Method for spatial magnetic field compensation and magnetic field compensation system

Abstract

The application provides a spatial magnetic field compensation method and a magnetic field compensation system, comprising the following steps: S1, collecting magnetic fields of a first magnetic field sensor and a second magnetic field sensor at the same time to obtain a first magnetic field signal and a second magnetic field signal; S2, when the absolute value of a correlation coefficient is equal to 1, compensating the first magnetic field signal by a constant coefficient compensation method to obtain a signal source real magnetic field; when the absolute value of the correlation coefficient is greater than 0 and less than 1, compensating the first magnetic field signal by a variable coefficient compensation method to obtain the signal source real magnetic field; wherein the correlation coefficient is a correlation coefficient between an environmental field magnetic field signal of the first magnetic field sensor and an environmental field magnetic field signal of the second magnetic field sensor. The application effectively solves the problems of complex magnetic field compensation methods in different environments and low signal-to-noise ratio of output signals in the prior art.

Description

Technical Field

[0001] This invention relates to the field of signal detection, and in particular to a spatial magnetic field compensation method and a magnetic field compensation system. Background Technology

[0002] Extracting high signal-to-noise ratio (SNR) signals submerged in noisy or complex environments has always been a crucial issue in signal detection. Compared to the Earth's magnetic field of 30-50 μT, the spatial magnetic fields generated by bioelectrical activities such as those of the heart, brain, and neuromuscular systems are extremely weak. For example, the magnetocardiogram (MCT) of an adult heart is 100 pT, while that of a fetus is only a dozen pT. However, the MCT signal exhibits a typical QRS complex, making information relatively easy to read. The magnetoencephalogram (MEG) of the brain is even weaker, only a few tens to hundreds of fT, and varies among individuals, with different signal characteristics corresponding to different locations. The nervous system within the human body is even more complex, with each nerve controlling different muscle groups. Therefore, the magnetic field signals generated by neuromuscular action potentials are highly complex and diverse, lacking distinct signal characteristics. Thus, for complex and diverse human magnetic field signals, a higher SNR simplifies subsequent signal analysis. In complex magnetic fields mixed with noise and signal, high noise suppression is crucial.

[0003] Currently, physical shielding methods, such as shielded rooms and shielded cylinders, can achieve a noise suppression ratio of 80dB, reducing the ambient field to the nT level. However, this measurement method still deviates from the true signal, requiring further noise reduction to more closely approximate the real signal. There are also methods to cancel out environmental noise, further suppressing it; however, the design methods for different magnetic field sensors are complex, depending on the environment and signal characteristics.

[0004] For the reasons mentioned above, this invention provides a spatial magnetic field compensation method applicable to different environments and signal characteristics. Based on this method, a suitable noise suppression method can be found in a variety of signals and complex environments, thereby obtaining a magnetic field signal with an extremely high signal-to-noise ratio.

[0005] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating understanding by those skilled in the art. It should not be assumed that these technical solutions are known to those skilled in the art simply because they have been described in the background section of this application. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a spatial magnetic field compensation method and a magnetic field compensation system to solve the problems of complex magnetic field compensation methods under different environments and low signal-to-noise ratio of output signals in the prior art.

[0007] To achieve the above and other related objectives, the present invention provides a space magnetic field compensation method, comprising:

[0008] S1. Collect the magnetic fields of the first magnetic field sensor and the second magnetic field sensor at the same time to obtain the first magnetic field signal and the second magnetic field signal; wherein, the first magnetic field sensor is used to acquire the superimposed magnetic field of the signal source and the environmental field; the second magnetic field sensor is used to acquire the magnetic field of the environmental field;

[0009] S2. When the absolute value of the correlation coefficient is equal to 1, the first magnetic field signal is compensated by the fixed coefficient compensation method to obtain the true magnetic field of the signal source; when the absolute value of the correlation coefficient is greater than 0 and less than 1, the first magnetic field signal is compensated by the variable coefficient compensation method to obtain the true magnetic field of the signal source; when the absolute value of the correlation coefficient is equal to 0, the positions of the first magnetic field sensor and / or the second magnetic field sensor are changed, and step S1 is executed again until the absolute value of the correlation coefficient is not equal to 0; wherein, the correlation coefficient is the correlation coefficient between the environmental magnetic field signal of the first magnetic field sensor and the environmental magnetic field signal of the second magnetic field sensor.

[0010] Optionally, in step S1, the acquisition time is set to be greater than or equal to 10 seconds.

[0011] Optionally, in step S1, when the location of the signal source is unknown, a third magnetic field sensor is configured to collect a third magnetic field signal at the location of the first magnetic field sensor and a fourth magnetic field signal at the location of the second magnetic field sensor. If the third magnetic field signal is greater than the fourth magnetic field signal, the distance between the first magnetic field sensor and the signal source is less than the distance between the second magnetic field sensor and the signal source. If the third magnetic field signal is less than or equal to the fourth magnetic field signal, the location of the first magnetic field sensor and / or the location of the second magnetic field sensor is adjusted until the distance between the first magnetic field sensor and the signal source is less than the distance between the second magnetic field sensor and the signal source.

[0012] Optionally, the method for collecting the environmental magnetic field signal of the first magnetic field sensor and the environmental magnetic field signal of the second magnetic field sensor includes: in step S1, in the same environmental field without a signal source, collecting the magnetic field signal at the location of the first magnetic field sensor and the magnetic field signal at the location of the second magnetic field sensor at the same time, respectively as the environmental magnetic field signal of the first magnetic field sensor and the environmental magnetic field signal of the second magnetic field sensor.

