Weak magnetic field synchronous measurement device and weak magnetic field synchronous measurement system

Abstract

The invention discloses a weak magnetic field synchronous measurement device and a weak magnetic field synchronous measurement system, and the device comprises a signal generator which is used for outputting a first AC constant current power supply and a second AC constant current power supply; the reference magnetic field generation device is electrically connected with the signal generator, and the reference magnetic field generation device is used for being connected with a direct-current constant-current power supply and a first alternating-current constant-current power supply to generate a reference magnetic field; the magnetic field detection device is electrically connected with the signal generator, and the magnetic field detection device is used for being driven by a second alternating-current constant-current power supply, detecting a reference magnetic field and outputting a reference magnetic field detection signal; and the signal demodulating device is electrically connected with the magnetic field detection device, the signal demodulating device is used for demodulating the reference magnetic field detection signal to obtain a reference signal and outputting the amplitude and phase of the reference signal on a first reference frequency and a second reference frequency, and the second reference frequency is twice of the first reference frequency. According to the invention, a complex magnetic field formed by superposing a steady magnetic field and an alternating magnetic field can be measured.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of magnetic field measurement, and particularly relates to a weak magnetic field synchronous measurement device and a weak magnetic field synchronous measurement system. BACKGROUND

[0002] Precise measurement of weak magnetic field plays an important role in many fields such as geoscience, material science and life science. These weak magnetic fields (with intensity ranging from millitesla (mT) to nanotesla (nT)) often appear as steady magnetic field, alternating magnetic field with different frequencies, or superimposed form of the two. For example, the steady magnetic field generated by industrial power system, the geomagnetic field and the biomagnetic field in living organisms all belong to this category.

[0003] The common magnetic field measurement methods at present include fluxgate method, Hall effect method, superconducting effect method and magnetoresistance effect method, etc. Among them, the sensor based on giant magnetoresistance effect (GMR) is particularly suitable for the measurement of weak magnetic field due to its high sensitivity and strong anti-interference ability. However, the magnetic field measurement module of the prior art is limited to the measurement of single steady magnetic field. When facing a complex magnetic field environment superimposed by steady magnetic field and alternating magnetic field, the traditional method is difficult to realize the synchronous, real-time and accurate distinction and measurement of the two magnetic field components. SUMMARY

[0004] In view of the above deficiencies of the prior art, the purpose of the present application is to provide a weak magnetic field synchronous measurement device and a weak magnetic field synchronous measurement system to measure the complex magnetic field superimposed by steady magnetic field and alternating magnetic field.

[0005] The technical solution of the present application is as follows: A weak magnetic field synchronous measurement device, comprising: a signal generator for outputting a first alternating constant current power supply and a second alternating constant current power supply; a reference magnetic field generating device electrically connected with the signal generator, the reference magnetic field generating device being used for connecting a direct current constant current power supply, the reference magnetic field generating device being used for receiving the first alternating constant current power supply and the direct current constant current power supply to generate a reference magnetic field; a magnetic field detecting device electrically connected with the signal generator, the magnetic field detecting device being used for being driven by the second alternating constant current power supply, detecting the reference magnetic field and outputting a reference magnetic field detection signal; a signal demodulating device electrically connected with the magnetic field detecting device, the signal demodulating device being used for demodulating the reference magnetic field detection signal to obtain a reference signal, and outputting the amplitude and phase of the reference signal at a first reference frequency and a second reference frequency, the second reference frequency being twice the first reference frequency.

[0006] Optionally, the signal generator includes: A constant current source output circuit is used to output a first AC constant current power supply and a second AC constant current power supply. The first AC constant current power supply and the second AC constant current power supply have the same frequency, but different phases. A synchronization signal output circuit is electrically connected to the signal demodulation device, and the synchronization signal output circuit is used to output a synchronization signal to the signal demodulation device.

[0007] Optionally, the constant current source output circuit includes a first resistor, a second resistor, a third resistor, a first operational amplifier, and a first NMOS transistor. The first end of the first resistor is connected to the positive input terminal of the first operational amplifier, the second end of the first resistor is grounded, the negative input terminal of the first operational amplifier is connected to the first end of the second resistor, the second end of the second resistor and the first end of the third resistor are interconnected with the source of the first NMOS transistor, the second end of the third resistor is used to connect to the negative power supply, the output terminal of the first operational amplifier is connected to the gate of the first NMOS transistor, and the drain of the first NMOS transistor is the output terminal of the constant current source output circuit.

[0008] Optionally, the magnetic field generating device includes: The first coil is used to connect to the DC constant current power supply and generate the first magnetic field; The second coil is used to connect to the second AC constant current power supply and generate a second magnetic field; the first magnetic field and the second magnetic field are superimposed to generate the reference magnetic field.

