U.S. patent application number 12/685412 was filed with the patent office on 2010-09-23 for energetic material detector.
This patent application is currently assigned to L-3 COMMUNICATIONS CORPORATION. Invention is credited to Edward E.A. Bromberg, Steven Bullock, Sean C. Christiansen, Herbert Duvoisin, III, David H. Fine, C. Andrew Helm, David P. Lieb, Eric Moy.
Application Number | 20100240140 12/685412 |
Document ID | / |
Family ID | 39157707 |
Filed Date | 2010-09-23 |
United States Patent
Application |
20100240140 |
Kind Code |
A1 |
Fine; David H. ; et
al. |
September 23, 2010 |
ENERGETIC MATERIAL DETECTOR
Abstract
A method of detecting energetic materials, such as explosives,
includes energizing a sample area that contains particles of
energetic materials. In the method, temperature characteristics
from the sample area are monitored, and a temperature released from
exothermic decomposition of the particles is detected. The method
further includes analyzing the detected temperature to determine
the presence of the exothermic compound which caused the
decomposition.
Inventors: |
Fine; David H.; (Cocoa
Beach, FL) ; Duvoisin, III; Herbert; (Orlando,
FL) ; Bromberg; Edward E.A.; (Orlando, FL) ;
Bullock; Steven; (Orlando, FL) ; Lieb; David P.;
(Lexington, MA) ; Helm; C. Andrew; (Oviedo,
FL) ; Christiansen; Sean C.; (Orlando, FL) ;
Moy; Eric; (Orlando, FL) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
L-3 COMMUNICATIONS
CORPORATION
Carlsbad
CA
|
Family ID: |
39157707 |
Appl. No.: |
12/685412 |
Filed: |
January 11, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11460586 |
Jul 27, 2006 |
7645069 |
|
|
12685412 |
|
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|
|
60702616 |
Jul 27, 2005 |
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60743083 |
Dec 29, 2005 |
|
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60743402 |
Mar 3, 2006 |
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Current U.S.
Class: |
436/147 ;
422/68.1 |
Current CPC
Class: |
G01N 33/227 20130101;
G01N 25/54 20130101; G01N 33/22 20130101 |
Class at
Publication: |
436/147 ;
422/68.1 |
International
Class: |
G01N 33/22 20060101
G01N033/22 |
Claims
1. A method of detecting explosive materials, the method comprising
providing energy to a sample area; monitoring the sample area with
a pixel-array detector; detecting, based on the monitoring of the
sample area with the pixel-array detector, a signature from
decomposition of particles of the sample area; analyzing the
detected signature from the decomposition of the particles of the
sample area; and determining, based on the analyzing of the
detected signature from the decomposition of the particles of the
sample area, whether the particles of the sample area include one
or more explosive materials.
2. The method of claim 1 wherein detecting the signature from the
decomposition of the particles of the sample area includes
detecting an energy release signature from the decomposition of the
particles of the sample area.
3. The method of claim 2 wherein detecting the energy release
signature from the decomposition of the particles of the sample
area includes detecting a thermal energy release signature from the
decomposition of the particles of the sample area.
4. The method of claim 1 wherein each pixel of the pixel-array
detector is configured to have a different instantaneous field of
view.
5. The method of claim 4 wherein each pixel of the pixel-array
detector is configured such that the pixel's instantaneous field of
view centers on a different portion of the sample area.
6. The method of claim 4 wherein each pixel of the pixel-array
detector is configured such that the pixel's instantaneous field of
view includes a region of the sample area spanning 10 to 100
microns in diameter.
7. The method of claim 4 wherein each pixel of the pixel-array
detector is configured such that the pixel's instantaneous field of
view is between 50 and 150 microns in diameter.
8. The method of claim 1 wherein providing energy to the sample
area includes resistively heating the sample area.
9. The method of claim 8 wherein resistively heating the sample
area includes generating a current through a conductive collection
material.
10. The method of claim 9 wherein generating the current through
the conductive collection material includes generating a step
current.
11. The method of claim 1 wherein determining whether the particles
of the sample area include one or more explosive materials includes
determining, based on the analyzing of the detected signature from
the decomposition of the particles of the sample area, that
triacetone triperoxide was present on the sample area.
12. The method of claim 1 wherein analyzing the detected signature
includes analyzing energy data for the difference between an energy
level of a first pixel and a background pixel.
13. The method of claim 1 wherein analyzing the detected signature
includes analyzing a change of the signature with respect to
time.
14. The method of claim 1 wherein analyzing the detected signature
includes analyzing the detected signature to determine a heat of
decomposition of a material that underwent anaerobic exothermic
decomposition.
15. The method of claim 1 wherein analyzing the detected signature
includes analyzing the detected signature to determine an
activation energy of a material that underwent anaerobic exothermic
decomposition.