[0013] Optionally, in step S2, the correlation coefficient satisfies:

[0014] ;

[0015] Where ρ represents the correlation coefficient between the environmental magnetic field signals of the first magnetic field sensor and the second magnetic field sensor, s1(t) represents the environmental magnetic field signal of the first magnetic field sensor, and r1(t) represents the environmental magnetic field signal of the second magnetic field sensor. This represents the covariance between the ambient magnetic field signal of the first magnetic field sensor and the ambient magnetic field signal of the second magnetic field sensor. This represents the variance of the ambient magnetic field signal of the first magnetic field sensor. This represents the variance of the ambient magnetic field signal of the second magnetic field sensor.

[0016] Optionally, the fixed coefficient compensation method includes: multiplying the second magnetic field signal by a compensation coefficient and then outputting the differential output with the first magnetic field signal to obtain the true magnetic field of the signal source.

[0017] Optionally, the fixed coefficient compensation method includes: obtaining the compensation coefficient based on the ratio of the amplitude values ​​of the first magnetic field signal and the second magnetic field signal.

[0018] Optionally, the variable coefficient compensation method includes: performing variable coefficient adaptive filtering on the second magnetic field signal based on the first magnetic field signal, and outputting the filtered signal and the first magnetic field signal differentially to obtain the true magnetic field of the signal source.

[0019] Optionally, the variable coefficient compensation method further includes: acquiring the average power spectrum of the filtered second magnetic field signal, adjusting the filtering parameters of the second magnetic field signal until the average power spectrum of the filtered second magnetic field signal is minimized, and then outputting the true magnetic field of the signal source.

[0020] Optionally, the second magnetic field signal is filtered and then differentially output with the first magnetic field signal to obtain an error signal function; wherein, the parameter values ​​of the error signal function are adjusted by an adaptive algorithm to minimize the mean square value of the error signal function, thereby outputting the true magnetic field of the signal source.

[0021] Optionally, the adaptive algorithm is selected from any one of the following: steepest descent method, recursive least squares algorithm, least mean square error algorithm, adaptive filtering algorithm based on orthogonal triangular decomposition, adaptive filtering algorithm based on subband decomposition, conjugate gradient algorithm, affine projection algorithm, and transform domain adaptive filtering algorithm.

[0022] To achieve the above and other related objectives, the present invention provides a magnetic field compensation system, comprising:

[0023] The system comprises a first magnetic field sensor, a second magnetic field sensor, a correlation coefficient calculation module, a correlation coefficient determination module, a compensation module, and an adder.

[0024] The first magnetic field sensor and the second magnetic field sensor are located in the same environmental field, and the distance between the first magnetic field sensor and the signal source is less than the distance between the second magnetic field sensor and the signal source; wherein, the first magnetic field sensor is used to acquire the superimposed magnetic field of the signal source and the environmental field to obtain a first magnetic field signal; the second magnetic field sensor is used to acquire the magnetic field of the environmental field to obtain a second magnetic field signal;

[0025] The first input terminal of the correlation coefficient calculation module is connected to the first magnetic field signal, and the second input terminal is connected to the second magnetic field signal, and is used to calculate the correlation coefficient between the environmental magnetic field signal of the first magnetic field sensor and the environmental magnetic field signal of the second magnetic field sensor.

[0026] The correlation coefficient determination module is connected to the output of the correlation coefficient calculation module, determines the result of the correlation coefficient, and inputs the determination result to the control terminal of the compensation module;

[0027] The compensation module includes a fixed coefficient setting unit and an adaptive filtering unit. The input of the compensation module is connected to the second magnetic field signal, and it controls the second magnetic field signal to pass through the fixed coefficient setting unit or the adaptive filtering unit based on the output signal of the correlation coefficient determination module. When the absolute value of the correlation coefficient is equal to 1, the input of the fixed coefficient setting unit is connected to the second magnetic field signal, and the output is connected to the adder, amplifying the second magnetic field signal by a compensation coefficient before outputting it. When the absolute value of the correlation coefficient is greater than 0 and less than 1, the input of the adaptive filtering unit is connected to the second magnetic field signal, and the output is connected to the adder, adaptively filtering the second magnetic field signal before outputting it.

[0028] The first input terminal of the adder is connected to the first magnetic field signal, and the second input terminal is connected to the output terminal of the compensation module. The adder performs differential output on the first magnetic field signal and the output signal of the compensation module, thereby compensating the first magnetic field signal to obtain the true magnetic field of the signal source.

[0029] Optionally, the second magnetic field sensor is configured as a low-sensitivity sensor.

[0030] Optionally, the first magnetic field sensor is configured as any one of a magnetometer, gradiometer, full tensor magnetic gradiometer, optical microcavity sensor, atomic magnetometer, fluxgate, Hall sensor, magnetoresistive sensor, magnetoelectric sensor, single-turn coil, and multi-turn coil; the second magnetic field sensor is configured as any one of a magnetometer, gradiometer, full tensor magnetic gradiometer, optical microcavity sensor, atomic magnetometer, fluxgate, Hall sensor, magnetoresistive sensor, magnetoelectric sensor, single-turn coil, and multi-turn coil.

