U.S. patent application number 10/176897 was filed with the patent office on 2003-02-13 for ultra sensitive magnetic field sensors.
Invention is credited to Jarratt, Raymond L. JR., Summers, Stephen D., Tiernan, Timothy C..
Application Number | 20030029345 10/176897 |
Document ID | / |
Family ID | 46280765 |
Filed Date | 2003-02-13 |
United States Patent
Application |
20030029345 |
Kind Code |
A1 |
Tiernan, Timothy C. ; et
al. |
February 13, 2003 |
Ultra sensitive magnetic field sensors
Abstract
A magnetic sensor and magnetic field sensing method for
ordnance, comprising locating a magnetoresistance detector within
the ordnance and detecting magnetic fields with the detector. Also
other sensing method and sensors employing such detectors.
Inventors: |
Tiernan, Timothy C.;
(Albuquerque, NM) ; Jarratt, Raymond L. JR.; (Los
Lunas, NM) ; Summers, Stephen D.; (Albuquerque,
NM) |
Correspondence
Address: |
PEACOCK MYERS AND ADAMS P C
P O BOX 26927
ALBUQUERQUE
NM
871256927
|
Family ID: |
46280765 |
Appl. No.: |
10/176897 |
Filed: |
June 20, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10176897 |
Jun 20, 2002 |
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09969946 |
Oct 2, 2001 |
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09969946 |
Oct 2, 2001 |
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09265991 |
Mar 9, 1999 |
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6295931 |
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60077525 |
Mar 11, 1998 |
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60092717 |
Jul 14, 1998 |
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60301786 |
Jun 29, 2001 |
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Current U.S.
Class: |
102/221 |
Current CPC
Class: |
F42C 15/40 20130101;
G01R 33/093 20130101; B82Y 25/00 20130101; G01R 33/09 20130101;
G01V 3/081 20130101; F42C 13/08 20130101 |
Class at
Publication: |
102/221 |
International
Class: |
F42C 015/00 |
Goverment Interests
[0003] The U.S. Government has a paid-up license in this invention
and the right in limited circumstances to require the patent owner
to license others on reasonable terms as provided for by the terms
of Contract No. SOL DAAE30-01-BAA-0500 and Contract No.
DAAE30-99-C-1068 awarded by the U.S. Army TACOM-ARDEC, by the terms
of Contract Nos. DMI-0060397 and DMI-9704080 awarded by the
National Science Foundation, and a contract with the U.S. Navy.
Claims
What is claimed is:
1. A magnetic field sensing system for locating defects in objects
in two or three dimensions, said system comprising a sensor
comprising a magnetoresistance detector and means for sensing at a
plurality of frequencies.
2. The system of claim 1 wherein said means for sensing provides
for sensing defects at a plurality of depths in the objects.
3. The system of claim 2 wherein the objects are printed circuit
boards.
4. A magnetic field sensing system for imaging objects comprising a
magnetoresistance detector, means for non-magnetic imaging, and
means for analyzing images produced by both said magnetoresistance
detector and said means for non-magnetic imaging.
5. The system of claim 4 wherein said means for non-magnetic
imaging comprises optical imaging means.
6. A system for mechanical system identification comprising a
magnetoresistance detector.
7. The system of claim 6 wherein said system comprises a system for
vehicle identification.
8. The system of claim 6 additionally comprising means for
analyzing output of said magnetoresistance detector and comparing
results to known characteristics of items selected from the group
consisting of: perturbations of the earth's field by a moving
metallic object or vehicle; fields associated with electric motors;
fields associated with generators and alternators; fields
associated with spark plugs, wires and coils; fields related to
rapidly moving metallic parts; and fields associated with large
masses of metals.
9. The system of claim 6 wherein said system comprises at least
three magnetoresistance detectors.
10. The system of claim 6 wherein said magnetoresistance detector
detects perturbations of the earth's magnetic field by the
mechanical system.
11. The system of claim 6 wherein said magnetoresistance detector
detects magnetic fields generated by electromagnetic components of
the mechanical system.
12. The system of claim 6 wherein said magnetoresistance detector
detects radio waves generated by the mechanical system.
13. A magnetic field sensing method for locating defects in objects
in two or three dimensions, the method comprising the steps of
providing a sensor comprising a magnetoresistance detector and
sensing at a plurality of frequencies.
14. The method of claim 13 wherein the sensing step senses defects
at a plurality of depths in the objects.
15. The method of claim 14 wherein the objects are printed circuit
boards.
16. A magnetic field sensing method for imaging objects, the method
comprising the steps of providing a magnetoresistance detector,
employing means for non-magnetic imaging, and analyzing images
produced by both the magnetoresistance detector and the means for
non-magnetic imaging.
