A real-time active noise reduction device and method for ground magnetic resonance

Abstract

The present application belongs to the field of geophysical exploration technology, and is a real-time active noise reduction device and method for ground magnetic resonance, comprising: a detection coil for collecting nuclear magnetic signals after noise cancellation; a reference coil for collecting environmental noise, coplanar with the detection coil and placed at a position away from the detection coil; a noise cancellation coil, placed overlappingly above the detection coil; an FPGA module for receiving the nuclear magnetic signals after noise cancellation collected by the detection coil and the environmental noise collected by the reference coil, and according to the environmental noise, passing a corresponding changing current into the noise cancellation coil, thereby generating a changing magnetic field, so that the detection coil induces a cancellation response with the same amplitude and opposite phase as its own noise. The present application can suppress noise in real time at the instrument source end, significantly enhancing the anti-interference and weak signal detection capabilities of the ground magnetic resonance instrument in complex electromagnetic environments.

Description

Technical Field

[0001] The present application belongs to the field of geophysical exploration technology and is a ground magnetic resonance real-time active noise reduction device and method. Background Art

[0002] Ground magnetic resonance (GMR) technology is a non-invasive geophysical method for directly and quantitatively detecting groundwater and assessing pore size distribution. It has been widely used in hydrogeological exploration. However, GMR signals are extremely weak, typically only in the nanovolt range, and are highly susceptible to interference from electromagnetic noise. In tunnels, mines, and urban environments, MRI signals can be overwhelmed by power frequency harmonics, leading to data saturation and distortion.

[0003] In order to achieve noise reduction, existing research uses multiple reference coils and front-end processing modules, which significantly increases the complexity of the instrument equipment. The huge amount of data is also not conducive to real-time noise reduction of the data.

[0004] Other studies have constructed a time-frequency image by performing a short-time Fourier transform on noisy data, iteratively updating the time-frequency image using a manifold dimension-constrained optimization equation, and then using the inverse short-time Fourier transform to denoise the image to obtain a pure signal after noise removal. However, this method still uses conventional post-data acquisition software processing to denoise the data, and cannot suppress noise in real time at the instrument source, making it difficult to increase the amplification factor of the instrument's collected data. Summary of the Invention

[0005] The present application provides a real-time active noise reduction device and method for ground magnetic resonance, which solves the problem that a cancellation response cannot be generated at the instrument source end to suppress electromagnetic noise in real time.

[0006] The present invention provides a real-time active noise reduction device for terrestrial magnetic resonance imaging, which includes:

[0007] Detection coil, used to collect nuclear magnetic field signals after noise cancellation;

[0008] A reference coil, used for collecting environmental noise, is coplanar with the detection coil and is placed away from the detection coil;

[0009] The noise cancellation coil is placed overlapping on top of the detection coil;

[0010] The FPGA module is used to receive the noise-canceled nuclear magnetic field signal collected by the detection coil and the environmental noise collected by the reference coil. Based on the environmental noise, a corresponding current is passed into the noise cancellation coil, thereby generating a changing magnetic field, so that the detection coil induces a cancellation response with the same amplitude and opposite phase as its own noise.

[0011] Furthermore, the FPGA module uses the ambient noise as the input signal of the adaptive filter and the nuclear magnetic signal after noise cancellation as the error signal to minimize the error, and updates the coefficient of the adaptive filter. The output signal of the adaptive filter is converted into a driving voltage value and transmitted to the DA digital-to-analog conversion module in real time. The DA digital-to-analog conversion module drives the voltage-controlled current source module to pass current in the noise cancellation coil according to the driving voltage value.

[0012] Furthermore, the adaptive filter obtains an output signal by multiplying a transposed signal of the filter coefficient with the minimum error by the input signal.

[0013] Furthermore, converting the output signal of the adaptive filter into a driving voltage value includes:

[0014] Calculate the mutual inductance between the noise cancellation coil and the detection coil;

[0015] According to the output signal of the adaptive filter, the mutual inductance coefficient and The current value at the moment is used to calculate the noise cancellation coil Current value at the moment;

[0016] according to The driving voltage value is calculated based on the current value at that moment.

[0017] Furthermore, according to the output signal of the adaptive filter, the mutual inductance coefficient and The current value at the moment is used to calculate the noise cancellation coil The current value at the moment is expressed as:

[0018] ,

[0019] in, for The current value output to the noise cancellation coil at any moment, for The current value output to the noise cancellation coil at any moment, is the output signal of the adaptive filter, is the mutual inductance coefficient, is the data sampling rate.