[0031] Optionally, the correlation coefficient calculation module calculates the correlation coefficient to satisfy:

[0032] ;

[0033] Where ρ represents the correlation coefficient between the environmental magnetic field signals of the first magnetic field sensor and the second magnetic field sensor, s1(t) represents the environmental magnetic field signal of the first magnetic field sensor, and r1(t) represents the environmental magnetic field signal of the second magnetic field sensor. This represents the covariance between the ambient magnetic field signal of the first magnetic field sensor and the ambient magnetic field signal of the second magnetic field sensor. This represents the variance of the ambient magnetic field signal of the first magnetic field sensor. This represents the variance of the ambient magnetic field signal of the second magnetic field sensor.

[0034] Optionally, when the absolute value of the correlation coefficient is greater than 0 and less than 1, the output signal of the adder is fed back to the adaptive filtering unit, and the adaptive filtering unit is adjusted based on the feedback signal so that when the mean square value of the feedback signal is minimized, the true magnetic field of the signal source is output.

[0035] As described above, the space magnetic field compensation method and magnetic field compensation system of the present invention have the following beneficial effects:

[0036] 1. The spatial magnetic field compensation method and magnetic field compensation system of the present invention summarize the configuration for suppressing noise and improving signal-to-noise ratio from the perspective of spatial correlation. It is suitable for different sensor types, has a wide range of applications, and is simple to implement.

[0037] 2. Based on the time correlation of the magnetic field, the spatial magnetic field compensation method and magnetic field compensation system of the present invention summarize the cooperation relationship between sensors with different characteristic signals and under different environments, so as to achieve the requirement of obtaining a higher signal-to-noise ratio. Attached Figure Description

[0038] Figure 1 The diagram shown is a framework flowchart of the space magnetic field compensation method of the present invention.

[0039] Figure 2The diagram shown is a schematic representation of the principle of this invention.

[0040] Figure 3 The diagram shown is a schematic diagram of the magnetic field induction line of the signal source of the present invention.

[0041] Figure 4 The diagram shows the structure of the magnetic field compensation system corresponding to the constant coefficient compensation method of the present invention.

[0042] Figure 5 The diagram shows the structure of the magnetic field compensation system corresponding to the variable coefficient compensation method of the present invention.

[0043] Figure 6 The diagram shown is a structural schematic of the magnetic field compensation system of the present invention.

[0044] Figure 7 The diagram shown is a schematic representation of the device structure of the magnetic field compensation system of the present invention.

[0045] Figure 8 The waveform is shown as an uncompensated magnetocardiogram detection waveform.

[0046] Figure 9 The image shown is a waveform diagram of the magnetocardiogram signal detection compensated by the present invention.

[0047] Component designation explanation Detailed Implementation

[0048] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0049] Please refer to 1~ Figure 9 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0050] like Figures 1-9 As shown, this embodiment provides a method for compensating for a spatial magnetic field, such as... Figure 1 As shown, it includes:

[0051] S1. Collect the magnetic fields of the first magnetic field sensor 11 and the second magnetic field sensor 12 at the same time to obtain the first magnetic field signal s(t) and the second magnetic field signal r(t); wherein, the first magnetic field sensor 11 is used to acquire the superimposed magnetic field of the signal source and the environmental field; the second magnetic field sensor 12 is used to acquire the magnetic field of the environmental field.

[0052] In this embodiment, as Figure 2 As shown, the first magnetic field sensor 11 and the second magnetic field sensor 12 are located within the same environmental field 02, and the distance L1 between the first magnetic field sensor 11 and the signal source 01 is less than the distance L2 between the second magnetic field sensor 12 and the signal source 01. Since magnetic signals have spatial correlation, meaning that within a certain range, magnetic fields exhibit similar vector directions, magnetic field compensation can be performed as long as the first magnetic field sensor 11 and the second magnetic field sensor 12 have a certain spatial distance from the signal source.

[0053] Its principle is as follows Figure 3 As shown, the first magnetic field signal s(t) obtained by the first magnetic field sensor 11 is a superposition field signal of the first signal source magnetic field signal S1(t) and the first environmental field magnetic field signal N1(t), i.e.: s(t) = S1(t) + N1(t); the magnetic field signal detected by the second magnetic field sensor 12 is the second magnetic field signal r(t), which is a superposition field signal of the second signal source magnetic field signal S2(t) and the second environmental field magnetic field signal N2(t), i.e.: r(t) = S2(t) + N2(t). Since both the first magnetic field sensor 11 and the second magnetic field sensor 12 are located within the same environmental field O2, the magnetic field signals collected by the two sensors, including the portion of the environmental field O2, are correlated. The magnetic field signal of the environmental field O2 collected by the second magnetic field sensor 12 can be used to suppress the portion of the environmental field O2 in the first magnetic field sensor 11, thereby obtaining the magnetic field signal of the signal source O1. The method of magnetic field compensation based on the above principle is relatively complex and prone to introducing interference.

[0054] To address the aforementioned issues, this invention configures the first magnetic field sensor 11 to acquire the superimposed magnetic field of the signal source and the ambient field; and configures the second magnetic field sensor 12 to acquire the magnetic field of the ambient field. Specifically, the second magnetic field sensor 12 is positioned far from the signal source. Furthermore, in this embodiment, both the first magnetic field sensor 11 and the second magnetic field sensor 12 are configured as low-sensitivity magnetic field sensors; in this case, it can be considered that the second magnetic field sensor 12 is not acquiring the magnetic field signal S2(t) of the second signal source, i.e., S2(t) = 0. Finally, the differential output of the first magnetic field signal s(t) and the second magnetic field signal r(t) is the compensated magnetic field S(t) = (S1(t) + N1(t)) - (S2(t) + N2(t)). Since S2(t) = 0, the output at this time is the data with a higher signal-to-weight ratio after compensation.

