Weak magnetic field measuring device and method based on Einstein-DeHaas effect

Abstract

The invention discloses a weak magnetic field measuring device and method based on the Einstein-Dehauss effect, and relates to weak magnetic field measurement. A Helmholtz coil, an optical platform, a single-pole double-throw switch, an optical supporting rod, a clamping device, a connecting rod right-angle clamp, a wire, a programmable direct-current power supply and a signal generator are used for building a magnetic field generating device and a demagnetizing device; arranging the needle gauge holder with the silicon wafer according to a certain orientation and position by using the optical fiber clamp and the quartz fiber; a permalloy bar is arranged at the other end of the needle gauge chuck to construct a mechanical rotating part responding to the magnetic field; a light path system is constructed by using a red light laser and two reflectors; a displacement sensor, a data acquisition card and a computer are used for processing light spot speed data, and the magnetic field size is obtained through calculation. The real-time and accurate measurement of a weak magnetic field is realized by utilizing the change of external macroscopic angular momentum caused by the change of internal atomic spin angular momentum of a permalloy rod under the action of a magnetic field and combining the accurate measurement of an optical path amplification system and a displacement sensor.

Description

Technical Field

[0001] The present invention relates to the field of weak magnetic field measurement, and in particular to a weak magnetic field measurement device and method based on the Einstein-de Haas effect. Background Art

[0002] The precise measurement of weak magnetic fields (B≤50Gs) has important applications in many fields, such as submarine detection in military technology, non-destructive testing in industry, geomagnetic measurement in geophysical exploration, magnetic nanoparticle detection in biomedicine, and magnetic field detection in space science. Existing measurement technologies, such as atomic magnetometers, superconducting quantum interference devices (SQUIDs), fluxgate sensors, and Hall sensors, although they have high sensitivity and accuracy, are usually complex in structure, expensive, and difficult to operate.

[0003] The Einstein-de Haas effect reveals the relationship between the atomic spin inside a substance and the external macroscopic angular momentum, providing a new idea for measuring weak magnetic fields. However, how to effectively use this effect to build an efficient and economical measurement device is still a hot topic in current research. Summary of the invention

[0004] The purpose of the present invention is to provide a low-cost, high-precision, easy-to-operate, and weak magnetic field measurement device and method based on the Einstein-de Haas effect that can accurately measure weak magnetic fields, in view of the problems of existing technologies such as atomic magnetometers and superconducting quantum interference devices (SQUIDs), which are extremely expensive despite their high precision, and usually have complex structures, high operating requirements, lengthy experimental processes, and are susceptible to environmental interference, making them difficult to promote and use in ordinary laboratories or scientific research and teaching. The present invention significantly reduces the cost of equipment by using a simple optical path system, a Permalloy rod, and a Helmholtz coil. The invention has a simple structure, the device is easy to assemble, and the operation is relatively simple, which is convenient for scientific researchers or students to conduct experiments and data analysis, and can achieve real-time and accurate measurement of weak magnetic fields.

[0005] In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0006] The present invention provides a weak magnetic field measuring device based on the Einstein-de Haas effect, comprising a magnetic field generation and rotation system, an optical path amplification system, and an information acquisition system;

[0007] The magnetic field generation and rotation system is used to generate a magnetic field of known size and calibrate the relationship between the magnetic field and the rotation speed of the Permalloy rod. After the calibration, the rotation system can be placed in an unknown magnetic field to measure the unknown magnetic field size; the magnetic field generation and rotation system is provided with a Helmholtz coil, two single-pole double-throw switches, a plurality of optical support rods, an optical fiber clamp, a needle gauge chuck, a plurality of U-shaped tiger clamps, a Permalloy rod, a cross fixing clamp, a programmable DC power supply and a signal generator; the Helmholtz coil is used to generate a controllable magnetic field, and the Helmholtz coil is fixed on four long vertical optical support rods by a plurality of short optical support rods, a cross fixing clamp and a U-shaped tiger clamp, and is connected to the middle terminal of two single-pole double-throw switches through a wire; the single-pole double-throw switch Used to switch the DC power supply or AC power supply in the circuit, and control the output of the magnetic field generating system or signal generator; the programmable DC power supply and the signal generator are respectively connected to the single-pole double-throw switch through wires to provide a stable DC current or alternating current for the Helmholtz coil; the optical fiber clamp is fixed on the optical support rod to clamp the quartz fiber; the needle gauge clamp is placed between the quartz fiber and the Permalloy rod to connect the quartz fiber and the Permalloy rod; the Permalloy rod is set at the center of the magnetic field, and the Permalloy rod rotates under the action of the magnetic field generated by the Helmholtz coil; the programmable DC power supply is used to generate and adjust the required DC current, which is used to control and adjust the size of the output stable magnetic field. The signal generator is used to generate and adjust the required AC power supply, and the voltage knob is adjusted to generate a gradually decreasing alternating magnetic field to demagnetize the Permalloy rod for the next measurement;

[0008] The optical path amplification system is used to amplify the tiny rotation of the Permalloy rod under the action of the magnetic field, so as to accurately measure its displacement change through the displacement sensor, and then convert it into the measurement value of the magnetic field intensity through calculation; the optical path amplification system is provided with a focusable laser, a silicon chip, and two parallel and slightly staggered plane reflectors in sequence along the optical path; the silicon chip is glued to the surface of the pin gauge fixture to reflect the incident light point of the focusable laser, wherein the pin gauge fixture is located between the quartz fiber and the Permalloy rod to connect the quartz fiber and the Permalloy rod; the focusable laser is used to generate a laser beam, and the focusable laser and the plane reflector are both fixed on the optical support rod through relevant clamps and adjusted to a suitable position so that the laser irradiates the silicon chip and is guided by the plane reflector arranged in parallel and slightly staggered in the optical path, so as to amplify the tiny rotation of the Permalloy rod for accurate measurement or operation; the plane reflector amplifies the rotation displacement and transmits it to the displacement sensor; the focusable laser is connected to a DC regulated power supply through a power line, and the DC regulated power supply supplies power for the focusable laser;

