A method for measuring magnetic microwire toroidal AC loop based on LabVIEW

Abstract

The present invention discloses a method for measuring the toroidal AC loop of a magnetic microwire based on LabVIEW. The method realizes loop measurement based on LabVIEW program control, and the steps include: connecting the magnetic microwire and a resistor in series and then connecting them to a signal generator, while connecting another channel of the signal generator to an oscilloscope. The other two channels of the oscilloscope simultaneously measure the voltage signals at both ends of the magnetic microwire and the resistor, and connect them to a computer to realize control. The LabVIEW program reads the voltage signal measured by the oscilloscope, performs digital filtering processing, numerical integration processing, image display processing, and data recording and preservation. After the above two steps, the toroidal AC hysteresis loop of the magnetic microwire can be measured. The present invention avoids the use of an induction coil, and obtains and demonstrates an indirect measurement method through physical deduction to obtain the toroidal AC hysteresis loop of the material. The measurement method is simple enough, and only two common devices, a signal generator and an oscilloscope, are needed.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and in particular to a method for measuring a magnetic microwire toroidal AC loop based on LabVIEW. Background Art

[0002] The giant magneto-impedance (GMI) effect refers to the phenomenon in which soft magnetic materials experience significant changes in their impedance under the influence of an external magnetic field. Leveraging this property, these materials have found numerous applications in magnetic sensor technology, including fluxgate and GMI sensors. For example, a fundamental-wave orthogonal fluxgate sensor consists of a magnetic core and a pickup coil wrapped around it. The core is a magnetic filament with a strong GMI effect. When AC excitation is applied to the probe, the filament generates an alternating magnetic field in the circumferential direction, causing the core to become magnetized in that direction. This is the primary cause of magnetic noise in the sensor. This dynamic magnetization process occurs. Within a single AC excitation cycle, the circumferential projection of the filament's magnetization intensity undergoes periodic variations, generating hysteresis, which results in energy loss (hysteresis loss). AC excitation also generates eddy current losses. This energy loss is dissipated as heat, which in turn generates thermal disturbances in the magnetic moment, which are reflected in the pickup coil and generate significant noise. The hysteresis loop measured using a dynamic excitation field is called an AC loop. This loop includes both hysteresis and eddy current losses. Therefore, measuring the toroidal AC loop of a microfilamentary core can help evaluate magnetic materials and sensor performance, as well as aid in the selection of relevant magnetic materials. Summary of the Invention

[0003] The technical problem to be solved by this invention is a LabVIEW-based method for measuring the toroidal AC loop of a magnetic microwire, developed to study the source mechanism of sensor probe noise. This method theoretically calculates the toroidal AC hysteresis loop of the magnetic microwire simply by measuring the voltage across the wire and the current in the loop.

[0004] In order to solve the technical problems of the present invention, the following technical solutions are adopted:

[0005] A method for measuring a magnetic microwire loop AC loop based on LabVIEW includes: connecting a magnetic microwire and a resistor in series and then connecting them to the first channel of a signal generator; connecting the second channel of the signal generator to channel I of an oscilloscope; the first channel and the second channel of the signal generator generate identical excitation signals; the oscilloscope is used to collect voltage signals; channels II and III of the oscilloscope simultaneously measure the voltage signals at both ends of the magnetic microwire and the resistor; the three channels of the oscilloscope are channel I receiving the excitation signal of the signal generator itself, channel II receiving the voltage signals at both ends of the magnetic microwire, and channel III receiving the voltage signals at both ends of the series resistor. Voltage signal, and then use LabVIEW program to control the oscilloscope and read and process the collected voltage signal, process the voltage signals of channel I and channel II to obtain the induced voltage, and integrate the induced voltage to obtain the waveform Φ(t) of the magnetic flux in the circular direction of the magnetic microwire changing with time, and then divide the voltage signal of channel III by the resistance value of the series resistor to obtain the current waveform I(t) flowing through the magnetic microwire, and use the current waveform I(t) flowing through the magnetic microwire and the waveform Φ(t) of the magnetic flux in the circular direction of the magnetic microwire changing with time as X and Y axes respectively to obtain the magnetic microwire circular AC loop.

[0006] In the LabVIEW program, the DC resistance of the magnetic filament is pre-input. The excitation signal, read from oscilloscope channel I, is then used to calculate the theoretical DC voltage divider value of the filament using voltage divider theory. This DC voltage divider is then subtracted from the data from channel II to obtain the induced voltage. The product of the current waveform I(t) flowing through the filament and the time-varying waveform Φ(t) of the circumferential magnetic flux in the filament is the energy dimension, which can be used to assess the energy loss of the filament.

