Vector magnetic field detection method based on surface acoustic wave magnetic field directivity model

Abstract

The invention provides a vector magnetic field detection method based on a surface acoustic wave magnetic field directivity model, and the method employs an external magnetic field to act on a magnetic sensitive film on a sound propagation path to generate a dynamic magnetoelastic coupling effect, modulates the propagation characteristics of surface acoustic waves, and carries out the decoupling of a sound signal, and obtains the magnetic field information. The response value of the sensor is influenced by the included angle between the direction of the external magnetic field and the anisotropic axis, so that the angle orientation of the sensor in the space and the size and direction of the magnetic field can be quantitatively calibrated by projecting the magnetic field to be measured in the space into a coordinate system of the sensor, and a surface acoustic wave magnetic field directivity model is constructed. The surface acoustic wave magnetic field sensing technology has the advantages of high sensitivity, quick response and the like, and the vector magnetic field detection method can realize the direction positioning function of a full-plane magnetic field and has important practical value in the application field of space vector magnetic field detection.

Description

Technical Field

[0001] This application belongs to the field of magnetic field detection technology, specifically relating to a vector magnetic field detection method based on a surface acoustic wave magnetic field directivity model. Background Technology

[0002] In the field of aerospace exploration technology, magnetic field detectors are used for both spacecraft attitude and orbit control and space magnetic field environment monitoring, and also serve as an important payload for landing probes. Because magnetic fields of varying intensities exist in space, the magnetic field environment has a significant impact on the operation and safety of spacecraft. Therefore, accurately acquiring and utilizing vector magnetic field information in the complex space environment has become one of the fundamental core technologies that must be mastered and overcome in the development of the aerospace field. Currently, the main method for measuring space magnetic fields is to use Hall effect magnetic field sensors, where a Hall plate is used as the sensing element. Depending on the measurement range, this type of sensor can be called a teslameter or a gaussmeter, and is mainly used to measure DC static magnetic fields. Although Hall effect magnetic field sensing technology has made rapid progress, traditional Hall effect magnetic field sensors can only effectively sense magnetic fields in a single direction, either the X-axis or the Y-axis. Therefore, to achieve multi-directional magnetic field measurement, multiple Hall effect sensors need to be installed on different circuit boards, ensuring appropriate angles between them and with the motherboard to accurately obtain the magnetic field direction. However, this method often increases the number and cost of components, system complexity, and assembly costs. Therefore, there is an urgent need to develop new vector magnetic field detection principles and advance corresponding sensing technology research to solve this problem and meet broader application needs.

[0003] Compared to other magnetic field sensing technologies, surface acoustic wave (SAW) technology boasts advantages such as high sensitivity, miniaturization, low cost, and strong anti-interference capabilities, offering a novel solution for highly sensitive magnetic field detection in complex environments. Consequently, it has attracted significant attention from scholars and research institutions both domestically and internationally. The basic principle of SAW magnetic field sensors involves depositing a magnetically sensitive thin film along the sound wave propagation path. When an external magnetic field acts on the film, a dynamic magnetoelastic coupling effect is generated, thereby altering the film's shear modulus G. This modulates the sound wave propagation characteristics, and by decoupling the acoustic signal, the value of the external magnetic field can be accurately obtained. Currently, research on SAW magnetic field sensing technology is still in the basic research stage, primarily focusing on unidirectional magnetic field strength measurement. Vector SAW magnetic field sensors with practical application capabilities have not yet emerged. Summary of the Invention

[0004] The purpose of this application is to overcome the limitation of existing technologies that can only measure magnetic field strength in a single direction. It provides a surface acoustic wave magnetic field sensor for detecting magnetic fields in a space plane. This sensor calibrates the detection of the magnitude and direction of the magnetic field by using different response values, achieving advantages such as high sensitivity, fast response, and high integration. By using host computer software for data collection and analysis, it can achieve the function of directional positioning of the magnetic field in the entire space plane.

[0005] To achieve the above objectives, this application proposes a vector magnetic field detection method based on a surface acoustic wave magnetic field directivity model, comprising:

[0006] Step 1: Horizontally mount one or more surface acoustic wave magnetic field sensors at a certain angle on a flat worktable;

[0007] Step 2: Apply the magnetic field to be measured. The response value of the surface acoustic wave magnetic field sensor changes. After the response value of the surface acoustic wave magnetic field sensor stabilizes, obtain the magnitude of the response value of the surface acoustic wave magnetic field sensor at different angles.

[0008] Step 3: Based on the surface acoustic wave magnetic field directivity model, obtain N magnetic fields along the sensor coordinate system, and then obtain the magnetic field in the geographic coordinate system using the coordinate system transformation formula.

[0009] Step 4: Using the vector summation rule, obtain the total magnetic field in the geographic coordinate system from the magnetic fields obtained in the multiple geographic coordinate systems.

[0010] Step 5: Obtain the magnetic field to be measured in the geographic coordinate system based on the geomagnetic field in the local geographic coordinate system.

[0011] As an improvement to the above method, the surface acoustic wave vector magnetic field detection sensor includes, from bottom to top, a piezoelectric crystal substrate, an input interdigital transducer, an output interdigital transducer, a temperature compensation layer, and a magnetostrictive thin film layer.