[0055] Specifically, in step S1, when the location of the signal source is unknown, the third magnetic field sensor is configured to collect the third magnetic field signal M3(t) at the location of the first magnetic field sensor 11 and the fourth magnetic field signal M4(t) at the location of the second magnetic field sensor 12. If the third magnetic field signal M3(t) is greater than the fourth magnetic field signal M4(t), then the distance between the first magnetic field sensor and the signal source is less than the distance between the second magnetic field sensor and the signal source; if the third magnetic field signal M3(t) is less than or equal to the fourth magnetic field signal M4(t), then the location of the first magnetic field sensor and / or the location of the second magnetic field sensor is adjusted until the distance L1 between the first magnetic field sensor and the signal source is less than the distance L2 between the second magnetic field sensor and the signal source.

[0056] It should be noted that if the signal source is a known signal source, the positions of the first magnetic field sensor 11 and the second magnetic field sensor 12 are directly set so that the first magnetic field sensor 11 acquires the superimposed magnetic field of the signal source and the ambient field, and the second magnetic field sensor 12 acquires the magnetic field of the ambient field. If the location of the signal source is uncertain, the signal source can be a dynamic magnetic field or a static magnetic field. By detecting it with the same magnetic field sensor (i.e., the third magnetic field sensor), the distance between the location and the signal source can be obtained. Using the same sensor to collect magnetic field data at different locations ensures that parameters other than the location parameter that affect the magnetic field measurement are as consistent as possible, making the determination of the distance to the signal source more accurate and facilitating a better determination of the signal source distance. In fact, detection can also be performed directly by the first magnetic field sensor or the second magnetic field sensor. As long as the final set position of the magnetic field sensor ensures that the first magnetic field sensor 11 and the second magnetic field sensor 12 are both in the same ambient field, and the first magnetic field sensor 11 can acquire the magnetic field of the signal source while the second magnetic field sensor 12 can only acquire the ambient field, this is within the scope of protection of this embodiment.

[0057] Specifically, since the magnetic field has a time correlation, in step S1, the magnetic fields of the first magnetic field sensor 11 and the second magnetic field sensor 12 are collected within the same time period. By setting the sampling to be synchronized within the same time period, it is convenient to determine the compensation method for the first magnetic field signal based on the correlation coefficient. Preferably, the sampling time is set to be greater than or equal to 10s, including but not limited to 20s, 50s, and 100s, which can make the signals collected by the first magnetic field sensor 11 and the second magnetic field sensor 12 more stable and the acquisition more accurate.

[0058] S2. When the absolute value of the correlation coefficient ρ is equal to 1, the first magnetic field signal is compensated by the fixed coefficient compensation method to obtain the true magnetic field of the signal source; when the absolute value of the correlation coefficient ρ is greater than 0 and less than 1, the first magnetic field signal is compensated by the variable coefficient compensation method to obtain the true magnetic field of the signal source; when the absolute value of the correlation coefficient ρ is equal to 0, the positions of the first magnetic field sensor and / or the second magnetic field sensor are changed, and step S1 is executed again until the absolute value of the correlation coefficient ρ is not equal to 0; wherein, the correlation coefficient is the correlation coefficient between the environmental magnetic field signal of the first magnetic field sensor and the environmental magnetic field signal of the second magnetic field sensor.

[0059] Specifically, the method for collecting the environmental magnetic field signals of the first magnetic field sensor and the second magnetic field sensor includes: in step S1, within the same environmental field without a signal source, collecting the magnetic field signals at the locations of the first magnetic field sensor 11 and the second magnetic field sensor 12 at the same time. Since the magnetic field signals collected here are collected when there is no signal source, the magnetic field signals collected by the first magnetic field sensor 11 and the second magnetic field sensor 12 can be directly used as the environmental magnetic field signals of the first magnetic field sensor and the second magnetic field sensor. It should be noted that "no signal source" includes, but is not limited to, shielding the signal source or preventing the signal source from being placed in this environmental field.

[0060] More specifically, the correlation coefficient satisfies:

[0061] ;

[0062] Where ρ represents the correlation coefficient between the environmental magnetic field signals of the first magnetic field sensor and the second magnetic field sensor, s1(t) represents the environmental magnetic field signal of the first magnetic field sensor, and r1(t) represents the environmental magnetic field signal of the second magnetic field sensor. This represents the covariance between the ambient magnetic field signal of the first magnetic field sensor and the ambient magnetic field signal of the second magnetic field sensor. This represents the variance of the ambient magnetic field signal of the first magnetic field sensor. This represents the variance of the ambient magnetic field signal of the second magnetic field sensor.

[0063] It should be noted that the correlation coefficient can also be calculated using methods including, but not limited to, the Spearman correlation coefficient method and the Kendall rank correlation coefficient method.

[0064] Specifically, such as Figure 1 and Figure 4 As shown, the fixed coefficient compensation method includes: multiplying the second magnetic field signal r(t) by the compensation coefficient K and then differentially outputting it with the first magnetic field signal s(t), thereby obtaining the true magnetic field S(t) of the signal source. Figure 5 As shown, the first magnetic field sensor 11 serves as the signal channel, acquiring the first magnetic field signal s(t) as one input; the second magnetic field signal r(t) serves as the reference channel, acquiring the second magnetic field signal r(t), multiplying it by the compensation coefficient K, and using it as another input; a differential output is made between the two inputs to output the true magnetic field M(t) of the signal source. It should be noted that the compensation coefficient K at this time is a constant value that is less than 1 and greater than 0.

