Ground magnetic resonance real-time active noise reduction device and method

Abstract

The invention belongs to the technical field of geophysical exploration, and relates to a ground magnetic resonance real-time active noise reduction device and method, and the device comprises a detection coil which is used for collecting a nuclear magnetic signal after noise cancellation; the reference coil is used for collecting environmental noise, is coplanar with the detection coil and is placed at a position far away from the detection coil; the noise counteracting coil is placed above the detection coil in an overlapping manner; and the FPGA module is used for receiving the nuclear magnetic signal acquired by the detection coil after noise cancellation and the environmental noise acquired by the reference coil, and introducing correspondingly changing current into the noise cancellation coil according to the environmental noise so as to generate a changing magnetic field, so that the detection coil induces a cancellation response which has the same amplitude as the noise of the detection coil and is opposite to the noise of the detection coil in phase. According to the invention, the noise can be suppressed in real time at the source end of the instrument, and the anti-interference and weak signal detection capabilities of the ground magnetic resonance instrument in a complex electromagnetic environment are remarkably enhanced.

Description

Technical Field

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

[0002] Ground nuclear magnetic resonance technology is a non-invasive geophysical method that directly detects groundwater quantitatively and evaluates the pore size distribution, and has been widely used in the field of hydrogeological exploration. However, the ground nuclear magnetic resonance signal is extremely weak, usually only at the nano-volt level, and is extremely vulnerable to electromagnetic environmental noise interference. In tunnels, mines, and urban environments, the nuclear magnetic signal will be submerged by power frequency harmonics, resulting in saturated and distorted collected data.

[0003] In order to achieve noise reduction, multiple reference coils and a front-end processing module are used in existing research, which will significantly increase the complexity of the instrument and equipment, and the huge amount of data is also not conducive to realizing real-time noise cancellation of the data.

[0004] In other research, a time-frequency image is constructed by short-time Fourier transform of the noisy data, the time-frequency image is iteratively updated by using the manifold dimension constraint optimization equation, and then the short-time inverse Fourier transform is used to obtain the denoised pure signal from the denoised image. However, this method still uses the conventional noise reduction strategy of software processing after data acquisition, and cannot suppress the noise in real time at the instrument source end, resulting in difficulty in increasing the amplification factor of the instrument collected data. Summary of the Invention

[0005] This application provides a ground nuclear magnetic resonance real-time active noise reduction device and method, which solves the problem that it is impossible to generate a cancellation response at the instrument source end to suppress electromagnetic noise in real time.

[0006] An embodiment of this application provides a ground nuclear magnetic resonance real-time active noise reduction device, which includes: A detection coil for collecting the nuclear magnetic signal after noise cancellation; A reference coil for collecting environmental noise, which is coplanar with the detection coil and placed at a position far from the detection coil; A noise cancellation coil is overlapped and placed above the detection coil; An FPGA module for receiving the nuclear magnetic signal 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 a cancellation response with the same amplitude and opposite phase as its own noise is induced in the detection coil.

[0007] Further, the FPGA module uses the environmental noise as the input signal of the adaptive filter, and uses the nuclear magnetic signal after noise cancellation as the error signal, so as to minimize the error, update the coefficients of the adaptive filter, convert the output signal of the adaptive filter into a drive voltage value, and transmit it 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 through the noise cancellation coil according to the drive voltage value.

[0008] Further, the adaptive filter obtains the output signal by multiplying the transposed signal of the filter coefficient at the time of minimum error by the input signal.

[0009] Further, the conversion of the output signal of the adaptive filter into a drive voltage value includes: Calculating the mutual inductance coefficient 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 time calculate the current value in the noise cancellation coil at time Calculate the drive voltage value according to the current value at

[0010] Further, according to the output signal of the adaptive filter, the mutual inductance coefficient, and the current value at time The calculation formula for the current value in the noise cancellation coil at time is: , where is the current value output to the noise cancellation coil at time, is the current value output to the noise cancellation coil at time, is the output signal of the adaptive filter, is the mutual inductance coefficient, is the data sampling rate.

[0011] Further, both 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 synchronous signal generated by the host computer, it controls the multi-channel AD synchronous acquisition module to synchronously acquire the nuclear magnetic signal after noise cancellation and the environmental noise.

[0012] A real-time active noise reduction method for ground nuclear magnetic resonance, the method includes: Setting a detection coil, a reference coil, and a noise cancellation coil, overlapping the noise cancellation coil above the detection coil, and placing the reference coil in the same plane as the detection coil and at a position far from the detection coil; Collect the nuclear magnetic resonance signal after canceling the noise through a detection coil; Collect the ambient noise through a reference coil; According to the ambient noise, pass a correspondingly changing current into the noise cancellation coil, thereby generating a changing magnetic field, so that a cancellation response with the same amplitude and opposite phase as the self-noise is induced in the detection coil.

