Device and method for detecting weak magnetic field on surface of object based on giant magneto-impedance effect

Abstract

The present invention relates to a device and method for detecting a weak magnetic field on a surface of an object based on the giant magnetoimpedance effect. A method for measuring a magnetic field includes positioning a giant magnetoimpedance probe at a first position near a surface of an object to be measured; applying an alternating current to the giant magnetoimpedance probe and measuring a first alternating voltage of the giant magnetoimpedance probe; calculating an impedance based on the alternating current and the first alternating voltage and determining a first magnetic field based on the impedance; positioning the giant magnetoimpedance probe at a second position above the first position; applying the alternating current to the giant magnetoimpedance probe and measuring a second alternating voltage of the giant magnetoimpedance probe; calculating an impedance based on the alternating current and the second alternating voltage and determining a second magnetic field based on the impedance; and calculating a measured magnetic field at the first position based on the first magnetic field and the second magnetic field.

Description

Technical Field

[0001] This application generally relates to the field of magnetism, and more particularly to a device and method for detecting weak magnetic fields on object surfaces based on the giant magnetoresistance (GMI) effect. Background Technology

[0002] Magnetic detection technology has been widely applied in fields such as storage, navigation, power transmission, home appliances, and industrial control. Utilizing different magnetic effects, a wide variety of magnetic sensors have been developed to meet the needs of various detection scenarios. Currently, commonly used magnetic sensors include Hall effect sensors, anisotropic magnetoresistive (AMR) sensors, giant magnetoresistive (GMR) sensors, tunneling magnetoresistive (TMR) sensors, and giant magnetoresistance (GMI) sensors.

[0003] Unlike measuring spatial magnetic fields, a specific application scenario involves measuring weak magnetic fields on object surfaces, which has applications in materials science, anti-counterfeiting, and other fields. Hall sensors have low sensitivity, and AMR sensors require a Wheatstone bridge for use; neither is suitable for measuring weak magnetic fields on object surfaces. GMR and TMR sensors have high sensitivity, and the free magnetic layer used for measuring the magnetic field can be formed to a thickness of nanometers, making them suitable for measuring weak magnetic fields on object surfaces. However, GMR and TMR sensors have complex multilayer film structures, requiring cumbersome and complex semiconductor manufacturing processes, including thin film deposition, photolithography, etching, and vacuum annealing under magnetic fields. The manufacturing equipment is expensive, resulting in high costs. While traditional GMI sensors have advantages such as high sensitivity, small size, fast response speed, and low power consumption, they detect the average magnetic field along the entire length of the solenoid coil, making them suitable only for measuring spatial magnetic fields and not for measuring weak magnetic fields on object surfaces. Summary of the Invention

[0004] In view of the above problems, the present invention is proposed.

[0005] This invention provides a device and method for detecting weak magnetic fields on object surfaces based on the giant magnetoresistance (GMI) effect. As mentioned above, traditional GMI sensors measure the average magnetic field along the entire length of a solenoid coil. However, the weak magnetic field on an object surface is characterized by a thin spatial distribution and rapid attenuation with distance from the surface, making it unsuitable for measurement using traditional methods with GMI sensors. This invention proposes a novel measurement method: by measuring the magnetic field at two height positions on the object surface and then calculating the difference between them, a micro-region magnetic field close to the object surface can be obtained. This invention not only utilizes the advantages of high sensitivity and low cost of GMI sensors but also eliminates system noise and environmental noise through this differential measurement method, thus enabling more accurate measurement of the weak magnetic field on the object surface.

[0006] According to one embodiment, a magnetic field detection device may include: a giant magnetoresistive (GMT) probe; an AC power supply for applying an AC current to the GMT probe; a measuring circuit for measuring an AC voltage on the GMT probe; a calculation unit for calculating impedance based on the AC current and the AC voltage, and determining the magnitude of a magnetic field based on the impedance; and a positioning unit for supporting the GMT probe and positioning the GMT probe at a predetermined position. When the positioning unit positions the GMT probe at a first position near the surface of an object to be measured, the measuring circuit measures a first AC voltage on the GMT probe, and the calculation unit calculates a first magnetic field based on the first AC voltage. When the positioning unit positions the GMT probe at a second position above the first position, the measuring circuit measures a second AC voltage on the GMT probe, the calculation unit calculates a second magnetic field based on the second AC voltage, and calculates a measured magnetic field at the first position near the surface of the object to be measured based on the first magnetic field and the second magnetic field.

