U.S. patent application number 13/539608 was filed with the patent office on 2013-05-09 for cantilevered probe detector with piezoelectric element.
This patent application is currently assigned to Board of Regents of the Nevada System of Higher Education, on behalf of the University of Nevada. The applicant listed for this patent is Jesse D. Adams, Stuart C. Feigin, Todd A. Sulchek. Invention is credited to Jesse D. Adams, Stuart C. Feigin, Todd A. Sulchek.
Application Number | 20130116137 13/539608 |
Document ID | / |
Family ID | 36143092 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130116137 |
Kind Code |
A1 |
Adams; Jesse D. ; et
al. |
May 9, 2013 |
CANTILEVERED PROBE DETECTOR WITH PIEZOELECTRIC ELEMENT
Abstract
A disclosed chemical detection system for detecting a target
material, such as an explosive material, can include a cantilevered
probe, a probe heater coupled to the cantilevered probe, and a
piezoelectric element disposed on the cantilevered probe. The
piezoelectric element can be configured as a detector and/or an
actuator. Detection can include, for example, detecting a movement
of the cantilevered probe or a property of the cantilevered probe.
The movement or a change in the property of the cantilevered probe
can occur, for example, by adsorption of the target material,
desorption of the target material, reaction of the target material
and/or phase change of the target material. Examples of detectable
movements and properties include temperature shifts, impedance
shifts, and resonant frequency shifts of the cantilevered probe.
The overall chemical detection system can be incorporated, for
example, into a handheld explosive material detection system.
Inventors: |
Adams; Jesse D.; (Reno,
NV) ; Sulchek; Todd A.; (Oakland, CA) ;
Feigin; Stuart C.; (Reno, NV) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Adams; Jesse D.
Sulchek; Todd A.
Feigin; Stuart C. |
Reno
Oakland
Reno |
NV
CA
NV |
US
US
US |
|
|
Assignee: |
Board of Regents of the Nevada
System of Higher Education, on behalf of the University of
Nevada
Reno
NV
|
Family ID: |
36143092 |
Appl. No.: |
13/539608 |
Filed: |
July 2, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11845661 |
Aug 27, 2007 |
8136385 |
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13539608 |
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11576443 |
Mar 30, 2007 |
7694346 |
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PCT/US05/35216 |
Sep 30, 2005 |
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11845661 |
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60614592 |
Oct 1, 2004 |
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Current U.S.
Class: |
506/9 ; 506/12;
506/7 |
Current CPC
Class: |
G01N 2291/0257 20130101;
G01N 29/036 20130101; G01N 33/0031 20130101; G01N 27/007 20130101;
G01N 25/00 20130101; G01N 33/0057 20130101; G01N 29/022 20130101;
G01N 33/227 20130101 |
Class at
Publication: |
506/9 ; 506/12;
506/7 |
International
Class: |
G01N 33/22 20060101
G01N033/22 |
Goverment Interests
ACKNOWLEDGMENT OF GOVERNMENT SUPPORT
[0002] This invention was made with Government support under Prime
Contract No. DE-AC05-00OR22725 awarded to UT-Battelle, LLC, by the
U.S. Department of Energy and a subcontract awarded to the
University of Nevada, Reno by UT-Battelle, LLC. The Government may
have certain rights in this invention.
Claims
1. A method for analyzing a target chemical species, the method
comprising: driving signals to a plurality of sensor probes of a
chemical detection system, the sensor probes having an outer
surface including a material that interacts with one or more target
chemical species; sensing input signals received from the sensor
probes after interaction of the target chemical species with the
outer surface of the sensor probes; and detecting, identifying,
and/or characterizing the target chemical species on at least one
sensor probe via a first process based on the input signals
received from the sensor probe, and detecting, identifying, and/or
characterizing the target chemical species on another sensor probe
via a second process based on the input signals received from the
sensor probe, the second process being different than the
first.
2. The method of claim 1 wherein detecting, identifying, and/or
characterizing the target chemical species via a first and second
process occurs simultaneously.
3. The method of claim 1 further including detecting, identifying,
and/or characterizing the target chemical species on another sensor
probe via a third process based on the input signals received from
the sensor probe, the third process being different than the first
and second processes.
4. The method of claim 1 wherein the first process includes a
plurality of processes.
5. The method of claim 4 wherein the plurality of processes are
selected from selective adsorption of the target chemical species,
selective absorption of the target chemical species, reaction of
the target chemical species, phase change of the target chemical
species, deflagration of the target chemical species, an impedance
shift of one or more sensor probes among the plurality of sensor
probes in the presence of the target chemical species, or any
combination thereof.
6. The method of claim 1 wherein driving signals to a plurality of
sensor probes includes driving at least one sensor probe with a
waveform to induce movement in the sensor probe, and wherein
sensing input signals received from the sensor probes includes
sensing movements of the at least one sensor probe, and wherein one
of the processes includes detecting the target chemical species
through a change in movement of the at least one sensor probe as
influenced by the target chemical species.
7. The method of claim 1 further comprising heating the sensor
probes after interaction of the target chemical species with the
outer surface of the sensor probes.
8. The method of claim 7 wherein the first or second process
includes where a change in mass of the target chemical species is
detectable over time as the heating evaporates the target chemical
species.
9. The method of claim 7 wherein heating the sensor probes occurs
while driving the sensor probes, and wherein sensing input signals
includes sensing input signals received from at least one sensor
probe after heating and interaction of the target chemical species
with the outer surface of the sensor probe.
10. The method of claim 7 wherein driving signals to a plurality of
sensor probes includes driving at least one sensor probe with a
waveform and heating the at least one sensor probes to induce
movement, and wherein sensing input signals received from the
sensor probes includes sensing movements of the at least one sensor
probe, and wherein one of the processes includes detecting,
identifying, and/or characterizing the target chemical species
through a change in movement of the at least one sensor probe as
influenced by the target chemical species.
11. The method of claim 7 wherein driving signals to a plurality of
sensor probes includes driving at least one sensor probe with a
waveform and heating the at least one sensor probe to induce
movement, and wherein sensing input signals received from the
sensor probes includes sensing an electrical response of the at
least one sensor probe, and wherein one of the processes includes
detecting, identifying, and/or characterizing the target chemical
species through a change in electrical impedance of the at least
one sensor probe as influenced by the target chemical species.
12. The method of claim 1 wherein sensing input signals includes
sensing the temperature of at least one sensor probe.
13. The method of claim 1 wherein the material of the outer surface
sorbs one or more target chemical species.
14. The method of claim 1 wherein at least one sensor probe
includes a unitary piezoelectric element so as to perform driving
and sensing operations of the sensor probe.
15. The method of claim 1 wherein the sensor probes are connected
in parallel.
16. The method of claim 1 wherein the sensor probes define an
array.
17. A method for analyzing a target chemical species, the method
comprising: driving signals to a plurality of sensor probes of a
chemical detection system, the sensor probes having an outer
surface including a material that interacts with one or more target
chemical species; sensing input signals received from the sensor
probes after interaction of the target chemical species with the
outer surface of the sensor probes; and detecting, identifying,
and/or characterizing the target chemical species of each of the
plurality of sensor probes via a plurality of processes based on
the input signals received from the sensor probes.
18. The method of claim 17 wherein the plurality of processes are
selected from selective adsorption of the target chemical species,
selective absorption of the target chemical species, reaction of
the target chemical species, phase change of the target chemical
species, deflagration of the target chemical species, an impedance
shift of one or more sensor probes among the plurality of sensor
probes in the presence of the target chemical species, or any
combination thereof.
19. The method of claim 17 wherein at least one sensor probe
includes a unitary piezoelectric element so as to perform driving
and sensing operations of the sensor probe.
20. The method of claim 17 wherein a plurality of sensor probes is
connected in parallel.
21. The method of claim 17 further comprising heating a plurality
of sensor probes after interaction of the target chemical species
with the outer surface of the sensor probes.
22. The method of claim 17 wherein sensing input signals includes
sensing the temperature of at least one sensor probe.
23. The method of claim 17 wherein the material of the outer
surface sorbs one or more target chemical species.
24. A method for analyzing a target chemical species, the method
comprising: driving signals to a plurality of sensor probes of a
chemical detection system, the sensor probes having an outer
surface including a material that interacts with one or more target
chemical species; sensing input signals received from the sensor
probes after interaction of the target chemical species with the
outer surface of the sensor probes; and detecting, identifying,
and/or characterizing the target chemical species based on results
from a plurality of processes and comparing those results to a
database.
25. The method of claim 24 wherein the plurality of processes are
selected from selective adsorption of the target chemical species,
selective absorption of the target chemical species, reaction of
the target chemical species, phase change of the target chemical
species, deflagration of the target chemical species, an impedance
shift of one or more sensor probes among the plurality of sensor
probes in the presence of the target chemical species, or any
combination thereof.
26. The method of claim 24 wherein at least one sensor probe
includes a unitary piezoelectric element so as to perform driving
and sensing operations of the sensor probe.
27. The method of claim 24 wherein a plurality of sensor probes is
connected in parallel.
28. The method of claim 24 further comprising heating a plurality
of sensor probes after interaction of the target chemical species
with the outer surface of the sensor probes.
29. The method of claim 24 wherein sensing input signals includes
sensing the temperature of at least one sensor probe.
30. The method of claim 24 wherein the material of the outer
surface sorbs one or more target chemical species.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of the earlier filing
date of U.S. Provisional Application No. 60/614,592, filed Oct. 1,
2004, which is hereby incorporated by reference in its
entirety.
FIELD
[0003] This disclosure relates generally to chemical detection, and
more particularly to systems and methods for sensing target
materials, such as explosive materials, using cantilevered
probes.
BACKGROUND
[0004] The burgeoning market for explosives screening equipment and
an increase in research on chemical and explosive detection
technologies are in response to the greater need to perform
real-time detection of undesirable chemicals and hidden explosives,
such as those concealed in luggage, shipping containers, land
mines, and unexploded ordinances. The market for devices that
screen people for explosives and various types of biological,
chemical or nuclear/radiological weapons is estimated by Homeland
Security Research Corp. to reach $3.5 billion by 2006 and $9.9
billion by 2010.
[0005] Among the wide range of materials from which explosives can
be made are organic nitrates, organonitro compounds, ketone and
acyl peroxides, inorganic chlorates, perchlorates, nitrates,
fulminates, and acetylides. Some of the explosive residue chemical
compounds for detection and identification include
2,4,6-trinitrotoluene (TNT), 2,4,6,n-tetranitro-n-methylaniline
(Tetryl), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX),
1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX),
pentaerythritol tetranitrate (PETN), glycerol trinitrate
(nitroglycerin), and ethylene glycol dinitrate (EGDN).