17. The method of claim 16 wherein the means for non-magnetic
imaging comprises optical imaging means.
18. A method for mechanical system identification, the method
comprising the steps of providing a magnetoresistance detector and
using the detector to sense characteristics of a passing mechanical
system.
19. The method of claim 18 wherein the passing mechanical system is
a vehicle.
20. The method of claim 18 additionally comprising the step of
analyzing output of the magnetoresistance detector and comparing
results to known characteristics of items selected from the group
consisting of: perturbations of the earth's field by a moving
metallic object or vehicle; fields associated with electric motors;
fields associated with generators and alternators; fields
associated with spark plugs, wires and coils; fields related to
rapidly moving metallic parts; and fields associated with large
masses of metals.
21. The method of claim 18 wherein the providing step comprises
providing at least three magnetoresistance detectors.
22. The method of claim 18 wherein in the using step the
magnetoresistance detector detects perturbations of the earth's
magnetic field by the mechanical system.
23. The method of claim 18 wherein in the using step the
magnetoresistance detector detects magnetic fields generated by
electromagnetic components of the mechanical system.
24. The method of claim 18 wherein in the using step the
magnetoresistance detector detects radio waves generated by the
mechanical system.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part application of
U.S. patent application Ser. No. 09/969,946, entitled ULTRA
SENSITIVE MAGNETIC FIELD SENSORS, to Timothy C. Tiernan, et al.,
filed on Oct. 2, 2001, which is a continuation-in-part application
of U.S. patent application Ser. No. 09/265,991, entitled INTEGRATED
MAGNETIC FIELD SENSORS FOR FUZES, to David W. Cutler, et al., filed
on Mar. 9, 1999, issued on Oct. 2, 2001, as U.S. Pat. No.
6,295,931, which claimed the benefit of the filing of U.S.
Provisional Patent Application Serial No. 60/077,525, entitled
SENSITIVE INTEGRATED MAGNETIC FIELD SENSORS FOR FUZES, filed on
Mar. 11, 1998; and of U.S. Provisional Patent Application Serial
No. 60/092,717, entitled SENSITIVE INTEGRATED MAGNETIC FIELD
SENSORS FOR FUZES, filed on Jul. 14, 1998; and the specifications
thereof are incorporated herein by reference.
[0002] This application also claims the benefit of the filing of
U.S. Provisional Patent Application Serial No. 60/301,786, entitled
ULTRA SENSITIVE MAGNETIC FIELD SENSORS, filed on Jun. 29, 2001, and
the specification thereof is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention (Technical Field)
[0005] The present invention relates to sensors made of giant
magnetoresistance materials (GMR), colossal magnetoresistive (CMR)
materials, or anisotropic magnetoresistive (AMR) materials. The
terms magnetoresistance and GMR, as used throughout the
specification and claims, are intended to include giant, colossal,
and anisotropic magnetoresistance or magnetoresistive
materials.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)
[0006] The present invention is of a magnetic sensor and magnetic
field sensing method for ordnance, comprising locating a giant
magnetoresistance detector within the ordnance and detecting
magnetic fields with the detector. In one embodiment, turns of
spinning ordnance are counted, with autonulling being employed,
such as injecting a charge into a circuit comprising the giant
magnetoresistance detector, the charge injection being triggered
upon exit or when a rate of spin of the ordnance exceeds a
predetermined rate. In another embodiment, ordnance is armed a
pre-determined time after exit of the ordnance from a weapon firing
the ordnance, which can involve one or more of the following:
determining exit of the ordnance from a weapon firing the ordnance
(preferably by detecting concentrated earth's magnetic field lines
at an opening of a weapon firing the ordnance), determining exit
velocity, determining proximity to metallic targets, and
determining direction to metallic targets. Turns count and other
information can be programmed into the sensor using an inductive
programmer or other approach, using data from the targeting system
of the munitions delivery system, to enable programming of the
sensor just before it is fired. In another embodiment, incoming
munitions are detected either through purturbation of the earth
magnetic field, or by their intrinsic magnetic properties, such as
by employing a biasing magnet, employing an oscillation frequency,
employing a coil proximate the exterior or nose of the ordnance,
employing multiple detectors and triangulation means, and/or
employing an array of detectors. The detector is preferably
fabricated on a printed circuit board, hybrid circuit, or
integrated circuit. The sensor can also perform one or more of the
following functions: outputting a signal characteristic of impact
of the ordnance, employing a map of local magnetic fields to
determining position and direction of an object, detecting flying
objects by looking for response to an emitted magnetic field, and
determining eddy currents output by flying object traversing
earth's magnetic field.