[0007] According to one embodiment, the positioning unit positions the giant magnetoresistive probe perpendicular to the surface of the object to be measured, and the second position is located vertically above the first position.

[0008] According to one embodiment, the computing unit calculates the measurement magnetic field at a first location near the surface of the object under test based on the following formula:

[0009] Htip = (H1 - H2) * L / ΔZ

[0010] Wherein, Htip is the measuring magnetic field at a first position near the surface of the object to be measured, H1 is the first magnetic field, H2 is the second magnetic field, L is the effective length of the giant magnetoresistance probe, and ΔZ is the distance between the second position and the first position.

[0011] According to one embodiment, the distance between the second position and the first position is in the range of 1 μm to 2 mm, preferably in the range of 10 μm to 1 mm. The effective length of the giant magnetoresistance probe is in the range of 1 mm to 3 cm, preferably in the range of 3 mm to 2 cm.

[0012] According to one embodiment, the positioning unit is further configured to move the giant magnetoresistive probe along the surface of the object to be measured to measure the magnetic field at multiple locations.

[0013] According to one embodiment, the magnetic field detection device may further include a control unit for controlling one or more of the AC power supply, the measurement circuit, the computing unit, and the positioning unit to automatically measure the magnetic field at multiple locations on the surface of the object to be measured.

[0014] According to one embodiment, a magnetic field measurement method may include: positioning a giant magnetoresistive (GME) probe at a first position near the surface of an object to be measured; applying an alternating current to the GME probe and measuring a first alternating voltage of the GME probe; calculating the impedance of the GME probe based on the alternating current and the first alternating voltage, and determining a first magnetic field based on the impedance; positioning the GME probe at a second position above the first position; applying the alternating current to the GME probe and measuring a second alternating voltage of the GME probe; calculating the impedance of the GME probe based on the alternating current and the second alternating voltage, and determining a second magnetic field based on the impedance; and calculating a measurement magnetic field at the first position near the surface of the object to be measured based on the first magnetic field and the second magnetic field.

[0015] According to one embodiment, the giant magnetoresistive probe is positioned perpendicular to the surface of the object to be measured, and the second position is located vertically above the first position.

[0016] According to one embodiment, the measurement magnetic field at a first location near the surface of the object under test is calculated based on the following formula:

[0017] Htip = (H1 - H2) * L / ΔZ

[0018] Wherein, Htip is the measuring magnetic field at a first position near the surface of the object to be measured, H1 is the first magnetic field, H2 is the second magnetic field, L is the effective length of the giant magnetoresistance probe, and ΔZ is the distance between the second position and the first position.

[0019] According to one embodiment, the method may further include: moving the giant magnetoresistive probe along the surface of the object to be measured to measure the magnetic field at multiple locations.

[0020] The above and other features and advantages of the present invention will become apparent from the following description of exemplary embodiments taken in conjunction with the accompanying drawings. Attached Figure Description

[0021] Figure 1 This is a schematic circuit diagram of a current technology for measuring magnetic fields based on the giant magnetoresistance (GMI) effect.

[0022] Figure 2 This is a schematic diagram of another type of GMI probe.

[0023] Figure 3 This is a schematic diagram of another type of GMI probe.

[0024] Figure 4This is a functional block diagram of a magnetic field detection device for detecting weak magnetic fields on the surface of an object based on the GMI effect, according to an embodiment of the present invention.

[0025] Figure 5 This is a schematic diagram illustrating the principle of detecting weak magnetic fields on the surface of an object based on the GMI effect according to an embodiment of the present invention.

