CN106597557A - Fundamental frequency controllable broadband nuclear magnetic resonance and optimal response extraction method - Google Patents

Abstract

The invention provides a fundamental frequency controllable broadband nuclear magnetic resonance and optimal response extraction method. Laser pulses are composed of groups of multi-period unipolarity/bipolarity period square-wave pulses in different frequencies, the square-wave pulses rather than traditional single-frequency sine waves are used for excitation, a huge resonance module can be omitted from a pulse emission circuit, and the emission circuit is easy to realize in a solid state; and the laser pulses include multi-spectral components, and can excite nuclear magnetic resonance response in multiple frequency points simultaneously. According to the signal extraction method, multiple frequency components can be extracted from received nuclear magnetic resonance response signals, whether a signal is an optimal response signal is determined, and a pulse emission exciting parameter is adjusted, according to a determination result, to carry out electron scanning in the excitation frequency within a certain frequency band range and extract the optimal nuclear magnetic resonance response signal; and signal extraction is realized via a value filtering algorithm, and the amount of receivers is not increased.

Description

A kind of controllable broadband nuclear magnetic resonance, NMR of fundamental frequency and its optimal response extracting method

Technical field

The invention belongs to applied geophysics field, and in particular to a kind of fundamental frequency controllable broadband, multiple frequency components side Ripple nuclear magnetic resonance, NMR excitation pulse, and the method for work based on the optimal NMR response signal of this DISCHARGE PULSES EXTRACTION.

Background technology

Nuclear magnetic resonance, NMR is detected as a kind of non-intruding electromagnetic surveying that quantitative judge directly can be carried out to underground water content Method, is applied at present many earth things such as underground water detecting, landslide detection, oil well logging and rock sample detection Reason field.Based on atomic energy order transition and the principle of nuclear magnetic relaxation, nuclear magnetic resonance, NMR detection utilizes macroscopical magnetic of Hydrogen Proton in water Square is excited by artificial radio-frequency (RF) magnetic field, and produced free damping signal after shut-off excitation current directly verifies water-bearing layer (body) and the aqueous moisture content for causing calamity construction, Penetration Signature and (filling) pore structure.

In field work, the nuclear magnetic resonance, NMR detection resonance condition to be met is to excite the frequency in magnetic field and survey Rameau in area Your frequency is equal.Due to earth's magnetic field skewness, the time change in earth's magnetic field, local magnetic anomaly and instrumental error etc. it is complicated because Element, stimulating frequency often inevitably deviates real Larmor frequency, and resulting NMR response is referred to as inclined Resonance response.Compared to resonance response, off resonance response signal there occurs greatly abnormal on amplitude, phase place and wave character Become, so as to disturb the estimation of the inverting of data and moisture content and infiltration coefficient, ultimately result in water-bearing layer (body) locus and The erroneous judgement of the information such as the filling water yield.Additionally, in real work, because depth and the resolution of nuclear magnetic resonance, NMR detection can be subject to swash Hair line circle magnetic moment, stratum conduction property, the NMR response for exciting the impact of the factors such as field frequency, water-bearing layer or water body is believed Number there is a problem of being difficult to being excited and being extracted by reliable.Specifically, there is a following difficult problem with deficiency：

(1) due to the inhomogeneities in magnetic field of the earth in survey area, there is certain frequency between stimulating frequency and Larmor frequency Rate deviation, so as to the NMR response in causing underground reservoir or water body can not be excited reliably.Now observed Response be off resonance response.Compared to resonance response, off resonance responds the impact of the frequency departure that is stimulated, in amplitude, phase place And there is different degrees of distortion on wave character；So as to disturb follow-up Data Inversion and moisture content and water guide characteristic Estimation and judgement.

(2) it is ultrabasic rock when underground country rock in area is surveyed, the high magnetic rock such as mafic, intermediate rock or metamorphic rock and encloses When containing ferromagnetic mineral in rock, carrying out nuclear magnetic resonance, NMR detection using the stimulating frequency obtained using traditional method possibly cannot be by Hydrogen Proton in whole water-bearing layer or water body is reliably excited.