[0009] The information acquisition system is used to receive, collect, transmit and process data; the information acquisition system includes a displacement sensor, a data acquisition card and a computer; the displacement transducer is arranged at the end of the optical path amplification system, and is used to receive the reflected light of the plane reflector and measure the change of the light spot position; the displacement sensor is connected to the data acquisition card through a data line, and then connected to the computer through the data acquisition card to realize real-time data collection and transmission; the data acquisition card is used to obtain the displacement sensor signal in real time and process and display it by computer software; the computer is configured with Python and Matlab software, runs Python software for collecting and real-time display of displacement data, and runs Matlab program for analyzing the displacement and time information collected by Python software to fit the speed size and thus realize the calibration of the relationship between magnetic field and speed; the programmable DC power supply and signal generator provide stable DC current or alternating current for the Helmholtz coil, and are respectively connected to the single-pole double-throw switch through wires.

[0010] Furthermore, the two poles of the programmable DC power supply are respectively connected to the left terminals of two single-pole double-throw switches, the two poles of the signal generator are connected to the right terminals of the two single-pole double-throw switches, and the two connection ports of the Helmholtz coil are respectively connected to the middle terminals of the single-pole double-throw switches through wires. By switching the positions of the two single-pole double-throw switches, a DC current can be selectively provided to the Helmholtz coil to generate a stable magnetic field, or an alternating current can be provided to generate an alternating magnetic field for demagnetization operation, thereby realizing the switching of magnetic field generation and demagnetization functions.

[0011] Furthermore, the Helmholtz coil is fixed on the optical support rod, and the Helmholtz coil can be firmly fixed on the optical support rod by using a cross fixing clamp and a short support rod through a U-shaped tiger clamp.

[0012] Furthermore, the needle gauge holder with the silicon wafer is placed in a magnetic field generating device in a certain direction and position using an optical fiber clamp and a quartz fiber filament; a Permalloy rod is then placed at the other end of the needle gauge chuck to construct a mechanical rotating part that responds to the magnetic field; a red light laser and two reflectors are then used to construct an optical path system; a displacement sensor, a data acquisition card and a computer are used to process the light spot speed data, and the magnetic field size is obtained through further calculation.

[0013] Furthermore, the displacement sensor adopts a high-precision one-dimensional displacement sensor, including a signal processing module, a photosensitive strip length of 12mm, and an accuracy of 1μm. The high-precision one-dimensional displacement sensor can accurately measure the change of the light spot position and convert it into an electrical signal output.

[0014] Furthermore, a connecting rod right-angle clamp is included, which is used to achieve a right-angle turn or height adjustment at a position where a right-angle connection or height adjustment is required.

[0015] Furthermore, the data acquisition card can provide power for the displacement sensor.

[0016] Furthermore, the diameter of the quartz fiber wire may be 125 μm, and is used to connect the pin gauge chuck and the Permalloy rod to ensure the stability and accuracy of the rotation.

[0017] During the experiment, when the magnetic field generation function is required, the two single-pole double-throw switches are switched to the left terminal. At this time, the Helmholtz coil is powered by a programmable DC power supply to generate a stable magnetic field, which serves as a magnetic field generating device. On the contrary, when the demagnetization function is required, the two single-pole double-throw switches are switched to the right terminal. At this time, the Helmholtz coil is powered by a signal generator to generate an alternating magnetic field. By rotating the voltage adjustment knob to gradually reduce the output voltage, the demagnetization operation of samples such as Permalloy rods can be achieved. Such a layout and connection relationship ensures the flexible switching of the device functions and the convenience of experimental operation.

[0018] The present invention provides a method for measuring a weak magnetic field based on the Einstein-de Haas effect, comprising the following steps:

[0019] 1) Equipment initialization and calibration: Build the weak magnetic field measurement device based on the Einstein-de Haas effect and ensure that all equipment has been correctly installed and calibrated to the best state;

[0020] 2) Setting the magnetic field size of the Helmholtz coil: Calculate and set the current required to generate the corresponding magnetic field according to the required magnetic field strength and coil parameters;

[0021] 3) Adjust the optical path and displacement sensor: put the system in the initial test state, ensure that the optical path is clear and the displacement sensor can accurately record the change of the light spot position;

[0022] 4) Start the programmable DC power supply: throw the single-pole double-throw switch to one side of the programmable DC power supply, start the programmable DC power supply, and allow the power supply to pass the DC current required to generate the magnetic field to generate a stable magnetic field;

[0023] 5) Data acquisition: Turn on the computer and use the data acquisition program written in Python to record the light spot displacement data at a predetermined sampling rate and time length to start data acquisition;

[0024] 6) Data analysis: The measured light spot displacement data is imported into the Matlab program to calculate its maximum speed according to the set relevant code analysis, the magnetic field strength is calculated using the Einstein-de Haas effect model, and the speed is converted into magnetic field strength according to the preset calibration curve;

[0025] 7) Demagnetization: Switch the single-pole double-throw switch to the signal generator side, start the signal generator to make the Helmholtz coil generate an alternating magnetic field, and adjust the relevant knob to generate a gradually decreasing current to demagnetize the magnetized Permalloy rod;

[0026] 8) Data processing and verification: Process the collected data, verify the accuracy and reliability of the results, and compare them with the results of preset standards or other measurement methods.

