Magnetism measurement method and device of light-force magnetometer based on Terfenol-D magnetostrictive material

Abstract

The invention discloses a Terfenol-D magnetostrictive material-based optical force magnetometer magnetic measurement method, which comprises the following steps of: firstly, densely winding a single-mode optical fiber on the surface of a Terfenol-D magnetostrictive element in multiple circles, so that the magnetostrictive deformation of the Terfenol-D magnetostrictive element under the action of an external magnetic field is transmitted to the single-mode optical fiber; an unequal-arm Mach-Zehnder interferometer is constructed; the method comprises the following steps: applying magnetic fields under magnetic fields with different intensities, measuring change values of interference phases under the magnetic fields with different intensities according to a magnetostrictive strain relationship of a Terfenol-D magnetostrictive element, and establishing a calibration curve between the change values of the interference phases and the external magnetic field intensity; when a magnetic field to be measured acts on the sensing arm, the corresponding external magnetic field intensity is calculated according to the calibration curve. The magnetic measurement method is simple in structure, all signals are transmitted through an optical path, and electromagnetic interference can be effectively resisted; the measuring process is quick in response, and is suitable for quickly changing magnetic field measurement.

Description

Technical Field

[0001] This invention relates to the field of magnetic field measurement technology, specifically to a method and apparatus for measuring magnetic fields using an optical magnetometer based on Terfenol-D magnetostrictive material. Background Technology

[0002] Magnetic field detection technology has wide applications in many fields, and in some areas it is even a core indicator of technological advancement. Currently, the development of an increasing number of fields is constrained by the level of magnetic field detection technology, making the research and development of more advanced magnetic field detection instruments crucial. Traditional magnetic field detection instruments generally use elements with the Hall effect or electrical sensors such as magnetoresistive sensors to detect magnetic fields. While these instruments offer high accuracy, they are structurally complex and easily affected by background electromagnetic interference, making them difficult to operate in complex environments such as high-voltage power systems and strong interfering magnetic fields. Improving both the sensitivity of magnetic field measurements and the anti-interference capability of the measurement system remains a challenge in magnetic field measurement technology. Therefore, it is necessary to propose a method capable of accurately measuring magnetic fields in complex environments to overcome the aforementioned technical shortcomings. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and propose a method and device for measuring magnetic fields using an optical magnetometer based on Terfenol-D magnetostrictive material. This method has a simple structure, all signals are transmitted through an optical path, and it can effectively resist electromagnetic interference. The measurement process has a rapid response and is suitable for measuring rapidly changing magnetic fields. Therefore, by utilizing the giant magnetostrictive effect of Terfenol-D, high-sensitivity magnetic field detection can be achieved.

[0004] To achieve the above objectives, the technical solution specifically adopted by the present invention is as follows:

[0005] A method for measuring magnetism using an optical magnetometer based on Terfenol-D magnetostrictive material includes the following steps:

[0006] Step 1: Wrap single-mode fiber tightly around the surface of the Terfenol-D magnetostrictive element multiple times, so that the magnetostrictive deformation of the Terfenol-D magnetostrictive element under the action of an external magnetic field is transferred to the single-mode fiber.

[0007] Step 2: Construct an unequal-arm Mach-Zehnder interferometer using a Terfenol-D magnetostrictive element made of multiple tightly wound single-mode fiber. The Terfenol-D magnetostrictive element made of multiple tightly wound single-mode fiber is used as the sensing arm of the unequal-arm Mach-Zehnder interferometer, and the other arm of the unequal-arm Mach-Zehnder interferometer is used as the reference arm.

[0008] Step 3: By applying magnetic fields of different intensities, and based on the magnetostrictive strain relationship of the Terfenol-D magnetostrictive element in the magnetic field, measure the change value of the interference phase under different magnetic fields, and establish a calibration curve between the change value of the interference phase and the intensity of the applied magnetic field.

[0009] Step 4: When the magnetic field to be measured acts on the sensing arm, monitor the light intensity signal at the output end of the unequal-arm Mach-Zehnder interferometer to obtain the phase change, and calculate the corresponding applied magnetic field strength according to the calibration curve.