[0012] The piezoelectric crystal substrate is made of a piezoelectric substrate that can excite shear wave modes in surface acoustic waves;

[0013] The input interdigital transducer and the output interdigital transducer are located on both sides of the upper surface of the piezoelectric crystal substrate, and are at a set distance from the side surface of the piezoelectric crystal substrate;

[0014] The temperature compensation layer uses a material with a positive temperature coefficient and covers the top of the input interdigital transducer, the output interdigital transducer, and the piezoelectric crystal substrate.

[0015] The magnetostrictive thin film layer is an amorphous soft magnetic alloy with dynamic magnetoelastic coupling effect, covering the top layer of the sensor, and is placed in the central region between the input interdigital transducer and the output interdigital transducer.

[0016] As an improvement to the above method, the input interdigital transducer adopts a unidirectional single-phase transducer SPUDT structure with 72 pairs; the output interdigital transducer adopts a single-group IDT repeating arrangement structure with an acoustic aperture of 70λ and 40 pairs; the acoustic propagation path between the input interdigital transducer and the output interdigital transducer is set to 210λ; λ is the wavelength of surface acoustic wave.

[0017] As an improvement to the above method, the normalized thickness of the temperature compensation layer is defined as follows: Where h is the thickness of the temperature compensation layer and λ is the wavelength of the surface acoustic wave; the normalized thickness of the temperature compensation layer ranges from 0 to 0.16.

[0018] As an improvement to the above method, the thickness of the magnetostrictive thin film layer is greater than 5 times the wavelength of surface acoustic waves and less than 800 nm.

[0019] As an improvement to the above method, the magnetic field directivity model of the surface acoustic wave is expressed as follows:

[0020]

[0021]

[0022]

[0023] Where χ is the magnetic susceptibility; ω m ω is the magnetization angular frequency. m = 2πf, where f is the center frequency of the surface acoustic wave magnetic field sensor; H ext H represents the magnitude of the magnetic field along the hard axis of the sensor coordinate system. k denoted as uniaxial anisotropy coefficient; γ as gyromagnetic ratio; α as damping factor; d as magnetic film thickness. The free magnetization direction angle is the angle between the free magnetization intensity and the easy axis, which is the major axis of the sensor; i is the imaginary unit; ω is the angular frequency, ω = 2πf SAW f SAW R is the frequency of the surface acoustic wave; F I Φ R is the phase voltage conversion coefficient of the phase detector. The relationship between the phase and the actual test response value is 1° = 10mV. F I Φ =10mV / °; ΔR is the sensor response change value; k is the magnetic field directivity model constant; ΔG is the change in shear modulus; ρ is the density of the magnetic sensitive film; B2 is the dynamic magnetoelastic coupling coefficient of the system; μ0 is the vacuum permeability; m0 is the saturation magnetization.

[0024] As an improvement to the above method, the process of obtaining the magnetic field in the geographic coordinate system via the rotation coordinate system transformation formula includes:

[0025] H′ j =H j cos(θ′ j cos(θ) j )+H j sin(θ′ j sin(θ) j )

[0026] Among them, H′ j H represents the magnitude of the magnetic field in the coordinate system of the j-th sensor; j θ represents the magnitude of the magnetic field in the j-th geographic coordinate system. j Let θ′ be the counterclockwise rotation angle of the j-th sensor coordinate system along geographic north; j Let be the counterclockwise rotation angle of the j-th sensor coordinate system along the geographical east direction.

[0027] As an improvement to the above method, obtaining the magnetic field to be measured in the geographic coordinate system includes:

[0028]

[0029] in, The magnetic field to be measured is in a geographic coordinate system; The geomagnetic field in the local geographic coordinate system; This refers to the total magnetic field in the geographic coordinate system.

[0030] As an improvement to the above method, the method further includes:

[0031] Step 6: Repeat steps 3 to 5 multiple times to obtain the magnetic field to be measured in multiple geographic coordinate systems in order to eliminate the influence of piezoelectric or thermoelectric bias components on the geometric structure.

[0032] As an improvement to the above method, N is 2.

[0033] Compared with existing technologies, the advantages of this application are:

[0034] 1. The highly sensitive SAW vector magnetic field detection sensor of the present invention has the characteristics of high repeatability, high consistency, miniaturization, lightweight and mass production capability;

[0035] 2. The magnetic thin film used in the highly sensitive SAW vector magnetic field detection sensor of the present invention is an amorphous soft magnetic material, which is easy to magnetize and easy to demagnetize. The magnetic field sensor made of this thin film has the advantages of fast response, easy recovery and long life.

[0036] 3. The highly sensitive SAW vector magnetic field detection sensor of the present invention does not require heating treatment, thus having the characteristic of low power consumption;

[0037] 4. Traditional Hall effect sensors can only read magnetic field values ​​in a single direction. Generally, two orthogonal sensors are used to read H1 and H2 respectively for the synthesis and detection of the spatial magnetic field. However, the two sensors in this method have differences, and their response values ​​are not completely consistent. For accurate testing, both sensors need to be calibrated and adjusted separately. Furthermore, for ease of calculation during installation, they must be placed vertically, increasing installation costs, requiring higher installation accuracy, increasing the difficulty of multi-sensor calibration, and enhancing system complexity. The high-sensitivity SAW vector magnetic field detection sensor of this invention, Scheme 1, utilizes a single sensor rotating in space to detect the magnitude and direction of the magnetic field to be measured in real time at a fixed point. This method has fewer components, lower cost, simpler assembly, and lower system complexity. Scheme 2 allows the two sensors to be placed in a non-ideal orthogonal orientation, similarly avoiding the problems of increased installation costs, accuracy adjustments, and system complexity.