[0006] Many obstacles remain for scientists and engineers working
to develop equipment and processes for detecting explosives. Dogs
continue to be the preferred explosive detectors, yet widespread
deployment of canine teams is neither practical nor cost effective.
Moreover, currently available non-canine explosive sensor equipment
tends to be complex, bulky, and expensive, and cannot be
miniaturized easily.
[0007] Currently available explosive and bomb detection systems
typically absorb particulate or vapor matter onto a surface, and
analyze the matter using techniques such as ion mobility
spectrometry (IMS), mass spectroscopy, nuclear magnetic resonance
analysis, and gas chromatography. Successful explosive and chemical
detection techniques can require sensitivity as low as parts per
trillion to parts per quadrillion, in that small explosive devices
such as anti-personnel land mines may be constructed from plastic
and other non-metallic substances having low vapor pressures. One
exemplary explosive and chemical detection system used in airports
exposes luggage to a stream of air that dislodges chemicals into
the air as vapors, which are subsequently concentrated to create
detectable levels of the chemicals. Unfortunately, many
conventional explosive and chemical detection systems still have
high false alarm rates, slow throughput, operator dependences, and
high transaction costs.
[0008] Some conventional explosive detection systems include
cantilevered elements. One example of this type of system is
described by Thundat in "Microcantilever Detector for Explosives,"
U.S. Pat. No. 5,918,263, issued Jun. 29, 1999 (Thundat). As
disclosed in Thundat, explosive gas molecules that have been
adsorbed onto a microcantilever are subsequently heated to cause
combustion, which in turn causes bending and a transient resonance
response of the microcantilever. Movement of the microcantilever is
detected by a laser diode, which is focused on the microcantilever,
and a photodetector, which detects deflection of the reflected
laser beam caused by a heat-induced deflection and resonance
response of the microcantilever. Conventional explosive detectors
that include cantilevered elements, such as the detector disclosed
in Thundat, have a variety of limitations. For example, many such
detectors cannot be miniaturized because they require external
cantilever actuation and external sensing.
SUMMARY
[0009] Disclosed herein are embodiments of a chemical detection
system for detecting a target material, such as an explosive
material. Some of these embodiments have potential as extremely
sensitive yet inexpensive sensors that can be mass-produced,
thereby enabling large-scale sensor deployment. For example, some
embodiments may offer several orders of magnitude greater
sensitivities when compared to other micro-electrical-mechanical
systems (MEMS) such as quartz crystal microbalances (QCM), flexural
plate wave oscillators (FPW), and surface acoustic wave devices
(SAW).
[0010] Embodiments of the disclosed chemical detection system can
include, for example, a cantilevered probe, a probe heater
thermally coupled to the cantilevered probe, and a piezoelectric
element disposed on the cantilevered probe. The piezoelectric
element can be configured to detect the target material by a
variety of processes, such as by detecting bending, vibrations,
recoil, or other movements of the cantilevered probe, a temperature
change of the cantilevered probe, an impedance shift of the
cantilevered probe, or a resonant frequency shift of the
cantilevered probe. In some embodiments, the piezoelectric element
is configured to actuate movement of the cantilevered probe. This
movement can be useful in the detection process, such as to detect
a resonant frequency shift of the cantilevered probe.
[0011] The piezoelectric element can include a piezoelectric film
disposed on a surface of the cantilevered probe. In some
embodiments, the piezoelectric element comprises zinc oxide, lead
zirconate titanate, aluminum nitride, a piezoelectric material, or
a derivative or combination thereof. The piezoelectric element also
can comprise a pyroelectric material. In some embodiments, the
probe heater includes piezoresistive element formed in the
cantilevered probe, a heater element disposed on the cantilevered
probe, or both.
[0012] Embodiments of the disclosed chemical detection system can
include a variety of additional elements. Some embodiments include
an interface circuit electrically coupled to the piezoelectric
element. For example, some embodiments include an interface circuit
comprising the piezoelectric element as a bridge element in an AC
bridge circuit. This AC bridge can be tuned, for example, to one of
an on-resonance condition or an off-resonance condition to detect
the target material. Embodiments of the disclosed chemical
detection system also can include a thermally conductive mesh
substantially surrounding the cantilevered probe. This can be
useful, for example, to limit the egression of thermal energy
liberated by exothermic reactions, such as the deflagration of
explosive materials. Embodiments of the disclosed chemical
detection system also can include a mechanical stop configured to
contact the cantilevered probe. This stop can be used, for example,
to detect movement of the cantilevered probe. Some embodiments are
handheld. These and other embodiments can include an enclosure,
such as a handheld enclosure.
[0013] Examples of target materials that can be detected by some
embodiments of the disclosed chemical detection system include
2,4,6-trinitrotoluene, 2,4,6,n-tetranitro-n-methylaniline,
1,3,5-trinitro-1,3,5-triazacyclohexane,
1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane, pentaerythritol
tetranitrate, glycerol trinitrate, ethylene glycol dinitrate, and
derivatives and combinations thereof. To aid in the detection of
trace concentrations, some embodiments include a target material
concentrator coupled to the cantilevered probe. These and other
embodiments also can include a selective coating disposed on at
least a portion of the cantilevered probe, the selective coating
being configured for selective adsorption of the target material.
In these and other embodiments, additional selectivity can be
achieved by fabricating multiple cantilevered probes in a
cantilevered probe array. In these arrays, at least two of the
cantilevered probes can be frequency-differentiated. For example,
at least one cantilevered probe can be tuned to an on-resonance
condition while at least one other cantilevered probe is tuned to
an off-resonance condition. Multiple cantilevered probes in a
cantilevered probe array, such as frequency-differentiated
cantilevered probes, can be connected in series.
[0014] Also disclosed are embodiments of a method of detecting a
target material, such as an explosive material. These embodiments
can include, for example, exposing a cantilevered probe to a
carrier including a target material such that the target material
is transferred onto the cantilevered probe. Some embodiments also
include heating the cantilevered probe, such as to a temperature
sufficient to cause the target material to undergo a phase change
or to a temperature sufficient to cause the target material to
deflagrate or ignite. These and other embodiments also can include
piezoelectrically detecting a movement of the cantilevered probe or
a property of the cantilevered probe, such as by generating an
electrical signal with a piezoelectric element connected to the
cantilevered probe. The same or another piezoelectric element also
can be used to piezoelectrically actuate a movement of the
cantilevered probe. In some embodiments, piezoelectric elements are
driven by a variable-frequency drive voltage, such as to isolate
the responses of frequency-differentiated cantilevered probes.
[0015] In some disclosed embodiments, the movement of the
cantilevered probe or a change in the property of the cantilevered
probe is caused by transferring the target material onto the
cantilevered probe. Some disclosed embodiments also include causing
the target material to undergo a phase change or a reaction. This
phase change or reaction also can cause the movement of the
cantilevered probe or a change in the property of the cantilevered
probe. Also among the movements and property changes that can be
piezoelectrically detected are resonant frequency shifts,
cantilever bending, thermal signatures, recoil responses,
pyroelectric charge generation, impedance shifts and temperature
shifts. Based on the movement of the cantilevered probe or a change
in the property of the cantilevered probe, some embodiments also
include identifying the target material. Identifying the target
material can involve comparing a cantilevered probe response to a
reference cantilevered probe response.
[0016] Also disclosed are embodiments of a method for making a
chemical detection system. These embodiments can include providing
a cantilevered probe, providing a probe heater thermally coupled to
the cantilevered probe, and providing a piezoelectric element
disposed on the cantilevered probe. In some of these embodiments,
providing the piezoelectric element includes depositing a
piezoelectric film on a surface of the cantilevered probe. These
and other embodiments also can include depositing a selective
coating on a surface of the cantilevered probe. More than one
cantilevered probe can be assembled to form a cantilevered probe
array.
[0017] Various embodiments are illustrated in part by the
accompanying drawings and the detailed description given below. The
drawings and the detailed description should not be taken to limit
the invention to the specific embodiments, but are for explanation
and understanding. Furthermore, the drawings are not drawn to
scale. The drawings and the detailed description are merely
illustrative of the invention rather than limiting, the scope of
the invention being defined by the appended claims and equivalents
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic diagram of a chemical detection system
for detecting at least one explosive material, in accordance with
some embodiments of the current invention;
[0019] FIG. 2 is a perspective view of a self-sensed cantilevered
probe array, in accordance with some embodiments of the current
invention;
[0020] FIG. 3 is a plan view of a pair of cantilevered probes with
probe heaters and piezoelectric detectors, in accordance with some
embodiments of the current invention;
[0021] FIG. 4 is a schematic diagram of a system for detecting an
explosive material, in accordance with some embodiments of the
current invention;
[0022] FIG. 5a, FIG. 5b and FIG. 5c are graphs showing
characteristic resonant frequencies of a cantilevered probe prior
to exposure to an explosive material, after exposure to the
explosive material, and after deflagration or ignition of the
explosive material, respectively, in accordance with some
embodiments of the current invention;
[0023] FIG. 6a, FIG. 6b and FIG. 6c are elevation views showing
characteristic bending of a cantilevered probe prior to exposure to
an explosive material, after exposure to the explosive material,
and after deflagration or ignition of the explosive material,
respectively, in accordance with some embodiments of the current
invention;
[0024] FIG. 7a, FIG. 7b and FIG. 7c are elevation views showing
bending and vibrations of a cantilevered probe prior to exposure to
an explosive material, after exposure to the explosive material,
and after deflagration or ignition of the explosive material,
respectively, in accordance with some embodiments of the current
invention;
[0025] FIG. 8a, FIG. 8b and FIG. 8c are graphs showing periodic
heating of a cantilevered probe prior to exposure to an explosive
material, during exposure to the explosive material, and after
deflagration or ignition of the explosive material, respectively,
along with a generated piezoelectric detector output signal, in
accordance with some embodiments of the current invention;
[0026] FIG. 9 is a plan view of an array of cantilevered probes
with an explosive material concentrator surrounding the
cantilevered probe array, in accordance with some embodiments of
the current invention;
[0027] FIG. 10 is a perspective view of a handheld system for
detecting an explosive material, in accordance with some
embodiments of the current invention; and
[0028] FIG. 11 is a flow chart of a method for detecting an
explosive material, in accordance with some embodiments of the
current invention.