(3) when detecting in the hole for carrying out Tunnel prediction, due to observation space it is narrow and small, front geomagnetic field variation degree Unknown, the estimated value that earth induction intensity is obtained by the way of multimetering is averaged is only capable of reacting face rear Tunnel Indoor fifty-fifty magnetic induction；In addition excite the radiation scope in magnetic field limited with intensity, now stimulating frequency is small Skew substantially reduces just can the initial amplitude of NMR signal so that the probability judged by accident in follow-up data interpretation is significantly Improve.

(4) at present, the mode of excitation of nuclear magnetic resonance, NMR is excited for single frequency sinusoidal wave impulse, is once excited and is only capable of sending a frequency The excitation pulse of rate.In order to launch the sine pulse signal of characteristic frequency, transmitter needs a whole set of power device and phase Close trigger control circuit and bulky resonance circuit.Under complex work environment, due to stimulating frequency and Larmor frequency When there is deviation and leading to not observe NMR response signal, needs readjust the resonant frequency of transmitting resonance circuit Excite again.Due to being accurately positioned Larmor frequency, therefore can not judge that stimulating frequency should be increasedd or decreased；It is real In the work of border, often by virtue of experience to carry out multiple frequency regulation resonance and excite.

The content of the invention

For above-mentioned problems of the prior art, the present invention proposes a kind of controllable broadband nuclear magnetic resonance, NMR of fundamental frequency And its optimal response extracting method, it is that the reliability of NMR response in actual detection is excited and carried with the extraction of optimal response signal New feasible program is supplied.

In order to realize above-mentioned task, the present invention is employed the following technical solutions：

The optimal corresponding signal extracting method of the controllable broadband nuclear magnetic resonance, NMR excitation pulse of fundamental frequency, comprises the following steps：

Step one, using magnetometer magnetic induction intensity value B in magnetic field of the earth in area is measured₀And calculate corresponding Larmor Frequency γ_p|B₀|=2 π f_L, wherein γ_pIt is the gyromagnet specific ray constant of Hydrogen Proton in water；

Step 2, stimulating frequency f that selecting step one is calculated_LAs pulse center frequencies f_cAnd in f_cBoth sides it is symmetrical Take 2m frequency, constitute 2m+1 fundamental frequency；

Step 3, adjusts the lasting periodicity n of the square wave of each fundamental frequency_iSo that the fundametal compoment of excitation pulse frequency spectrum The main band of one fixed width is formed, the width of main band is controlled by the fundamental wave number of excitation pulse；N number of frequency spectrum in main band Peak value is evenly distributed and corresponding spectrum amplitude between difference be not more than 10%；

Step 4, to adjust and launch excitation pulse after different excitation current intensity sizes, to obtain one group of excitation pulse square, Launch excitation pulse successively according to each excitation pulse square corresponding current intensity, and nuclear magnetic resonance, NMR is received after each pulse-off Response signal；

Step 5, according to the N number of channel of the corresponding frequency configuration of N number of spectrum peak in main band, for extracting N number of frequency On NMR response signal, the mid frequency of each channel is the corresponding frequency size of N number of spectrum peak；

Step 6, using the method for numerical filtering, according to N number of channel that step 5 is arranged, institute in correspondence extraction step four Real component of the NMR signal of reception in N number of frequency, quadrature component and phase place；

Step 7, repeat step four to step 6 is completed after all pulse square transmittings and response signal observation, and each is believed The real component of the response signal extracted in road draws respectively respective E with quadrature component_i- q curves, according to real in each channel Component E_iThe feature of-q curves judges whether to extract optimal response signal；Described E_i- q curves are referred in i-th reception channel The initial amplitude of response signal and the relation curve of excitation pulse square；

Step 8, after optimal response signal is extracted, records the center frequency of reception channel that optimal response signal is located Rate, using the mid frequency as the optimum excitating frequency in this survey area, and completes whole detection operations according to optimum excitating frequency；

Step 9, if not extracting optimal response signal, adjusting mid frequency size makes main band on the frequency axis To the left/move right and be scanned, repeat step three arrives step 7, until receiving optimal response signal.