[0026] Figure 6 It is a graph of the magnetic field strength on the sample surface obtained by measuring using the magnetic field detection device of the present invention. Detailed Implementation

[0027] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. Note that the drawings may not be drawn to scale.

[0028] Figure 1 This is a circuit diagram for measuring magnetic fields based on the giant magnetoresistance (GMI) effect in existing technology. The GMI effect refers to the phenomenon that when a high-frequency current passes through a soft magnetic material, the inductive (or imaginary) and resistive (or real) components of the material's AC impedance change with an external magnetic field. This phenomenon is extremely sensitive, one to two orders of magnitude higher than the giant magnetoresistance (GMR) effect, typically reaching 10% to 120% / Oe, hence the name giant magnetoresistance effect. Utilizing this principle, by pre-calibrating the relationship between the material's AC impedance and the magnetic field, and then measuring the material's AC impedance, the external magnetic field can be detected. For example... Figure 1 As shown, AC power supply 10 can apply current through GMI material 12, and resistor 11 can be connected in series with GMI material 12 to detect the current flowing through GMI material 12. Us represents the voltage of power supply 10, Iac represents the AC current flowing through GMI material 12, Uac represents the AC voltage detected across GMI material 12, and Hex represents the external magnetic field. The AC impedance Z = Uac / Iac of GMI material 12 can be calculated using the AC current Iac flowing through GMI material 12 and the AC voltage Uac across GMI material 12, thereby determining the magnitude of the corresponding external magnetic field Hex. In other embodiments, the relationship between the giant magnetoresistance GMI of the material and the external magnetic field Hex can be pre-calibrated, then the AC impedance of the material can be measured, and the GMI value can be calculated. The magnitude of the external magnetic field Hex can then be determined based on the GMI value. The above two methods are equivalent. For ease of description, this application describes the above process as determining the external magnetic field based on AC impedance. The GMI value can be determined based on the following formula 1 or formula 2:

[0029] GMI=ΔZ / Z=(Z(Hex)-Z(Hmax)) / Z(Hmax) Formula 1

[0030] GMI=ΔZ / Z=(Z(Hex)-Z(H0)) / Z(H0) Formula 2

[0031] Where Z(Hex), Z(H0), and Z(Hmax) represent the AC impedance of the material when the external magnetic field is of arbitrary value, zero value, and saturation state, respectively.

[0032] Figure 1 The GMI material 12 shown can also be referred to as a GMI probe, and it generally includes soft magnetic alloy materials, such as Co-based alloys (e.g., CoSiB, CoFeSiB, etc.) and Fe-based alloys (e.g., NiFe, FeSiBNbCu, etc.). The GMI material 12 can be formed as an amorphous filament or a glass-encapsulated amorphous filament. In some embodiments, the GMI material 12 can be formed as a single-layer film structure of alloy material, or as a sandwich structure or a multilayer film structure. A sandwich structure includes two soft magnetic film layers and a high-conductivity metal layer sandwiched between them; the high-conductivity metal may include Cu, Ag, Au, etc. Examples of multilayer film structures may include an alternating stacked structure of soft magnetic films and conductive metal films, or an insulating layer such as SiO2 may be inserted therein. It is understood that various materials exhibiting the GMI effect have been extensively and thoroughly studied, and this invention is not limited to any specific GMI material or structure.

[0033] exist Figure 1 In the example shown, the GMI probe may consist only of GMI material 12 (e.g., a soft magnetic alloy material), an alternating current Iac may be applied to GMI material 12, and the alternating voltage Uac across GMI material 12 may be measured, thereby measuring the external magnetic field Hex. In another embodiment of the GMI probe, such as Figure 2 As shown, the GMI probe may include a core 12 formed of GMI material (e.g., a soft magnetic alloy material) and a solenoid coil 13 surrounding the core 12. An alternating current Iac may be applied to the core 12, and the alternating voltage Uac output across the solenoid coil 13 is measured, thereby measuring the external magnetic field Hex. Figure 3 Another embodiment of the GMI probe is shown, including a Helmholtz coil 14, to which an alternating current Iac can be applied. A core 12 is placed in a uniform magnetic field generated by the Helmholtz coil 14, and a solenoid coil 13 surrounds the core 12. The alternating current voltage Uac output across the solenoid coil 13 is measured. In yet another embodiment (not shown here), [the following can be omitted]. Figure 3 The probe shown uses a solenoid coil 13 to directly measure the AC voltage Uac across the core 12. It is understood that any of the GMI probe structures described herein can be applied to embodiments of the present invention.

