Estimation Method of Soft Magnetic Core Noise

Abstract

The present disclosure provides a method for estimating the noise of a soft magnetic core, comprising: obtaining a soft magnetic core on which an excitation coil is wound; measuring the impedance value of the excitation coil under a natural geomagnetic field by frequency sweeping, and determining a peak frequency point when the impedance value has a peak value; measuring the inductance value and resistance value of the excitation coil at the peak frequency point along the axial direction of the soft magnetic core under different DC bias magnetic fields, and obtaining an unsaturated inductance value and a resistance peak value of the soft magnetic core respectively; and obtaining an equivalent noise of the soft magnetic core based on the unsaturated inductance value and the resistance peak value.

Description

Technical Field

[0001] The present disclosure relates to the field of magnetic sensor performance detection, and in particular to a method for estimating noise of a soft magnetic core. Background Art

[0002] The fluxgate magnetic field sensor is a vector magnetic sensor that can measure quasi-static and low-frequency AC magnetic fields by demodulating changes near the excitation harmonics. It is usually composed of a soft magnetic core, an excitation coil, an induction coil, and an excitation demodulation circuit. Research has found that the sources of sensor noise can be divided into three parts: soft magnetic core, copper coil, and circuit. The main noise source comes from the soft magnetic core noise. In comparison, the thermal noise and circuit noise of the coil can be ignored. However, for many years, the noise estimation inside the soft magnetic core has not formed a clear and analytical expression with specific physical meanings like thermal noise or circuit noise, which has caused the fluxgate sensor to be unable to form an effective optimization algorithm. Therefore, in the optimization process of soft magnetic core materials, there is a lack of evaluation indicators, and it is impossible to connect material research and development and sensor design. Summary of the invention

[0003] 1. Technical issues to be resolved

[0004] In view of the above problems, the present disclosure provides a method for estimating the noise of a soft magnetic core, so as to at least partially solve the technical problems such as the difficulty in optimizing a fluxgate sensor, unstable performance, and difficulty in accurately predicting and reducing the noise level in practical applications due to the lack of a clear method for estimating the noise of a soft magnetic core.

[0005] (II) Technical solution

[0006] The present disclosure provides a method for estimating the noise of a soft magnetic core, comprising: obtaining a soft magnetic core, on which an excitation coil is wound; measuring the impedance value of the excitation coil under a natural geomagnetic field by frequency sweeping, and determining a peak frequency point when the impedance value reaches a peak value; measuring the inductance value and resistance value of the excitation coil at the peak frequency point along the axial direction of the soft magnetic core under different DC bias magnetic fields, and obtaining an unsaturated inductance value and a resistance peak value of the soft magnetic core, respectively; and obtaining an equivalent noise of the soft magnetic core based on the unsaturated inductance value and the resistance peak value.

[0007] According to an embodiment of the present disclosure, the method also includes: fitting the inductance values ​​under different DC bias magnetic fields using a high-order polynomial to obtain the differential value of the inductance value; comparing the sizes of the differential values ​​under different DC bias magnetic fields, and determining that the DC bias magnetic field corresponding to the maximum differential value is the optimal excitation magnetic field; and using the optimal excitation magnetic field to excite the soft magnetic core to a saturated magnetization state.

[0008] According to an embodiment of the present disclosure, the material of the soft magnetic core includes one of Permalloy, amorphous and nanocrystalline.

[0009] According to an embodiment of the present disclosure, the method further includes: using an electromagnet to balance the natural geomagnetic field to zero, so as to apply different DC bias magnetic fields on the soft magnetic core.

[0010] According to an embodiment of the present disclosure, the method further includes: setting the annealing temperature of the soft magnetic core to different preset values, and measuring the soft magnetic core at each of the annealing temperatures.

[0011] According to an embodiment of the present disclosure, the method further includes: measuring the DC resistance of the excitation coil, and determining the noise power spectrum density of the excitation coil based on the DC resistance and the resistance peak value.

[0012] According to an embodiment of the present disclosure, the formula for determining the noise power spectrum density of the excitation coil based on the DC resistance and the resistance peak value is as follows:

[0013]

[0014] Among them, V noise represents the noise power spectral density, k represents the Boltzmann constant, T represents the absolute temperature, Rind represents the resistance peak value, and Rg represents the DC resistance of the excitation coil.