[0038] 5. The first method of highly sensitive SAW vector magnetic field sensing and detection proposed in this invention is based on a turntable with a precise rotation angle. The response of a single sensor can correspond to the model, and there will be no deviation in the response values ​​of different sensors. Moreover, the sensor has a fast response speed, and the host computer can record the magnetic field magnitude corresponding to the response value in each direction in real time, and calculate the magnitude and direction of the magnetic field to be measured in real time, which has timeliness.

[0039] 6. The second method for high-sensitivity SAW vector magnetic field sensing and detection proposed in this invention is based on dual sensors whose responses can correspond to the model after debugging. The dual sensors have a fast response speed, and the host computer can simultaneously record the magnetic field magnitude corresponding to the response values ​​in two directions. The magnitude and direction of the vector magnetic field in the space platform can be obtained through vector synthesis without the need for secondary rotation testing of the sensors on the turntable. Attached Figure Description

[0040] Figure 1 The diagram shows a schematic of a vector magnetic field detection scheme based on the magnetic field directivity model of surface acoustic waves.

[0041] Figure 2 The diagram shows a second vector magnetic field detection scheme based on the magnetic field directivity model of surface acoustic waves.

[0042] Figure 3 The diagram shown is a theoretical schematic of the magnetic field directivity model for surface acoustic waves.

[0043] Figure 4 The diagram shows a sensitivity test of a highly sensitive surface acoustic wave magnetic field sensor.

[0044] Figure 5The figure shows a simulation diagram of the magnetic field directivity model of surface acoustic waves;

[0045] Figure 6 The figure shown is a schematic diagram of a real test for vector magnetic field detection based on the magnetic field directivity model of surface acoustic waves;

[0046] Figure 7 The diagram shows a flowchart of a vector magnetic field detection method based on a surface acoustic wave magnetic field directivity model.

[0047] Attached image labels:

[0048] 1. Piezoelectric crystal substrate 2. Input interdigital transducer

[0049] 3. Output interdigital transducer 4. Temperature compensation layer

[0050] 5. Magnetostrictive thin film layer; 6. Fixed turntable

[0051] 7. Background geomagnetic field; 8. Magnetic field to be measured Detailed Implementation

[0052] The technical solution of this application will be described in detail below with reference to the accompanying drawings.

[0053] This invention proposes a vector magnetic field detection method based on a surface acoustic wave (SAW) magnetic field directivity model. This method utilizes the dynamic magnetoelastic coupling effect, combined with the easy magnetization and demagnetization characteristics of amorphous soft magnetic thin films, to achieve rapid response and highly sensitive detection of magnetic fields. Since the magnetization degree of the magnetically sensitive thin film corresponds to the magnitude and direction angle of the magnetic field being measured, it exhibits different response values ​​under planar magnetic fields in different directions. Furthermore, the response value fluctuation after repeated detection is less than 10mV. Therefore, a SAW magnetic field directivity model can be established based on this correspondence. This method can be used to locate the direction of spatial magnetic fields using the magnetic field sensor involved in this invention. This proposed method overcomes the limitation of traditional SAW magnetic field sensors, which can only detect a single magnetic field direction, and has significant practical value in the field of spatial magnetic field detection and location.

[0054] like Figure 3 As shown, the Directionality Theory Model (DTM) is based on the magnetostriction phenomenon of magnetically sensitive thin films. When a ferromagnetic material or magnetocrystalline material is magnetized in an external magnetic field, its size and volume change, leading to changes in the Young's modulus and shear modulus of the material, i.e., the ΔE / ΔG effect.

[0055] Magnetostriction arises from the magnetoelastic coupling energy within materials. The spin-orbit coupling of atoms or ions causes the magnetization vector Ms to change with the magnetic field, generating corresponding stress to minimize the total energy. Therefore, magnetostriction is a result of the balance between spin-orbit coupling energy and the elastic energy of the material, and a dynamic magnetoelastic coupling model can be established by analyzing the changes in magnetoelastic coupling energy.

[0056] The anisotropic axis (easy axis) of the magnetically sensitive thin film represents the initial direction of the free magnetization m. During magnetization, when the free magnetization forms different angles with the magnetic field to be measured, the magnetization will rotate to the direction of the magnetic field to be measured, resulting in an increase in the magnetization along the easy axis, thereby increasing the shear modulus of the material.

[0057] When a surface acoustic wave (SAW) propagates through a magnetically sensitive thin film with increased shear modulus, its sound velocity increases. The relationship between the shear modulus of the magnetically sensitive thin film and the sound velocity is as follows:

[0058]

[0059] Where G is the shear modulus of the material, and ρ is the density of the magnetostrictive film.