DETAILED DESCRIPTION
[0029] The following terms may be abbreviated in this disclosure:
1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX),
1,3,5-trinitro-1,3,5-triazacyclohexane (RDX),
2,4,6,n-tetranitro-n-methylaniline (Tetryl), 2,4,6-trinitrotoluene
(TNT), atomic force microscopy (AFM), central processing unit
(CPU), deep reactive ion etching (D-RIE), digital signal processor
(DSP), ethylene glycol dinitrate (EGDN), field-programmable gate
array (FPGA), flexural plate wave oscillators (FPW), fast Fourier
transform (FFT), glycerol trinitrate (nitroglycerin), ion mobility
spectrometry (IMS), lead zircanate titinate (PZT), local area
network (LAN), micro-electrical-mechanical systems (MEMS),
pentaerythritol tetranitrate (PETN), quality (O), quartz crystal
microbalances (QCM), silicon-on-insulator (SOI), surface acoustic
wave devices (SAW), universal serial bus (USB), and wide area
network (WAN).
[0030] Unless otherwise explained, all technical and scientific
terms used herein have the same meaning as commonly understood by
one of ordinary skill in the art to which this disclosure belongs.
The singular terms "a," "an," and "the" include plural referents
unless context clearly indicates otherwise. Similarly, the word
"or" is intended to include "and" unless the context clearly
indicates otherwise. The terms "comprises" and "includes" are
equivalent. The same reference numerals are used throughout the
Figures to indicate similar or identical features. U.S. application
Ser. No. 10/967,748 is incorporated herein by reference.
[0031] Disclosed herein are embodiments of a chemical sensor,
embodiments of a method for making the disclosed chemical sensor
and embodiments of a method for sensing chemicals. Although not
limited by any particular advantages, the disclosed embodiments may
have one or more advantages over the prior art. Some disclosed
embodiments require detection surface areas that are orders of
magnitude smaller than the surface areas required by other types of
sensors. In addition, some embodiments are capable of operating in
several detection modes, such as mass loading and bending. Most
other sensors operate in only a single detection mode. Furthermore,
many of the disclosed embodiments can be mass-produced at
relatively low cost. For example, silicon cantilevered probes can
be manufactured using standard semiconductor manufacturing
equipment. Finally, some of the disclosed embodiments have
demonstrated superior detection sensitivities in comparison to at
least some conventional sensors.
[0032] FIG. 1 illustrates a chemical detection system 10 for
detecting one or more explosive materials 16 or other target
chemical species 12 also referred to as target materials, in
accordance with some embodiments of the present invention. As
shown, the chemical detection system 10 includes a cantilevered
probe 30, a probe heater 36 thermally coupled to the cantilevered
probe 30, and a piezoelectric element 32 disposed on the
cantilevered probe 30. The piezoelectric element 32 can be
configured to detect explosive material 16 adsorbed onto the
cantilevered probe 30, such as when the probe heater 36 heats the
cantilevered probe 30. In various embodiments, the piezoelectric
element 32 can provide a piezoelectric element output signal
related to, for example, a resonant frequency shift, cantilever
bending, a thermal signature, a recoil response, a pyroelectric
charge generation, an impedance shift, a temperature shift, or
combinations thereof. Throughout this disclosure, descriptions of
the adsorption of explosive material 16 or other target chemical
species 12 refer to the attachment or inclusion of such material
onto or into the cantilevered probe 30, whether by adsorption,
absorption, reaction, or any other form of attachment or
incorporation.
[0033] The explosive material 16 can include, for example,
2,4,6-trinitrotoluene (TNT), 2,4,6,n-tetranitro-n-methylaniline
(Tetryl), 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX),
1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX),
pentaerythritol tetranitrate (PETN), glycerol trinitrate
(nitroglycerin), ethylene glycol dinitrate (EGDN), derivatives
thereof, or combinations thereof.
[0034] The cantilevered probes 30 can be self-sensing. The chemical
detection system 10 can include multiple cantilevered probes 30
arranged in a cantilevered probe array 20. Each cantilevered probe
30 can have one or more suspended cantilevered element and one or
more associated piezoelectric element 32. The piezoelectric element
32 can include, for example, a deposited layer of piezoelectric
material, such as zinc oxide (ZnO), lead zircanate titinate (PZT),
aluminum nitride, a piezoelectric material, or a derivative or
combination thereof. The piezoelectric element 32 also can include
a pyroelectric material. The piezoelectric element 32 can be
configured to bend, deflect or vibrate the cantilevered element
when excited or actuated by an applied drive voltage. The
piezoelectric element 32 also can be configured to generate a
voltage as the associated cantilevered probe 30 bends, deflects or
vibrates. In this way, the piezoelectric element 32 can be
configured to sense movements of the associated cantilevered probe
30 such as shifts in bending, vibrations, or recoil and/or to
actuate movement of the associated cantilevered probe 30. Some
embodiments, however, include a separate piezoelectric drive
mechanism or other mechanism that drives the cantilevered probe
30.
[0035] As mentioned above, the cantilevered probe 30 may be part of
a cantilevered probe array 20. The cantilevered probes 30 in the
cantilevered probe array 20 may be frequency-differentiated such
that cantilevered probes having different effective masses or
effective spring constants exhibit different resonant frequencies.
The cantilevered probes 30 can be manufactured, for example, with
small differences in cantilever lengths, resulting in separations
in resonant frequencies that allow the resonant frequency of each
cantilevered probe in the cantilevered probe array 20 to be
detected with as few as two wires connected to the cantilevered
probe array 20. Thus, the cantilevered probe arrays 20 with two or
more cantilevered probes 30 can be packaged and connected to an
interface circuit 40 with a minimal number of bond pads,
interconnection traces and bond wires to external interface and
control electronics. The interface circuit 40, which can be coupled
to the cantilevered probe array 20, can be configured to actuate
and sense movement of the cantilevered probes 30. Parallel arrays
of cantilevered probes 30 can be configured with elements that
number from a few to a million or more cantilevered probes on one
substrate or die. Groups of cantilevered probe arrays 20 may be
connected, for example, during on-chip trace definition, while
being wire-bonded to a leadframe or package, or at the socket or
board level.
[0036] Non-overlapping, independent and orthogonal explosive and
chemical-sensing effects on individual cantilevered probes 30 in
the cantilevered probe array 20 may be desirable but not necessary
when many cantilevered probes 30 with various coatings and coating
thicknesses are used for detection. Signal processing and pattern
recognition of the resonance-frequency data from multiple
cantilevered probes 30 may be employed to differentiate between
various explosive materials and chemicals in varying concentrations
having sometimes small and sometimes null effects. Differentiation
between similar chemical substances can be made, and their
constituency and concentration can be determined, in a system where
a variety of selective coatings 34 are applied to multiple
cantilevered probes 30. These selective coatings 34, for example,
can be used to selectively adsorb different types of chemicals-onto
the cantilevered probes 30. The selective coating 34 can be
positioned on or around one or more of the cantilevered probes 30
of a cantilevered probe array 20, such as one or more cantilevered
probes 30 with or without probe heaters 36, to provide, for
example, two or more differentiable output signals for identifying
the target chemical species 12.
[0037] The chemical detection system 10 can be configured to detect
one or more target chemical species 12, such as mercury, hydrogen,
an alcohol, water vapor, an explosive material, a chemical element,
a chemical compound, an organic material, an inorganic material, a
gaseous substance, a liquid, a biological material, a DNA strand, a
bioactive agent, a toxin, or derivatives or combinations thereof.
Throughout this disclosure, the target chemical species 12 can be
any chemical, biological, or explosive material targeted for
detection.
[0038] Typically, one or more cantilevered probes 30 can be
configured to respond when exposed to the explosive material 16.
For example, the cantilevered probes 30 may respond when absorbing,
adsorbing, or otherwise reacting to the explosive material 16
and/or other target chemical species 12. When the cantilevered
probe array 20 is exposed to the explosive material 16 and is
actuated by the interface circuit 40, one or more of the
cantilevered probes 30 in the cantilevered probe array 20 may
exhibit a response, such as a shift in bending, a change in a
resonant frequency, an impedance shift, or a shift in temperature.
When exposed to the explosive material 16 or other target chemical
species 12, the cantilevered probes 30 also may increase or
decrease in mass, or become more or less rigid. These and other
responses may result in the generation of a piezoelectric element
output signal.
[0039] In one example, the cantilevered probe 30 comprises a
patterned layer of gold. When exposed to mercury, the gold and
mercury react to form an amalgam. The gold-mercury amalgam adds
mass to the cantilevered probe 30 and therefore tends to decrease
the resonant frequency of the cantilevered probe 30. Amalgam
formation, however, also increases the mechanical stiffness of the
cantilevered probe 30, thereby increasing its natural resonant
frequency. These two effects tend to cancel each other, though one
effect can be made dominant by careful selection and placement of a
chemical-sensitive selective coating 34 on the cantilevered probe
30.
[0040] In one exemplary detection mode, the adsorbed explosive
material 16 deflagrates or ignites when heated by a probe heater 36
to cause an exothermic reaction, which in turn causes a
piezoelectric output signal to be generated by a piezoelectric
element 32. For example, the piezoelectric element 32 may generate
an electrical charge when the probe heater 36 heats the
cantilevered probe 30. The piezoelectric element 32 also may detect
an increase in temperature of the cantilevered probe 30 when the
exothermic reaction occurs. Alternatively, the explosive material
16 may melt or evaporate when the probe heater 36 heats the
cantilevered probe 30 and the phase transformation may be detected
with the piezoelectric element 32. Alternatively, the explosive
material 16 may be detected by an impedance shift of the
piezoelectric element 32 when the probe heater 36 heats the
cantilevered probe 30. The reactive portion, the resistive portion
or a combination of both may shift in response to heating of the
cantilevered probe 30.
[0041] In some embodiments, the piezoelectric characteristics of
the piezoelectric element 32 may detect a shift in bending of the
cantilevered probe 30 as the explosive material 16 is adsorbed onto
a surface of the cantilevered probe 30, is desorbed from the
cantilevered probe 30, or reacts exothermically on the cantilevered
probe 30. For example, as the explosive material 16 accumulates on
the cantilevered probe 30, the cantilevered probe 30 may bend
upwards or downwards depending on the stress state of the added or
removed material. Alternatively or in conjunction, the
piezoelectric element 32 may detect a shift in a resonant frequency
of the cantilevered probe 30 when the explosive material 16 is
adsorbed onto the cantilevered probe 30, is desorbed from the
cantilevered probe 30, or reacts exothermally on the cantilevered
probe 30. For example, as the explosive material 16 accumulates on
the cantilevered probe 30, the resonant frequency may decrease due
to the additional mass loading. Similarly, as the explosive
material 16 desorbs or is otherwise removed, the resonant frequency
may return towards its previous condition prior to mass loading.