[0034] The above discussion outlines the principle of measuring the external magnetic field Hex based on the GMI effect. It can be understood that the GMI probe measures the average magnetic field along the probe's extension direction within its effective length. Here, the effective length of the probe refers to the length of the probe providing the AC voltage Uac, for example, in... Figure 1 If the AC voltage Uac is measured across the core 12, then the effective length of the probe refers to the extended length of the core 12; while... Figure 2 and Figure 3 The example shown measures the AC voltage Uac across the solenoid coil 13 surrounding the core 12. Therefore, the effective length of the probe refers to the extended length of the solenoid coil 13. This GMI probe structure is not suitable for directly measuring weak magnetic fields on an object's surface. The weak magnetic field on an object's surface is generally perpendicular to the surface and decays rapidly after leaving the surface, meaning it is distributed in a very thin region close to the surface. The effective length of the GMI probe may be much greater than the attenuation distance of the weak magnetic field on the object's surface (e.g., the distance from the object's surface to where the magnetic field attenuates to a certain percentage), making it difficult to accurately measure the weak magnetic field in a micro-region on the object's surface.

[0035] This invention proposes a novel measurement method that can use a traditional GMI probe to measure the weak magnetic field on the surface of an object. Figure 4 A magnetic field detection device according to an embodiment of the present invention is shown, including a GMI probe 22, a positioning unit 23, an AC power supply 24, a measurement circuit 25, and a calculation unit 26.

[0036] The GMI probe 22 can be any of the GMI probes described above. It is supported by the positioning unit 23, which can position the GMI probe 22 to the desired measurement position, such as near the surface of the object 21 to be measured. The positioning unit 23 may include a servo motor and a suitable transmission mechanism to move and position the GMI probe 22 in three-dimensional space, or at least in a straight line along the object surface and in a vertical direction perpendicular to the object surface.

[0037] AC power supply 24 can provide AC current Iac to GMI probe 22, and measurement circuit 25 can measure AC voltage Uac on GMI probe 22. In one embodiment, AC power supply 24 can also be connected to measurement circuit 25 to provide information related to the applied AC current Iac, such as a clock signal, to measurement circuit 25 so that measurement circuit 25 can accurately measure the voltage signal on GMI probe 22. For example, measurement circuit 25 can use this signal to filter the detected AC voltage signal on GMI probe 22 to eliminate noise and accurately extract AC voltage Uac. Calculation unit 26 can be connected to AC power supply 24 and measurement circuit 25 to receive AC current value Iac and AC voltage value Uac, and use AC current value Iac and AC voltage value Uac to calculate the impedance Z = Uac / Iac of GMI probe 22, thereby further determining the magnitude of the external magnetic field based on impedance Z. In another embodiment, calculation unit 26 can also calculate the GMI value based on the measured impedance value Z, for example, using formula 1 or formula 2 above, and then determine the magnitude of the corresponding external magnetic field based on the GMI value. In another embodiment, the AC power supply 24 can be configured to provide a predetermined AC current Iac, which is equivalent to the AC current Iac being known and fixed. In this case, the calculation unit 26 can directly determine the magnitude of the external magnetic field based on the measured AC voltage Uac. It should be understood that determining the magnitude of the external magnetic field based on impedance Z, based on the GMI value, or based on AC voltage Uac when the AC current Iac is fixed, are equivalent. Essentially, they all rely on the relationship between AC impedance and the external magnetic field, determining the magnitude of the external magnetic field based on the measured AC impedance value. For the sake of convenience and brevity, the following description will describe determining the magnitude of the external magnetic field based on impedance Z; however, it should be understood that this description encompasses the three methods mentioned above and any other equivalent methods.