[0027] Compared with the prior art, the present invention has the following outstanding technical effects and advantages:

[0028] The present invention generates a magnetic field through a Helmholtz coil, a Permalloy rod senses magnetic field changes, an optical path amplification system and a high-precision displacement sensor measure light spot displacement changes, and a data acquisition card and computer software process and analyze data in real time, thereby achieving high-precision measurement of weak magnetic fields (1 to 20 Gs) (resolution reaches 0.01 Gs). The weak magnetic field measurement device based on the Einstein-de Haas effect of the present invention is simple in design, low in manufacturing cost, and suitable for weak magnetic field measurement in scientific research and teaching. The present invention is particularly suitable for intuitively demonstrating the response of atomic spin angular momentum to external weak magnetic fields (1 to 20 Gs), and can intuitively observe that the rotation of the Permalloy plate reflects the change of microscopic angular momentum on the macroscopic object. It is also suitable for scientific research and industrial fields to achieve the measurement of weak magnetic fields at a relatively low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the structure of a weak magnetic field generating device and a demagnetizing device in an embodiment of the present invention.

[0030] Figure 2 This is a simplified diagram of the circuit principle of the weak magnetic field generating device and the demagnetizing device.

[0031] Figure 3 It is the mechanical rotating part that responds to the magnetic field.

[0032] Figure 4 Schematic diagram of the optical path amplification system structure.

[0033] Figure 5 This is a diagram showing the relationship between each system and the optical path.

[0034] Figure 6 This is the data transmission and data processing flow chart of the information acquisition system.

[0035] Figure 7 It is a schematic diagram of the overall structure of the weak magnetic field measuring device of the present invention.

[0036] Figure 8 This is the operating logic diagram of this device.

[0037] Fig. 9 This is the program logic diagram of the Python program.

[0038] Fig.10 This is the displacement-time relationship of the PSD reading when the magnetic induction intensity is 6.89 Gs.

[0039] Fig.11 Fit the curve to the selected interval.

[0040] Fig.12 is the light spot speed-time relationship.

[0041] Fig.13 This is the calibration curve of light spot speed and magnetic induction intensity.

[0042] Figures 1 to 7 The marks are:

[0043] 1. Magnetic field generation and rotation system; 2. Optical path amplification system; 3. Information acquisition system;

[0044] 11. Helmholtz coil; 12. Single-pole double-throw switch; 13. Optical support rod; 14. Fiber optic clamp; 15. Pin gauge chuck; 16. U-shaped tiger clamp; 17. Permalloy rod; 18. Programmable DC power supply; 19. Signal generator; 110. Quartz fiber; 111. Wire; 112. Cross fixing clamp;

[0045] 21. Adjustable focus laser; 22. Silicon wafer; 23. Plane reflector; 24. DC regulated power supply;

[0046] 31. Displacement sensor; 32. Data acquisition card; 33. Computer. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the following embodiments will further illustrate the present invention in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. On the contrary, the present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention as defined by the claims.

[0048] The embodiment of the present invention provides a weak magnetic field measurement device based on the Einstein-de Haas effect, including the following specific accessories and design methods:

[0049] Focusable laser, high-precision one-dimensional displacement sensor (including signal processing module, photosensitive strip length 12mm, accuracy 1μm), DC regulated power supply (to power the focusable laser), computer (including Python software), data acquisition card (to power the PSD), optical breadboard, several optical supports, cross fixing clamps, silicon wafer, quartz fiber (diameter 125μm), single-pole double-throw switch, support, Permalloy rod, optical fiber clamp, U-shaped tiger clamp, programmable DC power supply, signal generator, plane reflector.

[0050] Among them, the Helmholtz coil magnetic field generating system is used to generate a controllable magnetic field; the Permalloy rod produces rotational changes under the action of the magnetic field, the adjustable focus laser and the optical path amplification system are used to amplify the rotational displacement and transmit it to the high-precision one-dimensional displacement sensor; the data acquisition card obtains the sensor signal in real time and is processed and displayed by computer software; the signal generator is used to generate a gradually decreasing alternating magnetic field to demagnetize the Permalloy rod to facilitate the next measurement.

[0051] The embodiment of the present invention provides a method for measuring a weak magnetic field based on the Einstein-de Haas effect, comprising the following steps:

[0052] 1) Equipment initialization and calibration: Build the weak magnetic field measurement device based on the Einstein-de Haas effect and ensure that all equipment has been correctly installed and calibrated to the best state;

[0053] 2) Setting the Helmholtz coil: Calculate and set the current required to generate the corresponding magnetic field according to the required magnetic field strength and coil parameters;

[0054] 3) Adjust the optical path and displacement sensor: put the system in the initial test state, ensure that the optical path is clear and the displacement sensor can accurately record the change of the light spot position;

[0055] 4) Start the programmable DC power supply: throw the single-pole double-throw switch to one side of the programmable DC power supply, start the programmable DC power supply, and allow the power supply to pass the DC current required to generate the magnetic field to generate a stable magnetic field;

[0056] 5) Data acquisition: Turn on the computer and use the data acquisition program written in Python to record the light spot displacement data at a predetermined sampling rate and time length to start data acquisition;

[0057] 6) Data analysis: measure the light spot displacement and calculate its maximum speed, calculate the magnetic field strength using the Einstein-de Haas effect model, and convert the speed into magnetic field strength according to the preset calibration curve;

[0058] 7) Demagnetization: Switch the single-pole double-throw switch to the programmable signal generator side, start the programmable signal generator to make the Helmholtz coil generate an alternating magnetic field, and demagnetize the magnetized Permalloy rod;

[0059] 8) Data processing and verification: Process the collected data, verify the accuracy and reliability of the results, and compare them with the results of preset standards or other measurement methods.

