CN1142266A - Method and apparatus for detection and method of configuring such apparatus - Google Patents

Abstract

A method of detecting the presence of a given quadrupolar nucleus in a sample, the resonance frequency and spin-lattice relaxationtime of the nucleus varying with a given environmental parameter, comprises determining a range of the resonance frequency which corresponds to a selected range of the parameter, applying excitation to the sample to excite nuclear quadrupole resonance, and detecting the resonance response signal, the excitation being such that a detectable resonance response signal can be excited over the resonance frequency range, and being such as to produce a constant flip angle of less than 45 degrees actual.

Description

Detection method and checkout equipment and the method that this equipment is shaped

The present invention relates to a kind of detection and have a kind of nuclear quadrupole resonance (NQR) characteristic (longitudinal relaxation time T particularly at least ₁) sample in have the method and the checkout equipment of four polar cores, described characteristic changes with given environment parameter (as temperature).Also relate to a kind of method that this equipment is shaped.

As an example, the present invention is used for detecting from parcel, luggage, or hides on the person, perhaps explosive release explosive TNT, the RDX, HMX or the PETN that scatter ¹⁴The occasion of N quadrupole resonance signal.Give an example as another kind, also be used for drugs, as heroin and cocaine such as the airport detection of concealed.Exist if record these materials, alarm bell will sound.What should illustrate is, when locating to detect the existing of explosive or drugs on the airport etc., the temperature of sample can not be known, and in fact may be very wide.May there be tangible thermograde in the sample.

The advantage of NQR test is that they need not sample is placed high-intensity magnetic field, thereby does not need magnet structure big and expensive and that be subjected to the sample size restriction, and said this structure just is that nuclear magnetic resonance (NMR) test is needed.

The method that from a kind of as can be known test sample of International Patent Application PCT/GB92/00580 (British Technology Group Ltd.-British Technology Group Co., Ltd-), has four polar cores, this sample has a kind of NQR characteristic that changes with given environment parameter at least, disclosing of it is drawn to be list of references here.This method comprises the excitation that applies wide energy level to sample, excites NQR resonance, and detects the NQR resonance signal, excites the NQR resonance signal with such excitation, can detect whole predetermined environment parameter scope at this signal of detection step.

In this way, can detect relevant nuclear existence to required detection sensitivity.Be meant the whole given test duration according to " detection sensitivity ", in the sample volume of determining, can record the number (or amount of substance) of selected atom nuclear by given probability grade.Utilize the fourier transform of institute's accumulating signal to provide an absorption spectra, by measure the area under this spectrum at integration between the suitable limit, this sensitivity is improved again.

The present invention is based on such new discovery, i.e. the NQR characteristic of sample is as resonant frequency (ν) and longitudinal relaxation time (T ₁) can change significantly as temperature, pressure or magnetic field etc. with given environment parameter.Therefore, when carrying out the NQR test, must consider or compensate these and change, to cover predetermined environment parameter scope.

Because (as the airport) generally carried out in the NQR test under certain occasion, so the parameter scope that the given range of described environment parameter normally may run under this kind occasion (may be described parameter country or the whole world average value ranges, also or maximum range).If described parameter is a temperature, total the saying of then described preset range can be ± 10 ℃ (may between 5 ℃ and 25 ℃) or ± 20 ℃ (may-10 ℃ and+30 ℃ between).This scope may be big like this to+40 ℃ (corresponding to desert situations) from-30 ℃ (corresponding to polar region situations).In some commercial Application, may run into the temperature range of non-constant width.If described environment parameter is a pressure, then described preset range can be for example ± 10% (corresponding to typical every day of average pressure scope) or ± 5% (corresponding to maximum range), if perhaps higher-test condition in the pressure vessel is adopted described method.

Therefore, if material under a cloud is explosive RDX in the luggage on airport, then can stand-25 to+15 ℃ temperature variation, i.e. from-5 to+35 ℃ variation around 20 ℃ mean value.The sample difference, temperature may be inequality, and/or same sample has inconsistent temperature.

Consider NQR characteristic-longitudinal relaxation time (T now ₁), the same longitudinal relaxation time (T that finds temperature (also having pressure) variation ₁) influence may be very tangible.For example, be unexpectedly, for above-mentioned RDX sample, ¹⁴The frequency ν of N+under T ₁Be by near 8 factor variations between 5 and 25 ℃.

We also find, T ₁The influence of a particular importance that changes is ratio τ/T ₁, τ is the recurrent interval (pulse-recurrence time) between the pulse of continuous agitation repeats here.As an example, referring to Fig. 1 of this instructions, it derives from Fig. 1 of PCT/GB92/00580, wherein shows different τ/T ₁Signal intensity under the value is with trigger angle (flip angle) variation (α).All these figure lines in turn all by Vega about spin be 1 nuclear gained equation (J.Chem.Phys., 1974,61,1099, Eq.IV-29) draw.The intensity of the stable state NQR signal in these nuclear indication gunpowder is as given T ₁The function of τ.The figure line of delivering in people's such as these figure lines and Buess the paper (" NQR DetectionUsing a Meanderline Surface Coil ", J.Mag.Res., Vol.92,348-362 (1991)) is similar.What should illustrate is that the curve shown in these figure is the meaning that the most general face of land shows them, and does not lie in especially at any particular matter.

Fig. 1 shows, at given ratio τ/T ₁Under (＜5) situation, along with the change of trigger angle, can expect that signal passes through a maximal value, this maximal value moves on to trigger angle and locates less than 119 degree (α m), and at ratio τ/T ₁Reduce to 1 when following, signal intensity is lower.At τ/T ₁Under=5 the situation, suppose corresponding to the maximum free induction decay (fi.d.) of trigger angle α m bigger than 1; At τ/T ₁Under=0.1 the situation, f.i.d. moves to 0.3 α m place, and it has relative signal intensity 0.25.For normal value τ and under the situation of constant trigger angle α m, τ/T ₁Variation between 1 and 0.1 is (among the RDX ¹⁴The frequency ν of N+, increase near about 20 ℃ environment T corresponding to temperature ₁Increase 10 times) cause that the response signal loss of intensity is about 70%.If such loss is fallen into oblivion by noise, resonance signal can not be detected.

Therefore, the invention that PCT/GB92/00580 disclosed comprises a kind of compensation T ₁The method that changes.A plurality of different pulse recurrence rates and/or thereby produce under the situation of a plurality of different trigger angle, this method comprises and exciting as one group of excitation pulse described, so that detectable NQR resonance response signal can with the corresponding whole relaxation time scope of the scope of environment parameter in be excited, and preferably be excited really, so that the intensity of described response signal is constant substantially in gamut.

Though this method is succeeded, be that it can carry out highly sensitive test, but its shortcoming is in some applications, variation aspect comprising trigger angle in the test process or pulse-recurrence time, perhaps two aspects all may make this test become complicated, and may increase the complicacy of this checkout equipment, and may influence the continuation of test.

The present invention attempts to address these problems.

According to the present invention, based on the pulse-recurrence time and the trigger angle that are provided are selected meticulously, they can be maintained for specific test is the value of constant, and can not impair the sensitivity of this law significantly.

The invention provides and have four given polar cores in a kind of test sample, the method that nuclear response frequency and longitudinal relaxation time change with given environment parameter, it comprises determines and the corresponding resonant frequency scope of selected parameter scope; Apply to sample and to excite, with the excited nucleus quadrupole resonance; And detect the resonance response signal, can in the resonant frequency scope, excite the resonance response signal that can detect, and feasible generation reality is less than 45 ° constant trigger angle.

Used " constant " is not interpreted as a meaning especially accurately here; On the contrary, should be by the lower angle of accuracy, always in conjunction with existing the method for four polar cores to go to understand it in the test sample.For example in the whole time, the variation of 25% or more (for example 50%) of trigger angle normally can be received.

In addition, quote that " reality " trigger angle of certain number of degrees compares with the trigger angle of " effectively ", the two is with known manner relevant with Bessel's function (for example referring to above-mentioned Vega list of references).For example, for an autonomous I=1 four utmost point spin systems, the free induction decay of a maximum of the actual generation of 119 ° trigger angle, thereby corresponding to 90 ° trigger angle in the nuclear magnetic resonance, so 119 ° trigger angle reality is corresponding to effective trigger angle of 90 °.

Having, is in order to produce a constant trigger angle, can to understand though excite again, and is constant (promptly not changing in time) though the trigger angle that excites generation under a lot of situations is arranged, may be different according to the distance from excitaton source in sample.