16. The method of claim 1 further comprising using a determined
heat of decomposition or activation energy to determine a specific
type or category of material that has undergone anaerobic
exothermic decomposition at the sample area.
17. The method of claim 1 further comprising lowering atmospheric
oxygen available for combustion.
18. A system for detecting explosive materials, the system
comprising: a sample energizer configured to provide energy to a
sample area; a pixel-array detector configured to monitor the
sample area and detect, based on the monitoring of the sample area,
a signature from decomposition of particles of the sample area; and
an analyzing device configured to analyze the detected signature
from the decomposition of the particles of the sample area and
determine, based on the analyzing of the detected signature from
the decomposition of the particles of the sample area, whether the
particles of the sample area include one or more explosive
materials.
19. The system of claim 18 wherein, to detect the signature from
the decomposition of the particles of the sample area, the
pixel-array detector is configured to detect an energy release
signature from the decomposition of the particles of the sample
area.
20. A system for detecting explosive materials, the system
comprising: a sample energizer configured to provide energy to a
sample area; a pixel-array detector configured to monitor the
sample area and detect, based on the monitoring of the sample area,
a signature from decomposition of particles of the sample area; and
means for an analyzing device configured to analyze the detected
signature from the decomposition of the particles of the sample
area and determine, based on the analyzing of the detected
signature from the decomposition of the particles of the sample
area, whether the particles of the sample area include one or more
explosive materials.
Description
CROSS-REFERENCE
[0001] This application is a continuation of and claims priority to
U.S. patent application Ser. No. 11/460,586, filed Jul. 27, 2006,
issuing Jan. 12, 2010 as U.S. Pat. No. 7,645,069, and titled
"Energetic Material Detector," which also claims priority from U.S.
Provisional Application Nos. 60/702,616, filed Jul. 27, 2005, and
titled "Trace Explosives Detector Based Upon Detecting Exothermic
Decomposition"; and 60/743,083, filed Dec. 29, 2005, and titled
"Energetic Material Detector For Explosive Trace Detection"; and
60/743,402, filed Mar. 3, 2006, and titled "Energetic Material
Detector For Explosive Trace Detection." Each of these applications
is incorporated by reference.
TECHNICAL FIELD
[0002] This disclosure relates to detecting energetic materials,
such as explosives.
BACKGROUND
[0003] In order to detect the presence of energetic materials,
particles of the material may be analyzed.
SUMMARY
[0004] In one general aspect, detecting energetic materials, such
as explosives, includes energizing a sample area that may contain
particles of energetic materials. Temperature characteristics from
the sample area are monitored, and a temperature released from
exothermic decomposition of the particles is detected when
particles of energetic materials are present. The monitored
temperature characteristics are analyzed to determine whether the
particles are present.
[0005] Implementations may include one or more of the following
features. For instance, the sample area may be resistively heated.
A current may be applied through a conductive collection material,
such as a metal mesh. The applied current may be a step or ramp
current.
[0006] The sample area also may be energized through radiative
heating, such as with a flash-lamp or laser. The sample area may be
radiatively heated from a distance beyond the adjacent vicinity of
the device.
[0007] Infrared radiation may be monitored, and infrared radiation
released from exothermic decomposition of materials may be
detected. Temperature data may be analyzed for the difference
between a pixel and a background temperature or the change with
respect to time. The temperature data also may be analyzed to
determine a heat of decomposition or an activation energy of the
material that underwent exothermic decomposition. A determined heat
of decomposition or activation energy may be used to determine a
specific type or category of material, such as, triacetone
triperoxide, that underwent exothermic decomposition.
[0008] Atmospheric oxygen available for combustion may be lowered.
The air-pressure may be reduced and non-reactive gases may be
introduced.
[0009] In another general aspect, a system for detecting energetic
materials, such as explosives, includes a sample energizer
configured to energize a sample that contains with particles of
energetic materials. A sensor is configured to monitor temperature
characteristics from the sample area and detect a temperature
released from exothermic decomposition of the particles. An
analyzing device is configured to analyze the detected temperature
to determine the presence of an exothermic compound which caused
the decomposition.
[0010] Implementations may include one or more of the features
noted above. The details of one or more implementations are set
forth in the accompanying drawings and the description below. Other
features and advantages will be apparent from the description and
drawings, and from the claims.
DESCRIPTION OF DRAWINGS
[0011] FIG. 1 illustrates a decomposition system.
[0012] FIG. 2 illustrates a detection system employing resistive
heating.
[0013] FIG. 3 illustrates a detection system employing radiative
heating.
[0014] FIG. 4 illustrates a detection chamber employing atmospheric
alteration.
[0015] FIG. 5 illustrates an impact collector.
[0016] FIGS. 6A and 6B illustrate a top and side view of a
collection and detection system.
[0017] FIG. 6C illustrates a collection and detection system with a
continuous collection material.
[0018] FIG. 7A illustrates a hand-held detection system.