Further, the excitation pulse square in described step four refers to duration T and the excitation pulse of excitation pulse The product of each spectrum amplitude in current intensity size and main band；The number of one group of excitation pulse square is 10～16.

Further, described excitation pulse by multigroup different frequency multicycle mono-/bis-polar cycle square-wave pulse group Into the function of excitation pulse is：

Wherein, ω_i(i=1,2 ..., m) be each square wave for constituting excitation pulse angular frequency, t is time parameter, θ₁~ θ_mBe control excitation pulse function electrical angle initial phase, f_i=ω_i/ 2 π be i-th fundamental frequency, T_i=f_iIt is the corresponding cycle； n_iIt is the lasting periodicity of square wave on i-th fundamental frequency, T=n₁T₁+n₂T₂+n₃T₃+······+n_mT_mIt is whole sharp The persistent period of pulse is sent out, k is the periodicity of whole excitation pulse.

Further, in described step two fundamental frequency of excitation pulse is controlled using frequencies below control function：

Wherein, f₁<f₂<…<f_m, when m is odd number, positioned at middle frequency mid frequency is referred to as.

The present invention has compared with prior art following technical characterstic：

1. the present invention proposes a kind of controllable broadband nuclear magnetic resonance, NMR excitation pulse of fundamental frequency and its optimal response signal is carried Method is taken, the extracting method of optimal response signal includes excitation pulse Waveform Design, and multichannel (frequency) frequency sweep nuclear magnetic resonance, NMR rings Induction signal excite with receive and optimal response signal identification with extract three parts, the technical scheme for being proposed be actual detection The reliability of middle NMR response is excited and provides new feasible program with the extraction of optimal response signal；

2. frequency sweep nuclear magnetic resonance, NMR excitation pulse proposed by the invention is all by the multicycle mono-/bis-polarity of multigroup different frequency Phase square-wave pulse is constituted, and the square-wave pulse transmitting of mono-/bis-polarity can be the flexible of instrument by half/full-bridge IGBT circuit realirations Design leaves space；Excited using square-wave pulse due to having abandoned traditional single frequency sinusoidal ripple so that impulse ejection circuit is saved Huge resonance modules are removed, radiating circuit is realized easily by solid-state, volume is light and handy and easily controllable；

3. excitation pulse proposed by the invention has multiple spectra composition, and its spectrum signature can area is actual to be carried out according to surveying Flexible, the pulse frequency spectrum for being suitable to detect has taken into account the width of main band, the density of spectrum component and the uniformity coefficient being distributed, Excitation pulse containing multiple frequency components can simultaneously be excited to the response of the NMR response on multiple frequencies；

4. multichannel proposed by the invention (frequency) NMR response signal excitation and optimal response signal identification with Extracting method can be to the NMR response signal on multiple frequencies for once exciting while receive, according to what is received The mid frequency of Signal Regulation excitation pulse enables main band to move left and right to be scanned；During being scanned, Operator can judge whether receive according to the amplitude of response signal in each reception channel, form and channel center frequency Regulated quantity when having arrived optimal response signal and having excited next time to excitation pulse mid frequency；Finally scan and extract optimal Stimulating frequency simultaneously records optimal response signal.Above-mentioned functions avoid the blindness adjusted to stimulating frequency in actual observation, So that the regulation of stimulating frequency has the direction (increase or reduction) of a determination and a controllable size.

