U.S. patent application number 11/302561 was filed with the patent office on 2007-02-15 for metal shield alarm in a nuclear quadrupole resonance/x-ray contraband detection system.
Invention is credited to Daniel B. Laubacher.
Application Number | 20070035295 11/302561 |
Document ID | / |
Family ID | 36218772 |
Filed Date | 2007-02-15 |
United States Patent
Application |
20070035295 |
Kind Code |
A1 |
Laubacher; Daniel B. |
February 15, 2007 |
Metal shield alarm in a nuclear quadrupole resonance/X-ray
contraband detection system
Abstract
This invention relates to a combined nuclear quadrupole
resonance and X-ray contraband detection system with a metal shield
alarm that is activated when the area of the metal in the object
being scanned as determined by the resonance frequency shifts of
the NQR sensors exceeds the area of the metal in the object being
scanned as determined by X-rays by an amount sufficient to shield
contraband.
Inventors: |
Laubacher; Daniel B.;
(Wilmington, DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
36218772 |
Appl. No.: |
11/302561 |
Filed: |
December 13, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60635527 |
Dec 13, 2004 |
|
|
|
Current U.S.
Class: |
324/300 ;
378/63 |
Current CPC
Class: |
G01R 33/441 20130101;
G01V 11/00 20130101; G01V 5/0033 20130101; G01T 1/1603
20130101 |
Class at
Publication: |
324/300 ;
378/063 |
International
Class: |
G01V 3/00 20060101
G01V003/00; G01N 23/04 20060101 G01N023/04 |
Claims
1. A detection system to scan an object comprising (a) at least one
pair of sensors to detect nuclear quadrupole resonance in the
object, (b) an X-ray system to determine the presence of metal in
the object, and (c) an alarm that is activated when the area of
metal in the object, as determined by resonance frequency shifts of
the sensors, exceeds the area of the metal in the object, as
determined by X-ray, by at least a pre-selected amount.
2. The detection system of claim 1 further comprising a tunnel,
having an axis, through which the object being scanned passes.
3. The detection system of claim 2 wherein each sensor is a planar
sensor, and the normal to the plane of the sensor is perpendicular
to the axis of the tunnel.
4. The detection system of claim 3 wherein, in a pair of first and
second sensors, the first sensor is located on one side of the
tunnel and the second sensor is located directly opposite and
facing the first sensor on another side of the tunnel, and the
normals to the planes of the first and second sensors are collinear
and the planes of the sensors are parallel.
5. The detection system of claim 3 further comprising at least one
pair of planar excitation coils; wherein each sensor only detects
NQR signals, and each excitation coil only excites nuclear
quadrupole nuclei.
6. The detection system of claim 5 wherein the normal to the plane
of each excitation coil is perpendicular to the axis of the
tunnel.
7. The detection system of claim 5 which comprises at least two
excitation coils; wherein a first excitation coil is located on one
side of the tunnel and a second excitation coil is located directly
opposite and facing the first excitation coil on another side of
the tunnel, and the normals to the planes of the first and second
excitation coils are collinear and the planes of the excitation
coils are parallel.
8. The detection system of claim 5 wherein the sensors and the
excitation coils occupy the same sides of the tunnel, and the
planes of the sensors are parallel to the planes of the excitation
coils.
9. The detection system of claim 1 wherein each sensor is a high
temperature superconductor self-resonant planar coil.
10. The detection system of claim 5 wherein each excitation coil is
a shielded-loop resonator coil.
11. The detection system of claim 5 wherein each sensor is a
YBa.sub.2Cu.sub.3O.sub.7 or a Tl.sub.2Ba.sub.2CaCu.sub.2O.sub.8
high temperature superconductor self-resonant planar coil, and each
excitation coil is a copper shielded-loop resonator coil.
12. The detection system of claim 5 wherein an excitation coil
applies excitation to an object to be screened for the detection of
the presence of explosives, drugs or other contraband.
13. A method for scanning an object to determine the presence
therein of a target substance shielded by metal, comprising: (a)
scanning the object with X-rays to determine the area of metal
contained in the object; (b) scanning the object to determine the
area of metal contained in the object as measured by the resonance
frequency shifts of at least one pair of nuclear quadrupole
resonance sensors; (c) comparing the size of the area of metal
determined in step (a) with the size of the area determined in step
(b); and (d) activating an alarm if the area determined in step (b)
exceeds the area determined in step (a) by at least a pre-selected
amount.
14. The method of claim 13 wherein the object being scanned is
passed through a tunnel having an axis.
