Weak magnetic field detection device and detection method based on magnetic field regulation and control technology

Abstract

The invention discloses a weak magnetic field detection device and method based on a magnetic field regulation and control technology. The weak magnetic field detection device comprises a signal generation circuit, a magnetoelectric probe, a phase-locked amplification circuit and a second-order filter circuit, the output end of the signal generation circuit is divided into two paths, one path serves as an excitation signal to be connected with the magnetoelectric probe, the other path serves as a reference signal to be connected with the phase-locked amplification circuit, the magnetoelectric probe is connected to the phase-locked amplification circuit, and the phase-locked amplification circuit is connected with the second-order filter circuit and used for filtering high-frequency noise in the circuit. Stable excitation signals are generated through the signal generation circuit, and the sensitivity of the sensor is improved. The phase-locked amplifier is introduced to demodulate an output signal, so that the noise influence is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the field of magnetic field detection, and particularly relates to a weak magnetic field detection device and a detection method based on magnetic field regulation technology. Background Art

[0002] Existing magnetic sensors, such as magnetoresistive sensors, optically pumped magnetometers, magnetic rod magnetometers, fluxgates, superconducting quantum interference devices (SQUIDs), etc., are difficult to fully meet the requirements in terms of sensitivity, bandwidth, range, temperature range, power consumption, volume, cost, etc. Better performance corresponds to higher costs, and low-cost devices lack sufficient accuracy. A magnetoelectric heterojunction formed by combining magnetostrictive materials and piezoelectric materials can sense an external magnetic field or electric field through the "magnetic-mechanical-electric" coupling interaction and convert it into an electrical signal output. The research on the magnetic sensing mechanism based on the magnetoelectric coupling effect is still a hot scientific research issue today.

[0003] Traditional magnetic sensing mechanisms are based on the linear magnetoelectric coupling effect. A fixed DC bias magnetic field is applied through a permanent magnet, etc., to obtain the maximum sensing sensitivity, and it works in the linear region of the magnetostriction curve. In the length expansion mode of a symmetric layered bulk device, the resonance frequency is above 20 kHz, making it difficult to perform highly sensitive detection of low-frequency magnetic fields (within 200 Hz). Summary of the Invention

[0004] The purpose of the present invention is to provide a weak magnetic field detection device and a detection method based on magnetic field regulation technology to solve the above problems.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A weak magnetic field detection device based on magnetic field regulation technology includes a signal generation circuit, a magnetoelectric probe, a lock-in amplifier circuit, and a second-order filter circuit; the output end of the signal generation circuit is divided into two paths, one path is used as an excitation signal to connect to the magnetoelectric probe, and the other path is used as a reference signal to connect to the lock-in amplifier circuit. The magnetoelectric probe is connected to the lock-in amplifier circuit, and the lock-in amplifier circuit is connected to the second-order filter circuit for filtering high-frequency noise in the circuit.

[0006] Further, the signal generation circuit includes a DDS waveform generation circuit and a power amplifier circuit. The DDS waveform generation circuit is connected to the power amplifier circuit. The output end of the power amplifier circuit is divided into two paths, one path is connected to the magnetoelectric probe, and the other path is connected to the lock-in amplifier circuit.

[0007] Further, the magnetoelectric probe includes a housing, a magnetoelectric composite piezoelectric layer, an electrode, and an excitation coil. The excitation coil is wound around the housing to generate an excitation signal. The magnetoelectric composite piezoelectric layer is arranged in the housing, and the magnetoelectric composite piezoelectric layer is connected to the output end of the magnetoelectric probe through the electrode.

[0008] Further, the envelope signal output by the magnetoelectric probe is connected to a lock-in amplifier circuit, which is used to demodulate the mixed-frequency signal output by the magnetoelectric probe.

[0009] Further, the second-order filter circuit includes an input terminal P1, an input terminal P2, an AD630 chip, a resistor R1, a resistor R2, a resistor R3, a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, and an operational amplifier. The signals of the input terminals P1 and P2 are respectively input into the AD630 chip through the capacitors C1 and C2, and the other ends of the capacitors C1 and C2 are grounded to form a high-pass filter network; the inverting input terminal of the operational amplifier is connected to the series-connected resistors R1 and R2. The other end of the resistor R1 is connected to the ground through the capacitor C3, and the other end of the resistor R2 is connected to the output terminal through the capacitor C4 to form a feedback network; the output terminal OUT of the operational amplifier is fed back to the inverting input terminal through the resistor R3 and the capacitor C4 to form a second-order filter.