[0065] In practical applications, if the signal source is a known type of signal (including but not limited to magnetocardiogram signals and magnetoencephalogram signals), the compensation coefficient K can be directly obtained based on the signal characteristics using methods including but not limited to table lookup, and then used to compensate the first magnetic field signal s(t). This achieves fixed-coefficient compensation, eliminating the need to calculate the compensation coefficient K and perform fixed-coefficient compensation on the magnetic field signals collected by the first magnetic field sensor 11 and the second magnetic field sensor 12 in the same environmental field without a signal source. This ultimately yields the true magnetic field of the signal source. It should be noted that in another example, a variable-coefficient compensation method can also be used based on the signal characteristics. If the signal source is of an unknown type or its type is complex, since the absolute value of the correlation coefficient between the environmental magnetic field signals of the first magnetic field sensor 11 and the second magnetic field sensor 12 is 1, they are highly correlated. This means that the collected magnetic field waveforms change almost identically, differing only in amplitude. In this case, the ratio of the amplitude values ​​of the first magnetic field signal s(t) and the second magnetic field signal r(t) can be used as the value of the compensation coefficient K to compensate the first magnetic field signal, and then the compensated true magnetic field of the signal source can be differentially output. At this time, the compensation coefficient K can be stored in the storage unit (not shown in the figure) as a fixed compensation coefficient K for the signal source, which is convenient for subsequent measurement.

[0066] Specifically, such as Figure 1 and Figure 5As shown, the variable coefficient compensation method includes: performing variable coefficient adaptive filtering on the second magnetic field signal r(t) based on the first magnetic field signal s(t), and outputting the filtered signal and the first magnetic field signal differentially to obtain the true magnetic field of the signal source.

[0067] In one embodiment, after acquiring the second magnetic field signal r(t), the average power spectrum of the filtered second magnetic field signal r(t) is collected. The filtering parameters of the second magnetic field signal r(t) are adjusted until the average power spectrum of the filtered second magnetic field signal r(t) is minimized. The signal output by differentially analyzing this signal with the first magnetic field signal s(t) is the true magnetic field S(t) of the signal source. Variable coefficient compensation can be achieved by adjusting a feedback-enabled adjustable parameter circuit. The feedback-enabled adjustable parameter circuit is adjusted until the noise of the first signal source's true magnetic field is minimized, at which point the true magnetic field of the signal source is output. In other words, the electronic circuit at the hardware level performs adaptive filtering to obtain the final true magnetic field of the signal source. Since the compensation coefficient is not a specific fixed value but changes with time and distance from the signal source, the feedback-enabled adjustable parameter circuit needs to be readjusted each time the positions of the first magnetic field sensor 11 and the second magnetic field sensor 12 are changed to minimize the noise of the final true magnetic field of the signal source.

[0068] In another embodiment, the second magnetic field signal r(t), after filtering, is differentially output with the first magnetic field signal s(t) to obtain an error signal function e(n). This error signal function e(n) is fed back to the adaptive filtering unit 152 after passing through an adaptive algorithm, thereby adjusting the value of the adaptive filtering unit 152. The parameter values ​​of the error signal function e(n) are adjusted through the adaptive algorithm to minimize its mean square value, thus outputting the true magnetic field of the signal source. In this embodiment, the second magnetic field signal collected by the second magnetic field sensor 12 is used as the reference channel input signal r(t). After passing through a parameter-adjustable digital filter, it is compared with the signal channel input signal s(t) to form the error signal function e(n). The parameters are then adjusted through an adaptive algorithm to minimize the mean square value of the error function e(n), which is the value with the best compensation effect, and the true magnetic field of the signal source obtained at this time is output. The adaptive algorithm selected includes, but is not limited to, any one of the following: steepest descent method, recursive least squares algorithm, least mean square error algorithm, adaptive filtering algorithm based on orthogonal triangular decomposition, adaptive filtering algorithm based on subband decomposition, conjugate gradient algorithm, affine projection algorithm, and transform domain adaptive filtering algorithm. In practice, any adaptive algorithm can be selected to optimize the error signal function e(n), thereby compensating for the first magnetic field signal s(t) to obtain the true magnetic field of the signal source. Through various adaptive algorithms, software-level adjustments to hardware-level parameters are achieved, reducing optimization time compared to purely hardware-based electronic circuits.

[0069] like Figure 6 As shown, this embodiment provides a magnetic field compensation system 1, which includes a first magnetic field sensor 11, a second magnetic field sensor 12, a correlation coefficient calculation module 13, a correlation coefficient determination module 14, a compensation module 15, and an adder 16.

[0070] like Figure 2 , Figure 4 , Figure 5 and Figure 6 As shown, the first magnetic field sensor 11 and the second magnetic field sensor 12 are located in the same environmental field, and the distance L1 between the first magnetic field sensor and the signal source is less than the distance L2 between the second magnetic field sensor and the signal source. Specifically, the first magnetic field sensor 11 is used to acquire the superimposed magnetic field of the signal source and the environmental field to obtain a first magnetic field signal s(t); the second magnetic field sensor 12 is used to acquire the magnetic field of the environmental field to obtain a second magnetic field signal r(t); the first magnetic field sensor 11 is defined as the signal channel, and the second magnetic field sensor 12 is defined as the reference channel.