[0015] According to an embodiment of the present disclosure, the method further includes: based on the unsaturated inductance value, calculating the conversion coefficient between the induced voltage of the excitation coil and the external magnetic field according to the following formula:

[0016]

[0017] Wherein, FS represents the conversion coefficient, f represents the peak frequency point, K1 represents the first constant, L p represents the unsaturated inductance value.

[0018] According to an embodiment of the present disclosure, the formula for obtaining the equivalent noise of the soft magnetic core based on the unsaturated inductance value and the resistance peak value is as follows:

[0019]

[0020] Among them, B noise represents the equivalent noise of the soft magnetic core, V noise represents the noise power spectrum density, FS represents the conversion coefficient, K2 represents the second constant, Rind represents the resistance peak value, Rg represents the DC resistance of the excitation coil, L p represents the unsaturated inductance value.

[0021] According to an embodiment of the present disclosure, the method also includes: using the soft magnetic core to make a fluxgate sensor and measuring the conversion sensitivity of the fluxgate sensor; placing the fluxgate sensor in the center of a shielded room and measuring the noise spectrum density value of the output voltage of the fluxgate sensor; obtaining the relationship between the noise and frequency of the soft magnetic core by calculating the ratio of the noise spectrum density value to the conversion sensitivity; and based on the relationship between the noise and frequency of the soft magnetic core, checking the consistency of the estimated equivalent noise.

[0022] (III) Beneficial effects

[0023] The method for estimating the soft magnetic core noise provided by the present invention estimates the sensor's equivalent input magnetic field noise by analyzing the impedance characteristics of the soft magnetic core and the excitation coil tightly wound around the soft magnetic core, and forms a complete and effective noise estimation method, which not only provides an important reference basis for the design and optimization of fluxgate sensors, but also points out a direction for improving sensor performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] For a more complete understanding of the present disclosure and its advantages, reference will now be made to the following description taken in conjunction with the accompanying drawings, in which:

[0025] Figure 1 The flowchart of the method for estimating the noise of the soft magnetic core provided by the embodiment of the present disclosure is schematically shown;

[0026] Figure 2 A schematic diagram of the swept frequency measurement result of the inductance of the excitation coil under the natural geomagnetic field provided by an embodiment of the present disclosure is schematically shown;

[0027] Figure 3 A schematic diagram schematically shows the results of a frequency sweep measurement of the resistance of an excitation coil under natural geomagnetic field conditions provided by an embodiment of the present disclosure;

[0028] Figure 4 The schematic diagram schematically shows the change of inductance value under different DC bias magnetic fields provided by the embodiment of the present disclosure;

[0029] Figure 5 A schematic diagram of differential values ​​of coil inductance under different DC bias magnetic fields provided by an embodiment of the present disclosure is schematically shown;

[0030] Figure 6 A schematic diagram schematically shows coil resistance values ​​under different DC bias magnetic fields provided by an embodiment of the present disclosure;

[0031] Figure 7 A schematic diagram schematically shows equivalent noise simulation values ​​under different bias magnetic fields provided by an embodiment of the present disclosure;

[0032] Figure 8 A schematic diagram schematically shows the conversion sensitivity of the sensor corresponding to the amorphous soft magnetic cores with different annealing temperatures provided by the embodiment of the present disclosure;

[0033] Fig. 9 A schematic diagram schematically shows the noise level of a sensor corresponding to amorphous wire soft magnetic cores with different annealing temperatures provided by an embodiment of the present disclosure. DETAILED DESCRIPTION

[0034] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0035] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0036] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0037] Fluxgate sensors have the advantages of small size, light weight, low power consumption, low noise, large dynamic range and good stability. Therefore, fluxgate sensors have been significantly applied in many fields such as space magnetic field measurement, magnetic anomaly detection, underwater target detection and tracking, non-destructive testing, positioning / navigation / timing, non-destructive testing and positioning navigation. However, the main noise source of fluxgate sensors, namely the soft magnetic core noise, has not formed a clear and explicit analytical expression containing specific physical meanings, so it is impossible to make an effective estimate. To address this problem, the disclosed embodiment proposes a method for estimating the soft magnetic core noise.

[0038] Figure 1 The flowchart of the method for estimating the noise of the soft magnetic core provided by the embodiment of the present disclosure is schematically shown.

