CN109633759B - Ground magnetic resonance signal rapid extraction device and method based on phase-locked amplification technology - Google Patents

Abstract

The invention relates to the technical field of nuclear magnetic resonance groundwater detection, in particular to a device and method for rapidly extracting ground magnetic resonance signals based on phase-lock amplification technology, comprising: a receiving coil for inducing magnetic resonance signals generated by groundwater; a bandwidth of 200 Hz center frequency Adjustable band-pass filter, the center frequency is adjusted to the Larmor frequency through the main control module, and the magnetic resonance signal is received; the main control module controls the signal generator to generate a cosine signal with the Larmor frequency, which is used as a reference signal and The output signal of the bandwidth 200Hz center frequency adjustable band-pass filter realizes frequency relocation through the in-phase channel; the main control module controls the signal generator to generate a cosine signal with Larmor frequency, and then converts it into a sine signal through a 90° phase shifter. The signal is used as the reference signal and the output signal of the bandwidth 200Hz center frequency adjustable band-pass filter realizes frequency relocation through the quadrature channel, which can realize fast extraction.

Description

Device and method for fast extraction of ground magnetic resonance signals based on lock-in amplification technology

technical field

The invention relates to the technical field of nuclear magnetic resonance groundwater detection, in particular to a device and method for rapidly extracting ground magnetic resonance signals based on phase-lock amplification technology.

Background technique

Ground magnetic resonance technology can directly detect groundwater, and has the advantages of qualitative and quantitative detection. However, the ground magnetic resonance signal is extremely weak, only at the nanovolt level, which is susceptible to noise interference and has a low signal-to-noise ratio. Especially in areas with severe human noise interference, the problem of amplifier saturation and inability to extract valid signals occurs.

CN102053280A discloses the "nuclear magnetic resonance groundwater detection system and detection method with reference coil", but this method can only eliminate the relevant power frequency harmonic noise, and the noise cancellation effect is affected by the structure, laying position and noise of the two coils. Mutagenicity has a big impact.

CN104614778A discloses "An ICA-based Noise Removal Method for Nuclear Magnetic Resonance Groundwater Detection Signals", which uses the ICA algorithm to weaken random noise. However, in the actual noise environment, it is difficult to achieve reliable suppression of colored noise.

CN108254794A discloses "a magnetic resonance denoising method based on modeling inverse recovery technology", which uses extremely narrow low-pass filtering to suppress noise, and restores the original signal through post-Laplace and derivative transformation. However, because the method is implemented in software, the problem of saturation of the amplifier of the acquisition device cannot be suppressed, and the data operation is complicated and it is difficult to realize rapid signal extraction in the on-chip embedded system.

At present, the traditional de-noising algorithms for detecting NMR signals mostly de-noise for a single noise, which cannot effectively deal with the complex environmental noise in practical work. In addition, none of the above three methods can suppress the problem of saturation of the amplifier of the acquisition device, and they are all subsequent software denoising, which cannot extract signals on the spot in real time. Therefore, it is of great significance to study a new technology that has anti-saturation function and can quickly extract ground magnetic resonance signals in field work sites.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a fast extraction device for ground magnetic resonance signals based on lock-in amplification technology on the one hand, and a method for fast extraction of ground magnetic resonance signals based on lock-in amplification technology on the other hand.

The present invention is realized in this way, a ground magnetic resonance signal fast extraction device based on phase-lock amplification technology, the device includes: a receiving coil, a bandwidth 200Hz center frequency adjustable band-pass filter, a signal generator, and a 90° phase shifter , in-phase channel, quadrature channel and main control module;

the receiving coil senses the magnetic resonance signal generated by the groundwater;

The center frequency adjustable band-pass filter with a bandwidth of 200Hz is adjusted to the Larmor frequency through the main control module, and the magnetic resonance signal is received;

The main control module controls the signal generator to generate a cosine signal with a Larmor frequency, and the signal is used as a reference signal and the output signal of the bandwidth 200Hz center frequency adjustable band-pass filter to achieve frequency relocation through the in-phase channel;

The main control module controls the signal generator to generate a cosine signal with a Larmor frequency, which is then converted into a sine signal through a 90° phase shifter, which is used as a reference signal and the output of a 200Hz center frequency adjustable bandpass filter The signal realizes frequency relocation through the quadrature channel;

The main control module collects the signals of the in-phase channel and the quadrature channel, and extracts the ground magnetic resonance signal.