[0010] Further, the capacitor C3 is connected between the node of the resistors R1 and R2 and the ground.

[0011] Further, the output terminal of the operational amplifier is connected to the output port P3 to output the filtered signal.

[0012] Further, the second-order filter circuit is also connected to an adder circuit to provide a DC bias for the output signal for the acquisition of the output signal.

[0013] Further, the adder circuit includes a resistor R12, a resistor R11, a power supply VCC, and a capacitor C6. The power supply VCC is connected to the output terminal OUT through the resistor R12 to provide voltage for the circuit. One end of the capacitor C6 is connected to the output port P3 to receive the input signal; the other end is connected to the ground through the resistor R11 to form a discharge loop of the capacitor, and the output terminal OUT is led out from the connection point of the resistor R12 and the capacitor C6.

[0014] A detection method for a weak magnetic field detection device based on a magnetic field control technology includes: Placing the magnetoelectric probe in the magnetic field to be measured, and the detection process corresponds to two externally applied components, a low-frequency magnetic field to be measured and an excitation magnetic field; Starting the signal generation circuit, and the power amplifier circuit simultaneously provides a reference signal and an excitation signal for the lock-in amplifier circuit and the magnetoelectric probe; The signal to be measured and the reference signal are respectively input from the P1 terminal and the P2 terminal. The AD630 chip modulates the mixed waveform, and the target waveform frequency is within the range of 0 - 200 Hz. The output signal of the lock-in amplifier circuit needs to pass through a second-order low-pass filter circuit to filter out the high-frequency components in the output signal to obtain the required waveform.

[0015] Compared with the prior art, the present invention has the following technical effects: The present invention generates a stable excitation signal through a signal generation circuit to improve the sensitivity of the sensor.

[0016] The present invention introduces a lock-in amplifier to demodulate the output signal, greatly reducing the influence of noise.

[0017] A second-order filter and isolation capacitors are introduced into the circuit of the present invention to avoid the influence of high-frequency noise and DC bias.

[0018] The circuit provided by the present invention can effectively cooperate with the magnetoelectric probe, improve the sensitivity while reducing the influence of noise, and achieve high-precision non-contact low-frequency magnetic field detection; compared with other current types of magnetic field detection devices, it improves the detection sensitivity and accuracy; it provides reliable technical support for the detection of low-frequency magnetic fields. Brief Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the circuit of the present invention.

[0020] Figure 2 It is a schematic diagram of the internal structure of the magnetoelectric probe provided by the present invention; Figure 3 It is a schematic diagram of the principle of the lock-in amplifier circuit and the second-order low-pass filter circuit provided by the present invention; Figure 4 It is a schematic diagram of the principle of the addition circuit of the present invention; Figure 5 (a)-(d) are schematic diagrams of the systematic test of the frequency conversion performance and bandwidth of the active weak magnetic field detection of the present invention. Detailed Embodiments

[0021] The following further describes the present invention with reference to the drawings: Embodiment 1, please refer to Figure 1 , A weak magnetic field detection device based on magnetic field regulation technology, including a signal generation circuit, a magnetoelectric probe, a lock-in amplifier circuit and a second-order filter circuit; the output end of the signal generation circuit is divided into two paths, one path is used as an excitation signal to connect to the magnetoelectric probe, and the other path is used as a reference signal to connect to the lock-in amplifier circuit. The magnetoelectric probe is connected to the lock-in amplifier circuit, and the lock-in amplifier circuit is connected to the second-order filter circuit for filtering high-frequency noise in the circuit.

[0022] For a magnetoelectric sensor based on the linear magnetostrictive effect, to achieve the best magnetoelectric coefficient, an external permanent magnet needs to be applied to provide the best DC bias, which increases the volume of the device, brings additional magnetic noise interference, and is difficult to perform high-sensitivity low-frequency magnetic field detection due to the high resonance frequency. Active detection overcomes the inherent defects of the traditional linear magnetoelectric effect, uses a modulation field with a frequency of the intrinsic resonance frequency of the device to excite the device to work in the resonance mode, and utilizes the nonlinearity of the magnetostrictive effect for sensing.