[0060] The Helmholtz coil 11, optical platform, single-pole double-throw switch 12, optical support rod 13, optical fiber clamp 14, needle gauge chuck 15, U-shaped tiger clamp 16, Permalloy rod 17, programmable DC power supply 18, signal generator 19, quartz fiber 110, wire 111, and cross fixing clamp 112 are assembled into a magnetic field generating device and a demagnetizing device (when the single-pole double-throw switch is thrown on the side of the programmable DC power supply to receive a constant DC power input, the coil outputs a steady magnetic field, which is a simple magnetic field generating device; when the single-pole double-throw switch is thrown on the side of the signal generator to receive a gradually decreasing alternating current input, the coil outputs a gradually decreasing alternating magnetic field, which is a simple demagnetizing device). The specific construction method is: select a suitable spacing to support the four optical support rods 13 on the optical platform, use the cross fixing clamp 112 and the short support rod to fix the U-shaped tiger clamp 16 on the four optical support rods 13, and use the U-shaped tiger clamp 16 to fix the Helmholtz coil 11. Use wire 111 to connect the connection of Helmholtz coil 11 to the middle terminal of two single-pole double-throw switches 12, connect the two poles of programmable DC power supply 18 to the left terminals of two single-pole double-throw switches 12, and connect the two poles of signal generator 19 to the right terminals of two single-pole double-throw switches 12. When the magnetic field generation function needs to be realized, the two single-pole double-throw switches 12 are placed on the left terminals. At this time, the Helmholtz coil 11 is powered by the programmable DC power supply 18, and a stable magnetic field is generated to act as a magnetic field generating device. When the demagnetization function needs to be realized, the two single-pole double-throw switches 12 are placed on the right terminals. At this time, the Helmholtz coil 11 is powered by the signal generator 19, and an alternating magnetic field is generated. By rotating the voltage adjustment knob to gradually reduce the output voltage, it can act as a demagnetization device for the Permalloy rod 17, such as Figure 1 shown.

[0061] The circuit schematic diagram after simplifying the circuit is as follows Figure 2 , through the programmable power supply or signal generator, the current is input and passed into the Helmholtz coil to generate the corresponding stable magnetic field or alternating magnetic field.

[0062] The optical fiber fixture 14, the quartz fiber 110 and the needle gauge fixture 15 with a silicon wafer are placed in a magnetic field generating device in a certain direction and position; the Permalloy rod 17 is then placed at the other end of the needle gauge fixture 15 to construct a mechanical rotating part that responds to the magnetic field, which is an important part of weak magnetic field measurement, such as Figure 3 shown.

[0063] Two parallel and slightly offset plane reflectors 23 reflect the light multiple times to increase the optical path and amplify the originally small displacement, thus forming an optical path amplification system. The adjustable focus laser 21 is connected to a DC stabilized power supply 24 through a power line, and the DC stabilized power supply supplies power for the adjustable focus laser; Figure 4 As shown. Working principle of the optical path amplification system: The adjustable focus laser generates a laser beam, which is precisely adjusted and irradiated onto the silicon wafer. The silicon wafer is glued to the surface of the pin gauge fixture, which is connected between the quartz fiber and the Permalloy rod. The silicon wafer reflects the laser beam to form a light spot. This light spot is then guided by two parallel and slightly offset plane mirrors to form an amplified optical path. The setting of these two mirrors enables the slight rotation of the Permalloy rod to be converted into a significant displacement of the light spot over a longer distance. Due to the offset setting of the mirrors, when the Permalloy rod rotates under the action of the magnetic field, the position of the light spot reflected by the silicon wafer will also change accordingly. This change is further amplified by the plane mirror to form a displacement that is easier to measure. The amplified light spot displacement is received by the displacement sensor, which can accurately measure the change in the light spot position and convert it into an electrical signal output. The electrical signal output by the displacement sensor is transmitted to the computer through the data acquisition card and processed by Python and Matlab software on the computer. These software can display displacement data in real time, calibrate the relationship between magnetic field and speed by fitting the speed-time curve, and finally calculate the magnetic field strength. The optical path amplification system plays a vital role in this device. It converts the tiny rotation of the Permalloy rod into an easily measurable light spot displacement, greatly improving the accuracy and sensitivity of magnetic field measurement.

[0064] The optical path amplification system is constructed by using a focusable laser 21, a silicon wafer 22 glued to a needle gauge fixture, and two parallel and slightly offset plane mirrors 23. The specific construction method is: adjust the height of the focusable laser 21 to be consistent with the height of the silicon wafer 22, and make the laser incident on the silicon wafer 22 at an appropriate slight angle, place two plane mirrors 23 at appropriate positions of the reflected light path, and place the two plane mirrors 23 in parallel and slightly offset so that the laser light spot can smoothly reach the displacement sensor 31. At this time, adjust the focal length of the focusable laser 21 to focus it on the displacement sensor 31. This shows how the magnetic field generation and rotation system, the optical path amplification system, and the information acquisition system are related by the laser beam, such as Figure 5 shown.