15. The method of claim 14 wherein each sensor is a planar sensor,
and the normal to the plane of the sensor is perpendicular to the
axis of the tunnel.
16. The method of claim 14 wherein, in a pair of first and second
sensors, the first sensor is located on one side of the tunnel and
the second sensor is located directly opposite and facing the first
sensor on another side of the tunnel, and the normals to the planes
of the first and second sensors are collinear and the planes of the
sensors are parallel.
17. The method of claim 14 wherein at least one pair of planar
excitation coils excites nuclear quadrupole nuclei in the object,
each sensor only detects NQR signals, and each excitation coil only
excites nuclear quadrupole nuclei.
18. The method of claim 17 wherein the normal to the plane of each
excitation coil is perpendicular to the axis of the tunnel.
19. The method of claim 17 wherein, in a pair of excitation coils,
a first excitation coil is located on one side of the tunnel and a
second excitation coil is located directly opposite and facing the
first excitation coil on another side of the tunnel, and the
normals to the planes of the first and second excitation coils are
collinear and the planes of the excitation coils are parallel.
20. The method of claim 17 wherein the sensors and the excitation
coils occupy the same sides of the tunnel, and the planes of the
sensors are parallel to the planes of the excitation coils.
21. The method of claim 13 wherein each sensor is a high
temperature superconductor self-resonant planar coil.
22. The method of claim 17 wherein each excitation coil is a
shielded-loop resonator coil.
23. The method of claim 17 wherein each sensor is a
YBa.sub.2Cu.sub.3O.sub.7 or a Tl.sub.2Ba.sub.2CaCu.sub.2O.sub.8
high temperature superconductor self-resonant planar coil, and each
excitation coil is a copper shielded-loop resonator coil.
24. The method of claim 17 wherein an excitation coil applies
excitation to an object to be screened for the detection of the
presence of explosives, drugs or other contraband.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/635,527, filed Dec. 13, 2004, which is
incorporated in its entirety as a part hereof for all purposes.
TECHNICAL FIELD
[0002] This invention relates to the activation of an alarm to
signal the possible presence of metal shielded contraband in a
detection system that combines nuclear quadrupole resonance sensors
and an X-ray detection system.
BACKGROUND
[0003] X-rays are currently used to scan luggage in security
systems. Typically, a dual-energy X-ray system is used to
distinguish organic, inorganic and metal materials. Most
explosives, biological agents that can be used for bioterrorism,
and drugs (controlled substances) fall within the broad organic
materials category. Since the X-ray system does not specifically
identify chemical compositions, detection of organic materials can
result in false positives and the need for further examination.
[0004] The use of nuclear quadrupole resonance (NQR) as a means of
detecting explosives, drugs and other contraband has been
recognized for some time; see, e.g., T. Hirshfield et al, J. Molec.
Struct. 58, 63 (1980); A. N. Garroway et al, Proc. SPIE 2092, 318
(1993); and A. N. Garroway et al, IEEE Trans. on Geoscience and
Remote Sensing 39, 1108 (2001). NQR provides some distinct
advantages over other detection methods. NQR requires no external
magnet such as required by nuclear magnetic resonance, and NQR is
sensitive to the compounds of interest, i.e. there is a specificity
of the NQR frequencies. Since NQR provides this specificity it can
identify particular compositions, e.g. specific explosives,
biological agents that can be used for bioterrorism, and drugs.
[0005] A NQR detection system can have one or more coils that serve
as both excitation and receive coils, or it can have separate coils
that only excite and only receive. An excitation, i.e. transmit,
coil of a NQR detection system provides a radio frequency (RF)
magnetic field that excites the quadrupole nuclei in the sample and
results in their producing their characteristic resonance signals
that the receive coil, i.e. sensor, detects.
[0006] It can be especially advantageous to use a sensor made of a
high temperature superconductor (HTS) rather than copper since the
HTS self-resonant coil has a quality factor Q of the order of
10.sup.3-10.sup.6. The NQR signals have low intensity and short
duration. In view of the low intensity NQR signal, it is important
to have a signal-to-noise ratio (S/N) as large as possible. The
signal-to-noise ratio is proportional to the square root of Q so
that the use of a HTS self-resonant coil as a sensor results in an
increase in S/N by a factor of 10-100 over that of a copper coil.
Therefore, the use of a high temperature superconductor coil with a
large Q as the sensor provides a distinct advantage over the use of
an ordinary conductor coil.
[0007] A combined nuclear quadrupole resonance and X-ray detection
system provides the existing detection capabilities of the X-ray
system with the specific compound detection capabilities of the NQR
system. Particular contraband can be unequivocally detected by NQR.
