Magnetic field measurement system based on laser speckles

Abstract

The invention provides a magnetic field measurement system based on laser speckles, which comprises a laser device, a non-contact magnetic field sensor, a condensation unit, an image acquisition unit and a processing unit which are connected in sequence, the laser speckles on the non-contact magnetic field sensor are changed under the action of an external magnetic field, and the changed laser speckles are transmitted to the image acquisition unit through the condensation unit for laser speckle image acquisition; and the processing unit performs image processing on the collected laser speckles to obtain correlation coefficients of the laser speckles, and determines the magnetic field size and change frequency of the external magnetic field according to changes of the correlation coefficients of the laser speckles. The magnetic field measurement sensitivity and accuracy are high, the intensity of a static magnetic field can be measured, and the intensity and change frequency of a dynamic magnetic field can also be measured.

Description

Technical Field

[0001] The present invention belongs to the field of magnetic field measurement, and particularly relates to a magnetic field measurement system based on laser speckle. Background Art

[0002] Magnetic field measurement in complex environments has great application prospects in fields such as industry, aerospace, and environmental monitoring. Currently, magnetic field measurement systems based on laser speckle usually use contact magnetic field sensors. This contact magnetic field sensor can sense magnetic field changes and cause changes in laser speckle. By evaluating the changes in the laser speckle pattern, the magnetic field strength is determined. However, the sensitivity of this system is relatively low. The contact magnetic field sensor may introduce interference during the measurement process, resulting in low measurement accuracy and being unable to be applied to non-contact magnetic field measurement scenarios. In addition, this system cannot measure the change frequency of dynamic magnetic fields. Summary of the Invention

[0003] The present invention provides a magnetic field measurement system based on laser speckle to solve the problems of relatively low sensitivity and accuracy of current magnetic field measurement systems based on laser speckle, and the inability to measure the change frequency of dynamic magnetic fields.

[0004] According to the first aspect of the embodiments of the present invention, a magnetic field measurement system based on laser speckle is provided, including a laser, a non-contact magnetic field sensor, a light condensing unit, an image acquisition unit, and a processing unit connected in sequence. The laser provides a laser signal to the non-contact magnetic field sensor. Under the action of an external magnetic field, the laser speckle on the non-contact magnetic field sensor changes. The changed laser speckle is transmitted to the image acquisition unit through the light condensing unit for laser speckle image acquisition. The processing unit performs image processing on the acquired laser speckle to obtain the correlation coefficient of the laser speckle, and determines the magnetic field magnitude and change frequency of the external magnetic field according to the change of the correlation coefficient of the laser speckle.

[0005] Optionally, the greater the intensity of the external magnetic field, the smaller the correlation coefficient of the laser speckle; the lower the change frequency of the magnetic field, the faster the response speed; when the change frequency is constant, the smaller the magnetic field change amount between adjacent peaks and valleys of the magnetic field, the slower the response speed, and the greater the magnetic field change amount between adjacent peaks and valleys of the magnetic field, the faster the response speed.

[0006] Optionally, the processing unit is specifically configured to determine the intensity of the external magnetic field according to the magnitude of the correlation coefficient of the laser speckle. When determining the change frequency of the external magnetic field, first determine the electromagnetic magnitudes corresponding to the adjacent peak and valley values of the correlation coefficient respectively, calculate the difference between the two determined electromagnetic magnitudes to obtain the electromagnetic change amount.

[0007] Determine the time difference between adjacent peak and valley values ​​of the correlation coefficient, determine the first response duration caused by the electromagnetic change according to the magnitude of the electromagnetic change, and determine the second response duration caused by the change frequency according to the time difference and the first response duration, thereby determining the change frequency.

[0008] Optionally, the processing unit locally stores the correspondence between the correlation coefficient and the magnetic field strength, the correspondence between the magnetic field change and the first response time, and the correspondence between the change frequency and the second response time; wherein the correspondence between the change frequency and the second response time is: the difference in the electromagnetic magnitudes corresponding to adjacent peak and valley values ​​of the correlation coefficient is 0, that is, when the electromagnetic change is 0, the correspondence between the change frequency and the second response time; the second response time is equal to the time difference plus the first response time.

[0009] Optionally, the contactless magnetic field sensor includes a substrate and a thin film disposed on the substrate, wherein the thin film is made by mixing magnetic nanoparticles and polydimethylsiloxane (PDMS). Under the action of an external magnetic field, the magnetic nanoparticles are magnetized or rearranged, causing the PDMS to deform, thereby changing the scattering properties of the film surface, causing the laser speckle to change.