Description of the drawings

Fig. 1 is the schematic diagram of excitation pulse proposed by the present invention and its voltage control functions；

Wherein, Fig. 1 (a) is the waveform diagram of excitation pulse, and Fig. 1 (b) is the schematic diagram of voltage control functions；

The schematic diagram of " frequency convergence " phenomenon when Fig. 2 is the square wave lasting periodicity for adjusting each fundamental frequency；

Wherein, Fig. 2 (a) is three fundamental frequencies, schematic diagram during n=10；Fig. 2 (b) is three fundamental frequencies, signal during n=110 Figure；Fig. 2 (c) is three fundamental frequencies, schematic diagram during n=450；Fig. 2 (d) is three fundamental frequencies, schematic diagram during n=20000；Fig. 2 E () is five fundamental frequencies, schematic diagram during n=10；Fig. 2 (f) is five fundamental frequencies, schematic diagram during n=450；Fig. 2 (g) is five Fundamental frequency, schematic diagram during n=950；Fig. 2 (h) is five fundamental frequencies, schematic diagram during n=50000；

Fig. 3 is the overall flow figure of the inventive method；

Fig. 4 is adapted for the excitation pulse spectrum diagram for detecting；

Fig. 5 is that virtual signal passage (channel) arranges schematic diagram；

Fig. 6 is the schematic diagram that resonance response and off resonance respond contrast；

Wherein, Fig. 6 (a) is resonance response signal schematic representation；Fig. 6 (b) is off resonance response signal real component schematic diagram；Figure 6 (c) is off resonance response signal quadrature component schematic diagram；

Fig. 7 is optimal response signal identification and extraction schematic diagram；

Specific embodiment

Problems of the prior art are directed in the present invention, it is proposed that a kind of controllable broadband nuclear magnetic resonance, NMR of fundamental frequency swashs Pulse (hereinafter referred to as excitation pulse) is sent out, the waveform of excitation pulse is with voltage control functions as shown in figure 1, the excitation pulse is by more The multicycle mono-/bis-polar cycle square-wave pulse composition of group different frequency, its function is as follows：

Wherein, ω_i(i=1,2 ..., m) be each square wave for constituting excitation pulse angular frequency, t is time parameter, θ₁~ θ_mIt is the initial phase of the electrical angle for controlling excitation pulse function, when its objective is to cause the square-wave transmission of next fundamental frequency, electric angle The value of degree is exactly the integral multiple of 2 π；f_i=ω_i/ 2 π be i-th fundamental frequency, T_i=f_iIt is the corresponding cycle；n_iIt is on i-th fundamental frequency The lasting periodicity of square wave, T=n₁T₁+n₂T₂+n₃T₃+······+n_mT_mBe whole excitation pulse it is lasting when Between, k is the periodicity of whole excitation pulse, s_i() (i=1,2 ..., m) refer to square-wave pulse.The present invention is using fundamental frequency control Mode is controlled and is defined as follows voltage control functions to the frequency of excitation pulse：

Wherein, f₁<f₂<…<f_m, when m is odd number, positioned at middle frequency mid frequency, the same formula of meaning of parameters are referred to as And formula (2) (1).

The spectrum signature of above-mentioned excitation pulse is：

1) spectrum component of excitation pulse includes fundamental wave component and odd harmonic terms, and fundamental wave component energy is predominantly Position；

2) spectrum peak of excitation pulse frequency spectrum fundamental wave component is as the increase of cycle number of repetition is with " frequency convergence " Phenomenon；

3) during frequency is converged, suitable cycle number of repetition is adjusted, the fundamental wave point of excitation pulse frequency spectrum can be made Amount forms the main band of one fixed width, there is N number of spectrum peak in main band, and it is spaced average and corresponding spectrum amplitude approximate Cause；

4) after the completion of frequency is converged, signal spectrum does not change with the increase of cycle number of repetition, except f₁Outer each fundamental frequency There is frequency displacement, the spectrum amplitude of high fundamental frequency is slightly above the spectrum amplitude of low fundamental frequency；

5) between each fundamental frequency spacing widen, complete square wave on each fundamental frequency required for frequency is converged lasting Periodicity progressively reduces.