[0060] The phase change during SAW propagation is used as the sensing quantity. The phase change of the sensor is related to the change in sound speed by the following equation:

[0061]

[0062] in, Let v be the phase of the SAW signal, and v be the speed of sound in the SAW signal. The phase and speed of sound change of SAW are related to Δv.

[0063] The change in response value of the SAW magnetic field sensor caused by the dynamic magnetoelastic coupling effect of the magnetically sensitive thin film is represented as follows:

[0064]

[0065]

[0066] Among them, R F I Φ R is the phase voltage conversion coefficient of the phase detector. The relationship between the phase and the actual test response value is 1° = 10mV. F I Φ =10mV / °. Where ΔR is the sensor response change, k is the magnetic field directivity model constant, ΔG is the change in shear modulus, and B2 is the system's dynamic magnetoelastic coupling coefficient. Let be the free magnetization direction angle, i.e., the angle between the free magnetization intensity and the easy axis; the easy axis direction (i.e., the anisotropic axis direction) is the major axis of the sensor; μ0 is the free permeability; and m0 is the saturation magnetization intensity. A theoretical schematic diagram of the directional orientation of its surface acoustic wave magnetic field sensor is shown below. Figure 3 As shown.

[0067] Changes in magnetic permeability and the total magnetic field H along the x-axis (difficult axis) of the sensor coordinate system ext Size-related:

[0068]

[0069] In the formula, χ is the magnetic susceptibility, and ω m ω is the magnetization angular frequency. m = 2πf, where f is the center frequency of the SAW magnetic field sensor. H ext H represents the total magnetic field magnitude along the hard axis of the sensor coordinate system. k Let be the uniaxial anisotropy coefficient, γ be the gyromagnetic ratio, α be the damping factor, and d be the magnetic film thickness. A simulation diagram of the surface acoustic wave magnetic field directivity model is shown below. Figure 5 As shown.

[0070] The magnitude and direction of the magnetic field to be measured, corresponding to the magnetic field directivity model of the surface acoustic wave magnetic field sensor, depend on the magnitude component of the magnetic field along the x-axis (difficult axis) in the sensor coordinate system. This is calculated using the coordinate transformation formula for the spatial magnetic field and is determined by the following formula:

[0071]

[0072] In the formula, (x,y) and (x',y') are the coordinate representations in the geographic coordinate system and the sensor coordinate system, respectively, and θ is the counterclockwise rotation angle of the sensor coordinate system along the geographic north direction.

[0073] The relationship between the total magnetic field in the geographic coordinate system and the total magnetic field along the x-axis (difficult axis) in the sensor coordinate system can be obtained from the coordinate system transformation formula (6):

[0074] H ext =H·cos(θ′)·cosθ+H·sin(θ′)·sinθ (7)

[0075] In the formula, H is the total magnetic field in the geographic coordinate system. ext θ represents the total magnetic field along the x-axis (difficult axis) in the sensor coordinate system. θ is the counterclockwise rotation angle of the sensor coordinate system along geographic north, and θ' is the counterclockwise rotation angle from the geographic coordinate system along east-west.

[0076] The relationship between the geomagnetic field in the geographic coordinate system and the geomagnetic field along the x-axis (difficult axis) in the sensor coordinate system can be obtained from the coordinate transformation formula (6):

[0077] H′ d =H d ·cos(d)·cosθ+H d ·sin(d)·sinθ (8)

[0078] In the formula, H d H' represents the geomagnetic field in geographic coordinates. d θ represents the geomagnetic field along the x-axis (difficult axis) in the sensor coordinate system. θ is the counterclockwise rotation angle of the sensor coordinate system along geographic north, and d is the counterclockwise offset angle of the geomagnetic field in the geographic coordinate system, which is obtained from the local geomagnetic field deflection angle table.

[0079] H in the magnetic field directivity model considering the geomagnetic field ext The magnetic field H' of the measured magnetic field and the Earth's magnetic field in the sensor coordinate system (difficult axis) is... d The sum,

[0080] The vector summation rule governing the magnetic field directivity model of a surface acoustic wave (SAW) magnetic field sensor is determined by the following formula:

[0081]

[0082] Preferably, the SAW detection sensor has a relatively long acoustic propagation path (10 to 1000λ, where λ is the wavelength of the sound wave).

[0083] Preferably, the SAW detection sensor operates at a frequency of 10MHz to 2.4GHz.

[0084] Preferably, the piezoelectric substrate of the SAW detection sensor can be ST-cut 90°X quartz, 36°YX lithium tantalate, 42°YX lithium tantalate, 64°YX lithium niobate, or 41°YX lithium niobate.

[0085] Preferably, the magnetic field to be measured is a vector magnetic field, which can have arbitrary directionality in the XOY plane and has a magnitude ranging from 0 to 2,000,000 nT.

[0086] A method for constructing a magnetic field directivity model for a surface acoustic wave magnetic field sensor includes the following steps:

[0087] Step 1: Ignoring the geomagnetic field, the sensor response value ΔR is calculated from the dynamic magnetoelastic coupling model relation (5) to obtain the change of the magnitude component of the magnetic field on the x-axis (difficult axis) of the magnetic field under the sensor coordinate system. Thus, the magnitude H and direction angle θ of the magnetic field under the geographic coordinate system are obtained by using Equation (7) from the component of the magnetic field under the sensor coordinate system.

