WO2004109314A1 - Nuclear quadrupole resonance inspection system - Google Patents

Nuclear quadrupole resonance inspection system Download PDF

Info

Publication number
WO2004109314A1
WO2004109314A1 PCT/GB2004/002182 GB2004002182W WO2004109314A1 WO 2004109314 A1 WO2004109314 A1 WO 2004109314A1 GB 2004002182 W GB2004002182 W GB 2004002182W WO 2004109314 A1 WO2004109314 A1 WO 2004109314A1
Authority
WO
WIPO (PCT)
Prior art keywords
inspection system
nqr
frequencies
mhz
signals
Prior art date
Application number
PCT/GB2004/002182
Other languages
French (fr)
Inventor
Garth Nigel SHILSTON
John Michael Bradley
Richard Ian Jenkinson
Original Assignee
The Secretary Of State For Defence
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The Secretary Of State For Defence filed Critical The Secretary Of State For Defence
Priority to AU2004245735A priority Critical patent/AU2004245735A1/en
Priority to JP2006508368A priority patent/JP2006527362A/en
Priority to GB0524897A priority patent/GB2418494B/en
Priority to US10/559,371 priority patent/US20060232274A1/en
Publication of WO2004109314A1 publication Critical patent/WO2004109314A1/en

Links

Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00Arrangements or instruments for measuring magnetic variables
    • G01R33/20Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/441Nuclear Quadrupole Resonance [NQR] Spectroscopy and Imaging