[0009] Optionally, the magnetic field detection device includes either a bridge-type giant magnetoresistive sensor or a tunnel magnetoresistive sensor.

[0010] Optionally, the bridge-type giant magnetoresistive sensor includes a fourth resistor, a fifth resistor, a sixth resistor, and a seventh resistor; the first end of the fourth resistor and the second end of the seventh resistor are connected and serve as the first input terminal of the bridge-type giant magnetoresistive sensor; the second end of the fourth resistor and the first end of the fifth resistor are connected and serve as the first output terminal of the bridge-type giant magnetoresistive sensor; the second end of the fifth resistor and the first end of the sixth resistor are connected and serve as the second input terminal of the bridge-type giant magnetoresistive sensor; the second end of the sixth resistor and the first end of the seventh resistor are connected and serve as the second output terminal of the bridge-type giant magnetoresistive sensor.

[0011] Optionally, the signal demodulation device includes either a digital lock-in amplifier or a dynamic signal analyzer.

[0012] Optionally, it also includes: A differential amplifier circuit, an input end of the differential amplifier circuit is connected with an output end of the magnetic field detection device, an output end of the differential amplifier circuit is connected with an input end of the signal demodulation device, and the differential amplifier circuit is used for amplifying and outputting the magnetic field detection signal output by the magnetic field detection device to the signal demodulation device.

[0013] Optionally, the differential amplifier circuit comprises an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor and a second operational amplifier, a first end of the eighth resistor is the first input end of the differential amplifier circuit, a second end of the eighth resistor, a first end of the ninth resistor and a negative input end of the second operational amplifier are interconnected, a second end of the ninth resistor and an output end of the second operational amplifier are connected, a first end of the tenth resistor is the second input end of the differential amplifier circuit, a second end of the tenth resistor, a first end of the eleventh resistor and a positive input end of the second operational amplifier are interconnected, and a second end of the eleventh resistor is grounded.

[0014] The present application also provides a weak magnetic field synchronous measurement system, comprising a computing device and the weak magnetic field synchronous measurement device as described above, and the computing device is used for receiving the reference signal output by the weak magnetic field synchronous measurement device.

[0015] The technical scheme of the present application comprises a signal generator, a reference magnetic field generation device, a magnetic field detection device and a signal demodulation device to form a weak magnetic field synchronous measurement device, wherein the signal generator is used for outputting a first alternating constant current power supply and a second alternating constant current power supply; the reference magnetic field generation device is electrically connected with the signal generator, the reference magnetic field generation device is used for connecting a direct current constant current power supply, and the reference magnetic field generation device is used for receiving the first alternating constant current power supply and the direct current constant current power supply to generate a reference magnetic field; the magnetic field detection device is electrically connected with the signal generator, the magnetic field detection device is used for being driven by the second alternating constant current power supply, detecting the reference magnetic field and outputting a reference magnetic field detection signal; and the signal demodulation device is electrically connected with the magnetic field detection device, the signal demodulation device is used for demodulating the reference magnetic field detection signal to obtain a reference signal, and outputting the amplitude and phase of the reference signal at a first reference frequency and a second reference frequency, and the second reference frequency is twice the first reference frequency. Thus, the weak magnetic field synchronous measurement device of the present application can demodulate the reference magnetic field by the signal demodulation device, obtain the amplitude and phase of the reference magnetic field at the first reference frequency and the second reference frequency, and take the amplitude and phase of the reference magnetic field at the first reference frequency and the second reference frequency as the standard, so that the synchronous, real-time and accurate distinction and measurement of two magnetic field components in other complex magnetic fields can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only show some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from the structures shown in the drawings without creative labor.

[0017] Figure 1 is a functional module schematic diagram of an embodiment of the weak magnetic field synchronous measurement device of the present application.

[0018] Figure 2 is a circuit structure schematic diagram of an embodiment of the constant current source output circuit in the weak magnetic field synchronous measurement device of the present application.

[0019] Figure 3 is a circuit structure schematic diagram of an embodiment of the bridge-type giant magnetoresistance sensor in the weak magnetic field synchronous measurement device of the present application.

[0020] Figure 4 is a circuit structure schematic diagram of an embodiment of the differential amplifier circuit in the weak magnetic field synchronous measurement device of the present application.

[0021] Figure 5 is a graph of the relationship between the base frequency signal and the magnetic field strength and a graph of the relationship between the frequency multiplication signal and the direct current in the weak magnetic field synchronous measurement device of the present application.

