Nuclear spin resonance spectrometer, method for detecting a nuclear spin resonance and method for determining a nuclear spin resonance spectrum

Abstract

Method for detecting a nuclear spin resonance, in particular a nuclear magnetic resonance and / or a nuclear quadrupole resonance, of a probe material with a nuclear spin resonance spectrometer (1) with the steps: / Emitting a probe excitation signal generated with the oscillator unit (3); - Exciting the nuclear spin resonance of the probe material (2) by means of the probe excitation signal; - Quenching the first oscillation pulse (8) by activating the quench unit (6); - Deactivating the quench unit (6) after the first oscillation pulse (8) is quenched; - Receiving a response signal from the probe material (2) by means of the oscillator unit (3) responsive to the excitation; - Detecting a delay time (10) of an RF envelope of a second oscillation pulse (9), wherein the delay time (10) depends on the received response signal from the probe material (2); - Comparing the detected delay time (10) to a predefined limit; and - Responsive to confirming that the delay time (10) is below the predefined limit, detecting the nuclear spin resonance of the probe material (2).

Description

[0001] Nuclear spin resonance spectrometer, method for detecting a nuclear spin resonance and method for determining a nuclear spin resonance spectrum

[0002] The disclosure concerns a nuclear spin resonance spectrometer for detecting a nuclear spin resonance , preferably a nuclear magnetic resonance and / or a nuclear quadrupole resonance , of a probe material comprising :

[0003] - an oscillator unit , wherein the oscillator unit is configured to oscillate with a tunable resonance frequency;

[0004] - a bias source configured to provide electrical power to the oscillator unit ;

[0005] - a quench unit configured to quench an oscillation of the oscillator unit , wherein the quench unit comprises a quench switch to activate and to deactivate the quench unit ; wherein the oscillator unit is configured to build-up an oscillation when the quench unit is deactivated, wherein the nuclear spin resonance spectrometer is configured to generate at least a first oscillation pulse and a second oscillation pulse by activating and deactivating the quench unit , wherein the oscillator unit is configured to generate a probe excitation signal during the first oscillation pulse in order to excite the probe material , wherein the oscillator unit is configured to receive a response signal from the probe material in response to the probe excitation signal , wherein the oscillator unit is configured such that a delay time of an RF envelope of the second oscillation pulse depends on the received response signal .

[0006] Furthermore , the disclosure concerns a method for detecting a nuclear spin resonance , in particular a nuclear magnetic resonance and / or a nuclear quadrupole resonance , of a probe material with a nuclear spin resonance spectrometer .

[0007] The disclosure further concerns a method for determining a nuclear spin resonance spectrum, in particular a nuclear magnetic resonance spectrum and / or a nuclear quadrupole resonance spectrum, of a probe material , with a nuclear spin resonance spectrometer . Nuclear spin resonance spectroscopy techniques , such as nuclear magnetic resonance (NMR) spectroscopy and nuclear quadrupole resonance (NQR) spectroscopy, are widely used in medical diagnostics , chemical analysis and drug development , and to study the structure of molecules and crystals to name j ust a few . In addition, NMR and NQR spectroscopy are used to detect illegal and potentially hazardous substances , such as drugs and explosives , in the context of security . Conventional security screening methods often face challenges in ef fectively detecting concealed materials , which can pose signi ficant risks to public safety . NMR and NQR spectroscopy enable rapid and accurate identi fication without requiring physical contact or sample alteration . Analysis of the unique NMR and / or NQR signatures of explosive substances or drugs enables precise identi fication and discrimination against interfering substances commonly encountered in security scenarios .

[0008] Nuclear magnetic resonance (NMR) spectroscopy relies on a relatively strong, static and homogeneous magnetic field . In contrast , nuclear quadrupole resonance (NQR) spectroscopy relies on an electric quadrupole moment of the nuclei in the probe .

[0009] Disadvantages of nuclear spin spectrometers include their relatively high acquisition and maintenance costs , power consumption, weight , and overall complexity . Most NMR and NQR spectrometers are typically bulky and require dedicated ( laboratory) space with appropriate environmental controls . These instruments often require stable and homogeneous magnetic fields , which necessitate speciali zed infrastructure , such as superconducting or cryogenic magnets . This limitation restricts their applications , portability, and usability in field applications , especially when precision and accuracy are less crucial compared to scienti fic or medical applications .

[0010] An approach that alleviates some of the above-mentioned disadvantages relies on marginal oscillators or super-regenerative receivers ( SRR) . These electric circuits of fer simplicity, and cost-ef fectiveness as well as a variable frequency range . For example , US 3 515 981 A shows a super-regenerative resonance spectrometer, which operates in a manner similar to a super-regenerative radio receiver . A super-regenerative oscillator is arranged to produce a continuous radio frequency signal whose frequency can be varied . In addition, the spectrometer comprises a quench waveform generator which alternately renders the super- regenerative oscillator oscillatory ( the active phase ) and non- oscillatory ( the decay phase ) by applying positive and negative pulses to the oscillator to make an active element , in this case a triode , conducting or nonconducting . There is accordingly a repeated build-up and decay of oscillations in the regenerative oscillator . The oscillations build-up when the quench signal is not applied and decay when the quench signal is applied during a so called "damping period" of the L-C circuit . A quench waveform generator is arranged to provide a quench waveform of adj ustable frequency . The spectrometer comprises a coil , which is placed adj acent a sample . The sample induces a signal voltage in the super-regenerative receiver . Oscillations will build-up from a small radio frequency voltage ( including the signal voltage ) when a preceding quenching pulse is removed .

[0011] However, SRR-based spectrometers lack repeatability in results , suf fer from low sensitivity, and face challenges in accurately determining both the resonance frequencies and bandwidths of detected NMR and NQR signals . For example , unwanted residual signals in the oscillator may influence the outcome . Furthermore , the receivers comprise a second lower frequency ( in addition to the resonance frequency) to control the quench signal . This second frequency determines the repetition rate and influences the spectral characteristics of the detected signals . The quenching process generates sidebands around the input signal frequency . These sidebands can be mistaken for NMR / NQR signals , leading to ambiguity and potential misinterpretation . This is especially problematic when analyzing samples with multiple closely spaced signals .

[0012] It is an obj ect of the invention to alleviate or eliminate at least some of the disadvantages of the prior art . In particular, it is an obj ect of the invention to provide a simple nuclear spin resonance spectrometer for detecting a nuclear spin resonance , preferably a nuclear magnetic resonance and / or a nuclear quadrupole resonance , of a probe material , a method for detecting a nuclear spin resonance and a method for determining a nuclear spin resonance spectrum with an enhanced repeatability, decreased measurement time , a reduced RF excitation current , a low power consumption, as well as reduced radiated and conducted emissions .

[0013] This obj ect is achieved by a nuclear spin resonance spectrometer of the above-mentioned type , wherein the nuclear spin resonance spectrometer comprises a detection unit configured to detect the delay time of an RF envelope of the second oscillation pulse , wherein the nuclear spin resonance spectrometer is configured to compare the detected delay time to a predefined limit , wherein the nuclear spin resonance spectrometer is configured to detect the nuclear spin resonance of the probe material i f the delay time is below the predefined limit .

[0014] Furthermore , this obj ect is achieved by a method for detecting a nuclear spin resonance , in particular a nuclear magnetic resonance and / or a nuclear quadrupole resonance , of a probe material with a nuclear spin resonance spectrometer according to the invention with the steps :

[0015] - Emitting a probe excitation signal generated with an oscillator unit ;

[0016] - Exciting the nuclear spin resonance of the probe material by means of the probe excitation signal ;

[0017] - Quenching the first oscillation pulse by activating the quench unit ;

[0018] - Deactivating the quench unit after the first oscillation is quenched;

[0019] - Receiving a response signal from the probe material by means of the oscillator unit responsive to the excitation;

[0020] - Detecting a delay time of an RF envelope of a second oscillation pulse , wherein the delay time depends on the received response signal ;

[0021] - Comparing the detected delay time to a predefined limit ; and

[0022] - Responsive to confirming that the delay time is below the predefined limit , detecting the nuclear spin resonance of the probe material .

[0023] The obj ect is also achieved by a method for determining a nuclear spin resonance spectrum, in particular a nuclear magnetic resonance spectrum and / or a nuclear quadrupole resonance spectrum, of a probe material , with a nuclear spin resonance spectrometer according to the invention, with the steps :

[0024] - Detecting a first nuclear spin resonance of the probe material with the method according to the invention, wherein the tunable resonance frequency comprises a first value ;

[0025] - Adj usting the tunable resonance frequency of the oscillator unit from the first value to a second value ;

[0026] - Detecting a second nuclear spin resonance of the probe material by the method according to the invention, wherein the tunable resonance frequency comprises the second value ; wherein the nuclear spin resonance spectrum comprises at least the detected first nuclear spin resonance and the detected second nuclear spin resonance .