[0010] Preferably, the Terfenol-D magnetostrictive element is a Tb-Dy-Fe alloy with a magnetostrictive strain of 2000 ppm. The Tb-Dy-Fe alloy exhibits the highest magnetostrictive rate, and its magnetostrictive strain can reach approximately 2000 ppm.

[0011] Preferably, the Terfenol-D magnetostrictive element has a rectangular structure, and the magnetostrictive direction of the Terfenol-D magnetostrictive element is symmetrically arranged with semi-cylinders. Placing semi-cylinders on two faces in the magnetostrictive direction increases the force-bearing area of ​​the magnetostrictive material, thus allowing for a larger upper limit on the number of tightly wound turns N of the optical fiber.

[0012] Preferably, the single-mode fiber has a radius of 2.25 μm and a refractive index of 1.454.

[0013] Preferably, the reference arm of the unequal-arm Mach-Zehnder interferometer is kept at a constant length.

[0014] Preferably, in step 3, the method for calculating the change in the interference phase is as follows:

[0015]

[0016]

[0017]

[0018] in, The change in the interference phase, For optical path difference, The refractive index of a single-mode fiber. It is the wavelength of the laser. It refers to the number of turns in a single-mode fiber. Terfenol-D magnetostrictive elements produce a length of curved edge along the direction of the magnetic field when subjected to an external magnetic field. This is the original length of the Terfenol-D magnetostrictive element. It is the magnetostriction coefficient of the Terfenol-D magnetostrictive element.

[0019] Among them, optical path difference The changes mainly come from the changes in the length of the optical fiber in the sensing arm, and the changes in the length of the optical fiber are directly affected by the magnetostrictive effect of the Terfenol-D material.

[0020] Preferably, in step 2, the initial optical path difference between the reference arm and the sensing arm is coarsely adjusted. By adjusting the initial optical path difference between the reference arm and the sensing arm, the optical path difference between the two arms is made smaller than the coherence length of the light source, thereby improving the contrast of the output interference signal. Then, the initial phase of the reference arm is adjusted by a phase adjuster to adjust the phase sensitivity of the interference signal to the peak range, thereby improving the response sensitivity to changes in optical path caused by magnetostriction.

[0021] Preferably, in step S2, a constant bias magnetic field is applied to the Terfenol-D magnetostrictive element so that the material operates in the linear region of the magnetostrictive characteristic curve.

[0022] By applying a constant bias magnetic field to the Terfenol-D material, the magnetostrictive material operates in the linear region of the magnetostrictive characteristic curve, thereby improving the linear response of the sensor and thus obtaining greater deformation to improve the sensitivity of magnetic field measurement.

[0023] Preferably, in step S2, a polarization-preserving single-mode fiber and a temperature control device are used to reduce the impact of environmental disturbances on the interference signal, thereby further improving the anti-interference performance and stability of the system.

[0024] This invention also provides an optical-magnetic meter based on Terfenol-D magnetostrictive material for measuring magnetic fields, comprising:

[0025] Terfenol-D magnetostrictive element;

[0026] Single-mode optical fiber is tightly wound in multiple turns on the surface of the Terfenol-D magnetostrictive element;

[0027] An unequal-arm Mach-Zehnder interferometer includes a sensing arm and a reference arm, wherein the sensing arm is composed of a Terfenol-D magnetostrictive element wound with the single-mode optical fiber, and the reference arm maintains a constant length.

[0028] A light source for providing laser light to the interferometer;

[0029] A detector is used to detect the light intensity signal at the output of the interferometer.

[0030] The processing unit is used to obtain the phase change based on the light intensity signal and calculate the applied magnetic field strength based on the pre-stored calibration curve.

[0031] Preferably, the Terfenol-D magnetostrictive element includes a cuboid body and semi-cylindrical structures disposed on two faces along the magnetostrictive direction. Placing semi-cylindrical structures on the two faces along the magnetostrictive direction increases the force-bearing area of ​​the magnetostrictive material, thereby allowing for a larger upper limit to the number of tightly wound optical fiber turns N.