Design as a result of square-wave pulse, the transmitting of excitation pulse can be using brilliant using high-power insulated gate bipolar The mono-/bis-polar transmission bridge of brake tube (IGBT) composition and its trigger control circuit transmitting, its emission parameter includes emission current Intensity, the fundamental frequency number periodicity lasting with the square wave of fundamental frequency size and each fundamental frequency.When pulse is designed, choose by Know earth induction intensity B₀Stimulating frequency f for calculating_L=γ_p|B₀|/2 π are used as pulse center frequencies f_cAnd in f_cBoth sides pair What is claimed takes 2m frequency, constitutes 2m+1 fundamental frequency.To control the Cycle Length of multifrequency pulse, fundamental frequency number typically chooses 3～5 It is advisable.The periodicity n of the square wave of each fundamental frequency can be made for the ease of control_i=n (i=1,2,3 ..., m).

The characteristics of frequency spectrum of excitation pulse proposed by the present invention has broadband, many (frequency) compositions, swashs when composition is changed During the lasting periodicity of square wave of each fundamental frequency for sending out pulse, there is " frequency convergence " phenomenon in pulse frequency spectrum.Adjust each fundamental frequency The lasting periodicity n of square wave_i, the main band of the fundametal compoment formation one fixed width of excitation pulse frequency spectrum, dominant frequency can be made There is N number of spectrum peak with interior, it is approximately consistent that it is spaced average and corresponding spectrum amplitude.By the big I for changing mid frequency So that dominant frequency window horizontally slips and carries out frequency sweep to the NMR response of water body in certain frequency band excite, until receiving Optimal NMR response.

Here " frequency convergence " phenomenon refers to the peak value of the frequency spectrum of excitation pulse fundametal compoment with cycle number of repetition Increase first gradually dissipate, after progressively concentrate on set fundamental frequency, meanwhile, the spectrum value near fundamental frequency is progressively decayed and each There is no significantly change in the spectrum amplitude of fundamental frequency.After the completion of frequency is converged, each fundamental component clearly indicate on frequency spectrum and Frequency spectrum no longer changes with the increase of cycle number of repetition.During frequency is converged, the frequency spectrum of excitation pulse fundamental wave component The quantity of peak value more than set fundamental frequency quantity, and when the value of cycle number of repetition is appropriate excitation pulse frequency spectrum base Wave component forms the main band of one fixed width, there is N number of spectrum peak in main band, and it is near that it is spaced average and corresponding spectrum amplitude Like consistent.

As shown in Fig. 2 mid frequency is 2243Hz, divides and take three and five fundamental frequencies three frequency pulses of composition and five frequency pulses. Wherein, that the fundamental frequency of three frequency pulses is respectively f₁=2223Hz, f₂=2243Hz and f₃=2263Hz；Spacing between each fundamental frequency For 20Hz.The fundamental frequency of five frequency pulses is respectively f₁=2233Hz, f₂=2238Hz, f₃=2243Hz, f₄=2248 and f₅= 2253Hz；Spacing between each fundamental frequency is 5Hz.When the periodicity n of excitation pulse starts to increase from an initial value, excitation pulse The peak value of the frequency spectrum of fundametal compoment first gradually dissipates with the increase of cycle number of repetition, after progressively collect on set fundamental frequency In, meanwhile, the spectrum value near fundamental frequency is progressively decayed and the spectrum amplitude of each fundamental frequency does not occur significantly change.Frequency has been converged Cheng Hou, each fundamental component is clearly indicated on frequency spectrum and frequency spectrum no longer changes with the increase of cycle number of repetition.Need Bright, there is a certain degree of frequency displacement in the waveform frequency spectrum after the displacement property of Fourier conversion causes frequency to converge.Additionally, Because Fourier conversion is distributed reflecting the average of signal frequency in the sampling time by obtaining the population frequency of a segment signal Feature；So such as the spectrum amplitude of the longer low fundamental component of pulsewidth in Fig. 2 (d) the high fundamental component shorter slightly larger than pulsewidth Spectrum amplitude.

