A Fast Feedback Control Method and Device for Magnetic Domains Based on an Event Camera

Abstract

The present invention relates to a method and device for rapid feedback control of magnetic domains based on an event camera. The method includes: setting the event camera on the eyepiece of a magneto-optical Kerr microscope; applying a magnetic field to the magnet material to be measured, and the event camera acquiring event information of the magnetic domain imaging of the ferromagnetic material to be measured; obtaining feedback control information for regulating the magnetic field according to the event information of the magnetic domain imaging; and outputting a command for adjusting the magnetic field according to the feedback control information and applying it to the magnet material to be measured. The present invention can achieve visual-based rapid feedback control.

Description

Technical Field

[0001] The present invention relates to the field of magnetic storage devices, and in particular to a method and device for rapid feedback control of magnetic domains based on an event camera. Background Art

[0002] When a linearly polarized light beam is reflected by a magnetic medium, the polarization plane of the reflected light has a small angular deflection relative to the polarization plane of the incident light, that is, the Kerr rotation angle. This phenomenon is called the magneto-optical Kerr effect. This effect combined with microscopy technology forms a magneto-optical Kerr microscope, which is widely used in magnetic measurement of magnetic materials, magnetic domain observation, etc.

[0003] Vision-based rapid feedback control refers to obtaining magnetic domain information of a magnetic sample through the optical signal of a magneto-optical Kerr (MOKE) microscope, and then adjusting the magnetic field, electric field or current, etc. according to this information to achieve rapid control of the dynamics of the magnetic sample, such as stopping the magnetic domain at a certain shape or size.

[0004] Currently, all magneto-optical Kerr microscope devices use ordinary CMOS cameras with an upper limit of 100 frames, that is, only 100 images can be acquired per second. Considering processes such as data transmission, it is generally 60 frames during testing. Although using a high-speed camera can increase the upper limit to 1000 frames, the amount of data generated is too large to be transmitted to the computer for real-time imaging in a timely manner. It can only be stored in a data card first and processed for imaging later. This method is basically impossible to achieve vision-based rapid feedback control. Summary of the Invention

[0005] According to the problems existing in the prior art, the present invention provides a method and device for rapid feedback control of magnetic domains based on an event camera, which uses a combination of an event camera and a magneto-optical Kerr microscope for rapid magnetic domain imaging in order to identify the movement of magnetic domains and feedback control the applied magnetic field.

[0006] The technical solution of the present invention is as follows:

[0007] In a first aspect, an embodiment of the present specification provides a method for rapid feedback control of magnetic domains based on an event camera, including:

[0008] Setting an event camera on the eyepiece of a magneto-optical Kerr microscope;

[0009] Applying a magnetic field to the magnet material to be measured, and the event camera obtains event information of magnetic domain imaging of the ferromagnetic material to be measured;

[0010] Obtaining feedback control information for regulating the magnetic field according to the event information of magnetic domain imaging;

[0011] Outputting a magnetic field adjustment instruction according to the feedback control information and applying it to the magnet material to be measured.

[0012] As a preferred technical solution, an event camera is used to quickly capture the event information of the magnetic domain imaging of the ferromagnetic material to be measured, and a series of polarity data are output according to the change of the light intensity of the magnetic domain. When the light intensity increases, the polarity is positive and marked as a positive event; when the light intensity decreases, the polarity is negative and marked as a negative event.

[0013] As a preferred technical solution, the threshold of the magnetic domain imaging of the magnetic material to be measured is that the number of negative events generated by the event camera is proportional to the time slice width.

[0014] As a preferred technical solution, the time slice width is 5 ms, and the number of negative events corresponding to the time slice width of 5 ms is 16,200.

[0015] As a preferred technical solution, the feedback control information includes: reducing the magnetic field below the threshold of the magnetic domain imaging of the magnetic material to be measured.

[0016] As a preferred technical solution, the magnetic field is reduced to zero.

[0017] As a preferred technical solution, the magnetic field adjustment command includes: adjusting the magnetic field strength and / or the magnetic field direction.

[0018] In a second aspect, an embodiment of the present specification provides an apparatus for implementing any of the above methods, including:

[0019] A magneto-optical Kerr microscope, which includes at least one eyepiece;

[0020] An event camera, which is arranged on the eyepiece and is used to obtain the event information of the magnetic domain imaging of the ferromagnetic material to be measured;

[0021] A computer system, which includes a driving module and a feedback control module; one end of the computer system is electrically connected to the event camera, and the other end of the computer system is electrically connected to the magnetic material to be predicted;

[0022] Among them, the driving module is configured to obtain the feedback control information for regulating the magnetic field according to the event information of the magnetic domain imaging; the feedback control module is configured to output a magnetic field adjustment command according to the feedback control information and act on the magnet material to be measured.