Further, it also includes: an LC matching network and a preamplifier, the LC matching network receives the magnetic resonance signal of the receiving coil, and realizes resonance to increase the signal amplitude and suppress noise interference;

The preamplifier amplifies the signal via the LC matching network for the first time, and transmits the amplified signal to a band-pass filter with a bandwidth of 200Hz that can be adjusted at the center frequency.

Further, the in-phase channel includes a first multiplier and a first low-pass filter to form a quadrature vector type lock-in amplifier and an in-phase two-stage amplifier, the receiving bandwidth is 200Hz center frequency adjustable band-pass filter, and the signal is The generator is connected, the cosine signal of the Larmor frequency and the output signal of the adjustable band-pass filter with the center frequency of 200Hz pass through the first multiplier to achieve frequency relocation, and then pass through the first low-pass filter to eliminate high-frequency components and most of the noise , which is further amplified by the non-inverting secondary amplifier.

Further, the quadrature channel includes a second multiplier and a second low-pass filter to form a quadrature vector type lock-in amplifier and a quadrature second-stage amplifier, and a cosine signal with a Larmor frequency is passed through a 90° phase shifter. Converted to a sine signal, this signal is used as a reference signal and the output signal of a bandwidth 200Hz center frequency adjustable band-pass filter through the second multiplier to achieve frequency relocation, and then through the second low-pass filter to eliminate high-frequency components and most of the noise, It is further amplified by quadrature secondary amplifiers.

Further, it also includes an A/D acquisition card, the main control module controls the A/D acquisition card to acquire the signal of the in-phase channel, and acquires the original data of the in-phase channel; controls the A/D acquisition card to acquire the signal of the channel, and acquires the positive signal. Raw data of traffic lanes.

Further, both the first low-pass filter and the second low-pass filter are first-order low-pass filters with a cutoff frequency of 20 Hz.

Further, the second low-pass filters are first-order low-pass filters with a cutoff frequency of 20 Hz.

A method for rapidly extracting ground magnetic resonance signals based on lock-in amplification technology, the method comprising:

The magnetic resonance signal generated by the groundwater is induced by the receiving coil;

The magnetic resonance signal is passed through a tunable bandpass filter with a bandwidth of 200Hz center frequency, and the center frequency is the Larmor frequency;

Generate a cosine signal with a Larmor frequency, which is used as a reference signal and the output signal of a 200Hz center frequency adjustable bandpass filter with a bandwidth of 200Hz to achieve frequency relocation through the in-phase channel;

Generate a cosine signal with Larmor frequency, and then convert it into a sine signal through a 90° phase shift. This signal is used as a reference signal and the output signal of a bandwidth 200Hz center frequency adjustable band-pass filter to achieve frequency relocation through a quadrature channel;

The signals of the in-phase channel and the quadrature channel are collected, and the ground magnetic resonance signal is extracted.

Further, the original data formula of the in-phase channel is expressed as

When the acquisition time is greater than 10ms, exp(-t/T ₂ *)>>exp(-ω _c t), the original data formula of the collected in-phase channel is simplified as

Take the logarithm of the above formula to get the equation of the straight line

T ₂ *=-1/k is obtained from the slope k of the straight line equation, and then the binary linear equation is obtained by the vertical intercept I(0) of the straight line equation:

In the same way, a binary linear equation of the orthogonal channel is obtained:

Q(0) is the vertical intercept of the straight line equation after the logarithm of the quadrature channel. The equations (4) and (5) are simultaneously established to obtain the initial amplitude E ₀ and phase θ.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The device and method for rapidly extracting ground magnetic resonance signals based on the lock-in amplification technology provided by the present invention can realize real-time on-site signal extraction with low computational complexity through the data acquired through the quadrature channel and the in-phase channel.