[0027] The nuclear spin resonance spectrometer is configured to detect a nuclear spin resonance , such as a nuclear magnetic resonance and / or a nuclear quadrupole resonance , of a probe material . The probe material may comprise any organic or in-organic material . The state of aggregation of the probe material being the subj ect of the study may be similar but not limited to the solid state .

[0028] For example , the probe material may comprise a drug, or an explosive . The probe material may comprise a crystal .

[0029] The nuclear spin resonance spectrometer comprises an oscillator unit , wherein the oscillator unit is configured to oscillate with a tunable resonance frequency . The oscillator unit comprises an oscillator circuit which may be configured as a feedback oscillator or a negative-resistance oscillator, for example . A feedback oscillator may comprise an active element , such as , for example , an electron tube , a transistor, BJT , J-FET , MOSFET or an operational ampli fier . A negative-resistance oscillator may comprise an electronic component that exhibits negative resistance and / or dif ferential negative resistance , such as , for example , an electron tube , a gas tube , a UJT (unij unction) transistor, as well as a tunnel , lambda, IMPATT or Gunn diode . The oscillator unit may comprise an inductive element L which may be a single wiring coil or an inductor coil with tap and / or sectional inductor coil and / or an inductive element L be considered a part of lumped elements of cavity resonator . The oscillator unit may comprise , for example , a parallel LC circuit with an inductance and a capacitance . The oscillator unit may further comprise an external resistance parallel to the LC circuit , which is arranged such that the oscillator unit comprises a RLC circuit and where an external resistance R can be connected and disconnected . The oscillator unit comprises a tunable resonance frequency with which it is configured to oscillate . The tunable resonance frequency may be adj usted . Furthermore , the nuclear spin resonance spectrometer comprises a bias source configured to provide electrical power to the oscillator unit .

[0030] The nuclear spin resonance spectrometer further comprises a quench unit configured to quench an oscillation of the oscillator unit . The oscillation may, for example , be quenched by interrupting an electrical power supply from the bias source to the oscillator unit . Quenching may be understood as interrupting the oscillation and / or causing the oscillation to decay . The first oscillation pulse is quenched when the quench unit is activated . Quenching may therefore relate to the ef fect of the quench unit on an oscillation of the oscillator unit ( such as the first oscillation pulse and the second oscillation pulse ) . For example , quenching may be ef fected by interrupting a power supply of the oscillator unit and forcing the oscillation to decay . Quenching may relate to unpowering the oscillator unit . The quench unit comprises a quench switch to activate and to deactivate the quench unit . The quench switch may be a digitally controlled mechanical or solid-state device such as an on / of f switch .

[0031] The oscillator unit is configured to build-up an oscillation when the quench unit is deactivated . When the quench unit is activated, the oscillation decays to a low amplitude level and may vanish entirely . The low amplitude level may be essentially zero volts or a low noise level , for example . The oscillator unit may be a regenerative circuit . Details on regenerative circuits , such as super-regenerative receivers , and / or negative-resistance oscillators and / or feedback oscillators can be found in J . R . Whitehead, Super-Regenerative Receivers . Cambridge Univ . Press , 1950 or R . W . Rhea, Oscillator Design and Computer Simulation, Noble Publishing, 1995 or I .M . Gottlieb, Practical Oscillator Handbook, Newnes , 1997 , for example .

[0032] The nuclear spin resonance spectrometer is configured to generate at least a first oscillation pulse and a second oscillation pulse by activating and deactivating the quench unit . By activating the quench unit , an oscillation of the oscillator unit is quenched . By deactivating the quench unit , an ( other ) oscillation builds up . Therefore , the quench unit can be utili zed to generate oscillation pulses by allowing oscillations to build-up and consequently quenching the oscillations . The nuclear spin resonance spectrometer is configured to generate at least a first oscillation pulse and a second oscillation pulse . The first oscillation pulse is ultimately utili zed to excite the probe material by means of a probe excitation signal , wherein properties of the second oscillation pulse are used to detect an excitation of the probe material and therefore the nuclear spin resonance . The frequency of the second oscillation pulse may be similar, but not limited to , the frequency of the first oscillation pulse . The frequency of the second oscillation pulse may be essentially equal to the frequency of the first oscillation pulse . The resonance frequency of the oscillator unit may be essentially equal for the first oscillation pulse and the second oscillation pulse .

[0033] The oscillator unit is configured to generate a probe excitation signal at least during the first oscillation pulse in order to excite the probe material . For example , the oscillator unit may comprise a coil to emit the probe excitation signal . The probe material may be placed inside the coil and / or in a region of near field of an inductive part ( e . g . , the coil ) of the LC circuit . The first oscillation pulse may cause the coil to emit the probe excitation signal . The probe excitation signal comprises electromagnetic radiation with a frequency equal to the tunable resonance frequency of the oscillator unit . The tunable resonance frequency may be a radio frequency . The probe material may be arranged adj acent to the coil . The first oscillation pulse may comprise a RF pulse width . The RF pulse width of the first oscillation pulse may be determines by a duration of the excitation signal or vice versa . The duration of the excitation signal may af fect the excitation of the probe material . The duration of the excitation signal may be set by deactivating and consequently activating the quench unit with a corresponding time interval .

[0034] I f the probe material comprises a nuclear spin resonance with a transition frequency matching the frequency of the emitted probe excitation signal ( i . e . , the resonance frequency of the oscillator unit ) , the probe material absorbs at least a portion of the energy of the probe excitation signal , such that the probe material is excited . Due to the excitation, the probe material emits a response signal . For example , magnetic nuclear spins of the probe material may be initially aligned, for example due to an external magnetic field . The probe excitation signal may lead to a perturbation of the alignment . The response signal arises from the precession of nuclear spins in the transverse plane and the consequent induction of a voltage in the oscillator unit , e . g . , in a detection coil of the oscillator unit . Relaxation processes determine how long this response signal lasts and how the sample magneti zation returns to its equilibrium state .

[0035] The oscillator unit is configured to receive the response signal from the probe material in response to the probe excitation signal . For example , the inductive element may be configured to receive the response signal from the probe material . The oscillator unit is configured such that a delay time of an RF envelope of the second oscillation pulse depends on the received response signal . "RF" is short for radio- frequency . The dependence of the oscillator start-up time ( i . e . , the delay time ) on the negligible noise present in the oscillator unit when the oscillator unit is powered up is well-known and, for example , described in patent US 3 515 981 . The received response signal contributes or adds to the residual signal and hence accelerates the build-up of the RF envelope of the second oscillation pulse . The second oscillation pulse comprises an RF envelope with a rising edge with a delay time . This delay time depends on whether or not the probe material emits a response signal or not . In other words , the delay time depends on whether or not the probe material comprises a nuclear spin resonance that matches the resonance frequency of the oscillator unit . In the case of a detected nuclear spin resonance , the response signal generated by the probe material adds to the residual signal of the LC circuit . It accelerates the time to build-up the RF envelope of the second oscillation pulse .

[0036] The nuclear spin resonance spectrometer furthermore comprises a detection unit configured to detect the delay time of the RF envelope of the second oscillation pulse . Detecting the instantaneous value of the amplitude of the RF signal ( e . g . , of the second oscillation pulse ) may be ef fected by measuring an electrical current flowing through the oscillator unit , wherein the magnitude of the RF oscillation is proportional to this current . The detection unit may comprise a signal edge detection element configured to detect the rising edge of the second oscillation pulse . The detection unit may comprise a time measurement unit , e . g . , comprising a timer, to measure the delay time . The delay time may be the time between deactivating the quench unit and the detection of the rising edge by the signal edge detection element . The delay time may be the time between deactivating the quench unit until the RF envelope of the second oscillation pulse reaches a predetermined value . The parameter for detecting the presence of a NQR and / or NMR signal ( i . e . , a nuclear spin resonance ) is the delay time . The delay time is the elapsed time between two well-defined time points . The measurement of the delay time may be initiated by an edge of the quench signal during the deactivation of the extinction of the first oscillation pulse . The measurement of the delay time is completed at the time at which the envelope of the RF envelope signal reaches a predetermined value of its amplitude . The second oscillation pulse may start as soon as the quench unit is deactivated ( after the first oscillation pulse has been attenuated) , wherein it takes a period of time until the RF envelope of the second oscillation pulse reaches the predetermined value . This period of time is the delay time . The delay time measurement may be performed as a transition state test when the RF envelope of the second oscillation pulse is in the rising phase ( i . e . , the second oscillation pulse builds up or rises ) . The nuclear spin resonance spectrometer is configured to compare the detected delay time of the RF envelope to a predefined limit . The nuclear spin resonance of the probe material is detected i f the delay time is below the predefined limit . The device may be calibrated, such that it can be used for quantitative analysis . The numerical values of a baseline and delay time limit ( i . e . , the predefined limit ) may be determined when the instrument is calibrated . The predefined limit may be a standard delay time of the RF envelope when the probe material is present but when the oscillator frequency is at a frequency where the probe material does not have a nuclear spin resonance ( e . g . , at a frequency, which is known not to correspond to a nuclear spin resonance of the probe material ) . The predefined limit may be a standard RF envelope delay time in the presence of the probe material , but when the oscillator frequency is set far from the frequency at which a nuclear spin resonance is expected .