[0023] As a preferred technical solution, the computer system is electrically connected to the predicted magnetic material through a data acquisition line.

[0024] In a third aspect, an embodiment of the present specification provides a magnetic memory, which includes any of the apparatuses provided in the second aspect above.

[0025] The beneficial effects achieved by the technical solution adopted by the present invention:

[0026] 1. The event camera is directly mounted on the eyepiece of the magneto-optical Kerr microscope. Due to the characteristic of small data volume of the event camera, the event camera can achieve low latency and faster data processing, effectively realizing fast vision-based feedback control.

[0027] 2. The data of magnetic domain imaging is transmitted to the computer through the data acquisition line. Information such as the size of the magnetic domain imaging is identified by software. Judgments are made based on this information and feedback control signals are output to the electromagnet, and the magnetic domain is controlled by adjusting the magnetic field strength, effectively shortening the time for collecting signals and the time for identifying the movement of the magnetic domain wall. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. It constitutes a part of the present invention. The schematic embodiments of the present invention and their descriptions explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0029] Figure 1 It is a flowchart of a method for rapid feedback control of magnetic domains based on an event camera disclosed in Embodiment 1 of the present invention;

[0030] Figure 2 It is a bar chart of time slice events of the entire process of feedback control disclosed in Embodiment 1 of the present invention;

[0031] Figure 3 It is a frame reconstruction image of some key time points during the feedback control process disclosed in Embodiment 1 of the present invention; (a) Nucleation time; (b) Time for identifying magnetic domain expansion; (c) Expansion deceleration time; (d) Final stop time.

[0032] Figure 4 It is a device diagram for implementing the method described in Embodiment 1 disclosed in Embodiment 2 of the present invention.

[0033] DESCRIPTION OF REFERENCE NUMERALS:

[0034] CMOS camera 10; Event camera 20; Computer system 30; Sample stage 40; Electromagnet 50; LED light source 101, Beam splitter 102, Polarizer 103; Analyzer 104. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] To make the objectives, technical solutions and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the specific embodiments and corresponding drawings of the present invention. In the description of the present invention, it should be noted that the term "or" is usually used in the sense of including "and / or", unless otherwise clearly specified in the content.

[0036] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0037] Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0038] Example 1

[0039] This embodiment provides a method for fast feedback control of magnetic domains based on an event camera. According to Figure 1 , it includes:

[0040] Set the event camera on the eyepiece of the magneto - optical Kerr microscope;

[0041] Apply a magnetic field to the magnet material to be measured, and the event camera acquires the event information of the magnetic domain imaging of the ferromagnetic material to be measured;

[0042] Obtain the feedback control information for regulating the magnetic field according to the event information of the magnetic domain imaging;

[0043] Output an instruction for adjusting the magnetic field according to the feedback control information and act on the magnet material to be measured.

[0044] Preferably, the event camera quickly captures the event information of the magnetic domain imaging of the ferromagnetic material to be measured, and outputs a series of polarity data according to the change in the light intensity of the magnetic domain. When the light intensity increases, the polarity is positive and marked as a positive event; when the light intensity decreases, the polarity is negative and marked as a negative event.

[0045] In a preferred implementation, when the magnetic domain expands, with the rapid movement of the magnetic domain wall, the event camera will generate a large number of events. In this embodiment, the sudden increase in the number of negative events, that is, the darkening of the light intensity, is used as the judgment criterion for observing the expansion of the magnetic domain.

[0046] Preferably, the threshold of the magnetic domain imaging of the magnetic material to be measured is that the number of negative events generated by the event camera is proportional to the time slice width.

[0047] In a preferred embodiment, with the sample and the system unchanged and the parameters of the event camera set unchanged, the number of negative events is proportional to the selected time slice width. It should be noted that if the fluctuations of random noise are taken into account, it is not a strictly proportional relationship, but the overall trend shows a proportional relationship.

[0048] Preferably, the time slice width is 5 ms, and the number of negative events corresponding to a time slice width of 5 ms is 16,200. Among them, for the setting of the time slice width, other widths can also be selected, such as 4 ms or 6 ms, but for better feedback control effect, the specific time slice width should be set according to actual needs.

[0049] Preferably, the feedback control information includes: reducing the magnetic field below the threshold for imaging the magnetic domains of the magnetic material to be measured.

[0050] Preferably, the magnetic field is reduced to zero.

[0051] Specifically, to block the expansion of the magnetic field, theoretically, it is only necessary to reduce it below the coercivity of the magnetic material, and it is not necessary to adjust the magnetic field to zero. It can also be reduced to a negative number, that is, to let the magnetic field reverse overshoot, so as to shorten the demagnetization time of the iron core and the overall feedback time. For example, when the magnetic field is 10 mT, the magnetic field can drive the movement of magnetic domain walls. However, if the magnetic field is suddenly reduced below a threshold, such as 5 mT, the driving force of the magnetic domains decreases. However, the most obvious is to reduce it to 0 or reverse, and the driving force of the magnetic domains basically disappears completely. Among them, the threshold corresponds to the coercivity of the hysteresis loop.

