U.S. patent application number 12/145625 was filed with the patent office on 2008-11-20 for metal detection system and method.
Invention is credited to Frederick Dean Fluck.
Application Number | 20080284425 12/145625 |
Document ID | / |
Family ID | 39497324 |
Filed Date | 2008-11-20 |
United States Patent
Application |
20080284425 |
Kind Code |
A1 |
Fluck; Frederick Dean |
November 20, 2008 |
Metal Detection System and Method
Abstract
This application describes a system for contraband and weapons
detection. The system comprises a coplanar sensor array, electronic
drive circuitry, a data acquisition circuit, a video frame grabber,
a video camera, and a computer control unit with a control module
installed. Properly constructed and aligned, the system allows for
the detection of very small magnetic moments, which surround
ferromagnetic materials. This ferromagnetic detection allows users
to screen personnel for contraband electronic devices and concealed
weapons.
Inventors: |
Fluck; Frederick Dean;
(Idaho Falls, ID) |
Correspondence
Address: |
Zarian Midgley & Johnson PLLC
University Plaza, 960 Broadway Ave., Suite 250
Boise
ID
83706
US
|
Family ID: |
39497324 |
Appl. No.: |
12/145625 |
Filed: |
June 25, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11329676 |
Jan 10, 2006 |
7408461 |
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12145625 |
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60642768 |
Jan 11, 2005 |
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Current U.S.
Class: |
324/253 |
Current CPC
Class: |
G01V 3/081 20130101 |
Class at
Publication: |
324/253 |
International
Class: |
G01R 33/04 20060101
G01R033/04 |
Claims
1. A metal detection system comprising: a sensor array comprising a
plurality of magnetic field fluxgate sensors mounted on a support
structure, the sensors being arranged to define a sensing region
within the sensor array; electronic drive circuitry in
communication with each magnetic field fluxgate sensor, the
electronic drive circuitry comprising one or more filtering digital
mixers and a frequency-to-voltage converter; data acquisition
circuitry in communication with the electronic drive circuitry of
each magnetic field fluxgate sensor; a video camera aimed at the
sensing region of the sensor array; a video frame grabber in
communication with the video camera; and a computer control unit
comprising a control module and a user interface, the computer
control unit in communication with the data acquisition circuitry
and the video frame grabber.
2. The metal detection system of claim 1, wherein the support
structure comprises a frame constructed of wood, plastic, or
aluminum.
3. The metal detection system of claim 1, wherein the support
structure comprises decor, landscaping concrete, or doorway
moldings.
4. The metal detection system of claim 1, comprising eight magnetic
field fluxgate sensors arranged in two columns of four sensors
each, wherein the sensors in each column are spaced approximately
16 inches apart, and wherein the lower most sensors in each column
are located approximately 9 inches off the ground.
5. The metal detection system of claim 1, wherein each magnetic
field fluxgate sensor comprises a drive coil wound around a
magnetically permeable core material, and a sensing coil wound
perpendicularly around the drive coil and the core material.
6. The metal detection system of claim 1, wherein each magnetic
field fluxgate sensor is configured to detect magnetic fields in
the range of about .+-.50 micro-tesla.
7. The metal detection system of claim 1, wherein each magnetic
field fluxgate sensor exhibits a sensitive radius region of about
20 inches.
8. The metal detection system of claim 1, wherein the electronic
drive circuitry is integrated into body of each magnetic field
fluxgate sensor.
9. The metal detection system of claim 1, wherein the electronic
drive circuitry is constructed using stand-alone electronic wiring
boards, printed circuit cards, or electronic bread boards.
10. The metal detection system of claim 1, wherein the digital
mixers comprise D-type flip-flop bistable circuits.
11. The metal detection system of claim 1, wherein the video camera
comprises an analog video camera, digital video camera, USB camera,
Firewire camera, or wireless network camera.
12. The metal detection system of claim 1, wherein the video frame
grabber is installed on the computer control unit.
13. The metal detection system of claim 1, wherein the control
module allows a user to customize alarm set points and colors.
14. The metal detection system of claim 1, wherein the magnetic
field fluxgate sensors, electronic drive circuitry, data
acquisition circuitry, and computer control unit are coupled
together via twisted pair wiring or shielded coaxial cable.
15. The metal detection system of claim 1, wherein a Field
Programmable Gate Array electronic device is utilized for signal
conditioning and routing of the output data from the sensor
array.
16. The metal detection system of claim 1, further comprising a
plurality of buffers configured to condition the output signals
generated by the magnetic field fluxgate sensors.
17. The metal detection system of claim 1, further comprising a
plurality of capacitors, wherein each capacitor is connected
between an output terminal of a corresponding frequency-to-voltage
converter and electrical ground.
18. The metal detection system of claim 17, wherein the capacitors
comprise aluminum capacitors, each having a capacitance of about
100 .mu.F.
19. The metal detection system of claim 1, further comprising a
plurality of double-regulated power supply circuits, wherein each
double-regulated power supply circuit is coupled to a corresponding
magnetic field fluxgate sensor.
20. The metal detection system of claim 19, wherein each
double-regulated power supply circuit comprises a plurality of
voltage regulators and a plurality of capacitors connected between
electrical ground and the voltage input and output pins of each
voltage regulator.
21. The metal detection system of claim 19, wherein each
double-regulated power supply circuit comprises a capacitor
connected between the input and ground terminals of the
corresponding magnetic field fluxgate sensor, and an inductor
connected in series with the input terminal of each magnetic field
fluxgate sensor.
22. The metal detection system of claim 1, further comprising a
self-contained power system.