[0065] The displacement sensor 31, data acquisition card 32 and computer 33 are placed in appropriate positions, wherein the computer software can be written based on Python and Matlab languages, and can realize automatic data collection and processing. The displacement sensor 31 and data acquisition card 32 used and the schematic diagram of data collection and processing are as follows: Figure 6As shown. The working principle of the information acquisition system: The displacement sensor receives the light spot position change information transmitted by the optical path amplification system. These change information is formed after being amplified by the optical path amplification system due to the tiny rotation of the Permalloy rod under the action of the magnetic field. The data acquisition card is responsible for real-time acquisition of the electrical signals output by the displacement sensor. These electrical signals represent the precise changes in the position of the light spot. The data acquisition card transmits the collected data to the computer through the data line. Ensure the fast and accurate transmission of data, and provide the possibility for real-time processing and display. The software configured on the computer (including Python and Matlab) processes and analyzes the received data. Python software is used to collect and display displacement data in real time, while Matlab program is used to analyze the displacement and time information collected by Python software, and obtain the speed by fitting, so as to realize the calibration of the relationship between magnetic field and speed. Finally, the magnetic field strength can be calculated and displayed on the computer screen. The data obtained by the information acquisition system, combined with the known relationship between magnetic field and speed (i.e. calibration result), can calculate the size of the unknown magnetic field.

[0066] The overall schematic diagram of the weak magnetic field measuring device of the present invention is as follows: Figure 7 shown.

[0067] After setting the DC current, the Helmholtz coil generates a constant magnetic field. The Permalloy rod is magnetized by the magnetic field and starts to rotate. The silicon wafer rigidly glued to it also starts to rotate. The laser beam of the adjustable focus laser hits the silicon wafer, causing the reflected light spot to move. An optical path amplification system is added to the optical path where the reflected light is located. The multi-stage amplification of the optical path is used to amplify the original weak movement of the light spot, so that the displacement sensor can collect the accurate xt relationship between the light spot displacement and time. The Python program reads and saves all the data of the displacement sensor, and then inputs the stored data into the Matlab program to calculate the light spot speed v, which is then brought into the calibration curve to obtain the magnetic induction intensity B. The operation logic diagram of the device is shown in the figure below. Figure 8 As shown, it can be specifically as follows: First, the Python program implements a program main window, and a control panel is designed through the window to set relevant parameters before the experiment (set sampling time, speed and frequency; set the current size of the programmable DC power supply; set the save path of the final data). After setting up the control panel, start the sampling program. At this time, the control thread of the programmable DC power supply and the acquisition thread of the data acquisition card will be started at the same time. The program will automatically read the previously set DC power supply size and start the programmable DC power supply. At the same time, the data acquisition card also starts sampling and processes and displays the displacement and time data according to the filtering conditions set at the beginning, and finally saves the displacement and time data. (Import the saved data into Matlab, select a suitable data interval, take multiple points, and use v=Δx / Δt to take the average, and you can get the speed of the light spot). The running logic diagram of the program is as follows Fig. 9 shown.

[0068] The structural design, data collection and processing methods of the device of the present invention are as follows:

[0069] 1. Device structure design

[0070] The weak magnetic field measuring device of the present invention comprises the following main parts:

[0071] The focusable laser 21 is used to emit a red laser beam, which is reflected in the optical path system to form a light spot.

[0072] Optical path magnification system 2: It is composed of two parallel and slightly offset plane mirrors 23, and is used to amplify the displacement of the light spot.

[0073] High-precision one-dimensional displacement sensor (PSD) 31: used to detect the displacement change of the light spot in real time.

[0074] Helmholtz coil 11 magnetic field generating system: includes a pair of coaxial coils, which generates a uniform and controllable magnetic field by precisely controlling the current of the coils.

[0075] The Permalloy rod 17 and its support system are placed in an induced magnetic field and rotate.

[0076] Data acquisition card 32 and computer control software: used to collect sensor signals and process and display them by computer software.

[0077] The device emits a light beam through a focusable laser 21, and after passing through an optical path amplification system 2, the light spot is projected onto a high-precision one-dimensional displacement sensor 31. The magnetic field generation system of the Helmholtz coil 11 forms a uniform magnetic field around the device, and the Permalloy rod 17 rotates slightly under the action of the magnetic field, so that the displacement of the light spot changes. The data acquisition card 32 obtains the output signal of the displacement sensor in real time and transmits it to the computer software for data processing and analysis.

[0078] Some of the equipment / components in the device can be the following commercially available products, and the manufacturer model is for reference only:

[0079] The displacement sensor 31 needs to be able to realize real-time measurement of the light spot position, and can use the DRX-1DPSD-OAO2-X high-precision one-dimensional PSD position sensor signal processing board, produced by Shenzhen Daruixin Optoelectronics Technology Co., Ltd.;

[0080] The programmable DC power supply 16 needs to be able to achieve a DC current output controlled by a computer, and an ODP3032 linear programmable DC power supply may be used.

[0081] The DC regulated power supply 24 needs to be able to stably output a voltage of 3V to power the laser, and a GW Instek GPS-3030DD dual-display DC digital regulated power supply can be used.

[0082] The adjustable focus laser 21 is recommended to be a laser that can achieve the function of focusing within the range of 75 to 100 cm. The high-quality glass lens 5mW 650nm red laser module point-shaped aiming laser produced by Zhongshan Yunxiang Optoelectronics Technology Co., Ltd. can be selected.

[0083] The optical fiber clamp 14 can be a HC-HF bare optical fiber clamp, produced by Oeabt Guangzhou Pedestal Optical Technology Co., Ltd., which can support and fix quartz fiber filaments.

[0084] The data acquisition card 32 needs to be able to power the displacement sensor and collect and store the output signal of the data sensor. It can adopt NI myDAQ data acquisition card, which is produced by National Instruments.

[0085] The U-shaped vise 16 is used to be fixed on the optical support rod to clamp the Helmholtz coil 11, and can be a related product produced by Tiancheng Stainless Steel Products Co., Ltd.