[0010] Optionally, the non-contact magnetic field sensor is manufactured according to the following steps:

[0011] Placing the magnetic nanoparticles in deionized water and thoroughly mixing and shaking the magnetic nanoparticles so that the magnetic nanoparticles are evenly distributed in the deionized water to obtain a magnetic nanoparticle solution;

[0012] PDMS includes prepolymer A and crosslinking agent B. The mechanical characteristics of PDMS are modulated by adjusting the ratio of prepolymer A to crosslinking agent B. A corresponding amount of magnetic nanoparticle solution is mixed with prepolymer A and stirred, and then crosslinking agent B is added and stirred continuously to obtain a magnetic PDMS solution.

[0013] The magnetic PDMS solution is evenly applied on a substrate, and placed in a drying oven for heating and drying to obtain the non-contact magnetic field sensor.

[0014] Optionally, the magnetic nanoparticles are Fe3O4 particles; and the substrate is a glass sheet, an iron sheet or a solid magnetostrictive material sheet.

[0015] Optionally, the laser is a spatial laser with adjustable power, and the focusing unit is a convex lens with adjustable position and focal length. The brightness and contrast of the laser speckle image are adjusted by adjusting the power of the laser, and the size and contrast of the laser speckle image are adjusted by adjusting the position and focal length of the focusing unit; the image acquisition unit is a CCD sensor.

[0016] Optionally, the correlation coefficient is the Pearson correlation coefficient.

[0017] Optionally, if the change frequency of the magnetic field is too high or the magnetic field change amount between adjacent peaks and valleys of the magnetic field is too large, it will cause material saturation or nonlinear effects, thus reducing the response speed.

[0018] When the processing unit determines the change frequency of the external magnetic field, it first judges whether the magnetic field change amount between adjacent peaks and valleys of the magnetic field is too large. If so, the system prompts that the magnetic field change amount is too large and the change frequency measurement cannot be performed. Otherwise, the system measures the change frequency.

[0019] After the system completes the measurement of the change frequency, it judges whether the change frequency is too high. If so, the system prompts that the change frequency is too high and the change frequency measurement cannot be performed. Otherwise, the measurement result is displayed.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. The present invention uses a non-contact magnetic field sensor to measure the magnetic field. Since the sensor does not directly contact the outside world and is only affected by the external magnetic field, the measurement sensitivity and accuracy are relatively high. Based on the non-contact magnetic field sensor, the present invention selects a correlation coefficient that is not sensitive to brightness changes but has high robustness to reflect the change of laser speckle. At this time, there is a linear relationship between the magnetic field strength and the correlation coefficient. The adjacent peaks and valleys of the correlation coefficient can be used to calibrate the time when the adjacent peaks and valleys of the magnetic field appear. And there is a linear relationship between the magnetic field change frequency and the response speed. The difference in the electromagnetic magnitudes corresponding to the adjacent peak and valley values of the correlation coefficient, that is, the electromagnetic change amount, also has a linear relationship with the response speed. Therefore, according to the change of the correlation coefficient, the present invention can not only measure the magnitude of the external magnetic field but also measure the change frequency of the magnetic field.

[0022] 2. The present invention sets a thin film made of a mixture of magnetic nanoparticles and polydimethylsiloxane (PDMS) on different types of substrates, which can meet the requirements of more magnetic field measurement scenarios. The present invention sets a thin film made of a mixture of magnetic nanoparticles and polydimethylsiloxane (PDMS) on a solid magnetostrictive material thin sheet, studies the response characteristics of this non-contact magnetic field sensor to a dynamic magnetic field, and optimizes the dynamic measurement performance of the system.