[0038] The following reference Figure 5 This describes the measurement process and principle of the magnetic field detection device of the present invention. For example... Figure 5As shown in the left figure, the GMI probe 22 is first positioned near the surface of the object to be measured using the positioning unit 23, referred to here as the first position. It can be understood that in the first position, the GMI probe 22 can directly contact the surface of the object to be measured 21, or the two can be separated by a small distance, with the lower end of the GMI probe 22 essentially located in the distribution area of ​​the magnetic field to be measured. The positioning unit 23 can make the GMI probe 22 substantially perpendicular to the surface of the object to be measured 21. In this state, the AC power supply 24 provides an AC current Iac to the GMI probe 22, the measurement circuit 25 can measure the first AC voltage Uac1 on the GMI probe 22, and the calculation unit 26 can calculate the first impedance Z1 = Uac1 / Iac of the GMI probe 22 based on the AC current value Iac and the first AC voltage value Uac1, thereby further determining the magnitude H1 of the first external magnetic field based on the first impedance Z1. As mentioned earlier, the first magnetic field H1 is the average magnetic field of the region where the GMI probe 22 is located (i.e., the region extended by the effective length L of the GMI probe 22) when the GMI probe 22 is in the first position.

[0039] Then, as Figure 5 As shown in the right figure, the positioning unit 23 moves the GMI probe 22 substantially vertically upward by a distance ΔZ, thereby moving the GMI probe 22 from the first position to a second position above it. In the second position, the AC power supply 24 similarly provides an AC current Iac to the GMI probe 22. The measurement circuit 25 can measure the second AC voltage Uac2 on the GMI probe 22. The calculation unit 26 can calculate the second impedance Z2 = Uac2 / Iac of the GMI probe 22 based on the AC current value Iac and the second AC voltage value Uac2, thereby further determining the magnitude H2 of the second external magnetic field based on the second impedance Z2. As mentioned earlier, the second magnetic field H2 is the average magnetic field of the region where the GMI probe 22 is located (i.e., the region extended by the effective length L of the GMI probe 22) when the GMI probe 22 is in the second position.

[0040] The inventors discovered that if the effective length L of the GMI probe 22 is divided into N parts, with ΔZ as the unit, and N = L / ΔZ, then... Figure 5 In the case shown in the left figure, the space occupied by the GMI probe 22 can be represented as P1, P2, ..., PN from bottom to top. When the GMI probe 22 moves upward by ΔZ, as shown in the left figure... Figure 5 As shown in the right figure, the space occupied by the GMI probe 22 can be represented as P2, P3, ..., PN, PN+1 from bottom to top. Then, the first magnetic field H1 and the second magnetic field H2 measured above can be represented by the following formulas 3 and 4 respectively:

[0041] H1 = (H P1 +HP2 +…+H PN ) / N Formula 3

[0042] H2 = (H P2 +H P3 +…+H PN+1 ) / N Formula 4

[0043] Where H Pi This refers to the magnetic field in the i-th spatial region as defined above. Therefore, subtracting Formula 4 from Formula 3 yields Formula 5:

[0044] H1-H2 = (H P1 -H PN+1 ) / N Formula 5

[0045] The inventors further analyzed the characteristics of the weak magnetic field on the object's surface, noting that it is generally distributed within a very thin, tiny region on the object's surface, such as in space P1 and several adjacent regions. Therefore, H can be... P1 The magnetic field strength is considered to be at the surface of the object. The length L of the GMI probe 22 is significantly larger than the magnetic field distribution area. Since the magnetic field attenuates rapidly with distance from the object surface, the upper end of the length L of the GMI probe 22 can be considered to extend beyond the weak magnetic field distribution area. Therefore, H can be considered... PN+1 It is almost zero, meaning it contains no magnetic field component from the surface of the object to be measured. Therefore, based on this analysis, Equation 6 can be derived from Equation 5:

[0046] Htip = (H1-H2)*N = (H1-H2)*L / ΔZ (Formula 6)

[0047] Therefore, the calculation unit 26 can use the first magnetic field H1 and the second magnetic field H2 measured at the first position and the second position respectively to calculate the magnetic field measurement value Htip at the surface position of the object to be measured 21 based on Formula 6, that is, the magnetic field Htip at the lower end position when the GMI probe 22 is in the first position.