[0019] FIG. 7B illustrates a ranged detection system.
[0020] FIGS. 8A and 8B illustrate particle detection data.
[0021] FIGS. 9A and 9B illustrate processed particle detection
data.
[0022] FIG. 10 is a flow chart of a method of detecting energetic
materials.
[0023] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0024] Individuals have been able to conceal explosives by using
unusual materials or precautionary methods to thwart detection. For
example, while a traditional weapon, such as a grenade, may be
detected on a person by means of a metal detector or in luggage by
means of an x-ray scanner, explosives, such as, C-4 and TNT, may
not be detected by such methods. Also, conventional explosive
detection equipment may be designed detect certain known explosive
material with specific chemical structures.
[0025] In order to screen a wider variety of potentially
threatening material, trace sampling of particles may be used.
Specifically, a sample of trace (e.g., microscopic) particles may
be collected from an item or individual, and analyzed for
properties indicative of explosives or threats. The analysis of
particles may be conducted using a variety of mechanisms, such as
an ion mobility detector (IMS), gas chromatography coupled with a
chemiluminescence detector (GC-CL), or mass spectrometry. Many
techniques are able to detect only specific chemicals, or chemicals
with very specific types of chemical structures.
[0026] Whether a particle is an explosive may be determined by
triggering a thermal decomposition (i.e., a thermal explosion) of
the particle. In particular, explosive particles may be rapidly
heated while monitoring for the presence of thermal decomposition.
Various methods, such as resistive, conductive, radiative, or laser
heating, may be used.
[0027] Resistive heating may be appropriate for systems where
particles are collected and analyzed at close range. For example, a
swipe or vacuum collection system may deposit particles on a steel
mesh, which may be directly resistively heated. For long-range
systems, radiative heating may be appropriate. For example, a
radiative heater may be incorporated into a x-ray baggage scanner
and may be used to detect explosive or other energetic particles
from a range of less than a meter. Other systems may be radiatively
heated and detected from much larger ranges, such as, for example,
tens or hundreds of meters.
[0028] Referring to FIG. 1, a detection system 100 analyzes a
sample 110 using a collection material 120 and an infrared (IR)
sensor 140. In the system 100, the sample 110 is placed on the
collection material 120 and then heated 125 to trigger thermal
decomposition. Energy 130 is released from the sample 110 during
decomposition, and a portion 135 of that energy is detected by the
IR sensor 140 to infer the presence of explosive particles.
[0029] The sample 110 may be collected from a variety of sources
and by means of a variety of methods. In general, people who handle
or work with explosives or other materials typically become
contaminated with trace residue of the materials. For example,
explosive particles may remain on the hands following manufacturing
and/or handling of a bomb or explosive material, and some of these
particles are may be transferred to the person's clothing. Such
trace residue may also be transferred to items such as wallets,
spectacles, keys, purses, and door handles, and these items may
serve to re-contaminate the hands, even when they are washed and
the individual changes clothing. The body, clothes, or articles may
be swabbed by a collection device or vacuumed onto the collection
material 120 to collect the trace residue as the sample 110 for
analysis.
[0030] The collection material 120 may be constructed out of a
variety of materials, such as, for example, Teflon, a stainless
steel mesh, woven carbon fibers, a deactivated glass wool pad, a
nichrome wire or ribbon, aluminum (and or stainless steel or nickel
or other metals) coated polyimide, or carbon filled polyimide. If
resistive heating is being employed, the collection material 120
may need to be conductive. If radiative heating is being employed,
conductivity of the collection material 120 is not required.
[0031] Triggering thermal decomposition of the sample relies on the
rapid kinetics and thermodynamics associated with the thermal
decomposition of explosives. Although most molecules decompose
endothermically when heated in an atmosphere deprived of oxygen, an
explosive compound decomposes exothermically and releases heat to
the environment. The released heat is immediately transferred to
the molecules surrounding the decomposing explosives, which results
in a localized increase in temperature that provides a measurable
indicator of the presence and/or type of an explosive sample
110.
[0032] Specifically, explosive samples 110 decompose exothermically
(they release heat to the surroundings) when heated anaerobically.
If the mass of the explosives is large enough, the temperature
rises, which accelerates the reaction rate even further, releasing
additional heat, and culminating in a runaway thermal explosion.
For sub-critical masses, the material is consumed before it
explodes as heat is lost to the surroundings. Nevertheless, even
for these sub-critical cases, the temperature rises above its
surroundings before decaying back to the ambient.