[0022] The reference signs are explained as follows: 10, signal generator; 20, reference magnetic field generating device; 30, magnetic field detecting device; 40, signal demodulating device; 50, differential amplifier circuit; R1, first resistor; R2, second resistor; R3, third resistor; R4, fourth resistor; R5, fifth resistor; R6, sixth resistor; R7, seventh resistor; R8, eighth resistor; R9, ninth resistor; R10, tenth resistor; R11, eleventh resistor; Q1, first NMOS tube; U1, first operational amplifier; U2, second operational amplifier. DETAILED DESCRIPTION

[0023] In order to make the objects, technical solutions and effects of the present application more clear and explicit, the following will further describe the present application with reference to the drawings and examples. It should be understood that the specific embodiments described here are only used to explain the present application, and are not used to limit the present application.

[0024] In the embodiments and the claims, unless otherwise limited, the articles "a," "an," and "the" are intended to include one or more than one, and the singular term "the" is also intended to include the plural form as well, unless the context clearly indicates otherwise. The terms "comprising," "having," "including," and the like, when used in the specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It is also to be understood that the term "connected" or "coupled to" as used herein refers to any connection or coupling, either direct or indirect, between otherwise-individually referenced elements, and can encompass the presence of one or more intermediate elements or intervening components.

[0025] It should further be understood that the word "comprise", "comprising", "comprises" and the like in the specification, are used herein to specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements can be present. In addition, the word "connected" or "coupled" as used herein can include wirelessly connected or wirelessly coupled. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0026] Those skilled in the art will understand that the terms used herein, including technical terms and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present application pertains, unless otherwise defined. It should also be understood that terms such as those defined in a generally used dictionary have meanings consistent with those in the context of the related art, and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0027] In addition, the technical solutions of various embodiments can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it, and when the combination of technical solutions contradicts each other or cannot be realized, it should be considered that the combination of technical solutions does not exist and is not within the protection scope required by the present application.

[0028] Precise measurement of weak magnetic fields plays an important role in many fields such as geosciences, material science, and life science. These weak magnetic fields (with strength ranging from millitesla (mT) to nanotesla (nT)) often appear as steady magnetic fields, alternating magnetic fields with different frequencies, or superimposed forms of the two. For example, the steady magnetic field generated by industrial power systems, the geomagnetic field, and the biomagnetic field in living organisms all belong to this category.

[0029] The common magnetic field measurement methods include flux-gate method, Hall effect method, superconducting effect method and magnetoresistance effect method. Among them, the sensor based on giant magnetoresistance (GMR) is particularly suitable for the measurement of weak magnetic field due to its high sensitivity and strong anti-interference ability. However, the magnetic field measurement module in the prior art is limited to the measurement of a single steady magnetic field. When facing a complex magnetic field environment formed by superimposing a steady magnetic field and an alternating magnetic field, the traditional method is difficult to realize the synchronous, real-time and accurate distinction and measurement of the two magnetic field components.

[0030] To solve the above problems, the present application provides a weak magnetic field synchronous measurement device.

[0031] Reference Figure 1 In an embodiment, the weak magnetic field synchronous measurement device comprises: A signal generator 10 for outputting a first alternating constant current power supply and a second alternating constant current power supply; A reference magnetic field generating device 20 electrically connected with the signal generator 10, the reference magnetic field generating device 20 is used for connecting a direct current constant current power supply, the reference magnetic field generating device 20 is used for receiving the first alternating constant current power supply and the direct current constant current power supply to generate a reference magnetic field; A magnetic field detecting device 30 electrically connected with the signal generator 10, the magnetic field detecting device 30 is used for being driven by the second alternating constant current power supply, detecting the reference magnetic field and outputting a reference magnetic field detection signal; A signal demodulating device 40 electrically connected with the magnetic field detecting device 30, the signal demodulating device 40 is used for demodulating the reference magnetic field detection signal to obtain a reference signal, and outputting the amplitude and phase of the reference signal at a first reference frequency and a second reference frequency, the second reference frequency is twice the first reference frequency.

