阅读说明：本技术 一种提高Overhauser磁传感器拉莫尔旋进信号信噪比的系统及方法 (System and method for improving Larmor precession signal-to-noise ratio of Overhauser magnetic sensor ) 是由 董浩斌 王洪鹏 葛健 刘欢 张艳丽 于 2019-06-28 设计创作，主要内容包括：本发明提供了一种提高Overhauser磁传感器拉莫尔旋进信号信噪比的系统及方法,包括Overhauser磁传感器、传感器激励单元、FID信号处理单元和供电电池；Overhauser磁传感器的信号激励端连接传感器激励单元中的射频激励信号,信号接收端通过单刀双掷开关连接到直流脉冲激励端以及FID信号处理单元,通过控制单刀双掷开关选择Overhauser磁传感器信号连接通路。先利用LC谐振与窄带滤波器限制拉莫尔信号的频带,进行一次降噪,使用时频峰值滤波算法对拉莫尔信号进行二次降噪和信号重建,可以进一步抑制随机噪声以及调理电路引入的噪声,大幅度提高拉莫尔信号信噪比。(The invention provides a system and a method for improving the signal-to-noise ratio of Larmor precession signals of an Overhauser magnetic sensor, which comprise an Overhauser magnetic sensor, a sensor excitation unit, an FID signal processing unit and a power supply battery; the signal excitation end of the Overhauser magnetic sensor is connected with a radio frequency excitation signal in the sensor excitation unit, the signal receiving end is connected to the direct current pulse excitation end and the FID signal processing unit through the single-pole double-throw switch, and the signal connection passage of the Overhauser magnetic sensor is selected by controlling the single-pole double-throw switch. The band of the Larmor signal is limited by the LC resonance and the narrow-band filter, primary noise reduction is carried out, secondary noise reduction and signal reconstruction are carried out on the Larmor signal by using a time-frequency peak filtering algorithm, random noise and noise introduced by a conditioning circuit can be further inhibited, and the signal-to-noise ratio of the Larmor signal is greatly improved.)

1. A system for improving the signal-to-noise ratio of Larmor precession signals of an Overhauser magnetic sensor is characterized by comprising the Overhauser magnetic sensor, a sensor excitation unit, an FID signal processing unit and a power supply battery; the signal excitation end of the Overhauser magnetic sensor is connected with a radio frequency excitation signal in the sensor excitation unit, the signal receiving end is connected to the direct current pulse excitation end and the FID signal processing unit through the single-pole double-throw switch, and the signal connection passage of the Overhauser magnetic sensor is selected by controlling the single-pole double-throw switch.

2. The system for improving the signal-to-noise ratio of the larmor precession signal of an Overhauser magnetic sensor of claim 1, wherein the sensor excitation unit comprises a radio frequency excitation and a dc pulse excitation, the radio frequency excitation is a 60.7MHz sinusoidal signal generated by the DDS signal generator, and the dc pulse excitation is a microsecond dc signal generated by the gate control switch.

3. The system for improving the signal-to-noise ratio of the larmor precession signal of the Overhauser magnetic sensor of claim 1, wherein the FID signal processing unit comprises a tuning capacitor, a JEFT amplifier, a narrow-band filter, an ADC, and a digital signal processor; the tuning capacitor and an inner inductance coil of the Overhauser magnetic sensor form an LC resonance network, frequency selection is carried out on Larmor precession signals, a JEFT amplifier is connected behind the LC resonance network and amplifies the Larmor precession signals, a narrow-band filter is connected behind an amplifier circuit and used for limiting the bandwidth of the Larmor precession signals and carrying out preliminary noise reduction on the Larmor signals. The 16-bit ADC analog-to-digital conversion circuit is connected behind the filter, continuous Larmor signals are discretized and digitized, analog-to-digital conversion results are sent to the digital signal processor, the module is used for filtering discretized Larmor precession signals, secondary noise reduction is carried out on the Larmor precession signals by means of a video peak value filtering algorithm, and the signal-to-noise ratio is improved.

4. The utility model provides a method for improving Overhauser magnetic sensor larmor precession signal-to-noise ratio, is based on the systematic realization that improves Overhauser magnetic sensor larmor precession signal-to-noise ratio, its characterized in that includes:

s1, exciting an Overhauser magnetic sensor by using a sensor exciting unit to generate a Larmor precession signal;

s2, performing preliminary noise reduction on the Larmor precession signal obtained in the step one by utilizing hardware circuits such as LC series resonance, a narrow-band filter and the like, limiting the frequency bandwidth of the Larmor precession signal, and reducing thermal noise, contact noise and high-frequency noise of the sensor;

and S3, acquiring the Larmor precession signal obtained in the second step by using the ADC, and sending the dispersed Larmor precession signal S (n) to the digital signal processor.