[0020] Furthermore, the detection coil and the reference coil are connected to the multi-channel AD synchronous acquisition module through their respective signal conditioning modules. The FPGA module is connected to the host computer. After receiving the synchronization signal generated by the host computer, it controls the multi-channel AD synchronous acquisition module to synchronously acquire the nuclear magnetic signal and environmental noise after noise cancellation.

[0021] A real-time active noise reduction method for ground magnetic resonance imaging, comprising:

[0022] Arrange a detection coil, a reference coil, and a noise cancellation coil, overlap the noise cancellation coil and place it above the detection coil, and place the reference coil in the same plane as the detection coil and away from the detection coil;

[0023] The nuclear magnetic field signal after noise cancellation is collected through the detection coil;

[0024] Ambient noise is collected through a reference coil;

[0025] According to the environmental noise, a corresponding changing current is passed into the noise cancellation coil, thereby generating a changing magnetic field, which induces a cancellation response in the detection coil with the same amplitude and opposite phase as the self-noise.

[0026] Furthermore, according to the ambient noise, a correspondingly changing current is supplied to the noise cancellation coil, including:

[0027] The ambient noise is used as the input signal of the adaptive filter, and the nuclear magnetic signal after noise cancellation is used as the error signal to minimize the error, and the coefficient of the adaptive filter is updated. The output signal of the adaptive filter is converted into a driving voltage value and transmitted to the DA digital-to-analog conversion module in real time. The DA digital-to-analog conversion module drives the voltage-controlled current source module according to the driving voltage value to pass current in the noise cancellation coil.

[0028] Furthermore, the output signal of the adaptive filter is obtained by multiplying the transposed signal of the filter coefficient when the error is minimized by the input signal.

[0029] Furthermore, converting the output signal of the adaptive filter into a driving voltage value includes:

[0030] Calculate the mutual inductance between the noise cancellation coil and the detection coil;

[0031] According to the output signal of the adaptive filter, the mutual inductance coefficient and The current value at the moment is used to calculate the noise cancellation coil Current value at the moment;

[0032] according to The driving voltage value is calculated based on the current value at that moment.

[0033] Compared with the existing technology, the present application has the following beneficial effects: the present application can suppress noise in real time at the instrument source end, significantly enhancing the anti-interference and weak signal detection capabilities of the ground magnetic resonance instrument in complex electromagnetic environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a structural block diagram of a ground magnetic resonance real-time active noise reduction device provided in an embodiment of the present application;

[0035] Figure 2 A diagram showing the relationship between the field installation positions of the detection coil, reference coil, and noise cancellation coil provided in an embodiment of the present application;

[0036] Figure 3 2 is a comparison of the denoising results in the embodiment of the present application, where (a) is a time domain image of the original data and the denoised data, and (b) is a frequency domain image of the original data and the denoised data. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0038] Conventional ground-based magnetic resonance receiving systems must be used in conjunction with a transmitting system. After the transmitting system transmits current through the transmitting coil, the receiving system is started synchronously to collect nuclear magnetic resonance signals through the receiving coil or detection coil.

[0039] The embodiment of the present application realizes noise reduction at the instrument source end, that is, the acquisition end of the receiving system realizes that the collected nuclear magnetic resonance signal is a signal without environmental noise.

[0040] See also Figure 1 The structural block diagram of a ground magnetic resonance real-time active noise reduction device is shown in FIG. Figure 2 A diagram showing the relationship between the field placement positions of the detection coil, reference coil, and noise cancellation coil. A ground magnetic resonance real-time active noise reduction device includes:

