A magnetic field sensor

Abstract

The application belongs to the technical field of magnetotelluric sounding systems, and specifically discloses a magnetic field sensor, wherein the chopper frequency is set to be outside the working bandwidth, and then the chopper residual interference is filtered out through a low-frequency channel chopper low-noise amplification module and a low-frequency channel low-pass filter, so that the problem that the existing magnetic field sensor is only limited to be applied to a low-frequency band and a high-frequency band, or the problem that although the working frequency band is wide, high-frequency signals and low-frequency signals cannot be collected simultaneously is solved, and high-frequency signals and low-frequency signals of a wide-frequency-band magnetic field sensor are collected simultaneously.

Description

Technical Field

[0001] This application belongs to the technical field of magnetotelluric detection systems, and more specifically, relates to a magnetic field sensor. Background Technology

[0002] In the field of magnetotelluric exploration, magnetic field sensors need to be calibrated before field data acquisition to determine if they are functioning correctly and to obtain accurate phase and amplitude frequency data. This facilitates accurate calculations during subsequent data processing. Calibration tests are typically conducted using magnetically shielded Helmholtz coils or in environments with minimal field interference. Furthermore, current magnetic field sensors often suffer from operating frequency band limitations due to low-frequency 1 / f noise from amplifiers, limiting their ability to acquire both low-frequency (below 100Hz) and high-frequency (above 100Hz) signals separately. While using magnetic field sensors with different operating frequency bands to acquire high and low frequency signals, or switching operating modes of broadband magnetic field sensors to acquire high and low frequency signals, neither approach allows for simultaneous acquisition of both high and low frequency signals from a single broadband magnetic field sensor, resulting in low efficiency. Utility Model Content

[0003] In view of the shortcomings of the prior art, the purpose of this application is to provide a magnetic field sensor, which aims to solve the problem that the prior art usually uses magnetic field sensors with different operating frequency bands to collect high and low frequency signals, or uses a wideband magnetic field sensor to switch operating modes to collect high and low frequency signals, neither of which can achieve simultaneous collection of high and low frequency signals by a single wideband magnetic field sensor, resulting in low working efficiency.

[0004] The first aspect of this application relates to a magnetic field sensor, comprising: a magnetic core induction main coil module, a high-frequency channel low-noise amplification module, a DC blocking compensation capacitor, a chopper modulation carrier module, a low-frequency channel chopper low-noise amplification module, a low-frequency channel low-pass filter, a high- and low-frequency channel adder amplifier circuit, a magnetic core feedback coil circuit module, a first single-pole double-throw switch, a second single-pole double-throw switch, and a third single-pole double-throw switch. The output of the core-induction main coil module is connected to the high-frequency channel low-noise amplifier module and the low-frequency channel chopper low-noise module; the input of the low-frequency channel chopper low-noise amplifier module is also connected to the chopper modulation carrier module; the other input of the high-frequency channel low-noise amplifier module is equipped with a third single-pole double-throw switch to switch between the normally closed state and the chopper modulation carrier module; the first output of the high-frequency channel low-noise amplifier module is directly connected to the normally closed end of the first single-pole double-throw switch, and the other output is connected to the other end of the first single-pole double-throw switch through a DC blocking compensation capacitor; the output of the low-frequency channel chopper low-noise amplifier module is connected to the low-frequency channel low-pass filter, the output of the low-frequency channel low-pass filter is connected to one end of the second single-pole double-throw switch, the other end of the second single-pole double-throw switch is connected to the normally closed end, the input of the high- and low-frequency channel adder amplifier circuit is connected to the first single-pole double-throw switch and the second single-pole double-throw switch, its output is connected to the core-induction feedback coil circuit module, and the output of the core-induction feedback coil circuit module is connected to the input of the core-induction main coil module; The chopping frequency in the low-frequency channel chopper low-noise amplifier module is set outside the operating bandwidth.

[0005] In some implementations, when the magnetic field sensor is used to amplify high-frequency signals, the first single-pole double-throw switch, the second single-pole double-throw switch, and the third single-pole double-throw switch are in normally closed positions, and the magnetic core induction main coil module, the high-frequency channel low-noise amplification module, the first single-pole double-throw switch, the high- and low-frequency channel adder amplification circuit, and the magnetic core feedback coil circuit module are connected in series.