Definitions

  • This invention relates to the field of nuclear quadrupole resonance inspection systems and particularly to a multi-resonant system for simultaneously detecting the presence of a plurality of target materials.
  • Nuclear quadrupole resonance occurs when a resonant radio frequency (RF) field is applied to excite transitions between such energy levels.
  • RF radio frequency
  • NQR inspection is a technique for probing transitions between the split energy levels, which are excited by resonant RF fields, to produce RF spectra, thereby enabling detection of a range of materials.
  • nuclei having a spin quantum number I greater than ⁇ ⁇ , such as 14 N and 35 C1 possess an electric quadrupole moment and, hence, display a NQR response.
  • NQR can be used for the potentially unambiguous identification of a compound containing quadrupolar nuclei.
  • Application of signal processing and thresholding of the return signal means that the detection process can be fully automated with little need for operator training. This gives NQR detection the potential of high probability of detection with low false alarm rates for a known target material.
  • NQR inspection for example, at airports to detect the presence of substances such as narcotics, pharmaceuticals or explosives in baggage, although in principle, NQR could be used to detect the presence of any material incorporating quadrupolar nuclei.
  • radio frequency (RF) pulses at the specific resonance frequency for the material of interest, are applied to the sample to be inspected. If the material of interest is present transitions between the energy levels are excited, and during relaxation the corresponding return signal can be detected. However, other materials, which may also be of interest, will be missed because the NQR device is not tuned to detect them. In other words, the high specificity of sample detection, which provides the desired low false alarm rates, means that the use of NQR as a generic detector is not currently possible. In order to detect different materials an optimised transmitter/receiver is required for each frequency. In practice this requires fast electronic and mechanical switching to re-tune the device or, more likely, a separate device tuned for each frequency.
  • this invention provides a nuclear quadrupole resonance (NQR) inspection system for simultaneously detecting the presence of a plurality of target materials
  • NQR nuclear quadrupole resonance
  • the transmission means and receiver circuit comprise a multi-resonant circuit tuned to simultaneously transmit and receive a plurality of signals at a plurality of predetermined frequencies which frequencies substantially match characteristic resonant frequencies of a plurality of target materials and the receiver circuit further comprises passive circuit protection means to permit simultaneous reception of a plurality of return signals.
  • the system advantageously comprises a spectrometer capable of operating at a plurality of frequencies within a single pulse sequence.
  • the spectrometer may have a single channel or multiple channels.
  • the receiver circuit preferably includes signal processing means adapted to modify widely separated return signals so that they can be monitored simultaneously by the spectrometer.
  • the signal processing means may comprise a signal generator which, in use, produces a phase coherent mixing signal of predetermined frequency to bring the plurality of return signals within the maximum bandwidth of the spectrometer.
  • the passive circuit protection means preferably comprises a lumped element quarter- wave unit tuned to provide protection of the receiver circuit during signal transmission whilst allowing the plurality of return signals to be received. This acts as a low pass filter for low voltage signals and blocks high voltage signals at all frequencies. It therefore provides passive protection i.e. without the need for electronic switching, thereby maximising sensitivity.
  • the plurality of transmitted signals is ideally applied to excite target materials in such a way that the plurality of return signals can be received simultaneously. If a multiple channel spectrometer is used the signals may be transmitted as separate simultaneous signals. However, if a single channel spectrometer is used it will be necessary to interleave the transmitted signals so that pulses of one frequency are applied during the coil ringdown times arising from pulses applied at another frequency.
  • NQR inspection would be for generic explosive detection. There would be significant benefit in being able to simultaneously detect the presence of cyclotrimethylene trinitrarnine (RDX) and pentaerythritol tetranitrate (PETN) which are found in several plastic compositions, for example PE-4 and Detasheet respectively. These two materials are also found as a mixture, of variable ratio, in the plastic explosive Semtex. In common with many explosives, RDX and PETN contain nitrogen and since they are solid state compounds this leads to the possibility of performing 14 N NQR on these materials. The three ring- I4 N nuclei in RDX are inequivalent in the solid state giving nine possible transitions.
  • RDX cyclotrimethylene trinitrarnine
  • PETN pentaerythritol tetranitrate
  • the room temperature frequencies of these transitions are 5.239 MHz; 5.190 MHz; 5.044 MHz; 3.458 MHz; 3.410 MHz; 3.359 MHz; 1.781 MHz (2 transitions); 1.685 MHz.
  • the molecular symmetry of PETN in the solid state gives rise to three possible transitions.
  • the room temperature frequencies arising from the nitrate- 14 N nuclei are 0.890 MHz; 0.495 MHz; 0.395 MHz.
  • the type of pulse sequence that is used for excitation is dependent on the relaxation parameters (and in practical applications, the efficacy in rejecting spurious responses).
  • T spin lattice relaxation time
  • PSL pulsed spin locking
  • SSFP steady state free precession
  • the NQR inspection system may transmit a steady state free precession pulse sequence at 3.410 MHz interleaved with a pulsed spin locking pulse sequence at 0.890 MHz for the simultaneous detection of RDX and PETN. These frequencies assume room temperature conditions but should be adjusted for higher or lower ambient temperatures.