[0032] In the embodiment, the signal generator 10 can output two alternating constant current power supplies; selecting the alternating constant current source driving simplifies the relationship between the output voltage of the magnetic field detecting device 30 and the magnetic field, so that it shows good linearity, and improves the reliability of calibration. Assuming that an alternating constant current I=i0sin(ωt+α) with an amplitude i0 and an angular frequency ω is input; taking the magnetic field detecting device 30 as a magnetoresistance sensor as an example, when being driven by the alternating constant current source, the output voltage UCD of the magnetoresistance sensor is simply proportional to the resistance change amount ΔR of the magnetoresistance sensor (UCD= ΔR= i0sin(ωt+α)·R0). 1 / 2IΔR), the linearity is better, the relationship is more intuitive, and the complex influence of the hysteresis effect on the output signal is effectively avoided. The reference magnetic field generating device 20 can be composed of a coil, which forms a magnetic field when current passes through. By receiving a direct current constant current power supply and a first alternating current constant current power supply through two coils, a stable constant magnetic field and an alternating magnetic field can be generated. The stable constant magnetic field and the alternating magnetic field are superimposed to form a complex magnetic field environment, and the superimposed magnetic field is used as the reference magnetic field. For example, the reference magnetic field B is the superposition of a stable constant magnetic field B0 and an alternating magnetic field b0sin(ωt+β), that is, B=B0+b0sin(ωt+β). The output voltage UCD of the magnetic resistance sensor is proportional to the product of the working current I and the reference magnetic field B, that is, UCD=kIB, wherein k is a proportional coefficient. Substituting the expressions of I and B, we get: UCD=k[i0sin(ωt+α)][B0+b0sin(ωt+β)]; and using the product-to-sum and difference-to-product formula of trigonometric functions, we get: UCD=ki0B0sin(ωt+α)+ki0b0sin(ωt+α)sin(ωt+β). Further, the output voltage UCD can be expressed as a combination of signals containing the base frequency (ω), the multiple frequency (2ω) and the direct current component: UCD=ki0B0sin(ωt+α) 2ki0b0cos(2ωt+α+β)+2ki0b0cos(α β). Then, the reference signal is obtained by demodulating the reference magnetic field detection signal by the signal demodulation device 40, such as a lock-in amplifier. Through digital Fourier analysis, the amplitudes and phases of the reference signal at the reference frequency (base frequency ω) and its multiple frequency (2ω) can be calculated simultaneously. By measuring the amplitude of the base frequency (ω) component, the strength B0 of the stable constant magnetic field can be obtained, because the amplitude is proportional to ki0B0. By measuring the amplitude of the multiple frequency (2ω) component, the strength amplitude b0 of the alternating magnetic field can be obtained, because the amplitude is proportional to 2ki0b0. The two amplitudes and phases corresponding to the reference magnetic field are used as standard reference values, and the standard reference values correspond to the strength of the reference magnetic field. When other complex magnetic fields are detected by the weak magnetic field synchronous measurement device subsequently, the amplitudes and phases obtained are compared and calculated with the standard reference values, and the strengths of the other complex magnetic fields can be obtained.

[0033] The technical scheme of the present application comprises a weak magnetic field synchronous measurement device composed of a signal generator 10, a reference magnetic field generating device 20, a magnetic field detecting device 30 and a signal demodulating device 40, wherein the signal generator 10 is used to output a first alternating constant current power supply and a second alternating constant current power supply; the reference magnetic field generating device 20 is electrically connected with the signal generator 10, the reference magnetic field generating device 20 is used to connect a direct constant current power supply, the reference magnetic field generating device 20 is used to receive the first alternating constant current power supply and the direct constant current power supply to generate a reference magnetic field; the magnetic field detecting device 30 is electrically connected with the signal generator 10, the magnetic field detecting device 30 is used to be driven by the second alternating constant current power supply, detect the reference magnetic field and output a reference magnetic field detection signal; the signal demodulating device 40 is electrically connected with the magnetic field detecting device 30, the signal demodulating device 40 is used to demodulate the reference magnetic field detection signal to obtain a reference signal, and output the amplitude and phase of the reference signal at a first reference frequency and a second reference frequency, the second reference frequency being twice the first reference frequency. Thus, the weak magnetic field synchronous measurement device of the present application can demodulate the reference magnetic field by the signal demodulating device 40 to obtain the amplitude and phase of the reference magnetic field at the first reference frequency and the second reference frequency, and take the amplitude and phase of the reference magnetic field at the first reference frequency and the second reference frequency as the standard, so that the synchronous, real-time and accurate distinction and measurement of two magnetic field components in other complex magnetic fields can be realized.

[0034] In an embodiment, the signal generator 10 comprises: a constant current source output circuit, used to output a first alternating constant current power supply and a second alternating constant current power supply, the first alternating constant current power supply and the second alternating constant current power supply having the same frequency, and the first alternating constant current power supply and the second alternating constant current power supply having different phases; a synchronous signal output circuit, electrically connected with the signal demodulating device 40, the synchronous signal output circuit being used to output a synchronous signal to the signal demodulating device 40.

[0035] In the embodiment, the constant current source output circuit can have two output channels, respectively outputting the first alternating constant current power supply and the second alternating constant current power supply. The same frequency of the first alternating constant current power supply and the second alternating constant current power supply can make the current frequency of the driving magnetic field detection device 30 and the frequency of the alternating magnetic field in the reference magnetic field the same, ensuring the consistency of the detection result. And the different phase of the first alternating constant current power supply and the second alternating constant current power supply is to ensure the accuracy of the subsequent calculation result; and the frequency of the first alternating constant current power supply is also the same as the frequency of the direct current constant current power supply, so as to superimpose the reference magnetic field. In addition, the synchronous signal output circuit outputs the synchronous signal to the signal demodulation device 40, which is to realize the phase locking and synchronous detection of the signal. The frequency of the synchronous signal is the same as the frequency of the second alternating constant current power supply. Taking the signal demodulation device 40 as a phase-locked amplifier as an example, the phase-locked amplifier can extract the specific frequency component in the reference signal by comparing the phase of the reference signal with the synchronous signal. The synchronous signal provides a reference, and the phase comparison can help the phase-locked amplifier to judge the phase deviation of the reference signal.