(2) The device for rapidly extracting ground magnetic resonance signals based on the lock-in amplification technology provided by the present invention adopts the LC matching network to improve the detection sensitivity, and at the same time effectively solves the problem of preamplifier saturation;

(3) The device for rapidly extracting ground magnetic resonance signals based on the lock-in amplification technology provided by the present invention adopts multi-stage hardware filtering, especially the first and second low-pass filters based on low cut-off frequencies can effectively suppress the saturation of the secondary amplifier , and can realize the full amplification of the secondary amplifier, without using the A/D capture card with high conversion bits, which reduces the cost;

Additional aspects and advantages of the present invention will become apparent from the following description, or learned by practice of the present invention.

Description of drawings

1 is a device for rapidly extracting ground magnetic resonance signals based on a lock-in amplification technology according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a main control module of the present invention.

FIG. 3 is a circuit diagram of the LC matching network of the present invention.

FIG. 4 is a test device according to an embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

1 shows a schematic block diagram of a device for rapidly extracting ground magnetic resonance signals based on lock-in amplification technology according to the present invention; a device for rapidly extracting ground magnetic resonance signals based on lock-in amplification technology, the device includes: a receiving coil , LC matching network, preamplifier, bandwidth 200Hz center frequency adjustable bandpass filter, signal generator, 90° phase shifter, first multiplier, second multiplier, first low pass filter, second low Pass filter, non-inverting secondary amplifier, quadrature secondary amplifier, A/D acquisition card, main control module.

2 shows a schematic block diagram of the main control module of the present invention; the main control module includes a DSP module, an FPGA module, a key, and a display.

Among them, the receiving coil 1 is connected to the preamplifier 3 through the LC matching network 2 in the connection relationship, and the preamplifier 3 is connected to the first multiplier 7 and the second multiplier 8 respectively through the bandwidth 200Hz center frequency adjustable bandpass filter 4. The first multiplier 7 is connected to the in-phase second-stage amplifier 11 through the first low-pass filter 9, the second multiplier 8 is connected to the quadrature second-stage amplifier 12 through the second low-pass filter 10, and the in-phase second-stage amplifier 11 and the quadrature secondary amplifier 12 are respectively connected with the A/D acquisition card 13, and the A/D acquisition card 13 is respectively connected with the signal generator 5 and the wide 200Hz center frequency adjustable bandpass filter 4 through the main control module 14, and the signal generation The multiplier 5 is connected to the first multiplier 7 and the 90° phase shifter 6 respectively, the 90° phase shifter 6 is connected to the second multiplier 8 , the DSP module 15 is respectively connected to the FPGA module 16 , the key 17 and the display 18 .

The receiving coil 1 senses the magnetic resonance signal generated by the groundwater, and transmits the signal to the LC matching network 2;

3 shows a circuit diagram of the LC matching network of the present invention, the LC matching network 2 is composed of a matching capacitor C and an LC passive filter, and the LC passive filter is composed of L1, C1, L2, C2, L3, The 3rd-order Π-type filter composed of C3, the matching capacitor and the receiving coil realize resonance to improve the signal amplitude, and the LC passive filter suppresses noise interference to prevent the saturation of the preamplifier 3;

The preamplifier 3 amplifies the signal for the first time, and transmits the amplified signal to the adjustable bandpass filter 4 with a bandwidth of 200Hz center frequency;