The effects described above may occur in various combinations.
Analysis of one or a multiplicity of these effects may be used to
identify an explosive or a non-explosive material absorbed onto
cantilevered probe 30.
[0042] The probe heater 36, a piezoresistor serving as a
temperature sensor, the piezoelectric element 32, or another
on-board temperature sensor may be used to indicate the temperature
of the cantilevered probe 30, from which the ignition temperature
or deflagration temperature of the explosive material 16 may be
determined. Alternatively, an onboard temperature sensor may be
used to determine the heat of vaporization, melting temperature,
phase change, chemical reactions, exothermic reactions, endothermic
reactions, or time dependencies thereof associated with the
explosive material 16 or other target chemical species 12 to aid in
the identification.
[0043] As discussed above, one or more selective coatings 34 may be
disposed on one or more cantilevered probes 30 in the cantilevered
probe array 20 to facilitate chemical detection and specificity.
For example, one or more cantilevered probes 30 in the cantilevered
probe array 20 may be coated, uncoated, or otherwise treated to
detect the explosive material 16. The selective coating 34 may be
applied to a portion of one or more of the cantilevered probes 30
in the cantilevered probe array 20. For example, the selective
coating 34 may be applied to the topside or bottom side of one or
more of the cantilevered probes 30 or to portions thereof. The
selective coating 34 can include, for example, an epoxy resin such
as Novolac.TM., a fluoropolymer such as FluoroPel.TM., a gold
layer, a palladium layer, an alcohol-absorbent polymer, a
water-absorbent material, a chemical-sensitive polymer, a
chemical-sensitive layer, a biosensitive material, a thiol, or
derivatives or combinations thereof.
[0044] Various application methods can be used to deposit or apply
the selective coating 34 and to otherwise treat surfaces of the
cantilevered probes 30. The selective coatings 34 can comprise, for
example, a dipped coating, a sprayed coating, or a dispensed
coating disposed on at least a portion of one or more of the
cantilevered probes 30. An exemplary chemical-sensitive selective
coating 34 includes a masked coating disposed on a portion of one
or more of the cantilevered probes 30. In an alternative
application method, a non-homogeneous coating material is applied
to a set of cantilevered probes 30 in the cantilevered probe array
20, such that constituents of the non-homogeneous coating material
are deposited on the cantilevered probes 30 with suitable
variations in composition, coverage, and/or thickness.
[0045] In some disclosed embodiments, the chemical detection system
10 includes one or more reference cantilevered probes 30r in the
cantilevered probe array 20. The reference cantilevered probe 30r
can provide a reference cantilevered probe response when the
cantilevered probe array 20 is exposed to the explosive material 16
or other target chemical species 12. The reference cantilevered
probes 30r can be formed, for example, with no coating materials
disposed thereon to reduce or eliminate sensitivity to the
explosive material 16 or other target chemical species 12.
Alternatively, the reference cantilevered probes 30r can have an
inert coating disposed on their surface to reduce or eliminate
sensitivity to the explosive material 16. Alternatively, one or
more reference cantilevered probes 30r can be mechanically isolated
from exposure to the explosive material 16 while other portions of
the cantilevered probe array 20 are exposed.
[0046] The explosive material 16, which may be located in a liquid
or gas carrier 14, such as air, water, low-pressure gas, or plasma,
can be transported in a forced or free manner towards the
cantilevered probes 30. Once the explosive material 16 makes
contact with surfaces of the cantilevered probes 30 it may invoke,
for example, shifts in resonant frequency, Q factor, impedance,
phase, or deflection amplitudes. Impedance shifts may be obtained,
for example, by absorbing explosive material 16 or other target
chemical species 12 directly into the bulk of a piezoelectric or
pyroelectric film of the piezoelectric element 32. The absorption
may be enhanced, for example, by increasing the periphery of
unpassivated sidewalls, such as with narrow line widths and small
spaces between multiple segments of the piezoelectric element
32.
[0047] The cantilevered probe array 20 may be actuated with an
excitation voltage applied to a piezoelectric drive mechanism
serving optionally as the piezoelectric element 32 disposed on each
of the cantilevered probes 30 in the cantilevered probe array 20.
To reduce the number of external pads and connections, a group of
cantilevered probes 30 may be connected in series and electrically
connected to a pair of cantilevered probe array drive pads 24,
which may be electrically connected to an interface circuit 40.
While this configuration can increase the series resistance of the
string, differentiation of individual cantilevered probes 30 may be
made by detection of signals at or near the resonant frequency of
the selected cantilevered probes 30. Alternatively, a group of
cantilevered probes 30 may be connected in parallel and
electrically connected to a pair of cantilevered probe array drive
pads 24, increasing the effective capacitance and decreasing the
effective resistance, while still allowing differentiation of
individual cantilevered probe responses based on frequency.
Alternatively, cantilevered probes 30 may be connected in a network
of series-connected and parallel-connected cantilevered probes with
frequency-identifiable addressable elements.
[0048] The interface circuit 40 can provide excitation voltages for
piezoelectric material on the cantilevered probes 30 and sense
deflections and vibrations of the cantilevered probes 30 with the
same or a different piezoelectric material. In one example, the
interface circuit 40 includes an adjustable frequency generator
that is scanned through a predetermined frequency range to excite
one or more of the cantilevered probes 30 in the cantilevered probe
array 20. In another example, the interface circuit 40 includes an
impedance analyzer that is scanned through a resonant frequency of
at least one cantilevered probe 30, measuring the magnitude and
phase from the cantilevered probes 30 and monitoring for any
variations in impedance as the cantilevered probes 30 are exposed
to one or more explosive materials 16. In another example, the
interface circuit 40 includes an oscillator circuit operating at a
resonant frequency of at least one cantilevered probe 30 in the
cantilevered probe array 20.
[0049] In another example, the interface circuit 40 includes an
oscillator circuit operating at a predetermined frequency that is
near, yet off-resonance with respect to one or more of the
cantilevered probes 30 in the cantilevered probe array 20. This
configuration may result in the generation of higher amplitudes of
vibration and therefore higher output signals as the resonant
frequency of the selected cantilevered probe 30 shifts and moves
towards the predetermined frequency. The predetermined frequency
may be set, for example, slightly above or slightly below the
resonant frequency of one or more of cantilevered probes 30.
[0050] In another example, the amplitude of bending and/or
vibration is monitored as the cantilevered probe 30 strikes against
a fixed or adjustable mechanical stop such as a piezoelectric slab
or a piezotube. In another example, the interface circuit 40
includes an impulse circuit for applying an electrical impulse to
the cantilevered probe array 20, and the ring-down of the
cantilevered probes 30 is monitored. In another example, noise,
such as pink noise or white noise, is applied to excite the
cantilevered probe array 20. In some embodiments, the interface
circuit 40 includes a network analyzer for detecting signals from
the cantilevered probe array 20. The interface circuit 40 or a
controller 50 may include a fast Fourier transform generator to
perform a fast Fourier transform (FFT) on the shifted cantilevered
probe response, and to provide respective frequencies of the
cantilevered probes 30 in the cantilevered probe array 20, which
can be correlated with previously measured probe responses and used
to identify the explosive material 16 and/or other target chemical
species 12.
[0051] As discussed above, the chemical detection system 10 may
include an interface circuit 40 electrically coupled to a
piezoelectric element 32 that enables the detection of an explosive
material 16 and/or a target chemical species 12. The interface
circuit 40 may contain, for example, the piezoelectric element 32
as a bridge element in an AC bridge circuit. The AC bridge circuit
may be tuned to an on-resonance condition or on off-resonance
condition to detect the explosive material 16. In operation, the
output of the AC bridge circuit may shift as the resonant frequency
of the cantilevered probe 30 moves off-resonance with the addition
or subtraction of mass. Alternatively, the output of the AC bridge
circuit may shift as the resonant frequency of the cantilevered
probe 30 moves towards the off-resonance tuned condition.
Off-resonance tuning can allow any signals generated by the
piezoelectric element 32 to be distinguished from any output due to
vibrations of the cantilevered probe 30. In some embodiments, one
or more of the cantilevered probes 30 in the cantilevered probe
array 20 are tuned to an on-resonance condition, and one or more
other cantilevered probes 30 in the cantilevered probe array 20 are
tuned to an off-resonance condition to detect the explosive
material 16.
[0052] The interface circuit 40 may detect shifted cantilevered
probe responses from one or more actuated cantilevered probes 30 in
the cantilevered probe array 20. Examples of shifted cantilevered
probe responses include a shift in a resonant frequency of one or
more of the cantilevered probes 30, a shift in a quality (Q) factor
of one or more of the cantilevered probes 30, a shift in impedance
of one or more of the cantilevered probes 30, a shift in phase of
one or more of the cantilevered probes 30, a shift in deflection
amplitude of one or more of the cantilevered probes 30, and
combinations thereof. With exposure to the explosive material 16 or
other target chemical species 12, one or more cantilevered probes
30 in the cantilevered probe array 20 can exhibit shifts in various
properties. Similarly, with exposure to more than one explosive
material 16 or other target chemical species 12, one or more
cantilevered probes 30 in the cantilevered probe array 20 may
exhibit shifts from which multiple explosive materials 16 and/or
other target chemical species 12 can be determined.
[0053] A controller 50 such as a central processing unit (CPU), a
digital signal processor (DSP), a microcontroller, or a
field-programmable gate array (FPGA) may be included in the
chemical detection system 10 to execute programmed code and provide
monitoring, controlling and analyzing functions. The controller 50
can be in electrical communication with the interface circuit 40
and may be located, for example, on a substrate 22 along with the
cantilevered probe array 20, within an enclosure 60 on the same
circuit board or in the same package as the cantilevered probe
array 20, or located remotely with respect to the enclosure 60. The
controller 50 may internally contain the functions and capabilities
of the interface circuit 40. The controller 50 may receive shifted
cantilevered probe responses from a set of one or more of the
cantilevered probes 30 in the cantilevered probe array 20.