[0048] In the above-described measurement process of the present invention, in order to accurately and precisely measure the magnetic field in a small area on the surface of an object, the vertical movement distance ΔZ should not be too large, generally within the range of 1 μm to 2 mm, preferably within the range of 10 μm to 1 mm. If the value of the movement distance ΔZ is too large, since the average magnetic field within the movement distance ΔZ range of the lower end of the probe is being measured, the measurement value may be inaccurate and cannot reflect the actual magnetic field distribution and changes within the range of distance ΔZ. On the other hand, if the movement distance ΔZ is too small, for example, less than 1 μm, the differential signal between the two measurements may be too small, and the change in magnetic field between the first and second positions may not be accurately measured. Furthermore, as mentioned above, the GMI probe 22 should have an effective length L of appropriate size, so that it can extend to the vicinity of or even beyond the boundary of the magnetic field distribution area on the surface of the object, that is, the magnetic field distribution near the upper end of the GMI probe 22 is essentially zero. In some embodiments of the present invention, the effective length L of the GMI probe 22 can be within the range of 1 mm to 3 cm, preferably within the range of 3 mm to 2 cm. A length L that is too long is detrimental to the sensitivity of the above-described measurement process. If the sensitivity of the GMI probe 22 itself is S, with units of V / nT (volts per nanotesla), then the sensitivity S' of the above process of measuring the magnetic field by the differential method can be expressed as S'=S*ΔZ / L.

[0049] The above describes the process and method for measuring a weak magnetic field on the surface of an object using the magnetic field detection device of the present invention. It should be understood that although the above description first positions the GMI probe 22 at a first position to measure a first magnetic field H1, and then positions the GMI probe 22 at a second position above the first position to measure a second magnetic field H2, it is also possible to first position it at the second position to measure the second magnetic field H2, and then position it at the first position to measure the first magnetic field H1.

[0050] In some embodiments, the positioning unit 23 can move the GMI probe 22 not only vertically but also in a plane, thereby measuring the magnetic field distribution on the surface of the object under test 21. In some embodiments, the positioning unit 23 can move the GMI probe 22 multiple times in the vertical direction, for example, to a third position above the second position, a fourth position above the third position, and so on. In this way, the magnetic field magnitude at the second position can be determined using magnetic measurements performed at the second and third positions, the magnetic field magnitude at the third position can be determined using magnetic measurements performed at the third and fourth positions, and so on. Therefore, a three-dimensional magnetic field intensity distribution above the surface of the object under test 21 can be obtained.

[0051] The magnetic field detection device of the present invention determines the magnetic field in a thin region of the object's surface by measuring the magnetic field at two height positions on the object's surface and then calculating the difference between the two values. This not only utilizes the advantages of high sensitivity and low cost of GMI sensors, but also eliminates system noise and environmental noise through differential measurement, thus enabling more accurate measurement of the weak magnetic field on the object's surface. In one embodiment, the magnetic field detection device may further include a magnetic shield, inside which the sample 21 to be tested and the GMI probe 22 can be placed, thereby shielding the Earth's magnetic field and further improving the accuracy of the measurement.

[0052] The above has been referenced Figure 4-5 The magnetic field measurement method of the present invention has been described, and for ease of understanding, it is summarized here again.