[0007] The present invention is also of a magnetic field sensor and
sensing method for locating defects in objects in two or three
dimensions, comprising providing to a sensor a giant
magnetoresistance detector and traversing the sensor over an
object. In the preferred embodiment, one or more of the following
functions are performed: measuring induced or intrinsic magnetic
fields to determining type of defect, determining volume lost to
defect, determining depth of defect, imaging the defect,
determining dimensions of defect, and producing Lissajous plots of
amplitude versus phase for magnetic fields.
[0008] The present invention is further of a magnetic field sensor
and sensing method for medical imaging, comprising providing to a
sensor a giant magnetoresistance detector and traversing the sensor
over a patient. In the preferred embodiment, one or more of the
following functions are performed: measuring electromagnetic
activity in the patient's heart, measuring electromagnetic activity
in the patient's brain, performing biomagnetics analysis,
performing nuclear magnetic resonance imaging, and imaging skin
defects or tissue anomolies.
[0009] The invention is additionally of a magnetometer and
magnetometry method comprising providing a giant magnetoresistance
detector and operating the detector. In the preferred embodiment,
one or more of the following functions are performed: detecting
conductive materials on a surface, detecting conductive materials
beneath a surface, detecting conductive materials in a body of
liquid, locating naval vessels, detecting electrical currents
flowing through printed circuit board traces, detecting electrical
currents flowing through integrated circuit components, measuring
amplitudes of electrical currents, and detecting breaks in
electrical conductors. Operation may be in DC detection mode or
employing oscillating magnetic fields or ambient fields.
[0010] The present invention is also of a magnetic field sensing
system and method for locating defects in objects in two or three
dimensions, comprising providing a sensor comprising a
magnetoresistance detector and sensing at a plurality of
frequencies. In the preferred embodiment, defects at a plurality of
depths in the objects (e.g., printed circuit boards) are
sensed.
[0011] The invention is further of a magnetic field sensing system
and method for imaging objects, comprising providing a
magnetoresistance detector, employing means for non-magnetic
imaging, and analyzing images produced by both the
magnetoresistance detector and the means for non-magnetic imaging.
In the preferred embodiment, the means for non-magnetic imaging
comprises optical imaging means.
[0012] The invention is additionally of a system and method for
mechanical system identification, comprising providing a
magnetoresistance detector and using the detector to sense
characteristics of a passing mechanical system. In the preferred
embodiment, the passing mechanical system is a vehicle. Output of
the magnetoresistance detector is analyzed and compared to known
characteristics of one or more of the following: perturbations of
the earth's field by a moving metallic object or vehicle; fields
associated with electric motors; fields associated with generators
and alternators; fields associated with spark plugs, wires and
coils; fields related to rapidly moving metallic parts; and fields
associated with large masses of metals. Preferably at least three
magnetoresistance detectors are employed. The detector can detect
perturbations of the earth's magnetic field by the mechanical
system, magnetic fields generated by electromagnetic components of
the mechanical system, and/or radio waves generated by the
mechanical system.
[0013] Objects, advantages and novel features, and further scope of
applicability of the present invention will be set forth in part in
the detailed description to follow, taken in conjunction with the
accompanying drawings, and in part will become apparent to those
skilled in the art upon examination of the following, or may be
learned by practice of the invention. The objects and advantages of
the invention may be realized and attained by means of the
instrumentalities and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings, which are incorporated into and
form a part of the specification, illustrate one or more
embodiments of the present invention and, together with the
description, serve to explain the principles of the invention. The
drawings are only for the purpose of illustrating one or more
preferred embodiments of the invention and are not to be construed
as limiting the invention. In the drawings:
[0015] FIG. 1 is an electrical schematic of the preferred spinning
round sensor of the invention;
[0016] FIG. 2 is a diagram of a circuit board incorporating the
sensor of the invention;
[0017] FIG. 3 is a graph showing signal pulse upon exit from a
mortar tube of a munition incorporating the sensor;
[0018] FIG. 4 illustrates the sine wave detected by the sensor as
generated by the rotation of a munition, with each cycle being
equivalent to one rotation of the munition;
[0019] FIG. 5 is an electrical schematic of the barrel exit