23. The metal detection system of claim 22, wherein the
self-contained power system comprises a solar power system, fuel
cell, battery, gas operated generator, or air operated
generator.
24. A metal detection system comprising: an array of magnetic field
sensors mounted on a support structure, each sensor being
configured to generate an output signal having a frequency that is
substantially proportional to a magnetic field detected by the
sensor; means for physically aligning the magnetic field sensors;
means for electronically tuning the magnetic field sensors;
electronic drive circuitry in communication with each magnetic
field sensor; and data acquisition circuitry in communication with
the electronic drive circuitry of each magnetic field sensor,
wherein the data acquisition circuitry is configured to communicate
with a computer via cabling.
25. The metal detection system of claim 24, wherein the magnetic
field sensors comprise magnetic field fluxgate sensors.
26. The metal detection system of claim 24, wherein the magnetic
field sensors comprise magneto-resistive effect type magnetic field
sensors.
27. The metal detection system of claim 24, wherein the means for
physically aligning each magnetic field sensor comprises a ball and
socket joint configured to enable angular adjustment of the
corresponding sensor.
28. The metal detection system of claim 27, wherein the ball and
socket joint enables about 6 degrees of angular adjustment to the
corresponding sensor.
29. The metal detection system of claim 24, wherein the means for
physically aligning each magnetic field sensor comprises an
electromechanical device and a feedback system.
30. The metal detection system of claim 29, wherein the
electromechanical device comprises a motor, linear positional
device, or an electronic muscle wire.
31. The metal detection system of claim 24, wherein the means for
electronically tuning each magnetic field sensor comprises a
digital mixer.
Description
RELATED APPLICATION
[0001] This application is a continuation application of U.S.
patent application Ser. No. 11/329,676, filed Jan. 10, 2006, which
claims priority to U.S. Provisional Patent Application No.
60/642,768, filed Jan. 11, 2005, the entire contents of which are
hereby incorporated by reference in its entirety.
BACKGROUND
[0002] This disclosure relates generally to systems and methods for
detecting metallic objects and, more specifically, to systems and
methods for detecting concealed weapons and/or contraband.
[0003] Many different kinds of metal detection systems are known
and are used in a wide range of situations in order to provide
added security against violent crimes and terrorist attacks. Well
known, is the use of metal detection screening systems to screen
for concealed weapons in airports, and increasingly they are being
used in courthouses, schools, and other public and governmental
facilities that may be subject to threats or attacks.
[0004] Currently, there is an increased demand for contraband
screening systems by industries, represented by banks, convenience
stores, sports arenas, amusement parks, and concert venues. Many of
these industries are looking for screening systems that are low
cost, to allow the installation of these devices at all entrances
of their desired secured zones. These industries prefer screening
systems that have very high throughput rates to allow for
continuous movement of incoming customers at venue entrances.
[0005] In some applications, there is a desire to utilize screening
systems to not only screen for concealed weapons, but also to
detect and limit the entry of items such as video/audio recorders,
digital cameras, and other copyright-encroaching electronic
devices. In some applications, it is also desired that the
screening systems are covert in appearance, to not diminish the
customer's experience as they enter an event.
BRIEF DESCRIPTION
[0006] The above-mentioned drawbacks associated with existing metal
detection systems are addressed by embodiments of the present
application, which will be understood by reading and studying the
following specification.
[0007] In one embodiment, a metal detection system comprises a
sensor array comprising a plurality of magnetic field fluxgate
sensors mounted on a support structure, the sensors being arranged
to define a sensing region within the sensor array. The system
further comprises electronic drive circuitry in communication with
each magnetic field fluxgate sensor, the electronic drive circuitry
comprising one or more filtering digital mixers and a
frequency-to-voltage converter. The system further comprises data
acquisition circuitry in communication with the electronic drive
circuitry of each magnetic field fluxgate sensor, a video camera
aimed at the sensing region of the sensor array, and a video frame
grabber in communication with the video camera. The system further
comprises a computer control unit comprising a control module and a
user interface, the computer control unit in communication with the
data acquisition circuitry and the video frame grabber.
[0008] In another embodiment, a metal detection system comprises an
array of magnetic field sensors mounted on a support structure,
each sensor being configured to generate an output signal having a
frequency that is substantially proportional to a magnetic field
detected by the sensor. The system further comprises means for
physically aligning the magnetic field sensors and means for
electronically tuning the magnetic field sensors. The system
further comprises electronic drive circuitry in communication with
each magnetic field sensor and data acquisition circuitry in
communication with the electronic drive circuitry of each magnetic
field sensor. The data acquisition circuitry is configured to
communicate with a computer via USB cabling.
[0009] In another embodiment, a method for detecting ferromagnetic
objects within a sensing region of an array of magnetic field
fluxgate sensors comprises receiving a signal to initiate a data
acquisition and image acquisition cycle, generating a plurality of
first output signals, each first output signal having a frequency
that is substantially proportional to a magnetic field detected by
a corresponding magnetic field fluxgate sensor, and generating a
plurality of second output signals, each second output signal
having a frequency that substantially comprises an absolute
difference between the frequency of a first output signal and the
frequency of a corresponding background reference signal. The
method further comprises converting the frequency of each second
output signal to a corresponding voltage level, acquiring an image
of a person within the sensing region of the array of magnetic
field fluxgate sensors, and displaying the image of the person,
overlaid with data representing the voltage levels corresponding to
the frequencies of the plurality of second output signals. The
overlaid data indicates the magnitude and location of magnetic
moments surrounding ferromagnetic objects within the sensing
region.
[0010] These and other embodiments of the present application will
be discussed more fully in the detailed description. The features,
functions, and advantages can be achieved independently in various
embodiments of the present application, or may be combined in yet
other embodiments.