[0088] Step 2: Introduce the local geomagnetic field as the actual condition, check the local geomagnetic distribution, and use Equation (8) to calculate the components of the geomagnetic field on the x-axis (difficult axis) of the sensor coordinate system according to the rotation coordinate system transformation formula of the spatial magnetic field.

[0089] Step 3: Substitute it into the H of the dynamic magnetoelastic coupling model. ext H at this time ext This represents the sum of the magnitudes of the magnetic fields of the target magnetic field and the Earth's magnetic field along the sensor coordinate system (the hard axis). The corresponding simulation response value is then obtained, thus yielding a complete directional model.

[0090] The magnetic field directivity model of the surface acoustic wave magnetic field sensor involved in this invention has the following independent variables: the magnitude and direction of the geomagnetic field, the magnitude and direction of the magnetic field to be measured, the azimuth angle of the sensor's geographical location, and the anisotropic axis angle of the sensor in the geographic coordinate system. The model can obtain the correspondence between the magnitude and direction of the magnetic field to be measured and the sensor response value, and establish a complete magnetic field directivity model.

[0091] In the SAW vector magnetic field detection method, actual sensors exhibit slight differences in response values. To achieve more accurate testing, the simulation model needs to be fine-tuned using the test results of actual sensors. The actual sensor calibration method for the magnetic field directivity model includes the following steps:

[0092] Step 1: Install the surface acoustic wave magnetic field sensor on the fixed turntable 6 of the planar worktable, ensuring the sensor is ideally placed parallel to the turntable. The sensor's response value is transmitted to the host computer in real time via a signal line.

[0093] Step 2: Rotate the turntable one full turn (360 degrees). The baseline of the sensor's response value changes. When the baseline value is the smallest, it means that the easy axis of the sensor is in the same direction as the geomagnetic field in space. At this time, the azimuth angle of the sensor's turntable is parallel to the direction of the geomagnetic field in the XOY plane.

[0094] Step 3: Apply a constant magnetic field to be measured in all directions in space, and the host computer displays the changes in the sensor response values ​​under the action of the magnetic field in each direction.

[0095] Step 4: Substitute the results into the simulation model for comparison and verification, correct the gap between the simulation model and the actual response value of the sensor, and complete the calibration of the sensor.

[0096] The calibration process for the magnetic field directivity model and the actual SAW magnetic field sensor should be performed at the factory, involving minor adjustments to the magnetic field directivity model. This magnetic field directivity model is then stored in the host computer. The issue of storing the model in the host computer will be addressed later through algorithm design.

[0097] like Figure 1The diagram shows the structure of a surface acoustic wave (SAW) vector magnetic field detection sensor. The sensor includes, from bottom to top, a piezoelectric crystal substrate 1, an input interdigital transducer 2, an output interdigital transducer 3, a temperature compensation layer 4, and a magnetostrictive thin film layer 5. The vector magnetic field detection method also involves a SAW sensor, a spatial planar turntable 6, a background geomagnetic field 7, and the magnetic field to be measured 8.

[0098] An input interdigital transducer 2 and an output interdigital transducer 3 are formed by depositing a 200 nm thick layer of aluminum on the surface of an ST-90°X piezoelectric crystal substrate 1 with dimensions of 15 mm × 5 mm × 0.5 mm using electron beam evaporation. The distance between the input interdigital transducer 2, the output interdigital transducer 3 and the edge of the piezoelectric crystal substrate 1 along the longitudinal direction is 1 mm. The input interdigital transducer 2 adopts a unidirectional single-phase transducer (SPUDT) structure. The output interdigital transducer 3 adopts a single-group IDT repeating arrangement structure with an acoustic aperture of 70λ. The number of pairs of input interdigital transducers 2 and output interdigital transducers 3 is 72 and 40 respectively, with a wavelength λ = 24.752 μm. The acoustic propagation path between the input interdigital transducers 2 and the output interdigital transducers 3 is set to 210λ.

[0099] A temperature compensation layer 4 with a thickness of 0.5 μm is formed by depositing silicon dioxide material on the surface of a piezoelectric crystal substrate 1 on which an input interdigital transducer 2 and an output interdigital transducer 3 are electroplated.

[0100] A schematic diagram of the sensitivity test of a highly sensitive surface acoustic wave magnetic field sensor is shown below. Figure 4 As shown, the designed high-sensitivity SAW vector magnetic field sensor is fixed in a plane, and different magnitudes of the target magnetic field are applied along the sensor's fixed axis. The magnetic field test range is 0-20 Oe (0-2000000 nT). The response value of the SAW vector magnetic field sensor gradually increases with the increase of the magnetic field. It exhibits excellent linear response at one-tenth of the magnetic field range, with a linearity of up to 2% FS; the circuit response value changes by 1912.15 mV, and the phase change is approximately 190°. When the magnitude of the target magnetic field increases to 20 Oe, the SAW sensor response value tends to saturate, with a response value change of approximately 5421.5 mV and a phase change of approximately 540°. The phase sensitivity at the point of maximum slope is 160° / Oe. The SAW magnetic field sensor proposed in this invention exhibits characteristics such as high sensitivity and fast response.