[0071] Specifically, the second magnetic field sensor 12 is configured as a low-sensitivity magnetic field sensor, which can be considered as the second magnetic field sensor 12 not collecting the magnetic field of the signal source, i.e., S2(t) = 0. In this embodiment, both the first magnetic field sensor 11 and the second magnetic field sensor 12 are configured as low-sensitivity magnetic field sensors.

[0072] More specifically, the first magnetic field sensor 11 is configured with, but is not limited to, a magnetometer, a gradiometer, a full-tensor magnetic gradiometer, an optical microcavity sensor, an atomic magnetometer, a fluxgate magnetometer, a Hall sensor, a magnetoresistive sensor, a magnetoelectric sensor, a single-turn coil, and a multi-turn coil. The second magnetic field sensor 12 is configured with, but is not limited to, a magnetometer, a gradiometer, a full-tensor magnetic gradiometer, an optical microcavity sensor, an atomic magnetometer, a fluxgate magnetometer, a Hall sensor, a magnetoresistive sensor, a magnetoelectric sensor, a single-turn coil, and a multi-turn coil. In fact, any sensor capable of detecting magnetic fields can use this method for magnetic field compensation.

[0073] Specifically, the first input terminal of the correlation coefficient calculation module 13 is connected to the first magnetic field signal s(t), and the second input terminal is connected to the second magnetic field signal r(t), used to calculate the correlation coefficient ρ between the environmental magnetic field signal of the first magnetic field sensor and the environmental magnetic field signal of the second magnetic field sensor. The calculation method of the correlation coefficient has been described above and will not be repeated here.

[0074] Specifically, the correlation coefficient determination module 14 is connected to the output terminal of the correlation coefficient calculation module 13, determines the result of the correlation coefficient, and inputs the determination result to the control terminal of the compensation module 15. The correlation coefficient determination result is divided into three types: when the absolute value of the correlation coefficient ρ is equal to 1, the first magnetic field signal s(t) is compensated by the fixed coefficient compensation method to obtain the true magnetic field of the signal source; when the absolute value of the correlation coefficient ρ is greater than 0 and less than 1, the first magnetic field signal s(t) is compensated by the variable coefficient compensation method to obtain the true magnetic field of the signal source; when the absolute value of the correlation coefficient ρ is equal to 0, the position of the first magnetic field sensor 11 and / or the second magnetic field sensor 12 is changed, and step S1 is executed again until the absolute value of the correlation coefficient ρ is not equal to 0.

[0075] Specifically, such as Figure 6 As shown, the compensation module 15 includes a fixed coefficient setting unit 151 and an adaptive filtering unit 152; the input terminal of the compensation module 15 is connected to the second magnetic field signal r(t), and controls the second magnetic field signal r(t) to pass through the fixed coefficient setting unit 151 or the adaptive filtering unit 152 based on the output signal of the correlation coefficient determination module 14.

[0076] More specifically, when the absolute value of the correlation coefficient ρ is equal to 1, the fixed coefficient setting unit of the compensation module 15 is turned on (that is, the output signal of the correlation coefficient determination module 14 controls the second magnetic field signal r(t) to pass through the fixed coefficient setting unit 151). The input end of the fixed coefficient setting unit 151 is connected to the second magnetic field signal r(t), and the output end is connected to the adder 16. The second magnetic field signal r(t) is amplified by a compensation coefficient of K times and then output, so as to facilitate subsequent compensation of the first magnetic field signal s(t).

[0077] More specifically, when the absolute value of the correlation coefficient ρ is greater than 0 and less than 1, the adaptive filtering unit 152 of the compensation module 15 is turned on (that is, the output signal of the correlation coefficient determination module 14 controls the second magnetic field signal r(t) to pass through the adaptive filtering unit 152): the input end of the adaptive filtering unit 152 is connected to the second magnetic field signal r(t), and the output end is connected to the adder 16. The second magnetic field signal is adaptively filtered and then output, which facilitates subsequent compensation of the first magnetic field signal s(t).

[0078] Specifically, the first input terminal of the adder 16 is connected to the first magnetic field signal s(t), and the second input terminal is connected to the output terminal of the compensation module 15. The first magnetic field signal s(t) and the output signal of the compensation module 15 are differentially output to compensate the first magnetic field signal s(t) and obtain the true magnetic field of the signal source.

[0079] As one implementation of the present invention, such as Figure 7 As shown, the first magnetic field sensor 11 is configured as an axial second-order gradiometer, and the second magnetic field sensor 12 is configured as a three-dimensional magnetometer; at this time, the first magnetic field signal G and the second magnetic field signal acquired magnetic field information including three axial components are denoted as B. X B Y B Z The components acquired along each axis are compensated using the spatial magnetic field compensation system 1. If the absolute value of the correlation coefficient ρ is equal to 1, then compensation is performed in each direction using the fixed coefficient method, with each compensation parameter set to K. X K Y K Z The final signal source's true magnetic field Bout = GK X B X -K Y B Y -K Z B Z The specific calculation principles have been described above and will not be repeated here.