[0033] The IR sensor 140 senses the portion 135 of the thermal
energy 130 released during decomposition, which enables detection
of explosives, including nitro-organics and nitro-salts, peroxides,
perchlorates, and gun powder, as well as homemade explosives of as
yet unknown composition. The IR sensor 140 employs an IR detection
array to detect the thermal signature of the decomposition. In one
implementation, the IR detection array is configured to detect heat
in the mid-wave IR (MWIR), 3 to 5 micron wavelength, 5 to 8 micron
wavelength, or long-wave IR (LWIR), 8 to 12 micron wavelength,
regions to observe the temperature of the environment surrounding
an explosive particle. Thermal imaging sensors employing detection
in the MWIR region benefit from superior resolution and contrast
while those detecting in the LWIR region offer enhanced sensitivity
to smaller temperature fluctuations and are less affected by
atmospheric conditions (e.g., LWIR radiation can be transmitted
through mist and smoke).
[0034] For trace explosive decomposition, the inherently small
particle sizes complicate the detection process. For an explosive
compound undergoing anaerobic thermal decomposition, the heat
released is expected to be equivalent to about a 100.degree. C.
temperature rise in a 200.degree. C. environment within a five to
five hundred millisecond time frame, depending upon the type of
explosive, its mass, the heating rate and the rate of heat loss. In
some cases, the time frame is 5 to 30 milliseconds. If all of the
exothermic energy produced by the decomposition of the explosive
occupied one instantaneous field of view (IFOV) of the IR detection
array, this would be easily detectable, since most MWIR/LWIR
sensors have sensitivities near 0.05.degree. C. However, trace
amounts of explosive particles emitting this heat may weigh as
little as a few nanograms and their emitted energy may only occupy
a region 0.1 to 0.01 millimeters in diameter. Since the IFOV per
pixel of a typical sensor lens is about two millimeters in diameter
at close range (approximately one foot away from the source), the
released energy from a trace explosive is undetectable across the
IFOV area. In this case, the temperature rise has been diluted
across the entire IFOV and appears as a temperature increase as
small as 0.003.degree. C. for a nanogram-size particle.
[0035] In one implementation, in order to detect localized heat
signatures, an IR detection array is appropriately configured to
record fast, microscopic reactions. Because of these constraints,
the IR sensor 140 has a macro (close-up) lens capable of achieving
an IFOV of less than between 50 and 150 microns in diameter per
pixel. In addition, the resolution of the IR sensor 140 is
sufficient to provide numerous individual pixels which act as their
own individual heat detectors and serve to increase the sensitivity
of the detection of energetic particles. For example, doubling the
resolution of the IR sensor 140 leads to a four to eight time
reduction of the lower detection limit. If the IR sensor 140
integration time between frames is long relative to the energy
release, the energy is time averaged and may not be captured by the
sensor. For example, for a five to ten millisecond reaction and
using a 60 Hz (16 ms) imaging rate, the observed energy released
from an energetic particle is reduced by less than a factor of
3.
[0036] In one implementation, the IR sensor 140 includes a long
wave infrared detector (LWIR) that is sensitive in the 7.5 to 14
micron range. The detector is equipped with a focusing lens in
order to resolve pixels down to about 50 microns. The refresh rate
of the system is 60 Hz. The detector is a 320.times.240 array with
76,800 pixels. The sensitivity of each pixel is specified as
0.05.degree. C., which facilitates sensitivity at the mid-picogram
level. Since the particle mass is inversely proportional to the
third power of the pixel size, the sensitivity can be enhanced by
using a more powerful focusing lens.
[0037] The previous description provides an exemplary
implementation of a decomposition system. Other implementations may
include other or different features. For instance, the collection
material 120 may be an individual sample which is clamped down for
heating.
[0038] Referring to FIG. 2, a detection system 200 employing
resistive heating includes a conductive collection material 210, a
control system 230 and an IR sensor 240. In the system 200, an
electrical current is run through the collection material 210,
which heats due to inherent resistance and triggers energetic
decomposition of the sample.
[0039] The control system 220 directs the flow and duration of
current through the conductor 210. Depending on implementation,
varying types of current signals may be produced by the control
system 220. A step current may be used to quickly adjust the
current to a desired level and is useful in triggering all
explosive materials to decompose quickly with minimal oxidation in
an atmosphere.
[0040] In other implementations, a ramp current that increases at a
constant rate is used. Since thermal decomposition is triggered at
differing energy levels for differing explosive materials, ramped
current enables the system 200 to more precisely determine the
nature of the explosive. Other currents shapes, such as, for
example, plateaus, may be included to determine further
characteristics of the sample.
[0041] A rapid heating rate facilitates near anaerobic heating
conditions, as oxygen requires time to reach the reaction site. In
particular, when heating a sample in an atmosphere with ambient
oxygen (e.g., air), rapid heating (e.g., tens of milliseconds to a
second), such as the heating produced by a step current, is
desirable to avoid combustion or oxidation of non-explosive
particles. When heated slowly enough to allow oxygen to reach the
reaction site (e.g., a few seconds), contaminants, such as diesel
fuel or sugar, may combust or oxidize. Since explosive materials
include the required oxygen for combustion within their chemical
structure or mixture, thermal decomposition is generally triggered
before any combustion with ambient air, during rapid heating.