During converging in frequency, the quantity of fundamental wave component intermediate frequency spectrum peak is more than the quantity of set fundamental frequency； And as a given appropriate periodicity n_iWhen, uniformly take in the frequency band of the fundametal compoment one fixed width of excitation pulse frequency spectrum N number of peak value is obtained, the frequency range of the one fixed width that this N number of peak value determines referred to as walks main band, the N number of spectrum peak in main band Evenly distributed and corresponding spectrum amplitude is approximately consistent.

The invention provides a kind of optimal response signal extraction side of the controllable broadband nuclear magnetic resonance, NMR excitation pulse of fundamental frequency Method, specifically includes following steps：

Step one, using magnetometer magnetic induction intensity value B in magnetic field of the earth in area is measured₀And calculate corresponding Larmor Frequency γ_p|B₀|=2 π f_L, wherein γ_pIt is the gyromagnet specific ray constant of Hydrogen Proton in water；

Step 2, stimulating frequency f that selecting step one is calculated_LAs pulse center frequencies f_cAnd in f_cBoth sides it is symmetrical Take 2m frequency, constitute 2m+1 fundamental frequency；Fundamental frequency is shown with the corresponding relation such as formula (3) of time；

Step 3, adjusts the lasting periodicity n of the square wave of each fundamental frequency_iSo that the fundametal compoment of excitation pulse frequency spectrum The main band of one fixed width is formed, here the width of main band is controlled by the fundamental wave number of excitation pulse；It is N number of in main band Spectrum peak is evenly distributed and corresponding spectrum amplitude is approximately consistent, the approximate difference unanimously referred between spectrum amplitude here No more than 10%；

Being appropriate to the pulse frequency spectrum that frequency sweep excites should possess following characteristics：First, the frequency spectrum of excitation pulse should take into account master Bandwidth and frequency density two indices in main band；Secondly, obtaining the frequency of peak value should be uniformly distributed in main band；Most Afterwards, the spacing in main band between each spectrum peak should not be excessive.As shown in figure 4, the control of the spacing between each spectrum peak should The principle for following is：Ensure when Larmor frequency falls in the frequency f corresponding to a certain spectrum peak_aWhen upper, adjacent spectra peak value The off resonance response that correspondence is excited can be arrived by reception Channel Detection.

Step 4, to adjust and launch excitation pulse after different excitation current intensity sizes, to obtain one group of excitation pulse square, Launch excitation pulse successively according to each excitation pulse square corresponding current intensity size, and nuclear-magnetism is received after each pulse-off Resonance response signal；

Step 5, according to the N number of channel of the corresponding frequency configuration of N number of spectrum peak in main band, i.e. virtual signal passage, For extracting the NMR response signal in N number of frequency, the mid frequency of each channel is the corresponding frequency of N number of spectrum peak Size；

Above-mentioned N number of channel is referred to and led to by the signal extraction that numerical filtering program is realized based on orthogonal principle of lock- in amplifier Road, they are not in esse, but realized by software, do not increase receiver number.The mid frequency of this N number of channel Frequency by corresponding to spectrum peak in main band determines that N number of channel that receives corresponds to respectively N number of frequency that extraction excitation pulse is excited NMR response signal in rate.

Step 6, based on the principle that orthogonal locking is amplified, using the method for numerical filtering, according to the N number of of step 5 setting Channel, real component Re (E of the NMR signal received in correspondence extraction step four in N number of frequency_i), orthogonal (void) point Amount Im (E_i) and phase place ph (E_i)；The orthogonal locking amplification method is maturation method of the prior art, be will not be described here；

Step 7, repeat step four to step 6 is completed after all pulse square transmittings and response signal observation, and each is believed The real component of the response signal extracted in road draws respectively respective E with quadrature component_i- q curves, according to real in each channel Component E_iThe feature of-q curves judges whether to extract optimal response signal；According to the characteristics of off resonance response signal, to extracting To individual channel in response signal be estimated；As shown in fig. 6, Fig. 6 (a) is resonance response signal, Fig. 6 (b) off resonances ring Induction signal.The characteristics of off resonance response signal, is as follows：

1) compared to resonance response signal, the amplitude of off resonance response signal has reduced；

2) compared to resonance response signal, Ei-q tracing patterns and the resonance shown in Fig. 6 (a) of off resonance response signal Response signal is compared and there occurs and largely distort；

3) compared to the quadrature component of resonance response signal, the size of the quadrature component amplitude of off resonance response is much larger than altogether Vibration response.