DRAWINGS
[0011] FIG. 1 is a block diagram of a metal detection system in
accordance with one embodiment of the present application.
[0012] FIG. 2 is a schematic diagram of a double-regulated power
supply circuit in accordance with one embodiment of the present
application.
[0013] FIG. 3 is a cross-sectional diagram of a sensor mounted in a
fixture, in accordance with one embodiment of the present
application.
[0014] FIG. 4 is a block diagram of a sensor array in accordance
with one embodiment of the present application.
[0015] FIG. 5 is a schematic diagram of an exemplary D-type
flip-flop bistable circuit in accordance with one embodiment of the
present application.
[0016] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0017] In the following detailed description, reference is made to
the accompanying drawings that form a part hereof, and in which is
shown by way of illustration specific illustrative embodiments in
which the invention may be practiced. These embodiments are
described in sufficient detail to enable those skilled in the art
to practice the invention, and it is to be understood that other
embodiments may be utilized and that logical, mechanical, and
electrical changes may be made without departing from the spirit
and scope of the present invention. The following detailed
description is, therefore, not to be taken in a limiting sense.
[0018] Many metal detectors currently available do not fully meet
industry specific needs for one reason or another. This application
describes a new concealed weapons and contraband detection
screening system. This new system advantageously incorporates
certain desirable features, such as contraband detection
capabilities, low per unit cost, high patron throughput rate, and
versatile design for covert operation and installation.
[0019] The design criteria for the screening system involve
magnetic field sensors that are sensitive enough to detect not only
weapons, but also sensitive enough to detect the small magnetic
fields that surround electronic devices. Many interested users
consider electronic recording devices to be a very high threat to
their business, as they rely on copyright licensing to operate
profitably. Statistically, electronic recording devices are used
during presentations to steal copyrighted material. This pirated
material compromises the exclusivity of the copyrighted material
and greatly reduces industry profits.
[0020] The newly designed weapons/contraband screening system
utilizes unique methods to detect very small magnetic fields, using
commercially available magnetic field sensors and components. The
assembled sensor modules are highly sensitive and respond to
magnetic field moments very quickly. In some embodiments, the
walk-through gateway making up the weapons/contraband screening
system comprises an array of these sensor modules. This sensor
array is constructed of two columns of sensor modules. People walk
between these columns, through the sensing region, for the
screening process. This sensor array is tuned, physically and
electronically, to itself, which enhances the sensitivity of the
sensor array.
[0021] Digital imagery of the screened individual is obtained
during a screening process. The imagery is taken to provide
positive data tracking for the data collected during the screening
process. The imagery is saved only when the individual has a
detected contraband item or weapon. The imagery is utilized by the
control module to aid the system operator in visually locating the
detected contraband item. The imagery can be acquired from a
variety of digital camera technologies such as analog and digital
video cameras, USB cameras, Firewire cameras, or wireless network
cameras. The system may be set to not obtain imagery of screened
clients. In this mode, the system can substitute a universal patron
icon in place of the imagery and utilize a time-stamp identifier
for data tracking of the data collected during the screening
process.
[0022] The system's sensor array output data and imagery is sent to
the computer control unit via standard interface cabling. The
computer control unit can be any desktop personal computer or
laptop style computer, which has suitable control software
installed. The sensor array output data and digital imagery can be
sent to the computer control unit through interface cables, USB
cabling, Ethernet, or through a wireless network device. An
advantage of utilizing these listed methods is that one computer
control unit can read the data output of many screening gateways,
as the gateways can be designed as independent network-connectable
computer peripherals.
[0023] The designed system utilizes a control module that applies
artificial intelligence to aid in translating whether the detected
item is a threat or non-threat item. This artificial intelligence
is in the form of simple algorithmic functions. By instilling more
advanced artificial intelligent algorithms, such as neural network
functions or fuzzy logic style functions, further filtering of
commonly known items that cause false-positive readings, such as
under wires in brassieres and steel shanks in shoes, can be
achieved. The control module can also be modified to detect only
predetermined items for access control, using electromagnetic
badges or identification tags.
[0024] The control module can utilize audible alarms, door
closures, or other security mechanisms to aid the operator in
detaining contraband-carrying personnel. The control module can be
programmed to send the gateway output data and imagery to remote
security stations via wireless links, cellular telephone links, or
email and Internet links. The control module can be modified to
interface with other computer applications for patron badge
creation or other biometric applications.
[0025] The design of this screening gateway takes into
consideration the criterion that the screening system be covert.
There exists a desire to not have the patron even be aware that he
or she is being screened. This renders conventional metal detection
equipment unattractive due to its conspicuous appearance. The new
system utilizes an array of small sensors to detect contraband
items. This sensor array is not rigid by design and can be
configured in many variations for contraband detection purposes.
The small sensors can be placed in structures to mimic arena decor,
be mounted into doorway moldings of entrances, be incorporated
within landscaping concrete commonly used throughout amusement and
theme parks, or be enclosed into other non-magnetic structural
configurations.
[0026] The design of the system described in this application
provides the flexibility to detect weapons and electronic recording
devices through the hardware's configuration and the software's use
of artificial intelligence. The design takes into consideration the
requirements of high throughput rates for patron screening. The
designed system has an approximate throughput rate of about 1,000
persons per hour. The cost savings through component selection,
allows the system to be offered at a low cost, compared to
conventional metal detection systems. The design is versatile in
that it can be installed in a covert fashion at facilities. The
designed system's hardware and software can be modified for the
implementation of weapons/contraband screening by a wide variety of
end users.