[0037] The method for detecting the nuclear spin resonance of the probe material with a nuclear spin resonance spectrometer according to the invention comprises the following steps .

[0038] The probe excitation signal is generated with the oscillator unit and emitted by the oscillator unit . The probe excitation signal is emitted during the first oscillation pulse . The nuclear spin resonance of the probe material is excited by means of the probe excitation signal . Then, the first oscillation pulse is quenched by activating the quench unit . After the first oscillation pulse is quenched, i . e . , the first oscillation pulse has decayed, the quench unit is deactivated . A wait time between activating the quench unit for quenching the first oscillation pulse and deactivating the quench unit may depend on a fall time of a falling edge of the first oscillation pulse . The wait time may be at least the fall time or greater than the fall time . A time tO is the point on the timeline of a detection process when the second oscillation pulse starts to be generated, i . e . , when the quench unit is deactivated after the first oscillation pulse expired . The delay time is measured starting from the time tO . After activation of the quench unit for quenching the first oscillation pulse , the inductor of the RF oscillator unit and the probe material become two separate magnetic circuits . The rate of decay of the magnetic field of the inductor depends on the RLC parameters of the oscillator unit , while the decay rate of the magnetic field generated by the probe material is subj ect to the principle of exponential decay described by the tau ( i ) parameter of the isotope contained in the probe material . For example , a suf ficient condition for detecting the NQR / NMR signal ( i . e . , the response signal ) from the probe material at time tO may be that the level of the response signal is greater than a residual RF oscillation coming from the RLC tank of the RF oscillator unit . The wait time may also depend on an expected nuclear spin resonance . For example , the method according to the invention may be used to search for a certain substance within the probe material . For example , the substance may be a drug with known properties and known nuclear spin resonances . Therefore , a decay time of an expected response signal may be known . The wait time may be at least the fall time but may be lower than a decay time of the expected response signal .

[0039] A response signal from the probe material is received by the oscillator unit . Then, the delay time of the RF envelope of the second oscillation pulse is detected, wherein the delay time depends on the received response signal .

[0040] Then the detected delay time is compared to the predefined limit . Finally, responsive to confirming that the delay time is below the predefined limit , the nuclear spin resonance of the probe material is detected .

[0041] In contrast , i f the probe material does not comprise the nuclear spin resonance , the probe material is not excited by the probe excitation signal . Consequently, no response signal is received by the oscillator unit and the resulting delay time of the second oscillation pulse is not below the predefined limit . Therefore , no nuclear spin resonance is detected in this case .

[0042] By means of the quench switch, which is preferably digitally controlled, a second lower frequency, which is utili zed in super-regenerative receivers , can be omitted . A repetition rate of the measurement sequence may be defined ( e . g . , by a device operator ) in accordance with a spin-lattice relaxation time T1 of the probe material ( i . e . , the sample under investigation) . The time length of the RF excitation pulse ( i . e . , the first oscillation pulse ) during the measurement sequence is determined on the basis of the spin-spin relaxation time T2 of the tested probe material . The duration of the first oscillation pulse is linked to the spin-spin relaxation time T2 , of the probe material . Shortening the excitation time below the T2 value may lead to a signi ficant decrease or, potentially, to a complete signal loss . Extending the duration of the first oscillation pulse may not result in a qualitative change in the delay time . Therefore , the choice of the duration of the first oscillation pulse is signi ficantly influenced by the spin-spin relaxation time T2 of the probe material to ensure optimal impact on the delay time . The observed amplitude of the signal resulting from the change in the delay time depends on the properties of the observed isotope and its molar content in the sample under study . By utili zing the delay time of the RF envelope of the second oscillation pulse and comparing it to a predefined limit , a simple and robust estimator for the presence of a nuclear spin resonance of the probe material is provided . The disclosed nuclear spin resonance spectrometer is configured to qualitatively detect the presence of the nuclear spin resonance . The estimator, which is based on the delay time of the RF envelope of the second oscillation pulse , allows to utili ze the response signal from the probe material essentially at the level of the thermal noise of the oscillator unit at the time of deactivating the quench unit . The ability to detect NQR or NMR signals at the level of the thermal noise provides the opportunity to signi ficantly reduce the RF excitation current , i . e . , an electrical current of the first oscillation pulse . By reducing the RF excitation current , the probe material is less exposed to strong radiofrequency radiation, which, for example , may af fect crystal lattice parameters of the probe material . Overall , nuclear spin resonances can be detected with greater accuracy and an enhanced repeatability compared to , for example, state of the art SRR-based spectrome- ters . The measurement may be repeated to ( statistically) increase certainty but it is not intrinsically necessary to repeat single measurements .

[0043] The response signal is due to free induction decay ( FID) of the excited probe material . The disclosed method may be classi fied as a direct detection method, and in particular as a pulsed method using FID . However, methods based on free induction decay typically rely on measuring the FID signal ( i . e . , an amplitude of the FID signal ) over a period of time and a Fourier trans formation of the measured FID signal . In contrast , the disclosed method relies on the delay time of the RF envelope of the second oscillation pulse , which predominately depends on the FID signal at a single point in time - namely when the quench unit is deactivated . In contrast to the invention, standard FID-based techniques require Fourier trans formation for processing data .

[0044] According to the state of the art , NQR / NMR signal detectors can be classi fied as oscillator-based or pulse method devices . Devices working on the principle of pulse mode are processing information about detection of NQR / NMR resonance in the time domain . According to the invention, an oscillator unit in pulse mode is used for detection, in contrast to processing or extracting information about the detection of NQR / NMR resonance from the frequency domain .

[0045] The detection of a nuclear spin resonance based on the measured delay time , in particular based on a comparison of the measured delay time with a predefined limit , is particularly simple and robust . In contrast , techniques from the state of the art rely on more complex signal features and mathematical operations .

[0046] Optionally, the nuclear spin resonance spectrometer may be configured to confirm the absence of a nuclear spin resonance . In case the probe material does not comprise a nuclear spin resonance corresponding to the resonance frequency of the oscillator unit , the probe excitation signal does not excite a nuclear spin resonance of the probe material . Consequently, the probe material does not emit a response signal . Therefore , the oscillator unit does not receive a response signal in response to the probe excitation signal . In this case , the build-up of the RF envelope of the second oscillation pulse is not accelerated by a response signal . Consequently, the detected delay time is not below the predefined limit but equal to the predefined limit or greater than the predefined limit . The measured delay time may be compared to the predefined limit . Responsive to confirming that the predefined limit is equal to the detected delay time or below the detected delay time , the absence of a nuclear spin resonance is confirmed .

[0047] Optionally, a method for confirming the absence of a nuclear spin resonance , in particular a nuclear magnetic resonance and / or a nuclear quadrupole resonance , of the probe material with a nuclear spin resonance spectrometer according to the invention may comprise the steps :

[0048] - Emitting the probe excitation signal generated with the oscillator unit ;

[0049] - Quenching the first oscillation pulse by activating the quench unit ;

[0050] - Deactivating the quench unit after the first oscillation pulse is quenched;

[0051] - Detecting the delay time of the RF envelope of a second oscillation pulse ;

[0052] - Comparing the detected delay time to the predefined limit ; and

[0053] - Responsive to confirming that the predefined limit is equal to the detected delay time or smaller than the detected delay time , confirming the absence of a nuclear spin resonance of the probe material .

[0054] The method for determining a nuclear spin resonance spectrum, in particular a nuclear magnetic resonance spectrum and / or a nuclear quadrupole resonance spectrum, of the probe material , with a nuclear spin resonance spectrometer comprises the following steps . Initially, the tunable resonance frequency of the nuclear spin resonance spectrometer comprises a first value . A first nuclear spin resonance is detected by means of the method for detecting a nuclear spin resonance . Consequently, the tunable resonance frequency of the oscillator unit is adj usted from the first value to a second value . The second value is di f ferent from the first value . After the tunable resonance frequency has been adj usted, a second nuclear spin resonance is detected by means of the method for detecting a nuclear spin resonance , wherein the tunable resonance frequency comprises the second value . The nuclear spin resonance spectrum comprises at least the detected first nuclear spin resonance . Optionally, the nuclear spin resonance spectrum may comprise the detected second nuclear spin resonance .