Above-mentioned E_i- q curves refer to the relation of the initial amplitude of response signal and excitation pulse square in i-th reception channel Curve；

Step 8, after optimal response signal is extracted, records the center frequency of reception channel that optimal response signal is located Rate, using the mid frequency as the optimum excitating frequency in this survey area, and completes whole detection operations according to optimum excitating frequency；

Step 9, if not extracting optimal response signal, adjusting mid frequency size makes main band on the frequency axis To the left/move right and be scanned, repeat step three arrives step 7, until receiving optimal response signal；A specific example It is as follows：

First, if not extracting optimal response signal in all channels, shown in such as Fig. 7 (a) and Fig. 7 (b), Larmor Frequency not in the Base Band of current excitation pulse or in Base Band and not on the frequency for peak value occur, in step 4 Received response in described N number of reception channel is off resonance response signal；The characteristics of off resonance response signal, is as walked Described in rapid seven, at this time, it may be necessary to the mid frequency for further adjusting excitation pulse is excited again.

Secondly, the frequency spectrum included in current main band is judged according to the off resonance response signal criterion described in step 7 Composition and the departure degree Δ of real Larmor frequency, refer to afterwards the mid frequency size and each letter of current each reception channel The form of response signal in road, judgement should increase or reduce the mid frequency of excitation pulse.By on the basis of mid frequency (or plus) corresponding disagreement value A is deducted, so that main band (right side) motion scan on the frequency axis to the left so that Larmor Frequency is just on a certain frequency of current excitation pulse frequency spectrum.Repeat step three and step 7, and by man-machine interaction to each Reception signal in channel is estimated, and repeats the process until extracting optimal response.

Claims (4)

1. a kind of controllable broadband nuclear magnetic resonance, NMR of fundamental frequency and its optimal response extracting method, it is characterised in that including following step Suddenly：

Step one, using magnetometer magnetic induction intensity value B in magnetic field of the earth in area is measured₀And calculate corresponding Larmor frequency γ_p|B₀|=2 π f_L, wherein γ_pIt is the gyromagnet specific ray constant of Hydrogen Proton in water；

Step 2, stimulating frequency f that selecting step one is calculated_LAs pulse center frequencies f_cAnd in f_cBoth sides symmetrical take 2m frequency, constitutes 2m+1 fundamental frequency；

Step 3, adjusts the lasting periodicity n of the square wave of each fundamental frequency_iSo that the fundametal compoment of excitation pulse frequency spectrum forms master Frequency band, the N number of spectrum peak in main band is evenly distributed and corresponding spectrum amplitude between difference be not more than 10%；

Step 4, to adjust and launch excitation pulse after different excitation current intensity sizes, to obtain one group of excitation pulse square, according to Each excitation pulse square corresponding current intensity launches successively excitation pulse, and receives NMR response after each pulse-off Signal；

Step 5, according to the N number of channel of the corresponding frequency configuration of N number of spectrum peak in main band, for extracting in N number of frequency NMR response signal, the mid frequency of each channel is the corresponding frequency size of N number of spectrum peak；

Step 6, using the method for numerical filtering, according to N number of channel that step 5 is arranged, is received in correspondence extraction step four Real component of the NMR signal in N number of frequency, quadrature component and phase place；

Step 7, repeat step four to step 6 is completed after all pulse square transmittings and response signal observation, by each channel The real component of the response signal extracted draws respectively respective E with quadrature component_i- q curves, according to real component in each channel E_iThe feature of-q curves judges whether to extract optimal response signal；Described E_i- q curves are referred in i-th reception channel and responded The initial amplitude of signal and the relation curve of excitation pulse square；

Step 8, after optimal response signal is extracted, records the mid frequency of reception channel that optimal response signal is located, will The mid frequency completes whole detection operations as the optimum excitating frequency in this survey area according to optimum excitating frequency；

Step 9, if not extracting optimal response signal, adjust mid frequency size make main band on the frequency axis to the left/ Move right and be scanned, repeat step three arrives step 7, until receiving optimal response signal.