[0013] Further, passing a correspondingly changing current into the noise cancellation coil according to the ambient noise includes: Take the ambient noise as the input signal of the adaptive filter, take the nuclear magnetic resonance signal after canceling the noise as the error signal, minimize the error, update the coefficients of the adaptive filter, convert the output signal of the adaptive filter into a driving voltage value, and transmit it 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 a current into the noise cancellation coil according to the driving voltage value.

[0014] Further, the output signal of the adaptive filter is obtained by multiplying the transposed signal of the filter coefficient at the time of minimum error by the input signal.

[0015] Further, the conversion of the output signal of the adaptive filter into a driving voltage value includes: Calculate the mutual inductance coefficient 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 time calculate the current value in the noise cancellation coil at time According to the current value at time calculate the driving voltage value.

[0016] Compared with the prior art, the beneficial effects of this application are as follows: This 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 nuclear magnetic resonance instrument in a complex electromagnetic environment. Description of the Drawings

[0017] Figure 1 It is a structural block diagram of a ground nuclear magnetic resonance real-time active noise reduction device provided by an embodiment of this application; Figure 2 It is a diagram showing the relationship of the field laying positions of the detection coil, the reference coil, and the noise cancellation coil provided by an embodiment of this application; Figure 3 It is a comparison of the noise cancellation results. Among them, (a) is the time-domain image of the original data and the data after noise cancellation, and (b) is the frequency-domain image of the original data and the data after noise cancellation. Detailed Embodiments

[0018] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0019] For a conventional ground magnetic resonance receiving system, it needs to be used in cooperation with a transmitting system. After the transmitting system emits current through a transmitting coil, the receiving system is synchronously started, and nuclear magnetic signals are collected through a receiving coil or a detection coil.

[0020] In the embodiment of the present application, noise cancellation is realized at the instrument source end, that is, the nuclear magnetic signals collected at the acquisition end of the receiving system are signals from which environmental noise has been removed.

[0021] See Figure 1 the structural block diagram of a ground magnetic resonance real-time active noise cancellation device shown in conjunction with Figure 2 the field laying position relationship diagram of the detection coil, the reference coil and the noise cancellation coil, a ground magnetic resonance real-time active noise cancellation device, comprising: A detection coil, a reference coil, and a noise cancellation coil. The detection coil is the receiving coil. The reference coil can be set to one or multiple. When multiple are set, one of them is used as the main reference coil, and the signals received by the other reference coils are used as reference signals for the main reference coil. Different from the detection coil and the reference coil in the existing structure, in the embodiment of the present application, a noise cancellation coil is also provided. 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 being set as rectangles, circles, ellipses, etc. However, the detection coil, the reference coil, and the noise cancellation coil need to meet the requirements. The noise cancellation coil is overlapped and placed 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 sizes 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, or the size of the noise cancellation coil can 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 arranged in the same plane as the detection coil and placed at a position far from the detection coil, so that only environmental noise can be received in the reference coil and no nuclear magnetic signal can be received. 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 size 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.

[0022] 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 under the denoising condition of this application, the nuclear magnetic signals here are almost the same as the pure nuclear magnetic signals.

[0023] The reference coil is used to collect environmental noise. Through the set position, it can be understood that the reference coil is only used to collect environmental noise and does not collect nuclear magnetic signals. However, this is not an absolute situation. Inevitably, some weak nuclear magnetic signals will be mixed into the reference coil. Within the allowable error range, this situation is allowed and does not affect the calculation accuracy.

[0024] It is also necessary to set up a module for receiving signals, transmitting signals, and performing signal processing. In the embodiment of this application, an FPGA module is selected to receive the nuclear magnetic signals after canceling noise collected by the detection coil and the environmental noise collected by the reference coil, and pass a corresponding changing current into the noise cancellation coil according to the environmental noise, thereby generating a changing magnetic field, so that a cancellation response with the same amplitude and opposite phase as its own noise is induced in the detection coil.