[0052] Those skilled in the art should understand that as long as the magnetic field is reduced below the threshold for imaging the magnetic domains of the magnetic material to be measured, the effect of controlling the expansion of magnetic domains can be achieved. Preferably, when the magnetic field is reduced to zero, the feedback effect is the best.

[0053] Specifically, according to Figure 2 , the time slice width is selected as 5 ms, and the threshold for magnetic domain expansion is set to 16,200 negative events per single time slice, that is, as long as there are more than 16,200 negative events within 5 ms, the magnetic field is reduced to 0. This selection of the judgment criterion takes into account the fluctuations in the number of negative events caused by noise. After statistically analyzing the number of negative events in the static state, a value higher than three times the standard deviation of the mean is selected to prevent "false triggering".

[0054] In the actual experimental scenario, the time point of reverse magnetic domain nucleation is found frame by frame from the video as t n = 1.150 s, and the time t when the magnetic domains finally stop expanding f＝ 1.230 s. In addition, at t s = 1.200 s, the number of negative events starts to decrease, and at the same time, it is found from the video that the expansion speed of the magnetic domains also significantly decreases, indicating that the change in the magnetic field affects the process of magnetic domain expansion.Figure 3 The frame reconstruction images corresponding to these time points are listed. It can be clearly seen that the magnetic domain wall indeed stops moving after expanding to a certain extent, which also confirms that the feedback process does play a role.

[0055] Preferably, the magnetic field adjustment instruction includes: adjusting the magnetic field strength and / or the magnetic field direction. Specifically, the entire feedback control operation from event-based visual data acquisition, analysis, recognition to issuing instructions to control the magnetic field is implemented through computer programming code. The feedback signal is recognized by the computer and directly outputs an instruction to adjust the magnetic field strength or the magnetic field direction to achieve fast feedback.

[0056] In the actual experimental scenario, from the nucleation time point to the final stop of the magnetic domain expansion, a total of 80 ± 5 ms has passed (the error is estimated based on the time slice width of 5 ms). However, this does not mean that the response time of our feedback control device is as long as 80 ms. There are four key time points in the whole process. According to Figure 3 it can be divided into three segments: The first segment is from t n to t r , from nucleation to the recognition of magnetic domain expansion; the second segment is from t r to t s , from recognition to a significant deceleration of expansion; the third segment is from t s to t f , from the deceleration of expansion to complete stop. In fact, the response time of the feedback system should only include the second segment, that is, 25 ± 5 ms, because the entire feedback process starts when the event camera receives a sufficiently strong change in the magneto-optical Kerr effect optical signal, and the significant deceleration of the magnetic domain expansion indicates that the magnetic field has responded to our feedback control. Even if it does not immediately drop to zero, it has at least weakened. From another perspective, the entire process of magnetic domain movement is also expected to be significantly shortened. For example, in the first period, we did not immediately determine that the magnetic domain was expanding after nucleation, thus wasting 25 ± 5 ms. This is mainly because our recognition algorithm is too simple and only relies on counting the number of negative events. If the recognition algorithm is designed properly, we can completely recognize the magnetic domain expansion earlier and initiate the feedback response earlier. In addition, the biggest constraint lies in the response speed of the electromagnet, that is, after the electromagnet receives the feedback signal, it cannot immediately reduce the magnetic field to zero. Simply put, the main contribution of this invention is to shorten the time for signal acquisition and the time for recognizing the movement of the magnetic domain wall.

[0057] Example 2

[0058] This embodiment provides a device for implementing any of the above methods. According to Figure 4 it includes:

[0059] A magneto-optical Kerr microscope, which includes at least one eyepiece;

[0060] An event camera 20 is disposed on the eyepiece. The event camera 20 is used to obtain event information of the magnetic domain imaging of the ferromagnetic material to be measured.

[0061] A computer system 30 includes a driving module and a feedback control module. One end of the computer system 30 is electrically connected to the event camera 20, and the other end of the computer system 30 is electrically connected to the ferromagnetic material to be predicted.

[0062] Among them, the driving module is configured to obtain feedback control information for regulating the magnetic field according to the event information of the magnetic domain imaging; the feedback control module is configured to output a magnetic field adjustment instruction to act on the magnet material to be measured according to the feedback control information.