And S4, performing noise reduction on the Larmor precession signal by utilizing a time-frequency peak value filtering algorithm in the digital signal processor.

5. The method according to claim 4, wherein the step S4 specifically includes:

s41, carrying out scale transformation, and obtaining a normalized signal S after the scale transformation of the discrete Larmor precession S (n)₁(n)：

Wherein, B_HAnd B_LRespectively, a maximum and a minimum satisfying the transformed signal, S (n) is a discrete Larmor precession signal, S₁(n) is the normalized signal, min [ S (n)]Is the minimum value of S (n), max [ S (n)]Is the maximum value in S (n);

s42, normalizing the signalS₁(n) encoding the signal to an instantaneous frequency to obtain an analysis signal Z (n) of unit amplitude, where μ is a frequency modulation index, λ is an integration parameter, and Z (n) is an analysis signal of unit amplitude,

s43, the peak of the pseudo-Wigner-wille distribution (PWVD) of the analysis signal z (n) in unit amplitude is taken, and the PWVD distribution of z (n) can be expressed as:

wherein, W_Z(n, k) is the PWVD profile of Z (n),is a windowing function. K is a two-dimensional parameter of PWVD distribution;

s44, according to the frequency variation, the maximum value of the time-frequency distribution of the analytic signal is the estimation of the instantaneous frequency, namely:

wherein f is_zIs the resulting estimate, μ is the frequency modulation index, arg max [ W [ ]_z(n,k)]To take W_Z(n, k) absolute value of maximum value;

s45, obtaining an estimated value of Larmor precession signal amplitude of the effective Overhauser magnetic sensor through inverse scale transformation:

wherein the content of the first and second substances,is an estimate of the clean larmor precession signal.

Technical Field

The invention relates to the technical field of electronic information, in particular to a system and a method for improving the signal-to-noise ratio of Larmor precession signals of an Overhauser magnetic sensor.

Background

The Overhauser magnetic sensor is a high-precision magnetic field measurement sensor based on nuclear magnetic resonance and electron paramagnetic resonance principles, and can be used in the fields of geomagnetic field observation, geological resource exploration, underground unexploded bomb detection and the like. The working principle is that high-frequency excitation and transient direct current excitation are utilized to act on free radical solution inside the sensor, after the direct current excitation is removed, protons in the free radical solution can do precession motion around the direction of a geomagnetic field, a Larmor precession signal is received by a group of induction coils which are connected in series reversely, the frequency of the precession signal and the total geomagnetic field value form a fixed relation, the geomagnetic field can be measured by measuring the frequency of the Larmor precession signal, and therefore the signal-to-noise ratio of the Larmor precession signal of the Overhauser magnetic sensor can directly influence the accuracy of the total geomagnetic field value measurement.

At present, the method for improving the signal-to-noise ratio of larmor precession signals of an Overhauser magnetic sensor mainly focuses on the aspect of circuit hardware, and improves the signal-to-noise ratio of larmor signals through filter circuits such as LC resonance and narrow-band filtering, although the bandwidth of a frequency band can be effectively shortened, and the signal-to-noise ratio is improved, the following problems still exist: 1) random noise is not well inhibited; 2) the hardware circuit can introduce circuit noise, add new noise source, it is difficult to obtain the larmor precession signal of higher SNR.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a system and a method for improving the signal-to-noise ratio of larmor precession signal of Overhauser magnetic sensor, aiming at the technical problem that the signal-to-noise ratio of larmor precession signal of the existing Overhauser magnetic sensor is not high.

A system for improving the Larmor precession signal-to-noise ratio of an Overhauser magnetic sensor comprises an Overhauser magnetic sensor, a sensor excitation unit, an FID signal processing unit and a power supply battery; the signal excitation end of the Overhauser magnetic sensor is connected with a radio frequency excitation signal in the sensor excitation unit, the signal receiving end is connected with the direct current pulse excitation end and the FID signal processing unit through the single-pole double-throw switch, and a signal connection circuit of the Overhauser magnetic sensor is selected by controlling the single-pole double-throw switch.

Further, the sensor excitation unit comprises radio frequency excitation and direct current pulse excitation, the radio frequency excitation is a 60.7MHz sinusoidal signal generated by the DDS signal generator, and the direct current pulse excitation is a microsecond direct current signal generated by the gate control switch.