[0054] The explosive material 16 and other target chemical species
12 may be determined based on the shifted cantilevered probe
response using, for example, an algebraic model that relates shifts
in cantilevered probe responses to explosive materials and
concentration. Alternatively, the explosive material 16 may be
determined based on a comparison between the shifted cantilevered
probe responses and a reference set of cantilevered probe
responses. Such reference sets can be obtained by exposing the
cantilevered probes 30 to controlled environments with known
explosive materials and concentrations during calibration at the
factory or on site. The controller 50 can determine one or more
explosive material 16, for example, through pattern recognition
techniques, statistical processes, or fuzzy logic with comparison
to the reference set of cantilevered probe responses. The reference
set of cantilevered probe responses can comprise, for example, a
learned set obtained from shifts in cantilevered probe responses by
cantilevered probes 30 that have been exposed to known explosive
materials and concentrations under controlled laboratory or factory
environments.
[0055] In some embodiments, heating of select cantilevered probes
30 burns off, evaporates off, or otherwise cleans and resets the
cantilevered probe 30 to a nascent condition. In these and other
embodiments, the probe heater 36 may be coupled to at least one
cantilevered probe 30 in the cantilevered probe array 20. The probe
heater 36 may be formed, for example, with a resistive layer
disposed on the surface of or formed within the cantilevered probe
30, such as by ion implantation. Exemplary probe heaters 36, which
may be connected in series or parallel or individually connected,
can be formed on one, several, or all of the cantilevered probes 30
within the cantilevered probe array 20. The probe heaters 36 also
may be used to react the explosive material 16 on the cantilevered
probe 30 by heating the probe to a predetermined temperature where
the reaction can occur. Alternatively, the probe heaters 36 may be
used to ignite or deflagrate condensate of explosive vapors on the
cantilevered probes 30. The probe heater 36 can comprise, for
example, a resistive or a piezoresistive element formed in one or
more of the cantilevered probes 30 or a heater element, such as a
patterned metal film, disposed on a surface of the cantilevered
probe 30.
[0056] The piezoelectric element 32, which may also serve as a
piezoelectric drive mechanism, can comprise, for example, zinc
oxide, lead zircanate titanate, aluminum nitride, a piezoelectric
material, or derivatives or combinations thereof. The piezoelectric
element 32 also can comprise a pyroelectric material. Piezoelectric
materials typically expand or contract when driving voltages are
applied, and conversely generate a voltage when stressed or
compressed. Piezoelectric materials are generally pyroelectric, in
that a pyroelectric charge, voltage or current is generated when
the material is heated. For example, the piezoelectric element 32
may generate a piezoelectric element output signal when the
explosive material 16 in proximity to the piezoelectric element 32
ignites, deflagrates or otherwise generates heat. In some
embodiments, the piezoelectric element 32 serves simultaneously as
a piezoelectric thermal detector and a piezoelectric drive
mechanism to drive and excite the cantilevered probe 30, such as
into resonance. In other embodiments, the piezoelectric element 32
is separated from a piezoelectric drive mechanism, such as a
piezoelectric drive mechanism that also is located on a surface of
cantilevered probe 30.
[0057] The chemical detection system 10 may contain one or more
cantilevered probe arrays 20 in an enclosure 60, which may include
an inlet port 62 and an outlet port 64 for transport of the
explosive material 16, the target chemical species 12, and the
carrier 14. The explosive material 16 may enter the enclosure 60
through the inlet port 62 and be exposed to the cantilevered probe
array 20. The explosive material 16 or byproducts thereof may exit
through the outlet port 64. The enclosure 60 also may include
filters, scrubbers, and other media treatment elements to aid in
the detection of the explosive material 16.
[0058] A transport mechanism 66 such as a pump or a fan with
ductwork or piping may be included for transporting the explosive
material 16 to the cantilevered probe array 20. The chemical
detection system 10 also may include an explosive material
concentrator 68 coupled to one or more of the cantilevered probes
30. The concentrator 68, such as a pressurizing system or a
condenser and heater system, may be included to concentrate the
explosive material 16 and/or other target chemical species 12
proximal to the cantilevered probe array 20 to facilitate
detection. In some embodiments, the explosive material 16 is
concentrated on one or more cantilevered probes 30 when the
concentrator 68 is locally heated.
[0059] The chemical detection system 10 may include a thermally
conductive mesh 58 such as a copper screen or a metal mesh
substantially surrounding the cantilevered probes 30 to limit the
egression of thermal energy, such as from an exothermic reaction.
As the explosive material 16 deflagrates, ignites or otherwise
burns, hot air may be generated near the cantilevered probe 30. The
thermally conductive mesh 58 may facilitate cooling of the hot air
and otherwise limit heat transfer away from the cantilevered probes
30, such as beyond the enclosure 60.
[0060] The chemical detection system 10 may be connected to a local
area network (LAN), a wide area network (WAN), the Internet, or
other networked communication system via one or more wired or
wireless connections. The chemical detection system 10 may be
installed, for example, into an air handling system of a building
or airport that has many inlets, into a standalone unit with a
portal for chemical detection, or into a handheld unit for portable
use. Moreover, the chemical detection system 10 may be installed in
shipping containers and crates during storage and transit for
chemical detection and monitoring.
[0061] FIG. 2 illustrates a self-sensed cantilevered probe array,
in accordance with some embodiments of the present invention. As
shown, the self-sensed cantilevered probe array 20 includes a
plurality of cantilevered probes 30 on a substrate 22. The
cantilevered probes 30 can include piezoelectric elements 32, probe
heaters 36, and/or chemical-sensitive selective coatings 34.
Variations in length or thickness of the cantilevered probes 30 and
variations in the thickness and coverage of the applied coatings
may allow for frequency differentiation between the cantilevered
probes 30 within the cantilevered probe array 20.
[0062] The cantilevered probes 30 may have a rectangular shape,
though other shapes may be suitably used, such as pointed
cantilevers, V-shaped cantilevers, triangular-shaped cantilevers,
dual-arm cantilevers, or balanced cantilevers. The cantilevered
probes 30 may be arranged and attached to the substrate 22 in an
array in which the cantilevered probes are all identical, all
different, or combinations thereof.
[0063] In some embodiments, the cantilevered probe array 20 is
actuated with an excitation voltage applied to a piezoelectric
element 32 that serves as a piezoelectric drive mechanism and as a
piezoelectric sense mechanism. In one example, the cantilevered
probes 30 are series-connected to a pair of cantilevered probe
array drive pads 24 on the substrate 22. The cantilevered probes 30
also can be parallel connected to the pair of cantilevered probe
array drive pads 24. The cantilevered probe array 20 also can
comprise a network of series-connected and parallel-connected
cantilevered probes that connect electrically to the pair of
cantilevered probe array drive pads 24. More than one group or
array of cantilevered probes 30 may be included on the substrate
22. Additional connections with associated pads may be made to the
piezoelectric elements 32 on particular cantilevered probes 30. The
substrate 22 also may have through-wafer vias for backside
connection to the drive pads 24.
[0064] The substrate 22 can include a semiconductor substrate such
as a silicon wafer, a silicon-on-insulator (SOI) wafer, a glass
substrate, or other suitable substrate for forming the cantilevered
probes 30 thereon. The cantilevered probes 30 can comprise
materials such as silicon, polysilicon, silicon nitride, zinc
oxide, aluminum nitride, metals, pyroelectric materials,
piezoelectric materials, or derivatives or combinations thereof.
These materials can be present in various forms, such as sheets,
films and layers. For example, a zinc oxide, PZT or aluminum
nitride film can be deposited on a layer of single-crystal silicon,
patterned, and etched. Conductive layers for top and bottom
electrodes, interconnections, and probe heater connections then can
be deposited and etched accordingly. The cantilevered probes 30 can
be defined with a photomask and associated lithographic sequences
along with deep reactive ion etching (D-RIE) or anisotropic etching
of the cantilevers and substrate. This allows the formation and
freeing of the silicon cantilevers with interconnected ZnO
electrodes in series, parallel, or series-parallel configurations.
Excitation and detection of the cantilevers can occur with voltages
applied to the piezoelectric material. The piezoelectric elements
32 may be formed with deposition and patterning processes as are
known in the art. The probe heaters 36 on the cantilevered probes
30 can be formed, for example, by selectively implanting portions
of the cantilevered probe 30 or by depositing, patterning and
etching a metal film on the cantilevered probe 30.
[0065] A chemical-sensitive selective coating 34 may be applied to
at least a portion of one or more of the cantilevered probes 30.
The chemical-sensitive coating 34 can include a material, such as
an epoxy resin, a fluoropolymer, gold, palladium, an
alcohol-absorbent polymer, a water-absorbent material, a
chemical-sensitive polymer, a chemical-sensitive material, a
biosensitive material, a thiol, or derivatives or combinations
thereof. The chemical-sensitive selective coating 34 may be
applied, for example, with techniques such as dipping, spraying, or
dispensing the coating on at least a portion of one or more of the
cantilevered probes 30. The chemical-sensitive coating material may
be applied onto a portion of one or more of the cantilevered probes
30 with the use of stencil masks or photomasks and
photolithographic patterning techniques. The chemical-sensitive
selective coating 34 may be applied in conjunction with
photolithographic patterning, for example, using standard
sputtering and other deposition techniques known in the art.
[0066] Multiple masking sequences can be used to apply multiple
coating materials. Alternatively, multiple-component
chemical-sensitive selective coatings 34 may be used. The
multiple-component chemical-sensitive selective coatings 34 can
comprise, for example, non-homogeneous coating materials, which can
be applied in such a way that variations in coating thickness
and/or composition occur when the materials are deposited.
[0067] When exposed to the explosive material 16 or to the target
chemical species 12, one or more of the cantilevered probes 30 in
the cantilevered probe array 20 may undergo an electrical or a
mechanical shift, such as a shifted resonant frequency, a shifted Q
factor, a shifted impedance, a shifted phase, or a shifted
deflection amplitude. The cantilevered probe array 20 may include
one or more reference cantilevered probes 30r to provide a
reference cantilevered probe response when the cantilevered probe
array 20 is exposed to the explosive material 16 or to the target
chemical species 12. The reference cantilevered probes 30r may be
uncoated, coated with an inert material, or otherwise protected
from exposure to the explosive material 16 and the target chemical
species 12.
[0068] FIG. 3 is a plan view of a pair of cantilevered probes 30
with probe heaters 36 and piezoelectric elements 32 for detecting
an explosive material, in accordance with some embodiments of the
present invention. As shown, one or more probe heaters 36 are
disposed on or formed in the cantilevered probes 30. The probe
heater 36 heats the cantilevered probes 30, for example, to
initialize the cantilevered probes 30 prior to exposing the
cantilevered probe array 20 to the explosive material. The probe
heaters 36 also can be used to burn off, deflagrate, or otherwise
react an explosive material that is adsorbed onto a surface of the
cantilevered probe 30.