[0055] Optionally, the nuclear spin resonance spectrometer may be used to scan the probe material for nuclear spin resonances . The tunable resonance frequency may be tuned over a frequency range , wherein for each resonance frequency ( i . e . , for each value of the tunable resonance frequency) , the delay time may be measured . The delay time as a function of the resonance frequency may signi ficantly decrease when the resonance frequency matches a nuclear spin resonance of the probe material . The predefined limit may relate to a relative or an absolute reduction of the delay time compared to a delay time of a resonance frequency without a corresponding nuclear spin resonance . For example , a baseline may be determined with a linear fit through the detected delay times . The predefined limit may be , for example , relative to the baseline . A nuclear spin resonance may be detected, for example , i f the delay time is signi ficantly below the baseline .

[0056] In an optional embodiment , the nuclear spin resonance spectrometer comprises a damp unit , wherein the damp unit comprises a damp switch for activating and deactivating the damp unit , wherein the damp unit is configured to damp, preferably critically damp, the first oscillation pulse when the damp unit is activated and the quench unit is activated .

[0057] The fall time of the first oscillation pulse should be as short as possible , such that nuclear spin resonances with a short decay time may be detected . In case the fall time of the first oscillation pulse exceeds the decay time of the response signal ( e . g . , the FID signal ) , it may not be possible to discriminate the response signal against a background signal of the falling edge of the first oscillation signal . Therefore , it is crucial to attenuate the first oscillation such that the fall time of the falling edge is as short as possible . This is achieved by means of the damp unit in combination with the quench unit . The damp unit may for example comprise a resistance parallel to the oscillator unit . The damp switch may be a digitally controlled mechanical or solid-state device such as an on / of f switch . The damp unit is configured to damp the first oscillation when the damp unit is activated . Preferably, the damp unit is configured to critically damp the first oscillation pulse . Without the damp unit , the first oscillation pulse may be underdamped . A particularly short fall time may be achieved by critical damping of the first oscillation pulse . Critical damping may be achieved, for example , i f the damp unit comprises a resistance with a value according to a damping criterion, wherein the resistance is parallel to the LC circuit of the oscillator unit . The oscillation decay characteristics of an RLC circuit are known in the literature . Damping may be understood as draining power from the oscillator unit . In order to dampen the first oscillation pulse , the damp unit is activated . Damping the first oscillation pulse refers to activating the damp unit . The ef fect of the damp unit on the first oscillation pulse may be referred to as damping . The damp unit may only be activated when also the quench is activated .

[0058] The method for detecting a nuclear spin resonance may further comprise the steps :

[0059] - Dampen, preferably critically dampen, the first oscillation pulse by activating the damp unit ; and

[0060] - Deactivating the damp unit after the first oscillation pulse is quenched, and preferably before the quench unit is deactivated .

[0061] The damp unit may be activated at the same time as the quench unit or preferably after the quench unit is activated . The damp unit may be activated before the first oscillation pulse has decayed . In order to avoid any potential influences of the damp unit on the second oscillation pulse , the damp unit may be deactivated before the quench unit is deactivated .

[0062] The nuclear spin resonance spectrometer may optionally comprise a control unit with : - a quench control module configured to switch the quench switch; and

[0063] - a damp control module configured to switch the damp switch; wherein the control unit is configured to receive the detected delay time from the detection unit and to compare the delay time to the predefined limit .

[0064] The control unit may be configured to execute an algorithm ( for implementing the method according to the invention) and to generate an algorithm speci fic sequence of events on the controlled elements ( i . e . , the quench switch, the damp switch and the detection unit ) , and to read and process feedback information from the control elements , with properties similar but not limited to the microcontroller or state machine implemented on a PLD device . The quench control module controls the quench switch . The damp control module controls the damp switch .

[0065] Optionally, the control unit comprises a frequency adj ustment module configured to adj ust the tunable resonance frequency of the oscillator unit . Frequency tuning may be ef fected by changing a capacitance of the oscillator unit , while maintaining the geometry of the inductive element . The resonance frequency of the oscillator unit may be adj usted by adj usting a capacitor of the oscillator unit . The capacitance of capacitor may for example be adj usted by an electronic stimulus and / or by electro-mechanical means .

[0066] In an optional embodiment , the damp unit comprises a variable resistance . The variable resistance may be adj usted such that critical damping is achieved . For example , the variable resistance may be adj usted according to a damping criterion . For example , the control unit may comprise a resistance adj ustment module configured to adj ust the variable resistance of the damp unit . When the tunable resonance frequency of the oscillator circuit is adj usted, the variable resistance may be adj usted, for example , according to a damping criterion in order to achieve critical damping .

[0067] Optionally, the oscillator unit comprises a variable capacitor for adj usting the tunable resonance frequency .

[0068] In a preferred embodiment , the oscillator unit comprises an inductor, preferably an air coil , wherein the inductor is configured to emit the probe excitation signal and to receive the response signal . The probe material may be arranged adj acent to the inductor .

[0069] The oscillator unit may comprise an electronic component similar, but not limited to a transistor . Optionally, the oscillator unit comprises a transistor, preferably a j unction-gate fieldef fect transistor ( JFET ) , wherein the transistor is coupled to the bias source . The transistor may be configured to provide ( enhanced) positive feedback for the oscillator unit . A residual signal in the oscillator unit may comprise the tunable resonance frequency of the oscillator unit . The residual signal may render the transistor conducting or non-conducting, such that electrical power is provided by the bias source in intervals according to the tunable resonance frequency and such that an oscillation is rapidly built up in the oscillator unit .

[0070] Optionally, the delay time is a period between the deactivation of the quench unit and a rising edge of the RF envelope of the second oscillation pulse .

[0071] In an optional embodiment , the delay time is the period between the deactivation of the quench unit and the time at which the rising edge reaches a predetermined value .

[0072] Optionally, the nuclear spin resonance spectrometer may be configured to shield external RF signals from the probe material and / or the oscillator unit . The spin resonance spectrometer may comprise a shielding for external RF signals .

[0073] By way of example , the disclosure is further explained with respect to some selected embodiments shown in the figures . However, these embodiments shall not be considered limiting for the disclosure .

[0074] Fig . 1 schematically shows a nuclear spin resonance spectrometer Fig . 2 schematically shows a timeline of relevant signals of the nuclear spin resonance spectrometer of fig . 1

[0075] Fig . 3 shows the dynamic response of the oscillator unit to the actions of the quench switch and the damp switch

[0076] Fig . 4 shows experimental data from a probe material comprising crystalline anhydrous NaC103measured with the nuclear spin resonance spectrometer of fig . 1

[0077] Fig . 5 shows the envelope signal of a sequence of measurements of the nuclear spin resonance spectrometer of fig . 1

[0078] Fig . 1 schematically shows a nuclear spin resonance spectrometer 1 for detecting a nuclear spin resonance , preferably a nuclear magnetic resonance and / or a nuclear quadrupole resonance , of a probe material 2 . The nuclear spin resonance spectrometer 1 comprises an oscillator unit 3 , wherein the oscillator unit 3 is configured to oscillate with a tunable resonance frequency .

[0079] Furthermore , the nuclear spin resonance spectrometer 1 comprises a bias source 5 configured to provide electrical power to the oscillator unit 3 , as well as a quench unit 6 configured to quench an oscillation of the oscillator unit 3 , wherein the quench unit 6 comprises a quench switch 7 to activate and to deactivate the quench unit 6. The oscillator unit 3 is configured to build-up an oscillation when the quench unit 6 is deactivated . The nuclear spin resonance spectrometer 1 is configured to generate at least a first oscillation pulse 8 ( see fig . 2 ) and a second oscillation pulse 9 ( see fig 2 ) by activating and deactivating the quench unit 6 . The oscillator unit 3 is configured to generate a probe excitation signal during the first oscillation pulse 8 in order to excite the probe material 2 . The oscillator unit 3 is configured to receive a response signal from the probe material 2 in response to the probe excitation signal . The oscillator unit 3 is configured such that a delay time 10 ( see fig . 2 ) of the RF envelope of the second oscillation pulse 9 depends on the received response signal . The nuclear spin resonance spectrometer 1 comprises a detection unit 11 configured to detect the delay time 10 of the RF envelope of the second oscillation pulse 9 . The nuclear spin resonance spectrometer 1 is configured to compare the detected delay time 10 to a predefined limit , wherein the nuclear spin resonance spectrometer 1 is configured to detect the nuclear spin resonance of the probe material 2 i f the delay time is below the predefined limit .