2. the controllable broadband nuclear magnetic resonance, NMR of described fundamental frequency as claimed in claim 1 described and its optimal response extraction side Method, it is characterised in that the excitation pulse square in step 4 refers to that the duration T of excitation pulse is big with excitation pulse current intensity The product of each spectrum amplitude in little and main band；The number of one group of excitation pulse square is 10～16.

3. the controllable broadband nuclear magnetic resonance, NMR of described fundamental frequency as claimed in claim 1 described and its optimal response extraction side Method, it is characterised in that described excitation pulse is made up of the multicycle mono-/bis-polar cycle square-wave pulse of multigroup different frequency, The function of excitation pulse is：

$s\left(t\right)=\left\{\begin{array}{cc}{s}_1({\mathrm{\&omega;}}_{1}t+{\mathrm{\&theta;}}_1)& (k-1)T\&le;t<(k-1)T+{\mathrm{kn}}_1{T}_1\\ s_2({\mathrm{\&omega;}}_{2}t+{\mathrm{\&theta;}}_2)& (k-1)T+{\mathrm{kn}}_1{T}_1\&le;t<(k-1)T+k(n_1{T}_1+n_2{T}_2)\\ .& .\\ .& .\\ .& .\\ s_m({\mathrm{\&omega;}}_{m}t+{\mathrm{\&theta;}}_m)& (k-1)T+k(n_1{T}_1+n_2{T}_2+\mathrm{...}+n_{m-1}{T}_{m-1})\&le;t<kT\end{array}\right.---\left(1\right)$

${\mathrm{\&theta;}}_m=\{\frac{\&lsqb;{\mathrm{\&omega;}}_m(k-1)T+k(T-n_m{T}_m)\&rsqb;}{2\mathrm{\&pi;}}+1\}2\mathrm{\&pi;}-{\mathrm{\&omega;}}_m\&lsqb;(k-1)T+k(T-n_m{T}_m)\&rsqb;---\left(2\right)$

Wherein, ω_i(i=1,2 ..., m) be each square wave for constituting excitation pulse angular frequency, t is time parameter, θ₁～θ_mIt is The initial phase of the electrical angle of control excitation pulse function, f_i=ω_i/ 2 π be i-th fundamental frequency, T_i=f_iIt is the corresponding cycle；n_iIt is The lasting periodicity of square wave on i-th fundamental frequency, T=n₁T₁+n₂T₂+n₃T₃+······+n_mT_mIt is entirely to excite arteries and veins The persistent period of punching, k is the periodicity of whole excitation pulse.

4. the controllable broadband nuclear magnetic resonance, NMR of fundamental frequency as claimed in claim 1 described and its optimal response extracting method, its It is characterised by, in described step two fundamental frequency of excitation pulse is controlled using frequencies below control function：

$f\left(t\right)=\left\{\begin{array}{cc}{f}_1& (k-1)T\&le;t<(k-1)T+{\mathrm{kn}}_1{T}_1\\ f_2& (k-1)T+{\mathrm{kn}}_1{T}_1\&le;t<(k-1)T+k(n_1{T}_1+n_2{T}_2)\\ .& .\\ .& .\\ .& .\\ f_m& (k-1)T+k(n_1{T}_1+n_2{T}_2+...+n_{m-1}{T}_{m-1})\&le;t<kT\end{array}\right.$

Wherein, f₁<f₂<…<f_m, when m is odd number, positioned at middle frequency mid frequency is referred to as.