[0032] Preferably, a bias magnetic field application device is also included for applying a constant bias magnetic field to the Terfenol-D magnetostrictive element. This allows the magnetostrictive material to operate in the linear region of the magnetostrictive characteristic curve, thereby improving the linear response of the sensor and thus obtaining greater deformation to enhance the sensitivity of magnetic field measurements.

[0033] Preferably, the processing unit is configured to convert the optical path difference into an electrical signal through phase measurement, thereby achieving highly sensitive detection of Terfenol-D deformation. Due to the high sensitivity of phase detection, minute changes in fiber length can be converted into significant electrical signal outputs, enabling amplified detection of Terfenol-D deformation.

[0034] This invention has the following characteristics and beneficial effects:

[0035] The Terfenol-D magnetostrictive material used can achieve the highest magnetostriction coefficient to date. When the external magnetic field changes, Terfenol-D can produce greater deformation than other magnetostrictive materials.

[0036] An unequal-arm Mach-Zehnder interferometer was selected, with one arm using Terfenol-D material wound with optical fiber as the sensing arm of the interferometer. High-sensitivity detection and amplification of the magnetic field signal were achieved by monitoring the phase change of the interferometer's output signal.

[0037] In the interferometer, the signal transmission medium is optical fiber, which avoids the electromagnetic interference problem in traditional electrical sensors and enables the measurement system to have good anti-interference performance in complex electromagnetic environments.

[0038] The system has a simple and compact structure. The entire optical-magnetic instrument does not require cascaded complex optical components and consists only of an unequal-arm Mach-Zehnder interferometer and a Terfenol-D magnetic coupling element. Compared with traditional fiber grating (FBG) or Fabry-Perot (FP) type optical-magnetic instruments, this scheme adopts a direct phase interferometry detection method, which does not rely on additional filter gratings or optical cavity mirrors.

[0039] The overall geometry of the scheme is easily expandable, enabling the monitoring of triaxial magnetic fields. In the magnetic-force coupling section, this invention uses Terfenol-D magnetostrictive material. Terfenol-D is a Tb-Dy-Fe alloy with the highest known magnetostrictive rate of all alloys, achieving a magnetostrictive strain of approximately 2000 ppm (i.e., 2 mm / m) under a suitable bias magnetic field. In the optical-force detection section, an unequal-arm Mach-Zehnder interferometer is used to monitor the deformation of the magnetostrictive material under the influence of a magnetic field.

[0040] This method utilizes the reversible deformation property of Terfenol-D material under the influence of an external magnetic field. By winding optical fibers around the surface of a Terfenol-D magnetostrictive element to form an interferometer arm, changes in the magnetic field cause a corresponding change in the length of the fiber along the magnetic field direction, thus altering the interference phase of the interferometer and achieving a direct conversion between magnetic field strength and interference phase. This magnetometry method features a simple structure, with all signals transmitted through an optical path, effectively resisting electromagnetic interference. The measurement process is rapid, making it suitable for measuring rapidly changing magnetic fields. Therefore, utilizing the giant magnetostrictive effect of Terfenol-D, highly sensitive magnetic field detection can be achieved.

[0041] In summary, this invention provides a novel, highly feasible, and reliable method for measuring high-sensitivity magnetic fields, meeting the needs of precision magnetic field measurement. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the Terfenol-D magnetostrictive element in an embodiment of the present invention.

[0043] Figure 2 This is a schematic diagram of a Terfenol-D magnetostrictive element wound with optical fiber in an embodiment of the present invention.

[0044] Figure 3 This is a light interferometer device in an embodiment of the present invention.

[0045] Figure 4 This is an approximate relationship between the magnetostriction coefficient A and the magnetic field strength B in an embodiment of the present invention.