[0027] FIG. 1 is a block diagram of a metal detection system 100 in
accordance with one embodiment of the present application. As
illustrated in FIG. 1, the system 100 comprises a coplanar sensor
array 105, which is built on a support structure 110, electronic
drive circuitry 115 to convert the sensor array's output data to
voltage or detection levels, a data acquisition circuit 120 to read
these detection levels, a video frame grabber 125 and a video
camera 130 to obtain imagery of the screened individual. The system
100 further comprises one or more infrared break-beam devices 170
mounted on the support structure 110, and a computer control unit
135 with a user interface 160 and a control module 165 installed to
operate the system 100.
[0028] As used herein, the term "module" may refer to any
combination of software, firmware, or hardware used to perform the
specified function or functions. It is contemplated that the
functions performed by the modules described herein may be embodied
within either a greater or lesser number of modules than is
described in the accompanying text. For instance, a single function
may be carried out through the operation of multiple modules, or
more than one function may be performed by the same module. The
described modules may be implemented as hardware, software,
firmware or any combination thereof. Additionally, the described
modules may reside at different locations connected through a wired
or wireless telecommunications network, or the Internet.
[0029] In the illustrated embodiment, the electronic drive
circuitry 115 comprises a frequency-to-voltage converter 140
coupled to filtering digital mixers 145, which are, in turn,
coupled to a reference frequency generator 150. The hardware, when
assembled and properly calibrated as described in this application,
enables an operator to screen clients for contraband electronic
hardware and ferrous containing concealed weapons.
[0030] In the illustrated embodiment, the coplanar sensor array 105
consists of eight magnetic field sensors 155, four sensors on each
side. The sensors 155 are mounted onto the support structure 110,
which is constructed of non-magnetic material. The support
structure 110 is preferably built such that people can walk through
the sensing region. In some embodiments, the recommended head
clearance height of the support structure 110 is approximately 80
inches, with the walk-through or sensing region inside width of
approximately 30 inches. The support structure 110 may be
constructed from any non-magnetic material such as wood, plastic,
or aluminum. The support structure 110 is preferably sturdy and
strong enough to support the sensors 155, support electronics, and
wiring for the sensor array 105.
[0031] The electronic drive circuitry 115 may comprise
signal-processing electronics configured to convert the output
signal generated by each sensor 155, which is a frequency signal
proportional to the magnetic field detected, to voltage or
detection levels. In operation, these detection levels are read
into the computer control unit 135 by the data-acquisition circuit
120, which can be installed into the computer control unit 135 and
controlled by the control module 165.
[0032] The video frame grabber 125 can be installed into the
computer control unit 135. The frame grabber 125 is used to acquire
an image from the video camera 130. The camera 130 is aimed at the
sensing region of the sensor array 105, such that the camera 130
captures imagery of the person as they walk through the sensing
region during a screening process. The image data is utilized by
the control module 165 for data identification purposes and
detected contraband/weapon item location determination.
[0033] The control module 165 manipulates the sensor array's output
data from the electronic drive circuitry 115, and displays this
data onto the user interface 160. This user interface 160 displays
the highest detection level recorded by each sensor 155 during the
screening process event. The detection level of each sensor 155 is
overlaid, in conjunction, at each sensor's physical location, on an
acquired image. This image is taken during the screening process
and is displayed along with the resultant data on the user
interface 160, to aid the operator in determining the location of
the item detected.
[0034] The user interface 160 allows the system operator to
manually operate the system 100 and to adjust various alarm set
points and colors, to aid the operator in differentiating between
non-threat and threat items. These set points are utilized, by the
control module 165 to display to the operator the type of alarm
that existed during the screening process, by using color.
[0035] For example, the system 100 may be set up to alert the
operator of any detected low magnetic field items, such as
electronic recording devices. Here the medium detection level alarm
set points would be set at low to medium values, and the medium
detection level alarm color would be set to yellow. This enables
the control module 165 to alert the operator of a detected low
magnetic field item, by showing on the user interface 160 a yellow
background after a screening event.
[0036] For weapons, which are surrounded by a much larger magnetic
fields, the high detection level alarm set point, would be set at
medium to high detection level values and the high detection level
alarm color would be set to red. This enables the control module
165 to alert the operator of detected high magnetic field items,
with a red background on the user interface 160. Individuals who
have no contraband items on their person during a screening event
would have no alarm condition. In this case, the system 100 would
display its default color after a screening event.
[0037] In some embodiments, the magnetic field sensors 155 comprise
commercially-available magnetic field fluxgate sensors. An example
fluxgate sensor for use in this design is Speake and Company's,
FGM-3 fluxgate magnetic field sensor. The fluxgate sensors utilize
a magnetically permeable core material that is periodically
saturated by a drive coil that is wound around the core material. A
second wound coil, the sensing coil, is wound perpendicular around
the drive coil and core. This sensing coil detects any changes in
the core material's magnetic permeability, caused by magnetic
fields near the sensor, through electromagnetic action. With
careful design implementation, these fluxgate sensors are able to
detect very small magnetic fields in the range of about .+-0.50
micro-tesla.
[0038] Since each sensor 155 has a sensitivity of a few percent due
to power variations, it is desirable to provide in the design,
power regulation and electronic filtering. This prevents power
variations and external electrical noise components from
interfering with the sensitivity of the sensors 155. In some
embodiments, power regulation and filtering is accomplished by
providing each sensor 155 with a doubly regulated and filtered
input power circuit. A 12-volt direct current (DC) power supply is
used to power the screening system 100. An example 12-volt DC power
supply that may be used is Phihong's model PSA31U-120, 120-volt
alternating current (AC) to 12-volt DC power supply. The double
regulation circuitry reduces the system's 12-volt power to the
5-volt DC power required by certain sensors 155.