[0036] In an exemplary technology, the design of the constant current source output circuit can also be based on the operational amplifier and the three-terminal voltage regulator chip. The constant current source based on the operational amplifier adjusts the degree of conduction of the power tube through negative feedback, forcing the voltage across the sampling resistor to equal the input voltage, thereby fixing the output current; the three-terminal voltage regulator chip can adjust the voltage difference between the output and the input. When the resistance is constant, the output current is constant.

[0037] Further, with reference to Figure 2 In an embodiment, the constant current source output circuit includes a first resistor R1, a second resistor R2, a third resistor R3, a first operational amplifier U1 and a first NMOS tube Q1. The first end of the first resistor R1 and the positive input end of the first operational amplifier U1 are connected, the second end of the first resistor R1 is grounded, the negative input end of the first operational amplifier U1 and the first end of the second resistor R2 are connected, the second end of the second resistor R2, the first end of the third resistor R3 and the source of the first NMOS tube Q1 are interconnected, the second end of the third resistor R3 is used to connect the negative power supply, the output end of the first operational amplifier U1 and the gate of the first NMOS tube Q1 are connected, and the drain of the first NMOS tube Q1 is the output end of the constant current source output circuit.

[0038] In the embodiment, Figure 2The load RL in the figure is the magnetic field detection device 30, and the constant current source output circuit outputs the current to the load RL, that is, outputs the second alternating constant current power to the magnetic field detection device 30. The first resistor R1 and the second resistor R2 can play a role of current limiting. The first NMOS tube Q1 works in the linear region by introducing negative feedback. Since the first operational amplifier U1 has the characteristic of virtual break, the voltage at the negative input end is 0V, and therefore the current IR3 flowing through the third resistor R3 is IR3=6V / R3=1mA. When the load RL changes, the circuit keeps the current flowing through the load unchanged by adjusting the gate voltage of the first NMOS tube Q1 when the first operational amplifier U1 works. In the actual working process, as long as RL is less than 5 kilo-ohms, the drain voltage of the first NMOS tube Q1 can be ensured to be higher than the source voltage, and the constant current source output circuit can operate normally. Figure 2 The voltage value of the power supply in the figure is only for reference, and can be adjusted according to actual conditions and user requirements.

[0039] In an embodiment, the magnetic field generation device comprises: a first coil for connecting to the direct constant current power source and generating a first magnetic field; a second coil for connecting to the second alternating constant current power source and generating a second magnetic field; the first magnetic field and the second magnetic field superimpose to generate the reference magnetic field.

[0040] In this embodiment, the magnetic field generation device is composed of the first coil and the second coil. The direct constant current power source passes through the first coil to generate the first magnetic field, and the second alternating constant current power source passes through the second coil to generate the second magnetic field. The frequency of the direct constant current power source and the second alternating constant current power source is kept the same, so that the first magnetic field and the second magnetic field superimpose to generate the reference magnetic field. The shape and the number of turns of the first coil and the second coil can be set according to actual conditions and user requirements.

[0041] In an embodiment, the magnetic field detection device 30 comprises any one of a bridge-type giant magnetoresistance sensor or a tunnel magnetoresistance sensor.

[0042] In this embodiment, the bridge-type giant magnetoresistance sensor can be applied to the scheme described in the above embodiments, and the method is also applicable in principle to other types of magnetoresistance sensors, such as tunnel magnetoresistance sensors, as long as the resistance value thereof has a certain functional relationship with the external magnetic field.

[0043] It should be noted that the frequency of the second alternating constant current power source selected to drive the magnetic field detection device 30 in this scheme is 3.14Hz, because the magnetoresistance sensor responds stably at this frequency and does not need to be frequency-corrected. Within the effective working bandwidth of the sensor (for example, less than 30Hz), different working frequencies can also be selected.

[0044] Reference is made toFigure 3 In an embodiment, the bridge-type giant magnetoresistance sensor comprises a fourth resistor R4, a fifth resistor R5, a sixth resistor R6 and a seventh resistor R7; a first end of the fourth resistor R4 and a second end of the seventh resistor R7 are connected, and are a first input end of the bridge-type giant magnetoresistance sensor; a second end of the fourth resistor R4 and a first end of the fifth resistor R5 are connected, and are a first output end of the bridge-type giant magnetoresistance sensor; a second end of the fifth resistor R5 and a first end of the sixth resistor R6 are connected, and are a second input end of the bridge-type giant magnetoresistance sensor; a second end of the sixth resistor R6 and a first end of the seventh resistor R7 are connected, and are a second output end of the bridge-type giant magnetoresistance sensor.