[0039] like Figure 1 As shown, the method for estimating the noise of the soft magnetic core of this embodiment includes S1 to S4.

[0040] In operation S1 , a soft magnetic core is obtained, and an excitation coil is wound around the soft magnetic core.

[0041] In operation S2, the impedance value of the excitation coil in the natural geomagnetic field is measured by frequency sweeping to determine the peak frequency point when the impedance value has a peak value.

[0042] In operation S3, under different DC bias magnetic fields, the inductance and resistance of the excitation coil at the peak frequency point are measured along the axis direction of the soft magnetic core to obtain the unsaturated inductance and resistance peak of the soft magnetic core.

[0043] In operation S4 , an equivalent noise of the soft magnetic core is obtained based on the unsaturated inductance value and the resistance peak value.

[0044] In an embodiment of the present disclosure, the material of the soft magnetic core includes one of Permalloy, amorphous and nanocrystalline.

[0045] Specifically, when obtaining a soft magnetic core, the material of the soft magnetic core is first selected. High permeability and low noise soft magnetic cores are key components of fluxgate sensors, and the magnetic properties of the soft magnetic cores play a decisive role in the performance indicators of the sensor. Common fluxgate soft magnetic core material choices mainly include Permalloy, Cobalt-based / Iron-based / Cobalt-Iron-based amorphous, Cobalt-based / Iron-based / Cobalt-Iron-based nanocrystals, etc.

[0046] For example, Permalloy was once a commodity iron-nickel alloy, and now refers to nickel-iron alloy. Permalloy has extremely high magnetic permeability and low magnetic loss in weak magnetic fields, and can be processed to a thickness of tens of microns through rolling, but the width remains at the millimeter level and cannot be further miniaturized.

[0047] For example, amorphous, also known as metallic glass, refers to a chaotic, lattice-free alloy formed by rapid cooling of liquid alloy. It is a high-permeability soft magnetic material developed in the 1980s. Compared with traditional Permalloy materials, cobalt-based amorphous soft magnetic alloys have high permeability, low coercive force and zero magnetostriction. With the maturity of cobalt-based amorphous wire technology, the diameter of the magnetic core can be controlled within the order of 100 microns, which promotes the further miniaturization of sensors and is currently the preferred soft magnetic core material.

[0048] For example, nanocrystalline soft magnetic materials are formed by highly controlled annealing on the basis of amorphous alloys to form materials with nanoscale microcrystals and amorphous mixed structures. Compared with traditional Permalloy soft magnetic materials, amorphous soft magnetic materials and other materials, nanocrystalline ultra-thin ribbons can reduce the volume of magnetic devices and reduce the loss of magnetic devices due to their high saturation magnetism, low coercivity, high initial magnetic permeability, high Curie temperature and other material properties. They are new magnetic materials with better comprehensive magnetic properties and have significant advantages in the pursuit of miniaturization, lightweight and complex temperature scenarios.

[0049] It is understandable that the above materials can all be used as soft magnetic core materials for fluxgate sensors to concentrate magnetic flux and improve the efficiency of magnetic-to-voltage conversion.

[0050] Further, based on the structural composition of the fluxgate, the performance of the soft magnetic core is related to the excitation coil tightly wound thereon, and can be estimated by measuring its impedance. Therefore, in some exemplary embodiments, a precision impedance analyzer (such as Agilent 4294a impedance analyzer) is used to measure the inductance (Lc) and resistance (Rc) of the excitation coil containing the soft magnetic core, that is, the selected measurement option is "inductance-resistance".

[0051] Figure 2 and Figure 3 Schematic diagrams of the swept frequency measurement results of the inductance and resistance of the excitation coil under natural geomagnetic field conditions provided by the embodiments of the present disclosure are schematically shown respectively.

[0052] Specifically, first, the excitation coil is measured under natural geomagnetic field conditions, and the measured inductance changes with the frequency. For example, an amorphous wire with a diameter of 0.1 mm and a length of 2 mm, an excitation coil with a wire diameter of 0.1 mm and 500 turns. Figure 2 and Figure 3 As shown, the peak frequency point when its inductance peaks is close to 53kHz, indicating that its magnetic permeability peak is around 53kHz, and the magnetic-voltage conversion coefficient also reaches its peak here. In addition, the resistance of the excitation coil increases rapidly after 40kHz, indicating that the loss of the soft magnetic core increases after 40khz and the noise increases.