In addition, here used " detectable " speech more preferably comprises a signal/noise ratio, in the Measuring Time that detects step, this ratio surpasses actual or desired noise level significantly, and said obvious degree is by determining such as standard statistical routines such as senior " student " t distributions.In addition, used here " pulse repetition rate " simply is exactly the inverse of pulse-recurrence time.The reason that illustrates more fully owing to the back, because the excitation energy of detectable resonance response signal is carried out in whole resonant frequency scope, and because this also feasible actual constant trigger angle that produces less than 45 °, so method of the present invention can be easier to detect relevant nuclear existence unknown and that can change in given environment parameter situation in very wide scope, and the sensitivity that detects in entire environment parameter scope big variation can not take place.By in simple mode, promptly not only allow resonant frequency to change, and allow longitudinal relaxation time to change with given parameter with given parameter, can realize this point.

The described preferably pulse excitation under the isopulse repetition frequency that excites.And described method preferably also comprises the environment parameter ultimate value of selecting expectation, and for described ultimate value, relaxation time has its shortest value (on the contrary, for the relative value of ultimate value therewith, described relaxation time has greatest length); Also comprise and determine pulse-recurrence time to this size of the ratio of short relaxation time, described pulse repetition rate is to make the size of described ratio be no more than a selected value.

By under isopulse repetition frequency situation, working, and therefore produce a constant trigger angle, can make said detection method obtain significantly simplifying with respect to International Patent Application PCT/GB92/00580.Select expection environment parameter ultimate value (as maximum phase value for the treatment of of temperature), determine as described in ratio measurement and guarantee that pulse repetition rate is that the measurement purpose that is no more than a selected value is as described in making, by eligibly selecting described set point value, can make described detection method more quick, and can not change described environment parameter delicately at the same time.

Therefore, according to maximally related situation of the present invention, provide a kind of and make that given four polar cores exist in the described test sample, described nuclear spin dot matrix relaxation time is with the manufacturing process of the equipment of given environment parameter variation, described equipment comprises to sample and applies pulse excitation, with the device of excited nucleus quadrupole resonance.Described method comprises the environment parameter ultimate value of selecting expection, and for described ultimate value, relaxation time has its shortest value; Arrange excitation apparatus, excite, produce a constant trigger angle in order under constant pulse repetition rate, to apply; Also comprise and determine pulse-recurrence time to this measurement of the ratio of short relaxation time, described pulse repetition rate is to make the size of described ratio be no more than a selected value.

The present invention expands aforesaid method, and in order to given nuclear existence in the test sample, described equipment also comprises the device that detects the resonance response frequency signal, comprises that also described excitation apparatus of control and pick-up unit are to detect the step that exists of this nuclear.

The present invention also provides the method that exists given four polar cores, described nuclear spin dot matrix relaxation time to change with given environment parameter in a kind of test sample, it comprises the environment parameter ultimate value of selecting expection, for described ultimate value, relaxation time has its shortest value; Apply pulse excitation to sample, with the excited nucleus quadrupole resonance; Also comprise and detect the resonance response signal.Wherein said exciting is to carry out under constant pulse repetition rate condition, and produces a constant trigger angle; Determine pulse-recurrence time to the described ratio of short relaxation time, described pulse repetition rate is to make the size of described ratio be no more than a selected value.

Described (pulse-recurrence time to this shortest relaxation time), ratio preferably was no more than 20, preferably was no more than 10, more preferably was no more than 3 or 5, or even 1.The special important shape of the value of this order of magnitude is to find that all other parameters all are the same, and signal intensity and signal sensitivity can not be increased to higher value significantly.Like this, the test of being carried out under high value will be unnecessary tediously long.Therefore, for quick test, utilize this order of magnitude or lower value that superiority is always arranged.More preferably, this selected ratio is no more than 0.2 or 0.3.Be this, the theoretical analysis that provides later shows that for enough little trigger angle, it is irrelevant with described environment parameter more or less that signal intensity will become.

This law preferably also comprises the environment parameter ultimate value of selecting expection, and for described ultimate value, relaxation time has its greatest length; It on the one hand is the repetition time to being on the other hand and aiming at it and expect that the ratio of the corresponding relaxation time of described environment parameter value between limit in 0.05 to 5 scope, is preferably in 0.1 to 1 scope.This is another characteristics, and it can guarantee detection method faster, and this method can not influence the change of described environment parameter significantly in the same time.

Preferably according to whether having surpassed the preset detection threshold value from alerting signal of described response signal generation.In this case, this law preferably also comprises the environment parameter ultimate value of selecting expection, and for described ultimate value, relaxation time has its greatest length; Determine that pulse-recurrence time is to this size of the ratio of long relaxation time; And according to whether having surpassed the preset detection threshold value from alerting signal of described response signal generation, described threshold value is corresponding to the response signal intensity level, described signal intensity be no more than with described pulse-recurrence time to this big or small corresponding value of the ratio of long relaxation time.This can guarantee just to obtain detectable resonance response signal between two ultimate value in whole selected environment parameter scope.

This law preferably also comprises the environment parameter ultimate value of selecting expection, and for described ultimate value, relaxation time has its greatest length; And definite pulse-recurrence time is to this size of the ratio of long relaxation time; With pulse-recurrence time to the corresponding signal strength values of ratio of the shortest relaxation time than the little selected multiple of the most equivalent signal intensity of long relaxation time relatively, preferably little 5 times, be more preferably for a short time 3 times, be well little twice again.Maintain in the acceptable limit by the variation of guaranteeing signal intensity in entire environment parameter scope, the sensitivity of detection is maintained in the acceptable limit in entire environment parameter scope.

In a preferred embodiment, the scope of given selected environment parameter and required response signal strength range select arteries and veins to fill the value of repetition frequency and trigger angle by the iterative processing between pulse repetition rate and these two amounts of trigger angle simultaneously.

Preferably described exciting make and produce one less than 45 ° actual trigger angle, be more preferably described exciting and make and produce one less than 35 °, preferably less than 25 °, better less than 15 °, better less than 10 ° until actual trigger angle less than 5 °.In fact, just as will be described, the value of trigger angle is more little, and this law is effective more.

Be simple meter, be preferably in single exciting and apply described exciting under the carrier frequency condition, although also can under two or more such frequency conditions, apply.

Desirable especially characteristics are to adopt so-called " shaping " pulse, and erect image back and UK Patent Application UK9319875 and International Patent Application PCT/GB94/02070 are described in detail like that.These broadbands that can be implemented under the low-power level condition excite, and only adopt single stimulating frequency.Say that in a broad sense shaped pulse can be considered as a kind of waveform, for it, the time domain waveform that excites is phase modulation (PM) or amplitude-modulated, or not only phase modulation (PM) but also amplitude-modulated.

As UK Patent Application UK9319875 is disclosed, the used equipment of nuclear quadrupole resonance (NQR) specimen is included in interior sample is applied of whole selected excitation frequency ranges and excites, to excite the device of NQR resonance, with the device that detects the NQR response signal, the described phase place that excites is a nonlinearities change with described stimulating frequency generally in whole selected frequency range.

Described exciting is at carrier frequency ν ₀Under pulse excitation, excite phase place with frequency shift (FS) (Δ _ν=ν-ν ₀) being generally nonlinearities change, this suits.

The shaped pulse invention is that the accident that comes from the nuclear quadrupole resonance occasion is found, promptly adopting and applying phase place is that nonlinearities change excites with stimulating frequency, can reduce the peak power that excites very significantly.In example first, peak power can reduce by one more than the order of magnitude.Peak value radio frequency rate magnetic field has also realized very significantly reducing.

From Guan, S. show, " Generation of optimal excitation pulses for twoenergylevel systems using an inverse Fourier transform method " (J.Chem.Phys. by name, Vol.96, No.11,1992, paper pp.7959ff.) can know that adopting phase place in different nuclear magnetic resonance (NMR) technology occasion is non-linear exciting with stimulating frequency.Exciting like this is used to solve different problems, mainly is that the solvent that solves NMR suppresses problem.This exciting at described frequency domain provides a stepped spectrum.Above-mentioned paper is to continue Guan, S. institute is famous is " General phase modulation method for stored waveform inverseFouriertransform excitation for Fourier transform ion cyclotronmass spectrometry ", J.Chem.Phys., Vol.91, No.2,1989, (also visible Marshall, the A.G. and the Verdun of pp.775ff. paper, F.R., show, the 4.2.3 joint of " Fourier Transform in NMR, Optical; and Mass spectrometry; AUsers ＇ Handbook " book by name, Elsevier, nineteen ninety version).