[0006] In some implementations, when the magnetic field sensor is used to amplify low-frequency signals, the output of the core-loaded induction main coil module is simultaneously connected to both a high-frequency channel low-noise amplification module and a low-frequency channel chopper low-noise amplification module. The input of the high-frequency channel low-noise amplification module is connected to a chopper modulation carrier module, and its output is connected in series with a DC blocking compensation capacitor. The low-frequency channel chopper low-noise amplification module and the low-frequency channel low-pass filter are connected in series sequentially. The outputs of the DC blocking compensation capacitor and the low-frequency channel low-pass filter are respectively connected to the high- and low-frequency channel adder amplification circuits via a first single-pole double-throw switch and a second single-pole double-throw switch. The output of the high- and low-frequency channel adder amplification circuit is connected to the core-loaded feedback coil circuit module.

[0007] In some implementations, the chopping frequency in the low-frequency channel chopping low-noise amplifier module is set to 20kHz; the frequency of the high-frequency signal is above 100Hz; and the frequency of the low-frequency signal is 0.001Hz to 100Hz.

[0008] In some embodiments, the magnetic core induction main coil module and the magnetic core feedback coil circuit module of the magnetic field sensor are installed in the middle cylinder. The middle cylinder is provided with a shielding copper foil, and calibration coils are evenly distributed on the shielding copper foil. The coils are in the shape of a solenoid. A memory with calibration data is provided on the circuit board inside the magnetic field sensor.

[0009] In some implementations, the chopper modulation carrier module includes an analog electronic switch and a field-effect transistor. A CLK square wave signal is applied to the four input control terminals of the analog electronic switch. The analog electronic switch is used for different switching to modulate the input signal into a high-frequency signal with the CLK square wave signal as the carrier. The field-effect transistor is used to amplify the signal output by the analog electronic switch.

[0010] In some implementations, the low-frequency channel chopper low-noise amplifier module includes a low-noise amplifier circuit and a chopper demodulation circuit connected in sequence. The low-noise amplifier circuit is connected to the chopper modulation carrier module. The low-noise amplifier circuit includes a DC blocking capacitor, a first amplifier, a second amplifier, and a high-pass filter connected in sequence. The input of the chopper demodulation circuit is connected to the chopper modulation carrier module for chopper demodulation and chopper noise cancellation.

[0011] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art: The magnetic field sensor provided in this application eliminates the need for switching between high and low frequency operating modes, and features simultaneous high and low frequency operation. Similarly, to avoid the influence of low-frequency 1 / f noise from the amplifier on weak low-frequency signals, a low-frequency channel chopper low-noise amplification module is used to modulate the low-frequency signal to a high-frequency band (20kHz) before amplification, which can effectively reduce the influence of low-frequency 1 / f noise from the amplifier. At the same time, after chopper amplification, a chopper demodulation circuit is added to simultaneously demodulate the signal and separate the signal from the chopper modulated carrier signal, eliminating some residual chopper noise. Finally, a 20kHz active low-pass filter circuit further filters out the 20kHz residual chopper noise, resulting in extremely low noise in the magnetic sensor operating frequency band from 0.001Hz to 10kHz. Attached Figure Description

[0012] Figure 1 This is a block diagram illustrating the high-frequency working principle of the magnetic field sensor provided in the embodiments of this application.

[0013] Figure 2 This is a block diagram illustrating the low-frequency working principle of the magnetic field sensor provided in this application embodiment.

[0014] Figure 3 This is a circuit diagram of an adder for switching between high and low frequencies provided in an embodiment of this application.

[0015] Figure 4 This is a block diagram of the principle of the wideband magnetic field sensor chopper amplifier circuit provided in the embodiments of this application.

[0016] Figure 5 This is a schematic diagram of the chopper modulation carrier module provided in the embodiments of this application.

[0017] Figure 6 This is a schematic diagram of the modulated low-noise amplifier circuit provided in the embodiments of this application.

[0018] Figure 7 This is a schematic diagram of the chopper demodulation circuit provided in the embodiments of this application.

[0019] Figure 8 This is a schematic diagram of a second-order active filter circuit provided in an embodiment of this application.

[0020] Figure 9 This is a schematic diagram of the independent calibration coil of the magnetic sensor provided in the embodiments of this application.

[0021] Figure 10 This is a schematic diagram of magnetic sensor calibration data storage and retrieval provided in an embodiment of this application. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A existing alone, A and B existing simultaneously, and B existing alone. In this application, the symbol " / " indicates that the related objects are in an "or" relationship, for example, A / B means A or B.

[0024] In this application, the terms “first” and “second” are used to distinguish different objects, rather than to describe a specific order of objects.

[0025] In this application, the term "electrical connection" can refer to a direct circuit connection or a signal transmission via a communication protocol.

