragon-Gregorian method, so that the dynamic behavior of the magnetic moment in the magnetizing process can be accurately captured, and the iterative computation is stopped by judging the magnetizing saturation, so that the computing resource can be effectively saved, unnecessary computation is avoided, and the simulation efficiency is improved.
In one embodiment, the un-magnetized state of the permanent magnet to be magnetized is simulated by:
Randomly distributing magnetic moment directions for each magnetic domain unit, wherein the magnetic moment directions of the magnetic domain units are uniformly distributed in a three-dimensional space;
The magnetic moment directions of the magnetic domain units are different from each other when the magnetic domain units are not magnetized, the magnetic domain units are offset to present a scattered state, the initial magnetization saturation degree when the magnetic domain units are not magnetized is calculated through the average included angle between the magnetic moment directions and the easy magnetization axis, and the included angle ranges from 85 degrees to 95 degrees.
In the initial stage of the simulated permanent magnet magnetizing process, magnetic moment directions are randomly distributed for each magnetic domain unit, and the magnetic moment directions of the magnetic domain units are uniformly distributed in a three-dimensional space. When the permanent magnet is not magnetized, the magnetic moment directions inside the permanent magnet are scattered, and the magnetic moment directions of the magnetic domain units are different and offset, so that the permanent magnet is not magnetized as a whole. The setting of the initial state accords with the actual situation, and can accurately reflect the physical characteristics of the non-magnetized permanent magnet.
Specifically, the initial magnetization saturation when not magnetized can be calculated by the average angle between the magnetic moment direction and the easy axis, and the angle range is set to 85 ° to 95 °. The physical meaning of the angle range setting is that the easy magnetization axis is the direction which is most easy to magnetize in the permanent magnet, and in the non-magnetizing state, the magnetic moment direction is almost perpendicular to the easy magnetization axis, so that the initial magnetizing saturation is low. The included angle range from 85 degrees to 95 degrees can ensure that the magnetic moment direction is almost perpendicular to the easy magnetization axis at the beginning, so that the initial magnetization saturation is close to zero, and the physical characteristics of the non-magnetization state are met.
In one embodiment, for a permanent magnet to be magnetized, the effective magnetic field has an active time less than the target magnetizing time and/or an effective magnetic field has a strength less than the target magnetic field strength, the magnetic moment direction of the magnetic domain unit does not exactly coincide with the effective magnetic field direction, and/or
For a permanent magnet to be magnetized, the acting time of the effective magnetic field is smaller than the target magnetizing time and/or the strength of the effective magnetic field is smaller than the target magnetic field strength, and the magnetic moment direction of the magnetic domain unit is not completely inverted relative to the initial magnetic moment direction.
The target magnetizing time may be the minimum time set to achieve sufficient magnetizing of the permanent magnet, and the target magnetic field strength is the minimum magnetic field strength required to enable the permanent magnet to reach a saturated magnetizing state.
When the effective magnetic field has a duration less than the target magnetizing time and/or a strength less than the target magnetic field strength, the magnetic moment direction of the magnetic domain unit does not completely coincide with the effective magnetic field direction nor completely flip with respect to the initial magnetic moment direction.
Specifically, if the effective magnetic field has insufficient acting time, the magnetic moment does not have enough time to completely align to the effective field direction, and if the effective magnetic field has insufficient intensity, the magnetic moment cannot obtain enough energy to overcome the barriers such as anisotropy and demagnetizing field, and thus the complete overturning process cannot be completed.
In this embodiment, both cases may cause the magnetic moment to stay in an intermediate state, neither perfectly aligned with the effective field direction nor fully returning to the original direction, thereby affecting the magnetizing effect.
In one embodiment, as shown in fig. 5, the non-magnetized magnet model has different magnetic moment vectors in each magnetic domain of the permanent magnet, and counteracts each other to present a scattered state when not magnetized. The unsaturated magnetization state of the magnet model is shown in fig. 6, when the magnetic field strength is insufficient or the duration is insufficient, each magnetic domain does not completely trend toward the external magnetic field direction, i.e., does not have saturated magnetization, although precession flip has occurred. The saturated magnetization state of the magnet model is shown in fig. 7, and when a sufficient magnetic field strength and a sufficient duration are given, the permanent magnet is saturated magnetized, and most magnetic domains complete inversion, and the effective field direction is completely trended.