[0042] In one particular implementation, the conductive collection
material 210 is a 400 mesh, 316 grade stainless steel, which
includes an opening that is 38 microns between wires. The mesh is
heated electrically using a power supply operating at 4.5 volts and
approximately 22 amps while an IR sensor is focused onto the mesh
using a 0.5.times. macro germanium lens with a nominal resolution
limit of 90 microns. The data is collected at 60 frames per second
via a Firewire connection between the IR detector and the data
collection electronics.
[0043] The previous description provides an exemplary
implementation of a decomposition system employing resistive
heating. Other implementations may include other or different
features. For instance, the conductive collection material 210 may
be replaced with a heat resistant collection material attached to a
conductor. Also, heating sensing devices connected to the control
system may detect the heat level. The detected heat level may be
used to generate a feedback loop with the control system.
[0044] Referring to FIG. 3, a detection system 300 employing
radiative heating includes a radiation device 310, a pyrometer 320,
an IR sensor 340 and a sample medium 350 that carries a sample 360.
In the system 300, radiation 315 is directed to the sample medium
350. Struck by the radiation, the sample medium 350 heats and
thermal decomposition of sample 360 is triggered.
[0045] The intensity or duration of the emitted radiation 315 by
the radiation device 310 may be based upon measurement of the
pyrometer 320, which measures the rapid heating of the sample 360
in real-time. In one implementation, the radiation device 310 is a
flash-lamp, which may rapidly release enough energy to trigger
thermal decomposition. By varying the power level and material
used, flash-lamp implementations may be used to flash objects at
several meters. If an infrared laser, such as a q-switched niobium
YAG system, is used to heat the sample 360, the heating may be
conducted over great distances (10-100 s of meters).
[0046] The previous description provides an exemplary
implementation of a decomposition system employing radiative
heating. Other implementations may include other or different
features. For instance, the radiative system may be designed to
release set amounts of energy without requiring a pyrometer for
control.
[0047] Referring to FIG. 4, a detection chamber 400 employing
atmospheric alteration, includes an input vent 420 and an output
vent 430 to generate an altered atmosphere 410 in the chamber 400
by reducing air-pressure, introducing non-reactive gases, or both.
The altered atmosphere 410 features less ambient oxygen available
for combustion or oxidation with contaminants.
[0048] The input vent 420 is optional, and introduces non-reactive
gases, such as, for example, nitrogen or neon, into the atmosphere.
The non-reactive gases decrease the availability of gaseous oxygen
for combustion or oxidation. The output vent 430 removes gas to
lower pressure, and, consequently, lower the amount of gaseous
oxygen in the chamber 400. By employing the input and output vents
420 and 430, the chances of contamination are lowered, and heating
to trigger thermal decomposition may be slowed to levels that would
create combustion in air. The chamber 400 may be particularly
useful in implementations employing a slow ramp or plateau style of
heating.
[0049] The previous description provides an exemplary
implementation of a decomposition chamber employing atmospheric
alteration. Other implementations may include other or different
features. For instance, the chamber may be designed to simply
remove the atmosphere without requiring an input vent.
[0050] Referring to FIG. 5, an impact collector 500 may be used to
deposit one or more air streams of vacuumed samples including
explosive particles onto a collection material 520 which may be
analyzed as described in the decomposition system 100 with respect
to FIG. 1. The air steams may be generated by vacuuming an object,
such as clothing, luggage, or an individual's skin, that is to be
tested. In the impact collector 500, there is a critical flow to
avoid particles falling out of the airflow and onto the tubing
walls. One implication of particles falling out of the sample
stream is a loss of sample that leads to a false negative. Another
implication is one of carry over. Specifically, if a particle falls
out of the sample stream, the particle has the potential of showing
up in later samples leading to a false positive. Because of such
implications, after every positive sampling, there may be a
clearing purge cycle, where the system is run without additional
sample material.
[0051] In the impact collector 500, the air and explosive vapors
divide according to the ratio of the bypass flow to the collector
flow. Typical collector flows are between 0 and 10 percent of the
total flow. Particles, however, are not able to make the
180.degree. turn 510 and thus impact upon the collection material
520. In order to keep the piping of the turnstile clean, valves may
be placed downstream of the collection system and kept closed
except during the sampling time.
[0052] In one particular implementation, the internal
inner-diameter of the impact collector 500 is about 1.5 cm. The
outer ring is about 3 cm in diameter. If the collection material
520 rotates, the impact collector 500 itself needs to clear the
collection material 520. The impact collector 500 may need to seal
against the portion of the collection material 520 at the outer
ring with the inner tube being from about 0.2-2.0 cm away from the
collection material 520. An O-ring may be included on the outer
tube to form a seal. In come cases, slight leakage may be
acceptable. Depending on implementation, either the impact
collector 500 is lowered to form the seal, or the collection
material 520 itself is raised to form the seal. Once the deposition
has occurred, the collection material 520 or a portion of the
collection material 520 may be heated to trigger decomposition.