[0039] FIG. 2 is a schematic diagram of a double-regulated power
supply circuit 200 in accordance with one embodiment of the present
application. The circuit 200 preferably comprises a plurality of
voltage regulators 205 and a plurality of capacitors 210 connected
between ground and the voltage input and output pins of each
regulator 205. In the illustrated embodiment, the voltage
regulators 205 comprise National Semiconductor's LM78XXX series,
3-terminal positive regulators, and the capacitors 210 comprise
tantalum capacitors with a capacitance of about 10-microfarads.
This provides minimal input power supply variation and permits the
temperature coefficient of the fluxgate sensor to be the limiting
performance factor.
[0040] As shown in FIG. 2, further noise filtering of the fluxgate
sensors can be accomplished by placing a capacitor 215 between the
input and ground terminals of each sensor 155, and placing an
inductor 220 in series with the input terminal of each sensor 155.
In the illustrated embodiment, the capacitor 215 has a capacitance
of about 33-microfarads, and the inductor 220 has an inductance of
about 56 micro-henries.
[0041] In some embodiments, the sensors 155 are highly directional,
meaning that variations in direction with respect to the earth's
naturally occurring magnetic field can easily swamp or mask out
small anomalies when the sensors 155 are moved. Due to the
directionality of the sensors 155, when building the sensor array
105 it is desirable to align the physical axes of the sensors 155
in the same direction. The physical axis of each sensor 155 can be
determined by observing the physical layout of the sensor 155. In
some embodiments, the sensors 155 comprise fluxgate sensors having
pin connections on one end of a tubular assembly that makes up the
sensor 155. These pins are preferably physically oriented in the
same direction when building the sensor array 105. This ensures the
physical axes are aligned to all other sensors 155 utilized in the
construction of the sensor array 105.
[0042] The sensors 155 can be further physically aligned and
electronically tuned. The sensor array 105 is constructed as a
gateway such that people are able to walk through the tuned sensor
array 105 to be screened. The alignment techniques described herein
allow the sensor array 105 to be very sensitive to magnetic fields,
which are present and surround ferromagnetic materials.
Ferromagnetic materials directly affect the earth's naturally
occurring magnetic field gradient. The physical alignments and
electrical tuning described herein produce a coplanar gradient
sensor array 105, with the ability to detect these small
disturbances in the naturally occurring earth magnetic field
gradient, as they pass through the sensing region of the coplanar
sensor array 105.
[0043] In one exemplary embodiment, eight fluxgate magnetic sensors
are used to construct the coplanar gradient sensor array 105. As
illustrated in FIG. 1, four sensors 155 are on the right side and
four sensors 155 are on the left side. In this exemplary
embodiment, the sensors 155 are spaced approximately sixteen inches
apart, with lower most sensors 155 in the array 105 being
approximately nine inches off the ground. This spacing allows a
full body screening for contraband items of persons of average
adult height. However, any combination of numbered fluxgate sensors
may be used. The number of sensors 155 used may be limited by the
physical layout of the desired walk-through coplanar sensor array
105 or the number of data acquisition channels desired or deemed
sensible when designing a weapons/contraband screening system.
[0044] The sensor array 105, when complete, may be oriented in a
vertical, slanted, or horizontal direction. The sensors 155 can be
placed at any perceived spacing interval deemed necessary for the
application. In some embodiments, the sensors 155 should be spaced
no greater than 16 inches apart. The sensors 155 may exhibit a
highly sensitive radius region, which surrounds the sensors 155, of
approximately 20 inches. This sensitivity radius region quickly
degrades beyond the 20-inch distance. When building the sensor
array 105, it is generally desirable that the physical direction or
axis of each sensor 155 be the same, and that the angular and
electronic adjustments described herein be performed. This allows
the coplanar gradient sensor array 105 to be constructed into
doorway frames, or be installed into landscaping concrete or any
other configuration for covert installations for personnel
screening.
[0045] Further physical alignment of the sensors 155 making up the
coplanar gradient sensor array 105 can be performed by adjusting
the physical angular orientation of each sensor. This adjustment is
made such that each sensor 155 in the array 105 is observing the
same natural earth magnetic field gradient as a selected reference
sensor in the sensor array 105. In some embodiments, to allow the
angular alignment to be performed, the sensors 155 are mounted in
an appropriately rigged mechanical fixture, which is attached to
the support structure 110.
[0046] FIG. 3 is a cross-sectional diagram of a sensor 155 mounted
in a fixture 300, in accordance with one embodiment of the present
application. In the illustrated embodiment, the fixture 300
comprises a tube 305 made from a non-magnetic material such as
wood, plastic, or aluminum. For example, in one embodiment, the
tube 305 comprises schedule 80 PVC pipe having a length of about
four inches and a diameter of about one inch. The PVC pipe can
bored out to an inside diameter of about one inch.
[0047] As shown in FIG. 3, the sensor 155 can be mounted to the
tube 305 with a spherical member 310. For example, in some
embodiments, the spherical member 310 comprises a nylon ball having
a diameter of about one inch, which is bored out with a hole having
a diameter of about 9/16 inch. The sensor 155, which may have a
tapered body as shown in FIG. 3, can be inserted firmly into the
hole to hold the sensor body in place and to allow angular
adjustment of the sensor 155. This assembly can then be placed into
the prepared length of PVC pipe described above. The pipe and the
inserted ball assembly act as a ball and socket or pivot point for
angular adjustment of the sensor 155. In some embodiments, this
configuration allows approximately six degrees of total angular
adjustment of the sensor 155. The completed assemblies can then be
mounted to the support structure 110 at the recommended spacing to
create the sensor array 105. The angular alignment can be performed
on each sensor 155, with the exception of a selected reference
sensor, as discussed in more detail below.