  • Figure 1 is a schematic diagram of the inspection system according to the invention.
  • Figure 2 provides schematic diagrams of two alternative doubly resonant circuits suitable for use according to the invention
  • FIG. 3 illustrates an interleaved pulse sequence for use with the invention.
  • Figure 4 shows the NQR spectrum for Semtex when excited with the interleaved pulse sequence of Figure 3 c.
  • an embodiment of a multi-resonant NQR inspection system includes a single channel spectrometer (Apollo LF 0.5 - 10 MHz from Tecmag Inc., Houston, USA) 2 which is controlled via a PC (NTNMR control software shipped with Apollo spectrometer).
  • the NTNMR software includes a graphical editor that provides the environment for fast development of pulse sequences.
  • the pre-amplifier 4 output is mixed with a signal generator (PTS 040) 6 output of the appropriate frequency.
  • the signal generator clock is provided externally by the 10 MHz clock output of the Apollo spectrometer 2.
  • the frequency mixer 8 used is a Mini-Circuits ZAD-6 mixer.
  • Receiver protection is provided by inserting a quarter-wave lumped, equivalent circuit 10 and crossed diodes to ground 12 immediately before the pre-amplifier 4.
  • a quarter- wave lumped, equivalent circuit has the property of being a low pass filter for low voltage signals (in addition to blocking high voltage signals at all frequencies). Therefore a quarter-wave element tuned to 3.41 MHz can be used to allow reception of both RDX and PETN signals.
  • Pre-amplification of the NQR signal before the spectrometer receiver input is via a commercial pre-amplifier (Miteq AU - 1464 - 8276, 0.4 - 200 MHz) 4.
  • Transmitter pulses to the probe 16 are amplified using a commercial broadband power amplifier (Kalmus LA100HP-CE, 100 W, 50 dB) 14 with a gating input for pulsed operation.
  • Nariable attenuator 19 is used to vary the voltage of the transmitted signal to the power amplifier 14 and to ensure that the probe 16 is not overloaded.
  • Crossed diodes 18 operate in transmit mode to remove high voltage noise and in receive mode to isolate the power amplifier 14 from the return signal.
  • the transmission means comprises spectrometer 2, variable attenuator 19, power amplifier 14, crossed diodes 18 and doubly resonant probe 16.
  • the receiver circuit comprises doubly resonant probe 16, crossed diodes 18, quarter- wave lumped equivalent circuit 10, crossed diodes 12, pre-amplifier 4, spectrometer 2 and the signal processing means which comprises signal generator 6 and frequency mixer 8.
  • FIG. 2a shows a schematic circuit diagram of one embodiment of a doubly resonant probe 16.
  • the probe comprises a sample coil 28, a secondary inductor 26 and variable capacitors 21-24 to generate the desired resonant frequencies.
  • the secondary inductor 26 is hand wound and incorporates an air core rather than a ferrite core to reduce signal loss.
  • Tuning and matching the sample coil 28 to the required frequency and impedance (50 ⁇ ) can be performed using an impedance gain phase analyser (HP 4194A) by adjustment of the variable capacitors 21-24. With care it is possible to simultaneously match the impedance at the probe input/output to 49 ⁇ at both 0.89 MHz and 3.41 MHz.
  • the Q at 0.89 MHz was found to be 75 and the Q at 3.41 MHz was found to be 65, where the doubly tuned probe was deliberately made more sensitive at 0.89 MHz to compensate to some degree for the intrinsically lower sensitivity at this frequency.
  • the sensitivity achieved simultaneously at each frequency compares favourably with that typically achieved for corresponding singly resonant probes at these frequencies, i.e. Q in the range of 60 - 90 for solenoids of similar dimensions and where we have used similar materials and components.
  • the dimensions of the solenoid coil 28 that contains the sample are: Diameter 53 mm Length 70 mm
  • Figure 2b shows a schematic circuit diagram of an alternative embodiment of a doubly resonant probe 16.
  • the probe comprises a tapped coil design, which can produce a doubly resonant circuit with only 3 capacitors 31-33 and a single inductor 38.
  • the sample coil 38 is wound as two separate inductors, which are then connected in series to form one inductor with a tap point. This enables measurement of the inductance of each coil to be made. It was found that both resonant frequencies could be matched to 50 ⁇ when the values of the two sample coil inductors were equal. In this case, the sample coil consisted of two coils, each with an inductance of approximately 25 ⁇ H.
  • PETN which has a long T l5 a pulsed spin locking (PSL) pulse sequence — a pulse train preceded with a preparation pulse where the phase of the train pulses differs by 90° with respect to the phase of preparation pulse — was selected. If the pulse spacing within the pulse train is 2 ⁇ then the pulse spacing between the preparation pulse and the first pulse in the pulse train is equal to ⁇ .
  • the pulse length of the preparation pulse is chosen to be an effective-90 o and the pulse length of the train pulses is typically either effective-90° or effective- 180°.
  • the PSL sequence is shown in Figure 3a.
  • SSFP steady state free precession
  • Figure 4 shows the room temperature NQR spectrum for Semtex, when excited with the interleaved sequence illustrated in Figure 3 c.
  • the NQR signals due to I4 N are clearly seen in each case, where the intermediate mixing frequency (1.22 MHz) has been deliberately chosen so that the RDX line and the PETN line appear offset from the spectrometer demodulation frequency (2.15 MHz) by +40 kHz and -40 kHz respectively.
  • the actual frequencies of the RDX and PETN lines are 3.41 MHz and 0.89 MHz respectively, which correspond to the room temperature resonant frequencies as described previously.
  • the choice of offset frequency was somewhat arbitrary but was made sufficiently large for the two lines to be well separated.
  • the embodiment described concerns the simultaneous detection of RDX and PETN, the person skilled in the art will appreciate that the invention is equally applicable to other pairs of substances, such as heroin and cocaine. Furthermore, the invention can be applied to more than two resonances by carefully tuning a multi- resonant circuit and developing a suitable pulse sequence.