[0053] Referring to FIG. 6A, a top view of a collection and
detection system 600 includes the impact collector 500 and
collection material 520 of FIG. 5, and a decomposition system 630.
The decomposition system 630 may be any of the systems 100-400 of
FIGS. 1-4. In the collection and detection system 600, the impact
collector 500 is used to deposit the sample onto the collection
material 520. A media moving mechanism 660 (FIG. 6B) moves the
collection material 520, which is mounted on a carousel wheel 610,
such that the collection material 520, including the sample, moves
from a region adjacent to the impact collector to a region within
the decomposition system 630. The deposited material is than
analyzed for traces of a specific material.
[0054] Referring to FIG. 6B, a side view of a collection and
detection system 600 includes a heating controller 650 and the
media moving mechanism 660. The discussion below refers to two
specific implementations directed to resistive and radiative
heating exothermic decomposition, but other methods of initiating
thermal decomposition may also be used. In particular, elevating
the temperature of a particle by using electromagnetic radiation,
lasers, the convection of heat via warm air to the particle, or the
conduction of heat to the particle would be sufficient for causing
thermal decomposition.
[0055] The particular collection and detection system 600 to be
used may be based on factors such as a desired period between
maintenance sessions, ease of maintenance, or cost. FIGS. 6A-6B
illustrate an implementation involving a carousel wheel 610 with a
reusable discreet collection material 520. Other implementations,
such as a "reel-to-reel" system with a one time or reusable
collection material 520, also may be used. Such a reel-to-reel
mechanism may be more costly to build and more difficult to
maintain (e.g., by replacing the worn collection material 520) than
the carousel wheel 610. Because the reel-to-reel mechanism could
hold more collection material, the time between replacements may be
greater than for the carousel implementation.
[0056] In the illustrated implementation including a carousel wheel
610, the collection material 520 is within the carousel wheel 610
and includes either a series of discreet collecting areas or a
continuous collecting area. In a series of steps, the collection
and detection system 600 gathers collected material onto an area of
the collection material 520 and then rotates to the decomposition
system 630 to enable the deposited material to be analyzed to
detect the presence of particles of materials.
[0057] According to various implementations employing the carousel
wheel, a first station is the impact collector 500, which may seal
to the carousel wheel 610. The term "station" refers to specific
locations or degrees of rotation of the carousel wheel 610. The
position of stations may be determined by the position of holes
along the circumference at angular positions of the carousel wheel
610. After particles are deposited with the impact collector 500 to
an area of the collection material 520, the carousel wheel 610
rotates to the second station, which is the decomposition system
630. Characteristics of the decomposition system 630 depend on the
detection unit employed.
[0058] A media moving mechanism 660 is employed to rotate the
collection material 520, and in the implementation discussed above,
the carousel wheel 610. For a high degree of positional accuracy, a
stepper motor may be employed. As a stepper motor is expensive and
requires specialized electronics to control, a simpler alternative
that may be used is a unidirectional or bidirectional DC motor. An
LED optical sensor may be used to determine and control the
position of the media moving mechanism 660. Maintenance of the
carousel wheel 610 may be conducted through an automatic disc
loading and unloading station to extend the time between routine
replacement of the collection material 520 to, for example, one
month.
[0059] In one implementation that includes resistive heating, the
collection material 520 area is three cm.sup.2 and includes two
contacts which are placed at opposite ends of the collection
material 520. The contacts may be shaped in various ways, such as,
for example, raised metallic bumps (e.g., like a contact for a
battery), rods, or plates. A spring loaded contact may be used to
complete the connection. The carousel wheel 610 may be designed
with upper and lower halves. In one assembly method, the two halves
are separated, the collection material 520 is installed on the
bottom half, and the top half is attached on top of the collection
material 520 forming a sandwich. In one implementation, for each
portion of the collection material 520, one of the contacts is in
the form of an electrode which is tied to a single common
connection point (not shown), and the other contact 660 is a unique
connection. In such an implementation, the common connection point
is constantly connected to the power supply, and only one unique
connection is connected at a time to enable only one portion to be
resistively heated. The collection material 520 may include holes
for the optical sensors (or LED sensor as discussed above with
respect to the carousel wheel 610 implementation).
[0060] Residual material, such as oils, may contaminate or mask
later measurements, or may shorten the life of a reusable
collection material 520. By heating the collection material 520 to
a higher temperature than that required to trigger decomposition of
energetic material, such residual material may be burned off.
Optionally, a high temperature bake out at temperatures in excess
of 300.degree. C. may be conducted in order to thermally decompose
remaining particles.