This eliminates the uncertainty connected with false positives of
the X-ray system. The detection of sheet explosives is one of the
capabilities of the NQR system.
[0008] The metal shielding of contraband such as explosives,
biological agents that can be used for bioterrorism, and drugs can
present a problem to both X-ray and NQR detection systems. A thick
metal shield will be detected by an X-ray system and prompt further
examination. However, a thin metal shield will be essentially
transparent to X-rays. For a NQR system, a metal shield as thin as
a 25.mu. thick aluminum foil will prevent detection by
identification of a particular NQR frequency that is characteristic
of a particular target substance. Sheet explosive is one type of
contraband for which thin metal shielding might be used.
[0009] An object of the present invention is to provide a combined
nuclear quadrupole resonance and X-ray detection system with a
metal shield alarm that will signal the existence of metal not
detected by X-ray and of sufficient area to shield contraband, e.g.
sheet explosives, from NQR detection.
SUMMARY
[0010] One embodiment of this invention is a detection system to
scan an object that includes (a) at least one pair of sensors to
detect nuclear quadrupole resonance in the object, (b) an X-ray
system to determine the presence of metal in the object, and (c) an
alarm that is activated when the area of metal in the object, as
determined by resonance frequency shifts of the sensors, exceeds
the area of the metal in the object, as determined by X-ray, by at
least a pre-selected amount.
[0011] The combined nuclear quadrupole resonance and X-ray
contraband detection system is typically comprised of a tunnel
through which the object to be scanned passes. Preferably, each
sensor is placed along a side of the tunnel with the normal to the
plane of the sensor perpendicular to the axis of the tunnel, each
pair of sensors is arranged directly opposite one another with one
sensor of a pair placed on one side of the tunnel, and the other
sensor of a pair placed on the opposite side of the tunnel, and the
normals to the planes of the two sensors of a pair are collinear
and the planes of the sensors are parallel.
[0012] Preferably, the sensors are high temperature superconductor
self-resonant coils. Most preferably, the sensors are high
temperature superconductor self-resonant planar coils.
[0013] Preferably, the sensors only detect NQR signals, and
separate transmit coils are provided that only excite nuclear
quadrupole nuclei.
[0014] Another embodiment of this invention is a method for
scanning an object to determine the presence therein of a target
substance shielded by metal, by: [0015] (a) scanning the object
with X-rays to determine the area of metal contained in the object;
[0016] (b) scanning the object to determine the area of metal
contained in the object as measured by the resonance frequency
shifts of at least one pair of nuclear quadrupole resonance
sensors; [0017] (c) comparing the size of the area of metal
determined in step (a) with the size of the area determined in step
(b); and [0018] (d) activating an alarm if the area determined in
step (b) exceeds the area determined in step (a) by at least a
pre-selected amount.
DETAILED DESCRIPTION
[0019] This invention addresses the problem of the detection of
contraband shielded by thin metallic coverings in an object being
scanned in a combined nuclear quadrupole resonance and X-ray
detection system. The detection system will typically have a tunnel
through which the object to be scanned passes.
[0020] As used herein, "tunnel" means an opening in a device that
performs the activities of scanning a sample for the detection of
the presence of nuclear quadrupole resonance. The sample is passed
into, down the length of the longitudinal axis of, and out of the
opening that forms the tunnel. The object is scanned for the
detection of nuclear quadrupole resonance while it is in the
tunnel. The cross-section of the tunnel, looking down its length,
can have various shapes. Typically, the tunnel will have a
rectangular cross-section, but the cross-section may be in other
shapes such as circular, substantially circular, elliptical or
polygonal. Typically, there will be a conveyor belt or other means
to transport the object to be scanned through the tunnel, i.e. from
one end of the tunnel to the other.
[0021] A dual-energy X-ray system is used to distinguish organic,
inorganic and metal materials. Thicker metallic items do not
transmit X-rays, and the shapes of their opaque, two-dimensional
images can aid identification. Guns, knives and other weapons can
be identified in this way, even when large portions are made of
plastics. Organic materials prove more of a challenge for a
dual-energy X-ray detection system, and an object that includes
organic material being scanned with an X-ray system may require
additional examination for positive identification. The addition of
nuclear quadrupole resonance detection capabilities complements
those of the X-rays. NQR can identify particular compositions, e.g.
specific explosives, biological agents that can be used for
bioterrorism, and drugs.