Abstract

A multi-resonant nuclear quadrupole resonance (NQR) inspection system is disclosed. The system comprises a multi-resonant circuit 16 tuned to simultaneously transmit and receive a plurality of signais. The receiver circuit comprises passive circuit protection in the form of a lumped element quarter-wave unit 10 and a signal generator 6 and frequency mixer 8 are used to modify the return signais in order to facilitate signal monitoring. The system has been shown to simultaneously detect RDX and PETN.

Description

NUCLEAR OUADRUPOLE RESONANCE INSPECTION SYSTEM
This invention relates to the field of nuclear quadrupole resonance inspection systems and particularly to a multi-resonant system for simultaneously detecting the presence of a plurality of target materials.
Interaction of the electric quadrupole moment of a nucleus with the electric field gradient around the nucleus causes the magnetic nuclear energy levels to split. Nuclear quadrupole resonance (NQR) occurs when a resonant radio frequency (RF) field is applied to excite transitions between such energy levels. NQR inspection is a technique for probing transitions between the split energy levels, which are excited by resonant RF fields, to produce RF spectra, thereby enabling detection of a range of materials. However, only those nuclei having a spin quantum number I greater than λλ, such as 14N and 35C1, possess an electric quadrupole moment and, hence, display a NQR response. Characteristic transitions between energy levels occur at frequencies that are unique to a particular material because the quadrupole interaction is sensitive to the position of the quadrupolar nucleus within a molecule and also the crystalline structure of the substance. Therefore NQR can be used for the potentially unambiguous identification of a compound containing quadrupolar nuclei. Application of signal processing and thresholding of the return signal means that the detection process can be fully automated with little need for operator training. This gives NQR detection the potential of high probability of detection with low false alarm rates for a known target material.
It is known to use NQR inspection, for example, at airports to detect the presence of substances such as narcotics, pharmaceuticals or explosives in baggage, although in principle, NQR could be used to detect the presence of any material incorporating quadrupolar nuclei.
Conventionally radio frequency (RF) pulses, at the specific resonance frequency for the material of interest, are applied to the sample to be inspected. If the material of interest is present transitions between the energy levels are excited, and during relaxation the corresponding return signal can be detected. However, other materials, which may also be of interest, will be missed because the NQR device is not tuned to detect them. In other words, the high specificity of sample detection, which provides the desired low false alarm rates, means that the use of NQR as a generic detector is not currently possible. In order to detect different materials an optimised transmitter/receiver is required for each frequency. In practice this requires fast electronic and mechanical switching to re-tune the device or, more likely, a separate device tuned for each frequency.
Simultaneous detection of a plurality of materials using a single NQR device, without the need for electronic or mechanical switching, would make the deployment of NQR inspection systems more attractive for a variety of applications.
It is an object of this invention to provide a multi-resonant NQR inspection system for simultaneously detecting the presence of a plurality of target materials.
Accordingly this invention provides a nuclear quadrupole resonance (NQR) inspection system for simultaneously detecting the presence of a plurality of target materials comprising transmission means for applying a pulsed radio frequency signal to a sample and a receiver circuit for receiving the return signal wherein the transmission means and receiver circuit comprise a multi-resonant circuit tuned to simultaneously transmit and receive a plurality of signals at a plurality of predetermined frequencies which frequencies substantially match characteristic resonant frequencies of a plurality of target materials and the receiver circuit further comprises passive circuit protection means to permit simultaneous reception of a plurality of return signals.
It is the combination of the multi-resonant probe with the passive circuit protection which enables the invention to function. Active circuit protection i.e. switching produces "ringing" which masks some of the signal thereby reducing the sensitivity of the system. In order to maintain sensitivity comparable to a singly tuned device it is necessary to minimise losses in the circuit by selecting high quality components and optimising the circuit design. The system advantageously comprises a spectrometer capable of operating at a plurality of frequencies within a single pulse sequence. The spectrometer may have a single channel or multiple channels.
The receiver circuit preferably includes signal processing means adapted to modify widely separated return signals so that they can be monitored simultaneously by the spectrometer. The signal processing means may comprise a signal generator which, in use, produces a phase coherent mixing signal of predetermined frequency to bring the plurality of return signals within the maximum bandwidth of the spectrometer.
The passive circuit protection means preferably comprises a lumped element quarter- wave unit tuned to provide protection of the receiver circuit during signal transmission whilst allowing the plurality of return signals to be received. This acts as a low pass filter for low voltage signals and blocks high voltage signals at all frequencies. It therefore provides passive protection i.e. without the need for electronic switching, thereby maximising sensitivity.
There are several designs that will produce a multi-resonant circuit. These include interleaved sample coils, series tuned coils and tapped coils, where a connection is made to the sample coil at an intermediate point along it's length, effectively separating the single coil into two inductors.
The plurality of transmitted signals is ideally applied to excite target materials in such a way that the plurality of return signals can be received simultaneously. If a multiple channel spectrometer is used the signals may be transmitted as separate simultaneous signals. However, if a single channel spectrometer is used it will be necessary to interleave the transmitted signals so that pulses of one frequency are applied during the coil ringdown times arising from pulses applied at another frequency.
One desirable application for NQR inspection would be for generic explosive detection. There would be significant benefit in being able to simultaneously detect the presence of cyclotrimethylene trinitrarnine (RDX) and pentaerythritol tetranitrate (PETN) which are found in several plastic compositions, for example PE-4 and Detasheet respectively. These two materials are also found as a mixture, of variable ratio, in the plastic explosive Semtex. In common with many explosives, RDX and PETN contain nitrogen and since they are solid state compounds this leads to the possibility of performing 14N NQR on these materials. The three ring-I4N nuclei in RDX are inequivalent in the solid state giving nine possible transitions. The room temperature frequencies of these transitions are 5.239 MHz; 5.190 MHz; 5.044 MHz; 3.458 MHz; 3.410 MHz; 3.359 MHz; 1.781 MHz (2 transitions); 1.685 MHz. There are also nine other transitions possible, arising from the three nitro-14N nuclei, but these have much lower frequencies and are not considered here. The molecular symmetry of PETN in the solid state gives rise to three possible transitions. The room temperature frequencies arising from the nitrate-14N nuclei are 0.890 MHz; 0.495 MHz; 0.395 MHz.
An important property of these transitions is their temperature dependence, which has implications for practical applications of this technique. Although the sensitivity of the technique increases with frequency it may be more appropriate to monitor a transition with a lower frequency. For example in the case of RDX, the 3.41 MHz transition has a temperature dependence (=-* -100 Hz KT1), which is one fifth that of the 5.19 MHz transition. It will be appreciated that where a room temperature resonant frequency is specified the transmitted frequency would in fact require adjustment to allow for the temperature dependency.