[0041] The detection coil, the reference coil, and the noise cancellation coil, the detection coil is the receiving coil, and the reference coil can be set as one or more. When multiple reference coils are set, one of them serves as the main reference coil, and the signals received by the other reference coils serve as the reference signals of the main reference coil. Different from the detection coil and the reference coil in the existing structure, the embodiment of the present application also provides a noise cancellation coil. The shapes of the detection coil, the reference coil, and the noise cancellation coil can be the same or different, and can be, but not limited to, rectangular, circular, and elliptical. However, the detection coil, the reference coil, and the noise cancellation coil must meet the requirement that the noise cancellation coil is placed overlappingly above the detection coil, that is, the noise cancellation coil and the detection coil belong to planes at different heights, and the planes where the two coils are located are arranged in parallel. The size of the noise cancellation coil and the detection coil can be the same or different. Preferably, the size of the noise cancellation coil is equal to the size of the detection coil. The size of the noise cancellation coil can also be set to be smaller than the size of the detection coil, so that the projection of the noise cancellation coil on the ground is located within the projection of the detection coil on the ground. The reference coil is set in the same plane as the detection coil and placed at a position far away from the detection coil, so that the reference coil only receives environmental noise but cannot receive nuclear magnetic signals. Therefore, this distance needs to be continuously tried and adjusted, or simulated to obtain an optimal distance. Without affecting the measurement effect, the closest distance between the reference coil and the detection coil is greater than the largest dimension of the detection coil. For example, when the detection coil is a square, the closest distance between the reference coil and the detection coil is approximately the side length of the detection coil. When the detection coil is a circle, the closest distance between the reference coil and the detection coil is approximately the diameter of the detection coil.

[0042] The detection coil is used to collect nuclear magnetic signals during the detection process. It can be understood that without denoising, the nuclear magnetic signals collected by the detection coil include pure nuclear magnetic signals and a large amount of environmental noise; it can also be understood that in the case of denoising in this application, the nuclear magnetic signals here are almost the same as the pure nuclear magnetic signals.

[0043] The reference coil is used to collect ambient noise. Based on its position, it's understood that it only collects ambient noise, not NMR signals. However, this isn't always the case. Some weak NMR signals may be introduced into the reference coil, but this is acceptable within the acceptable error range and doesn't affect calculation accuracy.

[0044] A module for receiving signals, transmitting signals, and performing signal processing is also required. In the embodiment of the present application, an FPGA module is selected to receive the nuclear magnetic field signal collected by the detection coil after noise cancellation and the environmental noise collected by the reference coil. A corresponding current is passed into the noise cancellation coil according to the environmental noise, thereby generating a changing magnetic field, so that the detection coil induces a cancellation response with the same amplitude and opposite phase as its own noise.

[0045] The principle of the above structure of the embodiment of the present application is that if the noise cancellation coil is not provided, the nuclear magnetic field signal with environmental noise is received by the detection coil, while the environmental noise is received by the reference coil. The conventional processing method is to remove the environmental noise from the nuclear magnetic field signal with environmental noise in a subsequent step. This process can be performed by, for example, a method based on wavelet transform, a method based on multilinear singular value tensor decomposition, and a method based on machine learning, etc., but it will increase the subsequent computational complexity. The embodiment of the present application processes the environmental noise of the reference coil at the instrument source end and converts it into an equivalent cancellation response. The cancellation response has the same amplitude and opposite phase as the environmental noise. The noise cancellation coil acts on the acquisition space where the detection coil is located, and the cancellation response is used to cancel the cancellation response with environmental noise. In fact, at this time, the nuclear magnetic field signal received by the detection coil is equivalent to a pure nuclear magnetic field signal.

[0046] In one embodiment, the FPGA module uses the ambient noise as the input signal of the adaptive filter and the nuclear magnetic field signal after noise cancellation as the error to minimize the error, and updates the coefficient of the adaptive filter. The output signal of the adaptive filter is converted into a driving voltage value and transmitted to the DA digital-to-analog conversion module in real time. The DA digital-to-analog conversion module drives the voltage-controlled current source module to pass current into the noise cancellation coil according to the driving voltage value.

[0047] The adaptive filter is implemented through an adaptive filtering algorithm and is integrated into the FPGA module through programming. The core idea of ​​the adaptive filter is to continuously adjust the parameters of the adaptive filter so that the output of the adaptive filter is as close as possible to the desired signal while minimizing the error signal.

[0048] Without a noise cancellation coil, the detection coil collects noisy NMR signals. However, during operation, the noise cancellation coil already flows with current, which may not be optimal. The adaptive filter ultimately outputs an optimal current, thereby minimizing the noise in the detection coil. During this process, the detection coil output signal received by the adaptive filter is actually a noise-canceled NMR signal, representing the error required by the adaptive filter. The adaptive filter minimizes this error.

[0049] In this embodiment, the adaptive filter first sets the adaptive filter length, filter coefficient, and step factor, and uses the nuclear magnetic signal after canceling the noise in the detection coil as the adaptive filter. The error signal at the moment; the ambient noise collected by the reference coil is the adaptive filter The input signal at time and several previous times; update the adaptive filter coefficients to minimize the error signal; multiply the transposed signal of the filter coefficient with the minimum error and the input signal to obtain Output signal at the moment.