The bandwidth 200Hz center frequency adjustable bandpass filter 4 is a bandpass filter with an adjustable center frequency and a bandwidth of 200Hz. The center frequency is adjusted by the main control module 14 and adjusted to the Larmor frequency, and the bandwidth of 200Hz is guaranteed. The ground magnetic resonance signal can be obtained without distortion, and the noise can be further suppressed;

The first multiplier 7 and the first low-pass filter 9 form the in-phase channel of the quadrature vector type lock-in amplifier, and the main control module 14 generates a cosine signal with a Larmor frequency through the control signal generator 5. The signal is used as a reference signal and the output signal of the bandwidth 200Hz center frequency adjustable band-pass filter 4 realizes frequency relocation through the first multiplier, and then passes through the first low-pass filter 9 to eliminate high-frequency components and most of the noise. Finally, the main The control module controls the A/D acquisition card 13 to obtain the signal further amplified by the in-phase secondary amplifier 11, and collects the original data of the in-phase channel;

The second multiplier 8 and the second low-pass filter 10 form the quadrature channel of the quadrature vector type lock-in amplifier, and the main control module 14 generates a cosine signal with a Larmor frequency by controlling the signal generator 5, Then, it is converted into a sinusoidal signal through a 90° phase shifter 6, which is used as a reference signal and the output signal of the bandwidth 200Hz center frequency adjustable bandpass filter 4 to achieve frequency relocation through the second multiplier 8, and then pass through the second low-pass filter. The device 10 de-noises high-frequency components and most of the noise, and finally, the main control module controls the A/D acquisition card 13 to obtain the signal further amplified by the quadrature secondary amplifier 12, and collects the original data of the quadrature channel;

The first low-pass filter 9 and the second low-pass filter 10 both use first-order low-pass filters with a cut-off frequency of 20 Hz. Due to the small pass-band range, the noise and signals outside the frequency band are effectively filtered out, effectively solving the problem. The problem of saturation of the secondary amplifier is solved, and the signal output by the low-pass filter is mainly composed of ground magnetic resonance signals, which can be further amplified by the secondary amplifier to the range that can be recognized by the low conversion bit A/D, which further reduces the cost of the device. .

The main control module 14 is composed of a DSP module 15, an FPGA module 16, a button 17 and a display 18, and the human-computer interaction is realized through the button 17 and the display 18. In addition to the above-mentioned control work, a ground magnetic resonance signal based on the lock-in amplification technology is The fast extraction method is implemented on the main control module 14 , and processes the collected raw data of the in-phase channel and the raw data of the quadrature channel in real time to quickly extract signals, and display the extracted signals on the display 18 .

A method for rapidly extracting ground magnetic resonance signals based on lock-in amplification technology, the method comprising:

The magnetic resonance signal generated by the groundwater is induced by the receiving coil;

The magnetic resonance signal is passed through a tunable bandpass filter with a bandwidth of 200Hz center frequency, and the center frequency is the Larmor frequency;

Generate a cosine signal with a Larmor frequency, which is used as a reference signal and the output signal of a bandwidth 200Hz center frequency adjustable band-pass filter to achieve frequency relocation through the in-phase channel;

A cosine signal with a Larmor frequency is generated, and then converted into a sine signal through a 90° phase shift. This signal is used as a reference signal and the output signal of a bandwidth 200Hz center frequency adjustable band-pass filter to achieve frequency relocation through the quadrature channel;

The signals of the in-phase channel and the quadrature channel are collected, and the ground magnetic resonance signal is extracted.