Yet, can not look to this method that so excites that adopts in the NMR test that Guan proposes is used for the NQR test, because it is based upon on the hypothesis, promptly tested material is the level two that satisfies Bloch equation.What should illustrate is that described Bloch (Bloch) equation can be used for NMR, ion cyclotron resonance, FT mass spectrometer and the electronic laser spectroscopy in the liquid.But they can not be used to present the material of NQR effect.Therefore, the refractory period method with Guan of hoping is used for NQR.

In fact, surprisingly still can not understand fully fully among the actual NQR of being used for of assorted petty described shaped pulse method.

It should be noted that also it is the amplitude-modulated time domain waveform that excites that the Guan method is limited to modestly, and can not be other phase modulation (PM) situation.(be appreciated that when amplitude on the occasion of and negative value between when changing, Modulation and Amplitude Modulation itself has comprised the modulation of phase place, such as between 0 and 180 degree)

For exciting of continuing, the modulation envelope of described time domain excitation waveform does not have zero crossing.This just can bring the advantage in the peak power that remarkable reduction excites (and radio frequency rate magnetic field).

In the preferred embodiment of shaped pulse first, make to apply the device that excites and be suitable for applying the time domain waveform that excites not only Modulation and Amplitude Modulation but also phase modulation (PM).As be amplitude-modulated reverse situation, this scheme can be used to produce the excitation waveform that its envelope does not have zero crossing.

In the present embodiment, the described device that excites that applies preferably includes in order to the device that produces two kinds of signals that are associated with 90 ° of phase shifts and makes up this two kinds of signals, forms the device that Modulation and Amplitude Modulation and phase modulation (PM) excite.In addition, said signal generation device preferably includes device that signal takes place and the device that this signal is divided into two signals that are associated with 90 ° of phase shifts.These two features can provide a kind of simple method, and the present invention is tried out.

Be noted that these features itself can be from people such as Wittebort, be entitled as " High-Speed Phase andAmplitude Modulator " paper (J.Magn.Reson., Vol.96,1992, pp.624ff.) learn.The described modulator of this article is designed to work under the carrier frequency of 30MHz, far away from being likely ¹⁴In the NNQR test interested 0.5 to 6 or the frequency range of 8MHz on.

Two class signals can take place after separately.This generating means can be suitable for taking place the carrier signal of fixed amplitude.Another point or to replenish a bit be that this generating means can be suitable for having the signal of amplitude variable.

In the preferred embodiment of another kind of shaped pulse, make to apply the device that excites and be suitable for applying the time domain waveform that excites amplitude modulation but can not phase modulation.This embodiment can not go to allow as other embodiment can accomplish and realize that such low peak power excites, but making is simpler, because do not need direct phase modulation.

In another preferred embodiment, make to apply the device that excites and be suitable for applying the time domain waveform that excites according to the chirp FUNCTION MODULATION.This is the simple especially mode that the present invention is tried out, because the chirp function is easy for equipment.For example, described chirp function can be cos (ω t ²) the chirp function of form; Also be that this modulation is pure pulsed modulation, phase place is subjected to linear modulation about frequency shift (FS).

In the preferred embodiment of any shaped pulse, the described device that excites that applies preferably includes the device that carrier signal takes place, with the device that modulated carrier signal excites with generation, its phase place that excites in whole selected excitation frequency ranges usually with the stimulating frequency nonlinearities change.This can become a kind of method that especially the present invention is tried out.Suitable modulating device comprises the device that is used to store the modulation waveform that modulated carrier signal uses.

Exciting phase place can be with respect to carrier frequency ν with the variation of stimulating frequency ₀Be symmetry or asymmetrical.No matter any in two kinds of situations, its phase change preferably quadratic power (also promptly be proportional to (ν-ν ₀) ²); Found that this will improve the exciting power of low peak.Another kind of possibility is to change phase place with statistical noise, but this will cause noise spectrum.Another shortcoming may be that described time domain waveform has a lot of zero crossings, so that can not effectively utilize the time.

If phase change is a quadratic power, in a kind of specific preferred embodiment, can apply a plurality of excitation pulses so, according to a kind of like this mode, produce at least one echo response signal.As with respect to free induction decay signal, particularly under the long situation of the longitudinal relaxation time T1 of measured matter, have to be beneficial to and produce the echo response signal.

This feature comes from the accident that is caused according to the invention of described shaped pulse to be found, promptly wherein phase change is the phase place that the described shaped pulse of quadratic power has kept the NQR response signal.It is necessary that this phase place keeps for echo successfully takes place.

The amplitude of frequency domain excitation spectrum preferably is substantially constant in whole selected excitation frequency ranges.Can make like this and excite in whole described frequency range to uniformly.

Described shaped pulse invention provides a kind of method of nuclear quadrupole resonance specimen, it is included in whole selected frequency range and sample is applied excites, to excite NQR resonance, also comprise and detect the NQR response signal, the described phase change that excites is generally nonlinear variation with stimulating frequency in whole selected frequency range.

Selected NQR resonance may be excited, and if like this, and the perdurability that excites accordingly with this resonance is preferably less than the free induction decay time T of twice ₂ ^*This is a very important feature, and it can be guaranteed, before the NQR response signal is detected, can not increase the unwanted loss of this signal.In fact, this perdurability is preferably less than T ₂ ^*100%, 75% or or even 50%.

A closely-related aspect of described invention shaped pulse is, provide a kind of nuclear resounce specimen used equipment, it is included in whole selected excitation frequency ranges and sample is applied excites, device with excited nucleus resonance, also comprise the device that detects response signal, described apply the device that excites be suitable for exciting be Modulation and Amplitude Modulation be again the time domain waveform of phase modulation (PM).

The closely-related aspect of another of described invention shaped pulse is, provide a kind of nuclear quadrupole resonance specimen used equipment, it is included in whole selected excitation frequency ranges and sample is applied excites, to excite the device of NQR resonance, also comprise the device that detects the NQR response signal, the described phase change that excites is generally nonlinear variation with stimulating frequency in whole selected frequency range.

Multiple similar method also is provided.

Above-mentioned all characteristics all are applicable to the above-mentioned aspect of described shaped pulse invention.

Another closely-related aspect of the present invention is that described shaped pulse invention provides a kind of prolongation sample free induction decay time T ₂ ^*Method, it is included in whole selected excitation frequency ranges and sample is applied excites, with excited nucleus resonance, the described phase place that excites changes with stimulating frequency in whole selected frequency range.

Described nuclear resounce is suitable for nuclear quadrupole resonance or nuclear magnetic resonance.The described phase change that excites is preferably nonlinear.

This of described shaped pulse invention originates from the one hand follows discovery of the present invention, if promptly excite a nuclear signal with a phase place that changes, the length of free induction decay just may be greater than situation about simply exciting with a constant phase place.It seems that its reason be similar to the assorted petty reason that excites itself to grow that adds in this case that is that hereinafter provides.

For the free induction decay time T that will observe ₂ ^*Remarkable change, add to excite in the bandwidth of nuclear signal tangible phase change must be arranged.Therefore, the test that this law adapted to is the nuclear resounce line (comparing with 5210kHz ν+line) of a broad, is 3460kHz (ν-) the NQR line of the RDX of 0.5kHz such as bandwidth.

The relevant method of described shaped pulse invention can be useful especially, for example at T ₂ ^*Less than T ₂The time, for avoiding dead time problem owing to the low frequency supervision of detector; The perhaps problem that just under the situation of little radio frequency amplitude, is produced, thereby can adopt little trigger angle.

Can also provide and the similar method feature of the various device feature of each side of the present invention; Vice versa.

Below from other direction of described shaped pulse invention, consider other situation of the present invention, best said environment parameter is a temperature.Desired higher ultimate value can be less than 50 ℃, preferably less than 40 ℃ or 30 ℃.Desired low ultimate value (be worth hereto, the relaxation time of most of materials has its greatest length) can be greater than-30 ℃, more preferably greater than-20 ℃ or-10 ℃.The T that desired is in most materials ₁To reduce with the rising of temperature,, will need two limit are intercoursed being under the correct situation conversely.

Pulse-recurrence time is more preferably greater than the free induction decay time of four polar cores, and preferably big 2 or 3 times, in order that detect the free induction decay time.