detection embodiment of the invention, useful with mortars and
non-rotating rounds;
[0020] FIG. 6 is a perspective view of a data logger PCB
incorporatable into a 40 mm round for testing purposes;
[0021] FIG. 7 is a front perspective view of a round incorporating
data logger and sensor PCBs just before final assembly;
[0022] FIG. 8 is a block diagram of a system useful in arming a
device according to the invention and collecting data from an
on-board data acquisition system;
[0023] FIG. 9 illustrates a conditioned signal output by the data
logger PCB, each square wave transition corresponding to one
revolution of the 40 mm round;
[0024] FIG. 10 illustrates use of the sensor of the invention
within a counter munition;
[0025] FIG. 11 is a perspective view of a handheld NDE unit
including graphical modes that can resolve defects to a depth of
more than 0.4" in 6061T6;
[0026] FIG. 12 is a top view of a 196-element tunnel junction
imaging array;
[0027] FIG. 13 is an 11 kHz C-scan of first and second layer rivet
heads in an aluminum sheet metal section simulating an aircraft
wing;
[0028] FIG. 14 shows 100 micron wide cuts in an aluminum sheet
metal sample;
[0029] FIG. 15 is an APET image of a 10% mass loss corroded region
measured through 60 mils of aluminum, made from the side opposite
the corrosion;
[0030] FIG. 16 illustrates use of the sensor of the invention for
guidance of a munition according to the invention to an under-sea
mine;
[0031] FIG. 17 is a top view of a 14.times.14 element array of GMR
sensors produced on a single substrate, each element being
approximately 10.times.10 microns;
[0032] FIG. 18 is output from a two-dimensional GMR sensor array
according to the invention showing variations in magnetic field
strength over an area of metal; and
[0033] FIG. 19 is a block diagram of a system according to the
invention used for non-destructive evaluation of a sample.
DESCRIPTION OF THE PREFERRED EMBODIMENTS (BEST MODES FOR CARRYING
OUT THE INVENTION)
[0034] Magnetic Field Sensors For Munitions
[0035] The present invention is directed to an advanced, giant
magnetoresistive (GMR) based sensor platform for detection of spin
rate and muzzle exit, muzzle exit velocity, range, proximity,
attitude, and/or guidance of munitions from within the fuze
assembly of an advanced munition. The sensor can operate with both
rotating rounds such as a 40 mm rotating round or with non-rotating
rounds such as a 60 mm mortar. The invention can also operate with
finned munitions. The sensor can be programmed at the time of
firing using induction programming techniques or similar
programming technology to cause the fuze system to activate based
on data obtained from a targeting system.
[0036] Extensive shock and thermal testing was employed to verify
the robustness of the sensor. The sensor and support electronics
were transferred to a production board package in order to provide
single board sensors for turns counting or barrel exit sensing.
Live-fire tests were successfully completed for a 40 mm rotating
round. The tests were successful and showed that it is possible to
monitor barrel exit, rotations, velocity, and range all with a
single ambient field sensor. The results showed that the sensor was
able to provide data that can monitor munition flight distance with
an error of less than 1% (0.84%). Evaluations of barrel exit
detection, tolerance of mechanical shock, and environmental
durability of the sensors were also positive using an 60 mm mortar
tube.
[0037] The preferred spinning round circuit design is as follows,
including an autonulling capability (see FIG. 1). Upon setback or
alternately as soon as the sensor begins to spin at a rate above a
few Hz, the circuit injects a small charge into the sensor to
compensate for any polling (due to large magnetic field exposure)
that has taken place during storage of the sensor or munition. The
rate of rotation for activation is high enough that it will not
null the sensor if the munition is dropped or rolled during
handling. When fired, the rotation due to rifling of the gun barrel
makes the sensor spin at a sufficient rate, while the sensor is
still in the barrel of the gun, to activate the autonulling. This
ensures that the sensor is biased properly to detect barrel exit
when it is fired, and begin counting turns when the munition exits
the barrel.
[0038] The circuit automatically nulls the GMR sensor during
power-up. This compensates for any residual magnetization that may
have occurred due to close proximity of the sensor to large
magnetic fields.
[0039] The circuits are preferably built on printed circuit boards
(PCB), which offer low power operation in a small enough package to
meet the demands of both 40 mm rounds and 60 mm mortars. Circuits
built this way are much less expensive to design layout, build and
test, than are circuits made with hybrid techniques. However,
hybrid circuits may be used where a smaller package is needed.
[0040] Shock testing was performed prior to firing the 40 mm test
rounds. The sensor and electronics system were unaffected by
exposure to shock. During live fire tests with 40 mm rounds the
sensor and electronics withstood the shock with no failures or any
signs of damaging effects.