[0061] A pyrometer may be included in the decomposition system 630
or the heating controller 650. During heating, there is slight
expansion of the collection material 520. In order to prevent
distortion, the design is such that there is a slight tension on
the collection material 520.
[0062] Referring to FIG. 6C, a continuous collection material
system 675 includes a continuous conductive collection material
680, and discrete contact points 685. In the system 675, the
continuous material 680 is wrapped around the width of a wheel. A
portion of the continuous material 680 is within the impact
collector 500 where particles may be deposited. As the wheel
rotates, the portion moves within the decomposition system 630.
[0063] The continuous system 675 includes numerous discrete contact
points 685 where an electrical connection is established. When the
decomposition system 630 is activated, discrete contact points 685
are used to generate a current through the continuous material 680,
resistively heating the particles. In order to prevent an
electrical path through the full circumference of the continuous
material 680, a portion of the continuous material 680 may be left
black or otherwise severed.
[0064] The previous description provides exemplary implementations
of a collection and detection system 600. Other implementations may
include different features, such as a checking solution injected
onto the collection material 520 on an infrequent but scheduled
basis to test the ability of the system to successfully detect
particles of a material. This mechanism may include a reservoir
that needs to be replaced periodically and may include, for
example, a LEE miniature variable volume pump model number
LPVX0502600B, (see www.theleeco.com) or a small KNF model UNMP830
(see www.knf.com) or similar pump and a LEE solenoid valve similar
to LEE model number INKX051440AA.
[0065] Referring to FIG. 7A, a hand-held detection device 700
includes a standoff ring 710, a trigger 720, a flash-lamp 730, a
pyrometer 735, an IR-detector array 740, and output displays 745.
The device 700 may be brought to the sample in order to detect
explosive particles.
[0066] In order to operate the device 700, the user first places
the standoff ring 710 on the area to be scanned for explosive
particles. The standoff ring 710 provides an appropriate distance
between the sample and the IR detector array 740. Next, the user
operates a trigger 720 to activate the flash-lamp 730 and cause
heating. The flash-lamp 730 is aimed at the standoff ring 710 and
heats the sample to trigger thermal decomposition. The real-time
temperature of the sample is measured through the pyrometer 735,
and such measurement is a part of a feedback loop to enable the
temperature to be actively controlled by the flash-lamp 730. The
IR-detector array 740 detects decomposition by explosive materials.
The detected results are indicated by the output displays 745.
[0067] Referring to FIG. 7B, a long-range detection system 750
includes a detection device 760 that operates as described above
and may be aimed at an object 770 at a distance. In the system 750,
the detection device 760 emits radiation in the direction of the
object 770. After striking the object 770, the radiation causes
localized heating that triggers thermal decomposition of trace
explosive particles. IR radiation released from the decomposition
is detected by the detection device 760.
[0068] In particular, the detection device 760 includes a
flash-lamp 764 and a distance focused IR detector array 768. The
flash-lamp 764 emits a pulse of high-energy radiation sufficient to
cause thermal decomposition at the object 770. Emitted IR radiation
strikes the IR detector 768 which enables a positive identification
of trace explosives.
[0069] The detection device 760 may be enabled to operate at a
distance of tens to hundreds of meters from the object 770. Laser
heating may be used as an alternative to flash-lamp heating. Laser
hardware may be considerably more complex, power consuming, and
expensive than hardware required for resistive or flash-lamp
heating. As such, the use of a laser may be practical mainly in
implementations where the object 770 is at a considerable distance
beyond the immediate vicinity of the detection device 760. Also, a
telephoto lens may be included that focuses the IR detector array
768 on an appropriately small area. In one implementation, the
telephoto lens focuses the IR detector array 768 such that the
array views the object 770 at a resolution that is similar to the
resolution of FIG. 1.
[0070] In one implementation, a checkpoint for explosives equips a
detection device 760 to detect vehicles for explosives. The
detection includes operation of the flash-lamp across the sides of
vehicles to detect explosives along various areas of the object 770
being scanned.
[0071] The previous descriptions provide exemplary implementations
of handheld and range detection devices. Other implementations may
include other, or different features. For example, various
implementation, the detection device may be mounted in a variety of
vehicles, such as, for example, an armored personal carrier, a
tank, an aircraft, or a seacraft.
[0072] FIG. 8A shows data 800 of an exothermic decomposition
detection. In particular, a picture is shown of a sample media with
a decomposing material at four different instances of time.
Specifically, data 800 for the energetic detection of a particle of
smokeless powder using a 60 Hz frame rate are shown. Element (a)
shows an initial IR image with a relatively cool particle and
filament. Next, element (b) shows an IR image showing elevated
temperatures around the particle just prior to explosion. Next,
element (c) shows an IR image showing the particle explosion.
Finally, element (d) shows an IR image showing elevated gas
temperatures resulting from the particle explosion.