The type of pulse sequence that is used for excitation is dependent on the relaxation parameters (and in practical applications, the efficacy in rejecting spurious responses). For materials with a long spin lattice relaxation time (T , such as PETN, a pulsed spin locking (PSL) pulse sequence — a pulse train preceded with a preparation pulse where the phase of the train pulses differs by 90° with respect to the phase of preparation pulse — might be appropriate. For materials with a short Ti, such as RDX, a steady state free precession (SSFP) pulse sequence — a train of equally spaced pulses of equal length — might be appropriate. However, it will be understood that different types of pulse sequence could equally be selected. The NQR inspection system may transmit a steady state free precession pulse sequence at 3.410 MHz interleaved with a pulsed spin locking pulse sequence at 0.890 MHz for the simultaneous detection of RDX and PETN. These frequencies assume room temperature conditions but should be adjusted for higher or lower ambient temperatures.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Figure 1 is a schematic diagram of the inspection system according to the invention;
Figure 2 provides schematic diagrams of two alternative doubly resonant circuits suitable for use according to the invention;
Figure 3 illustrates an interleaved pulse sequence for use with the invention; and
Figure 4 shows the NQR spectrum for Semtex when excited with the interleaved pulse sequence of Figure 3 c.
With reference to Figure 1, an embodiment of a multi-resonant NQR inspection system includes a single channel spectrometer (Apollo LF 0.5 - 10 MHz from Tecmag Inc., Houston, USA) 2 which is controlled via a PC (NTNMR control software shipped with Apollo spectrometer). The NTNMR software includes a graphical editor that provides the environment for fast development of pulse sequences.
To bring the signals within the same audio band of the spectrometer 2 the pre-amplifier 4 output is mixed with a signal generator (PTS 040) 6 output of the appropriate frequency. The signal generator clock is provided externally by the 10 MHz clock output of the Apollo spectrometer 2. The frequency mixer 8 used is a Mini-Circuits ZAD-6 mixer.
Receiver protection is provided by inserting a quarter-wave lumped, equivalent circuit 10 and crossed diodes to ground 12 immediately before the pre-amplifier 4. A quarter- wave lumped, equivalent circuit has the property of being a low pass filter for low voltage signals (in addition to blocking high voltage signals at all frequencies). Therefore a quarter-wave element tuned to 3.41 MHz can be used to allow reception of both RDX and PETN signals. Pre-amplification of the NQR signal before the spectrometer receiver input is via a commercial pre-amplifier (Miteq AU - 1464 - 8276, 0.4 - 200 MHz) 4. Transmitter pulses to the probe 16 are amplified using a commercial broadband power amplifier (Kalmus LA100HP-CE, 100 W, 50 dB) 14 with a gating input for pulsed operation.
Nariable attenuator 19 is used to vary the voltage of the transmitted signal to the power amplifier 14 and to ensure that the probe 16 is not overloaded. Crossed diodes 18 operate in transmit mode to remove high voltage noise and in receive mode to isolate the power amplifier 14 from the return signal.
In this embodiment the transmission means comprises spectrometer 2, variable attenuator 19, power amplifier 14, crossed diodes 18 and doubly resonant probe 16. The receiver circuit comprises doubly resonant probe 16, crossed diodes 18, quarter- wave lumped equivalent circuit 10, crossed diodes 12, pre-amplifier 4, spectrometer 2 and the signal processing means which comprises signal generator 6 and frequency mixer 8.
Figure 2a shows a schematic circuit diagram of one embodiment of a doubly resonant probe 16. The probe comprises a sample coil 28, a secondary inductor 26 and variable capacitors 21-24 to generate the desired resonant frequencies. The secondary inductor 26 is hand wound and incorporates an air core rather than a ferrite core to reduce signal loss. Tuning and matching the sample coil 28 to the required frequency and impedance (50 Ω) can be performed using an impedance gain phase analyser (HP 4194A) by adjustment of the variable capacitors 21-24. With care it is possible to simultaneously match the impedance at the probe input/output to 49 Ω at both 0.89 MHz and 3.41 MHz. The quality factor (Q) at each tuned frequency was determined from the power response curve measured on a network analyser (HP 8752C) from Q = v0/ΔV(3 dB), where Vo is the tuned frequency and ΔV(3 dB) is the bandwidth measured at the half-power points on the response curve. The Q at 0.89 MHz was found to be 75 and the Q at 3.41 MHz was found to be 65, where the doubly tuned probe was deliberately made more sensitive at 0.89 MHz to compensate to some degree for the intrinsically lower sensitivity at this frequency. Thus the sensitivity achieved simultaneously at each frequency compares favourably with that typically achieved for corresponding singly resonant probes at these frequencies, i.e. Q in the range of 60 - 90 for solenoids of similar dimensions and where we have used similar materials and components. The dimensions of the solenoid coil 28 that contains the sample are: Diameter 53 mm Length 70 mm
Wire diameter 1.25 mm (18 standard gauge)
Number of turns 49
Spacing of turns No gap between adjacent turns
Figure 2b shows a schematic circuit diagram of an alternative embodiment of a doubly resonant probe 16. The probe comprises a tapped coil design, which can produce a doubly resonant circuit with only 3 capacitors 31-33 and a single inductor 38. The sample coil 38 is wound as two separate inductors, which are then connected in series to form one inductor with a tap point. This enables measurement of the inductance of each coil to be made. It was found that both resonant frequencies could be matched to 50 Ω when the values of the two sample coil inductors were equal. In this case, the sample coil consisted of two coils, each with an inductance of approximately 25 μH.
In practice it was found that both probe designs were capable of detecting RDX and PETN simultaneously.
The type of pulse sequence that is used for excitation is dependent on the relaxation parameters (and in practical applications, the efficacy in rejecting spurious responses). For PETN, which has a long Tl5 a pulsed spin locking (PSL) pulse sequence — a pulse train preceded with a preparation pulse where the phase of the train pulses differs by 90° with respect to the phase of preparation pulse — was selected. If the pulse spacing within the pulse train is 2τ then the pulse spacing between the preparation pulse and the first pulse in the pulse train is equal to τ. The pulse length of the preparation pulse is chosen to be an effective-90o and the pulse length of the train pulses is typically either effective-90° or effective- 180°. The PSL sequence is shown in Figure 3a. For RDX, which has a short Ti, a steady state free precession (SSFP) pulse sequence — a train of equally spaced pulses of equal length — was selected. The SSFP sequence is shown in Figure 3b. The timings and phase cycling for the interleaved PSL/SSFP pulse sequence used is as follows:
PSL pulse lengths: preparation = 160 μs, train = 200 μs SSFP pulse lengths: preparation = N/A, train = 400 μs 2τ = 2 ms τ = 1 ms
PSL phase cycling: Tx [+X, (+Y)n | -X, (+Y)„]
Figure imgf000010_0001
SSFP phase cycling: Tx [(+X)n | (-X)n | (+X) „ | (-X)„ ]
Rx [(+X)n | (-X)n I (-X)„ I (+X)a]
For the PSL sequence we also implemented a 'reverse-phase' pulse after each of the excitation pulses in the train. In this way we were able to reduce the dead time at 0.89 MHz (dead time ∞ 1/frequency), thereby decreasing the pulse spacing, with a subsequent increase in the rate of signal acquisition for each substance. The pulse amplitude at each frequency was adjusted to give the following excitation fields: 215 μT at 3.41 MHz and 650 μT at 0.89 MHz. The pulse lengths for both materials were determined experimentally using the above excitation fields.
The interleaved PSL sequence at 0.89 MHz and SSFP sequence at 3.41 MHz which were used to detect PETN and RDX is shown in Figure 3 c.
Figure 4 shows the room temperature NQR spectrum for Semtex, when excited with the interleaved sequence illustrated in Figure 3 c. The NQR signals due to I4N are clearly seen in each case, where the intermediate mixing frequency (1.22 MHz) has been deliberately chosen so that the RDX line and the PETN line appear offset from the spectrometer demodulation frequency (2.15 MHz) by +40 kHz and -40 kHz respectively. The actual frequencies of the RDX and PETN lines are 3.41 MHz and 0.89 MHz respectively, which correspond to the room temperature resonant frequencies as described previously. The choice of offset frequency was somewhat arbitrary but was made sufficiently large for the two lines to be well separated.
Although, the embodiment described concerns the simultaneous detection of RDX and PETN, the person skilled in the art will appreciate that the invention is equally applicable to other pairs of substances, such as heroin and cocaine. Furthermore, the invention can be applied to more than two resonances by carefully tuning a multi- resonant circuit and developing a suitable pulse sequence.