[0050] This output signal is used to control the current in the noise cancellation coil, generating a cancellation response in the detection coil to cancel the ambient noise in the nuclear magnetic signal in the detection coil.

[0051] The output signal of the adaptive filter needs to be converted into a driving voltage value to drive the noise cancellation coil to generate a corresponding current. This includes:

[0052] Calculate the mutual inductance between the noise cancellation coil and the detection coil;

[0053] According to the output signal of the adaptive filter, the mutual inductance coefficient and The current value at the moment is used to calculate the noise cancellation coil Current value at the moment;

[0054] according to The driving voltage value is calculated based on the current value at that moment.

[0055] According to the output signal of the adaptive filter, the mutual inductance coefficient and The current value at the moment is used to calculate the noise cancellation coil The calculation formula of the current value at the moment is expressed as:

[0056] ,

[0057] in, for The current value output to the noise cancellation coil at any moment, for The current value output to the noise cancellation coil at any moment, is the output signal of the adaptive filter, is the mutual inductance coefficient, is the data sampling rate.

[0058] The design process of the calculation formula is as follows:

[0059] Based on the finite element method analysis, the coupling relationship between the noise cancellation coil and the detection coil can be obtained. According to the coupling relationship between the two coils, the mutual inductance coefficient between the two coils can be calculated.

[0060] If we assume that the coupling voltage between the noise cancellation coil and the detection coil is , the current flowing through the noise cancellation coil is , data sampling rate 30kHz, is time, and the following mutual induction relationship exists:

[0061] ,

[0062] Change the above differential equation into difference form:

[0063] ,

[0064] If the ambient noise in the detection coil is to be cancelled, the coupling voltage between the noise cancellation coil and the detection coil is used as the output signal of the adaptive filter, then:

[0065] ,

[0066] The ratio of the driving voltage value to the output current is , then the output signal of the adaptive filtering algorithm Corresponding driving voltage value for: .

[0067] In another embodiment, see Figure 1 As shown, a real-time active noise reduction device for terrestrial magnetic resonance imaging includes: a detection coil for collecting nuclear magnetic resonance signals after noise cancellation;

[0068] A reference coil, used for collecting environmental noise, is coplanar with the detection coil and is placed away from the detection coil;

[0069] The noise cancellation coil is placed overlapping on top of the detection coil;

[0070] The FPGA module is used to receive the noise-canceled nuclear magnetic field signal collected by the detection coil and the environmental noise collected by the reference coil. Based on the environmental noise, a corresponding current is passed into the noise cancellation coil, thereby generating a changing magnetic field, so that the detection coil induces a cancellation response with the same amplitude and opposite phase as its own noise.

[0071] The detection coil and reference coil are connected to the multi-channel AD synchronous acquisition module through their respective signal conditioning modules. The FPGA module is connected to the host computer through the data transmission module. After receiving the synchronization signal generated by the host computer, it controls the multi-channel AD synchronous acquisition module to synchronously acquire nuclear magnetic resonance signals and environmental noise.

[0072] The output end of the FPGA module is connected to the DA digital-to-analog conversion module, which generates a driving signal. The driving signal generates a current in the noise cancellation coil through the voltage-controlled current source module.

[0073] In a specific application, the detection coil, reference coil, and noise cancellation coil are all 10 turns and 4m square. The reference coil is laid 5m away from the detection coil, and the noise cancellation coil is laid 5cm above the detection coil.

[0074] The two signal conditioning modules both include a preamplifier and a bandpass filter, which are used to amplify and filter the nuclear magnetic signal and environmental noise respectively;

[0075] The noise cancellation coil is placed above the detection coil and is used to generate an electromagnetic field to cancel the environmental noise in the detection coil in real time;

[0076] The reference coil is used to obtain the ambient noise required as a reference for the adaptive filtering algorithm and to avoid collecting nuclear magnetic field signals;

[0077] After receiving the synchronization signal from the host computer, the FPGA module controls the multi-channel AD synchronous acquisition module to synchronously collect the nuclear magnetic field signal from the detection coil and the environmental noise from the reference coil. The FPGA module uses the collected environmental noise as the input signal of the adaptive filter. Based on the coupling relationship of the noise cancellation coil, the FPGA module converts the output signal of the adaptive filter into a driving voltage value, transmits it to the DA conversion module in real time, and updates the adaptive filter coefficients.