[0073] Referring to FIG. 8B, data 850 for the same decomposition
are shown from the perspective of a pixel viewing the smokeless
powder and a pixel viewing the sample media across time. In the
data 850, the four instances of time from the data 800 of FIG. 8A
are marked. Specifically, two-dimensional plots of the thermal
signatures of one pixel viewing the smokeless powder and one pixel
viewing the sample media are shown.
[0074] Analytical interpretation of the results is possible by
examining the temperature of individual pixels or the average of
several pixels as a function of time. Results may demonstrate that
a particle's rapid increase in temperature exceeds that of the
collection material. This feature can be used in algorithms to
automatically detect the presence of explosives. In particular,
each energetic compound has a quantifiable and positive heat of
decomposition (H) and a quantifiable activation energy (E). H
impacts the total heat that is released and E the rate of heat
release. These two properties interact in such a way that a
detector may distinguish classes of explosives and/or the chemical
composition.
[0075] Automatic algorithm based target recognition is used to
track multiple pixels simultaneously and to automatically recognize
the unique characteristics of explosives. Simple enhancements
include subtraction of the varying background temperature, and
displaying the differential so as to better visualize the peak
maximum. Local maxima and/or minima in a temperature versus time
plot are indicative of the presence of explosives and are
mathematically defined as points at which the time rate of change
of the temperature equals zero (i.e., dT/dt=0). However, local
maxima due to the fluctuating temperature of the collection
material may also be present. To correct for these artifacts, the
collection material temperature may be subtracted from the
temperature recorded at various points.
[0076] FIG. 9A shows processed data results 900 of a detected
exothermic decomposition. To determine the results 900, an
algorithm is used to analyze the time derivative of the raw data
for a threshold level that is characteristic of an explosive. The
raw data was obtained by heating 100 nanograms of triacetone
triperoxide (TATP) to trigger exothermic decomposition. As seen
from the image, approximately 12 pixels exceeded a threshold
analytically determined by the algorithm. This level of response
for TATP correlates to a detection limit of 8 nanograms/pixel.
[0077] Referring to FIG. 9B, the plot 950 shows a pixel at (95,
123) with a background pixel at (110, 140), from the processed data
results 900 of FIG. 9A. Detection of RDX, TNT, TATP and ANFO have
all been verified at the 100, 25 and even sub 10 ng level on dirty
substrates under conditions typical of use. Detection has also been
demonstrated for explosive materials such as PETN, Benzoyl
Peroxide, ammonium perchlorate and smokeless powder.
[0078] Testing was also performed for potential interference
materials such as sugar, diesel fuel, gasoline, numerous hand
creams and lotions, perfumes, dandruff, human skin oils, wipings of
sweat from the back of the neck, and fingerprints from touching
salami, bacon and other preserved meat and fish products, all of
which gave a clear "no-alarm" signal.
[0079] Referring to FIG. 10, detecting energetic materials, such as
explosives, includes energizing a sample area, monitoring
temperature characteristics, detecting a temperature released from
exothermic decomposition, and analyzing the detected temperature to
determine the presence of the exothermic compound.
[0080] A sample area is energized (step 1010). As shown with
respect to FIGS. 2 and 3, energizing the sample area may include
resistive or radiative heating. When the sample area is at a large
distance from the energizing mechanism, other methods, such as
lasers may be used.
[0081] Temperature characteristics of the sample area are monitored
(step 1020). Energy corresponding to the sample area's temperature
may be detected by using a sensor focused on the sample area. An
infrared sensor may be used to sense infrared emissions from the
sample area as well as a surrounding material or collection
area.
[0082] A temperature released from exothermic decomposition is
detected (step 1030). Specifically, as an exothermic compound in
the sample area heats, the exothermic compound may undergo thermal
decomposition. Energy released from the thermal decomposition may
be detected by the sensors monitoring the temperature
characteristics.
[0083] The detected temperature is analyzed to determine the
presence of the exothermic compound (step 1040). The analysis may
include determining a temperature difference between an area and
its surroundings, or a time rate of change of temperature. The
analysis also may include determining a heat of decomposition or an
activation energy of the thermal decomposition. Determined
information may be used to determine a specific type or category of
explosive that underwent exothermic decomposition.
[0084] Various implementations employ several other benefits. For
example, the performance of the detector may not be adversely
affected by the presence of a massive overload of background
materials. In particular, there may not be degradation in
performance when the sample is coated in oily substances and even
when smoke is clearly visible. With the detector, there may be
immediate recovery from massive overloads as big as 2,000 ng of
material. Further, the detector may detect chemicals that
conventional detectors may miss, such as, ammonium nitrate, nitro
cellulose, TATP, benzoyl peroxide, ammonium perchlorate, other
explosive chemicals, or mixtures of unknown chemistry. In general,
if a material can explode, the material's presence may be detected
through thermal decomposition.
[0085] Other implementations are within the scope of the following
claims.
* * * * *
References