[0046] Figure 5 This illustrates the relationship between the phase difference and the change in magnetic field when the initial background magnetic field is 0.05T in an embodiment of the present invention. Detailed Implementation

[0047] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0048] Example 1

[0049] This embodiment provides a method for measuring magnetism using an optical magnetometer based on Terfenol-D magnetostrictive material, including the following steps:

[0050] Step 1: Fiber winding. Single-mode fiber is tightly wound multiple turns onto the surface of the Terfenol-D magnetostrictive material. The tight winding ensures that the magnetostrictive deformation of the material under the action of an external magnetic field can be transmitted to the fiber. The multiple turns of winding can amplify the small deformation on the Terfenol-D material into a large optical path change in the fiber.

[0051] Specifically, in this embodiment, we selected Terfenol-D magnetostrictive material as the magnetic-force coupling element. This material exhibits a significant magnetostrictive effect under the influence of an external magnetic field; under the same applied magnetic field change, Terfenol-D can produce a larger length change, which is beneficial for improving detection sensitivity. The deformation of the Terfenol-D material has a nonlinear response to the magnetic field, but by applying a constant bias magnetic field, the operating point can be placed in a near-linear region, thereby improving the linear response of the sensor and thus obtaining a larger deformation to improve the magnetic field measurement sensitivity. Figure 1 As shown, the main body of the component is made of Terfenol-D magnetostrictive material and is [length missing]. Width Gao Wei A cuboid, with a diameter of [missing information] made of non-magnetic material bonded to its two faces along the magnetostrictive direction. , length is The semi-cylindrical shape allows for tighter bonding of the optical fiber during winding, thereby increasing the adhesion between the optical fiber and the component surface.

[0052] To further improve the accuracy of the fiber optic sensor, the Terfenol-D magnetostrictive element is uniformly and tightly wound along its length on its side. The single-mode fiber with multiple turns allows for a tight fit between the fiber and the component surface, such as... Figure 2 As shown, the total length of this section of optical fiber is The two ends of the optical fiber are connected to the sensing arms of the interferometer.

[0053] Step 2: Construction of the interferometer system. A unequal-arm Mach-Zehnder interferometer is constructed, with one arm using Terfenol-D material wound with optical fiber as the sensing arm, and the other reference arm maintained at a constant length. To obtain a high-contrast interference signal, the initial optical path difference between the two arms is adjusted to be less than the coherence length of the light source. Then, the initial phase of the reference arm is adjusted using a phase adjuster to ensure the interferometer operates in the orthogonal region where the interference signal is most sensitive to phase changes, guaranteeing high phase sensitivity of the interference signal.

[0054] Specifically, in this embodiment, a single-mode laser with a center wavelength of 795nm is selected as the light source. This laser can provide stable single-mode output, and by suppressing the interference caused by non-single-mode components and optical field noise, a high signal-to-noise ratio of the interference signal is ensured. A 50:50 fiber coupler is used to split the beam into a reference arm and a sensing arm, thereby constructing an unequal-arm Mach-Zehnder interferometer. Polarization-preserving single-mode fiber is used as the transmission medium for both the reference and sensing arms to maintain the polarization consistency of the optical signals in both arms; a temperature control device is also included to suppress Terfenol-D length changes caused by thermal effects and fiber thermo-optic effects. The length of the reference arm is fixed at approximately [value missing]. The sensing arm is made of the single-mode optical fiber mentioned in step 1 above, and its radius is... Refractive index ,length This optical fiber is tightly wound onto Terfenol-D material. When the external magnetic field changes, the Terfenol-D deforms, causing a change in the optical path of the sensing arm fiber. This change in optical path difference leads to a change in the interference pattern, reflecting the strength and variation of the magnetic field. To further improve the phase sensitivity of the interferometer, the initial optical path difference between the reference arm and the sensing arm is adjusted so that the difference is less than the coherence length of the light source, thereby improving the contrast of the output interference signal. Then, the initial phase of the reference arm is adjusted using a phase adjuster to bring the phase sensitivity of the interference signal to the peak range, improving the response sensitivity to changes in optical path caused by magnetostriction. To increase the response of Terfenol-D to changes in the magnetic field, a constant bias magnetic field is applied to the material, placing it in the range where magnetostrictive strain is most sensitive to changes in the magnetic field. The bias magnetic field can be generated by an external permanent magnet or a bias coil. The biased Terfenol-D element exhibits a larger strain output under weak magnetic field changes, thereby improving the measurement sensitivity. When the beams from the reference arm and the sensing arm propagate through their respective paths to the downstream 50:50 beam splitter, the two beams combine at the splitter. At this point, because the two beams have traversed different optical path lengths, the phase difference of the light waves changes, thus forming an interference signal. The combined optical signal is transmitted to a photodetector for detection. The detector converts the received interference signal into an electrical signal, which is then sent to the data acquisition card for processing, such as... Figure 3 As shown.