The original data formula of the non-inverting channel can be expressed as

The three key parameters of the magnetic resonance signal include the initial amplitude E ₀ , the average relaxation time T ₂ * and the phase θ. Since the average relaxation time of the magnetic resonance signal is 30≤T ₂ *≤1000ms, that is, 1<1/T ₂ *< 33.3, and the cutoff frequency of the low-pass filter is 20Hz, the corresponding cutoff angular frequency is ω _c =125.65rad/s, when the acquisition time is greater than 10ms, exp(-t/T ₂ *)>>exp(-ω _c t), the original data formula of the in-phase channel collected at this time can be simplified as

Take the logarithm of the above formula to get the equation of the straight line

First, T ₂ *=-1/k can be obtained through the slope k of the straight line equation, and then the binary linear equation can be obtained through the vertical intercept I(0) of the straight line equation

Similarly, a binary linear equation of the orthogonal channel can also be obtained

Q(0) is the vertical intercept of the straight line equation after the logarithm of the quadrature channel. The equations (4) and (5) are established simultaneously, and E ₀ and phase θ can be obtained. Ground magnetic resonance signals.

Example:

The device and method for rapidly extracting ground magnetic resonance signals based on the lock-in amplification technology proposed by the present invention are tested by using the measuring device shown in FIG. 4 . The programmable signal source generates an artificial magnetic resonance signal with E ₀ =200nV,f _L =2000Hz,T ₂ *=150ms and θ=30° in the signal coil through the voltage attenuator, and its expression is e(t)=200exp( -t/0.15)cos(2π×2000×t+30°), since the receiving coil is placed in parallel with the signal coil, and the same number of turns, wire diameter and structure are used, the same magnetic resonance is also coupled in the receiving coil. At the same time, the receiving coil is coupled with spatial electromagnetic noise, the controller starts the output signal of the programmable signal source through the synchronous trigger, and simultaneously starts the fast extraction device proposed by the present invention.

The reference signals output by the adjustment signal generator and the 90° phase shifter are cosine signal and sine signal with frequency f _L =2000Hz, order 1 of two low-pass filters and cut-off angular frequency ω _c =125.67rad/s. The key parameters of the extracted magnetic resonance signal are displayed on site, and the results are E ₀ =194.65nV, T ₂ *=152.78ms and θ=29.32°, and the accuracy of E ₀ , T ₂ * and θ is 97.32% compared with the original signal, respectively , 98.14% and 97.73%, effective signals are obtained, and the results can be processed and displayed in real time.

Claims (8)

1. A ground magnetic resonance signal rapid extraction device based on a phase-locked amplification technology is characterized by comprising: the device comprises a receiving coil, a band-pass filter with the bandwidth of 200Hz and the center frequency adjustable, a signal generator, a 90-degree phase shifter, an in-phase channel, a quadrature channel and a main control module;

the receiving coil is used for inducing magnetic resonance signals generated by underground water;

the band-pass filter with the adjustable central frequency of 200Hz of bandwidth adjusts the central frequency to be Larmor frequency through the main control module and receives magnetic resonance signals;

the master control module controls the signal generator to generate a cosine signal with Larmor frequency, and the signal is used as a reference signal and an output signal of a center frequency adjustable band-pass filter with the bandwidth of 200Hz to realize frequency relocation through an in-phase channel;

the master control module controls the signal generator to generate a cosine signal with Larmor frequency, the cosine signal is converted into a sine signal through the 90-degree phase shifter, and the sine signal serves as a reference signal and is frequency shifted through an orthogonal channel with an output signal of a center frequency adjustable band-pass filter with the bandwidth of 200 Hz;

the main control module collects signals of an in-phase channel and a quadrature channel and extracts a ground magnetic resonance signal;

the extraction of the ground magnetic resonance signal comprises the steps of formulating the original data of the in-phase channel into

Wherein,

to mean relaxation time, ω_cIn order to cut off the angular frequency of the antenna,

when the acquisition time is greater than 10ms,

the collected original data of the same-phase channel is reduced to

Logarithm of the above formula to obtain a linear equation

By the slope k of the linear equation

Then obtaining a linear equation of two-dimensional through the longitudinal intercept I (0) of the linear equation:

in the same way, a linear equation of two elements of the orthogonal channel is obtained:

q (0) is the longitudinal intercept of the linear equation after the logarithm of the orthogonal channel is solved, equations (4) and (5) are combined to establish an equation set, and the initial amplitude E is solved₀And a phase theta.