Further, the FID signal processing unit comprises a tuning capacitor, a JEFT amplifier, a narrow-band filter, an ADC and a digital signal processor; the tuning capacitor and an inner inductance coil of the Overhauser magnetic sensor form an LC resonance network, the frequency of a Larmor precession signal is selected, a JEFT amplifier is connected behind the LC resonance network and amplifies the Larmor precession signal, and a narrow-band filter is connected behind an amplifier circuit and used for limiting the bandwidth of the Larmor precession signal and initially reducing noise of the Larmor signal. The 16-bit ADC analog-to-digital conversion circuit is connected behind the filter, continuous Larmor signals are discretized and digitized, analog-to-digital conversion results are sent to the digital signal processor, the module is used for filtering discretized Larmor precession signals, secondary noise reduction is carried out on the Larmor precession signals by means of a video peak value filtering algorithm, and the signal-to-noise ratio is improved.

The method for improving the signal-to-noise ratio of the Larmor precession signal of the Overhauser magnetic sensor is realized based on a system for improving the signal-to-noise ratio of the Larmor precession signal of the Overhauser magnetic sensor, and comprises the following steps of:

s1, exciting an Overhauser magnetic sensor by using a sensor exciting unit to generate a Larmor precession signal;

s2, primarily denoising the Larmor precession signal obtained in the step one by utilizing hardware circuits such as LC series resonance and a narrow-band filter, limiting the frequency bandwidth of the Larmor precession signal, and reducing thermal noise, contact noise and high-frequency noise of the sensor;

and S3, acquiring the Larmor precession signal obtained in the second step by using the ADC, and sending the dispersed Larmor precession signal S (n) to the digital signal processor.

And S4, performing noise reduction on the Larmor precession signal by utilizing a time-frequency peak value filtering algorithm in the digital signal processor.

Further, step S4 specifically includes:

s41, carrying out scale transformation, and obtaining a normalized signal S after the scale transformation of the discrete Larmor precession S (n)₁(n)：

Wherein, B_HAnd B_LRespectively, a maximum and a minimum satisfying the transformed signal, S (n) is a discrete Larmor precession signal, S₁(n) is the normalized signal, min [ S (n)]Is the minimum value of S (n), max [ S (n)]Is the maximum value in S (n);

s42, normalizing signal S₁(n) encoding the signal to an instantaneous frequency to obtain an analysis signal Z (n) of unit amplitude, where μ is a frequency modulation index, λ is an integration parameter, and Z (n) is an analysis signal of unit amplitude,

s43, the peak of the pseudo-Wigner-wille distribution (PWVD) of the analysis signal z (n) in unit amplitude is taken, and the PWVD distribution of z (n) can be expressed as:

wherein, W_Z(n, k) is the PWVD profile of Z (n),is a windowing function. K is a two-dimensional parameter of PWVD distribution;

s44, according to the frequency variation, the maximum value of the time-frequency distribution of the analytic signal is the estimation of the instantaneous frequency, namely:

wherein f is_zIs obtained byEstimate, μ is the frequency modulation index, argmax [ W ]_z(n,k)]To take W_Z(n, k) absolute value of maximum value;

s45, obtaining an estimated value of Larmor precession signal amplitude of the effective Overhauser magnetic sensor through inverse scale transformation:

wherein the content of the first and second substances,is an estimate of the clean larmor precession signal.

Compared with the prior art, the invention has the beneficial effects that:

1. aiming at random noise of Larmor signals of an Overhauser magnetic sensor and noise introduced by a conditioning circuit, the method provided by the invention can effectively remove the influence of the noise, and the signal-to-noise ratio of the obtained Larmor precession signals is better;

2. larmor precession signal filtering of the Overhauser magnetic sensor can be realized in real time by utilizing a digital signal processor;

3. the geomagnetic field measurement precision of the Overhauser magnetic sensor can be further improved.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

FIG. 1 is a system diagram for improving the signal-to-noise ratio of Larmor precession signals of an Overhauser magnetic sensor according to the present invention;

FIG. 2 is a flowchart of a method for improving the signal-to-noise ratio of Larmor precession signals of an Overhauser magnetic sensor according to the present invention;

FIG. 3 is a comparison graph of filtering effects according to an embodiment of the present invention.

Detailed Description

For a more clear understanding of the technical features, objects and effects of the present invention, embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

A system for improving the Larmor precession signal-to-noise ratio of an Overhauser magnetic sensor comprises an Overhauser magnetic sensor, a sensor excitation unit, an FID signal processing unit and a power supply battery. As shown in fig. 1, a signal excitation end of the Overhauser magnetic sensor is connected to a radio frequency excitation signal in the sensor excitation unit, a signal receiving end is connected to the direct current pulse excitation end and the FID signal processing unit through the single-pole double-throw switch, and a signal connection path of the Overhauser magnetic sensor is selected by controlling the single-pole double-throw switch.