[0041] The present invention can also measure barrel exit time and
barrel exit velocity for mortars. Using techniques and sensors made
from giant magnetoresistance materials (GMR), highly durable, low
power sensors detect barrel exit in both 60 mm mortars, and 40 mm
spinning rounds (FIGS. 2 and 5). Larger diameter mortars (e.g., 80
mm and 120 mm) require that the sensor have the ability to
dependably detect the edge of the mortar tube using a passive
approach such as measuring the earth's magnetic field concentration
at the edge (exit) of the mortar, or using an active mode, for
example, a small permanent magnet mounted on the end of the mortar
tube having a large distance between the sensor and the edge of the
mortar tube. Laboratory tests with larger diameter mortars indicate
that the invention can measure both exit time and exit velocity in
these munitions.
[0042] The present invention also provides an advanced magnetic
safing and arming (S&A) sensor technology based on giant
magnetoresistive sensors. Extensive tests, including live fire
tests with 40 mm munitions were performed with both turns-counting
and barrel-exit sensing configurations for rotating rounds. The
present invention includes non-rotating rounds, specifically 60 mm
mortars. The sensors survived repeated mechanical shock tests in
excess of 100,000 gs and environmental cycling ranging from 150 C
to -180 C.
[0043] Tunnel-junction or spin valve GMR sensors with a resistance
change of 7-15% in a 2 Oe magnetic field applied perpendicular to
the easy axis of the device have been used. In general, high
sensitivity to magnetic field is desirable The sensor sizes used
range from 0.4 mm.times.1 mm to 10 .mu.m.times.10 .mu.m. The device
impedance used ranged from 100 .OMEGA. to 10 k.OMEGA. but other
device impedances can be used depending on the application. In
general high impedance (ohms per square) helps reduce the size of
the sensor, and this saves power and reduces the size of the
sensor. The bandwidth of the sensor used was >1 Ghz, making it
capable of detecting extremely rapid changes in magnetic fields.
Power consumption of the sensor and support electronics is has been
shown to be approximately 1 milliamp at 3 volts for the spinning
round sensor. Power requirement will vary depending on the sensors
and circuitry needed for each application. The size of the sensor
and its support electronics, mounted on a standard printed circuit
board, is not an impediment since the entire assembly easily fits
inside a 40 mm round or a 60 mm mortar fuse well without the need
for modifications to the munition. If a smaller sensor system is
needed the sensor and circuit can be fabricated as a hybrid
integrated circuit, greatly reducing the physical size of the
sensor device.
[0044] In one embodiment, the sensor operates by detecting the
magnetic field of the earth. In the case of a mortar round, the
local field gradient is concentrated by the metal mortar tube.
Inside the tube there is little or no magnetic field. At the
opening of the mortar tube, the earth's magnetic field lines are
concentrated by the edges of the mortar tube, resulting in a
relatively strong field. When the mortar is fired, the sensor does
not respond until it passes the end of the mortar tube where it
detects the concentrated magnetic field. The sensor outputs an
electrical pulse that can be used as a trigger to mark barrel exit,
and arm the mortar (FIG. 3).
[0045] In the case of a rotating round, the sensor is mounted such
that it spins along with the munition. As it spins, its sensitive
axis cycles from alignment with the earth's magnetic filed, to
nonalignment. This results in the sensor outputting a variable
amplitude sine wave corresponding to one revolution of the munition
(FIG. 4). Since the rifling dimensions for the gun from which the
sensor is fired are known, it is possible to detect barrel exit,
speed and range of the munition.
[0046] The sensor of the present invention has a wide range of uses
including barrel exit and velocity for mortars. It can also be used
for trajectory measurements and proximity to metallic targets for
non-rotating rounds. The sensor system has highly desirable
characteristics including: extremely small size, low power
operation, high shock resistance, wide temperature range, and
extremely fast response time. Its operation is based on the earth's
magnetic field making it highly reliable and independent of other
system such as GPS. The sensor system benefits munitions programs
by offering a high performance low cost alternative for arming and
safing applications for both non-rotating and rotating
munitions.
[0047] Design of the Barrel Exit Sensor and Circuitry for a 120 mm
Mortar
[0048] Accurate barrel exit detection is related to the ambient
noise level, signal state separation, and sensor bandwidth. The
sensor output when in the mortar tube compared to sensor output
during barrel exit is sufficient reliable barrel exit detection. If
the sensor bandwidth is much smaller than the event bandwidth both
event detection and timing accuracy are degraded. Bandwidth, and
signal output while inside the mortar tube do not pose problems.
The sensor can detect the threshold of the mortar tube where the
earth's magnetic field is concentrated by the metal mortar
tube.
[0049] Several techniques can be used to increase detection
capability and reliability:
[0050] Using the same sensors described above for a 60 mm mortar,
determine if there is sufficient sensitivity to detect barrel exit.
If not, refine the gain and frequency response of the circuitry to
improve performance as needed.