[0048] In some embodiments, the electronic tuning of the sensor
array 105 is accomplished by digitally mixing a reference
background-produced frequency with the background-produced output
frequency generated by each sensor 155, which is caused by the
earth's naturally occurring magnetic field. Since the physical axes
of the sensors 155 are in the same orientation, the
background-produced frequency of each sensor 155 will be within a
few hertz of the other sensors 155 in the sensor array 105. In some
embodiments, the sensors 155 have a background-produced frequency
that is in the range of about 50-hertz to about 120-kilohertz,
depending on the orientation of the sensor 155 to the earth's
natural magnetic field. The reference background-produced frequency
or reference oscillation frequency, can be measured and set by
selecting and measuring the output frequency of one of the midmost
sensors 155 in the coplanar gradient sensor array 105. This
selected sensor 155 becomes then the reference sensor, as all other
sensors 155 in the array will be aligned to it.
[0049] The reference oscillation frequency is measured and
reproduced by the control module 165. This measured and reproduced
frequency is then applied to the digital mixer circuitry of each
sensor 155, during operation of the screening gateway. The digital
mixing of the background-produced output frequency of each sensor
155 with the reference oscillation frequency effectively cancels
the background-produced frequency produced by the earth's naturally
occurring magnetic field, for each sensor 155. This allows very
small magnetic field anomalies to be detected by the coplanar
gradient sensor array 105 without interference from
background-produced noise caused by the earth's natural magnetic
field.
[0050] Each sensor 155 used to produce the coplanar gradient sensor
array 105 is electronically tuned to each other sensor 155 in the
sensor array 105. In some embodiments, the sensors 155 output a
5-volt rectangular pulse train with a period, or frequency
measurable signal that is directly proportional to the magnetic
field detected. The output frequency of each sensor 155 is
digitally mixed with a reference oscillation or background
frequency. This background frequency is measured from a selected
midmost reference sensor 155 in the sensor array 105, which is
oriented parallel to the earth's naturally occurring magnetic field
or on horizontal level. The output frequency from the digital mixer
145 of each individual sensor 155 is the absolute difference
between the reference oscillation frequency and the
background-produced frequency of the respective sensor 155. The
frequency output of each digital mixer 145 can then be converted to
a voltage level using a frequency-to-voltage converter 140, which
can be directly measured by commonly available test equipment and
computer data acquisition measurement instruments.
[0051] In some embodiments, the physical angular orientation of
each sensor 155 is adjusted to tune the coplanar gradient sensor
array 105 to one naturally occurring earth magnetic field gradient.
This angular alignment is accomplished by applying the reference
oscillation frequency to the digital mixer 145 of each sensor 155
as described above. The output of each sensor's
frequency-to-voltage converter 140 is then measured and the
physical angular orientation of each sensor 155 is adjusted to
obtain a near zero voltage output measurement from the output of
the respective sensor's frequency-to-voltage converter 140. In some
embodiments, this voltage level should be adjusted to about 200-400
millivolts to maintain maximum stability of the sensor array 105.
This alignment is completed for each sensor 155 in the coplanar
sensor array 105, with exception to the selected reference sensor
155, which is on horizontal level or parallel to the naturally
occurring earth magnetic field gradient.
[0052] In some embodiments, the sensors 155 output a 5-volt
rectangular pulse train or frequency signal. Due to the potentially
long wiring lengths used in the construction of the sensor array
105, the output signal can be degraded, making it necessary to
condition the output signals received from each sensor 155. This
can be accomplished by utilizing an inverting buffer with
Schmitt-trigger action or equivalent circuitry. An example of a
buffer device that may be used is a Philips Semiconductor 74HC14E.
This buffer device outputs a clean square-wave signal for the
digital mixing of the output frequency of each sensor 155.
[0053] FIG. 4 is a block diagram of a sensor array 105 in
accordance with one embodiment of the present application. As
described above, each sensor 155 has a corresponding digital mixer
145. In the illustrated embodiment, the digital mixers 145 comprise
D-type flip-flop bistable circuits.
[0054] FIG. 5 is a schematic diagram of an exemplary D-type
flip-flop bistable circuit 500 in accordance with one embodiment of
the present application. An example device that can be used is a
Fairchild Semiconductor CD4013BC. In the illustrated embodiment,
the D-input of each bistable circuit is supplied from the sensor's
output, which is buffered, and the clock source of the bistable
circuit is supplied from the reference sensor's background-produced
frequency, which is also buffered. The output of each digital mixer
is a frequency, with a range of zero to several kilohertz. In some
embodiments, unused inputs and outputs of the bistable device are
properly terminated or grounded, and proper digital filtering for
the circuitry is practiced.
[0055] In operation, the frequency output of each digital mixer 145
or bistable device is converted to a voltage or detection level
using a frequency-to-voltage converter 140. Example
frequency-to-voltage converters that can be used include the
National Semiconductor, LM2907N or LM2917. This
frequency-to-voltage converter has a programmable working frequency
range that is calculated against the working frequency range the
designer wishes to utilize. In some embodiments, the
frequency-to-voltage converter 140 is designed to have a response
range of approximately 212-hertz per one-volt output. Other
programmable frequency response ranges and output voltages for the
frequency-to-voltage converter may be calculated and used,
depending on the application and the objective.