2. The apparatus of claim 1, further comprising: the magnetic resonance circuit comprises an LC matching network and a preamplifier, wherein the LC matching network receives a magnetic resonance signal of a receiving coil, realizes resonance to improve signal amplitude and suppresses noise interference;

the preamplifier amplifies the signal passing through the LC matching network for the first time and transmits the amplified signal to a center frequency adjustable band-pass filter with the bandwidth of 200 Hz.

3. The device according to claim 1, wherein the in-phase channel comprises a quadrature vector type lock-in amplifier and an in-phase secondary amplifier which are composed of a first multiplier and a first low-pass filter, the quadrature vector type lock-in amplifier receives a center frequency tunable band-pass filter with a bandwidth of 200Hz and is connected with the signal generator, the frequency shift between the cosine signal of the larmor frequency and the output signal of the center frequency tunable band-pass filter with the bandwidth of 200Hz is realized through the first multiplier, the high-frequency component and most of noise are eliminated through the first low-pass filter, and the signals are further amplified through the in-phase secondary amplifier.

4. The apparatus of claim 1, wherein the quadrature channel comprises a quadrature vector type lock-in amplifier and a quadrature two-stage amplifier, the second multiplier and the second low-pass filter constitute a quadrature vector type lock-in amplifier, a cosine signal with larmor frequency is converted into a sine signal through a 90 ° phase shifter, the sine signal is used as a reference signal, the frequency shift is realized through the second multiplier with an output signal of a center frequency adjustable band-pass filter with a bandwidth of 200Hz, the high frequency component and most of noise are eliminated through the second low-pass filter, and the signal is further amplified through the quadrature two-stage amplifier.

5. The device according to claim 1, wherein the device further comprises an a/D acquisition card, and the main control module controls the a/D acquisition card to acquire signals of an in-phase channel and acquire original data of the in-phase channel; and controlling an A/D acquisition card to acquire a channel signal and acquiring the original data of the orthogonal channel.

6. The apparatus according to claim 3, wherein the first low-pass filter is a first-order low-pass filter having a cutoff frequency of 20 Hz.

7. The apparatus according to claim 4, wherein the second low-pass filters each employ a first-order low-pass filter having a cutoff frequency of 20 Hz.

8. A ground magnetic resonance signal fast extraction method based on a phase-locked amplification technology is characterized by comprising the following steps:

inducing a magnetic resonance signal generated by underground water through a receiving coil;

magnetic resonance signals pass through a band-pass filter with the bandwidth of 200Hz and the center frequency of the magnetic resonance signals is adjustable, and the center frequency is the Larmor frequency;

generating a cosine signal with Larmor frequency, wherein the signal is used as a reference signal and realizes frequency relocation through an in-phase channel with an output signal of a center frequency adjustable band-pass filter with a bandwidth of 200 Hz;

generating a cosine signal with Larmor frequency, converting the cosine signal into a sine signal through 90-degree phase shift, and realizing frequency relocation by taking the sine signal as a reference signal and an output signal of a center frequency adjustable band-pass filter with the bandwidth of 200Hz through an orthogonal channel;

collecting signals of an in-phase channel and a quadrature channel, and extracting a ground magnetic resonance signal;

the raw data of the in-phase channel is formulated as

Wherein,

to mean relaxation time, ω_cIn order to cut off the angular frequency of the antenna,

when the acquisition time is greater than 10ms,

the collected original data of the same-phase channel is reduced to

Logarithm of the above formula to obtain a linear equation

By the slope k of the linear equationThen obtaining a linear equation of two-dimensional through the longitudinal intercept I (0) of the linear equation:

in the same way, a linear equation of two elements of the orthogonal channel is obtained:

q (0) is the longitudinal intercept of the linear equation after the logarithm of the orthogonal channel is solved, equations (4) and (5) are combined to establish an equation set, and the initial amplitude E is solved₀And a phase theta.

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