Claims

1. A nuclear quadrupole resonance (NQR) inspection system for simultaneously detecting the presence of a plurality of target materials comprising transmission means for applying a pulsed radio frequency signal to a sample and a receiver circuit for receiving the return signal
wherein the transmission means and receiver circuit comprise a multi-resonant circuit tuned to simultaneously transmit and receive a plurality of signals at a plurality of predetermined frequencies which frequencies substantially match characteristic resonant frequencies of a plurality of target materials and the receiver circuit further comprises passive circuit protection means to permit simultaneous reception of a plurality of return signals.
2. A NQR inspection system according to claim 1 comprising a spectrometer capable of operating at a plurality of frequencies within a single pulse sequence.
3. A NQR inspection system according to claim 2 wherein the receiver circuit further comprises signal processing means adapted to modify a plurality of return signals so that they can be monitored simultaneously by the spectrometer.
4. A NQR inspection system according to claim 3 wherein the signal processing means comprises a signal generator which, in use, produces a phase coherent mixing signal of predetermined frequency to bring the plurality of return signals within the maximum bandwidth of the spectrometer.
5. A NQR inspection system according to any preceding claim wherein the passive circuit protection means comprises a lumped element quarter-wave unit tuned to provide protection of the receiver circuit during signal transmission whilst allowing the plurality of return signals to be received.
6. A NQR inspection system according to any preceding claim wherein the multi- resonant circuit comprises a tapped coil.
7. A NQR inspection system according to any preceding claim wherein the plurality of transmitted signals is applied to excite target materials in such a way that the plurality of return signals can be received simultaneously.
8. A NQR inspection system according to claim 7 wherein the plurality of transmitted signals is interleaved.
9. A NQR inspection system according to any preceding claim wherein the transmission means applies a steady state free precession pulse sequence at one of the characteristic resonance frequencies of RDX.
10. A NQR inspection system according to any preceding claim wherein the transmission means applies a pulsed spin locking pulse sequence at one of the characteristic resonance frequencies of PETN.
11. A NQR inspection system according to any preceding claim wherein the plurality of transmitted signals comprises a steady state free precession pulse sequence at 3.410 MHz interleaved with a pulsed spin locking pulse sequence at 0.890 MHz for the simultaneous detection of RDX and PETN.
12. A NQR inspection system substantially as described herein with reference to the accompanying drawings.
PCT/GB2004/002182 2003-06-06 2004-05-20 Nuclear quadrupole resonance inspection system WO2004109314A1 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
AU2004245735A AU2004245735A1 (en) 2003-06-06 2004-05-20 Nuclear quadrupole resonance inspection system
JP2006508368A JP2006527362A (en) 2003-06-06 2004-05-20 Nuclear quadrupole resonance inspection system
GB0524897A GB2418494B (en) 2003-06-06 2004-05-20 Nuclear quadrupole resonance inspection system
US10/559,371 US20060232274A1 (en) 2003-06-06 2004-05-20 Nuclear quadrupole resonance inspection system