[0023] The circuit of the present invention can generate a sinusoidal excitation for the magnetoelectric device to make it work in the best state, and output a useful voltage signal, whose sensitivity meets the requirements of most actual situations, and can be used for the detection of unknown magnetic fields in the laboratory and the current monitoring of the circuit system.

[0024] The present invention uses the excitation signal as the reference signal of the lock-in amplifier circuit at the same time, ensuring the phase consistency between the target signal and the reference signal during the demodulation process. A second-order low-pass filter circuit is designed to limit the sensor detection range within 200 Hz, meeting the requirements of most low-frequency weak magnetic field detection scenarios. Compared with ordinary filter circuits, the lock-in amplifier circuit has a more significant effect in combating various noise interferences.

[0025] Embodiment 2, a weak magnetic field detection device based on magnetic field regulation technology, includes: A signal generation circuit is designed with AD9834 as the core to generate a high-performance sine wave to drive the magnetoelectric probe to work. It integrates a comparator inside the chip, supports generating a square wave for clock generation, and provides phase modulation and frequency modulation functions at the same time. The supply voltage is 3V and the power consumption is only 20mV, which is suitable for scenarios with strict requirements for low power consumption.

[0026] Furthermore, a lock-in amplifier circuit is designed based on the chip AD630 to demodulate the mixed-frequency signal output by the magnetoelectric probe.

[0027] Furthermore, a power amplifier circuit is designed to amplify the signal output by the signal generation circuit to meet the excitation requirements.

[0028] Furthermore, an addition circuit is designed to provide a certain DC bias for the output signal, which is beneficial to the acquisition of the output signal.

[0029] Furthermore, a second-order filter circuit is designed to filter the high-frequency noise existing in the circuit and limit the bandwidth of the sensor.

[0030] The circuit system is integrated on a double-layer PCB board, and copper is plated on the signal layers on the front and back of the PCB respectively to form a double-layer copper plate, improving the device integration, reducing the device volume, and reducing the interference of non-measured signals.

[0031] The signal generation circuit can generate a specific frequency voltage signal for the excitation signal; preferably, the signal generation circuit can generate a high-frequency voltage signal with adjustable amplitude-frequency and supporting customization.

[0032] The amplifier circuit provides power amplification for the input signal. Preferably, the circuit parameters can be changed according to requirements to adjust the amplification factor, and the chip model used meets the requirements of low noise and low power.

[0033] Preferably, the circuit output signal is directly collected through the analog-to-digital conversion module.

[0034] See Figure 1 , the overall idea of the system is as follows: Using a constant-amplitude alternating current modulation magnetic field to replace the DC bias magnetic field , driving the magnetoelectric device to work near the resonance frequency, and detecting the low-frequency alternating magnetic field . When >> , the magnetoelectric sensitivity reaches , where represents the magnetostrictive coefficient. The novel active low-frequency weak magnetic sensor designed based on this has advantages such as lower power consumption, high sensitivity, simple structure, and low cost compared with traditional fluxgate and magnetoresistive sensors, and the detection bandwidth can reach 0 Hz - 200 Hz.

[0035] The internal structure of the probe package is as Figure 2 shown. The excitation signal is connected to the excitation coil through the input terminal to generate an excitation signal of sufficient magnitude. The piezoelectric layer of the magnetoelectric composite material is connected to the output terminal through the electrode. The magnetic signal is converted into an electrical signal by the probe and input into the lock-in amplifier circuit.

[0036] In the first application example, this product can be used as a low-frequency magnetic field detection device, and the application method is as follows: Place the magnetoelectric probe in the magnetic field to be measured. The detection process corresponds to two externally applied components, the low-frequency magnetic field to be measured and the excitation magnetic field. Considering a certain noise content, the probe output signal is expressed as:

[0037] where, and are the angular frequencies of the modulation signal (low-frequency signal) and the carrier signal (resonant excitation signal) respectively. and are the corresponding phases. and k are the average amplitude and modulation coefficient of the modulation signal respectively.