[0086] 2. Experimental process and steps

[0087] 2.1 Optical system calibration

[0088] First, turn on the DC stabilized power supply 24 of the adjustable focus laser 21, adjust the output voltage to 3V, and ensure that the laser works normally. The laser beam is reflected by the reflector and the magnifying lens, and its angle is adjusted to ensure that the laser beam is perpendicular to the magnifying lens. The light spot finally falls on the center of the PSD displacement sensor, and the stability and clarity of the light spot are confirmed to ensure the measurement accuracy.

[0089] 2.2 Setup of the Helmholtz coil system

[0090] A Helmholtz coil magnetic field generation system is used to control the current of the Helmholtz coil 11 through a programmable DC power supply 18 to generate a uniform magnetic field. In the experiment, the coil current is set by the programmable DC power supply 18, ranging from 0.1A to 1.6A, to measure the change in the light spot displacement under different magnetic field strengths.

[0091] 2.3 Data acquisition and processing software settings

[0092] A self-written Python program is run on the computer 33, the data acquisition card 32 and the power control system are connected, the sampling time is set to 6 seconds, the sampling frequency is set to 25000 Hz, and the data storage path is set to a pre-set location; after the program is started, the displacement data of the light spot on the PSD displacement sensor is collected in real time.

[0093] 2.4 Experimental procedures

[0094] After setting the magnetic field, open the computer software and start collecting data.

[0095] The displacement of the light spot on the displacement sensor 31 is measured under different current conditions, and the initial velocity is recorded.

[0096] According to the displacement change of the light spot, the maximum speed of the light spot is calculated.

[0097] According to the calibration curve, the measured light spot speed is converted into magnetic field intensity.

[0098] 2.5 Demagnetization and re-measurement

[0099] After each measurement, the signal generator 19 is started, the output frequency is set to 10 Hz, the output voltage is set to 10.96 V, and the voltage is gradually adjusted to 0 V to demagnetize the Permalloy rod 17. After the demagnetization is completed, the above experimental steps are repeated to obtain multiple sets of data.

[0100] 3. Data processing and error analysis

[0101] 3.1 Data processing

[0102] Use Python program and Matlab software for data processing: (Python program is mainly used to control the data acquisition card to collect data and set various data of the programmable DC power supply, and Matlab program is used to analyze and process the collected data to obtain the speed).

[0103] Data acquisition: Record the output voltage signal of the displacement sensor in real time and calculate the horizontal displacement of the light spot.

[0104] Data fitting: Select the displacement data within the time interval and use polynomial fitting to reduce noise interference during data acquisition.

[0105] Speed ​​calculation: Based on the fitting curve, the light spot speed is calculated by the difference method. The specific method is: select the time interval Δt = 0.02s, calculate the speed difference between consecutive moments, and take the maximum value as the maximum speed of the light spot.

[0106] Calibration curve construction: Based on multiple sets of experimental data, a calibration curve between the light spot speed and the magnetic field strength was constructed. The fitting results show that there is a linear relationship between the speed and the magnetic field strength, and the formula is: B = 1.068 × v (R2 = 0.998), where B is the magnetic field strength and v is the light spot speed.

[0107] Take a set of data as an example to illustrate the process of obtaining the light spot speed from the light spot displacement.

[0108] When the output current of the programmable DC power supply is set to 0.600A, that is, the output weak magnetic field is 6.89Gs, some of the time-displacement data obtained are shown in Table 1:

[0109] Table 1 Part of the data read by PSD when the magnetic induction intensity is 6.89Gs

[0110] Time t(s) <![CDATA[U C (V)]]> <![CDATA[U H (V)]]> Displacement x(cm) 0.50000 0.392799395 -0.219674414 -3.355520657 1.00000 0.394983160 -0.223511070 -3.395249614 1.50000 0.395181522 -0.220936435 -3.354454937 2.00000 0.404951484 -2.825687303 0.190711044 2.50000 0.407181190 -0.039007898 -0.574799115 3.00000 0.399434968 -0.176278298 -2.647914864 3.50000 0.395984591 -0.153918529 -2.332189667 4.00000 0.394694733 -0.054861290 -0.833980580 4.50000 0.396343334 -0.185378591 -2.806333423 5.00000 0.383111771 -0.108693098 -1.702267162

[0111] When the magnetic induction intensity is 6.89Gs, the displacement-time relationship read by PSD is as follows: Fig.10 .

[0112] Through MATLAB, we take the time point interval (46000, 62000) for polynomial fitting to make the curve smoother and reduce the slight deviation of the output light spot displacement data caused by the unstable PSD voltage of the displacement sensor. In addition, we still use the difference method in MATLAB to obtain the light spot speed at each moment and obtain the maximum speed. The specific method is as follows:

[0113] Read the moment t1 when vibration starts and the moment t2 when the maximum amplitude is reached for the first time. 1， The time interval of the difference method is selected as Δt = 0.0200s, and the light spot speed at time t3 is considered to be Calculate the interval (t1+Δt ， t2), the speed-time relationship is obtained as follows Fig.11 and 12 shown.

[0114] The maximum speed in the interval is read as v=6.2388 cm / s.

[0115] The DC programmable power supply current ranges from 0.1A to 1.6A, and the light spot speed-magnetic induction intensity calibration results are shown in Table 2.

[0116] Table 2 Calibration results of light spot speed and magnetic induction intensity

[0117] serial number Current (A) Magnetic induction intensity (Gs) Speed ​​(cm / s) 1 0.1 1.15 0.9865 2 0.2 2.30 1.9703 3 0.3 3.45 2.8345 4 0.4 4.60 4.1297 5 0.5 5.74 5.1916 6 0.6 6.89 6.2388 7 0.7 8.04 7.1193 8 0.8 9.19 8.4938 9 0.9 10.34 9.2687 10 1.0 11.49 10.7316 11 1.1 12.64 11.9252 12 1.2 13.79 12.5207 13 1.3 14.93 13.342 14 1.4 16.08 15.5202 15 1.5 17.23 16.5935 16 1.6 18.38 17.9072

[0118] According to Table 2, we can get the calibration curve of light spot speed-magnetic induction intensity, such as Fig.13 As shown. Fig.13 It can be seen that the NaCl solution-calibration curve changes linearly, and the fitting relationship is:

[0119] B=1.068ν

[0120] (R 2 =0.998)

[0121] The linear correlation coefficient reached above 0.998, and the linear relationship was good, indicating that the concentration and refractive index of the glucose solution conformed to a linear relationship.