[0053] Further, in an embodiment of the present disclosure, the annealing temperature of the soft magnetic core is set to different preset values, and the soft magnetic core is measured at each of the annealing temperatures.

[0054] For example, continue to refer to Figure 2 and Figure 3 , six cases of annealing temperatures of 275°C, 325°C, 375°C, 425°C, 475°C, and 525°C were listed, and the conclusions were similar.

[0055] In an embodiment of the present disclosure, the method further comprises: using an electromagnet to balance the natural magnetic field to zero, so as to apply different DC bias magnetic fields to the soft magnetic core, thereby dc ) is applied, and the relationship between the coil impedance and the frequency is measured along the length direction of the soft magnetic core.

[0056] For example, under different DC bias magnetic fields, the impedance analyzer provides a 20mA source current with a sweep bandwidth from 1khz to 500khz (frequency range). Then the inductance and resistance at the peak frequency point determined previously are recorded. The 20mA excitation current used in the test simulates the excitation current of the actual sensor. Please refer to Figure 4 , repeat the measurement process along the direction of the soft magnetic core under different DC bias magnetic fields, namely zero field, +5Gauss DC field (+50000nt), +10Gauss DC field (+100000nt), -5Gauss DC field (-50000nt) and -10Gauss DC field (-100000nt), optionally with a step of 0.5Gauss or less. The changes in inductance under six different annealing temperatures and different DC bias magnetic fields are shown in Figure 2. Figure 4 shown.

[0057] Normally, the inductance of the coil conforms to the following rules:

[0058]

[0059] Among them, L p is the unsaturated inductance of the coil, N is the number of turns of the coil, µ0 is the magnetic permeability of vacuum, μ app is the effective magnetic permeability of the soft magnetic core, S is the cross-section of the soft magnetic core, and l is the length of the soft magnetic core.

[0060] According to Faraday's law of electromagnetic induction, the conversion coefficient between the coil induced voltage and the external magnetic field is:

[0061]

[0062] Among them, FS is the magnetic field-voltage conversion coefficient, e(f) is the output voltage, B(f) is the magnetic induction intensity, and f is the frequency.

[0063] In summary, based on the unsaturated inductance value, the formula for calculating the conversion coefficient between the induced voltage of the excitation coil and the external magnetic field is as follows:

[0064]

[0065] Wherein, FS represents the conversion coefficient, f represents the peak frequency point, K1 represents the first constant, L p represents the unsaturated inductance value.

[0066] In an embodiment of the present disclosure, the method also includes: fitting the inductance values ​​under different DC bias magnetic fields using a high-order polynomial to obtain the differential value of the inductance value; comparing the sizes of the differential values ​​under different DC bias magnetic fields, and determining that the DC bias magnetic field corresponding to the maximum differential value is the optimal excitation magnetic field; and using the optimal excitation magnetic field to excite the soft magnetic core to a saturated magnetization state.

[0067] Specifically, the measured inductance value is fitted with a high-order polynomial. In order to reduce the sum of square errors (SSE), in some exemplary embodiments, a 9th-order polynomial is used for fitting:

[0068]

[0069] Where parameters p1-9 are the coefficients of the polynomial. Thus, the differential of the inductance is:

[0070]

[0071] Figure 5 A schematic diagram of the differential value of the coil inductance under different DC bias magnetic fields provided by an embodiment of the present disclosure is schematically shown.

[0072] like Figure 5 As shown, the soft magnetic core is close to saturation under a magnetic field of about 3.5 Gauss. At this time, the rate of change of the magnetic permeability of the soft magnetic core (which is proportional to the inductance of the coil) is the largest, and the optimal excitation magnetic field of the soft magnetic core can be obtained.

[0073] In an embodiment of the present disclosure, the method further includes: measuring the DC resistance of the excitation coil, and determining the noise power spectrum density of the excitation coil based on the DC resistance and the resistance peak value.

[0074] Specifically, similar to the inductance, the resistance value of the coil at the peak frequency point under different bias magnetic fields is measured, and the resistance peak mainly reflects the internal stress noise of the soft magnetic core.

[0075] Figure 6 A schematic diagram schematically shows coil resistance values ​​under different DC bias magnetic fields provided by an embodiment of the present disclosure.