[0038] The power amplifier circuit simultaneously provides a reference signal for the lock-in amplifier circuit, and the expression is:

[0039] As Figure 2 shown, the mixed signal is input into the chip from the P1 terminal, and the reference signal is input from the P2 terminal. The AD630 chip can multiply the two input signals. According to the principle of the lock-in amplifier, it can be obtained that:

[0040] At this time, let = , and =

[0041]

[0042] The excitation signal and the reference signal are simultaneously output by the power amplifier circuit to ensure exactly the same amplitude and phase.

[0043] The high-frequency components in the output signal are filtered to obtain the required waveform. A large-capacity capacitor is arranged between the lock-in amplifier circuit and the second-order filter circuit to remove the DC component.

[0044] Figure 3 The circuit diagram is a second-order filter circuit implemented based on an operational amplifier. The signal to be measured and the reference signal are input from the P1 terminal and the P2 terminal respectively. The AD630 chip modulates the mixed waveform. The frequency of the target waveform is within the range of 0 - 200 Hz, and the frequencies of the remaining waveforms are around the resonance frequency of the device, generally greater than 20 kHz. The output signal of the lock-in amplifier circuit needs to pass through a second-order low-pass filter circuit. The overall transfer function G(s) of the filter circuit is as follows:

[0045] Where R1 = R3 = 2kΩ, R2 = 1kΩ, C3 = 7.3μF, C4 = 1μF, and the bandwidth of the low-pass filter circuit is 0 - 200 Hz. The specific parameters can be adjusted according to actual requirements.

[0046] A non-contact current measurement method, which includes: Placing the probe above the wire to be measured, and the circular magnetic field generated by the wire serves as the magnetic field to be measured to excite the probe to generate a corresponding electrical signal. Preferably, a magnetic focusing device can be added to improve the magnetic field stability.

[0047] The adder circuit is an optional item. Adding a DC bias to the output signal makes it easier for subsequent acquisition. Figure 4 As the schematic diagram of the adder circuit, the output terminal P3 of the second-order filter circuit is connected to the input terminal of the adder circuit. Among them, the magnitude of the DC power supply is selected according to actual requirements, generally taking 3.3 - 5 V, the resistors R11 = R12 = 30 kΩ, and the capacitor C6 = 220 pF.

[0048] We combined the overall device with the lock-in amplifier SR865 and the dynamic signal analyzer SR785 to systematically test the frequency conversion performance and bandwidth of the active weak magnetic detection, such as Figure 5 (a) shows that the transfer function reflects that the probe has a flat response within 0~200Hz, that is, it meets the requirements of broadband detection. Combining with the low-pass filter designed in the backend circuit, it can accurately reflect the magnetic field changes within 200Hz. Figure 5(b) It reflects the efficacy of frequency conversion in the frequency domain: the low-frequency magnetic field signal (10 Hz, 0.01 Oe magnetic field in the figure) is shifted to the vicinity of the resonance frequency for detection by using non-linear magneto-electric coupling, avoiding the influence of 1 / f noise at low frequencies, and the output sensitivity is improved by using the resonance quality factor. In addition, combined with Figure 5 (c), we constructed a Labview system for reading the frequency-domain sideband signal, and obtained the detection limit of the probe relative to the low-frequency magnetic field through detection in the magnetic shielding system. It has a high linearity and can detect a low-frequency signal of 1 nT. Compared with passive direct detection, both the sensitivity and the detection limit are improved by two orders of magnitude.

[0049] The above embodiments of the present invention are only examples for clearly illustrating the invention, rather than limitations on the implementation methods of the present invention. Therefore, modifications, substitutions, improvement methods, etc. made within the spirit and principles of the present invention should all be within the protection scope of the claims of the present invention.

Claims

1. A weak magnetic field detection device based on magnetic field regulation technology, characterized in that, It includes a signal generation circuit, a magnetoelectric probe, a lock-in amplifier circuit, and a second-order filter circuit; the output end of the signal generation circuit is divided into two paths, one path is used as an excitation signal to connect to the magnetoelectric probe, and the other path is used as a reference signal to connect to the lock-in amplifier circuit. The magnetoelectric probe is connected to the lock-in amplifier circuit, and the lock-in amplifier circuit is connected to the second-order filter circuit for filtering high-frequency noise in the circuit.