The present invention also provides the equipment that has four given polar cores in the pulse excitation test sample that utilizes, it comprises memory storage, there is the information of at least two nucleids the inside, described atomic nucleus has with respect to suitable trigger angle and pulse repetition rate different NQR characteristics is arranged, so that desired temperature variation is taken into account; Also comprise the device that responds described memory storage, the atomic nucleus in order to for given type adds to sample with pulse excitation, with the excited nucleus quadrupole resonance; Also comprise being suitable under isopulse repetition frequency condition, applying exciting, thereby obtain being suitable for the excitation apparatus of the constant trigger angle of predetermined substance; And the device that detects the resonance response signal.

What should illustrate is that necessary pulse repetition rate and chosen trigger angle can be depending on the predetermined substance of tested person, can make different pulse repetition raties and trigger angle satisfy different materials.

Can provide and the similar apparatus characteristic of method feature recited above.

For example, whether described equipment also can comprise according to above the device of preset detection threshold value from detected response signal generation alerting signal.Have again, can under single stimulating frequency, apply and excite, and can obtain the shape of shaped pulse.

Below will theoretical foundation of the present invention be described by the mode of only just giving an example with reference to accompanying drawing, and preferred characteristics of the present invention and its working condition example, wherein:

Fig. 1 (prior art) is that static NQR response signal intensity is with respect to different τ/T ₁The relation curve of the trigger angle of value;

The rectangle excitation pulse (Fig. 2 (a)) of Fig. 2 (prior art) expression time domain and the equivalence value (Fig. 2 (b)) of frequency domain thereof;

Fig. 3 is the block scheme of NQR testing apparatus preferred embodiment of the present invention;

Fig. 4 (a) uses first example of the NQR test of shaped pulse to 4 (e) expression;

Fig. 5 (a) uses second example of the NQR test of shaped pulse to 5 (f) expression;

Fig. 6 is the block scheme of NQR testing apparatus preferred embodiment modification;

Fig. 7 (a) also uses the 3rd example of the NQR test of shaped pulse to 7 (f) expression;

Fig. 8 illustrates the used burst length figure of the preferred embodiment of the present invention.

According to the mode of summarizing, the preferred embodiments of the present invention comprise that the employing pulse radiation frequency excites, excited nucleus quadrupole resonance in the material that needs detection nuclear quadrupole resonance exists.The form of any suitable pulse train all can adopt, and the most frequently used is the uniform pulse sequence of rule.

Stimulating frequency, pulse repetition rate, trigger angle and other at first are discussed and are excited relevant Parameter selection mode.Give the detailed description of the equipment that the present invention that sends as an envoy to puts into practice then with the detailed description of special preferred pulse (" shaping " pulse) kind.Provide the example of a working condition of the present invention at last.

In this preferred embodiment, the invention enables the resonant frequency and the longitudinal relaxation time (T of four polar cores of giving ₁) the two all changes.Can also instruct as PCT/GB92/00580, consider other NQR characteristic.

Say with having, frequency is compensated by the mode that PCT/GB92/00580 instructed.Only use a kind of stimulating frequency in this preferred embodiment, under this single frequency, for covering whole interesting frequency range, promptly corresponding frequency range with influential temperature range, this bandwidth that excites is enough.Find that " shaping " pulse is specially adapted to produce required bandwidth under the radio-frequency power condition of minimum, and therefore these " shaping " pulses are used for present embodiment, although the pulse of other kind may also be suitable for.The back will be described " shaping " pulse in more detail.

Now T ₁With the mode that variation of temperature is taken into account, whole target be will by keep pulse-recurrence time τ and trigger angle α be constant, and these parameters of careful selection make the variation of signal intensity in whole interesting temperature range reduce to minimum and realize this point.Just opposite with disclosing of International Patent Application PCT/GB92/00580, this patented claim instruction says, for realizing appropriate compensation, can change one of these parameters or other.This back a kind of method the sensitiveest test that will be supposed to obtain.But for most realistic proposal, the method for the preferred embodiment of the present invention then is easy to most realize, and can operates under single stimulating frequency condition.

Below especially with reference to Fig. 1, in the present embodiment, at the particular detection duration of test that carries out, τ and α are constant, even described test is just being carried out under more than one stimulating frequency condition.Certainly, for the test that continues with same sample, perhaps for the separately test with different samples, trigger angle can be different.If adopt more than one stimulating frequency, when adopting alternative method, make exciting when obtaining single constant trigger angle of being carried out, then can adopt different (constant) trigger angle and/or pulse-recurrence time to every kind of frequency.

In sample, basic trigger angle also is a constant to whole interesting frequency range, though just generally speaking need not to make the trigger angle that is provided to keep enough low.

In the duration of whole test, by providing constant by the radio-frequency (RF) magnetic field B that excites the bringing device gained _Rf, can make trigger angle show as constant.Have again, excite used drive coil for applying, may show as constant whole sample by what adopt suitable kind.

Like this, for two ultimate values expecting the temperature that sample stands unique τ/T will be arranged ₁Value.Because for greater than 5 or be exactly this ratio of 5, the intensity of signal can significantly not increase, so for the shortest T ₁Value (for most of materials, corresponding to the higher ultimate value of temperature), the value of τ is chosen to make this ratio to be no more than a selected value with pulse-recurrence time, such as 5.If this value is higher, then the length that test will be unnecessary aspect signal density, thereby can not be attended by any improvement yet aspect sensitivity.

Then trigger angle is selected in enough low value, the variation of signal intensity all is in the acceptable limit in whole temperature range.For example, the signal strength values corresponding with the minimum temperature limit can be to be no more than 5 times of the corresponding signal intensity equivalence value of the maximum temperature limit, preferably is no more than 3 times, then is no more than 2 times well again.

Controlling chart 1 demonstrates, at high trigger angle value place, such as 119 ° actual value place, signal intensity is with ratio τ/T ₁, thereby also be the variation that broad is arranged with temperature.At such trigger angle place, the signal intensity ratio that at ratio is 5 places is big similar 7 times of the signal intensity at 0.1 place at ratio.Yet,, just be but not negative zone that signal intensity has less variation with described ratio in the gradient of the signal intensity of curve and trigger angle ratio at lower trigger angle value place.Such as for 30 ° trigger angle, be that the signal intensity ratio at 5 places is that the signal intensity at 0.1 place is no more than 100% greatly at ratio at ratio.

Being appreciated that the above-mentioned variation just like the signal intensity of the theoretical curve gained of Fig. 1, is impossible be exposed to same precision in practice.Its main cause will be, if the resonant frequency of four polar cores along with temperature change, and the excitation of said excitation non-equivalence ground all with the corresponding resonant frequency of temperature range of being interested in.But, in the tolerance deviation that is experienced in this class testing, signal intensity is with ratio τ/T ₁Variation whether also or by experiment determine will not to be important generally by the curve of Fig. 1.

So, as mentioned above, select trigger angle as much as possible little.Suiting less than 45 °, be preferably less than 35 °, be more preferably less than 25 °, is well less than 15 ° again, less than 10 °, especially is less than 5 ° also.

At last, be worth and the trigger angle value selected pulse-recurrence time, because these two parameters influence signal intensity, the value of revising them repeatedly may be gratifying, for example reduces the whole test duration, and can not influence the sensitivity of test.

It will be understood that described pulse-recurrence time is influential to the sensitivity of test at least two kinds of different modes.At first, pulse-recurrence time long more (until a definite limit), to signal intensity, thereby to the big more (see figure 1) of influence of sensitivity.Secondly, just on the other hand, pulse-recurrence time is short more, for given test time the influence of getable pulse sum big more, the influence to the free induction decay number that can accumulate is also big more thus.Signal is to the ratio of noise, thereby also to be sensitivity increase with the increase of measured umber of pulse.

People also will understand, and trigger angle has direct influence to the sensitivity of test, and wherein, in certain limit, trigger angle is more little, and signal intensity is more little.But, because under less trigger angle condition, pulse is smaller than the equivalent pulse under big trigger angle condition, and the pulse during littler trigger angle can be utilized in the given test duration; In other words, short more pulse, described pulse-recurrence time can be long more.

People also will understand, and must be noted that not adopt excessive trigger angle value.For example, for τ/T ₁=0.1, above-mentioned trigger angle is increased to such as 40 °, actually will reduce rather than increase the intensity of signal.

Therefore, as top said, because the interdependent property of this complexity between pulse-recurrence time and the trigger angle, so, just may need by handling the final value that influences each other strobe pulse repetition time and trigger angle between this two amount.