[0051] Use a more sensitive sensor and/or sensor arrays with
extremely high sensitivity.
[0052] Use a number of offset sensors each oriented in a different
direction to determine if any one of them or any combination of
them detect the concentrated field at the mouth of the mortar tube.
This array of sensor can be read in a logical mode (e.g., AND, OR)
to increase the detection capabilities and reliability of the
sensor configuration.
[0053] Use permanent magnet in conjunction with the sensor. For
example, a permanent magnet may be placed at the end of the mortar
tube where the field would be detected by the sensor(s) as the
munition exits the mortar tube.
[0054] The preferred barrel exit circuitry (see FIG. 5) is
preferably similar to the electronics developed and tested for
mortar exit and spinning rounds. In its simplest form, the circuit
has a self-nulling capability so that when it is activated by
powering the sensor, the bias point of the sensor is set to the
center of its full range output. The circuit will then continuously
compare the real-time output of the sensor to a preset voltage that
corresponds to the output of the sensor under low magnetic field
conditions.
[0055] When the sensor (and mortar) exit the mortar tube, the
sensor detects the earth's magnetic field concentrated at the mouth
of the launch tube (barrel). When the sensor detects the magnetic
field concentration, its output causes the on-board detection
circuitry to cross a preset comparison voltage. To accomplish the
same goal, the sensor may also detect permanent magnets mounted at
the end of the launch tube. This results in a high-speed digital
pulse that is used to trigger the fuzing system. If two sensors are
used with a known distance between the sensors, then the speed of
the munition can be determined at barrel exit. This information can
be used for range analysis and compensation due to weather, wind,
or other conditions. Additional filtering circuitry may be used so
that the sensor amplifier responds only to high frequency pulse
characteristic of high-speed barrel exit. This helps eliminate
noise and other spurious signals due to set back, permanent
magnetic fields in the mortar tube, and accidental dropping of the
mortar round or low speed exit (misfire).
[0056] The barrel exit sensors of the invention preferably use
standard printed circuit board (PCB) techniques utilizing SIOC
packaged ICs, and chip capacitors and resistors.
[0057] The barrel exit sensors of the invention were evaluated
using both a drop tower and a simulation station. The drop tower
consists of a metal tube made of materials and dimensions similar
to a 120 mm mortar tube. Alternatively, a modified 120 mortar tube
may be used. The test apparatus allowed for mechanical acceleration
to achieve high velocities for meaningful testing of the barrel
exit sensor.
[0058] The simulation test station was based on using an arbitrary
waveform generator, coupled to a discharge-capacitor driven current
source to simulate the transient of a much faster barrel exit than
that achievable using a drop tower configuration. In principle this
simulation station accurately reproduce the magnetic field
perturbation of a gun barrel exit at speeds in excess of 5,000 m/s,
a velocity actually achieved by some munitions such as the kinetic
energy rod. This velocity is well within the bandwidth limitations
of the sensor of the present invention.
[0059] 60, 80, and 120 mm mortar tubes were tested. Barrel exit
detectability was enhanced for the larger mortar tubes by improving
the sensor and circuitry specifically for the larger mortar by
using flux guides, optimized geometry and signal processing
techniques. The sensor was able to detect the edge of the larger
mortar tubes during barrel exit under simulated conditions.
[0060] Programs were performed related to GMR sensors for
applications in both safing and fuzing, and in the use of GMR
sensors and sensor arrays for nondestructive evaluation. In the
area of safing and fuzing it was shown that the sensor can be used
to detect revolutions in a 40 mm round during live fire testing.
The sensor provided information that enabled an on-munition system
to determine barrel exit, munition velocity, and range.
[0061] Tests with mortars were conducted. A sensor was made that
was able to detect barrel exit in a 60 mm mortar. Live fire tests
confirmed the utility of the sensor. In addition to sensor and
circuit design, mechanical shock testing, and environmental testing
were performed with good results.
[0062] Signal conditioning and readout electronics were also
developed. This resulted in tunnel junction GMR sensor arrays for
NDE. The sensor elements developed were only 10 microns on a side,
yet delivered 7% (AR in a 2 Oe field with nominal resistance near
10 k). Signal conditioning and readout electronics for the sensors
were also developed.
[0063] Sensors for Fuze Applications
[0064] As described previously, the present invention provides
technology to measure barrel exit, spin velocity, and range using
GMR sensors detecting the earth's magnetic field. Sensor systems
were fabricated for live-fire testing. Tests with the 40 mm
spinning round were done. Three (3) data recorder/spin sensor
assemblies were fabricated, tested and potted into 40 mm back
shells. Each final potted test unit was numbered 1, 2 and 3. Once
the operation of the data recorder and spin sensor were
individually functionally verified, the two PCBs were
interconnected and tested (assembly shown in FIGS. 6 and 7).