[0080] The oscillator unit 3 is configured as a class A, common-drain, split-capacitance feedback type JFET Colpitts oscillator . An advantage of the Colpitts oscillator over the Clapp oscillator is that the Colpitts configuration lacks a high-resistance resistor associated with the gate of JFET , which is a source of noise . The criterion for the configuration of oscillator unit 3 is the use of an inductor coil , which in provides cumulative electromagnetic coupling between any coil sections , or when using coils arranged perpendicular to each other, electromagnetic coupling between coils should be considered quasi- zero . The oscillator unit 3 may be configured as a split-capacitance oscillator or split-inductance oscillator .

[0081] The oscillator unit 3 comprises an LC circuit , which is ef fected by three capacitors 12A, 12B and 12C, and an inductor 13 . The capacitor 12A is a variable capacitor 14 for adj usting the tunable resonance frequency of the oscillator unit 3 . The inductor 13 is in this exemplary embodiment configured as an air coil 15 , wherein the inductor 13 ( i . e . , the air coil 15 ) is configured to emit the probe excitation signal and to receive the response signal . The air coil 15 acts in this case as the source of a magnetic field . The probe material 2 is arranged adj acent to the air coil 15 .

[0082] The oscillator unit 3 comprises a transistor 16 , which is in this case configured as a j unction-gate field-ef fect transistor ( JFET ) 17 , wherein the transistor 16 is coupled to the bias source 5 . The transistor 16 is configured to provide ( enhanced) positive feedback for the oscillator unit 3 . When the oscillator unit 3 is quenched and the quench unit 6 is then deactivated, a residual signal in the oscillator unit 3 comprises the resonance frequency of the oscillator unit 3 , since the oscillator unit 3 predominantly supports the ( tunable ) resonance frequency . This residual signal renders the transistor 16 conducting or non-conducting in periodic intervals ( corresponding to the resonance frequency) such that electrical power is provided by the bias source in intervals according to the tunable resonance frequency and such that an oscillation is rapidly built up in the oscillator unit 3 . An oscillation is rapidly built up in the oscillator unit 3 , once the quench unit 6 is deactivated .

[0083] The quench unit 6 comprises the quench switch 7 . The quench switch 7 is configured to activate and deactivate the quench unit 6 . The quench switch 7 is a digitally controlled circuit breaker, in this case a JFET transistor . The quench switch 7 is digitally controlled . When the quench unit 6 is activated, a source terminal of the JFET 17 is disconnected from ground 65 via the quench switch 7 as well as two resistors 18 and 19 and an inductor 20 . In case the quench unit 6 is activated, the bias source 5 does not provide electrical power to the oscillator unit 3 in a way that the oscillator unit 3 can oscillate . In addition, electrical energy stored in the oscillator unit 3 in form of an oscillation will be drawn out of the oscillator unit 3 , such that the oscillation decays .

[0084] The nuclear spin resonance spectrometer 1 further comprises a damp unit 21 , wherein the damp unit 21 comprises a damp switch 22 for activating and deactivating the damp unit 21 . The damp unit is configured to damp, in this case critically damp, the first oscillation pulse 8 ( see fig . 2 ) - or any other oscillation of the oscillator unit 3 - when the damp unit 21 is activated and the quench unit 6 is activated . The damp switch 22 is a digitally controlled circuit breaker, in this case a RE JFET transistor . The damp switch 22 is digitally controlled . The damp unit 21 comprises in addition to the damp switch 22 a variable resistance , in this example in form of a variable resistor 23 . The damp unit 21 , i . e . , the damp switch 22 and the variable resistor 23 in this example , is coupled to the oscillator unit 3 such that the resistor 23 is parallel to the air coil 15 and the capacitors 12A. Therefore , when the damp unit 21 is activated, the damp unit 21 and the oscillator unit 3 together form a parallel RLC circuit . The resistance of the resistor 23 is such that critical damping occurs , when the quench unit 6 is activated and the damp unit 21 is activated . The resistance of the resistor is set according to a critical damping criterion ( i . e . , to achieve critical damping) .

[0085] In summary, the nuclear spin resonance spectrometer 1 is configured to build-up an oscillation, when the quench unit 6 is deactivated and maintain the oscillation until the quench unit 6 is activated . By activating and deactivating the quench unit 6 , oscillation pulses are generated . The damp unit 21 critically damps any oscillation of the oscillator unit 3 , when activated .

[0086] The air coil 15 is configured to emit the probe excitation signal during the first oscillation pulse 8 . The first oscillation pulse 8 causes the air coil 15 to generate a RF magnetic field, which serves as the probe excitation signal . The probe material 2 is arranged adj acent to the air coil 15 , such that the probe excitation signal can efficiently interact with the probe material 2 . In response to the excitation by the probe excitation signal , the probe material 2 emits a response signal . The air coil 15 is configured to receive the response signal . Consequently, the response signal , which comprises the resonance frequency of the oscillator unit 3 , leads to an enhanced background signal or enhanced residual signal in the oscillator unit 3 , at least as long as the response signal is received . The response signal decays over time ( known as free induction decay ( FID) ) . When the quench unit 6 is deactivated and the response signal is received, the second oscillation pulse 9 is built up faster compared to the case when no response signal is received . Therefore , the signal level at the time when the quench unit 6 is deactivated is crucial for the delay time 10 of the RF envelope of the second oscillation pulse 9 . Consequently, the delay time 10 is indicative of the nuclear spin resonance of the probe material 2 .

[0087] The detection unit 11 is coupled to the oscillator unit 3 via a voltage follower 29 . The output of the voltage follower 29 is connected to the input of the analog signal edge detection element 25 . The detection of the point on the timeline where the measurement of the delay time 10 ends , can be done using a direct hardware implementation, or, alternatively, by software-assisted digital processing . Direct hardware implementation may be done , for example , using a comparator that monitors the magnitude of the RF envelope of the second oscillation pulse 9 . Soft- ware-assisted digital processing would involve digiti zing the RF envelope , and then processing the received data by a software- implemented algorithm to obtain the time at which the rising edge 59 ( see fig . 2 ) reaches a predetermined value . The exemplary embodiment of fig . 1 shows a hardware implementation .

[0088] The detection unit 11 comprises a flip- flop 24 , which is in this example a D-type positive-edge trigger flip- flop with reset , as well as an analog signal edge detection element 25 .

[0089] The analog signal edge detection element 25 comprises a comparator with a digital output 26 . The digital output 26 is connected to a clock ( CLK) terminal 27 of the flip- flop 24 . A data ( D) terminal 28 of the flip- flop 24 is held in logic 1 state ( i . e . , logic high) . The flip- flop 24 further comprises an output port 43A. Furthermore , the nuclear spin resonance spectrometer 1 comprises a timer 33 to determine the delay time 10 . The timer 33 determines the delay time 10 by measuring a time between deactivating the quench unit 6 until the analog signal edge detection element 25 detects the rising edge of an envelope of the second oscillation pulse and an output of the flip- flop 24 changes accordingly . The timer 33 is triggered by the control unit 30 . The control unit triggers the timer 33 once the quench unit 6 is deactivated to start a timing process of the timer 33 . Once the detection unit 11 detects the rising edge of an envelope of the second oscillation pulse and the output of the flipflop 24 changes accordingly, the control unit stops the timer 33 . The timer 33 consequently has measured the delay time 10 . The control unit 30 is configured to receive the measured delay time 10 from the timer 33 . Note that the first oscillation pulse 8 is used to excite the probe material 2 . The first oscillation pulse 8 is not used to measure the delay time 10 but only to excite the nuclear spin resonance of the probe material 2 . The flip- flop 24 is an event recorder . Its function is to register the occurrence of the rising edge of the envelope of the RF signal ( i . e . , the second oscillation pulse ) . The flip- flop 24 is in the reset state when the quench control signal is active . In the exemplary device , the flip-flop 24 registers the occurrence of an event when its CLK input receive a falling edge from the signal edge detection element 25 .

[0090] The detection unit 11 is configured to detect the rising edge ( see fig . 2 , fourth arrow 84D) of the RF envelope of the second oscillation pulse 9 , wherein the control unit 30 is configured to stop the timer 33 accordingly ( cf . fi fth arrow 84E in figure 2 ) . The nuclear spin resonance spectrometer 1 is configured to compare the detected delay time 10 to a predefined limit . The nuclear spin resonance spectrometer 1 is configured to detect the nuclear spin resonance of the probe material 2 i f the delay time 10 is below the predefined limit .