[0026] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0027] In the description of the embodiments in this application, unless otherwise stated, "multiple" means two or more.

[0028] The embodiments of this application are described below with reference to the accompanying drawings.

[0029] This application provides a broadband low-noise magnetic field sensor. The chopping frequency is set outside the operating bandwidth (20kHz), and residual chopping interference is filtered out by a low-frequency channel chopping low-noise amplification module and a low-frequency channel low-pass filter. This solves the problem that existing magnetic field sensors are limited to low-frequency or high-frequency bands, or that although the operating frequency band is wide, they cannot simultaneously acquire high and low frequency signals. This enables the simultaneous acquisition of high and low frequency signals (operating frequency band 0.001Hz~10kHz) by a single broadband magnetic field sensor. It also has the functions of storing and retrieving magnetic field sensor factory calibration data and comparing on-site calibration data, thus improving the efficiency of construction work.

[0030] The block diagram of the magnetic field sensor in this application is as follows: Figure 1 and Figure 2 As shown, when amplifying high-frequency signals (above 100Hz), the single-pole double-throw switches (K1, K2, K3) are in the normally closed contact state. The corresponding circuit includes a magnetic core induction main coil module, a high-frequency channel low-noise amplification module, a single-pole double-throw switch (K1), a high- and low-frequency channel adder amplifier circuit, and a magnetic core feedback coil circuit module connected in series. Figure 1 The working principle block diagram is shown. At this time, the signal is in the direct amplification state. Although the low-frequency signal can also be amplified and output through this channel, due to the low-frequency 1 / f noise that is common in amplifiers, the low-frequency signal is invalid and the data is unusable. At this time, only high-frequency data (above 100Hz) is available.

[0031] When amplifying low-frequency signals (0.001Hz~100Hz), amplifiers generally exhibit low-frequency 1 / f noise, which is relatively large compared to the weak effective signal. Amplifiers, however, have relatively low noise when operating in the high-frequency band. Utilizing this characteristic, the influence of the amplifier's low-frequency 1 / f noise on weak low-frequency signals can be avoided. A low-frequency channel chopper low-noise amplification module modulates the low-frequency signal to the high-frequency band (2kHz) before amplification, effectively reducing the impact of the amplifier's low-frequency 1 / f noise. In this operating state, the corresponding circuit configuration involves simultaneously feeding the output of the core-loaded induction coil module into both the high-frequency amplification channel low-noise amplification module and the low-frequency channel chopper low-noise amplification module. Simultaneously, an inverted chopper-modulated carrier signal is added to the high-frequency amplification channel and connected in series with the DC blocking compensation capacitor. The low-frequency channel chopper low-noise amplification module and the low-frequency channel low-pass filter are connected in series sequentially. The outputs of the DC blocking compensation capacitor and the low-frequency channel low-pass filter are simultaneously fed into the high- and low-frequency channel adder amplification circuits via relays. Figure 3As shown, the output of the high- and low-frequency channel adder amplifier circuit is connected to a circuit module with a magnetic core feedback coil; through the dual-channel working mode, the low-frequency signal is effectively amplified and the residual noise of the chopper is eliminated.

[0032] The magnetic field sensor provided in this application eliminates the need for switching between high and low frequency operating modes, and features simultaneous high and low frequency operation. Similarly, to avoid the influence of low-frequency 1 / f noise from the amplifier on weak low-frequency signals, a low-frequency channel chopper low-noise amplification module is used to modulate the low-frequency signal to a high-frequency band (20kHz) before amplification, which can effectively reduce the influence of low-frequency 1 / f noise from the amplifier. At the same time, after chopper amplification, a chopper demodulation circuit is added to simultaneously demodulate the signal and separate the signal from the chopper modulated carrier signal, eliminating some residual chopper noise. Finally, a 20kHz active low-pass filter circuit further filters out the 20kHz residual chopper noise, resulting in extremely low noise in the magnetic sensor operating frequency band from 0.001Hz to 10kHz.

[0033] like Figure 4 As shown, inside the magnetic field sensor, a calibration coil with 10-30 turns is evenly distributed along the length of the magnetic core on the shielding copper foil. The coil is solenoid-shaped. The calibration voltage signal emitted by the magnetotelluric receiver generates a current in the calibration coil inside the magnetic field sensor. The current flowing through the solenoid calibration coil generates a magnetic field inside the magnetic field sensor. The magnitude of the magnetic field is determined by the magnitude of the current in the calibration coil. The magnetic field sensor generates a voltage signal by sensing this magnetic field signal and sends it to the magnetotelluric receiver. The magnetotelluric receiver uses the collected voltage signal to calculate the amplitude and phase of the magnetic field sensor. By collecting calibration magnetic field signals at different frequencies, the amplitude of the magnetic field sensor over the entire broadband can be calculated.