[0007] The excitation signal of the signal generator is a sine wave with a frequency of 10 kHz and an amplitude of 5 V.

[0008] The resistance of the resistor is 5 ohms. The function of the series resistor is to obtain the current in the excitation circuit and convert the current signal into a voltage signal. In order not to reduce the current in the circuit, a small resistor is used as much as possible.

[0009] The changing magnetic field in the magnetic microfilament will induce a changing electric field, which will generate an induced voltage at both ends of the magnetic microfilament. V i , let the annular magnetic flux be Φ , then the following relationship is obtained approximately: , t represents time, and the formula represents magnetic flux Φ The differential with respect to time t is approximately the induced voltage V i .

[0010] The signal generator has two channels, and the two channels are coupled together to make the frequency, amplitude and phase of the voltage signals in the channels consistent. The first channel is used for excitation, and the voltage signal of the second channel is passed to the oscilloscope to calculate the theoretical DC voltage divider.

[0011] The LabVIEW program performs digital filtering on the data read from the oscilloscope and reads waveforms of multiple cycles.

[0012] The excitation signal of the signal generator can be adjusted to the form of AC plus DC bias, and is used to measure the magnetic micro-wire toroidal AC loop with DC bias.

[0013] The magnetic microwire is an amorphous wire or a composite wire and is used for the magnetic core of a fundamental wave orthogonal fluxgate sensor.

[0014] Principle of the present invention:

[0015] Considering the columnar structure of the magnetic microwire, a circular cross-section wire can be used as a model. When the wire is excited by a known sinusoidal current, at each given moment, the electric field on the surface of the wire is a certain value, that is, (1), where E Indicates the electric field strength, and const indicates a constant, which is determined by the instantaneous current flowing through the wire.

[0016] Under quasi-static conditions, there is (2), in formula (2), Represents the vector differential operator, the two formulas are the dot product and cross product of the vector respectively;

[0017] There is (3), where μ represents the magnetic permeability of the transmission medium, σ represents the conductivity of the transmission medium, c represents the speed of light, and t represents time;

[0018] The cylindrical coordinates are established with the axial direction of the wire as the z direction. Then the electric field in the wire has only the z component, and is related to the position in the radial direction r. Then, by introducing the time factor, the above formula can be written as: (4), in formula (4) r represents the radial position in cylindrical coordinates, k Defined as the propagation coefficient of electromagnetic waves in a medium, δ represents the skin depth, i represents an imaginary number;

[0019] Expand the above formula and rewrite it as: (5);

[0020] This formula satisfies the Bessel equation: (6), where x, y, and m represent the independent variables in the Bessel equation;

[0021] Then the finite solution of the electric field at r=0 is: (7), where E z represents the electric field in the z direction in the wire, J 0 represents the zero-order Bessel function, i represents an imaginary number, ω represents the frequency of the sinusoidal current, t represents the time, e represents a natural constant;

[0022] Also by (8), where B represents the magnetic induction intensity, c represents the speed of light, and t represents time;

[0023] Can get (9), where A subscript indicating the circumferential direction, Indicates the strength of the magnetic field in the circular direction of the conductor;

[0024] Also because (10), where J 1 represents the first-order Bessel function, x represents the independent variable of the Bessel function;

[0025] get (11), where H Indicates the magnetic field strength within the conductor;

[0026] Through the above derivation, the specific distribution of the electric and magnetic fields inside the magnetic microfilament under the excitation state is determined. However, the properties of the magnetic material itself are actually ignored, and the entire derivation process is based on quasi-static conditions. Therefore, there is definitely a deviation between the final result and the actual situation. However, this approximate result will be reflected in the test principle of the loop.

[0027] as follows Figure 1 As shown, consider a cylindrical conductor with a radius of R and a length of L. When current passes through it, the magnetic flux inside it can be deduced from formula (11):

[0028] (12), where Φ represents the magnetic flux in the annular direction inside the conductor, R represents the conductor radius, L Indicates the length of the conductor;

[0029] The time derivative of magnetic flux is: (13);

[0030] The voltage V across the conductor can be approximated by equation (7):

[0031] (14);

[0032] Under quasi-static conditions, considering only the DC resistance of the material, the voltage drop across it is: (15), where R i It represents the voltage drop across the conductor under quasi-static conditions;

[0033] Then, the following approximate relationship can be obtained from equations (13), (14), and (15): (16).