To understand like that just like the consideration that reaches Fig. 1 from above, ratio τ/T ₁Midrange (also promptly with the expection limit of temperature between a corresponding ratio of neutral temperature value) general in 0.05 to 5 scope, be preferably in 0.1 to 1 the scope.In this scope, adopt what kind of method to judge that such midrange then is unessential.Can understand, determining of this ratio can be a kind of useful inspection to chosen pulse repetition rate and trigger angle.

According to rule described above, one typically makes this checkout equipment manufacturing process as follows: 1) select the upper and lower bound value of temperature, this expection sample will run into.

2) in whole temperature range, select the acceptable scope of change in signal strength.

3) determine longitudinal relaxation time T ₁Greatest length and the shortest value, they correspond respectively to temperature lower or higher (perhaps may be higher or lower) expection ultimate value.This need all make of experimental technique each given significant four polar core.

4) value of strobe pulse repetition time τ makes ratio τ/T ₁For the shortest T ₁The value less than such as 5.

5) for the longest and the shortest T ₁Value is determined corresponding ratio τ/T ₁

6) select the value of trigger angle α, such as 30 °,, guarantee that the τ value is longer than the duration of pulse and guarantees free induction decay (f.i.d.) for the pulse and the selected trigger angle of used extraordinary type.It is free induction decay time (T at least that the duration of described f.i.d. is assumed to be usually ₂ ^*) 2 times or 3 times, may be 5 times.

7) determine at ratio τ/T from Fig. 3 curve of people's such as the curve of this instructions Fig. 1 or aforementioned Buess paper ₁Gamut in signal intensity to the variation of selected trigger angle value whether in its acceptable scope.

8), if perhaps in fact described variation is unnecessary little, then select the value of revising of τ and/or α, and the step 4) to 7 above repeating if do not exist), simultaneously between τ and α repeatedly, until obtaining an acceptable result.

9) for having longer T ₁Temperature value, check at given Measuring Time T _mInterior numerical value T _mThe f.i.d. intensity of/τ and accumulation is to be enough to guarantee that given amount of substance to be detected produces the accumulation signal greater than a given threshold value.

10) if not, then select the value of revising of τ and/or α, and the step 4) to 8 above repeating), simultaneously between τ and α repeatedly, until obtaining an acceptable result.

For example can increase described accumulation signal simply by increasing trigger angle α.

Another kind of alternative mode is, by with pulse-recurrence time τ be reduced to a new value τ ＇ and increase described accumulation signal.Now, at given Measuring Time T _mIn concentrated the bigger f.i.d. time, and signal has also improved a factor (τ/τ ＇) to the ratio of noise ^1/2Yet the signal intensity of the f.i.d. that each is single is lowered, and in order to compensate this point, may need to increase trigger angle α, makes before τ is reduced, and returns to its original value such as the signal intensity that makes each single f.i.d..

11) for τ, α and the T of some four polar cores in the different material with different N QR characteristic _mFinal value be stored in the described checkout equipment.

The theoretical rationality of inquiring into above from Vega equation (above-mentioned quoted passage) to by row τ pulse-recurrence time and the resulting stationary singnal S of pulse of trigger angle α _α ^τAnalysis be obvious:

(1)

S _α ^∞Be observed balance stationary singnal under long τ value situation, a _nBe a coefficient relevant, for owning of RDX with α ¹⁴N-signal, it shows as the index spin lattice relaxation,

F(τ)＝e ^-τ/ ^T ₁。

The Vega equation shows, for α＜30 °, a arranged ₁～0.Therefore, when ignoring the influencing of high-order term in the equation (1), we find, for little trigger angle (α),

S _α ^τ/S _α ^∞＝1－a ₂1－(2 _τ/T ₁)＋1/2(2 _τ/T ₁) ²－… (2)

α is enough little when providing, and 2 _τ/ T ₁＜＜1 o'clock, that was just very clear, viewed signal S _ατ becomes and τ/T ₁Irrelevant, thus also with influence T ₁The all changes of environment parameter irrelevant.If to the shortest observed value T ₁Condition 2 _τ/ T ₁＜＜1 sets up, then this will to all be correct than long value.

In fact, if τ/T ₁Less than 0.2 or 0.3, and signal intensity can be not relevant with environment parameter significantly, and then condition 2 _τ/ T ₁＜＜1 can be satisfied.Thereby can see, an immovable substantially τ/T of tangible signal intensity being arranged for enough little α ₁Scope.Therefore, for a wideer τ/T ₁Scope, the variation of signal intensity can be in the acceptable limit.

What more than should illustrate is, the Vega equation also shows, for α＜15 °, and a in the top equation (1) ₂Be proportional to α approx.

The step 10) that top analysis can be used for said method.With regard to mathematical meaning, the equation 2 that provides from above sets out, if having 2 _τ/ T ₁＜＜1, along with reducing of τ, just make a ₂Relevant item strengthens, and this just makes S _α ^τReduction; Increase along with α makes S _α ^∞Increase, also make a ₂Relevant item strengthens, thereby changes S _α ^τIf make α less than 30 °, preferably less than 20 °, S then _α ^∞Change preponderate S simultaneously _α ^τIncrease.

Basic theories as " shaping " pulse invention of early being referred to is discussed now.With reference to Fig. 2, it has represented known rectangle excitation pulse, and this pulse shows as the waveform among Fig. 2 (a) in time domain, and becomes spectrum among Fig. 2 (b) in the frequency domain medium value.Spectrum among Fig. 2 (b) comprises a sharp-pointed central peak and sideband, and described sideband weakens according to size from central peak.Be appreciated that the spectrum among Fig. 2 (b) is the fourier transform of Fig. 2 (a) waveform; Fig. 2 (a) waveform is the Fu Liye inverse transformation of spectrum among Fig. 2 (b).Can also understand, Fig. 2 (a) reality has only been represented pulse envelope (perhaps speaking by the book especially, just half of pulse envelope), and wherein, pulse is made up of many strengths.

For the duration is that T, half high bandwidth are that Δ ν and peak pulse power are the rect.p. of P, and T equals 0.6/ Δ ν as can be known, and P and 1/T ²Be directly proportional, (in NQR) provides B _RfT and trigger angle keep the result of constant.B _RfAmplitude under the expression vibration radio frequency occasion.Therefore, the shortcoming of known rect.p. is that with the increase of bandwidth, peak power sharply increases (in fact being that quadratic power ground increases).

From the analysis of rect.p. as can be seen, high-power requirement is attributable to two principal elements.At first, the appearance of secondary lobe consumes a lot of power in frequency domain, but the useful part (central peak) of spectrum is not contributed.Secondly, the scope of contained stimulating frequency is located homophase in the zero-time in the pulse.Therefore, locate and locate very much, have very big coherence between each frequency, but locating to exist harmful phase mutual interference At All Other Times near this in the zero-time.So the duration of pulse is short, and the peak power height.

In NQR, find now, be for adopting, so that to produce a reshaped spectrum (also promptly, in selected excitation frequency ranges, the frequency domain firing rate is constant substantially) for the solution of first problem in these problems near rectangle by the pulse of shaping.Utilize the Fu Liye inverse transformation of nearly rectangle frequency spectrum to produce the shape of required time domain excitation waveform, realize the shaping of pulse.

Having now found that, is adopt its phase place to be generally exciting of nonlinearities change with frequency, so that in the time domain scope, phase place to be by scramble for the solution of second problem in these problems (near the zero-time big coherence in place).Therefore, be in a ratio of in the sufficiently long duration, having long mutually the interference between each frequency, and, existing the long mutually of the identical loss of time to disturb at the zero-time place with simple rect.p. situation.So described excitation pulse just can have long duration and lower peak power.In fact, for the phase change of quadratic power, find, under normal trigger angle situation, just like such, for such phase place, compared with Δ ν for the situation of rectangle excitation pulse ²Come, power P is more approaching to be directly proportional with Δ ν.This conclusion is from concerning P ∝ Δ ν/t _p, perhaps B _Rf∝ (Δ ν/t _p) ^1/2Draw, wherein t _pIt is pulse length; Δ ν and t _pIrrelevant (they are for simple long-pending shape pulse), so, when keeping t _pDuring for constant, we just obtain B _Rf∝ (Δ ν) ^1/2With P ∝ Δ ν.Find that also the duration of power and pulse is inversely proportional to for the given bandwidth deltaf ν that excites.In fact, problem is the free induction decay time T that only is subjected to predetermined substance the described duration ₂ ^*The restriction that continues.This is with more detailed discussion in the back.