[0023] 3. Under the action of an external magnetic field, the magnetic nanoparticles in the non-contact magnetic field sensor of the present invention will be magnetized or rearranged, causing the PDMS to deform, thereby changing the scattering characteristics of the film surface and making the laser speckle change. The deformation can make the change of the correlation coefficient of the laser speckle linear, so as to further ensure the linear relationship between the magnetic field strength and the correlation coefficient, ensure that the adjacent peaks and valleys of the correlation coefficient can be used to calibrate the time when the adjacent peaks and valleys of the magnetic field appear, and there is a linear relationship between the magnetic field change frequency and the response speed, and there is also a linear relationship between the electromagnetic change amount corresponding to the adjacent peak and valley values of the correlation coefficient and the response speed;

[0024] 4. The present invention mixes Fe3O4 nanoparticles with PDMS to make a magnetic film with high magnetic response characteristics. The magnetic PDMS has both flexibility and magnetic sensitivity and can produce a small deformation under an external magnetic field, significantly improving the sensitivity and response speed of magnetic field measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic structural diagram of an embodiment of the magnetic field measurement system based on laser speckle of the present invention;

[0026] Figure 2 is the laser speckle pattern collected by the present invention under different magnetic field distributions;

[0027] Figure 3 is a schematic diagram of the magnetic field measurement response relationship of three non-contact magnetic field sensors with a glass sheet, an iron sheet and a solid magnetostrictive material sheet as the substrates of the present invention;

[0028] Figure 4 is a schematic diagram of the dynamic magnetic field change and dynamic magnetic field response of the present invention;

[0029] Figure 5 is a schematic diagram of the dynamic magnetic field change at different frequencies and the dynamic magnetic field response at different frequencies of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and make the above-mentioned objects, features and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be further described in detail below with reference to the drawings.

[0031] In the description of the present invention, unless otherwise specified and limited, it should be noted that the term "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the communication inside two components. It can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meaning of the above terms can be understood according to specific situations.

[0032] See Figure 1, which is a schematic structural diagram of an embodiment of the magnetic field measurement system based on laser speckle of the present invention. The magnetic field measurement system may include a laser, a non-contact magnetic field sensor, a condenser unit, an image acquisition unit, and a processing unit connected in sequence. The laser provides a laser signal to the non-contact magnetic field sensor. Under the action of an external magnetic field, the laser speckle on the non-contact magnetic field sensor changes, and the changed laser speckle is transmitted to the image acquisition unit through the condenser unit for laser speckle image acquisition; the processing unit performs image processing on the acquired laser speckle to obtain the correlation coefficient of the laser speckle, and determines the magnetic field magnitude and change frequency of the external magnetic field according to the change of the correlation coefficient of the laser speckle.

[0033] In this embodiment, the laser may be a spatially adjustable laser with adjustable power. By adjusting the power of the laser, the brightness and contrast of the laser speckle image can be adjusted, so as to obtain a speckle image with better quality. In order to obtain a better speckle image, the adjustment of the output power needs to consider multiple factors comprehensively. First, the reflectivity and roughness of the surface of the object to be measured will directly affect the scattering effect of the laser. A high reflectivity or smooth surface may require a lower power to avoid overexposure, while a rough or low reflectivity surface requires a higher power to enhance the signal. Secondly, the ambient light conditions will also affect the contrast of the speckle image. Under strong ambient light, the power needs to be increased to improve the signal-to-noise ratio, and under weak light conditions, the power can be appropriately reduced. By comprehensively considering these factors, the output power can be adjusted in advance to obtain a clear and high-contrast speckle image, providing a high-quality experimental data basis for subsequent image acquisition and data processing, and ensuring the accuracy and reliability of magnetic field measurement.

[0034] The condenser unit may be a convex lens with adjustable position and focal length, which is used to focus the laser speckle image and adjust the size and clarity of the speckle on the CCD sensor. By adjusting the position and focal length of the condenser unit, the image size and contrast of the laser speckle can be adjusted to ensure that the CCD can capture a high-quality speckle image. The use of the convex lens improves the optical efficiency and measurement accuracy of the system.

[0035] The image acquisition unit may be a charge-coupled device (CCD) sensor, which is used to automatically and continuously acquire laser speckle images. The CCD sensor has high sensitivity and high resolution, and can accurately record the minute changes of the speckle image. The acquired speckle image data provides the original input for subsequent magnetic field signal analysis and processing, and is a key link to achieve high-sensitivity magnetic field measurement.