[0055] Step 3: Establish calibration curves, including the following methods:

[0056] Calculate the change in interference phase, whereby the change in interference phase is the difference between the interference phase affected by the magnetic field and the original interference phase without the magnetic field.

[0057] The relationship between the change in the interference phase and the optical path difference is as follows: the change in the interference phase is equal to 2 times pi multiplied by the refractive index of the single-mode fiber, multiplied by the optical path difference, and then divided by the wavelength of the laser.

[0058] The optical path difference is related to the number of turns of the single-mode fiber and the deformation length of the Terfenol-D magnetostrictive element along the direction of the magnetic field when it is subjected to an external magnetic field. The optical path difference is equal to the number of turns of the single-mode fiber multiplied by the deformation length.

[0059] The magnetostriction coefficient of a Terfenol-D magnetostrictive element is defined as the ratio of the deformed length to the original length of the Terfenol-D magnetostrictive element.

[0060] Specifically, this embodiment utilizes the magnetostrictive strain relationship of Terfenol-D material in a magnetic field to convert a magnetic field signal into a phase signal for an interferometer. Subsequently, magnetic fields of varying intensities are applied... A magnetic field is applied, and the interference phase is read. Change value ,Establish The calibration curve between the applied magnetic field strength B and the external magnetic field strength B.

[0061] Specifically, in this step, this embodiment utilizes the magnetostrictive effect of Terfenol-D material to convert the external magnetic field signal into a phase signal of the interferometer and find their corresponding relationship. Furthermore, Helmholtz coils are used to generate magnetic fields of different intensities. The Terfenol-D element undergoes varying degrees of deformation under magnetic fields of different strengths, resulting in changes in the interference phase. Below, by reading the interference phase Change value It can be established The relationship between the applied magnetic field strength B and the external magnetic field strength B.

[0062] Furthermore, the change in the interference phase Subject to optical path difference The influence of optical path difference The changes primarily originate from the length variation of the optical fiber in the sensing arm, which is directly influenced by the magnetostrictive effect of the Terfenol-D material. The length change of the Terfenol-D material along the direction of the external magnetic field when subjected to an external magnetic field is described by the magnetostrictive coefficient A, defined as ∆h / h, where ∆h is the length change caused by the external magnetic field. Based on theoretical derivation, the interference phase can be obtained. Optical path difference The relation is: optical path difference The main reason is the change in the length of the optical fiber in the sensing arm, which can be obtained Therefore, there is The approximate relationship between the magnetostriction coefficient A and the magnetic field strength B is as follows: Figure 4 As shown, the approximate relationship between A and B obtained through fitting and calibration is as follows:

[0063]

[0064] Achieve from Quantitative conversion to B. The relationship between phase difference and magnetic field change when the initial background magnetic field is 0.05T is as follows: Figure 5 As shown, it can be seen that when the magnetic field changes by 2.494... The phase difference changes by 1 rad.

[0065] Step 4: Measurement Process. The light intensity at the interferometer output changes with the phase difference between the two arms. The change in phase is obtained by monitoring the light intensity signal at the output. The corresponding applied magnetic field strength B can be calculated based on the conversion relationship established in step 3.