[0034] The above derivation proves the feasibility of the measurement method. The physical mechanism behind it is correct. The magnetic flux obtained by integrating the induced voltage differs from the actual magnetic flux by a coefficient. By omitting the coefficient by approximation, Equation (16) can be obtained.

[0035] The above is the theoretical basis for measuring the toroidal AC loop of the magnetic microwire. It is only necessary to measure the voltage at both ends of the magnetic microwire and the current in the loop to obtain the toroidal AC hysteresis loop of the magnetic microwire according to the theory.

[0036] Therefore, as long as the voltage across the amorphous wire in the loop is measured and the theoretical DC voltage divider is subtracted, the induced voltage can be obtained, and the magnetic flux can be obtained by integrating the induced voltage over time. Since the voltage signal collected by the oscilloscope is discrete, integration is actually a cumulative process, and the magnetic flux obtained by integration is a set of arrays that change with time, which is used as the vertical coordinate. Regarding the horizontal coordinate, according to Ampere's loop theorem, the toroidal excitation field is proportional to the instantaneous value of the current flowing through the amorphous wire. Therefore, it is only necessary to obtain the waveform of the current changing with time at the same time, and the two are plotted as Lissajous figures to obtain the final toroidal AC hysteresis loop. Figure 2 In the circuit, the function of resistor R is to convert the current signal into a voltage signal, which is then collected and read by the oscilloscope.

[0037] The testing method of the toroidal AC hysteresis loop of the present invention is intended to serve the research on the performance of the probe material of the orthogonal fluxgate sensor. Currently, composite wire and amorphous wire are both materials used as the magnetic core of the sensor probe. When the sensor is working, the alternating current passing through the core will magnetize the core in the toroidal direction. This magnetization process will produce corresponding energy loss, and this energy loss will affect the noise of the sensor. Therefore, in the process of studying the sensor probe material, we found that the toroidal AC hysteresis loop is more important. However, the existing equipment for measuring hysteresis loops, such as VSM and BH-loop, cannot meet the needs, because the magnetic lines of force are closed in the material, and the induction coil cannot be used to directly detect the magnetic signal. The advantage of the present invention is that it avoids the use of induction coils, and derives and demonstrates an indirect measurement method through physical deduction, thereby obtaining the toroidal AC hysteresis loop of the material. Moreover, the measurement method is simple enough, and only two common devices, a signal generator and an oscilloscope, are required. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of magnetic field distribution inside a cylindrical conductor;

[0039] Figure 2 This is a schematic diagram of the experiment of measuring the circular AC loop of a magnetic microwire based on LabVIEW in the present invention;

[0040] Figure 3 The loop lines of the amorphous wire of the present invention at the same excitation amplitude and different frequencies;

[0041] Figure 4 The circular loops of the amorphous wire of the present invention are measured at 30 kHz and different sinusoidal excitation amplitudes;

[0042] Figure 5 It is the circular loop of the amorphous wire of the present invention measured under the condition of DC bias;

[0043] Figure 6 This is the circular loop of the composite yarn of the present invention measured at a sinusoidal excitation amplitude of 10 kHz and 5 V. DETAILED DESCRIPTION

[0044] Example 1

[0045] A LabVIEW-based method for measuring the toroidal AC loop of a magnetic microwire, where the magnetic microwire is an amorphous wire. The specific steps are as follows:

[0046] (1) Take a piece of amorphous wire and use a multimeter to measure the DC resistance of the amorphous wire, which is 10.6 ohms;

[0047] (2) Connect the amorphous wire and a 5-ohm resistor in series and connect them to the first channel of the signal generator. Connect the second channel of the signal generator to channel I of the oscilloscope and set the excitation condition to a sine wave with a frequency of 10 kHz and an amplitude of 5 V.

[0048] (3) Couple the first channel and the second channel of the signal generator together to ensure that the voltage signals in the two channels are exactly the same and have no phase difference;

[0049] (4) Connect the voltage signals at both ends of the amorphous wire and the resistor to channel II and channel III of the oscilloscope respectively. Channel II of the oscilloscope receives the voltage signals at both ends of the amorphous wire, and channel III receives the voltage signals at both ends of the series resistor.