[0078] The voltage-controlled current source module receives the driving voltage signal output by the DA digital-to-analog conversion module and converts it into a linearly proportional driving current. The driving current is injected into the noise cancellation coil, generating a canceling magnetic field based on the principle of electromagnetic induction, and generating a cancellation response in the detection coil with the same amplitude and opposite phase as the ambient noise, thereby suppressing the ambient noise in the detection coil in real time.

[0079] The present application also provides a method for real-time active noise reduction of ground magnetic resonance based on the ground magnetic resonance real-time active noise reduction device in each of the above embodiments, based on the same denoising principle, including:

[0080] Arrange a detection coil, a reference coil, and a noise cancellation coil, overlap the noise cancellation coil and place it above the detection coil, and place the reference coil in the same plane as the detection coil and away from the detection coil;

[0081] The nuclear magnetic field signal after noise cancellation is collected through the detection coil;

[0082] Ambient noise is collected through a reference coil;

[0083] According to the environmental noise, a corresponding changing current is passed into the noise cancellation coil, thereby generating a changing magnetic field, which induces a cancellation response in the detection coil with the same amplitude and opposite phase as the self-noise.

[0084] In one embodiment, the current flowing into the noise cancellation coil according to the ambient noise includes:

[0085] The ambient noise is used as the input signal of the adaptive filter, and the output signal of the adaptive filter is converted into a driving voltage value and transmitted to the DA digital-to-analog conversion module in real time to update the adaptive filter coefficient. The voltage-controlled current source module is driven according to the driving voltage value to pass current into the noise cancellation coil.

[0086] In one embodiment, the adaptive filter uses the nuclear magnetic signal after canceling the noise in the detection coil as the adaptive filter. Error signal at the moment;

[0087] The ambient noise collected by the reference coil is an adaptive filter Input signals at time and several previous times;

[0088] Update the adaptive filter coefficients to minimize the error signal;

[0089] The product of the transposed signal of the filter coefficient with the minimum error and the input signal is obtained Output signal at the moment.

[0090] In one embodiment, converting the output signal of the adaptive filter into a driving voltage value includes:

[0091] Calculate the mutual inductance between the noise cancellation coil and the detection coil;

[0092] According to the output signal of the adaptive filter, the mutual inductance coefficient and The current value at the moment is used to calculate the noise cancellation coil Current value at the moment;

[0093] according to The driving voltage value is calculated based on the current value at that moment.

[0094] To facilitate understanding of the terrestrial magnetic resonance real-time active noise reduction method and the terrestrial magnetic resonance real-time active noise reduction device proposed in the embodiments of the present application, the embodiments of the present application provide a workflow of the terrestrial magnetic resonance real-time active noise reduction device, including:

[0095] Lay out a 10-turn, 4-meter square detection coil, a 10-turn, 4-meter square reference coil, and a 10-turn, 4-meter square noise cancellation coil. The reference coil is laid 5 meters from the detection coil, and the noise cancellation coil is laid 5 cm above the detection coil.

[0096] Power on the system and initialize each module;

[0097] The host computer sends a start synchronization command, and the multi-channel AD synchronization acquisition module synchronously acquires data from the detection coil and the reference coil;

[0098] The FPGA module uses the collected environmental noise as the input signal of the adaptive filter. According to the coupling relationship of the noise cancellation coil, the output signal of the adaptive filter is converted into a driving voltage value and transmitted to the DA digital-to-analog conversion module in real time, and the adaptive filter coefficient is updated.

[0099] The voltage-controlled current source module receives the driving voltage signal from the DA digital-to-analog conversion module, converts it into a linearly proportional driving current and injects it into the noise cancellation coil;

[0100] Based on the principle of electromagnetic induction, the noise cancellation coil generates a cancelling magnetic field;

[0101] The detection coil generates a cancellation response with the same amplitude and opposite phase as the ambient noise, which achieves real-time suppression of ambient noise and avoids magnetic resonance signal distortion, thus realizing active noise reduction at the source end.

[0102] The data transmission module uploads the data after active noise reduction in real time, and the host computer displays and stores the data in real time.

[0103] The data obtained can be found in Figure 3 As shown, Figure 3 (a) is the time domain image of the original data and the denoised data. Figure 3 Figure (b) shows frequency domain images of the original and denoised data. A comparison of the time domain images reveals that the noise amplitude is reduced by approximately 50% compared to the original signal after denoising. A comparison of the frequency domain images reveals that the noise energy of the 50Hz fundamental and its main harmonic components in the signal is significantly suppressed. Furthermore, while effectively eliminating power frequency interference, this active noise reduction system maintains the full amplitude-frequency characteristics of the measured signal, validating the system's superior performance in noise suppression and signal fidelity.