[0066] Specifically, in actual measurements, when the magnetic field B is applied to the Terfenol-D sensing arm, the Terfenol-D element undergoes magnetostrictive deformation, causing a slight change in the length of the wound optical fiber, which in turn leads to a corresponding change in the light intensity output by the interferometer. The phase change is obtained by acquiring the interference signal using a coherent detector and demodulating it. Then, based on the conversion relationship established in step 3, the phase change is converted into the external magnetic field strength B, and the corresponding applied magnetic field strength B can be calculated. It is important to note that in actual measurements, the mechanical properties of the Terfenol-D material still affect the measurement results. Especially in high-intensity magnetic field environments, the material's elastic modulus may affect its deformation response, thus influencing the fiber length change. If the material's elastic modulus is too large, the magnetostrictive effect may be insignificant, thereby reducing measurement sensitivity. Therefore, in addition to optimizing the magnetostriction coefficient A, it is also necessary to comprehensively consider the material's mechanical properties to ensure that it can provide sufficient deformation within the actual magnetic field range to accurately reflect the external magnetic field strength.

[0067] Example 2

[0068] This embodiment also provides an optical-magnetic instrument based on Terfenol-D magnetostrictive material for measuring magnetostriction, used to implement the optical-magnetic instrument method based on Terfenol-D magnetostrictive material in Embodiment 1, specifically including:

[0069] Terfenol-D magnetostrictive element, wherein the Terfenol-D magnetostrictive element includes a cuboid body and a semi-cylindrical structure disposed on two sides in the magnetostrictive direction;

[0070] Single-mode optical fiber is tightly wound in multiple turns on the surface of the Terfenol-D magnetostrictive element;

[0071] An unequal-arm Mach-Zehnder interferometer includes a sensing arm and a reference arm, wherein the sensing arm is composed of a Terfenol-D magnetostrictive element wound with the single-mode optical fiber, and the reference arm maintains a constant length.

[0072] A light source for providing laser light to the interferometer;

[0073] A detector is used to detect the light intensity signal at the output of the interferometer.

[0074] The processing unit is used to obtain the phase change based on the light intensity signal and calculate the applied magnetic field strength according to a pre-stored calibration curve. Specifically, the processing unit is configured to convert the optical path difference into an electrical signal via phase measurement, thereby achieving high-sensitivity detection of Terfenol-D deformation.

[0075] A bias magnetic field applying device for applying a constant bias magnetic field to the Terfenol-D magnetostrictive element.

[0076] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for measuring magnetism using an optical-magnetic instrument based on Terfenol-D magnetostrictive material, characterized in that, Includes the following steps: Step 1: Wrap single-mode fiber tightly around the surface of the Terfenol-D magnetostrictive element multiple times, so that the magnetostrictive deformation of the Terfenol-D magnetostrictive element under the action of an external magnetic field is transferred to the single-mode fiber. Step 2: Construct an unequal-arm Mach-Zehnder interferometer using a Terfenol-D magnetostrictive element made of multiple tightly wound single-mode fiber. The Terfenol-D magnetostrictive element made of multiple tightly wound single-mode fiber is used as the sensing arm of the unequal-arm Mach-Zehnder interferometer, and the other arm of the unequal-arm Mach-Zehnder interferometer is used as the reference arm. Step 3: By applying magnetic fields of different intensities, and based on the magnetostrictive strain relationship of the Terfenol-D magnetostrictive element in the magnetic field, measure the change value of the interference phase under different magnetic fields, and establish a calibration curve between the change value of the interference phase and the intensity of the applied magnetic field. Step 4: When the magnetic field to be measured acts on the sensing arm, monitor the light intensity signal at the output end of the unequal-arm Mach-Zehnder interferometer to obtain the phase change, and calculate the corresponding applied magnetic field strength according to the calibration curve.

2. The method for measuring magnetism using an optical magnetometer based on Terfenol-D magnetostrictive material according to claim 1, characterized in that, The Terfenol-D magnetostrictive element is a Tb-Dy-Fe alloy with a magnetostrictive strain of 2000 ppm.

3. The method for measuring magnetism using an optical magnetometer based on Terfenol-D magnetostrictive material according to claim 1, characterized in that, The Terfenol-D magnetostrictive element has a rectangular structure, and the magnetostrictive direction of the Terfenol-D magnetostrictive element is symmetrically arranged with a semi-cylinder.

4. The method for measuring magnetism using an optical magnetometer based on Terfenol-D magnetostrictive material according to claim 1, characterized in that, The single-mode fiber has a radius of 2.25 μm and a refractive index of 1.