[0091] Additionally, the nuclear spin resonance spectrometer 1 comprises a control unit 30 . The control unit comprises a quench control module 31 configured to switch the quench switch 7 , as well as a damp control module 32 configured to switch the damp switch 22 . Furthermore , the control unit 30 is configured to receive the detected delay time 10 from the detection unit 11 and then, optionally after formatting, to resend it to the ( external ) timer 33 compare the delay time 10 with a predefined limit . Alternatively, the predefined limit may be stored by the control unit 30 . The nuclear spin resonance spectrometer 1 may comprise a comparison unit (not shown in this example ) , wherein the comparison unit is configured to receive the measured delay time 10 from the control unit 30 and to compare the delay time 10 to the predefined limit . The control unit 30 is in this example implemented in a computer . The timer 33 is controlled by the control unit 30 . The control unit 30 starts the timer 33 once the quench unit 6 is deactivated ( after quenching the first oscillation pulse 8 ; cf . third arrow 84C in fig . 2 ) and stops the timer 33 once the output port 43A of the flip- flop 24 switches from a detection logic 1 state to a detection logic 0 state ( see fourth arrow 84D in fig . 2 ) , i . e . , when the signal edge detection element 25 is triggered . The control unit 30 comprises an input port 43B for receiving a detection unit output signal 42 ( see fig . 2 ) . The control unit 30 comprises a timer output port for controlling the timer 33 . The control module 30 comprises a timer control module 33A for controlling the timer 33 . The control unit 30 comprises a number of registers used to store operator parameters . The registers may be implemented by electronical or electromechanical means .

[0092] Fig . 2 schematically shows a timeline of relevant signals of the nuclear spin resonance spectrometer 1 of fig . 1 . The time t advances from left to right indicated by a time axis 34 .

[0093] In general , the nuclear spin resonance spectrometer 1 comprises operation parameters which may be set by an operator, for example . The operation parameters are set by means of the control unit 30 . The control unit 30 operates based on these operation parameters and controls the nuclear spin resonance spectrometer accordingly . The operation parameters comprise , for example , the tunable resonance frequency, a duration of the first oscillation pulse 8 , a duration of the second oscillation pulse 9 and / or a duration of time during which the nuclear spin resonance spectrometer 1 is idle ( i . e . , between two separate measurements ) . The control unit 30 controls the quench unit 6 , the damp unit 21 , and the timer 33 (by triggering and stopping the timer 33 ) .

[0094] Fig . 2 shows five signals , which will be discussed in the following .

[0095] An envelope signal 35 shows an envelope of an electrical current flowing through the air coil 15 ( see fig . 1 ) of the oscillator unit 3 . The envelope signal 35 schematically shows the first oscillation pulse 8 and the second oscillation pulse 9 .

[0096] A quench signal 36 shows the logic state of the quench switch 7 . The quench signal 36 comprises a quench logic 1 state 37 and a quench logic 0 state 38 . The quench logic 1 state 37 translates to an opened quench switch 7 and an activated quench unit 6 . The quench logic 0 state translates to the quench switch 7 being closed and the quench unit 6 being deactivated . The quench unit 6 is controlled by the control unit 30 , in particular by the quench control module 31 , which controls the quench switch 7 of the quench unit 6 . The control unit 30 comprises a digital port for controlling the quench switch 7 . The quench signal 36 is also the logic state of said digital port .

[0097] A damp signal 39 shows the logic state of the damp switch 22 , which is controlled by the control unit 30 . The damp signal 39 comprises a damp logic 1 state 40 and a damp logic 0 state 41 . The damp logic 1 state 40 translates to an open damp switch 22 and a deactivated damp unit 21 . The damp logic 0 state translates to the damp switch 22 being closed and the damp unit 21 being activated . The damp unit 21 is controlled by the control unit 30 , in particular by the damp control module 32 , which controls the damp switch 22 . The damp signal 39 is also the logic state of this digital port .

[0098] A detection unit output signal 42 shows a logic state of the output port 43A of flip- flop 24 . The detection unit output signal 42 comprises a detection logic 1 state 44 and a detection logic 0 state 45 . A change of the logic state of the detection unit output signal 42 indicates , for example , that the second oscillation pulse 9 has reached the predetermined value .

[0099] A delay time signal 46 indicates the delay time 10 of the RF envelope of the second oscillation pulse 9 (note that the delay time is measured by means of the timer 33 , which is controlled by the control unit 30 ) . The delay time signal 46 indicates the logic state of a timer output port of the timer control module 33A of the control unit 30 . The delay time signal 46 comprises a rise logic 0 state 47A and a rise logic 1 state 47B . Rise logic 0 state 47A indicates that the respective point in time does not relate to a delay time of the RF envelope of the second oscillation pulse 9 . The rise logic 1 state 47B indicates the delay time 10 of the second oscillation pulse 9 . The control unit 30 triggers the timer 33 once the delay time signal 46 changes from rise logic 0 state 47A to rise logic 1 state 47B, i . e . , when the quench unit 6 is deactivated ( after the first oscillation pulse 8 has been quenched) . Once the detection unit 11 has detected the rising edge of the second oscillation pulse 9 , the control unit 30 stops the timer 33 . In this example , initially at a first point in time 49 ( indicated by a dashed vertical line ) , all signals and units are in a default state . The quench signal 36 , the damp signal 39 , and the detection unit output signal 42 are in the respective logic 1 ( i . e . , high) state . The operation parameters have been set by an operator prior to scanning the sample ( i . e . , the probe material 2 ) . The quench signal 36 is initially in the quench logic 1 state 37 , the damp signal is in the damp logic 1 state and the detection unit output signal 42 is in the detection logic 1 state 44 . Therefore , the oscillator unit 3 does not oscillate as the quench unit 6 is activated . The damp unit 21 is initially deactivated .

[0100] At a second point in time 50 , the quench signal 36 is switched from quench logic 1 state 37 to quench logic 0 state 38 . Therefore , the control unit 30 switches the quench switch 7 of the quench unit 6 , such that the quench unit 6 is deactivated, which allows the first oscillation pulse 8 to build-up based on a residual signal in the oscillator unit 3 , which is enhanced due to positive feedback by means of the JFET 17 . The first oscillation pulse 8 then builds up, as can be seen in the envelope signal 35 .

[0101] At a third point in time 51 , the analog signal edge detection element 25 detects a rising edge of the first oscillation pulse 8 , which triggers the flip-flop 24 . Therefore , the detection unit output signal 42 switches from detection logic 1 state 44 to detection logic 0 state 45 . In other words , the rising edge of the first oscillation pulse 8 causes a change of the detection unit output signal 42 as is indicated by a first arrow 84A. However, the first oscillation pulse 8 does not contribute to the delay time 10 . The control unit 30 does not trigger the timer 33 due to the detection of the rising edge of the first oscillation pulse 8 . The detection of the rising edge of the first oscillation pulse 8 does not lead to a change of the delay time signal 46 . The duration of the first oscillation pulse 71A is one of the operation parameters and may be set by an operator or user beforehand . Consequently, the probe excitation signal is generated with the oscillator unit 3 during the first oscillation pulse 8 . The first oscillation pulse 8 leads to an alternating electric current in the air coil 15 , which causes the air coil 15 to emit the probe excitation signal . By means of the probe excitation signal , a nuclear spin resonance of the probe material 2 is excited .

[0102] At a fourth point in time 53 , the quench unit 6 is activated (by switching the quench signal 36 to quench logic 1 state ) , such that the first oscillation pulse 8 is quenched . The detection unit output signal 42 switches back to detection logic 1 state at essentially the same time as is indicated by a second arrow 84B . Due to the activation of the quench unit 6 the envelope signal 35 decays .

[0103] At a fi fth point in time 54 , the damp unit 21 is activated to damp, in this example critically damp, the first oscillation pulse 8 . In other words , the damp unit 21 accelerates the attenuation of the envelope signal 35 . Due to the damp unit 21 , a fall time of the falling edge of the first oscillation pulse 8 is shortened ( compared to a case without an activated damp unit ) . There is an interval 60 between activating the quench unit 6 and activating the damp unit 21 ( i . e . , between the fourth point in time 53 and the fi fth point in time 54 ) . In other words , the attenuation of the first oscillation pulse 8 is accelerated by the damp unit 21 . The fall time is the time in between activating the quench unit ( the third point in time 53 in this example ) until the envelope signal 35 decays to a predefined low level . The fall time consists of the interval 60 and the time 55 between activating the damp unit 21 until the envelope signal 35 decays to a predefined low level .

[0104] At a sixth point in time 56 damp unit is deactivated, as can be seen in the damp signal 39 . The damp unit 21 is deactivated after the first oscillation pulse 8 is quenched, and before the quench unit 6 is deactivated .

[0105] At a seventh point in time 57 (which is also referred to as time tO ) after the first oscillation pulse 8 is attenuated ( i . e . , the envelope signal 35 has decayed) , the quench unit 6 is deactivated, such that the second oscillation pulse 9 can build-up in the oscillator unit 3 . Regardless of the quenching, the oscillator unit 3 receives the response signal from the ( excited) probe material 2 . However, the response signal does lead to a signi ficant re-excitation of oscillation of the oscillator unit 3 only when the quench unit is deactivated .