Appropriate frequency in order to ensure phase place is disturbed, and phase place should be nonlinear with the variation of frequency.Linear phase change only influences the generation time displacement, but to frequently disturbing not influence of phase place.In fact, the phase change of having found NQR test quadratic power may be optimum.

A preferred embodiment of NQR testing apparatus is described referring now to Fig. 3.This embodiment is particularly suitable for existing in the sample (as suitcase etc.) detection of particular matter.In general, this equipment comprises a control computer 100, one or more in order to apply to sample, be generally the radio frequency excitation pulse of several successive, cover a selected excitation frequency ranges and the device of a given duration 102, in order to the device 104 by the shaped pulse of described bringing device 102 to take place, be used to detect device 106 and the audio frequency or the visual alarm 108 of NQR response signal, it is to the existence of surveys material and sensitivity is moved.Though not expression, this equipment normally also should comprise some devices,, a row sample can be tested " in service " as transmit the transmitting device of sample with respect to this equipment.

Adopt the method for this preferred embodiment, make each excitation pulse be subjected to shaping, cause in the impulse duration phase change, and preferably in duration of pulse, such as at least 50%, be 75% or 90% at least preferably, be more preferably and spread all over whole impulse duration and substantially change with being directly proportional.Phase modulation (PM) is preferably continuous by the time, excitation pulse itself by the time continuous (that is to say, though excite may be instantaneous by null value, when exciting when finishing, at the not free interval of impulse duration).

With the more detailed relation of present embodiment be, described excitation pulse bringing device 102 comprises a radio-frequency power amplifier 110, radio frequency sensor 112 is linked in its output, and this sensor comprises one or more tested sample radio-frequency coil (not shown) on every side that are positioned at.

Described radio frequency sensor 112 also becomes the part of pick-up unit 106, and this pick-up unit also comprises radio frequency receiver and testing circuit 120.

Described shaped pulse generating means 104 comprises pulse protocol designer 130, in order to produce the trigger pip of mediation pulse; One by SMIS, and the energy depressive spectroscopy 132 that United Kingdom makes is in order to produce the radio-frequency carrier signal of known carrier wave reference frequency and fixed amplitude, promptly by the signal of trigger pip control; One by Farnell, the function generator 134 that United Kingdom (Model No.SFG25) makes, and in order to produce a waveform by the expression formula of being deposited, to modulate the amplitude of described carrier signal, the output of this function generator is also controlled by trigger pip; Also comprise a double balanced mixer 136, be used for modulation wave signal and carrier signal are mixed, and this mixed signal is passed through, arrive radio-frequency power amplifier 110.So just can understand, described shaped pulse generating means 104 can add that one has been amplified to sample, but the time domain excitation waveform of non-phase modulation (PM).

Described computing machine 100 is finally controlled all pulses, their radio frequency, time, width, amplitude and phase place.See with regard to the time, with applying of excitation pulse by lining up when occurring near described sensor 112 with specific sample basically.It also is used to accept the NQR response signal that records from described pick-up unit 106, and handles it, finishes the additions and deletions of signal, if suitably last, also controls alarm 108.

With alarm 108 by arranging to such an extent that be subjected to computing machine 100 control in such a way, i.e. sounding of Bao Jinging or indication depends on whether surpassed the preset detection threshold value, this threshold value is corresponding with a response signal intensity level, and described signal intensity be no more than with the pulse excitation time (τ) to longitudinal relaxation time T ₁The corresponding value of ratio (this longest ultimate value is usually corresponding to lower temperature extremes) of long ultimate value.This can guarantee in whole chosen temperature scope, just obtains the resonance response signal that can detect between two temperature extremes values.

As noted earlier, the present invention is based upon that to excite phase place generally be to be on the basis of nonlinearities change with stimulating frequency.So, can with excite be expressed as frequency domain (shape is E (ω)=E _Real(ω)+i.E _Imaginary(ω)) complex function.In general, described excite also will be time domain (shape is E (t)=E _Real(t)+i.E _Imaginary(t)) complex function.Therefore, a simple amplitude modulation time domain excitation waveform generally will be not enough for purpose of the present invention, so that the equipment of Fig. 3 is normally inappropriate.But some this equipment of special situation still can be adopted.

Followingly illustrate two kinds of such situations respectively with reference to Fig. 4 and Fig. 5.In these two examples, all do not have fixing length, cut them so must cut symmetrically at the two ends that they go to zero about the function of time domain.Cutting the result who cuts like this is in order to obtain various artificial effects in the frequency domain scope.If desired, can adopt some apodization to make these minimizings (but not cancelling these).

In first example (Fig. 4), select the frequency domain excitation spectrum of rectangle.In whole selected excitation frequency ranges, phase place is with respect to frequency shift (FS) (Δ ν=ν-ν ₀) to change be quadratic power, and with respect to (carrier wave) frequency (ν of central authorities ₀) antisymmetry.In other words, when lower frequency, half width phase place quadratic power ground changes and bears, and at the central frequency place, phase place is zero, and when upper frequency, half width phase place quadratic power ground changes and is positive.

The time domain waveform of Pu Fu Liye inverse transformation gained is shown among Fig. 4 (a) (real part of waveform) and Fig. 4 (b) (imaginary part of waveform) thus.Described waveform is blocked into the scope of 1ms.The explanation of this example, theoretically, imaginary part should be zero, and it seems also just like this, because being taken at the 512nd of 1024 points, the central authorities that will compose locate, rather than between the 512nd and the 513rd.

For clarity sake, in Fig. 4 (a) and Fig. 4 (b), saved radio-frequency carrier signal.In fact, Fig. 4 (a) and Fig. 4 (b) represent the modulation waveform (shaping function) of mixing with carrier signal.After this this custom is continued to use.

The fourier transform coefficient of Fig. 4 (c) presentation graphs 4 (a) and Fig. 4 (b) waveform.Because the intercepting of waveform causes waveform to deviate from simple rectangle.

Fig. 4 (d) is except time domain waveform (seeing Fig. 4 (b)) being set as zero, and is identical with Fig. 4 (c).Can see that Fig. 4 (d) and Fig. 4 (c) there is no too big different.This is because the imaginary part of waveform under any circumstance all is very little.Therefore, can not consider the imaginary part of waveform, and only use real part shown in Fig. 4 (a) as modulation waveform.

So in first example, the actual only waveform shown in Fig. 4 (a) being used is the modulation waveform among described equipment (Fig. 3) first embodiment.The described carrier signal of the Modulation and Amplitude Modulation of this waveform (but not phase modulation (PM)).Certainly can understand, " pure " Modulation and Amplitude Modulation (for example, amplifying mutually by two signals) causes the variation of phase place (between 0 to 180 °) exactly.

Fig. 4 (e) expression is the experimental result that the material be concerned about is done with explosive RDX.The NQR testing apparatus is used to excite ¹⁴N ν+RDX resonance (at room temperature have near 1.4ms free inbroduction decay time T ₂ ^*Nearly 5192kHz, and line width is approximately the resonance of 200Hz).The variation of gamut is showed under the NQR signal that is recorded with respect to the carrier frequency of energy depressive spectroscopy by described pick-up unit.Circular data point expression bandwidth (selected excitation frequency ranges) is the excitation pulse of 20kHz; For the Square Number strong point, bandwidth is 10kHz.Can see that two groups of experimental data points meet well.For the bandwidth of 20kHz, for 90 ° _EffectivePulse, its pulse peak power (P) is 208W.This 2000W peak power to the respective rectangular excitation pulse that excites bandwidth equally is similar.

In second example (Fig. 5), elect the frequency domain excitation spectrum with being again as about the rect.p. of carrier frequency symmetry, but only select the first half of required rectangle spectrum.Phase change in whole selected excitation frequency ranges is a quadratic power.This example is based upon on the basis of such fact, if i.e. carrier frequency ν ₀ν with linearly modulated signal _mMultiply each other (mixing Modulation and Amplitude Modulation), then conclusion is that one pair of frequency claims that in primary carrier, itself becomes ν carrier wave _1,2=ν ₀± ν _mSo, if obtain a side about carrier frequency cover required bandwidth half, thereby only get the complex wave of described waveform real part, then whole bandwidth is capped.This is shown among Fig. 5.

Fig. 5 (a) expression is by the coefficient of the Fu Liye inverse transformation gained time domain waveform of first half bandwidth.The line of getting ready is represented waveform is blocked, so that produce the pulse persistance of 1ms.Fig. 5 (b) represents the intercepted real part of this waveform.This real part is the modulation waveform that is used to modulate described carrier signal.The quilt of Fig. 5 (c) presentation graphs 5 (b) cuts the real part of the fourier transform of waveform, and Fig. 5 (d) represents the coefficient of this conversion.Because this section cut and made waveform deviate from rectangle once more.In Fig. 5 (d), carrier frequency is expressed as dotted line.Understand from Fig. 5 (d), have exciting of carrier frequency both sides.