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0312986.3 2003-06-06
GBGB0312986.3A GB0312986D0 (en) 2003-06-06 2003-06-06 Nuclear quadrupole resonance inspection system

Publications (1)

Publication Number Publication Date
WO2004109314A1 true WO2004109314A1 (en) 2004-12-16

Family

ID=9959418

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2004/002182 WO2004109314A1 (en) 2003-06-06 2004-05-20 Nuclear quadrupole resonance inspection system

Country Status (6)

Country Link
US (1) US20060232274A1 (en)
JP (1) JP2006527362A (en)
CN (1) CN1820209A (en)
AU (1) AU2004245735A1 (en)
GB (2) GB0312986D0 (en)
WO (1) WO2004109314A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2018124905A1 (en) * 2016-05-18 2018-07-05 Mira Technologies Group S.R.L. Mobile detector and method for detecting potentially explosive substances, explosives and drugs by nuclear quadrupole resonance (nqr)

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7868758B2 (en) * 2006-03-10 2011-01-11 Morpho Detection, Inc. Passenger screening system and method
US8570038B2 (en) * 2010-01-29 2013-10-29 R.A. Miller Industries, Inc. Long range detection of explosives or contraband using nuclear quadrupole resonance
US9476953B1 (en) 2012-08-24 2016-10-25 Bae Systems Information And Electronic Systems Integration Inc. Nuclear quadrupole resonance system
US9869739B2 (en) 2012-10-15 2018-01-16 Case Wetern Reserve University Heteronuclear nuclear magnetic resonance fingerprinting
CN103336311B (en) * 2013-06-28 2017-02-08 安徽瑞迪太检测技术有限公司 Explosive and drug detecting system based on NQR
CN112946544B (en) * 2021-02-01 2022-09-16 中国科学院精密测量科学与技术创新研究院 Double-resonance detection device for nuclear magnetic resonance radio frequency coil

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5206592A (en) * 1991-05-23 1993-04-27 Buess Michael L Detection of explosives by nuclear quadrupole resonance
WO1999045409A1 (en) * 1998-03-06 1999-09-10 Btg International Ltd. Nqr testing method and apparatus
US20020011842A1 (en) * 1993-06-02 2002-01-31 Daniel Fiat Method and apparatus of enhancing an MRI signal
US6486838B1 (en) * 1998-03-06 2002-11-26 Btg International Limited Apparatus for and method of Nuclear Quadrupole Resonance testing a sample
EP1416291A2 (en) * 2002-10-30 2004-05-06 Analogic Corporation Wideband NQR system using multiple de-coupled RF coils

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5424645A (en) * 1993-11-18 1995-06-13 Doty Scientific, Inc. Doubly broadband triple resonance or quad resonance NMR probe circuit
US5594338A (en) * 1995-03-08 1997-01-14 Quantum Magnetics, Inc. Automatic tuning apparatus and method for substance detection using nuclear quadrupole resonance and nuclear magnetic resonance
US6291994B1 (en) * 2000-01-14 2001-09-18 Quantum Magnetics, Inc. Active Q-damping sub-system using nuclear quadrupole resonance and nuclear magnetic resonance for improved contraband detection
AUPR868201A0 (en) * 2001-11-05 2001-11-29 Thorlock International Limited Q-factor switching method and apparatus for detecting nuclear quadrupole and nuclear magnetic resonance signals

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5206592A (en) * 1991-05-23 1993-04-27 Buess Michael L Detection of explosives by nuclear quadrupole resonance
US20020011842A1 (en) * 1993-06-02 2002-01-31 Daniel Fiat Method and apparatus of enhancing an MRI signal
WO1999045409A1 (en) * 1998-03-06 1999-09-10 Btg International Ltd. Nqr testing method and apparatus
US6486838B1 (en) * 1998-03-06 2002-11-26 Btg International Limited Apparatus for and method of Nuclear Quadrupole Resonance testing a sample
EP1416291A2 (en) * 2002-10-30 2004-05-06 Analogic Corporation Wideband NQR system using multiple de-coupled RF coils

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
GONNELLA N C ET AL: "DESIGN AND CONSTRUCTION OF A SIMPLE DOUBLE-TUNED SINGLE-INPUT SURFACE-COIL PROBE", JOURNAL OF MAGNETIC RESONANCE, ACADEMIC PRESS, ORLANDO, FL, US, vol. 85, no. 1, 15 October 1989 (1989-10-15), pages 24 - 34, XP000087257, ISSN: 1090-7807 *
TROPP J ET AL: "A DUAL-TUNED PROBE AND MULTIBAND RECEIVER FRONT END FOR X-NUCLEOUS SPECTROSCOPY WITH PROTON SCOUT IMAGING IN VIVO*", MAGNETIC RESONANCE IN MEDICINE, ACADEMIC PRESS, DULUTH, MN, US, vol. 11, no. 3, 1 September 1989 (1989-09-01), pages 405 - 412, XP000072987, ISSN: 0740-3194 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2018124905A1 (en) * 2016-05-18 2018-07-05 Mira Technologies Group S.R.L. Mobile detector and method for detecting potentially explosive substances, explosives and drugs by nuclear quadrupole resonance (nqr)
US10921271B2 (en) 2016-05-18 2021-02-16 Mira Technologies Group S.R.L. Mobile detector and method for detecting potentially explosive substances, explosives and drugs by nuclear quadrupole resonance (NQR)