[0104] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A real-time active noise reduction device for ground magnetic resonance, characterized in that: The device includes: Detection coil, used to collect nuclear magnetic field signals after noise cancellation; A reference coil, used for collecting environmental noise, is coplanar with the detection coil and is placed away from the detection coil; The noise cancellation coil is placed overlapping on top of the detection coil; The FPGA module is used to receive the noise-canceled nuclear magnetic field signal collected by the detection coil and the ambient noise collected by the reference coil. Based on the ambient noise, it supplies a correspondingly changing current to the noise cancellation coil, thereby generating a changing magnetic field. This causes the detection coil to induce a cancellation response with the same amplitude and opposite phase as the noise itself. The FPGA module uses the ambient noise as the input signal of the adaptive filter and the nuclear magnetic signal after the noise is canceled as the error signal to minimize the error, and updates the coefficient of the adaptive filter. The output signal of the adaptive filter is converted into a driving voltage value and transmitted to the DA digital-to-analog conversion module in real time. The DA digital-to-analog conversion module drives the voltage-controlled current source module according to the driving voltage value to pass current into the noise cancellation coil; Converting the output signal of the adaptive filter into a driving voltage value includes: Calculate the mutual inductance between the noise cancellation coil and the detection coil; According to the output signal of the adaptive filter, the mutual inductance coefficient and The current value at the moment is used to calculate the noise cancellation coil The current value at the moment is expressed as: ， in, for The current value output to the noise cancellation coil at any moment, for The current value output to the noise cancellation coil at any moment, is the output signal of the adaptive filter, is the mutual inductance coefficient, is the data sampling rate; according to The current value at that moment is used to calculate the driving voltage value.

2. The terrestrial magnetic resonance real-time active noise reduction device according to claim 1, characterized in that: The adaptive filter obtains an output signal by multiplying the product of the transposed signal of the filter coefficient with the minimum error and the input signal.

3. The terrestrial magnetic resonance real-time active noise reduction device according to claim 1, characterized in that: The detection coil and the reference coil are both connected to the multi-channel AD synchronous acquisition module through their respective signal conditioning modules. The FPGA module is connected to the host computer. After receiving the synchronization signal generated by the host computer, it controls the multi-channel AD synchronous acquisition module to synchronously acquire the nuclear magnetic signal and environmental noise after noise cancellation.

4. A real-time active noise reduction method for ground magnetic resonance imaging, characterized in that: The method comprises: Arrange a detection coil, a reference coil, and a noise cancellation coil, overlap the noise cancellation coil and place it above the detection coil, and place the reference coil in the same plane as the detection coil and away from the detection coil; The nuclear magnetic field signal after noise cancellation is collected through the detection coil; Ambient noise is collected through a reference coil; According to the environmental noise, a corresponding changing current is passed into the noise cancellation coil, thereby generating a changing magnetic field, which induces a cancellation response in the detection coil with the same amplitude and opposite phase as the self-noise; Depending on the ambient noise, a corresponding current is fed into the noise cancellation coil, including: The ambient noise is used as the input signal of the adaptive filter, and the nuclear magnetic signal after the noise is canceled is used as the error signal to minimize the error, and the coefficient of the adaptive filter is updated. The output signal of the adaptive filter is converted into a driving voltage value and transmitted to the DA digital-to-analog conversion module in real time. The DA digital-to-analog conversion module drives the voltage-controlled current source module according to the driving voltage value to pass current into the noise cancellation coil; Convert the output signal of the adaptive filter into a driving voltage value, including: Calculate the mutual inductance between the noise cancellation coil and the detection coil; According to the output signal of the adaptive filter, the mutual inductance coefficient and The current value at the moment is used to calculate the noise cancellation coil The current value at the moment is expressed as: ， in, for The current value output to the noise cancellation coil at any moment, for The current value output to the noise cancellation coil at any moment, is the output signal of the adaptive filter, is the mutual inductance coefficient, is the data sampling rate; according to The current value at that moment is used to calculate the driving voltage value.

5. The real-time active noise reduction method for terrestrial magnetic resonance according to claim 4, characterized in that: The output signal of the adaptive filter is obtained by multiplying the transposed signal of the filter coefficients with the minimum error by the input signal.

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