[0101] A schematic diagram of the actual test of the vector magnetic field detection method based on the surface acoustic wave magnetic field directivity model provided by this invention is shown below. Figure 6 As shown in the figure, the polar radius *r* represents the magnitude of the magnetic field to be measured, the polar angle represents the rotation angle of the entire-plane magnetic field, and the contour line color distribution represents the actual response change value of the sensor. The actual sensor response value is subtracted from the initial baseline response value, and then compared with... Figure 6The magnitude of the magnetic field to be measured can be obtained by corresponding the values ​​in the actual test diagram.

[0102] The vector magnetic field detection method based on the surface acoustic wave (SAW) magnetic field directivity model provided by this invention can be divided into two schemes for testing vector magnetic fields in a spatial plane. Scheme 1 is a single-sensor rotation test method. A single sensor is rotated in any two directions for testing. First, the geomagnetic field information is input into the model, and the sensor is tested at an arbitrary angle θ1. After applying a magnetic field of unknown direction and magnitude, the change in the response value of the SAW magnetic field sensor is observed. When the sensor's response value stabilizes, the magnitude of the response value is recorded, and the value of the magnetic field to be measured, H1, along the sensor's non-axis direction is determined according to the magnetic field directivity model calibrated by the SAW magnetic field sensor. To evaluate the magnitude and direction of the magnetic field to be measured in the entire space, the sensor's turntable is rotated to another arbitrary direction θ2, the response value is obtained, and the magnitude of the magnetic field H2 along the sensor's non-axis direction is obtained through the model. Since the magnitudes of the magnetic fields in the two directions are known, the magnitude and direction of the magnetic field to be measured in the spatial plane are successfully determined by summing the two magnetic field vectors.

[0103] Scheme 2 adopts the dual-sensor differential synchronous testing method. Figure 2 This is a schematic diagram of Scheme Two for detecting the vector magnetic field of surface acoustic waves. Two sensors are placed parallel to the platform, forming a fixed angle σ, where σ = θ2 - θ1, corresponding to Scheme One. The geomagnetic field information is input into the model, and the magnetic field to be measured is applied. The response values ​​of both sensors change. After the response values ​​of the two sensors stabilize, the magnitudes of the response values ​​are read. The response values ​​obtained by the two sensors at this time correspond to the magnitudes H1 and H2 of the magnetic field. According to the vector summation rule, the magnitude and direction of the magnetic field to be measured can be finally determined.

[0104] Example 1

[0105] The vector magnetic field detection method based on the magnetic field directivity model of surface acoustic waves provided in this application is implemented based on the surface acoustic wave vector magnetic field sensor and the surface acoustic wave magnetic field directivity model.

[0106] The surface acoustic wave vector magnetic field detection sensor includes, from bottom to top, a piezoelectric crystal substrate 1, an input interdigital transducer 2, an output interdigital transducer 3, a temperature compensation layer 4, and a magnetostrictive thin film layer 5.

[0107] The piezoelectric crystal substrate 1 is a piezoelectric substrate that can excite the shear wave (SH wave) mode in surface acoustic waves, such as ST-cut 90°X quartz, 36°YX lithium tantalate, 42°YX lithium tantalate, 64°YX lithium niobate, or 41°YX lithium niobate.

[0108] The input interdigital transducer 2 and the output interdigital transducer 3 are formed by depositing a 200nm thick layer of aluminum on the surface of an ST-90°X piezoelectric crystal substrate 1 with dimensions of 15mm × 5mm × 0.5mm using electron beam evaporation. The distance between the input interdigital transducer 2, the output interdigital transducer 3 and the edge of the piezoelectric crystal substrate 1 along the longitudinal direction is 1mm. The input interdigital transducer 2 adopts a unidirectional single-phase transducer SPUDT structure; the output interdigital transducer 3 adopts a single-group IDT repeating arrangement structure with an acoustic aperture of 70λ. The number of pairs of input interdigital transducers 2 is 72, and the number of pairs of output interdigital transducers 3 is 40, with a wavelength λ = 24.752um. The acoustic propagation path between the input interdigital transducers 2 and the output interdigital transducers 3 is set to 210λ.

[0109] The temperature compensation layer 4 typically uses a material with a positive temperature coefficient, such as silicon dioxide. This entire layer covers the top of the input interdigital transducer 2, the output interdigital transducer 3, and the piezoelectric crystal substrate 1. The normalized thickness is defined as... Where h is the thickness of the temperature compensation layer, λ is the wavelength of the surface acoustic wave, and its normalized thickness range is generally 0-0.16.

[0110] The magnetostrictive thin film layer 5 is an amorphous soft magnetic alloy with dynamic magnetoelastic coupling effect. Its magnetostrictive properties cause the shear modulus of the substrate to change in the direction of external magnetic field. The material is FeCo, FeSiBC, FeCoSiB or FeNi, etc. It covers the top layer of the sensor and is placed in the central region between the input interdigital transducer 2 and the output interdigital transducer 3. Its film thickness is greater than 5 times the wavelength of surface acoustic waves. Due to the influence of the manufacturing process, the maximum thickness of the magnetic sensitive film is generally less than 800nm.