[0045] In the embodiment, a Wheatstone bridge structure composed of four identical giant magnetoresistors is used, two resistors (the fourth resistor R4 and the sixth resistor R6) at diagonal positions are shielded, and the other two resistors (the fifth resistor R5 and the seventh resistor R7) are exposed to the magnetic field to be detected. In this way, the input end of the bridge-type giant magnetoresistance sensor is connected to the second alternating constant current power supply, and the resistance changes correspondingly due to the change of the magnetic field, so that the bridge-type giant magnetoresistance sensor outputs a corresponding magnetic field detection signal to the signal demodulation device 40 through the output end.

[0046] In another example technology, the resistors in the Wheatstone bridge structure can be replaced by strain gauges, and the sensitivity of the output signal is higher; the number of resistors in the bridge can also be increased, consistent with the principle of a four-resistor bridge; an LCR oscillation circuit can also be added to the bridge to form an alternating current bridge.

[0047] In an embodiment, the signal demodulation device 40 comprises any one of a digital lock-in amplifier or a dynamic signal analyzer.

[0048] In the embodiment, in addition to using a digital lock-in amplifier, a high-performance dynamic signal analyzer (spectrum analyzer) can also be used, or a high-speed data acquisition card can be used for sampling and then performing fast Fourier transform on a computer to analyze the fundamental frequency and multiple frequency components of the reference signal. The essence of the lock-in amplifier is digital Fourier analysis.

[0049] In an embodiment, the signal demodulation device 40 further comprises: a differential amplifier circuit 50, an input end of the differential amplifier circuit 50 is connected to an output end of the magnetic field detection device 30, an output end of the differential amplifier circuit 50 is connected to an input end of the signal demodulation device 40, and the differential amplifier circuit 50 is used to amplify and output the magnetic field detection signal output by the magnetic field detection device 30 to the signal demodulation device 40.

[0050] In this embodiment, the differential amplifier circuit 50 can effectively reduce noise and interference when processing weak signals; the differential amplifier has a high common-mode rejection ratio, can effectively suppress the noise and interference commonly existing in the input signal, and is suitable for precision measurement and signal processing; and the differential amplifier has good linear characteristics, can maintain linear amplification within a wide input range, and thus improves the accuracy of the signal.

[0051] In an exemplary technique, the differential amplifier can be replaced by a fully differential amplifier and a variable gain amplifier. The fully differential amplifier has differential input, differential output, no ground dependence, and strong anti-interference ability; the variable gain amplifier can adjust the gain in time to adapt to the scene where the signal amplitude changes.

[0052] Further, with reference to Figure 4 In an embodiment, the differential amplifier circuit 50 includes an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, and a second operational amplifier U2, a first end of the eighth resistor R8 is a first input end of the differential amplifier circuit 50, a second end of the eighth resistor R8, a first end of the ninth resistor R9, and a negative input end of the second operational amplifier U2 are interconnected, a second end of the ninth resistor R9 and an output end of the second operational amplifier U2 are connected, a first end of the tenth resistor R10 is a second input end of the differential amplifier circuit 50, a second end of the tenth resistor R10, a first end of the eleventh resistor R11, and a positive input end of the second operational amplifier U2 are interconnected, and a second end of the eleventh resistor R11 is grounded.

[0053] In this embodiment, the output signal is VOUT=(R11 / R10+R11)(R8+R9 / R8)V2 R9V1 / R1, in the formula, VOUT is the output end voltage of the second operational amplifier U2, R8, R9, R10, and R11 represent the resistance values of the eighth resistor R8, the ninth resistor R9, the tenth resistor R10, and the eleventh resistor R11 respectively, and V1 and V2 represent the voltages of the first input end and the second input end of the differential amplifier circuit 50 respectively. The differential amplifier in this embodiment is a 10-fold differential amplifier, wherein R8=R10=1 kΩ and R9=R11=10 kΩ. The specific differential amplifier amplification factor and resistance value can be set according to actual conditions and user requirements.