[0053] According to one embodiment, a magnetic field measurement method may include:

[0054] Step 1: Position the giant magnetoresistance probe at a first location near the surface of the object to be measured;

[0055] Step 2: Apply an alternating current to the giant magnetoresistance probe and measure the first alternating voltage of the giant magnetoresistance probe;

[0056] Step 3: Calculate the impedance of the giant magnetoresistive probe based on the alternating current and the first alternating voltage, and determine the first magnetic field based on the impedance;

[0057] Step 4: Position the giant magnetoresistance probe at a second position above the first position;

[0058] Step 5: Apply the alternating current to the giant magnetoresistance probe and measure the second alternating voltage of the giant magnetoresistance probe;

[0059] Step 6: Calculate the impedance of the giant magnetoresistive probe based on the AC current and the second AC voltage, and determine the second magnetic field based on the impedance; and

[0060] Step 7: Calculate the measurement magnetic field at a first location near the surface of the object under test based on the first magnetic field and the second magnetic field.

[0061] In steps 1 and 4, the giant magnetoresistance probe can be positioned substantially perpendicular to the surface of the object to be measured, and the second position can be located vertically above the first position.

[0062] In step 7, the measurement magnetic field at a first location near the surface of the object to be measured can be calculated based on the above formula 6.

[0063] Furthermore, in the magnetic field measurement method of the present invention, the giant magnetoresistive probe can be moved along the surface of the object under test to measure the magnetic field at multiple locations; and the giant magnetoresistive probe can be moved multiple times along the vertical direction to measure the magnetic field at multiple vertical locations. Ultimately, the magnetic field distribution in three-dimensional space above the surface of the object under test can be obtained.

[0064] For some details regarding the magnetic field measurement method of this invention, please refer to the above. Figure 4-5 The description will not be repeated here.

[0065] Figure 6 This is a graph showing the magnetic field strength obtained by measuring the magnetic ink area on a 20 Euro banknote using the magnetic field detection device and method of this invention. The horizontal axis represents the displacement distance along the horizontal line on the sample surface, and the vertical axis represents the measured magnetic field strength. During the measurement, the first position was approximately 0.2 mm from the sample surface, and the second position was approximately 0.7 mm from the sample surface, meaning the vertical movement distance ΔZ was approximately 0.5 mm. Figure 6 As can be seen from the curve, the magnetic field detection device and method of the present invention can accurately detect five hard magnetic regions on the sample surface, and successfully realize the detection of weak magnetic fields in the micro-regions of the sample surface.

[0066] Unless the context explicitly requires otherwise, throughout the specification and claims, the words “comprising,” “including,” “comprise,” “including,” etc., shall be interpreted in an inclusive sense, rather than an exclusive or exhaustive sense. That is, they mean “including but not limited to.” The term “connection” as commonly used herein refers to two or more elements that can be directly connected or connected via one or more intermediate elements. Furthermore, when used in this application, the terms “this,” “above,” “below,” and similar terms shall refer to the entire application and not any particular part thereof. Where the context permits, the term “or” refers to a list of two or more items, encompassing all of the following interpretations: any item in the list, all items in the list, and any combination of items in the list.

[0067] Furthermore, unless otherwise specifically stated or otherwise understood in the context in which they are used, the conditional language used herein, such as “can,” “may,” “possibly,” “can,” “for example,” “likely,” “such as,” etc., is generally intended to express that certain embodiments include certain features, elements, and / or states, while other embodiments do not. Therefore, such conditional language is not generally intended to imply that one or more embodiments require features, elements, and / or states in any way, or that one or more embodiments must include logic for making a decision, with or without author input or prompts, that determines whether such features, elements, and / or states are included in or will be performed in any particular embodiment.

[0068] While certain embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of this disclosure. In fact, the novel facilities, methods, and systems described herein can be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes can be made to the form of the methods and systems described herein without departing from the spirit of this disclosure. For example, although blocks are presented in a given arrangement, alternative embodiments may perform functions similar to different components and / or circuit topologies, and some blocks may be deleted, moved, added, subdivided, combined, and / or modified. Each of these blocks can be implemented in a variety of different ways. Any suitable combination of elements and actions of the various embodiments described above can be combined to provide further embodiments. The appended claims and their equivalents are intended to cover these forms or modifications that fall within the scope and spirit of this disclosure.