[0050] (5) Connect the oscilloscope to the upper computer and realize program control through serial communication of LabVIEW program;

[0051] (6) Turn on the two channels of the signal generator and start excitation. At this time, three voltage waveforms will be displayed in the oscilloscope. Run the LabVIEW program and input the DC resistance value of the amorphous wire. Then, in the program, the excitation signal read by the oscilloscope channel I is used to calculate the theoretical DC voltage divider value of the amorphous wire through the voltage divider theory. Then, the voltage signal data in channel II is subtracted from this DC voltage divider to obtain the induced voltage data. Finally, the induced voltage is integrated to obtain the waveform Φ(t) of the amorphous wire's annular magnetic flux that changes with time. For the voltage signal read by channel III, divide it by the resistance value of the series resistor to obtain the current waveform I(t) flowing through the amorphous wire in the loop. Finally, the current waveform I(t) flowing through the amorphous wire and the waveform Φ(t) of the amorphous wire's annular magnetic flux that changes with time are used as the X and Y axes respectively to obtain the amorphous wire annular AC loop.

[0052] like Figure 2 As shown, the signal generator has two signal output terminals that can generate the required excitation signals. The oscilloscope shown has four channels and is primarily used to collect voltage signals during loop measurements. An amorphous wire is connected in series with a 5-ohm resistor and connected to the signal generator to form an excitation loop. The signal generator in the loop has a built-in 50-ohm impedance. The sinusoidal excitation signal in the signal generator is set to: (17), where V 0 represents the amplitude of the sinusoidal excitation signal, represents a sinusoidal excitation signal;

[0053] The voltage across the amorphous wire is: (18), where V i represents the induced voltage, V represents the voltage across the amorphous wire,R 0 represents the DC resistance of the amorphous wire, R1 represents the resistance in series with the amorphous wire, Represents the theoretical DC voltage divider under quasi-static conditions.

[0054] like Figure 3 The following are the toroidal AC hysteresis loops of different frequencies measured for an amorphous wire under a 5 V sinusoidal excitation signal. These loops conform to the general rules of dynamic hysteresis loops. As the frequency increases, the loop changes from narrow and long to wide and rounded. This is because the dynamic hysteresis loop contains both hysteresis losses and eddy current losses. As the frequency increases, eddy current losses dominate, causing the loop to deform. Therefore, as long as the test frequency is low enough, the test results will be close to those of a static hysteresis loop. Figure 4 The following figure shows the measured hysteresis loops for amorphous wire at different excitation amplitudes at the same excitation frequency of 30 kHz. The figure shows that as the excitation amplitude increases, the loop shape approaches saturation. The measurement results generally meet the characteristics of an AC hysteresis loop, demonstrating the feasibility of the measurement method. Figure 5 This is the measured toroidal loop of an amorphous wire at 300 kHz, using 5V AC and 4.4V DC bias as excitation. The DC bias causes distortion in the toroidal AC loop, but the excitation conditions better match the sensor's operating mode.

[0055] Example 2

[0056] A LabVIEW-based method for measuring the circular AC loop of a magnetic microfilament, where the magnetic microfilament is a composite wire. The specific steps are as follows:

[0057] (1) Take a piece of composite wire and use a multimeter to measure the DC resistance of the composite wire, which is 0.5 ohms;

[0058] (2) Connect the composite wire and a 5-ohm resistor in series and connect them to the first channel of the signal generator. Connect the second channel of the signal generator to channel I of the oscilloscope and set the excitation condition to a sine wave with a frequency of 10 kHz and an amplitude of 5 V.

[0059] (3) Couple the first channel and the second channel of the signal generator together to ensure that the voltage signals in the two channels are exactly the same and have no phase difference;

[0060] (4) Connect the voltage signals at both ends of the composite wire and the resistor to channel II and channel III of the oscilloscope respectively. Channel II of the oscilloscope receives the voltage signals at both ends of the composite wire, and channel III receives the voltage signals at both ends of the series resistor.

[0061] (5) Connect the oscilloscope to the upper computer and realize program control through serial communication of LabVIEW program;

[0062] (6) Turn on the two channels of the signal generator and start excitation. At this time, three voltage waveforms will be displayed in the oscilloscope. Run the LabVIEW program and input the DC resistance value of the composite wire. Then, in the program, the excitation signal read by the oscilloscope channel I is used to calculate the theoretical DC voltage divider value of the composite wire through the voltage divider theory. Then, the DC voltage divider is subtracted from the voltage signal data in channel II to obtain the induced voltage data. Finally, the induced voltage is integrated to obtain the waveform Φ(t) of the circumferential magnetic flux of the composite wire that changes with time. For the voltage signal read by channel III, divide it by the resistance value of the series resistor to obtain the current waveform I(t) flowing through the composite wire in the loop. Finally, the current waveform I(t) flowing through the composite wire and the waveform Φ(t) of the circumferential magnetic flux of the composite wire that changes with time are used as the X and Y axes respectively to obtain the circumferential AC loop of the composite wire. The measurement results are as follows: Figure 6 shown.