[0111] The anisotropic axis of the magnetostrictive thin film layer 5 is the easy axis direction, where the magnetosensitive film is easily magnetized, and its perpendicular direction is the difficult axis direction, where the magnetosensitive film is difficult to magnetize. The anisotropic axis is induced to the long axis direction of the film during fabrication. At this point, the angle between the anisotropic axis of the magnetosensitive film and the long axis direction of the film is 0°. The easy axis direction is the direction of surface acoustic wave propagation. The difficult axis direction is perpendicular to the direction of surface acoustic wave propagation.

[0112] The easy axis of the magnetostrictive thin film layer 5, which is the major axis of the sensor, is designated as the y-axis of the sensor coordinate system. The difficult axis of the magnetostrictive thin film layer 5, which is the minor axis of the sensor, is designated as the x-axis of the sensor coordinate system.

[0113] The surface acoustic wave vector magnetic field sensor operates at frequencies ranging from 10MHz to 2.4GHz, and the modulated surface acoustic wave propagation characteristics include frequency, wave velocity, phase, and amplitude.

[0114] The surface acoustic wave (SAW) magnetic field directivity model has independent variables including the sensor parameters of the SAW magnetic field sensor, the sensor's azimuth angle in space, the background geomagnetic field 7, and the magnitude and direction of the magnetic field to be measured 8. The dependent variable is the response value of the SAW magnetic field sensor. The magnitude and direction of the magnetic field to be measured can be obtained based on the relationship between the SAW magnetic field directivity model and the response value of the SAW magnetic field sensor.

[0115] The model expression is:

[0116]

[0117]

[0118]

[0119] Where χ is the magnetic susceptibility, ω m ω is the magnetization angular frequency. m = 2πf, where f is the center frequency of the surface acoustic wave magnetic field sensor; H ext H represents the magnitude of the magnetic field along the hard axis of the sensor coordinate system. k denoted as uniaxial anisotropy coefficient, γ as gyromagnetic ratio, α as damping factor, and d as magnetic film thickness. i is the imaginary unit; ω is the angular frequency, ω = 2πf. SAW f SAW R is the frequency of the surface acoustic wave. F I φ R is the phase voltage conversion coefficient of the phase detector. The relationship between the phase and the actual test response value is 1° = 10mV. F I Φ =10mV / °. ΔR is the sensor response change, k is the magnetic field directivity model constant, ΔG is the change in shear modulus, ρ is the magnetic thin film density, and B2 is the system dynamic magnetoelastic coupling coefficient. denoted as the free magnetization direction angle, i.e., the angle between the free magnetization intensity and the easy axis, the direction of the easy axis (i.e., the direction of the anisotropy axis), which is the major axis of the sensor, μ0 is the vacuum permeability, and m0 is the saturation magnetization intensity.

[0120] like Figure 7 As shown, the vector magnetic field detection method based on the surface acoustic wave magnetic field directivity model includes:

[0121] Step 1: Install one or more surface acoustic wave magnetic field sensors at a certain angle on a fixed turntable 6 of a planar worktable, with the sensors placed horizontally on the turntable.

[0122] The fixed turntable 6 can be placed at any position in space parallel to the XOY plane.

[0123] Step 2: Apply the magnetic field to be measured. The sensor response value changes. After the sensor response value stabilizes, obtain the magnitude of the sensor response value at different angles.

[0124] Step 3: Based on the magnetic field directivity model of surface acoustic waves, obtain N magnetic fields along the sensor coordinate system (hard axis), and then obtain the magnetic field in the geographic coordinate system through the coordinate system transformation formula.

[0125] The relationship between the magnetic field in the geographic coordinate system and the sensor coordinate system is expressed as follows:

[0126] H′ j =H j cos(θ′ j cos(θ) j )+H j sin(θ′ j sin(θ) j )

[0127] Among them, H′ j The magnitude of the magnetic field in the coordinate system of the j-th sensor; H j θ represents the magnitude of the magnetic field in the j-th geographic coordinate system. j Let θ′ be the counterclockwise rotation angle of the j-th sensor coordinate system along geographic north; j Let be the counterclockwise rotation angle of the j-th sensor coordinate system along the geographical east direction.

[0128] Step 4: For the magnetic fields obtained in multiple geographic coordinate systems, the direction of their rotation angles follows the vector summation rule. Finally, the total magnetic field in the geographic coordinate system is determined by the vector summation rule.

[0129] The rule for vector summation is:

[0130]

[0131] in, Let be the magnetic field in the j-th geographic coordinate system.

[0132] Step 5: Obtain the geomagnetic field in the local geographic coordinate system. The magnetic field to be measured in the geographic coordinate system was calculated.

[0133]

[0134] Step 6: Using the principle of coordinate system rotation transformation, repeatedly adjust the position and orientation of the surface acoustic wave magnetic field sensor, and execute steps 1 to 5 in order to eliminate the influence of piezoelectric or thermoelectric bias components on the geometric structure.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application do not depart from the spirit and scope of the technical solutions of this application, and should all be covered within the scope of the claims of this application.