[0036] The non-contact magnetic field sensor may include a substrate and a film disposed on the substrate. The film may be made of a mixture of magnetic nanoparticles and polydimethylsiloxane (PDMS). Under the action of an external magnetic field, the magnetic nanoparticles are magnetized or rearranged, causing the PDMS to deform, thereby changing the scattering characteristics of the film surface and causing the laser speckle to change. As the core component of the magnetic field sensing probe, the non-contact magnetic field sensor has a magnetic response characteristic, can sense changes in the external magnetic field, and realize the conversion of magnetic field signals to optical signals. Under the action of the magnetic field, the rearrangement or magnetization behavior of the magnetic nanoparticles follows certain rules. When the magnetic field intensity is small, the magnetic moment of the particles will be partially aligned along the direction of the magnetic field, but due to the influence of thermal motion, the magnetic moment may show certain random fluctuations; as the magnetic field intensity increases and reaches the saturation magnetic field, the magnetic moment of the particles will be completely aligned along the direction of the magnetic field to achieve magnetization saturation. In a low-frequency magnetic field, the particles have enough time to respond to changes in the magnetic field, and the magnetic moment can be slowly rearranged; while in a high-frequency magnetic field, the magnetic moment of the particles may not be able to completely follow the rapid changes in the magnetic field, resulting in magnetization hysteresis.

[0037] The non-contact magnetic field sensor can be manufactured according to the following steps:

[0038] Step S1, placing magnetic nanoparticles in deionized water for thorough mixing and shaking, so that the magnetic nanoparticles are evenly distributed in the deionized water, and obtaining a magnetic nanoparticle solution; for example, 3 grams of magnetic nanoparticles with a particle size of 30-50 nanometers are taken and added to 50 milliliters of deionized water. To ensure that the particles are fully dispersed, an ultrasonic instrument is used for mixing and shaking for 30 minutes. The purpose of this step is to evenly disperse the magnetic nanoparticles in water, so as to prepare for the subsequent preparation of a magnetic PDMS film.

[0039] Step S2, PDMS includes prepolymer A and crosslinking agent B. The mechanical characteristics of PDMS are modulated by adjusting the ratio of prepolymer A to crosslinking agent B. A corresponding amount of magnetic nanoparticle solution is taken and fully mixed with prepolymer A, and then crosslinking agent B is added and continued to be stirred to obtain a magnetic PDMS solution; for example, 10 mL of magnetic nanoparticle solution can be taken and fully mixed with 25 g of prepolymer A, and after stirring for 20 minutes, 2.5 g of crosslinking agent B is added and continued to be stirred for 5 minutes.

[0040] Step S3, the magnetic PDMS solution is evenly applied on the substrate, and placed in a drying oven for heating and drying to obtain the non-contact magnetic field sensor. For example, the drying oven temperature is set to 50 degrees Celsius, the heating time is 15 minutes, and after the heating is completed, the non-contact magnetic field sensor can be prepared.

[0041] The magnetic nanoparticles can be Fe3O4 nanoparticles; in the present invention, Fe3O4 nanoparticles are mixed with PDMS to prepare a magnetic film with high magnetic response characteristics. The magnetic PDMS has both flexibility and magnetic sensitivity, and can generate minute deformations under an external magnetic field, significantly improving the sensitivity and response speed of magnetic field measurement. In addition, in order to meet different magnetic field measurement requirements, the substrate in this non-contact magnetic field sensor can be a glass sheet, an iron sheet or a thin sheet of solid magnetostrictive material. Among them, the non-contact magnetic field sensor with a glass sheet as the substrate is suitable for scenarios with low requirements for sensitivity and measurement accuracy and the need for transparency, and has low cost requirements; the non-contact magnetic field sensor with an iron sheet as the substrate is suitable for medium-precision and medium-sensitivity measurements, and has low cost requirements; the non-contact magnetic field sensor with a thin sheet of solid magnetostrictive material as the substrate is suitable for medium-precision and high-sensitivity magnetic field measurements. The measurement sensitivities of the three non-contact magnetic field sensors are -0.01658 mt-1, -0.03422 mt-1 and -0.22607 mt-1 respectively. The probe based on the magnetostrictive material has the highest sensitivity, which is 13.6 times higher than that of the glass sheet probe, demonstrating the flexibility and superiority of the multi-type probe design. In the present invention, the film made of magnetic nanoparticles and polydimethylsiloxane PDMS is disposed on different types of substrates, which can meet the requirements of more magnetic field measurement scenarios; the film made of magnetic nanoparticles and polydimethylsiloxane PDMS is disposed on a thin sheet of solid magnetostrictive material, and the response characteristics of this non-contact magnetic field sensor to a dynamic magnetic field are studied, and the dynamic measurement performance of the system is optimized.