Fig. 5 (e) expression is with respect to the described similar experimental result of Fig. 4 (e), but with the modulating wave of Fig. 5 (b) rather than Fig. 4 (a).The bandwidth of excitation pulse is 20kHz.The curve of Fig. 5 (e) conforms to closely with Fig. 4 (e).For 90 ° _EffectivePulse, the peak power of pulse (P) is 133W.

Fig. 5 (f) is and similar curve shown in Fig. 5 (e), except it be use that Fu Liye inverse transformation gained modulating wave by the bottom half-band width obtains.In fact, this modulating wave is time of Fig. 5 (b) to turn gained.The different of Fig. 5 (e) and Fig. 5 (f) only are that the former represents near the peak of a NQR response signal 5192kHz, and the latter represents a paddy of same scope.And if then the NQR response signal excites, then be expected described scope and be bordering on straight (shown in Fig. 5 (d)).

To this different being described as follows.For the experiment of Fig. 5 (e), add some frequencies at the pulse section start, and add some frequencies near carrier frequency at the place, end away from carrier frequency, this can be as Fig. 5 (b) finding person.Like this, just there is no NQR resonance to be excited in different moments.The specific resonant frequency of RDX in test, the free induction decay time T of 1.4ms ₂ ^*Pulse length unlike 1ms is long a lot.So in pulse process, the existing part of the resonance away from central frequency that pulse begins to locate to be excited is weakened, and therefore only becomes more weak than those resonance near the central authorities that are excited at place, pulse end because of the timing detection that takes place behind end-of-pulsing.When the employing time was turned function, swinging among Fig. 5 (f) was correct, and this has explained the reverse of the middle peak of Fig. 5 (e).

Therefore, when implementing to adopt NQR of the present invention to test, important is, in order to prevent the unacceptable loss of NQR response signal before detection, and be with respect to the T of the material of testing ₂ ^*Duration of gating pulse modestly.So the duration of pulse is preferably less than the T of twice ₂ ^*, being more preferably only is T ₂ ^*100%, 75% or or even 50%.Under present situation, it is 1ms/1.4ms ≈ 70%.

Make the duration of pulse with respect to T ₂ ^*Reaching maximum a kind of method is to arrange the NQR testing apparatus, makes it to produce the pulse of the described type relevant with Fig. 5 (e) of given number, accompanies by the pulse of the described type relevant with Fig. 5 (f) of equivalent simultaneously, otherwise perhaps also can.Thereupon, will to produce one be straight response whole excite in the bandwidth substantially in the addings of such two groups of responses.Under test explosive TNT and PETN situation, this method may be important because for such explosive compared with for RDX, T2 ^*By expection is short.

The T of aforesaid RDX ₂ ^*Be approximately the specific ν of 1.4ms ₊Line is a line that is particularly useful for research.Other ν ₊The T of line ₂ ^*Less than 1ms, therefore need to adopt short pulse.The shortcoming of doing like this is to strengthen the peak power of excitation pulse.

A kind of modification of NQR testing apparatus preferred embodiment is described referring now to Fig. 6.Only show shaped pulse generation device 204, remainder is the same with the described embodiment of Fig. 3.Put it briefly, the shaped pulse generation device 204 of this variant embodiment, except it is the layout of two balances but not single balance, similar to shaped pulse generation device 104.Therefore it can produce a phase modulation (PM) and amplitude-modulated waveform.This variant embodiment also comprises pulse protocol device 230 and energy depressive spectroscopy 232; Also be provided with two function generator 234a and 234b, and two double balanced mixers 236.In addition, also be provided with 238, one combiners 240 of 0-90 ° of phase-splitter and resistor 242 and 244 of 90 ° of phase shift hybrid circuits.In the present embodiment, described phase-splitter 238 is that MiniCircuits (U.S.A.) makes, and model is the 5MHz phase-splitter of PSCQ2-5-1; Described combiner 240 and mixer 236 boths are made by Hatfield (U.K.), and model is respectively DP102 and MC291.Resistor 242 is 56 Ω, and resistor 244 is 560 Ω.The net result of whole resistor 242 and the network of resistor 244 is the resistance of 50 Ω that seen by function generator 234.

The various functions of this variant embodiment are as described below.Described like that just like first embodiment, by the output of pulse protocol device 230 gating energy depressive spectroscopies 232 and starting function generator 234.Described phase-splitter 238 produces the relevant radiofrequency signal of two 90 ° of phase shifts by radio-frequency carrier signal.Function generator 234a and 234b produce the real part and the imaginary part of modulation waveform respectively.Resistor 242 provides the impedance matching with described function generator cable, and resistor 244 becomes to pass through the electric current output of mixer 236 with the voltage output transform of described function generator.Relevant modulation waveform is with after carrier signal is mixed in described mixer 236, and two synthetic waveforms are combined in combiner 240, forms one by the amplitude modulation of radio-frequency power amplifier 110 and the signal of phase modulation.

In a kind of remodeling of this variant embodiment, a function generator can be set.The output of this function generator will be by another 90 ° of phase shift hybrid circuits, and two outputs of this circuit are with the mixer 236 of being defeated by respectively separately.This remodeling will be created in the telecommunication occasion as the modulation with known type of single-sideband modulation of the carrier wave of being checked.The presumable shortcoming of this remodeling will work under the very low frequency at described 90 ° of phase shift hybrid circuits.

About Fig. 7 the 3rd example that the present invention adopts described now.Be used with reference to the described device variations of Fig. 6, nominally it has the phase change for the excitation spectrum of rectangle and quadratic power.Represented among Fig. 7 (a) to cut modulation by quilt to the resulting modulation waveform of Fu Liye inverse transformation of required rectangle frequency domain excitation spectrum.Real part and the imaginary part of representing this waveform among Fig. 7 (b) and Fig. 7 (c) respectively.The fourier transform coefficient of this waveform of expression among Fig. 7 (d), and the real part and the imaginary part of this spectrum of the middle expression of Fig. 7 (e).Because the waveform of Fig. 7 (a) has been cut and has been cut, so the waveform shown in Fig. 7 (d) is not accurate rectangle.At last, a waveform figure of expression time domain excitation pulse among Fig. 7 (f).This represents the influence of described modulation waveform to radio-frequency carrier signal.

The peak power of described pulse is 1.44W.At 30 ° _EffectiveUnder the trigger angle situation, excite for the bandwidth peak field (B of described excitation pulse for 15kHz _Rf) be not more than 0.16mT.There are described each routine peak power and B _RfMinimum.The realization of these low values mainly is because the modulation of described time domain waveform zero-crossing timing (for example Fig. 7 (a) compares with Fig. 4 (a)) not, but comparatively straight, cause described power just as the whole duration that excites possible distribution equably.

Find that in the 4th example of NQR test the NQR resonance of RDX may produce echo response under the 5.19MHz condition that adopts the above-mentioned type shaped pulse.Experiment is adopted a pair of 90 ° hereto _Effective

Shaped pulse.Except that bigger trigger angle, each pulse is all described the same with the 3rd example.Particularly adopt the phase change of quadratic power.The amplitude of finding echoed signal is less than adopting 90 ° in a pair of rectangle _EffThe resulting amplitude of pulse.B in the 4th example _RfValue is 0.47mT.

What should illustrate is that in above-mentioned any embodiment or example, utilizing the pass with known required phase place and frequency is the data processing on basis, should be able to eliminate the distortion of phase place in last excitation spectrum.Then, be testing goal, can adopt the absorption oscillator signal.

Have been found that shaped pulse as described herein may the most gladly be used to adopt in the experiment with the material that shows less live width.Less live width is best, because it makes that having exciting of low Brf and lower powered big frequency range becomes possibility.If have only the line of broad to be suitable for, then may need to use bigger power.For RDX, spectral line is 5190kHz preferably, and at room temperature, its live width has only about 200Hz.