Claims

1. A method for detecting a vector magnetic field based on a surface acoustic wave magnetic field directivity model, comprising: Step 1: horizontally installing one or N surface acoustic wave magnetic field sensors at an angle on a flat workbench; Step 2: applying a magnetic field to be detected, the response value of the surface acoustic wave magnetic field sensor changes, and after the response value of the surface acoustic wave magnetic field sensor stabilizes, the size of the response value of the surface acoustic wave magnetic field sensor at different angles is obtained; Step 3: obtaining N magnetic fields along the sensor coordinate system according to the surface acoustic wave magnetic field directivity model, and then obtaining the magnetic field in the geographic coordinate system through the rotation coordinate system transformation formula; Step 4: obtaining the total magnetic field in the geographic coordinate system by using the vector summation rule on the obtained magnetic fields in the geographic coordinate system; Step 5: obtaining the magnetic field to be detected in the geographic coordinate system according to the local geomagnetic field in the geographic coordinate system.

2. The method of claim 1, wherein the method is based on a surface acoustic wave magnetic field directivity model. The surface acoustic wave vector magnetic field detection sensor comprises, from bottom to top, a piezoelectric crystal substrate, an input interdigital transducer, an output interdigital transducer, a temperature compensation layer, and a magnetostrictive film layer; The piezoelectric crystal substrate is made of a piezoelectric substrate that can excite shear wave modes in surface acoustic waves; The input interdigital transducer and the output interdigital transducer are located on both sides of the upper surface of the piezoelectric crystal substrate, and have a set distance from the side surface of the piezoelectric crystal substrate; The temperature compensation layer uses a material with a positive temperature coefficient and covers the top of the input interdigital transducer, the output interdigital transducer, and the piezoelectric crystal substrate as a whole; The magnetostrictive film layer is an amorphous soft magnetic alloy with dynamic magneto-elastic coupling effect, covering the top layer of the sensor, and the placement area is the central area between the input interdigital transducer and the output interdigital transducer.

3. The method of claim 2, wherein the method is based on a surface acoustic wave magnetic field directivity model. The input interdigital transducer adopts a one-way single-phase transducer (SPUDT) structure, and the number of pairs is 72; the output interdigital transducer adopts a single IDT repeating arrangement structure, and the acoustic aperture is 70λ, and the number of pairs is 40; the acoustic propagation path between the input interdigital transducer and the output interdigital transducer is set to 210λ; λ is the wavelength of surface acoustic waves.

4. The method of claim 2, wherein the method is based on a surface acoustic wave magnetic field directivity model. The definition of the normalized thickness of the temperature compensation layer is where h is the temperature compensation layer thickness, and λ is the surface acoustic wave wavelength; the normalized thickness of the temperature compensation layer ranges from 0 to 0.

16.

5. The method of claim 2, wherein the method is based on a surface acoustic wave magnetic field directivity model. The thickness of the magnetostrictive film layer is greater than 5 times the wavelength of surface acoustic waves and less than 800 nm. 6.The method of claim 1, wherein, The surface acoustic wave magnetic field directivity model has the expression: where χ is the magnetic susceptibility; ω m is the magnetic angular frequency, ω m = 2πf, f is the center frequency of the surface acoustic wave magnetic field sensor; H ext is the magnetic field size in the hard axis direction of the sensor coordinate system; H k is the uniaxial anisotropy coefficient; γ is the gyromagnetic ratio; α is the damping factor; d is the magnetic film thickness; is the free magnetization direction angle, that is, the angle between the free magnetization and the easy axis, and the easy axis direction is the long axis of the sensor; i is the imaginary unit; ω is the angular frequency, ω = 2πf SAW , f SAW is the surface acoustic wave frequency; R F I Φ is the phase voltage conversion coefficient of the phase detector, and the relationship between the phase and the actual test response value is 1° = 10 mV, R F I Φ = 10 mV / °; ΔR is the response change value of the sensor; k is the magnetic field directivity model constant; ΔG is the change in the shear modulus; ρ is the density of the magnetic sensitive film; B2 is the system dynamic magnetic coupling coefficient; μ0 is the vacuum permeability; and m0 is the saturation magnetization.

7. The method of claim 1, wherein the method is based on a surface acoustic wave magnetic field directivity model. The magnetic field in the geographic coordinate system obtained through the rotation coordinate system transformation formula comprises: H j ' = H j cos(θ j ') cos(θ j ) + H j sin(θ j ') sin(θ j ) where H j is the magnitude of the magnetic field in the jth sensor coordinate system; H j is the magnitude of the magnetic field in the jth geographic coordinate system; θ j is the rotation angle of the jth sensor coordinate system counterclockwise along the geographic north direction; θ' j is the rotation angle of the jth sensor coordinate system counterclockwise along the geographic east direction.

8. The method of claim 1, wherein the method is based on a surface acoustic wave magnetic field directivity model. The magnetic field to be detected in the geographic coordinate system comprises: wherein, is the magnetic field to be measured in a geographic coordinate system; is the geomagnetic field in the local geographic coordinate system; is the total magnetic field in the geographic coordinate system. 9.The method of claim 1, wherein, The method further comprises: Step 6: repeatedly performing steps 3 to 5 multiple times to obtain multiple magnetic fields to be detected in the geographic coordinate system, so as to eliminate the bias component influence of the geometric structure of piezoelectricity or thermoelectricity.

10. The method of claim 1, wherein the method is based on a surface acoustic wave magnetic field directivity model. N is 2.

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