[0069] The piezoelectric elements 32, which may also serve as
piezoelectric drive mechanisms for the cantilevered probes 30, can
be configured to detect an explosive material adsorbed onto the
cantilevered probe 30 when the cantilevered probe 30 is heated by
the probe heater 36 to cause, for example, an exothermic reaction.
In one example, the piezoelectric element 32 generates a
piezoelectric element output signal when the probe heater 36 heats
the adsorbed explosive material and an exothermic reaction or a
phase change occurs. In another example, the piezoelectric element
32 detects an increase in temperature of the cantilevered probe 30
when an exothermic reaction occurs. In another example, the
piezoelectric element 32 detects a shift in bending of the
cantilevered probe 30 when the explosive material is adsorbed onto
the cantilevered probe 30, is desorbed from the cantilevered probe
30, or reacts exothermically on the cantilevered probe 30. In
another example, the piezoelectric element 32 detects a shift in a
resonant frequency of the cantilevered probe 30 when the explosive
material is adsorbed, is desorbed or exothermically reacts. In
another example, the piezoelectric element 32 detects an impedance
shift when the explosive or non-explosive material is adsorbed, is
desorbed or exothermically reacts.
[0070] As show in FIG. 3, the cantilevered probe 30 can include a
base end 26 and a tip 28. The cantilevered probe array 20 may be
attached to a common base such as a substrate 22. The cantilevered
probe 30 may have a rectangular shape, although other shapes may be
suitably used, such as pointed shapes, V-shapes, triangular-shapes,
or dual-arm shapes. A treated portion, such as the selective
coating 34 disposed on at least a portion of the cantilevered probe
30, may aid in discriminating between various explosive materials
and other target chemical species 12. In some embodiments, the
cantilevered probe 30 is attached at each end, with the center of
the cantilevered probe 30 free to vibrate. In another embodiment,
the cantilevered probe 30 is attached on all sides in a diaphragm
or membrane configuration.
[0071] A drive mechanism, such as the piezoelectric element 32
serving as a piezoelectric drive mechanism or a separate
piezoelectric drive element, can be coupled to the cantilevered
probe 30. The piezoelectric element 32 and/or the drive mechanism
may comprise, for example, a patterned thin film of zinc oxide, PZT
or aluminum nitride on a surface of the cantilevered probe 30. A
sense mechanism may also be coupled to the cantilevered probe 30.
The sense mechanism may comprise, for example, a piezoresistor
attached to or formed in the cantilevered probe 30.
[0072] The probe heater 36 can be coupled to the cantilevered probe
30. The probe heater 36 can comprise, for example, a probe heater
formed in or on the cantilevered probe 30. In addition to
initiating an exothermic reaction or a phase change, the probe
heater 36 may be used to heat the cantilevered probe 30 to an
elevated temperature that initializes or re-initializes the treated
portion or the selective coating 34. Alternatively, an external
probe heater such as a heat lamp or a hot gas system may be used to
heat and re-initialize the cantilevered probe 30. Chemical
re-initialization may be accomplished, for example, by using
cleaning processes or by reversing any chemical reactions that
occurred on the treated portion.
[0073] Multiple cantilevered probes 30 may be arranged in a
cantilevered probe array 20, the cantilevers being all identical,
all different, or some combination thereof. The cantilevered probes
30 of a cantilevered probe array 20 may be driven and sensed, for
example, with a piezoelectric drive element coupled to each
cantilevered probe 30. In one embodiment, the piezoelectric
elements in the array are connected in series. The series-connected
piezoelectric elements in the array may be driven with as few as
two electrical connections to the piezoelectric element array.
Scanning the drive voltage through a range of frequencies can
excite and sense one cantilevered probe 30 at a time, allowing
interrogation of any cantilevered probe 30 in the array while
minimizing the number of electrical connections required. In
another configuration, the piezoelectric elements in the array are
connected in parallel, such that as few as two electrical
connections may be used to drive and sense cantilevered probes 30.
In this configuration, failure of one cantilevered probe 30 does
not prevent others from operating. In another configuration, the
array of piezoelectric elements is connected in a series-parallel
arrangement.
[0074] FIG. 4 is a schematic diagram of a system for detecting an
explosive material, in accordance with some embodiments of the
present invention. As shown, the chemical detection system 10
includes one or more cantilevered probes 30, one or more probe
heaters 36 thermally coupled to the cantilevered probes 30, and one
or more piezoelectric elements 32 disposed on the cantilevered
probes 30. A controller 50 and an interface circuit 40 may be
connected to one or more of the self-sensed cantilevered probes 30
configured in the self-sensed cantilevered probe array 20. The
controller 50, which can be connected to the interface circuit 40,
can be configured to drive and sense a plurality of self-sensed
cantilevered probes 30 in the cantilevered probe array 20. It
should be observed that, in some embodiments, the cantilevered
probe array 20 may be electrically connected to the interface
circuit 40 with as few as two cantilevered probe array drive pads
24. At least one cantilevered probe 30 in the cantilevered probe
array 20 may exhibit a shifted cantilevered probe response when the
cantilevered probe array 20 is exposed to an explosive material 16
or a target chemical species 12 and the cantilevered probe array 20
is actuated by the interface circuit 40. The piezoelectric element
32 can generate a piezoelectric element output signal that may be
analyzed by the controller 50.
[0075] The interface circuit 40 can be configured to actuate the
cantilevered probe array 20 with an excitation voltage applied to a
piezoelectric material such as piezoelectric element 32 disposed on
each cantilevered probe 30 in the cantilevered probe array 20. In
one example, the interface circuit 40 includes an adjustable
frequency generator that is scanned through a predetermined
frequency range. In another example, the interface circuit 40
includes an impedance analyzer that is scanned through a resonant
frequency of one or more cantilevered probes 30 in the cantilevered
probe array 20. In another example, the interface circuit 40
includes an oscillator circuit operating at a resonant frequency of
at least one cantilevered probe 30 in the cantilevered probe array
20. In another example, the interface circuit 40 includes an
oscillator circuit operating at a predetermined frequency that is
set to be off-resonance with respect to at least one cantilevered
probe 30 in the cantilevered probe array 20. In another example,
the interface circuit 40 includes control circuitry to monitor the
amplitude of bending and vibration as the cantilevered probe 30
strikes against a fixed or adjustable mechanical stop. In another
example, the interface circuit 40 comprises an impulse circuit for
applying an electrical impulse to all of the cantilevered probes 30
in the cantilevered probe array 20. In another example, the
interface circuit 40 or the controller 50 includes a fast Fourier
transform (FFT) generator to perform a fast Fourier transform on
the shifted cantilevered probe response. The interface circuit 40
can be configured to detect a shifted cantilevered probe response
from one or more actuated cantilevered probes 30, such as a shifted
resonant frequency, a shifted Q factor, a shifted impedance, a
shifted phase, or a shifted deflection amplitude.
[0076] The controller 50 may receive a shifted cantilevered probe
response from a set of one or more cantilevered probes 30 in the
cantilevered probe array 20. The explosive material 16 or other
target chemical species 12 may be determined, for example, based on
the shifted cantilevered probe response. For example, the explosive
material 16 may be determined based on a comparison between the
shifted cantilevered probe response and a reference set of
cantilevered probe responses. The reference set of cantilevered
probe responses can comprise, for example, a learned set obtained
during the calibration of the chemical-sensing system or from a
statistical database of cantilevered probe responses.
[0077] To cancel out common mode effects such as temperature, one
cantilevered probe 30 in the cantilevered probe array 20 may be a
reference cantilevered probe 30r, wherein the reference
cantilevered probe 30r provides a reference cantilevered probe
response when the cantilevered probe array 20 is exposed to the
explosive material 16 or the target chemical species 12.
[0078] In some embodiments, the explosive material 16 and/or other
target chemical species 12 are adsorbed onto the cantilevered probe
30 by exposing the cantilevered probe 30 to an environment
containing the explosive material 16 and/or the other target
chemical species 12. To increase the rate of adsorption, transport
mechanisms and concentrators may be added to the chemical detection
system 10.
[0079] Using heat generated by the onboard probe heater 36 or an
external probe heater thermally coupled to the cantilevered probe
30, the adsorbed explosive material 16 may ignite, deflagrate or
otherwise burn. The chemical detection system 10 may include a
thermally conductive mesh 58 substantially surrounding the
cantilevered probes 30 to limit the egression of thermal energy
from an exothermic reaction. A piezoelectric element 32 disposed on
the cantilevered probe 30 can generate, for example, a
piezoelectric element output signal when an exothermic reaction
occurs. Alternatively or in addition, the piezoelectric element 32
may also serve as a piezoelectric drive mechanism and a
piezoelectric sense mechanism that senses the explosive material 16
by detecting bending or shifts in a resonant frequency of the
cantilevered probe 30.
[0080] Detection of a non-explosive material or other target
chemical species 12 adsorbed onto a surface of the cantilevered
probe 30 may be accomplished, for example, using characteristic
bending shifts, frequency shifts, exothermic or non-exothermic
reaction indicators, phase change indicators, impedance shifts, or
a combination thereof. Specificity and delineation of the explosive
material 16 and other target chemical species 12 may be increased
with selective coatings applied to one or more of the cantilevered
probes 30 in the cantilevered probe array 20.
[0081] FIG. 5a, FIG. 5b and FIG. 5c show characteristic resonant
frequencies of a cantilevered probe prior to exposure to an
explosive material, after exposure to the explosive material, and
after deflagration, ignition, or evaporation of the explosive
material, respectively, in accordance with some embodiments of the
present invention. An exemplary response of a cantilevered probe
with resonant frequency 90a is seen in FIG. 5a. As the explosive
material is adsorbed onto the cantilevered probe, the resonant
frequency decreases with mass loading indicated by shifted resonant
frequency 90b, as seen in FIG. 5b. After the explosive material
deflagrates, ignites, or otherwise desorbs from the cantilevered
probe, the response curve with resonant frequency 90c returns
towards the resonant frequency 90a, as seen in FIG. 5c. Time
dependencies of the frequency shifts prior to, during, or after
cantilevered probe heating may provide characteristics associated
with various absorbed and desorbed explosive and non-explosive
materials. Frequency shifts with the application of predetermined
cantilever heating profiles may also provide characteristic
signatures for the adsorbed materials.