[0076] like Figure 6 As shown in the figure, the resistance value in the coil decreases with the increase of the bias field value, and is positively correlated. The resistance value of the negative bias field is symmetrical with the resistance value of the positive bias field. The resistance peak appears under zero magnetic field conditions, and the resistance peak values ​​of different soft magnetic cores in the coil are also different. Assuming that the resistance peak value of the soft magnetic core related to noise (including Barkhausen noise and thermal noise) is Rind, and the DC resistance of the coil wire is Rg, the formula for the noise power spectrum density of the total resistance R can be expressed as:

[0077]

[0078] Among them, V noise represents the noise power spectral density, k represents the Boltzmann constant, T represents the absolute temperature, Rind represents the resistance peak value, and Rg represents the DC resistance of the excitation coil.

[0079] Furthermore, the formula for obtaining the equivalent noise of the soft magnetic core based on the unsaturated inductance value and the resistance peak value is as follows:

[0080]

[0081] Among them, B noise represents the equivalent noise of the soft magnetic core, V noise represents the noise power spectrum density, FS represents the conversion coefficient, K2 represents the second constant, K3 represents the third constant, Rind represents the resistance peak value, Rg represents the DC resistance of the excitation coil, L p represents the unsaturated inductance value.

[0082] Specifically, the equivalent input magnetic field noise, that is, the equivalent noise is defined as the magnetic field noise that can be seen from the sensor input side. Finally, the equivalent input magnetic noise is estimated, and the estimation result is as follows: Figure 7 shown.

[0083] According to an embodiment of the present disclosure, the method also includes: using the soft magnetic core to make a fluxgate sensor and measuring the conversion sensitivity of the fluxgate sensor; placing the fluxgate sensor in the center of a shielded room and measuring the noise spectrum density value of the output voltage of the fluxgate sensor; obtaining the relationship between the noise and frequency of the soft magnetic core by calculating the ratio of the noise spectrum density value to the conversion sensitivity; and based on the relationship between the noise and frequency of the soft magnetic core, checking the consistency of the estimated equivalent noise.

[0084] Specifically, in order to verify the accuracy of the method for estimating the noise of the soft magnetic core provided by the embodiment of the present disclosure, six probes of the fluxgate sensor were manufactured and tested. The induction coils and signal conditioning circuits of the six probes have the same parameters.

[0085] In this process, the sensor's conversion sensitivity is first characterized in mV / nT to compare the sensor's magnetic field-to-voltage conversion coefficient. The sensitivity value is measured using a dynamic signal analyzer (such as Agilent 35670A) and a Helmholtz coil (such as Bartington HC1).

[0086] Figure 8A schematic diagram schematically shows the conversion sensitivity of the sensor corresponding to the amorphous wire soft magnetic core with different annealing temperatures provided by the embodiment of the present disclosure.

[0087] like Figure 8 As shown in the figure, the sensitivity values ​​measured by the six sensors at 1Hz are almost the same. However, the operating frequency bands are different. Among them, the operating bandwidth of sensor T275 is significantly smaller than that of other sensors. This is mainly due to the decrease in the initial magnetic permeability of the soft magnetic core at the 275℃ annealing temperature, which leads to a decrease in the high-frequency open-loop gain of the T275 sensor. In this case, the deep negative feedback condition is not met, resulting in a decrease in the high-frequency closed-loop gain and a reduction in bandwidth.

[0088] Furthermore, the sensor is placed in the center of the shielded room and the output noise spectral density value is measured using an Agilent 35670A analyzer. The measured output voltage noise spectral density is divided by the measured sensitivity value to obtain the relationship between the equivalent input magnetic field noise and frequency.

[0089] Fig. 9 A schematic diagram schematically shows the noise level of a sensor corresponding to amorphous wire soft magnetic cores with different annealing temperatures provided by an embodiment of the present disclosure.

[0090] like Fig. 9 As shown, the input magnetic field noise of sensors with different soft magnetic cores varies greatly. The overall result is consistent with Figure 7 The simulation results are highly consistent with those of the previous method, which verifies the effectiveness of this method.

[0091] The method for estimating the noise of the soft magnetic core provided by the embodiment of the present disclosure can predict the noise performance of the core during the design stage, thereby avoiding unnecessary trial and error and reducing the trial and error cost. At the same time, the noise of a large number of cores can be estimated in a short time, and the cores that meet the requirements can be quickly screened out, thereby accelerating the screening process and improving production efficiency.