[0034] like Figure 5 As shown, the chopper modulation carrier module is specifically as follows: the differential signal of the induction coil is modulated by the analog electronic switch ADG453. The modulation principle is to apply a 20kHz CLK square wave signal to the four input control terminals of the electronic switch ADG453. When the square wave is at a high or low level, the electronic switch switches continuously. At this time, the input signals IN+ and IN- are modulated into a high-frequency signal with the 20kHz CLK square wave signal as the carrier. The input signal is modulated to 20kHz and then sent to the field-effect transistor Q1 for amplification, outputting OUT1+ and OUT1- differential output signals, thus avoiding the 1 / f noise effect of the field-effect transistor at low frequencies of tens of Hz. The low-frequency channel chopper low-noise amplifier module includes: a low-noise amplifier circuit and a chopper demodulation circuit; like Figure 6The circuit shown is a low-noise amplifier circuit after modulation. Specifically, the signals OUT1+ and OUT1- after chopping modulation are filtered out for low-frequency interference by DC blocking capacitors C3 and C4, and then sent to amplifier U4A for amplification. The amplification factor is 82 times. At the same time, the amplified signals are inverted by U4B and converted into differential signals OUT2+ and OUT2- again. The signals are then further filtered out for low-frequency interference signals by high-pass filters composed of C10, R18 and C11, R20. Figure 7 The chopper demodulation circuit provided in this application embodiment has differential OUT2+ and OUT2 synchronously demodulated by electronic switch U5 controlled by a 20kHz CLK square wave signal to restore the original input signal. At this time, there are still chopper residual components in the signal. In a set of switches, an inverted 20kHz CLK square wave signal CLK- is added to the demodulated signal, which is opposite in phase to the chopper residual signal of the demodulated signal, which can cancel some of the chopper noise. The demodulated signal after canceling the chopper noise is amplified again by 4.7 times by U6A, and the output signal OUT3 is output. Figure 8 The modulated, restored, and noise-cancelled signal OUT3 is passed through a second-order low-pass filter (10kHz low-pass) to further filter out the residual chopping components of 20kHz, so that the magnetic sensor has extremely low noise in the range of 0.001Hz to 10kHz. This enables a single magnetic sensor to work simultaneously in the range of 0.001Hz to 10kHz without switching operating modes.

[0035] like Figure 9 and Figure 10 As shown, the magnetic field sensor receiving coil and magnetic core are installed inside the middle cylinder. The middle cylinder is covered with shielding copper foil. Above the copper foil, 10-30 turns of calibration coil are evenly distributed along the coil's length. The coil is solenoid-shaped. The calibration voltage signal emitted by the magnetotelluric receiver generates a current in the calibration coil inside the magnetic field sensor. This current flowing through the solenoid calibration coil generates a magnetic field inside the sensor. The magnitude of the magnetic field is determined by the magnitude of the current in the calibration coil. The magnetic field sensor generates a voltage signal by sensing this magnetic field signal and sends it to the magnetotelluric receiver. The magnetotelluric receiver uses the acquired voltage signal to calculate the amplitude and phase of the magnetic field sensor. By acquiring calibration magnetic field signals of different frequency components, the amplitude and phase of the magnetic field sensor over the entire bandwidth can be calculated. The internal circuit board of the magnetic field sensor has a calibration data memory, storing the factory calibration data (amplitude and phase). After recalibration testing, the magnetotelluric receiver... The interface can read the factory calibration data of the magnetic field sensor in this internal memory and compare it with the field calibration test value to determine whether the magnetic field sensor is working properly or whether its characteristic curve has changed, providing a basis for judgment for the next step.