[0054] In order to better illustrate the technical concept of the present application, the above embodiment content and Figures 1 to 5 The present scheme is described as follows: The application uses an alternating constant current power supply to drive a bridge-type giant magnetoresistance sensor, so that it works in alternating current mode. When the bridge-type giant magnetoresistance sensor is placed in a reference magnetic field superimposed by a steady magnetic field and an alternating magnetic field, the output voltage signal of the sensor will contain specific frequency components related to the two magnetic field components. The output signal is demodulated and analyzed by a digital phase-locked amplifier, so that the fundamental frequency (ω) harmonic component and the frequency-doubled (2ω) harmonic component are extracted respectively. Thus, the application can realize real-time and synchronous measurement of the steady magnetic field and the alternating weak magnetic field by using a single bridge-type giant magnetoresistance sensor. The strength of the steady magnetic field can be obtained by analyzing the amplitude of the fundamental frequency component, and the strength of the alternating magnetic field can be obtained by analyzing the amplitude of the frequency-doubled component.

[0055] Reference Figure 5 When the strength of the alternating magnetic field is fixed and the steady magnetic field is changed (by changing the direct current excitation current), the measured frequency-doubled signal remains basically unchanged, and the fundamental frequency signal changes linearly with the steady magnetic field. This proves that the scheme can effectively distinguish and independently measure the two magnetic field components.

[0056] The scheme uses alternating current driving combined with phase-locked amplification technology, which can greatly suppress noise interference of non-related frequencies, extract weak signals from strong noise background, and thus significantly improve the signal-to-noise ratio and accuracy of measurement. Because in alternating current mode, the frequency of the output signal of the bridge-type giant magnetoresistance sensor is determined by the frequency of the driving signal (such as alternating constant current power supply), any noise unrelated to the frequency (such as low-frequency drift or environmental interference) will be effectively filtered out, thereby significantly improving the purity of the signal; the phase-locked amplifier locks the phase with the reference signal (driving frequency), and only extracts the signal component consistent with the reference frequency (such as the fundamental frequency and the frequency-doubled component). Thus, the background noise or interference signal of other frequencies (non-related frequencies) will be greatly suppressed. The relative uncertainty of the steady magnetic field measurement is 1.8%, and the alternating magnetic field is 3.0%.

[0057] In addition, the scheme uses a constant current mode to power the magnetic field detection device 30. In Figure 3 In the bridge shown in the figure, R4=R5=R6=R7=R, where R4, R5, R6 and R7 represent the resistance values of the fourth resistor R4, the fifth resistor R5, the sixth resistor R6 and the seventh resistor R7, respectively. The fourth resistor R4 and the sixth resistor R6 are shielded, and a magnetic field is applied outside the bridge. According to the giant magnetoresistance effect, R4=R5=R, R5=R7=R When a constant voltage is input, a constant voltage U is input between A and B, and B is grounded, then the potential difference UCD between C and D is R2R RU. When constant current input, A, B input constant current I, UCD= 12I R, sensor output voltage and giant magnetoresistance change form a more simple and intuitive proportional relationship. Therefore, the scheme uses constant current input for the sensor, simplifies the relationship between the sensor output voltage and the magnetic field, makes it show good linearity, and improves the reliability of calibration.

[0058] And the scheme uses a digital lock-in amplifier to realize the synchronous measurement of the steady and alternating magnetic field. The digital lock-in amplifier can perform digital Fourier analysis on the input signal and separate out the signal of a specific frequency. In the scheme, the input of the digital lock-in amplifier is the output signal UCD of the sensor and the reference signal with a frequency of ω, UCD is proportional to the working current I of the sensor i0sin(ωt+α) and the magnetic field strength B=B0+b0sin(ωt+β), UCD=ki0sinωt+α[B0+b0sin(ωt+β)]=ki0B0sin(ωt+α) k2i0b0[cos(2ωt+α+β) cos(α β)] wherein k is a proportional coefficient. After digital Fourier analysis by the lock-in amplifier, the amplitudes and phases of the signals at frequencies ω and 2ω can be calculated simultaneously, and then the amplitudes of the steady and alternating magnetic fields are obtained.

[0059] The present application also provides a weak magnetic field synchronous measurement system.

[0060] In an embodiment, the weak magnetic field synchronous measurement system comprises a computing device and the weak magnetic field synchronous measurement device as described above, and the computing device is used to receive the reference signal output by the weak magnetic field synchronous measurement device. The computing device in this embodiment can be a computer or the like, and the computing device can store and record the amplitudes and phases of the reference signal output by the weak magnetic field synchronous measurement device at the first reference frequency and the second reference frequency, and can be converted into corresponding digital signals. It can be understood that, since the above-mentioned weak magnetic field synchronous measurement device is used in the weak magnetic field synchronous measurement system of the present application, the embodiments of the weak magnetic field synchronous measurement system of the present application include all the technical solutions of all the embodiments of the above-mentioned weak magnetic field synchronous measurement device, and the technical effects achieved are also completely the same, which will not be described here.

[0061] It should be understood that the application of the present application is not limited to the above examples, and those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall belong to the protection scope of the claims of the present application.