[0063] During the measurement process, the following steps should be noted:

[0064] 1. The signal generator requires two channels, which must be coupled together to ensure consistent frequency, amplitude, and phase. The first channel is used for excitation, and the second channel's signal is fed to the oscilloscope, which is then used to calculate the theoretical DC voltage divider.

[0065] 2. The oscilloscope uses three channels. The signal received by Channel I is the excitation signal of the signal generator itself, Channel II receives the voltage signal at both ends of the magnetic microwire, and Channel III receives the voltage signal at both ends of the series resistor.

[0066] 3. To automate the measurement process, LabView was used to program the oscilloscope and process data. After connecting the test circuit, the LabView program read the signals from the oscilloscope's three channels. Numerical calculations were performed on the signals from channels I and II to obtain the induced voltage, which was then integrated to obtain the waveform Φ(t) of the magnetic flux flowing through the microfilament over time. The data from channel III was then divided by the DC resistance to obtain the waveform I(t) of the current flowing through the microfilament. A Lissajous figure was constructed between the waveform Φ(t) of the magnetic flux flowing through the microfilament over time and the waveform I(t) of the current flowing through the microfilament to obtain the corresponding AC loop.

[0067] 4. The LabView program needs to digitally filter the data read from the oscilloscope to remove high-frequency noise, making the final loop clear. It can also read multiple cycles of waveforms to ensure loop accuracy.

Claims

1. A method for measuring magnetic microwire toroidal AC loop based on LabVIEW, characterized in that include: After the magnetic microwire and the resistor are connected in series, they are connected to the first channel of the signal generator. The second channel of the signal generator is connected to the channel I of the oscilloscope. The first channel and the second channel of the signal generator generate exactly the same excitation signal. The function of the oscilloscope is to collect voltage signals. The channels II and III of the oscilloscope simultaneously measure the voltage signals at both ends of the magnetic microwire and the resistor. The three channels of the oscilloscope are channel I receiving the excitation signal of the signal generator itself, channel II receiving the voltage signals on both sides of the magnetic microwire, and channel III receiving the voltage signals at both ends of the series resistor. Then, through LabVI The EW program is used to control the oscilloscope and read and process the collected voltage signals. The voltage signals of channels I and II are processed to obtain the induced voltage, and the induced voltage is integrated to obtain the waveform Φ(t) of the magnetic flux of the magnetic microwire changing with time. Then, the voltage signal of channel III is divided by the resistance value to obtain the current waveform I(t) flowing through the magnetic microwire. The current waveform I(t) flowing through the magnetic microwire and the waveform Φ(t) of the magnetic flux of the magnetic microwire changing with time are used as the X and Y axes respectively to obtain the magnetic microwire circular AC loop. In the LabVIEW program, the DC resistance value of the magnetic microwire is input in advance, and then the excitation signal read from the oscilloscope channel I is used to calculate the theoretical DC voltage division value of the magnetic microwire through voltage division theory; then the data of channel II is subtracted from this DC voltage division to obtain the induced voltage data.

2. The method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 1, characterized in that: The excitation signal of the signal generator is a sine wave with a frequency of 10 kHz and an amplitude of 5V.

3. The method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 2, characterized in that: The resistance value of the resistor is 5 ohms.

4. A method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 1 or 3, characterized in that include: The changing magnetic field in the magnetic microfilament will induce a changing electric field, which will generate an induced voltage at both ends of the magnetic microfilament. V i , let the annular magnetic flux be Φ , then we can get the following approximate relationship: , t represents time, and this formula represents magnetic flux Φ Differentiate with respect to time t.

5. The method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 1, characterized in that: The LabVIEW program performs digital filtering on the data read from the oscilloscope and reads waveforms of multiple cycles.

6. The method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 5, characterized in that: The excitation signal of the signal generator can be adjusted into the form of AC plus DC bias, and is used to measure the magnetic micro-wire toroidal AC loop with DC bias.

7. The method for measuring a magnetic microwire toroidal AC loop based on LabVIEW according to claim 1 or 6, characterized in that: The magnetic micro-wire is an amorphous wire or a composite wire and is used for the magnetic core of a fundamental wave orthogonal fluxgate sensor.

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