[0122] 3.2 Error analysis

[0123] based on Fig.13 The calibration curve of light spot speed and magnetic induction intensity is used to compare the measured value with the actual value. The specific data is shown in Table 3.

[0124] Table 3 Comparison of measured and fitted values

[0125] serial number Measurement value (Gs) Actual value (Gs) <![CDATA[Relative error E B > 1 1.149 1.054 8.4％ 2 2.298 2.104 8.5％ 3 4.596 4.410 4.1％ 4 6.893 6.663 3.4％ 5 9.191 9.071 1.4％ 6 11.49 11.46 0.3％

[0126] From Table 3, we can see the measured values, actual values ​​and relative errors (EB%) between different numbers. From the relative error (EB%), the accuracy of the present invention is relatively high, especially the relative error between the measured value and the actual value of number 6 is only 0.3%, indicating that the accuracy of the measurement method of the present invention is at a high level. And it shows a certain stability as the measured value increases.

[0127] The main sources of experimental error include:

[0128] Optical path system calibration error: It is difficult to ensure complete parallelism during the manual adjustment of the reflector and magnifying lens.

[0129] Mechanical disturbance and airflow influence: Disturbance in the external environment can cause the Permalloy rod to shake slightly, affecting the measurement results.

[0130] Non-uniform light intensity distribution: The Gaussian light intensity distribution of the laser beam causes the instability of the sensor output voltage, affecting the accuracy of the data.

[0131] The uncertainty range of the calculated magnetic field strength is 0.48Gs to 0.62Gs through the error transfer formula. The method of multiple experimental measurements and data averaging can effectively reduce experimental errors and improve measurement accuracy and reliability.

[0132] The present invention uses a Helmholtz coil, an optical platform, two single-pole double-throw switches, several optical support rods, several clamps, several connecting rod right-angle clamps, several wires, a programmable DC power supply and a signal generator to build a magnetic field generating device and a demagnetizing device; uses an optical fiber clamp and a quartz fiber to place a needle gauge holder with a silicon chip in a certain direction and position in the magnetic field generating device; then places a Permalloy rod at the other end of the needle gauge clamp to construct a mechanical rotating part that responds to the magnetic field; uses a red laser and two reflectors to construct an optical path system; finally uses a displacement sensor, a data acquisition card and a computer to process the light spot speed data, and obtains the magnetic field size through further calculation. The principle is to use the change of external macroscopic angular momentum caused by the change of internal atomic spin angular momentum of the Permalloy rod under the action of the magnetic field, combined with the accurate measurement of the optical path amplification system and the displacement sensor, to achieve real-time and accurate measurement of weak magnetic fields (1 to 20Gs) (resolution of 0.01Gs). The device has a simple structure, low cost, a wide measurement range and an intuitive demonstration effect. It is suitable for the detection and analysis of weak magnetic fields in teaching, scientific research and industrial fields.

[0133] The above embodiments are only preferred embodiments of the present invention and cannot be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A weak magnetic field measurement device based on the Einstein-de Haas effect, characterized in that Including magnetic field generation and rotation system, optical path amplification system, information collection system; The magnetic field generation and rotation system is used to generate a magnetic field of known size and calibrate the relationship between the magnetic field and the rotation speed of the Permalloy rod. After the calibration, the rotation system can be placed in an unknown magnetic field to measure the unknown magnetic field size. The magnetic field generation and rotation system is provided with a Helmholtz coil, two single-pole double-throw switches, a plurality of optical support rods, an optical fiber clamp, a needle gauge chuck, a plurality of U-shaped tiger clamps, a Permalloy rod, a cross fixing clamp, a programmable DC power supply and a signal generator. The Helmholtz coil is used to generate a controllable magnetic field. The Helmholtz coil is fixedly arranged by a plurality of long vertical optical support rods and connected to the middle terminals of the two single-pole double-throw switches by wires. The programmable DC power supply and the signal generator are connected by wires respectively. connected to a single-pole double-throw switch to provide a stable direct current or alternating current for the Helmholtz coil; the optical fiber clamp is fixed on the optical support rod to clamp the quartz fiber; the needle gauge clamp is arranged between the quartz fiber and the Permalloy rod to connect the quartz fiber and the Permalloy rod; the Permalloy rod is arranged at the center of the magnetic field, and the Permalloy rod rotates under the action of the magnetic field generated by the Helmholtz coil; the programmable DC power supply is used to generate and adjust the required DC current, which is used to control and adjust the size of the output stable magnetic field; the signal generator is used to generate and adjust the required AC power supply, and the voltage knob is adjusted to generate a gradually decreasing alternating magnetic field to demagnetize the Permalloy rod for the next measurement; The optical path amplification system is used to amplify the tiny rotation of the Permalloy rod under the action of the magnetic field so as to accurately measure its displacement change through the displacement sensor; the optical path amplification system is provided with a focusable laser, a silicon chip, and two parallel and slightly offset plane reflectors in sequence along the optical path; the silicon chip is glued to the surface of the pin gauge fixture to reflect the incident light spot of the focusable laser, wherein the pin gauge fixture is located between the quartz fiber and the Permalloy rod to connect the quartz fiber and the Permalloy rod; the focusable laser is used to generate a laser beam, and the focusable laser and the plane reflector are both fixed on the optical support rod through relevant clamps and adjusted to appropriate positions so that the laser irradiates the silicon chip and is guided by the plane reflectors arranged in parallel and slightly offset in the optical path to amplify the tiny rotation of the Permalloy rod for accurate measurement or operation; the plane reflector amplifies the rotation displacement and transmits it to the displacement sensor; the focusable laser is connected to a DC regulated power supply through a power line, and the DC regulated power supply supplies power for the focusable laser; The information acquisition system is used to receive, collect, transmit and process data; the information acquisition system includes a displacement sensor, a data acquisition card and a computer; the displacement transducer is arranged at the end of the optical path amplification system, and is used to receive the reflected light of the plane reflector and measure the change of the light spot position; the displacement sensor is connected to the data acquisition card through a data line, and then connected to the computer through the data acquisition card to realize real-time data collection and transmission; the data acquisition card is used to obtain the displacement sensor signal in real time and process and display it by computer software; the computer is used to fit the collected displacement and time information to obtain the speed size and then realize the calibration of the relationship between the magnetic field and the speed.