[0065] Prior to triggering and recording, the data recorder was
powered and armed. This was accomplished through a 7.5 v battery or
power supply source, laptop computer and an RS-232 interface. This
setup is shown in FIG. 8. The computer communicates to the data
recorder through the RS-232 interface and cable. The data recorder
microprocessor firmware program is a self-contained program that
performs BIT functions, arming, data upload, sampling rate and
record time selection. The computer used the Windows program
"Hyperterminal" to communicate with the data recorder. This program
provides communication with the data recorder for operator
parameter entry as well as data upload "receive text file" mode to
upload the data from the data recorder to a file on the hard disk.
This text was then imported to "Excel" to plot the data to a graph
(see FIG. 9).
[0066] Flight Distance Calculations During Field Testing
Predicted Flight Distance==Muzzle Velocity*Flight
Time=831*0.25=207.75 ft
Turns Calculated Flight Distance=# of Turns*4 ft/Turn=51.5*4=206.0
ft 1 %Error = ((PredictedFlightDistance -
TurnsCalculatedFlightDistanc- e) / PredictedFlightDistance) * 100 =
( ( 207.75 - 206 ) / 207.75 ) * 100 % = 0.84 %
[0067] Safing and Arming Sensor--Counter Munitions
[0068] The present invention also relates to advanced magnetic
safing and arming (S&A) sensor technology based on giant
magnetoresistive (GMR) sensors (see FIG. 10). The counter munition
would initially be guided by radar which would also sense the
munition. Once the counter munition neared its target the GMR
sensor(s) would pinpoint its location and set the needed time delay
on the fuze for maximum destructive power to the target. The
present invention provides a sensor that can detect incoming
munitions such as the KE rod or TOW missile. The sensor provides
proximity information that is used by ISP to destroy the incoming
munition before it reaches its target (e.g., a tank).
[0069] The sensor is mounted in the nose of the counter munition.
It senses the local field strength. When nearing an incoming
munition, it detects a change in the magnetic field strength due to
permanent magnetic fields generated by ferromagnetic metal in the
munition. It also detects the change in the Earth's magnetic field
due to the variations in the field lines caused by metal in the
munition. Changes in field strength detected by the sensor provides
the proximity information needed to detonate the counter munition
at the most advantageous time
[0070] One approach to increase sensitivity is to place a permanent
magnet near the sensor as a biasing magnet. As the sensor
approaches the metallic munition, the bias point changes due to the
ferromagnetic metal in the munition.
[0071] An active sensor with an oscillation frequency selected for
the type of munition can be used. The sensor is inductively
programmed at the time of counter munition launch for the type of
incoming munition, based on radar information from the ISP system.
A coil wrapped around the nose or any surface of the counter
munition emanates an electromagnetic frequency selected for the
type of incoming munition. The magnetic field properties generated
by the coil change as the counter munition nears its target, thus
providing the information needed for optimum detonation of the
counter munition.
[0072] In all of these cases, multiple sensors can be used for
triangulation. This increases angular sensitivity, and provide more
detailed information about the incoming munition which can be used
to enhance the performance of the counter munition.
[0073] The sensor preferably has the following properties:
[0074] Reponse time: 1 ns
[0075] Bandwidth: >1 GHz
[0076] Signal to noise ratio: depending on application CAN be
>1000
[0077] Power consumption: .about.3V at 2 mA for passive sensor
[0078] Field of view: 3600
[0079] Environmental ruggedness: The sensor and circuit on a PCB
have been tested to 100,000 g in live fire tests of rotating
rounds; temperature tolerance of sensor has been demonstrated at
-1800 C to +1500 C
[0080] Size and weight: Current fuze circuit and sensor fit on
round PCB 25 mm diameter that weighs 1.8 grams. Could be smaller as
a hybrid circuit. Actual sensor is approximately 100.times.100
microns.
[0081] The sensor technology has a wide range of uses including
barrel exit and velocity for mortars, and range for spinning
rounds. It also can be used for trajectory measurements and
proximity to metallic targets. The sensor system has highly
desirable characteristics including: extremely small size, low
power operation, high shock resistance, wide temperature range, and
extremely fast response time. Its operation is based on the local
magnetic fields, making it highly reliable and independent of other
system such as GPS. The sensor system benefits munitions programs
by offering a high-performance, low-cost alternative for arming and
safing applications for both non-rotating and rotating
munitions.