In one embodiment, the relationship of magnetizing saturation to pulse magnetic field strength and pulse duration comprises:
When the pulse magnetic field strength does not reach the target pulse magnetic field strength, the magnetizing saturation is increased along with the increase of the pulse magnetic field strength and the pulse duration;
Specifically, when the pulsed magnetic field strength does not reach the target pulsed magnetic field strength, the magnetizing saturation increases as the pulsed magnetic field strength and the pulse duration increase. When the pulsed magnetic field strength is low, the magnetic moment requires more pulse duration to overcome the internal resistance, progressively aligning in the direction of the magnetic field. As the strength of the pulsed magnetic field increases, the magnetic moments align more easily, while an increase in the pulse duration provides more time for the magnetic moments to respond to the magnetic field. Thus, when the target magnetic field strength is not reached, the increase in the pulse magnetic field strength and the pulse duration together promote an increase in the magnetizing saturation.
Increasing the pulse duration at a constant pulsed magnetic field strength stabilizes the magnetizing saturation at a certain value, rather than increasing it indefinitely;
Specifically, at a constant pulse magnetic field strength, as the pulse duration increases, the magnetic moment direction is gradually aligned to the magnetic field direction, and the magnetizing saturation increases gradually. After most of the magnetic moments have been aligned, the number of remaining unaligned magnetic moments is small, with limited boosting of magnetizing saturation, even if the pulse duration continues to increase. Due to damping effect and energy dissipation in the material, the alignment speed of magnetic moment gradually slows down along with the extension of the acting time, and finally, dynamic balance is achieved, so that the magnetizing saturation tends to a stable value. Thus, at a constant pulsed magnetic field strength, increasing the pulse duration gradually tends to a steady value for magnetizing saturation, rather than an infinite increase.
Under the target pulse magnetic field intensity, if the pulse duration reaches the target magnetizing time, the permanent magnet to be magnetized can be saturated and magnetized, and if the pulse duration is smaller than the target magnetizing time, the permanent magnet to be magnetized cannot reach the saturated and magnetized.
In particular, when the magnetic field strength is sufficient, the magnetic moment needs a certain time to overcome the internal resistance and gradually align to the magnetic field direction. If the pulse duration is long enough, the magnetic moment has enough time to complete alignment, thereby achieving saturation magnetization. However, if the pulse duration is less than the target magnetization time, the magnetic moments do not have enough time to align properly, resulting in insufficient saturation of magnetization and failure to reach saturation magnetization. Therefore, sufficient alignment of the magnetic moments can be ensured only when the pulse duration reaches the target magnetizing time, and saturation magnetization is achieved.
In one embodiment, as shown in fig. 8, the graph shows the relationship of magnetizing saturation as a function of magnetic field strength for different pulse durations. Wherein the horizontal axis represents magnetic field strength (in a/m) and the vertical axis represents saturation of magnetization, and curves of different colors and symbols correspond to different pulse durations (from 1.ms to 6 ms). When the intensity of the externally applied magnetic field is 600kA/m, the maximum magnetic field intensity does not reach the saturation magnetization magnetic field intensity of the permanent magnet model. Even if the duration is long enough, the final magnetizing saturation remains around 50%. When the intensity of the externally applied magnetic field is increased to 800kA/m, the magnetization speed is obviously accelerated within 0-1.5 ms. However, the field strength still does not reach saturation magnetization, and although most of the domains complete inversion, about 40% of the domains are still displaced from the easy axis, resulting in a final saturation level of about 80%.
When the peak value of the magnetizing magnetic field reaches 1000kA/m, the permanent magnet reaches a saturated state, the magnetic domain unit basically finishes turning over, and the magnetizing speed is obviously improved. After saturation magnetization is reached, the external magnetic field strength is further increased, and the magnetizing saturation is increased to a certain extent within the same duration.
In summary, the dynamic equations of the magnetic domain units constructed based on the LLG equation can effectively reflect the influence of the magnetization field strength and duration on the magnetization effect. The relationship between magnetic field strength and duration can be summarized in that when the saturation magnetization magnetic field strength is not reached, the magnetization saturation increases as the magnetic field strength and duration increase. Further increases in duration at a given field strength will stabilize the magnetizing saturation at a given value, rather than an infinite increase. Once the saturation magnetization is reached, the sample can be saturated if the duration is sufficient. However, if the duration is insufficient, saturation magnetization cannot be achieved.