[0025] The principle of the above structure in the embodiment of this application is that if the noise cancellation coil is not set, the nuclear magnetic signals with environmental noise are received through the detection coil, and the environmental noise is received through the reference coil. The conventional processing method is to remove the environmental noise from the nuclear magnetic signals with environmental noise in subsequent steps. This process can be achieved through methods such as wavelet transform-based methods, multi-linear singular value tensor decomposition methods, and machine learning-based methods, etc., but it will increase the subsequent calculation amount. In the embodiment of this application, the environmental noise of the reference coil will be processed at the instrument source end and converted into an equivalent cancellation response. The cancellation response has the same amplitude and opposite phase as the environmental noise. Through the action of the noise cancellation coil in the acquisition space where the detection coil is located, the cancellation response is used to cancel the cancellation response with environmental noise. In fact, at this time, the nuclear magnetic signals received by the detection coil are equivalent to pure nuclear magnetic signals.

[0026] In one embodiment, the FPGA module uses the environmental noise as the input signal of the adaptive filter, uses the nuclear magnetic signals after canceling noise as the error, minimizes the error, updates the coefficients of the adaptive filter, converts the output signal of the adaptive filter into a driving voltage value, and transmits it 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 a current into the noise cancellation coil according to the driving voltage value.

[0027] The adaptive filter is implemented through an adaptive filtering algorithm and integrated into the FPGA module in a programmatic way. 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.

[0028] If the noise cancellation coil is not set, the nuclear magnetic signal with noise collected by the detection coil. However, during the operation of this device, a current has been passed through the noise cancellation coil, and this current may not be the optimal current. Through the adaptive filter, an optimal current is ultimately to be output. Thus, the noise in the detection coil is cancelled as much as possible. During this process, the output signal of the detection coil received by the adaptive filter is actually a nuclear magnetic signal with the noise already cancelled, that is, the error required by the adaptive filter. The adaptive filter tries to minimize this error as much as possible.

[0029] In this embodiment, for the adaptive filter, first set the length of the adaptive filter, the filter coefficients, and the step factor, and use the nuclear magnetic signal with the noise cancelled in the detection coil as the error signal of the adaptive filter at a certain moment; the environmental noise collected by the reference coil is the input signal of the adaptive filter at a certain moment and several previous moments; update the adaptive filter coefficients to minimize the error signal; multiply the transposed signal of the filter coefficients when the error is minimized by the input signal to obtain the output signal at a certain moment.

[0030] This output signal is used to control the current in the noise cancellation coil to generate a cancellation response in the detection coil so as to cancel the environmental noise in the nuclear magnetic signal in the detection coil.

[0031] The output signal of the adaptive filter needs to be converted into a driving voltage value to drive a corresponding current in the noise cancellation coil. It includes: Calculate the mutual inductance coefficient 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 a certain moment, calculate the current value in the noise cancellation coil at a certain moment; According to the current value at a certain moment, calculate the driving voltage value.

[0032] According to the output signal of the adaptive filter, the mutual inductance coefficient, and the current value at a certain moment, the calculation formula for the current value in the noise cancellation coil at a certain moment is expressed as: , where, is the current value output to the noise cancellation coil at a moment, is the current value output to the noise cancellation coil at a moment, is the output signal of the adaptive filter, is the mutual inductance coefficient, is the data sampling rate.

[0033] The design process of the calculation formula is as follows: Based on the finite element method analysis, the coupling relationship between the noise cancellation coil and the detection coil can be obtained, and the mutual inductance coefficient between the two coils can be calculated according to the coupling relationship between the two coils; If it is assumed that the coupling voltage between the noise cancellation coil and the detection coil is , the current passing through the noise cancellation coil is , the data sampling rate is 30 kHz, is time, and there is the following mutual inductance relationship: , The above differential equation is changed to a difference form: , If the environmental 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: , The ratio of the drive voltage value to the output current is , then the drive voltage value corresponding to the output signal of the adaptive filtering algorithm is: .

[0034] In another embodiment, as shown in Figure 1 , a ground nuclear magnetic resonance real-time active noise reduction device includes: a detection coil for collecting nuclear magnetic signals after noise cancellation; a reference coil for collecting environmental noise, which is coplanar with the detection coil and placed at a position far from the detection coil; a noise cancellation coil, which is overlapped and placed 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 passing a corresponding changing current into the noise cancellation coil according to the environmental noise, thereby generating a changing magnetic field to induce a cancellation response in the detection coil with the same amplitude and opposite phase as its own noise.

[0035] Both 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 through the data transmission module. After receiving the synchronous signal generated by the host computer, it controls the multi-channel AD synchronous acquisition module to synchronously acquire nuclear magnetic signals and environmental noises.

[0036] 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.