Also Published As

Publication number Publication date
US20060232274A1 (en) 2006-10-19
GB2418494B (en) 2007-01-17
JP2006527362A (en) 2006-11-30
GB0312986D0 (en) 2003-07-09
GB0524897D0 (en) 2006-01-11
CN1820209A (en) 2006-08-16
AU2004245735A1 (en) 2004-12-16
GB2418494A (en) 2006-03-29

Similar Documents

Publication Publication Date Title
EP1060403B1 (en) Apparatus for and method of nuclear quadrupole resonance testing a sample in the presence of interference
US6291994B1 (en) Active Q-damping sub-system using nuclear quadrupole resonance and nuclear magnetic resonance for improved contraband detection
US7279897B2 (en) Scanning a band of frequencies using an array of high temperature superconductor sensors tuned to different frequencies
US7511500B2 (en) Detecting quadrupole resonance signals using high temperature superconducting resonators
US7279896B2 (en) Methods and apparatus for scanning a band of frequencies using an array of high temperature superconductor sensors
US6822444B2 (en) Wideband NQR system using multiple de-coupled RF coils
US7265549B2 (en) Scanning a band of frequencies using an array of high temperature superconductor sensors tuned to the same frequency
Hirschfeld et al. Short range remote NQR measurements
EP1801607A2 (en) NQR testing method and apparatus
US20070176600A1 (en) Use of two or more sensors in a nuclear quadrupole resonance detection system to improve signal-to-noise ratio
EP0928973A2 (en) Method of and apparatus for NQR testing
US6577128B1 (en) NQR method and apparatus for testing a sample by applying multiple excitation blocks with different delay times
EP0838036B8 (en) Apparatus for and method of nuclear quadrupole testing of a sample
JP2007502989A (en) Nuclear quadrupole resonance detection system using high temperature superconductor self-resonant coil
US6573720B1 (en) Resonant structure for spatial and spectral-spatial imaging of free radical spin probes using radiofrequency time domain electron paramagnetic resonance spectroscopy
US20060232274A1 (en) Nuclear quadrupole resonance inspection system
CA2307307A1 (en) Methods of and apparatus for nqr testing a sample
Monea et al. The use of nuclear quadrupole resonance spectroscopy for detection of prohibited substances: Techniques and equipment
US20060226838A1 (en) NQR method and apparatus for testing a sample by applying multiple excitation blocks with different delay times
Jenkinson et al. Nuclear quadrupole resonance of explosives: Simultaneous detection of RDX and PETN in semtex
EP1253433A1 (en) Magnetic resonance probe
Ostafin et al. Detection of plastic explosives in luggage with14N nuclear quadrupole resonance spectroscopy
Mozzhukhin et al. Sensing System for 14 N NQR Remote Detection of Explosives
Tachiki et al. Sensing of chemical substances using SQUID-based nuclear quadrupole resonance
JPH04326051A (en) Pulse nucleus four-pole resonance device

Legal Events

Date Code Title Description
WWE Wipo information: entry into national phase

Ref document number: 200480019542.8

Country of ref document: CN

AK Designated states

Kind code of ref document: A1

Designated state(s): AE AG AL AM AT AU AZ BA BB BG BR BW BY BZ CA CH CN CO CR CU CZ DE DK DM DZ EC EE EG ES FI GB GD GE GH GM HR HU ID IL IN IS JP KE KG KP KR KZ LC LK LR LS LT LU LV MA MD MG MK MN MW MX MZ NA NI NO NZ OM PG PH PL PT RO RU SC SD SE SG SK SL SY TJ TM TN TR TT TZ UA UG US UZ VC VN YU ZA ZM ZW

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): BW GH GM KE LS MW MZ NA SD SL SZ TZ UG ZM ZW AM AZ BY KG KZ MD RU TJ TM AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IT LU MC NL PL PT RO SE SI SK TR BF BJ CF CG CI CM GA GN GQ GW ML MR NE SN TD TG

121 Ep: the epo has been informed by wipo that ep was designated in this application
DPEN Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed from 20040101)
WWE Wipo information: entry into national phase

Ref document number: 2006508368

Country of ref document: JP

WWE Wipo information: entry into national phase

Ref document number: 0524897.6

Country of ref document: GB

Ref document number: 0524897

Country of ref document: GB

WWE Wipo information: entry into national phase

Ref document number: 2004245735

Country of ref document: AU

ENP Entry into the national phase

Ref document number: 2004245735

Country of ref document: AU

Date of ref document: 20040520

Kind code of ref document: A

WWP Wipo information: published in national office

Ref document number: 2004245735

Country of ref document: AU

WWE Wipo information: entry into national phase

Ref document number: 2006232274

Country of ref document: US

Ref document number: 10559371

Country of ref document: US

122 Ep: pct application non-entry in european phase
WWP Wipo information: published in national office

Ref document number: 10559371

Country of ref document: US

DPE2 Request for preliminary examination filed before expiration of 19th month from priority date (pct application filed from 20040101)