[0069] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of the invention to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

Claims

1. A magnetic field detection device, comprising: Giant magnetoresistance probe; An AC power supply is used to apply an alternating current to the giant magnetoresistance probe; The measuring circuit is used to measure the AC voltage on the giant magnetoresistance probe; A calculation unit is used to calculate the impedance based on the alternating current and the alternating voltage, and to determine the magnitude of the magnetic field based on the impedance; as well as A positioning unit is used to support the giant magnetoresistive probe and position the giant magnetoresistive probe at a predetermined position. Specifically, when the positioning unit positions the giant magnetoresistive probe at a first position near the surface of the object to be tested, the measuring circuit measures a first AC voltage of the giant magnetoresistive probe, and the calculation unit calculates a first magnetic field based on the first AC voltage. When the positioning unit positions the giant magnetoresistive probe at a second position above the first position, the measuring circuit measures a second AC voltage of the giant magnetoresistive probe, and the calculation unit calculates a second magnetic field based on the second AC voltage. Furthermore, the unit calculates the measured magnetic field at the first position near the surface of the object to be tested based on the first magnetic field and the second magnetic field.

2. The magnetic field detection device as described in claim 1, wherein, The positioning unit positions the giant magnetoresistive probe perpendicular to the surface of the object to be measured, and the second position is located vertically above the first position.

3. The magnetic field detection device as described in claim 1, wherein, The calculation unit calculates the measurement magnetic field at a first location near the surface of the object under test based on the following formula: Htip = (H1 - H2) * L / ΔZ Wherein, Htip is the measuring magnetic field at a first position near the surface of the object to be measured, H1 is the first magnetic field, H2 is the second magnetic field, L is the effective length of the giant magnetoresistance probe, and ΔZ is the distance between the second position and the first position.

4. The magnetic field detection device as described in claim 1, wherein, The distance between the second position and the first position is in the range of 1 μm to 2 mm, preferably in the range of 10 μm to 1 mm. The effective length of the giant magnetoresistive probe is in the range of 1 mm to 3 cm, preferably in the range of 3 mm to 2 cm.

5. The magnetic field detection device as described in claim 1, wherein, The positioning unit is also configured to move the giant magnetoresistive probe along the surface of the object under test to measure the magnetic field at multiple locations.

6. The magnetic field detection device according to any one of claims 1-5, further comprising a control unit for controlling one or more of the AC power supply, the measurement circuit, the calculation unit, and the positioning unit to automatically measure the magnetic field at multiple locations on the surface of the object to be measured.

7. A method for measuring a magnetic field, comprising: Position the giant magnetoresistive probe at a first location near the surface of the object to be measured; An alternating current is applied to the giant magnetoresistive probe, and a first alternating voltage of the giant magnetoresistive probe is measured; The impedance of the giant magnetoresistive probe is calculated based on the alternating current and the first alternating voltage, and the first magnetic field is determined based on the impedance. Position the giant magnetoresistive probe at a second position above the first position; The alternating current is applied to the giant magnetoresistance probe, and the second alternating voltage of the giant magnetoresistance probe is measured; The impedance of the giant magnetoresistive probe is calculated based on the alternating current and the second alternating voltage, and the second magnetic field is determined based on the impedance. The measurement magnetic field at a first location near the surface of the object under test is calculated based on the first magnetic field and the second magnetic field.

8. The method of claim 7, wherein, The giant magnetoresistance probe is positioned perpendicular to the surface of the object under test, and the second position is located vertically above the first position.

9. The magnetic field detection device as described in claim 7, wherein, The measurement magnetic field at a first location near the surface of the object under test is calculated based on the following formula: Htip = (H1 - H2) * L / ΔZ Wherein, Htip is the measuring magnetic field at a first position near the surface of the object to be measured, H1 is the first magnetic field, H2 is the second magnetic field, L is the effective length of the giant magnetoresistance probe, and ΔZ is the distance between the second position and the first position.

10. The method of claim 7, further comprising: The giant magnetoresistance probe is moved along the surface of the object under test to measure the magnetic field at multiple locations.

Images