[0092] It will be appreciated by those skilled in the art that the features described in the various embodiments and / or claims of the present disclosure may be combined and / or combined in a variety of ways, even if such combinations and / or combinations are not explicitly described in the present disclosure. In particular, the features described in the various embodiments and / or claims of the present disclosure may be combined and / or combined in a variety of ways without departing from the spirit and teachings of the present disclosure. All of these combinations and / or combinations fall within the scope of the present disclosure.

[0093] Although the present disclosure has been shown and described with reference to specific exemplary embodiments of the present disclosure, it should be understood by those skilled in the art that various changes in form and details may be made to the present disclosure without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents. Therefore, the scope of the present disclosure should not be limited to the above-mentioned embodiments, but should be determined not only by the appended claims, but also by the equivalents of the appended claims.

Claims

1. A method for estimating noise of a soft magnetic core, characterized in that: include: Obtaining a soft magnetic core, wherein an excitation coil is wound around the soft magnetic core; Sweep frequency to measure the impedance value of the excitation coil in the natural geomagnetic field, and determine the peak frequency point when the impedance value reaches a peak value; Under different DC bias magnetic fields, measuring the inductance and resistance of the excitation coil at the peak frequency point along the axial direction of the soft magnetic core, and obtaining the unsaturated inductance and resistance peak of the soft magnetic core respectively; Measuring the DC resistance of the excitation coil, and determining the noise power spectrum density of the excitation coil based on the DC resistance and the resistance peak value; Based on the unsaturated inductance value, the formula for calculating the conversion coefficient between the induced voltage of the excitation coil and the external magnetic field is as follows: Wherein, FS represents the conversion coefficient, f represents the peak frequency point, K1 represents the first constant, L p represents the unsaturated inductance value; Based on the unsaturated inductance value and the resistance peak value, obtaining an equivalent noise of the soft magnetic core; The formula for obtaining the equivalent noise of the soft magnetic core based on the unsaturated inductance value and the resistance peak value is as follows: Among them, V noise represents the noise power spectrum density, FS represents the conversion coefficient, K2 represents the second constant, Rind represents the resistance peak value, Rg represents the DC resistance of the excitation coil, L p represents the unsaturated inductance value.

2. The method for estimating the noise of a soft magnetic core according to claim 1, characterized in that: The method further comprises: The inductance values ​​under different DC bias magnetic fields are fitted using a high-order polynomial to obtain a differential value of the inductance value; Comparing the magnitudes of the differential values ​​under different DC bias magnetic fields, and determining that the DC bias magnetic field corresponding to the maximum differential value is the optimal excitation magnetic field; The soft magnetic core is excited to a saturated magnetization state by using the optimal excitation magnetic field.

3. The method for estimating the noise of the soft magnetic core according to claim 1, characterized in that: The material of the soft magnetic core includes one of Permalloy, amorphous and nanocrystalline.

4. The method for estimating the noise of a soft magnetic core according to claim 1, characterized in that: The method further comprises: The natural magnetic field is balanced to zero using an electromagnet to apply different DC bias magnetic fields on the soft magnetic core.

5. The method for estimating the noise of a soft magnetic core according to claim 1, characterized in that: The method further comprises: The annealing temperature of the soft magnetic core is set to different preset values, and the soft magnetic core is measured at each of the annealing temperatures.

6. The method for estimating the noise of a soft magnetic core according to claim 1, characterized in that: The formula for determining the noise power spectrum density of the excitation coil based on the DC resistance and the resistance peak value is as follows: Among them, V noise represents the noise power spectral density, k represents the Boltzmann constant, T represents the absolute temperature, Rind represents the resistance peak value, and Rg represents the DC resistance of the excitation coil.

7. The method for estimating the noise of a soft magnetic core according to claim 1, characterized in that: The method further comprises: Making a fluxgate sensor using the soft magnetic core, and measuring the conversion sensitivity of the fluxgate sensor; Placing the fluxgate sensor at the center of the shielding room and measuring the noise spectrum density value of the output voltage of the fluxgate sensor; By calculating the ratio of the noise spectrum density value to the conversion sensitivity, the relationship between the noise and the frequency of the soft magnetic core is obtained; Based on the relationship between the noise and frequency of the soft magnetic core, the consistency with the estimated equivalent noise is checked.

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