[0036] It should be understood that expressions such as “comprising” and “may include” used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as “comprising” and / or “having” are to be interpreted as indicating a particular characteristic, number, operation, constituent element, component, or combination thereof, but not to exclude the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0037] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. The directional terms mentioned in the embodiments of this application, such as "top," "bottom," "inner," "outer," "left," and "right," are only for reference to the directions in the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of this application, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0038] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A magnetic field sensor, characterized in that, include: The circuit includes a magnetic core induction main coil module, a high-frequency channel low-noise amplifier module, a DC blocking compensation capacitor, a chopper modulation carrier module, a low-frequency channel chopper low-noise amplifier module, a low-frequency channel low-pass filter, a high- and low-frequency channel adder amplifier circuit, a magnetic core feedback coil circuit module, a first single-pole double-throw switch, a second single-pole double-throw switch, and a third single-pole double-throw switch. The output of the core-induction main coil module is connected to the high-frequency channel low-noise amplifier module and the low-frequency channel chopper low-noise module; the other input of the low-frequency channel chopper low-noise amplifier module is connected to the chopper modulation carrier module; the other input of the high-frequency channel low-noise amplifier module is equipped with a third single-pole double-throw switch to switch between the normally closed state and the chopper modulation carrier module; the first output of the high-frequency channel low-noise amplifier module is directly connected to the normally closed end of the first single-pole double-throw switch, and the other output is connected to the other end of the first single-pole double-throw switch through a DC blocking compensation capacitor; the output of the low-frequency channel chopper low-noise amplifier module is connected to the low-frequency channel low-pass filter, the output of the low-frequency channel low-pass filter is connected to one end of the second single-pole double-throw switch, the other end of the second single-pole double-throw switch is connected to the normally closed end; the input of the high- and low-frequency channel adder amplifier circuit is connected to the first single-pole double-throw switch and the second single-pole double-throw switch, and its output is connected to the core-induction feedback coil circuit module; the output of the core-induction feedback coil circuit module is connected to the input of the core-induction main coil module. The chopping frequency in the low-frequency channel chopper low-noise amplifier module is set outside the operating bandwidth.

2. The magnetic field sensor according to claim 1, characterized in that, When the magnetic field sensor is used to amplify high-frequency signals, the first single-pole double-throw switch, the second single-pole double-throw switch, and the third single-pole double-throw switch are in the normally closed position. The main coil module with magnetic core induction, the high-frequency channel low-noise amplification module, the first single-pole double-throw switch, the high- and low-frequency channel adder amplification circuit, and the feedback coil circuit module with magnetic core are connected in series.

3. The magnetic field sensor according to claim 1, characterized in that, When the magnetic field sensor is used to amplify low-frequency signals, the output of the magnetic core induction main coil module is simultaneously connected to both the high-frequency channel low-noise amplification module and the low-frequency channel chopper low-noise amplification module. The input of the high-frequency channel low-noise amplification module is connected to the chopper modulation carrier module, and its output is connected in series with a DC blocking compensation capacitor. The low-frequency channel chopper low-noise amplification module and the low-frequency channel low-pass filter are connected in series in sequence. The outputs of the DC blocking compensation capacitor and the low-frequency channel low-pass filter are connected to the high- and low-frequency channel adder amplification circuits through a first single-pole double-throw switch and a second single-pole double-throw switch, respectively. The output of the high- and low-frequency channel adder amplification circuit is connected to the magnetic core feedback coil circuit module.

4. The magnetic field sensor according to any one of claims 1 to 3, characterized in that, The magnetic field sensor has a magnetic core induction main coil module and a magnetic core feedback coil circuit module installed in the middle cylinder. The middle cylinder is covered with shielding copper foil, and calibration coils are evenly distributed on the shielding copper foil. The coils are in the shape of solenoids. A memory with calibration data is set on the circuit board inside the magnetic field sensor.

5. The magnetic field sensor according to claim 1, characterized in that, The chopper modulation carrier module includes an analog electronic switch and a field-effect transistor. A CLK square wave signal is applied to the four input control terminals of the analog electronic switch. The analog electronic switch is used for different switching to modulate the input signal into a high-frequency signal with the CLK square wave signal as the carrier. The field-effect transistor is used to amplify the signal output by the analog electronic switch.

6. The magnetic field sensor according to claim 1 or 5, characterized in that, The low-frequency channel chopper low-noise amplifier module includes a low-noise amplifier circuit and a chopper demodulation circuit connected in sequence. The low-noise amplifier circuit is connected to the chopper modulation carrier module. The low-noise amplifier circuit includes a DC blocking capacitor, a first amplifier, a second amplifier, and a high-pass filter connected in sequence. The input of the chopper demodulation circuit is connected to the chopper modulation carrier module for chopper demodulation and chopper noise cancellation.

7. The magnetic field sensor according to claim 3, characterized in that, The chopping frequency in the low-frequency channel chopper low-noise amplifier module is set to 20kHz; the frequency of the low-frequency signal is 0.001Hz~100Hz.

8. The magnetic field sensor according to claim 2, characterized in that, The chopping frequency in the low-frequency channel chopper low-noise amplifier module is set to 20kHz; the frequency of the high-frequency signal is above 100Hz.

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