In one embodiment, as shown in fig. 9, the graph shows the relationship of remanence as a function of field strength at different pulse durations. Wherein the horizontal axis represents the magnetic field strength (in a/m) and the vertical axis represents the remanence (in mT), the curves for different colors and symbols correspond to different pulse durations (from 1.05ms to 6.20 ms). The remanence refers to the magnetization intensity of the magnetic material remained after the external pulse magnetic field is removed, and is an important index for measuring the magnetization capability of the magnetic material.
At low magnetic field strength, the remanence increases rapidly with the increase of the magnetic field strength, and the curve difference of different durations is large, which means that the influence of the pulse duration on the remanence is remarkable. At high magnetic field strengths, the remanence tends to saturate, the curves tend to flatten, and the curves of different durations tend to agree, indicating that the impact of the pulse duration on the remanence is reduced when the magnetic field strength is sufficiently high. Thus, remanence is not only related to field strength, but also to pulse duration, especially in the low field strength region. When the magnetic field strength reaches the saturation value, further increase of the magnetic field strength or duration has little effect on the improvement of the remanence.
In one embodiment, the effective magnetic field strength is not generally constant during magnetizing, but rather varies dynamically over time, such variation may be due to characteristics of the magnetizing apparatus, fluctuations in power supply, or intentionally designed to achieve a particular magnetizing strategy. The effect of such dynamically varying effective magnetic field strength on the direction of the magnetic moment can be simulated by introducing time-varying terms into the kinetic equation, such as in the (LLG) equation, where the effective magnetic field strength is set as a function of time, thereby more accurately describing the dynamic behavior of the magnetic moment under the influence of an external field. In this way, the magnetizing process can be optimized, and the magnetizing effect can be improved.
Based on the same conception, the application also provides a magnetizing apparatus, comprising:
The magnetizing circuit is used for magnetizing the permanent magnet to be magnetized as shown in fig. 10;
The 0-1000V direct current power supply on the left side in the magnetizing circuit is used for providing energy for the whole circuit. The charging process of the circuit can be controlled by the switch K1 and the current limiting resistor R1 (1 kΩ). A plurality of capacitors (c=400 μf, u=1800V) are connected in parallel to form a storage capacitor for storing electrical energy. These capacitors accumulate energy during charging and then release rapidly during discharging, producing a pulsed current. The switch K2 is used to control the start of the magnetizing process. When the switch K2 is closed, the capacitor bank discharges through the magnetizing coil, generating a pulsed magnetic field. The diode DL serves as a protection to prevent reverse current flow during discharge and damage to other components in the circuit. The magnetizing coil is a core part of the circuit, and the inductance l= 106.65mH and the resistance RL =0.63Ω are measured through experiments. When the capacitor bank is discharged through the coil, a pulsed magnetic field is generated in the coil for magnetizing the permanent magnet. The Ground (GND) is used for grounding the circuit, ensuring safe and stable operation of the circuit.
The magnetizing circuit works in the principle that a power supply charges a capacitor bank by closing a switch K1, and the capacitor bank stores electric energy. When the capacitor bank is charged to a required voltage, the switch K1 is opened and the switch K2 is closed, and the capacitor bank is rapidly discharged through the magnetizing coil to generate a pulse magnetic field. The magnetic field acts on the permanent magnet to be magnetized to change the magnetic moment direction of the permanent magnet, thereby realizing the magnetizing process. The parameters in the circuit (such as the capacity of the capacitor, the size of the inductor, etc.) can be adjusted according to the required pulse magnetic field strength and duration to meet different magnetizing requirements.
The controller comprises a memory and a processor, wherein the memory stores a computer program, and the processor realizes a permanent magnet magnetizing control method based on magnetic domain dynamics when executing the computer program.
The processor can dynamically adjust magnetizing parameters, such as magnetic field strength and duration, according to real-time data and a preset control strategy in the magnetizing process so as to ensure that the permanent magnet can achieve the optimal magnetizing effect.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples merely represent a few embodiments of the present application, which are described in more detail and are not to be construed as limiting the scope of the application. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of the application should be assessed as that of the appended claims.