2. The weak magnetic field detection device based on the magnetic field regulation technology according to claim 1, characterized in that The signal generation circuit includes a DDS waveform generation circuit and a power amplifier circuit. The DDS waveform generation circuit is connected to the power amplifier circuit. The output end of the power amplifier circuit is divided into two paths, one path is connected to the magnetoelectric probe, and the other path is connected to the lock-in amplifier circuit.

3. A weak magnetic field detection device based on magnetic field regulation technology according to claim 1, characterized in that The magnetoelectric probe includes a housing, a magnetoelectric composite piezoelectric layer, an electrode, and an excitation coil. The excitation coil is wound around the housing to generate an excitation signal. The magnetoelectric composite piezoelectric layer is arranged in the housing, and the magnetoelectric composite piezoelectric layer is connected to the output end of the magnetoelectric probe through the electrode.

4. A weak magnetic field detection device based on magnetic field regulation technology according to claim 1, characterized in that, The envelope signal output by the magnetoelectric probe is connected to the lock-in amplifier circuit, and the lock-in amplifier circuit is used to demodulate the mixed-frequency signal output by the magnetoelectric probe.

5. A weak magnetic field detection device based on magnetic field regulation technology according to claim 1, characterized in that, The second-order filter circuit includes an input terminal P1, an input terminal P2, an AD630 chip, a resistor R1, a resistor R2, a resistor R3, capacitors C1, C2, C3, C4, and an operational amplifier. The signals of the input terminals P1 and P2 are respectively input to the AD630 chip through the capacitors C1 and C2. The other ends of the capacitors C1 and C2 are grounded to form a high-pass filter network; the inverting input terminal of the operational amplifier is connected to the series-connected resistors R1 and R2. The other end of the resistor R1 is connected to the ground through the capacitor C3, and the other end of the resistor R2 is connected to the output end through the capacitor C4 to form a feedback network; the output end OUT of the operational amplifier is fed back to the inverting input terminal through the resistor R3 and the capacitor C4 to form a second-order filter.

6. The weak magnetic field detection device based on the magnetic field regulation technology according to claim 5, characterized in that The capacitor C3 is connected between the node of the resistors R1 and R2 and the ground.

7. A weak magnetic field detection device based on magnetic field regulation technology according to claim 5, characterized in that The output end of the operational amplifier is connected to the output port P3 to output a filtered signal.

8. A weak magnetic field detection device based on magnetic field regulation technology according to claim 7, characterized in that The second-order filter circuit is also connected to an adder circuit to provide a DC bias for the output signal for the acquisition of the output signal.

9. A weak magnetic field detection device based on magnetic field regulation technology according to claim 8, characterized in that The adder circuit includes a resistor R12, a resistor R11, a power supply VCC, and a capacitor C6. The power supply VCC is connected to the output end OUT through the resistor R12 to provide voltage for the circuit. One end of the capacitor C6 is connected to the output port P3 to receive the input signal; the other end is connected to the ground through the resistor R11 to form a discharge loop of the capacitor. The output end OUT is led out from the connection point of the resistor R12 and the capacitor C6.

10. A detection method for a weak magnetic field detection device based on magnetic field regulation technology, characterized in that, The weak magnetic field detection circuit based on magnetic field regulation according to any one of claims 1 to 9 includes: Placing the magnetoelectric probe in the magnetic field to be measured, and the detection process corresponds to two externally applied components, a low-frequency magnetic field to be measured and an excitation magnetic field; Starting the signal generation circuit, and the power amplifier circuit simultaneously provides a reference signal and an excitation signal for the lock-in amplifier circuit and the magnetoelectric probe; The signal to be measured and the reference signal are respectively input from the P1 terminal and the P2 terminal. The AD630 chip modulates the mixed waveform. The frequency of the target waveform is within the range of 0 - 200 Hz. The output signal of the phase-locked amplifier circuit needs to pass through a second-order low-pass filter circuit to filter out the high-frequency components in the output signal to obtain the required waveform.

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