[0106] The envelope signal 35 comprises both the RF envelope of the first oscillation pulse 8 and the RF envelope of the second oscillation pulse 9 . The second oscillation pulse 9 , i . e . , the envelope of the second oscillation pulse 9 , starts at the seventh point in time 57 ( i . e . , at time tO ) . The deactivation of the quench unit 6 after the first oscillation pulse 8 is attenuated triggers the second oscillation pulse 9 and also triggers the measurement of the delay time 10 (note that the control unit 30 triggers the timer 33 ) as is indicated by a third arrow 84C . The control unit 30 is configured to deactivate the quench unit 6 after the first oscillation pulse 8 is attenuated . The control unit 30 is configured to switch the delay time signal 46 to rise logic state 1 state 47B, thereby activating the timer 33 .

[0107] At an eight point in time 58 , the analog signal edge detection element 25 detects a rising edge 59 of the envelope of the second oscillation pulse 9 (with respect to a positive or upper hal f of the envelope ) . The rising edge 59 is detected when the RF envelope of the second oscillation pulse 9 reaches a predetermined value 70 of its amplitude ( see hori zontal dashed line ) . Due to the detection of the rising edge 59 , the control unit 30 switches the detection unit output signal 42 to detection logic 0 state 45 ( as is indicated by the fourth arrow 84D) . The delay time signal 46 is then switched back to rise logic 0 state 47A by the control unit 30 ( as is indicated by a fi fth arrow 84E ) . Consequently, the control unit 30 stops the timer 33 . The timer 33 detects the delay time 10 of the RF envelope of the second oscillation pulse 9 . The control unit 30 receives the detected delay time 10 and compares the detected delay time 10 to a predefined limit . Alternatively, the nuclear spin resonance spectrometer 1 may comprise a personal computer, wherein the personal computer is configured to receive the detected delay time 10 and to compare the detected delay time 10 to a predefined limit . In this example , the predefined limit has been set by the operator beforehand . The predefined limit relates to a delay time corresponding to a resonance frequency which does not correspond to a nuclear spin resonance of the probe material 2 . Since the delay time 10 is below the predefined limit , i . e . , lower than the standard delay time 52 , the nuclear spin resonance of the probe material 2 is detected .

[0108] Afterwards , at a ninth point in time 61 , the quench unit 6 is again activated by the control unit 30 to quench the second oscillation pulse 9 . This also causes the detection unit output signal 42 to switch back to detection logic 0 state 45 .

[0109] At a tenth point in time 62 , the damp unit 21 is activated to accelerate the decay of the second oscillation pulse 9 .

[0110] At an eleventh point in time 63 , the damp unit is deactivated again .

[0111] The configuration of the nuclear spin resonance spectrometer 1 at a twel fth point in time 64 is essentially equal to the configuration at the first point in time 49 . The nuclear spin resonance spectrometer 1 is again ready to excite and detect a nuclear spin resonance of the probe material 2 .

[0112] The duration of the second oscillation pulse 71B may be an operation parameter of the nuclear spin resonance spectrometer 1 .

[0113] Overall , the method for detecting the nuclear spin resonance , in particular a nuclear magnetic resonance and / or a nuclear quadrupole resonance , of the probe material 2 with the nuclear spin resonance spectrometer 1 comprises the following steps :

[0114] - Emitting the probe excitation signal generated with the oscillator unit 3 ;

[0115] - Exciting the nuclear spin resonance of the probe material 2 by means of the probe excitation signal ;

[0116] - Quenching the first oscillation pulse 8 by activating the quench unit 6 ;

[0117] - Deactivating the quench unit 6 after the first oscillation pulse 8 is quenched; - Receiving the response signal from the probe material 2 by means of the oscillator unit 3 responsive to the excitation;

[0118] - Detecting the delay time of the RF envelope of the second oscillation pulse 9 , wherein the delay time depends on the received response signal ;

[0119] - Comparing the detected delay time to a predefined limit ; and

[0120] - Responsive to confirming that the delay time is below the predefined limit , detecting the nuclear spin resonance of the probe material .

[0121] In this exemplary embodiment , these further steps are taken :

[0122] - Dampen, in this example critically dampen, the first oscillation pulse 8 by activating the damp unit 21 ; and

[0123] - Deactivating the damp unit 21 after the first oscillation pulse 8 is quenched, in this example before the quench unit 6 is deactivated .

[0124] The delay time 10 is a period between the deactivation of the quench unit 6 and the rising edge of the envelope of the second oscillation pulse 9 . In particular, the delay time 10 is the period between the deactivation of the quench unit 6 and the time at which the rising edge of the second oscillation pulse 9 reaches the predetermined value 70 ( see , for example , the eights point in time 28 ) .

[0125] In order to determine a nuclear spin resonance spectrum, in particular a nuclear magnetic resonance spectrum and / or a nuclear quadrupole resonance spectrum, of the probe material 2 , with the nuclear spin resonance spectrometer 1 of fig . 1 , the following steps may be performed :

[0126] - Detecting a first nuclear spin resonance of the probe material with the method as discussed above with respect to fig . 2 , wherein the tunable resonance frequency comprises a first value ;

[0127] - Adj usting the tunable resonance frequency of the oscillator unit 3 from the first value to a second value , in this exemplary embodiment by adj usting a capacitance of the variable capacitor 14 ( see fig . 1 ) ; - Detecting a second nuclear spin resonance of the probe material 2 by the method as discussed above with respect to fig . 2 , wherein the tunable resonance frequency comprises the second value ; wherein the nuclear spin resonance spectrum comprises at least the detected first nuclear spin resonance and the detected second nuclear spin resonance .

[0128] Adj usting the tunable resonance frequency further comprises adj usting the damp unit 21 , in this exemplary embodiment by adj usting the resistance of the resistor 23 , according to the damping criterion, such that the damp unit 21 is configured to critically dampen the first oscillation pulse 8 of the oscillator unit 3 at the second value of the resonance frequency .

[0129] Fig . 3 shows the oscillator units 3 dynamic response to the actions of the quench switch 7 and the damp switch 22 , especially emphasi zing the rapid decay when both the quench unit 6 and the damp unit 21 are activated . Similar to fig . 2 , the figure shows the quench signal 36 , an inverted damp signal 39A (which is inverted compared to the damp signal 39 shown in fig . 2 but has the same function as the damp signal 39 ) as well as the envelope signal 35 ( details see description of fig . 2 above ) . The behavior of an RF excitation pulse ( as shown in the envelope signal 35 ) is controlled by two switches : the quench switch 7 and the damp switch 22 ( see fig . 1 ) . Initially, the RF excitation pulse exhibits an exponential decay upon the sole activation of the quench unit 6 by switching the quench switch 7 accordingly ( see first pulse 66 of the envelope signal 35 ) . When the quench unit 6 is deactivated, the RF oscillation builds up within the delay time 10 ( see fig . 2 ) . When the quench unit 6 and the damp unit 21 are activated, the RF oscillation undergoes a considerably faster decay as a second pulse 67 shows . Note that the damp unit 21 should only be activated when the quench unit is already activated .

[0130] Fig . 4 shows a plot 68 the response of the delay time Ts 10 measured with a nuclear spin resonance spectrometer 1 , when examining a sample ( i . e . , a probe material 2 ) of crystalline anhy- drous NaC103, with the isotope Chlorine-35, to changes in operating frequency (i.e., resonance frequency) . The first oscillation pulse 8 (see fig. 2, for example) was set to have a pulse length of 160 ps . Conducted at 20°C, the measurement reveals that at a resonance 69 (at a resonance frequency of approximately 29.931 MHz) , the delay time notably decreases (and is below a predefined limit, which is not indicated in this plot) . Each data point represents a mean value of 2048 repetitions, repeated five times. A Gaussian curve on a linear background best represents the data, with error bars illustrating the precision of each measurement. The signal-to-noise ratio (SNR) , demonstrates the clarity of the resonance peak. The sample weighed approximately 0.2 grams and was excited by an RE current of approximately 120 mA RMS.

[0131] The data was measured with the nuclear spin resonance spectrometer 1 of figure 1. The tunable resonance frequency was tuned over a frequency range, wherein for each resonance frequency (i.e., for each value of the tunable resonance frequency) , the delay time 10 was measured. The delay time 10 as a function of the resonance frequency significantly decreased when the resonance frequency matched a nuclear spin resonance of the probe material 2.

[0132] Fig. 5 schematically shows the envelope signal 35 of a sequence of measurements of the nuclear spin resonance spectrometer 1 of fig. 1. Fig. 5 schematically visualizes the sequencing and timing of Radio Frequency (RF) pulses 72 as a function of time 82. A single measurement consists of a first oscillation pulse 8 (which - via the emission of the probe excitation signal - leads to an excitation of a nuclear spin resonance of the probe material 2) and a second oscillation pulse 9, which is essential for measuring the delay time 10.