2. A weak magnetic field measuring device based on the Einstein-de Haas effect as claimed in claim 1, characterized in that The two poles of the programmable DC power supply are respectively connected to the left terminals of two single-pole double-throw switches, the two poles of the signal generator are connected to the right terminals of the two single-pole double-throw switches, and the two connection ports of the Helmholtz coil are respectively connected to the middle terminals of the single-pole double-throw switches through wires, and the Helmholtz coil is selectively provided with a DC current to generate a stable magnetic field, or an alternating current to generate an alternating magnetic field for demagnetization operation, so as to realize the switching of the magnetic field generation and demagnetization functions.

3. A weak magnetic field measuring device based on the Einstein-de Haas effect as claimed in claim 1, characterized in that The Helmholtz coil is fixed on the optical support rod, and the Helmholtz coil is firmly fixed on the optical support rod by using a cross fixing clamp and a short support rod through a U-shaped tiger clamp.

4. A weak magnetic field measuring device based on the Einstein-de Haas effect as claimed in claim 1, characterized in that Using an optical fiber fixture and a quartz fiber wire, a needle gauge holder with a silicon wafer is placed in a magnetic field generating device in a certain direction and position; Then, a Permalloy rod is placed at the other end of the pin gauge chuck to construct a mechanical rotating part that responds to the magnetic field; Then, a red light laser and two reflectors are used to construct an optical path system. A displacement sensor, a data acquisition card and a computer are used to process the light spot speed data, and the magnetic field size is obtained through further calculation.

5. A weak magnetic field measuring device based on the Einstein-de Haas effect as claimed in claim 1, characterized in that The displacement sensor adopts a high-precision one-dimensional displacement sensor, including a signal processing module, a photosensitive strip length of 12mm, and an accuracy of 1μm.

6. A weak magnetic field measuring device based on the Einstein-de Haas effect as claimed in claim 1, characterized in that It also includes a post right-angle clamp for achieving right-angle turns or height adjustments where a right-angle connection or height adjustment is required.

7. A weak magnetic field measuring device based on the Einstein-de Haas effect as claimed in claim 1, characterized in that The data acquisition card supplies power to the displacement sensor.

8. A weak magnetic field measuring device based on the Einstein-de Haas effect as claimed in claim 1, characterized in that The quartz fiber wire has a diameter of 125 μm and is used to connect the pin gauge chuck and the Permalloy rod to ensure the stability and accuracy of the rotation.

9. A weak magnetic field measuring device based on the Einstein-de Haas effect as claimed in claim 1, characterized in that The computer is configured with Python and Matlab software, the Python software is used to collect and display displacement data in real time, and the Matlab program is used to analyze the displacement and time information collected by the Python software to fit the velocity size and thus realize the calibration of the relationship between the magnetic field and the velocity.

10. A method for measuring weak magnetic fields based on the Einstein-de Haas effect, characterized in that The following steps are involved: 1) Equipment initialization and calibration: Build a weak magnetic field measurement device based on the Einstein-de Haas effect as described in any one of claims 1 to 9, and ensure that all equipment has been correctly installed and calibrated to the best state; 2) Setting the magnetic field size of the Helmholtz coil: Calculate and set the current required to generate the corresponding magnetic field according to the required magnetic field strength and coil parameters; 3) Adjust the optical path and displacement sensor: put the system in the initial test state, ensure that the optical path is clear and the displacement sensor can accurately record the change of the light spot position; 4) Start the programmable DC power supply: throw the single-pole double-throw switch to one side of the programmable DC power supply, start the programmable DC power supply, and allow the power supply to pass the DC current required to generate the magnetic field to generate a stable magnetic field; 5) Data acquisition: Turn on the computer and use the data acquisition program written in Python to record the light spot displacement data at a predetermined sampling rate and time length to start data acquisition; 6) Data analysis: The measured light spot displacement data is imported into the Matlab program to calculate its maximum speed according to the set relevant code analysis, the magnetic field strength is calculated using the Einstein-de Haas effect model, and the speed is converted into magnetic field strength according to the preset calibration curve; 7) Demagnetization: Switch the single-pole double-throw switch to the signal generator side, start the signal generator to make the Helmholtz coil generate an alternating magnetic field, and adjust the relevant knob to generate a gradually decreasing current to demagnetize the magnetized Permalloy rod; 8) Data processing and verification: Process the collected data, verify the accuracy and reliability of the results, and compare them with the results of preset standards or other measurement methods.

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