The sensor excitation unit comprises radio frequency excitation and direct current pulse excitation, wherein the radio frequency excitation is a 60.7MHz sinusoidal signal generated by the DDS signal generator, and the direct current pulse excitation is a microsecond direct current signal generated by the gating switch.

The FID signal processing unit comprises a tuning capacitor, a JEFT amplifier, a narrow-band filter, an ADC and a digital signal processor; the tuning capacitor and an inner inductance coil of the Overhauser magnetic sensor form an LC resonance network, the frequency of a Larmor precession signal is selected, a JEFT amplifier is connected behind the LC resonance network and amplifies the Larmor precession signal, and a narrow-band filter is connected behind an amplifier circuit and used for limiting the bandwidth of the Larmor precession signal and preliminarily reducing noise of the Larmor signal. The 16-bit ADC analog-to-digital conversion circuit is connected behind the filter, continuous Larmor signals are discretized and digitized, analog-to-digital conversion results are sent to the digital signal processor, the module is used for filtering discretized Larmor precession signals, secondary noise reduction is carried out on the Larmor precession signals by means of a video peak value filtering algorithm, and the signal-to-noise ratio is improved.

The method for improving the signal-to-noise ratio of the Larmor precession signal of the Overhauser magnetic sensor is realized based on a system for improving the signal-to-noise ratio of the Larmor precession signal of the Overhauser magnetic sensor, and comprises the following steps of:

s1, exciting an Overhauser magnetic sensor by using a sensor exciting unit to generate a Larmor precession signal;

s2, primarily denoising the Larmor precession signal obtained in the step one by utilizing hardware circuits such as LC series resonance and a narrow-band filter, limiting the frequency bandwidth of the Larmor precession signal, and reducing thermal noise, contact noise and high-frequency noise of the sensor;

and S3, acquiring the Larmor precession signal obtained in the second step by using the ADC, and sending the dispersed Larmor precession signal S (n) to the digital signal processor.

S4, performing noise reduction on the larmor precession signal by using a time-frequency peak filtering algorithm in the digital signal processor, as shown in fig. 2, specifically including:

s41, carrying out scale transformation, and obtaining a normalized signal S after the scale transformation of the discrete Larmor precession S (n)₁(n)：

Wherein, B_HAnd B_LRespectively the maximum and minimum values that satisfy the transformed signal. S (n) is a discrete Larmor precession signal, S₁(n) is the normalized signal. min [ S (n)]Is the minimum value of S (n), max [ S (n)]Is the maximum value in S (n).

S42, normalizing signal S₁(n) encoding the signal to an instantaneous frequency to obtain an analysis signal z (n) of a unit amplitude, where μ is a frequency modulation index, λ is an integration parameter, and z (n) is an analysis signal of a unit amplitude.

S43, the peak of the pseudo-Wigner-wille distribution (PWVD) of the analysis signal z (n) in unit amplitude is taken, and the PWVD distribution of z (n) can be expressed as:

wherein, W_Z(n, k) is the PWVD profile of Z (n),is a windowing function. K is a two-dimensional parameter of the PWVD distribution.

S44, according to the frequency variation, the maximum value of the time-frequency distribution of the analytic signal is the estimation of the instantaneous frequency, namely:

wherein f is_zIs the resulting estimate, μ is the frequency modulation index, argmax [ W [ ]_z(n,k)]To take W_ZAbsolute value of the maximum value of (n, k).

S45, obtaining an estimated value of Larmor precession signal amplitude of the effective Overhauser magnetic sensor through inverse scale transformation:

wherein the content of the first and second substances,is an estimate of the clean larmor precession signal.

By the method, a pure signal can be recovered from the Larmor precession signal of the Overhauser magnetic sensor containing noise.

The invention firstly utilizes LC resonance and narrow band filter to limit the frequency band of Larmor signal, carries out primary noise reduction, and uses time-frequency peak filtering algorithm to carry out secondary noise reduction and signal reconstruction on Larmor signal, thus further inhibiting random noise and noise introduced by a conditioning circuit and greatly improving the signal-to-noise ratio of Larmor signal. The signal in fig. 3 is a larmor precession signal of an unconditioned Overhauser magnetic sensor acquired by an ADC collector, and it can be seen that the larmor signal is completely annihilated by noise, the upper diagram in fig. 3 is an original larmor precession signal output by the sensor, and the lower diagram in fig. 3 is a larmor precession signal obtained after LC resonance and narrow-band filtering primary processing and time-frequency peak filtering secondary filtering processing proposed by the present invention.

While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and various modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention as defined in the appended claims.