[0042] Common methods for analyzing the change of speckle patterns, and common evaluation parameters include inner product, contrast, correlation coefficient, etc. The present invention selects the Pearson correlation coefficient as the key parameter for evaluating the change of speckle patterns. Compared with other speckle processing methods, the Pearson correlation coefficient is insensitive to the overall brightness change of the image and has stronger robustness. Its calculation formula is as follows:

[0043]

[0044] Traditionally, when using contact magnetic field sensors and using indicators such as inner product and contrast to reflect the changes in laser speckle, the influence of magnetic field intensity and magnetic field change frequency on these indicators is not linear, and it is impossible to calibrate the adjacent peaks and valleys of the magnetic field based on these indicators, so it is impossible to determine the magnetic field change frequency based on the time difference between the appearances of adjacent magnetic field peaks and valleys. In this invention, based on non-contact magnetic field sensors, a correlation coefficient that is insensitive to brightness changes but has high robustness is selected to reflect the changes in laser speckle. At this time, there is a linear relationship between the magnetic field intensity and the correlation coefficient. The adjacent peaks and valleys of the correlation coefficient can be used to calibrate the time when the adjacent peaks and valleys of the magnetic field appear, and there is a linear relationship between the magnetic field change frequency and the response speed. The difference in the electromagnetic magnitudes corresponding to the adjacent peak and valley values of the correlation coefficient, that is, the electromagnetic change amount, is also linearly related to the response speed. Therefore, according to the changes in the correlation coefficient, this invention can not only measure the magnitude of the external magnetic field, but also measure the change frequency of the magnetic field. In addition, under the action of an external magnetic field, the magnetic nanoparticles in the non-contact magnetic field sensor will be magnetized or rearranged, causing the PDMS to deform, thereby changing the scattering characteristics of the thin film surface and causing the laser speckle to change. The deformation can make the change in the correlation coefficient of the laser speckle linear, so as to further ensure the linear relationship between the magnetic field intensity and the correlation coefficient, ensure that the adjacent peaks and valleys of the correlation coefficient can be used to calibrate the time when the adjacent peaks and valleys of the magnetic field appear, and there is a linear relationship between the magnetic field change frequency and the response speed, and the electromagnetic change amount corresponding to the adjacent peak and valley values of the correlation coefficient is also linearly related to the response speed.

[0045] In this embodiment, the greater the intensity of the external magnetic field, the smaller the correlation coefficient of the laser speckle; the lower the change frequency of the magnetic field, the faster the response speed; when the change frequency is constant, the smaller the magnetic field change amount between adjacent magnetic field peaks and valleys, the slower the response speed, and the greater the magnetic field change amount between adjacent magnetic field peaks and valleys, the faster the response speed. Among them, when the magnetic field change amount ΔB is small (or the relative magnetic field change ΔB / B0 is small), the sensor needs higher sensitivity to detect weak changes, resulting in a slower response speed; at the same time, the magnetization process of the material may take longer. When the magnetic field change amount ΔB is large (or the relative magnetic field change ΔB / B o is large), the sensor can more easily detect the change, and the response speed is usually fast, but if the change is too large, it may cause the material to saturate or non-linear effects (such as hysteresis), which will instead affect the dynamic response characteristics. Therefore, the magnitude of the magnetic field change amount directly determines the response speed and measurement accuracy of the sensor.

[0046] The processing unit can specifically be used to determine the intensity of the external magnetic field according to the magnitude of the correlation coefficient of the laser speckle; when determining the change frequency of the external magnetic field, first determine the electromagnetic magnitudes corresponding to the adjacent peak and valley values of the correlation coefficient respectively, calculate the difference between the two determined electromagnetic magnitudes to obtain the electromagnetic change amount; determine the time difference between the occurrences of the adjacent peak and valley values of the correlation coefficient, determine the first response duration caused by the electromagnetic change amount according to the magnitude of the electromagnetic change amount, and determine the second response duration caused by the change frequency according to the time difference and the first response duration, so as to determine the change frequency. The processing unit can locally store the corresponding relationship between the correlation coefficient and the magnetic field intensity, the corresponding relationship between the magnetic field change amount and the first response duration, and the corresponding relationship between the change frequency and the second response duration; among them, the corresponding relationship between the change frequency and the second response duration is: when the difference between the electromagnetic magnitudes corresponding to the adjacent peak and valley values of the correlation coefficient is 0, that is, when the electromagnetic change amount is 0, the corresponding relationship between the change frequency and the second response duration; the second response duration is equal to the sum of the time difference and the first response duration.