[0022] Contraband may, however, be shielded with metal sufficiently
thin to be essentially transparent to X-rays but sufficiently thick
to prevent detection of the chemical composition by nuclear
quadrupole resonance sensors, and this presents a severe detection
problem for the combined NQR/X-ray contraband detection system. A
shield of 25.mu.-thick aluminum foil will create the type of
problem described above. This invention solves the problem by
providing a combined nuclear quadrupole resonance and X-ray
contraband detection system with a metal shield alarm that is
activated under appropriate circumstances.
[0023] The combined nuclear quadrupole resonance and X-ray
contraband detection system is comprised of at least one pair of
sensors. As used herein, "sensors" refer to NQR detectors. Each
sensor is placed so that the normal to the plane of the sensor is
perpendicular to the longitudinal axis, i.e. the centerline, of the
tunnel. The sensor is placed along the side of the tunnel wall.
[0024] The reference to a side of a tunnel is used here in the
sense of distinguishing the placement of one sensor (or excitation
coil) in a certain location about the wall or perimeter of the
tunnel that is different from the location in which another sensor
(or excitation coil) is placed. A tunnel that has a
rectangular-shaped, or even polygonal-shaped, cross-section will
have flat surfaces that clearly qualify as "sides" of the tunnel in
this sense. In a tunnel with a rectangular cross-section, for
example, "sides" may refer to the top and bottom walls of the
tunnel as well as to the two vertical walls. Even a tunnel with a
circular, substantially-circular or elliptical cross-section,
however, despite not having flat surfaces in the shape of its
cross-section, may be thought of as having "sides" in the sense
that the location in which one sensor (or excitation coil) is
placed may be distinguished from the location in which another
sensor (or excitation coil) is placed by reference to other
features or attributes that enable distinguishing the location of
one "side" from that of another.
[0025] A pair of sensors is arranged directly opposite one another
on opposite sides of the tunnel with one sensor of a pair placed on
one side of the tunnel and the other sensor of a pair placed on the
opposite side of the tunnel facing the first sensor. The normals to
the planes of the two sensors of a pair are collinear and the
planes of the sensors are parallel. More than one pair of sensors
may be needed to provide the desired sensitivity to NQR signals.
When more than one pair is used, each pair should be arranged as
described above, directly opposite one another. Different pairs of
sensors can be arranged on different sides of the tunnel.
[0026] Preferably, the sensors are used solely to detect the NQR
signals and separate excitation coils are used solely to excite the
nuclear quadrupole nuclei.
[0027] When separate coils are used for excitation and detection,
an excitation coil preferably has the same orientation as the
sensors, i.e. along the side of the tunnel wall with the normal to
the plane of the coil perpendicular to the axis of the tunnel.
Separate excitation coils are preferably arranged in a
configuration similar to that used for the sensors, i.e. in pairs,
directly opposite one another on opposite sides of the tunnel with
one excitation coil of a pair placed on one side of the tunnel and
the other excitation coil of a pair placed on the opposite side of
the tunnel facing the first coil. Preferably, the normals to the
planes of the two excitation coils of a pair are collinear and the
planes of the excitation coils are parallel. Preferably, the
sensors and the excitation coils occupy the same sides of the
tunnel so that the planes of the pairs of sensors are parallel to
the planes of the excitation coils.
[0028] In one embodiment, two pairs of excitation coils and at
least two pairs of sensors are used. The first pair of excitation
coils is arranged directly opposite one another on opposite sides
of the tunnel. The second pair of excitation coils is also arranged
directly opposite one another on opposite sides of the tunnel. The
planes of one or both of the first pair of excitation coils may
thus not be parallel with the planes of one or both of the second
pair of excitation coils. When those planes are not parallel, they
form an angle with each other, and may, for example, be
perpendicular to each other.
[0029] Each pair of sensors is arranged directly opposite one
another on opposite sides of the tunnel with one sensor of a pair
placed on one side of the tunnel and the other sensor of a pair
placed on the opposite side of the tunnel. The sensors are placed
on the same sides being occupied by the excitation coils. At least
one pair of sensors is arranged on the sides being occupied by the
first pair of excitation coils. At least one pair of sensors is
arranged on the sides being occupied by the second pair of
excitation coils. The planes of one or both of the first pair of
sensors may thus not be parallel with the planes of one or both of
the second pair of sensors. When those planes are not parallel,
they form an angle with each other, and may, for example, be
perpendicular to each other.
[0030] In a preferred embodiment, the result is two orthogonal
pairs of excitation coils and at least two pairs of sensors that
are orthogonal. Typically when more than two pairs of sensors are
used they would be divided about equally between the two orthogonal
positions.