454.

5. The method for measuring magnetism using an optical magnetometer based on Terfenol-D magnetostrictive material according to claim 1, characterized in that, The reference arm of the unequal-arm Mach-Zehnder interferometer maintains a constant length.

6. The method for measuring magnetism using an optical-magnetic instrument based on Terfenol-D magnetostrictive material according to claim 1, characterized in that, In step 3, the method for establishing the calibration curve between the change in interference phase and the applied magnetic field strength includes: Calculate the change in interference phase, whereby the change in interference phase is the difference between the interference phase affected by the magnetic field and the original interference phase without the magnetic field. The relationship between the change in the interference phase and the optical path difference is as follows: the change in the interference phase is equal to 2 times pi multiplied by the refractive index of the single-mode fiber, multiplied by the optical path difference, and then divided by the wavelength of the laser. The optical path difference is related to the number of turns of the single-mode fiber and the deformation length of the Terfenol-D magnetostrictive element along the direction of the magnetic field when it is subjected to an external magnetic field. The optical path difference is equal to the number of turns of the single-mode fiber multiplied by the deformation length. The magnetostriction coefficient of a Terfenol-D magnetostrictive element is defined as the ratio of the deformed length to the original length of the Terfenol-D magnetostrictive element.

7. The method for measuring magnetism using an optical magnetometer based on Terfenol-D magnetostrictive material according to claim 6, characterized in that, In step 3, the curve is calibrated based on the approximate relationship between the magnetostriction coefficient and the magnetic field strength.

8. The method for measuring magnetism using an optical magnetometer based on Terfenol-D magnetostrictive material according to claim 7, characterized in that, In step 2, the initial optical path difference between the reference arm and the sensing arm is adjusted to make the optical path difference between the two arms less than the coherence length of the light source, so as to improve the contrast of the output interference signal. Then, the initial phase of the reference arm is adjusted by the phase adjuster to adjust the phase sensitivity of the interference signal to the peak range, thereby improving the response sensitivity to optical path changes caused by magnetostriction.

9. The method for measuring magnetism using an optical-magnetic instrument based on Terfenol-D magnetostrictive material according to claim 1, characterized in that, In step S2, a constant bias magnetic field is applied to the Terfenol-D magnetostrictive element so that the material operates in the linear region of the magnetostrictive characteristic curve.

10. The method for measuring magnetism using an optical-magnetic instrument based on Terfenol-D magnetostrictive material according to claim 1, characterized in that, In step S2, a polarization-preserving single-mode optical fiber and a temperature control device are used.

11. A photomagnetic instrument based on Terfenol-D magnetostrictive material for measuring magnetic fields, characterized in that, include: Terfenol-D magnetostrictive element; Single-mode optical fiber is tightly wound in multiple turns on the surface of the Terfenol-D magnetostrictive element; An unequal-arm Mach-Zehnder interferometer includes a sensing arm and a reference arm, wherein the sensing arm is composed of a Terfenol-D magnetostrictive element wound with the single-mode optical fiber, and the reference arm maintains a constant length. A light source for providing laser light to the interferometer; A detector is used to detect the light intensity signal at the output of the interferometer. The processing unit is used to obtain the phase change based on the light intensity signal and calculate the applied magnetic field strength based on the pre-stored calibration curve.

12. The optical-magnetic instrument based on Terfenol-D magnetostrictive material according to claim 11, characterized in that, The Terfenol-D magnetostrictive element includes a cuboid body and a semi-cylindrical structure disposed on two faces in the magnetostrictive direction.

13. The optical-magnetic instrument based on Terfenol-D magnetostrictive material according to claim 11, characterized in that, It also includes a bias magnetic field application device for applying a constant bias magnetic field to the Terfenol-D magnetostrictive element.

14. The optical-magnetic instrument based on Terfenol-D magnetostrictive material according to claim 11, characterized in that, The processing unit is configured to convert the optical path difference into an electrical signal through phase measurement, thereby achieving high-sensitivity detection of Terfenol-D deformation.

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