[0063] The event camera 20 features high temporal resolution and small data volume, enabling low latency and faster data processing. These advantages are crucial for realizing vision-based fast feedback control. Specifically, the event camera 20 is directly mounted on the eyepiece of the magneto-optical Kerr. The magneto-optical Kerr microscope further includes an LED light source 101, a beam splitter 102, a polarizer 103, and an analyzer 104. The ferromagnetic material to be measured is placed on the sample stage 40 of the magneto-optical Kerr microscope. The CMOS camera 10 is used to adjust the position and focus of the sample, and the event camera 20 is used to quickly record the movement process of the magnetic domain. Then, a magnetic field is applied to the magnet material to be measured. The data of the magnetic domain imaging is transmitted into the computer system 30 through a data acquisition line. By identifying information such as the size of the magnetic domain imaging, judgments are made based on this information and a feedback control signal is output to the electromagnet, and the magnetic domain is controlled by adjusting the intensity of the magnetic field.

[0064] Preferably, the computer system 30 is electrically connected to the predicted magnetic material through a data acquisition line.

[0065] The event camera 20 itself is equipped with a USB3.0 data cable, which is connected to any USB3.0 port of the computer. There are more than one way to connect the computer to the electromagnet. In a preferred embodiment, a data acquisition card is connected to the PCIE slot on the computer motherboard, which can convert the commands issued by the computer into analog voltage signals. The analog voltage signal output terminal of the data acquisition card is connected to the input terminal of a dedicated amplifier, and the output terminal of the amplifier is the large current for driving the electromagnet, which is directly connected to the electromagnet. The dedicated amplifier is designed for large current and large inductance circuits such as electromagnets.

[0066] The computer system 30 is divided into two layers. The first layer is the driving module. The event camera 20 and the data acquisition card enable the computer to identify the hardware and perform basic underlying communication. The second layer is the feedback control module, which realizes the entire feedback control operation from event-based visual data acquisition, analysis, recognition to issuing commands to control the magnetic field based on the driving.

[0067] Example 3

[0068] The embodiments of this specification provide a magnetic memory, and the magnetic memory includes the device provided in the above Embodiment 2.

[0069] The above has introduced in detail a method and device for fast magnetic domain feedback control based on an event camera in the embodiments of the present application. Specific examples are used herein to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A fast feedback control method for magnetic domains based on an event camera, characterized in that, Comprising: Setting an event camera on the eyepiece of a magneto-optical Kerr microscope; Applying a magnetic field to the magnet material to be measured, and the event camera acquiring event information of the magnetic domain imaging of the ferromagnetic material to be measured; Obtaining feedback control information for regulating the magnetic field according to the event information of the magnetic domain imaging; Outputting a command for regulating the magnetic field according to the feedback control information and acting on the magnet material to be measured; The feedback control information includes: reducing the magnetic field below the threshold of the magnetic domain imaging of the ferromagnetic material to be measured, reducing the driving force of the magnetic domain, controlling the effect of magnetic domain expansion, so as to shorten the demagnetization time of the iron core and the overall feedback time, wherein the threshold corresponds to the coercive force of the hysteresis loop.

2. The method according to claim 1, characterized in that, Applying a magnetic field to the magnet material to be measured, and the event camera acquiring event information of the magnetic domain imaging of the ferromagnetic material to be measured, including: Quickly capturing event information of the magnetic domain imaging of the ferromagnetic material to be measured by using an event camera, and outputting a series of polarity data according to the change of the light intensity brightness of the magnetic domain. When the brightness increases, the polarity is positive and marked as a positive event; when the brightness decreases, the polarity is negative and marked as a negative event.

3. The method according to claim 2, wherein The threshold of the magnetic domain imaging of the ferromagnetic material to be measured is that the number of negative events generated by the event camera is proportional to the time slice width.

4. The method according to claim 3, wherein The time slice width is 5 ms, and the number of negative events corresponding to the time slice width of 5 ms is 16,200.

5. The method according to claim 1, wherein Reducing the magnetic field to zero.

6. The method according to claim 1, characterized in that, Outputting a command for regulating the magnetic field according to the feedback control information and acting on the magnet material to be measured, including: The command for regulating the magnetic field includes: regulating the magnetic field strength and / or the magnetic field direction.

7. An apparatus for implementing the method according to any one of claims 1-6, characterized in that Comprising: A magneto-optical Kerr microscope, which includes at least one eyepiece; An event camera, which is set on the eyepiece, and the event camera is used to acquire event information of the magnetic domain imaging of the ferromagnetic material to be measured; A computer system, which includes a driving module and a feedback control module; one end of the computer system is electrically connected to the event camera, and the other end of the computer system is electrically connected to the magnetic material to be predicted; Wherein, the driving module is configured to obtain feedback control information for regulating the magnetic field according to the event information of the magnetic domain imaging; The feedback control module is configured to output a command for regulating the magnetic field according to the feedback control information and act on the magnet material to be measured.

8. The device according to claim 7, wherein The computer system is electrically connected to the magnetic material to be predicted through a data acquisition line.

9. A magnetic memory, characterized in that, The magnetic memory includes the device according to any one of claims 7 or 8.

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