[0031] The excitation coils used in this invention can be made of
copper, silver, aluminum or a high temperature superconductor. A
copper, silver or aluminum coil is preferably in the form of a
shielded-loop resonator (SLR) coil. SLR's have been developed to
eliminate the detuning effect of the electrical interaction between
the coil and the surrounding material. Preferably, one or more SLR
copper excitation coils are used to apply the RF signal to the
sample. Preferably, one or more pairs of excitation coils are used
and each pair is arranged directly opposite one another on opposite
sides of the tunnel.
[0032] The sensors are preferably high temperature superconductor
self-resonant coils. The high temperature superconductor
self-resonant coil is preferably in the form of a self-resonant
planar coil, i.e. a surface coil, with a coil configuration of HTS
on one or both sides of a substrate. High temperature
superconductors are those that superconduct above 77K. The high
temperature superconductors used to form the HTS self-resonant coil
are preferably selected from the group consisting of
YBa.sub.2Cu.sub.3O.sub.7, Tl.sub.2Ba.sub.2CaCu.sub.2O.sub.8,
TlBa.sub.2Ca.sub.2Cu.sub.3O.sub.0, (TlPb)Sr.sub.2CaCu.sub.2O.sub.7
and (TlPb)Sr.sub.2Ca.sub.2Cu.sub.3O.sub.9. Most preferably, the
high temperature superconductor is YBa.sub.2Cu.sub.3O.sub.7 or
Tl.sub.2Ba.sub.2CaCu.sub.2O.sub.8.
[0033] The X-ray portion of the detection system is operated in a
conventional manner. A dual-energy X-ray system provides the usual
identification of metallic, inorganic and organic materials. In
addition, the cross sectional area of the two-dimensional image of
a metallic object, as measured by the X-rays, is determined.
Preferably, the direction of the impinging X-rays is parallel to
the normals to the planes of the sensors.
[0034] The NQR portion of the detection system is also operated in
a conventional manner with the sensors detecting any NQR signals
from targeted quadrupole nuclei. In addition, the cross sectional
area of a metallic object as measured by shifts in the resonance
frequency of the sensors is determined. The resonance frequency of
a sensor shifts as a result of the presence of metal, e.g. metal in
the object being scanned. The magnitude of the frequency shift is a
function of the area of the metal seen by the sensor and the
position of the metal with respect to the sensor. The larger the
metal area, the larger the frequency shift. The closer the metal to
the sensor, the larger the frequency shift. By using the frequency
shifts of a pair of sensors on opposite sides of the tunnel as
described above, the area of a metal object can be determined. The
pair of sensors can be calibrated using known samples of metal at
various positions to ensure that the calculation of the area of a
metal object using the frequency shifts provides an accurate
result. When more than one pair of sensors is used, the array of
sensor pairs can likewise be calibrated so that the area of metal
can be calculated using the sensor frequency shifts.
[0035] The area of metal in the object being scanned as determined
by the resonance frequency shifts of the sensors, and the area of
metal in the object being scanned as determined by X-rays, can be
used to trigger a metal shield alarm. The situation being addressed
is the presence of contraband being shielded by metal sufficiently
thin to be essentially transparent to X-rays but sufficiently thick
to prevent detection of chemical composition by nuclear quadrupole
resonance sensors. The area of metal as determined by the NQR
sensor frequency shifts is a total of the area of the thicker metal
pieces that the X-rays also measure as well as the area of the thin
metal pieces that are essentially transparent to X-rays. The
difference between the area of metal as determined by the NQR
sensor frequency shifts and the area of metal as determined by
X-rays is thus the area of the thin metal pieces. This metal could
be shielding contraband, such as sheet explosives, from the
sensors.
[0036] An alarm is provided with the combined nuclear quadrupole
resonance and X-ray contraband detection system, and this alarm is
activated when the metal area determined by the NQR sensors exceeds
the metal area determined by X-rays by at least a pre-selected
amount, which is an amount sufficient to shield contraband. The
threshold for activating the metal shield alarm, i.e. the area of
metal sufficient to shield contraband, will be determined by the
area of metal needed to cover a certain quantity of contraband of
particular interest, for example an amount of explosives that can
produce a certain amount of damage. For example, the area of metal
that is needed to shield an amount of sheet explosives such as RDX
that would cause unacceptable damage is readily determined. The
threshold for activating the metal shield alarm would then be set
at a fraction of the determined area so as to provide a margin of
safety.
[0037] Other arrangements of sensors and coils useful in this
invention are described in U.S. Provisional Application No.
60/635,583, and in the U.S. regular application claiming the
benefit thereof (Ser. No. ______), each of which is incorporated in
its entirety as a part hereof for all purposes.
* * * * *