[0056] In some embodiments, to obtain clean output voltages from
the frequency-to-voltage converter 140, its output terminal is
filtered using a capacitor 505 connected between the output
terminal and ground. In the illustrated embodiment, the capacitor
505 comprises a 100 .mu.F aluminum capacitor. This supplies output
voltages that have very little ripple for measurement purposes. The
circuitry described can be included and constructed into the sensor
body assembly itself or constructed separately, using stand-alone
electronic wiring boards, printed circuit cards, or electronic
bread boards.
[0057] The output of each sensor 155 is buffered and digitally
mixed with the buffered background-produced reference frequency
produced by the earth's natural magnetic field and output via a
D-type bistable. The frequency output of each bistable device is
converted to a voltage level by a frequency-to-voltage converter
140. These voltage levels are read by computerized data acquisition
circuitry 120. The data acquisition circuitry 120 reads the voltage
data from the coplanar gradient sensor array 105 into a
computer-readable format, so that software can be programmed to
manipulate the data, to provide an end user an easily decipherable
user interface 160. In some embodiments, when constructing the
coplanar gradient sensor array 105, proper electronic signal
conditioning and routing techniques should be utilized, which
include using twisted pair wiring or shielded coaxial cable for
signal routing, to minimize outside electrical interference and
noise from entering into the system 100.
[0058] The data acquisition circuitry 120 may comprise any
appropriate data acquisition device that can convert voltage data
into computer decipherable data. For example, a National
Instruments', PCI-6024E data acquisition circuit card (DAQ) may be
utilized. Many suitable computerized DAQ cards exist and can be
selected for use in the system 100 if they have the proper number
of analog and digital input and output channels. In some
embodiments, the DAQ must have at least eight analog input channels
for reading the voltage levels of the coplanar sensor array 105.
Also desired for the DAQ is one digital input/output channel for
reading the infrared break-beam trigger signal, and two timing
input/output channels for measurement and reproduction of the
background produced reference frequency of the coplanar array
105.
[0059] In operation, the data acquisition circuitry 120 can be
controlled by its supplied software drivers and the system's
control module 165. The control module 165 described herein can be
written to interpret the voltage readings obtained from the
coplanar gradient sensor array 105 or gateway during a screening
process. As people walk through the gateway, one or more infrared
break-beam devices 170 are triggered. The infrared break-beam
device 170 may comprise any of a wide variety of suitable devices
available commercially, with a sufficient operational range. In
some embodiments, the infrared break-beam device 170 has an
operational range greater than about 30 inches, the recommended
inside width of the coplanar sensor array 105.
[0060] In some embodiments, the infrared break-beam device 170 is
placed near the foot region of the gateway, to ensure individuals
of all statures cause a trigger by breaking the infrared beam. The
infrared break-beam trigger is detected by the control module 165.
When a trigger from the infrared break-beam device 170 is detected,
the control module 165 starts a data and imagery acquisition read
event, beginning the screening process.
[0061] In some embodiments, the control module 165 acquires 2,000
points of data from the coplanar sensor array 105, per channel,
during the screening process. In these embodiments, the screening
process takes approximately one second to complete. The sensor
array output data is then mathematically or algorithmically
manipulated, and the artificial intelligent algorithms in the
control module 165 interpret the manipulated data as necessary to
produce a user decipherable output to the user interface 160.
[0062] In some embodiments, the control module 165 utilizes simple
to complex algorithms to translate the gateway output data into
human interpretable displays on the user interface 160. The control
module 165 may utilize geometric parameters to mathematically
interpret the output data from the sensor array 105. The control
module 165 may comprise software written in any suitable computer
language. For example, National Instrument's LabVIEW, version 7.0
can be used to write suitable software for use in the control
module 165.
[0063] In some embodiments, the user interface 160 utilizes color
to quickly alert the operator if an alarm condition occurred during
a screening process. The user interface 160 contains threshold
controls to set alarm set points and colors to aid the operator in
the differentiation of detected items. The control module 165 for
the screening system 100 also gives the operator access to other
system parameters and programs. These programs and parameters
include a warm-up routine, alignment and maintenance routines, user
logon routines, historical screening image and data review, and
system operational logs. The user interface 160 can be customized
to suit the varying requirements of any end user.
[0064] The control module 165 controls the image acquisition during
a screening process via the infrared break-beam trigger. When a
trigger is received, the control module 165 begins the data
acquisition and image acquisition cycle. A video frame grabber 125
is installed into the computer control unit 135, which converts the
video image data into computer decipherable data. The video frame
grabber 125 may comprise a monochrome or color video image capture
device. For example, a National Instruments', PCI-1407 Frame
Grabber circuit card may be utilized. When an infrared break-beam
trigger is received by the control module 165, the frame grabber
125 is triggered by the control module 165 to immediately acquire
an image of the person entering the screening gateway. This image
is then overlaid with the manipulated data read from the coplanar
sensor array. This overlaid data depicts the peak detection levels
measured during the screening process.
[0065] In some embodiments, a video camera 130 is connected to the
frame grabber 125 in the computer control unit 135 via a BNC
connector equipped RG-59 coax cable. The video camera 130 may
comprise any suitable monochrome or color RS170 video camera. For
example, a Pulnix, model TM-7AS monochrome camera may be utilized.
As shown in FIG. 1, the camera 130 is fitted with a lens 175. The
focal length of the lens 175 is calculated to obtain a stature
image of the gateway in the field of view of the captured image.
For example, a Tamron, 2.8-12 mm, varifocal length lens may be
utilized. In some embodiments, the camera 130 is aimed at the
coplanar sensor array 105 and placed in the portrait orientation,
meaning that the camera's typical horizontal width is oriented
vertically.