[0082] FIG. 6a, FIG. 6b and FIG. 6c show characteristic bending of
a cantilevered probe prior to exposure to an explosive material,
after exposure to the explosive material, and after deflagration or
ignition of the explosive material, respectively, in accordance
with some embodiments of the present invention. In some
embodiments, the cantilevered probe 30 initially has a tip 28 that
is essentially straight, as seen in FIG. 6a. With exposure to and
adsorption of the explosive material 16 or other target chemical
species 12 onto a surface of the cantilevered probe 30, the probe
may remain neutral, bend upwards, or bend downwards depending on
the stress state of the cantilevered probe 30, with the tip 28
deflecting an amount equal to a displacement 92b, as seen in FIG.
6b. When the cantilevered probe 30 is heated with an onboard or
external probe heater, the explosive material 16 may deflagrate,
ignite, or otherwise desorb from the surface of the cantilevered
probe 30, allowing the cantilevered probe 30 to return towards the
initial, undeflected state with the tip 28 back in a neutral
position, as seen in FIG. 6c. It should be noted that localized
heating of the cantilevered probe 30 may contribute to beam
bending, as thermal gradients across the cantilever produce moments
that can cause bending.
[0083] FIG. 7a, FIG. 7b and FIG. 7c illustrate simultaneous bending
and vibration of a cantilevered probe prior to exposure to an
explosive material, after exposure to the explosive material, and
after deflagration or ignition of the explosive material,
respectively, in accordance with some embodiments of the present
invention. The cantilevered probe 30 vibrates at resonant frequency
90a about a neutral position prior to mass loading, as seen in FIG.
7a. With the addition of explosive material on the cantilevered
probe 30, the tip may deflect an average amount equal to a
displacement 92b while vibrating at a shifted or unshifted resonant
frequency 90b, as seen in FIG. 7b. After deflagration, ignition, or
desorption of the explosive material from the cantilevered probe
30, the tip may return towards the initial, undeflected state while
vibrating at a resonant frequency 90c, as seen in FIG. 7c.
[0084] FIG. 8a, FIG. 8b and FIG. 8c illustrate periodic heating of
a cantilevered probe prior to exposure to an explosive material,
during exposure to the explosive material, and after deflagration
or ignition of the explosive material, respectively, along with a
generated piezoelectric element output signal, in accordance with
some embodiments of the present invention. A piezoelectric element
may generate a relatively small peak during each periodic heating
cycle 94a of the cantilevered probe and return to a low level as
the cantilevered probe cools, as indicated by the piezoelectric
element output signal 96a in FIG. 8a. As the explosive material
deposits and is adsorbed onto the cantilevered probe, the
piezoelectric element output signal 96a replicates relatively small
peaks during each periodic heating cycle 94b, until sufficient
explosive material is adsorbed so that the explosive material
deflagrates and ignites or otherwise combusts, thereby generating a
high-level piezoelectric element output signal 96b corresponding to
the energy released by the exothermic reaction, as seen in FIG. 8b.
Other mechanisms such as melting or evaporation may provide
piezoelectric element output signals 96b with higher, lower, or
time-dependent characteristics different from that shown. As the
cantilevered probe cools down from the energy release, the
piezoelectric element output signal 96c generally decreases towards
a baseline with relatively small peaks coinciding with periodic
heating cycles 94c applied to the cantilevered probe, as indicated
in FIG. 8c. Heat pulses of the periodic heating cycles may be
tailored, for example, to allow the cantilevered probe to reach
characteristic melting, evaporation, and deflagration temperatures
associated with a given explosive material.
[0085] FIG. 9 illustrates an array of cantilevered probes with an
explosive material concentrator surrounding the cantilevered probe
array, in accordance with some embodiments of the present
invention. One or more selective coatings 34 are optionally applied
to the cantilevered probe array 20 having a plurality of
self-sensed cantilevered probes 30. In the example shown, the
cantilevered probes 30a, 30b, 30n are selectively coated with
selective coatings 34a, 34b, 34n, respectively. The reference
cantilevered probe 30r is shown with no coating.
[0086] In this example, the cantilevered probes 30a, 30b, 30n are
nominally the same size and thickness. Frequency differentiation
for this set of cantilevered probes can be achieved by varying the
area of the cantilevered probes that is covered by the coating.
Different amounts of selective coating material can be disposed on
each cantilevered probe, varying the effective mass of each
cantilevered probe and changing the resonant frequencies
accordingly. Piezoelectric elements 32a, 32b, 32n and probe heaters
36a, 36b, 36n on the cantilevered probes 30a, 30b, 30n and 30r,
respectively, may be coated, partially coated, or uncoated with the
selective coatings 34.
[0087] An explosive material concentrator 68 can be coupled to one
or more cantilevered probes 30. The concentrator 68, such as a
condenser and heater system, may be included to concentrate the
explosive material and/or other target chemical species 12 proximal
to the cantilevered probe array 20 for detection. In some
embodiments, the concentrator 68 with one or more heaters 68a, 68b,
68c and 68d surrounding the cantilevered probe array 20 is heated
after the explosive material is adsorbed thereon, increasing the
concentration of the explosive material in the vicinity of the
cantilevered probes 30 and allowing a higher adsorption rate of the
explosive material onto one or more of the cantilevered probes 30.
The heaters 68a, 68b, 68c and 68d that surround the cantilevered
probe array 20 can comprise, for example, discrete heaters,
integrated resistive heaters, or integrated circuitry.
[0088] FIG. 10 illustrates a handheld system for detecting an
explosive material, in accordance with some embodiments of the
present invention. As shown, the handheld system 70 includes an
enclosure 60, one or more cantilevered probes 30 within the
enclosure 60, probe heaters 36 thermally coupled to the
cantilevered probes 30, and piezoelectric elements 32 disposed on
the cantilevered probes 30. One or more of the cantilevered probes
30 in the cantilevered probe array 20 have probe heaters 36 to
locally heat selected cantilevered probes 30. Piezoelectric
elements 32 can be configured to detect an explosive material 16
adsorbed onto the cantilevered probes 30 when the probe heaters 36
heat the cantilevered probes 30.
[0089] In some embodiments, the piezoelectric element 32 also
serves as a piezoelectric drive and as a piezoelectric sense
mechanism. The piezoelectric element 32 can detect the explosive
material 16 adsorbed onto one or more of the cantilevered probes
30. One or more selective coatings 34 may be applied to one or more
of the cantilevered probes 30 in the cantilevered probe array 20.
An interface circuit 40 may be coupled to the cantilevered probe
array 20. The enclosure 60 can have an inlet port 62 to allow
ingression of the explosive material 16 into the enclosure 60 and
an outlet port 64 to allow egression of the explosive material 16
or a byproduct thereof from the enclosure 60. When the cantilevered
probe array 20 is exposed to the explosive material 16 and the
interface circuit 40 actuates the cantilevered probe array 20
during or after heating, one or more of the cantilevered probes 30
in the cantilevered probe array 20 may exhibit a response such as a
resonant frequency shift, a shift in bending, a thermal signature,
a recoil response such as an impulse followed by ring down, a
pyroelectric charge generation, an impedance shift, a temperature
shift, or a combination thereof.
[0090] The cantilevered probe array 20 may include a plurality of
cantilevered probes 30 that are frequency-differentiated. The
plurality of cantilevered probes 30 in the cantilevered probe array
20 may be electrically connected to a single pair of cantilevered
probe array drive pads, and one or more groups of cantilevered
probes 30 may be included within the enclosure 60.
[0091] The handheld system 70 may include a controller 50 in
communication with the interface circuit 40. The controller 50 can
be configured to receive a shifted cantilevered probe response and
piezoelectric element output signals from a set of cantilevered
probes 30 in the cantilevered probe array 20. The shifted
cantilevered probe responses and the piezoelectric element output
signals can be analyzed and used to determine the constituency and
concentration of the explosive material 16.
[0092] The cantilevered probe array 20 may include a reference
cantilevered probe 30r. The reference cantilevered probe 30r may
provide a reference cantilevered probe response when the
cantilevered probe array 20 is exposed to the explosive material 16
and the target chemical species 12.
[0093] The handheld system 70 may include a thermally conductive
mesh 58 such as a copper or metal screen substantially surrounding
cantilevered probes 30, such as to limit the egression of thermal
energy from an exothermic reaction when the probe heater heats the
cantilevered probe. The handheld system 70 also may include a
transport mechanism 66 such as a pump, fan or blower and ductwork
or piping for transporting the explosive material 16 and/or the
target chemical species 12 to the cantilevered probe array 20. The
handheld system 70 may include a concentrator 68 such as a
compressor or a condenser to concentrate the explosive material 16
proximal to one or more of the cantilevered probes 30 in the
cantilevered probe array 20. In some embodiments, one or more
heaters of the concentrator 68 are located near the cantilevered
probe array 20 so that the explosive material 16 is concentrated on
one or more of the cantilevered probes 30 when the concentrator 68
is locally heated to desorb the explosive material collected by the
concentrator 68.
[0094] Command and data entry input devices such as buttons,
keypads, or softkeys, can be incorporated to allow the selection of
functions and operation of the handheld system 70. Results of
measurements can be displayed on an output device, such as an LCD,
or communicated to another analysis system through a wired
communication port such as a universal serial bus (USB) port or
through a wireless communication protocol.
[0095] FIG. 11 is a flow chart of a method for detecting an
explosive material, in accordance with some embodiments of the
present invention. The chemical detection method can include
various steps to detect and identify one or more explosive
materials and/or target chemical species, such as with a
self-sensed cantilevered probe array that includes a piezoelectric
element disposed on one or more cantilevered probes in the
cantilevered probe array.
[0096] The cantilevered probes in the cantilevered probe array may
be frequency-differentiated, separated in the frequency domain such
that any one of the cantilevered probes can be measured
independently of the others using, for example, a frequency
generator, a frequency synthesizer, a controlled oscillator, or an
impedance analyzer when the cantilevered probes are configured in
series or in parallel with other cantilevered probes. The
cantilevered probe array includes, for example, at least two-series
connected cantilevered probes electrically connected to a pair of
cantilevered probe array drive pads. Alternatively, the
cantilevered probe array may include at least two
parallel-connected cantilevered probes electrically connected to a
pair of cantilevered probe array drive pads. Alternatively, the
cantilevered probe array may include a network of series-connected
and parallel-connected cantilevered probes electrically connected
to a pair of cantilevered probe array drive pads. One or more
groups of cantilevered probes may be connected to the same set of
cantilevered probe array drive pads or to a different set of
cantilevered probe array drive pads on the same substrate for
external connection to an interface circuit.