[0133] Such single measurements can be repeated within trains of measurements. Each single measurement incorporates a sequence of RF pulses 72 (i.e., first oscillation pulses 8 and second oscillation pulses 9) intended for excitation and detection respectively. The number of measurements (i.e., repetitions of single measurements comprising one first oscillation pulse 8 and one second oscillation pulse 9 ) may be an operation parameter of the nuclear spin resonance spectrometer 1 and may accordingly be set by an operator . The number of measurements determines the number of measurement sequences and therefore the number of oscillation pulses within a train 72 of measurements .

[0134] An initial first oscillation pulse 73 represents the initial RF pulse in a first train 74 . The start of the first train 74 is indicated by a dashed line 75A, and its end is marked by another dashed line 75B . After the first train 74 further measurements ( i . e . , further measurement trains ) may be done .

[0135] In between two measurements within the first train 74 ( or any other train of measurements ) there is a waiting time 76 in between the second oscillation pulse 9 of one measurement and the first oscillation pulse 8 of the following measurement . The waiting time 76 is chosen based on the spin-lattice relaxation time of the probe material 2 . The accurate setting of this waiting time 76 ensures that the sample has suf ficient recovery time , preventing potential saturation . The waiting time 76 is an operation parameter of the nuclear spin resonance spectrometer 1 and can be set by an operator .

[0136] Within one train of measurements , the tunable resonance frequency is not changed . The measurements within one train comprise essentially the same first value of the tunable resonance frequency . The measurement may be repeated to achieve a greater statistical certainty .

[0137] The other dashed line 75B marks the end of the first train 74 of measurements . By the end of the first train 74 the nuclear spin resonance spectrometer 1 is ready to adj ust the tunable resonance frequency, or, alternatively, repeat the first train 74 without adj usting the tunable resonance frequency . Alternatively, the overall measurement may be terminated .

[0138] In this example , the tunable resonance frequency is adj usted from the first value to a second value . The further dashed line 77 indicates the time when this adj ustment is completed . There is an overall time period 81 for adjusting the tunable resonance frequency .

[0139] The start of a second train 78 of measurements is indicated by another dashed line 79.

[0140] A stabilization time 80 in between the completion of the adjustment of the tunable resonance frequency (indicated by dashed line 77) and the start of the second train 78 (indicated by 79) may be required for stabilization of the oscillator unit 3. The stabilization time 80 is an operation parameter and may be set by the operator.

[0141] The first train 74 has total duration 83.

Claims

Claims :

1. Nuclear spin resonance spectrometer (1) for detecting a nuclear spin resonance, preferably a nuclear magnetic resonance and / or a nuclear quadrupole resonance, of a probe material (2) comprising :- an oscillator unit (3) , wherein the oscillator unit (3) is configured to oscillate with a tunable resonance frequency;- a bias source (5) configured to provide electrical power to the oscillator unit (3) ;- a quench unit (6) configured to quench an oscillation of the oscillator unit (3) , wherein the quench unit (6) comprises a quench switch (7) to activate and to deactivate the quench unit ( 6 ) ; wherein the oscillator unit (3) is configured to build-up an oscillation when the quench unit (6) is deactivated, wherein the nuclear spin resonance spectrometer (1) is configured to generate at least a first oscillation pulse (8) and a second oscillation pulse (9) by activating and deactivating the quench unit (6) , wherein the oscillator unit (3) is configured to generate a probe excitation signal during the first oscillation pulse (8) in order to excite the probe material (2) , wherein the oscillator unit (3) is configured to receive a response signal from the probe material (2) in response to the probe excitation signal, wherein the oscillator unit (3) is configured such that a delay time (10) of an RF envelope of the second oscillation pulse (9) depends on the received response signal; characterized in that the nuclear spin resonance spectrometer (1) comprises a detection unit (11) configured to detect the delay time (10) of the RF envelope of the second oscillation pulse (9) , wherein the nuclear spin resonance spectrometer (1) is configured to compare the detected delay time (10) to a predefined limit, wherein the nuclear spin resonance spectrometer (1) is configured to detect the nuclear spin resonance of the probe material (2) if the delay time is below the predefined limit.

2. Nuclear spin resonance spectrometer (1) according to claim 1, characterized by a damp unit (21) , wherein the damp unit (21) comprises a damp switch (22) for activating and deactivating thedamp unit (21) , wherein the damp unit (21) is configured to damp, preferably critically damp, the first oscillation pulse (8) when the damp unit (21) is activated and the quench unit (6) is activated.

3. Nuclear spin resonance spectrometer (1) according to claim2, characterized by a control unit (30) with:- a quench control module (31) configured to switch the quench switch (7; and- a damp control module (32) configured to switch the damp switch ( 22 ) ; wherein the control unit (30) is configured to receive the detected delay time (10) from the detection unit (11) and to compare the delay time (10) to the predefined limit.

4. Nuclear spin resonance spectrometer (1) according to claim3, characterized in that the control unit (30) comprises a frequency adjustment module configured to adjust the tunable resonance frequency of the oscillator unit.

5. Nuclear spin resonance spectrometer (1) according to anyone of the previous claims, characterized in that the damp unit (21) comprises a variable resistance.

6. Nuclear spin resonance spectrometer (1) according to anyone of the previous claims, characterized in that the oscillator unit (3) comprises a variable capacitor (14) for adjusting the tunable resonance frequency.

7. Nuclear spin resonance spectrometer (1) according to anyone of the previous claims, characterized in that the oscillator unit (3) comprises an inductor (13) , preferably an air coil (15) , wherein the inductor (13) is configured to emit the probe excitation signal and to receive the response signal.

8. Nuclear spin resonance spectrometer (1) according to anyone of the previous claims, characterized in that the oscillator unit (3) comprises a transistor (16) , preferably a junction-gate field-effect transistor (JFET) (17) , wherein the transistor (16) is coupled to the bias source (5) .

9. Method for detecting a nuclear spin resonance, in particular a nuclear magnetic resonance and / or a nuclear quadrupole resonance, of a probe material with a nuclear spin resonance spectrometer (1) according to any one of claims 1 to 8 with the steps :- Emitting a probe excitation signal generated with the oscillator unit (3) ;- Exciting the nuclear spin resonance of the probe material (2) by means of the probe excitation signal;- Quenching the first oscillation pulse (8) by activating the quench unit (6) ;- Deactivating the quench unit (6) after the first oscillation pulse (8) is quenched;- Receiving a response signal from the probe material (2) by means of the oscillator unit (3) responsive to the excitation;- Detecting a delay time (10) of an RE envelope of a second oscillation pulse (9) , wherein the delay time (10) depends on the received response signal;- Comparing the detected delay time (10) to a predefined limit; and- Responsive to confirming that the delay time (10 is below the predefined limit, detecting the nuclear spin resonance of the probe material (2) .

10. Method according to claim 9 with a nuclear spin resonance spectrometer (1) according to anyone of claims 2 to 8, characterized by the further steps:- Dampen, preferably critically dampen, the first oscillation pulse (8) by activating the damp unit (21) ; and- Deactivating the damp unit (21) after the first oscillation pulse (8) is quenched, and preferably before the quench unit (6) is deactivated.

11. Method according to claim 9 or claim 10, characterized in that the delay time (10) is a period between the deactivation of the quench unit (6) and a rising edge (59) of the RE envelope of the second oscillation pulse (9) .

12. Method according to claim 11, characterized in that the delay time (10) is the period between the deactivation of the quench unit (6) and the time at which the rising edge (59) reaches a predetermined value.

13. Method for determining a nuclear spin resonance spectrum, in particular a nuclear magnetic resonance spectrum and / or a nuclear quadrupole resonance spectrum, of a probe material (2) , with a nuclear spin resonance spectrometer (1) according to anyone of claims 1 to 8, with the steps:- Detecting a first nuclear spin resonance of the probe material (2) with the method according to any one of claims 9 to13, wherein the tunable resonance frequency comprises a first value ;- Adjusting the tunable resonance frequency of the oscillator unit (3) from the first value to a second value;- Detecting a second nuclear spin resonance of the probe material by the method according to anyone of claims 9 to 13, wherein the tunable resonance frequency comprises the second value ; wherein the nuclear spin resonance spectrum comprises at least the detected first nuclear spin resonance and the detected second nuclear spin resonance.

14. Method according to claim 13, wherein adjusting the tunable resonance frequency further comprises adjusting the damp unit, preferably by adjusting a variable resistance, according to a damping criterion, such that the damp unit is configured to critically dampen a first oscillation pulse (8) of the oscillator unit (6) at the second value of the tunable resonance frequency .

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