[0080] If magnetic field compensation is not performed using the magnetic field compensation system 1 provided in this embodiment, and the known magnetocardiogram signal (i.e., the known signal source) is detected directly using an electronic gradient meter, the output waveform will be as follows: Figure 8 As shown, at this time, the baseline of the R peak and T wave portion of the acquired magnetic field signal with QRS complex has shifted significantly, making further analysis of the waveform impossible. However, magnetic field compensation system 1 provided in this embodiment is used for magnetic field compensation, such as... Figure 9 As shown, the acquired magnetocardiogram (MCC) signal is generally stable, and baseline drift is effectively reduced, which is beneficial for subsequent waveform reading and analysis. In another embodiment, if a variable coefficient compensation method is adopted, the baseline can be further flattened, which is even more beneficial for subsequent MCC signal analysis. It should be noted that since this embodiment acquires a MCC signal, which is a known signal source and whose signal characteristics are easily identifiable, a fixed coefficient compensation method can be directly used to compensate for the signal optimally. If the acquired signal source is unknown or the signal characteristics are not obvious, both fixed coefficient compensation and variable coefficient compensation methods can be used simultaneously to compensate for the unknown signal or the signal with indistinct signal characteristics.

[0081] Therefore, this embodiment can effectively suppress ambient noise of the signal source, improve the signal-to-noise ratio of the acquired signal, and facilitate subsequent signal analysis and processing when applied in the field of weak magnetic fields.

[0082] In summary, this invention provides a spatial magnetic field compensation method and a magnetic field compensation system, comprising: S1, acquiring the magnetic fields of a first magnetic field sensor and a second magnetic field sensor simultaneously to obtain a first magnetic field signal and a second magnetic field signal; S2, when the absolute value of the correlation coefficient is equal to 1, compensating the first magnetic field signal using a fixed coefficient compensation method to obtain the true magnetic field of the signal source; when the absolute value of the correlation coefficient is greater than 0 and less than 1, compensating the first magnetic field signal using a variable coefficient compensation method to obtain the true magnetic field of the signal source; wherein, the correlation coefficient is the correlation coefficient between the environmental magnetic field signal of the first magnetic field sensor and the environmental magnetic field signal of the second magnetic field sensor. This invention effectively solves the problems of complex magnetic field compensation methods under different environments and low signal-to-noise ratio of output signals in existing technologies. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial application value.

[0083] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method of spatial magnetic field compensation, characterized in that, The space magnetic field compensation method includes at least the following: S1. Collect the magnetic fields of the first magnetic field sensor and the second magnetic field sensor at the same time to obtain the first magnetic field signal and the second magnetic field signal; wherein, the first magnetic field sensor is used to acquire the superimposed magnetic field of the signal source and the environmental field; the second magnetic field sensor is used to acquire the magnetic field of the environmental field; S2. When the absolute value of the correlation coefficient is equal to 1, the first magnetic field signal is compensated using the fixed coefficient compensation method to obtain the true magnetic field of the signal source; when the absolute value of the correlation coefficient is greater than 0 and less than 1, the first magnetic field signal is compensated using the variable coefficient compensation method to obtain the true magnetic field of the signal source; when the absolute value of the correlation coefficient is equal to 0, the positions of the first magnetic field sensor and / or the second magnetic field sensor are changed, and step S1 is executed again until the absolute value of the correlation coefficient is not equal to 0; wherein, the correlation coefficient is the correlation coefficient between the environmental magnetic field signal of the first magnetic field sensor and the environmental magnetic field signal of the second magnetic field sensor; The fixed coefficient compensation method includes: multiplying the second magnetic field signal by a compensation coefficient and then outputting the differential signal with the first magnetic field signal to obtain the true magnetic field of the signal source; obtaining the compensation coefficient based on the ratio of the amplitude values ​​of the first magnetic field signal and the second magnetic field signal; the variable coefficient compensation method includes: performing variable coefficient adaptive filtering on the second magnetic field signal based on the first magnetic field signal, and outputting the differential signal with the first magnetic field signal to obtain the true magnetic field of the signal source.

2. The space magnetic field compensation method according to claim 1, characterized in that: In step S1, the acquisition time is set to be greater than or equal to 10 seconds.

3. The space magnetic field compensation method according to claim 1, characterized in that: In step S1, when the location of the signal source is unknown, the third magnetic field sensor is set to collect the third magnetic field signal at the location of the first magnetic field sensor and the fourth magnetic field signal at the location of the second magnetic field sensor. If the third magnetic field signal is greater than the fourth magnetic field signal, then the distance between the first magnetic field sensor and the signal source is less than the distance between the second magnetic field sensor and the signal source. If the third magnetic field signal is less than or equal to the fourth magnetic field signal, then adjust the position of the first magnetic field sensor and / or the position of the second magnetic field sensor until the distance between the first magnetic field sensor and the signal source is less than the distance between the second magnetic field sensor and the signal source.

4. The space magnetic field compensation method according to claim 1, characterized in that: A method for collecting the environmental magnetic field signal of the first magnetic field sensor and the environmental magnetic field signal of the second magnetic field sensor includes: in step S1, in the same environmental field without a signal source, collecting the magnetic field signal at the location of the first magnetic field sensor and the magnetic field signal at the location of the second magnetic field sensor at the same time, respectively as the environmental magnetic field signal of the first magnetic field sensor and the environmental magnetic field signal of the second magnetic field sensor.