[0097] The cantilevered probe array may include one or more
selective coatings applied to one or more cantilevered probes in
the cantilevered probe array. Exemplary chemical-sensitive coating
materials include an epoxy resin, a fluoropolymer, a gold layer, a
palladium layer, an alcohol-absorbent polymer, a water-absorbent
material, a chemical-sensitive polymer, a chemical-sensitive layer,
a biosensitive material, a thiol, and derivatives and combinations
thereof. The selective coating can be applied, for example, by
standard deposition techniques such as sputter depositions,
electron beam depositions, or plasma-enhanced chemical vapor
depositions, or by dipping, spraying or dispensing the coating
material onto at least a portion of one or more cantilevered
probes. In another example, a chemical-sensitive selective coating
is applied to one or more cantilevered probes with a stencil mask
and the selective masking of one or more cantilevered probes. A
single material may be applied through the mask.
[0098] A plurality of chemical-sensitive coating materials may be
applied to a set of cantilevered probes in the cantilevered probe
array. For example, multiple masks may be used for multiple
coatings with different coating materials on selected portions of
one or more cantilevered probes. Alternatively, coating with
multiple materials through a single mask may be accomplished by
spraying a non-homogenous coating material onto a set of
cantilevered probes in the cantilevered probe array such that
cantilevered probes in the array are coated with differences in
coating constituency, thickness, or fraction of coverage.
[0099] A probe heater on or near the cantilevered probe can be
thermally coupled to at least one cantilevered probe, which may be
heated to initialize the cantilevered probe prior to exposing it to
the explosive material or to initiate an exothermal reaction. For
example, the probe heater can be used to locally heat the
cantilevered probe to an elevated temperature to evaporate, burn
off, or otherwise remove material from the surfaces of the
cantilevered probe.
[0100] The cantilevered probe array may be initialized, as seen at
block 100. Initialization of the array can be accomplished, for
example, by running a scan through the resonant frequencies of the
cantilevered probes in the cantilevered probe array to establish a
baseline or to ensure that all the cantilevered probes and the
interface electronics are functioning properly.
[0101] Explosive material can be exposed to and adsorbed onto one
or more cantilevered probes, as seen at block 102. For example, the
self-sensed cantilevered probe array can be exposed to an explosive
material. A valve and associated piping may be used to expose the
cantilevered probe array to the explosive material and a carrier.
The explosive material may be transported to the cantilevered probe
array using, for example, fans, blowers, or pumps to force flow of
the explosive material and a carrier gas or liquid onto the
cantilevered probe array. Convective processes or normal diffusive
processes due to concentration gradients may be used, for example,
to transport the explosive material to the cantilevered probe array
for detection.
[0102] An explosive material, such as 2,4,6-trinitrotoluene (TNT),
2,4,6,n-tetranitro-n-methylaniline (Tetryl),
1,3,5-trinitro-1,3,5-triazacyclohexane (RDX),
1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX),
pentaerythritol tetranitrate (PETN), glycerol trinitrate
(nitroglycerin), ethylene glycol dinitrate (EGDN) or derivatives or
combination thereof, can be adsorbed onto one or more cantilevered
probes in the cantilevered probe array.
[0103] The explosive material may be concentrated near or on the
cantilevered probe array. Concentration of the explosive material
may be accomplished, for example, with a compressor and a valve
system to increase the pressure in the vicinity of the cantilevered
probe array. A condenser and a heater may be used, for example, to
collect samples of the explosive material and then release the
explosive material in proximity to the cantilevered probe array. In
some embodiments, a concentrator with one or more heating elements
surrounding a cantilevered probe array is heated locally after an
explosive material is adsorbed thereon, increasing the
concentration of explosive material in the vicinity of the
cantilevered probes and allowing a higher adsorption rate of
explosive material onto one or more of the cantilevered probes.
[0104] The cantilevered probe can be heated to cause, for example,
an exothermic reaction or a phase change with the adsorbed
explosive material, as seen at block 104. The probe heaters coupled
to one or more cantilevered probes may be heated to react the
explosive material. The piezoelectric element may generate a
piezoelectric element output signal when the explosive material is
reacted. Alternatively, the reaction of the explosive material can
result in the volatile material being desorbed from a cantilevered
probe, which causes a shift in the resonant frequency of the
cantilevered probe due to its decreased mass. Alternatively, the
reaction of the explosive material may result in a formation of a
material on the surface of the cantilevered probe that increases
the vibrational stiffness of the cantilevered probe and produces a
frequency shift. Alternatively, reaction of the explosive material
may result in a stressed film on the surface of the cantilevered
probe that causes a static deflection of the cantilevered probe.
The static deflection can be measured, for example, with a tapping
mode where the cantilevered probe is tapped against a reference
surface at a fixed distance away from the cantilevered probe, or
with a tapping mode where the cantilevered probe is tapped against
an adjustable mechanical stop that is adjusted so the cantilevered
probe has a consistent amount of contact with the mechanical stop.
Alternatively, recoil of the cantilevered probe when the adsorbed
explosive material is ignited or deflagrated may produce an impulse
response with a ring-down characteristic to identify the event.
[0105] A piezoelectric element output signal can be detected, as
seen at block 106. The piezoelectric element output signal
generated by the piezoelectric element can be detected, for
example, with an analog-to-digital converter or a threshold
detector. To validate the measurement, additional cantilevered
probe responses may be detected. A cantilevered probe response may
be detected, for example, from at least one self-sensed
cantilevered probe in the cantilevered probe array by actuating one
or more cantilevered probes.
[0106] In some embodiments, an exposed cantilevered probe array is
actuated by applying an excitation voltage to a piezoelectric
material disposed on each cantilevered probe in the cantilevered
probe array. The exposed cantilevered probe array can be actuated
with a signal generator or a frequency generator by scanning the
cantilevered probes through a predetermined frequency range,
allowing the resonant frequencies of one or more cantilevered
probes to be determined. In another example, the exposed
cantilevered probe array is actuated by driving the exposed array
at a resonant frequency of one cantilevered probe in the
cantilevered probe array, then switching as desired to a resonant
frequency of another cantilevered probe for additional
measurements. In another example, the exposed cantilevered probe
array is actuated by driving the exposed array at a predetermined
frequency, wherein the predetermined frequency is off-resonance
with respect to at least one cantilevered probe in the cantilevered
probe array. In another example, the amplitude of vibration is
controlled as the cantilevered probe strikes against a fixed or
adjustable mechanical stop. In another example, the exposed
cantilevered array is actuated with an electrical impulse applied
to the cantilevered probe array.
[0107] The piezoelectric element output signal can be analyzed, as
seen at block 108. Analyzing the piezoelectric element output
signals and the cantilevered probe response from one or more
actuated cantilevered probes comprises, for example, measuring a
shifted resonant frequency, a shifted Q factor, a shifted
impedance, a shifted phase, a shifted deflection amplitude, or a
combination thereof and comparing the responses to known or
calibrated responses. A fast Fourier transform (FFT) may be
performed on the cantilevered probe responses from one or more
actuated cantilevered probes. The entire array of cantilevered
probes, a subset thereof, or an individual cantilevered probe may
be addressed by selective actuation and detection. With the
availability of a reference cantilevered probe, a reference
cantilevered probe response may be detected from one or more
reference cantilevered probes in the cantilevered probe array. The
explosive material may be determined based on comparing a measured
shift from one or more actuated cantilevered probes to a reference
set of cantilevered probe responses, and determining the explosive
material based on the reference set of cantilevered probe
responses.
[0108] The explosive material can be determined, for example, based
on the piezoelectric element output signal from a piezoelectric
element disposed on the cantilevered probe, as seen at block 110.
Alternatively or in addition to, a non-explosive material may be
adsorbed onto the surface of the cantilevered probe and determined
Determining the explosive material, non-explosive material or other
target chemical species may include, for example, analyzing the
piezoelectric element output signal and other cantilevered probe
responses such as a resonant frequency shift of the cantilevered
probe, a shift in bending of the cantilevered probe, a thermal
signature, a recoil response, a pyroelectric charge generation, an
impedance shift, a temperature shift, or a combination thereof.
[0109] To determine the explosive material or other target chemical
species, the self-sensed cantilevered probe array may be scanned
through a predetermined frequency range. When activated, for
example, with an interface circuit that scans through the resonant
frequencies of one or more cantilevered probes, each cantilevered
probe, in turn, may be excited and oscillated by the interface
circuit as the frequency of the oscillator or frequency generator
is scanned through each resonant frequency. Depending on the type
and amount of a explosive material and the coating on the
cantilevered probe, the cantilevered probes in the array may
exhibit shifted cantilevered probe responses such as a shifted
resonant frequency, a shifted Q factor, a shifted impedance, a
shifted phase, a shifted deflection amplitude, or a combination
thereof.
[0110] Temperature measurements from one or more probe heaters
serving as a temperature sensor or other on-board temperature
sensors may be used to indicate the temperature of the heated
cantilevered probe, from which the ignition temperature of the
explosive material can be determined Characteristic properties such
as the heat of vaporization, melting temperature, phase change,
chemical reactions, exothermic reactions, or endothermic reactions
associated with adsorbed explosive material and other target
chemical species may be interpreted to aid in the determination of
the explosive material or target chemical species.
[0111] A controller or a software application running on a computer
or digital device may be used to analyze the cantilevered probe
responses and determine one or more components and their
concentration in the sample. The explosive material may be
determined in part based on the detected reference cantilevered
probe response, for example, by a common mode correcting for
effects such as temperature, pressure and viscosity of the sampled
medium. The detected explosive material or target chemical species
may include, for example, mercury, hydrogen, an alcohol, water
vapor, a chemical element, a chemical compound, an organic
material, an inorganic material, a gaseous substance, a liquid, a
biological material, a DNA strand, a bioactive agent, a toxin, and
derivatives and combinations thereof.
[0112] Using pattern recognition, modeling functions or signal
processing techniques such as fuzzy logic, the explosive material
may be determined based on comparing a measured shift from one or
more actuated cantilevered probes to a reference set of
cantilevered probe responses, and determining the explosive
material based on the reference set of cantilevered probe
responses. The reference set of cantilevered probe responses may
comprise, for example, a learned set from calibration runs or from
a statistical database with expectation values for various
explosive materials and target chemical species.
[0113] Having illustrated and described the principles of the
invention in exemplary embodiments, it should be apparent to those
skilled in the art that the illustrative embodiments can be
modified in arrangement and detail without departing from such
principles. In view of the many possible embodiments to which the
principles of the invention can be applied, it should be understood
that the illustrative embodiments are intended to teach these
principles and are not intended to be a limitation on the scope of
the invention. We therefore claim as our invention all that comes
within the scope and spirit of the following claims and their
equivalents.
* * * * *