[0037] In a specific application, the detection coil, the reference coil, and the noise cancellation coil are all squares with 10 turns and a side length of 4 m. The reference coil is laid 5 m away from the detection coil, and the noise cancellation coil is overlapped and laid 5 cm directly above the detection coil. Both signal conditioning modules include a preamplifier and a band-pass filter, which are respectively used for conditioning such as amplifying and filtering nuclear magnetic signals and environmental noises. The noise cancellation coil is overlapped and placed above the detection coil to generate an electromagnetic field to cancel the environmental noise in the detection coil in real time. The reference coil is used to obtain the environmental noise as a reference required by the adaptive filtering algorithm and avoid collecting nuclear magnetic signals. After receiving the synchronous signal generated by the host computer, the FPGA module controls the multi-channel AD synchronous acquisition module to synchronously acquire the nuclear magnetic signal in the detection coil and the environmental noise in the reference coil. The FPGA module takes the collected environmental noise as the input signal of the adaptive filter, and according to the coupling relationship of the noise cancellation coil, converts the output signal of the adaptive filter into a driving voltage value and transmits it to the DA digital-to-analog conversion module in real time, and updates the adaptive filter coefficients. The voltage-controlled current source module receives the driving voltage signal output by the DA digital-to-analog conversion module, converts it into a linearly proportional driving current, and injects the driving current into the noise cancellation coil. Based on the principle of electromagnetic induction, a cancellation magnetic field is generated, and a cancellation response with the same amplitude and opposite phase as the environmental noise is generated in the detection coil, so as to suppress the environmental noise in the detection coil in real time.

[0038] The embodiment of the present application also provides a ground magnetic resonance real-time active noise reduction method based on the ground magnetic resonance real-time active noise reduction device in the above embodiments. Based on the same noise reduction principle, it includes: Set up a detection coil, a reference coil, and a noise cancellation coil, overlap and place the noise cancellation coil above the detection coil, and place the reference coil in the same plane as the detection coil and at a position far from the detection coil. Collect the nuclear magnetic signal after canceling the noise through the detection coil. Collect the environmental noise through the reference coil. According to the ambient noise, a corresponding varying current is passed into the noise cancellation coil, thereby generating a varying magnetic field, so that a cancellation response with the same amplitude and opposite phase as the self-noise is induced in the detection coil.

[0039] In one embodiment, passing a corresponding varying current into the noise cancellation coil according to the ambient noise includes: Taking the ambient noise as the input signal of the adaptive filter, converting the output signal of the adaptive filter into a driving voltage value, and transmitting it to the DA digital-to-analog conversion module in real time, updating the adaptive filter coefficients, and driving the voltage-controlled current source module to pass a current into the noise cancellation coil according to the driving voltage value.

[0040] In one embodiment, the adaptive filter uses the nuclear magnetic signal after canceling the noise in the detection coil as the error signal at a certain moment; at a certain moment; The ambient noise collected by the reference coil is the input signal of the adaptive filter at a certain moment and several previous moments; at a certain moment and several previous moments; Update the adaptive filter coefficients to minimize the error signal; Multiply the transposed signal of the filter coefficients at the moment when the error is minimized by the input signal to obtain the output signal at a certain moment.

[0041] In one embodiment, converting the output signal of the adaptive filter into a driving voltage value includes: Calculating the mutual inductance coefficient 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 a certain moment, calculate the current value in the noise cancellation coil at a certain moment; According to the current value at a certain moment, calculate the driving voltage value.

[0042] To facilitate a better understanding of the real-time active noise reduction method and device for ground nuclear magnetic resonance proposed in the embodiments of the present application, the embodiments of the present application provide a working process of a real-time active noise reduction device for ground nuclear magnetic resonance, including: Lay a square detection coil with 10 turns and a side length of 4m, a square reference coil with 10 turns and a side length of 4m, and a square noise cancellation coil with 10 turns and a side length of 4m. Among them, the reference coil is laid 5m away from the detection coil, and the noise cancellation coil is overlapped and laid 5cm directly above the detection coil; Power on the system and initialize each module; The host computer sends a start synchronization command, and the multi-channel AD synchronization acquisition module synchronously acquires the data of the detection coil and the reference coil. The FPGA module takes the collected environmental noise as the input signal of the adaptive filter. According to the coupling relationship of the noise cancellation coil, it converts the output signal of the adaptive filter into a drive voltage value and transmits it to the DA digital-to-analog conversion module in real time, and updates the adaptive filter coefficients.

[0043] The voltage-controlled current source module receives the drive voltage signal from the DA digital-to-analog conversion module, converts it into a linearly proportional drive current, and injects it into the noise cancellation coil; Based on the principle of electromagnetic induction, the noise cancellation coil generates a cancellation magnetic field; A cancellation response with the same amplitude and opposite phase to the environmental noise is generated in the detection coil, realizing the real-time suppression of environmental noise, avoiding the distortion of magnetic resonance signals at the same time, and realizing the active noise reduction function of source-end noise; 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.