5. The space magnetic field compensation method according to claim 4, characterized in that: In step S2, the correlation coefficient satisfies: ； Where ρ represents the correlation coefficient between the environmental magnetic field signals of the first magnetic field sensor and the second magnetic field sensor, s1(t) represents the environmental magnetic field signal of the first magnetic field sensor, and r1(t) represents the environmental magnetic field signal of the second magnetic field sensor. This represents the covariance between the ambient magnetic field signal of the first magnetic field sensor and the ambient magnetic field signal of the second magnetic field sensor. This represents the variance of the ambient magnetic field signal of the first magnetic field sensor. This represents the variance of the ambient magnetic field signal of the second magnetic field sensor.

6. The space magnetic field compensation method according to claim 1, characterized in that: The variable coefficient compensation method also includes: The average power spectrum of the filtered second magnetic field signal is acquired, and the filtering parameters of the second magnetic field signal are adjusted until the average power spectrum of the filtered second magnetic field signal is minimized. Then, the true magnetic field of the signal source is output.

7. The space magnetic field compensation method according to claim 1, characterized in that: The variable coefficient compensation method includes: The second magnetic field signal is filtered and then output differentially with the first magnetic field signal to obtain an error signal function. The parameter values ​​of the error signal function are adjusted by an adaptive algorithm to minimize the mean square value of the error signal function, thereby outputting the true magnetic field of the signal source.

8. The space magnetic field compensation method according to claim 7, characterized in that: The adaptive algorithm is selected from any one of the following: steepest descent method, recursive least squares algorithm, least mean square error algorithm, adaptive filtering algorithm based on orthogonal triangular decomposition, adaptive filtering algorithm based on subband decomposition, conjugate gradient algorithm, affine projection algorithm, and transform domain adaptive filtering algorithm.

9. A magnetic field compensation system, characterized in that: The magnetic field compensation system includes a first magnetic field sensor, a second magnetic field sensor, a correlation coefficient calculation module, a correlation coefficient determination module, a compensation module, and an adder; The first magnetic field sensor and the second magnetic field sensor are located in the same environmental field, and the distance between the first magnetic field sensor and the signal source is less than the distance between the second magnetic field sensor and the signal source; wherein, the first magnetic field sensor is used to acquire the superimposed magnetic field of the signal source and the environmental field to obtain a first magnetic field signal; the second magnetic field sensor is used to acquire the magnetic field of the environmental field to obtain a second magnetic field signal; The first input terminal of the correlation coefficient calculation module is connected to the first magnetic field signal, and the second input terminal is connected to the second magnetic field signal, and is used to calculate the correlation coefficient between the environmental magnetic field signal of the first magnetic field sensor and the environmental magnetic field signal of the second magnetic field sensor. The correlation coefficient determination module is connected to the output of the correlation coefficient calculation module, determines the result of the correlation coefficient, and inputs the determination result to the control terminal of the compensation module; The compensation module includes a fixed coefficient setting unit and an adaptive filtering unit. The input of the compensation module is connected to the second magnetic field signal, and it controls the second magnetic field signal to pass through the fixed coefficient setting unit or the adaptive filtering unit based on the output signal of the correlation coefficient determination module. When the absolute value of the correlation coefficient is equal to 1, the input of the fixed coefficient setting unit is connected to the second magnetic field signal, and the output is connected to the adder, amplifying the second magnetic field signal by a compensation coefficient before outputting it. When the absolute value of the correlation coefficient is greater than 0 and less than 1, the input of the adaptive filtering unit is connected to the second magnetic field signal, and the output is connected to the adder, adaptively filtering the second magnetic field signal before outputting it. The first input terminal of the adder is connected to the first magnetic field signal, and the second input terminal is connected to the output terminal of the compensation module. The adder performs differential output on the first magnetic field signal and the output signal of the compensation module, thereby compensating the first magnetic field signal to obtain the true magnetic field of the signal source.

10. The magnetic field compensation system according to claim 9, characterized in that: The second magnetic field sensor is configured as a low-sensitivity sensor.

11. The magnetic field compensation system according to claim 9 or 10, characterized in that: The first magnetic field sensor is configured as any one of a magnetometer, gradiometer, full tensor magnetic gradiometer, optical microcavity sensor, atomic magnetometer, fluxgate, Hall sensor, magnetoresistive sensor, magnetoelectric sensor, single-turn coil, and multi-turn coil; the second magnetic field sensor is configured as any one of a magnetometer, gradiometer, full tensor magnetic gradiometer, optical microcavity sensor, atomic magnetometer, fluxgate, Hall sensor, magnetoresistive sensor, magnetoelectric sensor, single-turn coil, and multi-turn coil.

12. The magnetic field compensation system according to claim 9, characterized in that: The correlation coefficient calculation module calculates the correlation coefficient to satisfy: ； Where ρ represents the correlation coefficient between the environmental magnetic field signals of the first magnetic field sensor and the second magnetic field sensor, s1(t) represents the environmental magnetic field signal of the first magnetic field sensor, and r1(t) represents the environmental magnetic field signal of the second magnetic field sensor. This represents the covariance between the ambient magnetic field signal of the first magnetic field sensor and the ambient magnetic field signal of the second magnetic field sensor. This represents the variance of the ambient magnetic field signal of the first magnetic field sensor. This represents the variance of the ambient magnetic field signal of the second magnetic field sensor.

13. The magnetic field compensation system according to claim 9, characterized in that: When the absolute value of the correlation coefficient is greater than 0 and less than 1, the output signal of the adder is fed back to the adaptive filtering unit. The adaptive filtering unit is adjusted based on the feedback signal so that when the mean square value of the feedback signal is minimized, the true magnetic field of the signal source is output.

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