[0066] Typically, video cameras output two fields of video
information, an odd field and an even field, which makes up a video
frame. In some embodiments, the video frame grabber 125 is set up,
via its supplied software driver, to acquire or grab only the even
field. This prevents field streaking in the obtained image due to
motion of the person being screened. This motion streaking is
caused by the delay between the odd and even video fields. This
delay is typically 16.67 milliseconds for the RS170 video standard.
The control module 165 manipulates and corrects the video image
grabbed during a screening event, by placing the even field grabbed
image information in both the even and odd fields, for the computer
control unit's display on the user interface 160.
[0067] This application describes a system 100 for contraband and
weapons detection. As described above, the system 100 comprises a
coplanar sensor array 105, electronic drive circuitry 115, a data
acquisition circuit 120, a video frame grabber 125, a video camera
130, and a computer control unit 135 with the control module 165
installed. Properly constructed and aligned, the system 100 allows
for the detection of very small magnetic moments, which surround
ferromagnetic materials. This ferromagnetic detection allows users
to screen personnel for contraband electronic devices and concealed
weapons.
[0068] In some embodiments, modifying the control module 165 to
operate the screening system 100 in a continuous scan mode allows
for the detection of items tossed or kicked into the sensing region
of the gateway. In this mode, the data acquisition system is
continually reading the coplanar sensor array's output data. This
data is compared to predetermined threshold limits set by the
system operator. If any of the read data is above the predetermined
set threshold limits, a complete screening event is triggered,
including the acquisition of imagery of the item tossed or kicked
into the screening region. The control module 165 manipulates the
data and the resultant output data is sent to the user interface
160 informing the operator of the detection event.
[0069] In some embodiments, a Field Programmable Gate Array (FPGA)
electronic device is utilized for signal conditioning and routing
of the output data from the coplanar sensor array 105. FGPA devices
offer many configurations and interfaces for manipulation of
electronic data. The advantages of using FPGA devices are the
reduction of electronic components used, the deletion of the
computer hardware, and the ability to design the data acquisition
circuitry and computer interface into one electronic component.
These advantages allow the system 100 to be constructed such that
the weapons/contraband detection apparatus can be a standalone
device. This can reduce the cost for manufacturing the completed
system and allow for cost effective mass production of a
stand-alone system.
[0070] Further enhancement of the data acquisition circuitry 120
can be realized by implementing USB bus, Ethernet, or wireless data
acquisition to obtain the voltage readings from the coplanar
gradient sensor array. These technologies can advantageously
provide networking capability, wireless data acquisition
capability, or allow the manufacturer the ability to offer the
completed coplanar gradient sensor array 105 as a stand-alone
computer peripheral. In some embodiments, wired data acquisition
circuitry 120 is utilized. In some settings (e.g., certain homeland
security applications), it is desirable to perform contraband
detection from a safe distance to protect system operators from
possible hazards introduced by untrustworthy patrons upon the
system detecting a contraband item. In these settings, wireless
transmission of the resultant screening event would protect
security personnel and enable long distance personnel
screening.
[0071] Though fluxgate style sensors are utilized to detect the
presence of a magnetic field in some embodiments, many other
magnetic field sensing devices are available on the market, which
can also be utilized. One such device is a magneto-resistive effect
type magnetic field sensor. These sensors output voltage levels in
the microvolt range and require only amplification of the output
voltage levels to be useful in the system 100.
[0072] In some embodiments, eight fluxgate sensors are utilized for
the detection of small magnetic moments, enabling the system 100 to
detect weapons and electronic recording devices. In other
embodiments, many more sensors 155 can be utilized in the
construction of the system 100. The advantages of increasing the
number of sensors 155 would be an increase in the output data
resolution of the detected ferromagnetic item within the sensing
region 105. This resolution increase would allow better magnetic
field signature data to be collected for detected items. This
enhanced data would then allow for very accurate probabilistic
identification of the detected items using neural network or
artificial intelligence algorithms. The increased resolution data
collected also allows for the possibility of three dimensional
location data to be derived for the detected item.
[0073] In some embodiments, basic artificial intelligence is used
in the control module 165. In other embodiments, more complex
artificial intelligence is utilized, greatly improving the
identification abilities of the system 100. This artificial
intelligence can be in the form of neural network functions, fuzzy
logic functions, or other algorithmic artificial intelligence
functions.
[0074] In some embodiments, self-contained power systems can be
used for complete system power and operation, allowing portable use
of the contraband/weapons screening system 100. These power systems
include solar, fuel cell, battery, gas or air operated
generators.
[0075] In some embodiments, the user interface 160 is instilled
into the screening gateway itself, rather than utilizing a computer
system such as a desktop or laptop computer. Many self-contained
micro controller unit (MCU) integrated circuits exist on the
commercial market. The implementation and programming of such
devices allows the operational code, including the user interface
160, to be contained completely in these devices. The
implementation of such devices, eliminating the computer hardware,
advantageously allows the contraband/weapons detection gateway to
be constructed as a standalone apparatus.
[0076] In some embodiments, electromechanical devices and feedback
are used to automate the physical angular alignment of the sensors
155, thereby improving the usability of the system 100 and more
readily maintaining the calibration of the system 100 when moved
from one location to another. These electromechanical devices may
be motors, linear positional devices, or electronic muscle wire,
which contracts when electrical power is applied. The feedback
system may comprise any suitable system, such as, for example,
fuzzy logic style controlled feedback.
[0077] Although this invention has been described in terms of
certain preferred embodiments, other embodiments that are apparent
to those of ordinary skill in the art, including embodiments that
do not provide all of the features and advantages set forth herein,
are also within the scope of this invention. Accordingly, the scope
of the present invention is defined only by reference to the
appended claims and equivalents thereof.
* * * * *