At last, describe the example of a method, utilize this method, can make checkout equipment of the present invention obtain configuration with reference to Fig. 8.In this example, described equipment is configured, in order to detect the existence of explosive RDX.Be used for applying the pulse that repeats regularly shown in the burst length figure that the device that excites is used to apply a row image pattern 8.Described pick-up unit is used to detect the free induction decay of following each pulse.These pulses as above Fig. 7 described, be subjected to shaping being about under the 5.2MHz, in order to the RDX resonance that excites 5.191MHz at ambient temperature.They have enough bandwidth (about 20kHz) to deacclimatize-5 to+35 ℃ temperature range.They respectively have the duration (t of about 1ms _f).

In such temperature range, longitudinal relaxation time T1 when the lower temperature limit 500ms and the 5ms during the higher temperature limit between change by the factor 100.Have such situation, τ is set at 25ms with pulse-recurrence time, simultaneously a given ratio τ/T ₁Scope is 0.05 to 5.With trigger angle α actual set is 30 °.Adopt these values, can see from Fig. 3 of people's such as Buess paper, the signal intensity when+35 ℃ of temperature only is (at least theoretically) 2.5 times big of signal intensity when-5 ℃ of temperature.This is considered to a kind of suitable variation.What should illustrate is that τ is significantly greater than t _fThe duration sum of (being 1ms) and free induction decay matches with material and selected frequency.The described duration is approximately the free induction decay time T ₂ ^*(1.4ms) 2 or 3 times.

Certainly merely describe the present invention above should be appreciated that by way of example, but can do the improvement of various thin portions within the scope of the invention.

Can be independently or provide each feature that this instructions is disclosed in the mode of any appropriate combination, and (suitable) claim and accompanying drawing.

Claims (26)

1. there are four given polar cores in a test sample, the method that nuclear response frequency and longitudinal relaxation time change with given environment parameter, it comprises determines and the corresponding resonant frequency scope of selected parameter scope; Apply to sample and to excite, with the excited nucleus quadrupole resonance; And detect the resonance response signal, can in the resonant frequency scope, excite the resonance response signal that can detect, and feasible generation reality is less than 45 ° constant trigger angle.

2. the method for claim 1 is characterized in that, described exciting is exciting under the isopulse repetition frequency.

3. method as claimed in claim 2, it is characterized in that, it also comprises selects desired environment parameter ultimate value, for described ultimate value, relaxation time has its shortest value, also comprise and determine pulse-recurrence time to this size of the ratio of short relaxation time, described pulse repetition rate is to make the size of described ratio be no more than a selected value.

4. method that the equipment that exists given four polar cores, described nuclear spin dot matrix relaxation time to change with given environment parameter in the test sample is shaped, described equipment comprise to sample and apply pulse excitation, with the device of excited nucleus quadrupole resonance; Described method comprises the environment parameter ultimate value of selecting expection, and for described ultimate value, relaxation time has its shortest value; Arrange excitation apparatus, excite, produce a constant trigger angle in order under constant pulse repetition rate, to apply; Also comprise and determine pulse-recurrence time to this measurement of the ratio of short relaxation time, described pulse repetition rate is to make the size of described ratio be no more than a selected value.

5. method as claimed in claim 4, in order there to be given atomic nucleus in the test sample, described equipment also comprises the device that detects the resonance response frequency signal, comprises that also described excitation apparatus of control and pick-up unit are to detect the step that exists of this nuclear.

6. the method that exists given four polar cores, described nuclear spin dot matrix relaxation time to change in the test sample with given environment parameter, it comprises the environment parameter ultimate value of selecting expection, for described ultimate value, relaxation time has its shortest value, apply pulse excitation to sample, with the excited nucleus quadrupole resonance; Also comprise and detect the resonance response signal; It is characterized in that described exciting is to carry out, and produces a constant trigger angle under constant pulse repetition rate condition; Determine pulse-recurrence time to the described ratio of short relaxation time, described pulse repetition rate is to make the size of described ratio be no more than a selected value.

7. one kind as claim 3,4,5 or 6 described methods, it is characterized in that described ratio is no more than 20, preferably are no more than 10, are more preferably and are no more than 5, particularly are no more than 1.

8. one kind as each described method of claim 3 to 7, it is characterized in that, also comprises the environment parameter ultimate value of selecting expection, and for described ultimate value, relaxation time has its greatest length; It on the one hand is the repetition time to being on the other hand and aiming at it and expect that the ratio of the corresponding relaxation time of described environment parameter value between limit in 0.05 to 5 scope, is preferably in 0.1 to 1 scope.

9. one kind as claim 1 to 3 or 5 to 8 each described methods, it is characterized in that, produce an alerting signal according to whether having surpassed the preset detection threshold value from described response signal.

10. one kind as claim 2,3 or 5 to 7 each described methods, it is characterized in that, also comprise the environment parameter ultimate value of selecting expection, and for described ultimate value, relaxation time has its greatest length; Determine that pulse-recurrence time is to this size of the ratio of long relaxation time; And surpassed the preset detection threshold value according to whether, produce an alerting signal from described response signal, described threshold value is corresponding to the response signal intensity level, described signal intensity be no more than with described pulse-recurrence time to this big or small corresponding value of the ratio of long relaxation time.

11. one kind as each described method of claim 3 to 7, it is characterized in that, also comprises the environment parameter ultimate value of selecting expection, for described ultimate value, relaxation time has its greatest length; And definite pulse-recurrence time is to this size of the ratio of long relaxation time, determine with the repetition time to the corresponding signal strength values of ratio of short relaxation time, this signal intensity ratio is the little selected multiple of the most equivalent signal intensity of long relaxation time relatively, preferably little 5 times, being more preferably for a short time 3 times, is well little twice again.

12. method as claimed in claim 11, it is characterized in that, the scope of given selected environment parameter and required response signal strength range are come the value of strobe pulse repetition frequency and trigger angle simultaneously by the iterative processing between pulse repetition rate and these two amounts of trigger angle.

13. one kind as each described method of claim 4 to 6, it is characterized in that, described exciting is to make to produce actual trigger angle less than 45 degree.

14. one kind as claim 1,2,3 or 13 described methods, it is characterized in that, described exciting make and produce one less than 35 °, preferably less than 25 °, better less than 15 °, better less than 10 ° until actual trigger angle less than 5 °.

15. one kind as claim 1 to 3 or 5 to 14 each described methods, it is characterized in that, apply described exciting with single stimulating frequency.

16. one kind as claim 1 to 3 or 5 to 15 each described methods, it is characterized in that, apply described exciting to sample in whole frequency range, the described time domain waveform that excites be phase modulation or amplitude modulation, perhaps be phase modulation be again amplitude modulation.

17. a method as claimed in claim 16 is characterized in that, in whole selected frequency range, the described phase place that excites generally is non-linearly to change with stimulating frequency.

18. one kind as claim 16 or 17 described methods, it is characterized in that exciting is pulse, the described phase place that excites is that quadratic power ground changes with frequency shift (FS) generally.

19. one kind as claim 16,17 or 18 described methods, it is characterized in that, selected NQR resonance is excited by at least one excitation pulse, and this excitation pulse, and perhaps the duration of each excitation pulse is less than the twice of the free induction decay time that is suitable for resonating.

20. one kind as each described method of claim formerly, it is characterized in that described environment parameter is a temperature.

21. one kind as each described method of claim 3 to 7, it is characterized in that described environment parameter is a temperature, its higher expection ultimate value is less than 50 ℃, preferably less than 40 or 30 ℃.

22. one kind as claim 8,10,11 or 12 described methods, it is characterized in that described environment parameter is a temperature, its lower expection ultimate value is greater than-30 ℃, more preferably greater than-20 or-10 ℃.

23. one kind as claim 2 to 8,10 to 13,21 or 22 each described methods, it is characterized in that described pulse-recurrence time is greater than the free induction decay time T of four polar cores ₂ ^*, preferably big 3 times.

24. one kind is utilized the equipment that has four given polar cores in the pulse excitation test sample, it comprises memory storage, there is the information of at least two nucleids the inside, described atomic nucleus has with respect to suitable trigger angle and pulse repetition rate different NQR characteristics is arranged, so that desired temperature variation is taken into account; Also comprise the device that responds described memory storage, the atomic nucleus in order to for given type adds to sample with pulse excitation, with the excited nucleus quadrupole resonance; Also comprise being suitable under isopulse repetition frequency condition, applying exciting, thereby obtain being suitable for the excitation apparatus of the constant trigger angle of predetermined substance; And the device that detects the resonance response signal.

25. an equipment as claimed in claim 24 is characterized in that, whether described equipment also can comprise according to above the device of preset detection threshold value from detected response signal generation alerting signal.

26. have the equipment of four given polar cores in the test sample, it is characterized in that it is formed according to the method for claim 4 or 5.

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