[0044] The obtained data is shown in Figure 3 as follows, where Figure 3 in (a) is the time-domain image of the original data and the denoised data, Figure 3 in (b) is the frequency-domain image of the original data and the denoised data. It can be seen from the comparison results of the time-domain image that the noise amplitude is reduced by about 50% after the noise reduction process compared with the original signal. It can be seen from the comparison results of the frequency-domain image that the noise energy of the 50Hz fundamental wave and its main harmonic components in the signal is significantly suppressed. At the same time, while effectively eliminating the power frequency interference, the active noise reduction system realizes the complete preservation of the amplitude-frequency characteristics of the measurement signal, verifying the excellent performance of the system in noise suppression and signal fidelity.

[0045] The above is only a preferred embodiment of the present application, and it is not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A ground magnetic resonance real-time active noise reduction device, characterized in that, The device includes: A detection coil for collecting nuclear magnetic signals after noise cancellation; A reference coil for collecting environmental noise, which is coplanar with the detection coil and placed at a position far from the detection coil; A noise cancellation coil, which is overlapped and placed 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 a cancellation response with the same amplitude and opposite phase as its own noise is induced in the detection coil.

2. The real-time active noise reduction device for ground magnetic resonance according to claim 1, wherein, The FPGA module uses the environmental noise as the input signal of the adaptive filter, and the nuclear magnetic signals after noise cancellation as the error signal, so as to minimize the error, update the coefficients of the adaptive filter, convert the output signal of the adaptive filter into a driving voltage value, and transmit it 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 a current into the noise cancellation coil according to the driving voltage value.

3. The ground magnetic resonance real-time active noise reduction device according to claim 2, characterized in that, The output signal of the adaptive filter is obtained by multiplying the transposed signal of the filter coefficient at the time of minimum error by the input signal.

4. The ground magnetic resonance real-time active noise reduction device according to claim 3, characterized in that, The conversion of the output signal of the adaptive filter into a driving voltage value includes: Calculating the mutual inductance coefficient between the noise cancellation coil and the detection coil; Based on the output signal of the adaptive filter, the mutual inductance coefficient, and the current value at a moment, calculate the current value at a moment in the noise cancellation coil; Calculate the drive voltage value based on the current value at a moment.

5. The ground magnetic resonance real-time active noise reduction device according to claim 4, characterized in that, According to the output signal of the adaptive filter, the mutual inductance coefficient, and the current value at the moment, the current value in the noise cancellation coil is calculated as follows: ， wherein, is the current value output to the noise cancellation coil at time is the current value output to the noise cancellation coil at time is the output signal of the adaptive filter, is the mutual inductance coefficient, is the data sampling rate.

6. The ground magnetic resonance real-time active noise reduction device according to claim 1, characterized in that Both 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 upper computer. After receiving the synchronous signal generated by the upper computer, it controls the multi-channel AD synchronous acquisition module to synchronously acquire the nuclear magnetic signals after noise cancellation and the environmental noise.

7. A method for real-time active noise reduction of ground magnetic resonance, characterized in that, The method includes: Setting up a detection coil, a reference coil and a noise cancellation coil, overlapping the noise cancellation coil above the detection coil, and placing the reference coil coplanar with the detection coil and at a position far from the detection coil; Collecting the nuclear magnetic signals after noise cancellation through the detection coil; Collecting environmental noise through the reference coil; According to the environmental noise, passing a corresponding changing current into the noise cancellation coil, thereby generating a changing magnetic field, so that a cancellation response with the same amplitude and opposite phase as its own noise is induced in the detection coil.

8. A real-time active noise reduction method for ground magnetic resonance according to claim 7, characterized in that, Passing a corresponding changing current into the noise cancellation coil according to the environmental noise includes: Using the environmental noise as the input signal of the adaptive filter, and the nuclear magnetic signals after noise cancellation as the error signal, so as to minimize the error, update the coefficients of the adaptive filter, convert the output signal of the adaptive filter into a driving voltage value, and transmit it 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 a current into the noise cancellation coil according to the driving voltage value.

9. The ground magnetic resonance real-time active noise reduction method according to claim 8, wherein The output signal of the adaptive filter is obtained by multiplying the transposed signal of the filter coefficient at the time of minimum error by the input signal.

10. The ground magnetic resonance real-time active noise reduction method according to claim 8, characterized in that, The conversion of the output signal of the adaptive filter into a driving voltage value includes: Calculating the mutual inductance coefficient 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, calculate the current value in the noise cancellation coil at the Calculate the driving voltage value according to the current value at a moment.

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