Claims

1. A weak magnetic field synchronous measurement device, characterized in that, include: A signal generator is used to output a first AC constant current power supply and a second AC constant current power supply. A reference magnetic field generating device is electrically connected to the signal generator. The reference magnetic field generating device is used to connect to a DC constant current power supply. The reference magnetic field generating device is used to receive the first AC constant current power supply and the DC constant current power supply to generate a reference magnetic field. A magnetic field detection device is electrically connected to the signal generator. The magnetic field detection device is driven by the second AC constant current power supply to detect the reference magnetic field and output a reference magnetic field detection signal. The signal demodulation device is electrically connected to the magnetic field detection device. The signal demodulation device is used to demodulate the reference magnetic field detection signal to obtain a reference signal, and outputs the amplitude and phase of the reference signal at a first reference frequency and a second reference frequency, wherein the second reference frequency is twice the first reference frequency.

2. The weak magnetic field synchronous measurement device as described in claim 1, characterized in that, The signal generator includes: A constant current source output circuit is used to output a first AC constant current power supply and a second AC constant current power supply. The first AC constant current power supply and the second AC constant current power supply have the same frequency, but different phases. A synchronization signal output circuit is electrically connected to the signal demodulation device, and the synchronization signal output circuit is used to output a synchronization signal to the signal demodulation device.

3. The weak magnetic field synchronous measurement device as described in claim 2, characterized in that, The constant current source output circuit includes a first resistor, a second resistor, a third resistor, a first operational amplifier, and a first NMOS transistor. The first end of the first resistor is connected to the positive input terminal of the first operational amplifier, the second end of the first resistor is grounded, the negative input terminal of the first operational amplifier is connected to the first end of the second resistor, the second end of the second resistor and the first end of the third resistor are interconnected with the source of the first NMOS transistor, the second end of the third resistor is used to connect to the negative power supply, the output terminal of the first operational amplifier is connected to the gate of the first NMOS transistor, and the drain of the first NMOS transistor is the output terminal of the constant current source output circuit.

4. The weak magnetic field synchronous measurement device as described in claim 1, characterized in that, The magnetic field generating device includes: The first coil is used to connect to the DC constant current power supply and generate the first magnetic field; The second coil is used to connect to the second AC constant current power supply and generate a second magnetic field; the first magnetic field and the second magnetic field are superimposed to generate the reference magnetic field.

5. The weak magnetic field synchronous measurement device as described in claim 1, characterized in that, The magnetic field detection device includes either a bridge-type giant magnetoresistive sensor or a tunnel magnetoresistive sensor.

6. The weak magnetic field synchronous measurement device as described in claim 5, characterized in that, The bridge-type giant magnetoresistive sensor includes a fourth resistor, a fifth resistor, a sixth resistor, and a seventh resistor; the first end of the fourth resistor and the second end of the seventh resistor are connected and constitute the first input terminal of the bridge-type giant magnetoresistive sensor; the second end of the fourth resistor and the first end of the fifth resistor are connected and constitute the first output terminal of the bridge-type giant magnetoresistive sensor; the second end of the fifth resistor and the first end of the sixth resistor are connected and constitute the second input terminal of the bridge-type giant magnetoresistive sensor; the second end of the sixth resistor and the first end of the seventh resistor are connected and constitute the second output terminal of the bridge-type giant magnetoresistive sensor.

7. The weak magnetic field synchronous measurement device as described in claim 1, characterized in that, The signal demodulation device includes either a digital lock-in amplifier or a dynamic signal analyzer.

8. The weak magnetic field synchronous measurement device as described in claim 1, characterized in that, Also includes: A differential amplifier circuit is provided, wherein the input terminal of the differential amplifier circuit is connected to the output terminal of the magnetic field detection device, and the output terminal of the differential amplifier circuit is connected to the input terminal of the signal demodulation device. The differential amplifier circuit is used to amplify the magnetic field detection signal output by the magnetic field detection device and output it to the signal demodulation device.

9. The weak magnetic field synchronous measurement device as described in claim 8, characterized in that, The differential amplifier circuit includes an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, and a second operational amplifier. The first terminal of the eighth resistor is the first input terminal of the differential amplifier circuit. The second terminal of the eighth resistor, the first terminal of the ninth resistor, and the negative input terminal of the second operational amplifier are interconnected. The second terminal of the ninth resistor is connected to the output terminal of the second operational amplifier. The first terminal of the tenth resistor is the second input terminal of the differential amplifier circuit. The second terminal of the tenth resistor, the first terminal of the eleventh resistor, and the positive input terminal of the second operational amplifier are interconnected. The second terminal of the eleventh resistor is grounded.

10. A weak magnetic field synchronous measurement system, characterized in that, It includes a computing device and a weak magnetic field synchronous measurement device as described in any one of claims 1-9, wherein the computing device is used to receive a reference signal output by the weak magnetic field synchronous measurement device.

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