[0047] In addition, if the change frequency of the magnetic field is too large or the magnetic field change amount between adjacent peaks and valleys of the magnetic field is too large, both will cause material saturation or nonlinear effects, thus reducing the response speed; when the processing unit determines the change frequency of the external magnetic field, first judge whether the magnetic field change amount between adjacent peaks and valleys of the magnetic field is too large. If so, the system prompts that the magnetic field change amount is too large and the change frequency measurement cannot be performed. Otherwise, the system measures the change frequency; after the system completes the measurement of the change frequency, judge whether the change frequency is too large. If so, the system prompts that the change frequency is too large and the change frequency measurement cannot be performed. Otherwise, display the measurement result.

[0048] As can be seen from the above embodiments, the present invention uses a non-contact magnetic field sensor to measure the magnetic field. Since the sensor does not come into direct contact with the outside world and is only affected by the external magnetic field, the measurement sensitivity and accuracy are relatively high. Based on the non-contact magnetic field sensor, the present invention selects a correlation coefficient that is insensitive to brightness changes but has high robustness to reflect the change of laser speckle. At this time, there is a linear relationship between the magnetic field strength and the correlation coefficient. The adjacent peaks and valleys of the correlation coefficient can be used to calibrate the time when the adjacent peaks and valleys of the magnetic field appear, and there is also a linear relationship between the magnetic field change frequency and the response speed. The difference in the electromagnetic magnitudes corresponding to the adjacent peak and valley values of the correlation coefficient, that is, the electromagnetic change amount, also has a linear relationship with the response speed. Therefore, according to the change of the correlation coefficient, the present invention can not only measure the magnitude of the external magnetic field, but also measure the change frequency of the magnetic field. The non-contact measurement of the present invention avoids the environmental interference of traditional sensors and is applicable to high-precision scenarios such as biomedical and industrial non-destructive testing. In addition, the design of multiple types of probes and the use of low-cost materials make the system flexible and economical, and easy to integrate and promote. The present invention provides a new solution for the field of magnetic field measurement and has important scientific significance and application value.

[0049] Figure 2 is the laser speckle pattern collected by the present invention under different magnetic field distributions. Figure 3 is a schematic diagram of the magnetic field measurement response relationship of three non-contact magnetic field sensors with a glass sheet, an iron sheet, and a thin solid magnetostrictive material sheet as the substrate of the present invention; it can be seen from the figure that the greater the intensity of the magnetic field, the smaller the correlation coefficient of the laser speckle. Figure 4 is a schematic diagram of the dynamic magnetic field change and dynamic magnetic field response of the present invention; it can be seen from the figure that the correlation coefficient can capture the change of the dynamic magnetic field in real time, and the adjacent peaks and valleys of the correlation coefficient can be used to calibrate the time when the adjacent peaks and valleys of the magnetic field appear. Figure 5 is a schematic diagram of the dynamic magnetic field change at different frequencies and the dynamic magnetic field response at different frequencies of the present invention. It can be seen from the figure that the present invention can produce different responses to magnetic fields of different frequencies, and the lower the magnetic field frequency, the better the response effect of the sensor.

[0050] After considering the specification and practicing the invention disclosed herein, those skilled in the art will readily conceive of other embodiments of the present invention. This application is intended to cover any variations, uses, or adaptations of the present invention, which follow the general principles of the present invention and include known common knowledge or conventional technical means in the technical field not disclosed by the present invention. The specification and embodiments are only regarded as exemplary, and the true scope and spirit of the present invention are pointed out by the following claims.

[0051] It should be understood that the present invention is not limited to the exact structures that have been described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only regulated by the appended claims.

Claims

1. A magnetic field measurement system based on laser speckle, characterized in that: The invention comprises a laser, a non-contact magnetic field sensor, a focusing unit, an image acquisition unit and a processing unit which are connected in sequence. The laser provides a laser signal to the non-contact magnetic field sensor. Under the action of an external magnetic field, the laser speckle on the non-contact magnetic field sensor changes. The laser speckle after the change is transmitted to the image acquisition unit through the focusing unit to acquire a laser speckle image. The processing unit performs image processing on the acquired laser speckle to obtain a correlation coefficient of the laser speckle. According to the change of the correlation coefficient of the laser speckle, the magnetic field size and the change frequency of the external magnetic field are determined.

2. The magnetic field measurement system based on laser speckle according to claim 1, characterized in that: The greater the intensity of the external magnetic field, the smaller the correlation coefficient of the laser speckle; the lower the frequency of change of the magnetic field, the faster the response speed; when the frequency of change is constant, the smaller the magnetic field change between adjacent peaks and valleys of the magnetic field, the slower the response speed, and the larger the magnetic field change between adjacent peaks and valleys of the magnetic field, the faster the response speed.

3. The magnetic field measurement system based on laser speckle according to claim 1 or 2, characterized in that: The processing unit is specifically used to determine the strength of the external magnetic field according to the correlation coefficient of the laser speckle; when determining the change frequency of the external magnetic field, first determine the electromagnetic magnitudes corresponding to the adjacent peak and valley values ​​of the correlation coefficient, calculate the difference between the two determined electromagnetic magnitudes, and obtain the electromagnetic change amount; Determine the time difference between adjacent peak and valley values ​​of the correlation coefficient, determine the first response duration caused by the electromagnetic change according to the magnitude of the electromagnetic change, and determine the second response duration caused by the change frequency according to the time difference and the first response duration, thereby determining the change frequency.

4. The magnetic field measurement system based on laser speckle according to claim 3, characterized in that: The processing unit locally stores the corresponding relationship between the correlation coefficient and the magnetic field strength, the corresponding relationship between the magnetic field change and the first response time, and the corresponding relationship between the change frequency and the second response time; wherein the corresponding relationship between the change frequency and the second response time is: the difference in the electromagnetic magnitudes corresponding to adjacent peak and valley values ​​of the correlation coefficient is 0, that is, when the electromagnetic change is 0, the corresponding relationship between the change frequency and the second response time; the second response time is equal to the time difference plus the first response time.

5. The magnetic field measurement system based on laser speckle according to claim 1, characterized in that: The non-contact magnetic field sensor includes a substrate and a film arranged on the substrate. The film is made of a mixture of magnetic nanoparticles and polydimethylsiloxane (PDMS). Under the action of an external magnetic field, the magnetic nanoparticles are magnetized or rearranged, causing the PDMS to deform, thereby changing the scattering properties of the film surface and causing the laser speckle to change.

6. The magnetic field measurement system based on laser speckle according to claim 5, characterized in that: The contactless magnetic field sensor is manufactured according to the following steps: Placing the magnetic nanoparticles in deionized water and thoroughly mixing and shaking them so that the magnetic nanoparticles are evenly distributed in the deionized water to obtain a magnetic nanoparticle solution; PDMS includes prepolymer A and crosslinking agent B. The mechanical characteristics of PDMS are modulated by adjusting the ratio of prepolymer A to crosslinking agent B. A corresponding amount of magnetic nanoparticle solution is mixed with prepolymer A and stirred, and then crosslinking agent B is added and stirred continuously to obtain a magnetic PDMS solution. The magnetic PDMS solution is evenly applied on a substrate, and placed in a drying oven for heating and drying to obtain the non-contact magnetic field sensor.

7. The magnetic field measurement system based on laser speckle according to claim 5 or 6, characterized in that: The magnetic nanoparticles are Fe3O4 particles; the substrate is a glass sheet, an iron sheet or a solid magnetostrictive material sheet.

8. The magnetic field measurement system based on laser speckle according to claim 1, characterized in that: The laser is a spatial laser with adjustable power, and the focusing unit is a convex lens with adjustable position and focal length. The brightness and contrast of the laser speckle image are adjusted by adjusting the power of the laser, and the size and contrast of the laser speckle image are adjusted by adjusting the position and focal length of the focusing unit; the image acquisition unit is a CCD sensor.

9. The magnetic field measurement system based on laser speckle according to claim 1 or 5, characterized in that: The correlation coefficient is the Pearson correlation coefficient.

10. The magnetic field measurement system based on laser speckle according to claim 3, characterized in that: If the frequency of magnetic field changes is too large or the amount of magnetic field change between adjacent peaks and valleys is too large, it will lead to material saturation or nonlinear effects, thereby reducing the response speed. When determining the frequency of change of the external magnetic field, the processing unit first determines whether the magnetic field change between adjacent peaks and valleys is too large. If so, the system prompts that the magnetic field change is too large and the frequency of change cannot be measured. Otherwise, the system measures the frequency of change. After the system completes the measurement of the change frequency, it determines whether the change frequency is too large. If so, the system prompts that the change frequency is too large and the change frequency measurement cannot be performed. Otherwise, the measurement result is displayed.

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