[0082] Targeting Sensor
[0083] The present invention also provides a targeting sensor. It
uses a single sensor or an array of sensors (see FIG. 17). The
sensors provide information regarding the location and/or proximity
of the munition to its target. Relative signal strengths and
frequency responses are used to identify types of targets for
positive identification or IFF (identification friend or foe).
[0084] Medical Imaging Sensor
[0085] This type of sensor or sensor array can also be used in the
medical field. For example, it can be used to measure
electromagnetic activity in the heart or brain. It can be used as a
sensor in the field of biomagnetics. It can also be used in nuclear
magnetic resonance imaging. The ability of the sensor to detect
magnetic fields in a single plane or line makes it suitable for use
in imaging skin defects or tissue anomalies. It can also be used
for imaging low volume point defects. The small signals from small
volume defects can be extremely difficult to detect using standard
NMR imaging because the signals from the small volume area are
overshadowed by those from larger volume areas which contain more
hydrogen, and therefore produce larger signals.
[0086] Target Identification
[0087] There are many different types of magnetic information
produced by vehicles and like mechanical systems, all of which can
be used to accurately identify and characterize the source of the
field. Among these sources are: perturbations of the earth's field
by a moving metallic object or vehicle; fields associated with
electric motors; fields associated with generators and alternators;
fields associated with spark plugs, wires and coils; fields related
to rapidly moving metallic parts such as cooling fans, gears and
motor parts; fields associated with large masses of metals such as
boat hulls, mines, trucks, aircraft, and tanks. Each source will
produce characteristic amplitudes, frequencies and periodicity
related to the layout of-vehicle and its speed when passing the
sensor. By using an integrated approach to the analysis of the all
the different types of magnetic fields generated, there will be
considerable information available for accurate determination of
the type of source and level of threat.
[0088] Vehicle Analysis and Differentiation
[0089] In the case of passive detection of the perturbations in the
earth's magnetic field caused by a moving metallic object
(vehicle), the resulting magnetic signature is produced by the
shape and metallic composition of the vehicle. For example, the x,
y and z components of the magnetic signature of a moving object can
be detected by sensors buried underneath the surface of a road or
beneath the surface of a body of water. In the case of a road, at
the surface of the road, the magnitude of the magnetic field
produced by a vehicle will be approximately the same as the earth's
magnetic field or .about.0.5 Oe. The sensor must have sensitivity
that is high enough to measure magnetic fields that could be at or
below the earth field. This calls for high sensitivity at low
frequencies (slow moving vehicles will produce field information
down to 1 Hz.). Sensors according to the present invention offer a
signal to noise ratio of .about.20,000 at 0.5 Oe and 1 Hz. This
type of sensor has both the sensitivity and low noise
characteristics required for the measurement of the small magnetic
fields that will be encountered by the buried sensors.
[0090] Using three sensors and vector analysis, it is possible to
obtain three-dimensional information concerning length, width and
height of the vehicle. Wide vehicles such as tanks produce a much
larger y component response compared to a thinner automobile or
bus. The amplitude of the signal provides information concerning
the metallic composition of the vehicle. For example a bulldozer,
tank, or armored personnel carrier would contain more steel than an
auto or school bus. Another approach is to determine the distance
between the front of the vehicle and the first axle, or simply
counting axles.
[0091] Sensor arrays are preferred to enhance the ability of the
system to characterize the vehicle. For example, it is possible to
analyze strips of information. The additional sensors also improve
the amount of data available so that statistical analysis can be
used to effectively reduce noise and increase vehicle confirmation
accuracy.
[0092] To supplement the information produced by the perturbation
of the earth's field, several other magnetic field sources are
preferably examined. In the case of magnetic fields emanating from
generators, electric motors, and fast moving mechanical parts, the
frequency, field amplitude and position of the source in the
vehicle can be used to identify the vehicle. These sources will
generally have higher frequencies than the perturbation of the
magnetic fields. This difference in frequency will allow the
sources to be separated for individual analysis. The field
magnitude may also be much larger due to the high currents and/or
voltages produced. This type of analysis can provide information
such as the number of motors, how large they are, where they are
located, and what their power output is. All of this provides
valuable information for vehicle characterization.
[0093] Moving mechanical components such as fans, gears, and moors
parts will also provide magnetic field information. Again,
frequency and amplitude information are likely to be differentiated
from other components of the vehicle. In general, they will be
higher frequency and lower noise than both the electrical
components of the vehicle and the signals generated by electrical
components. One can determine the distance of a cooling fan from
the front of the vehicle or the number of gears on a flywheel. This
sort of information will help detail the characteristics of the
vehicle.
[0094] Another potentially overlooked information source inherent
to many military and construction vehicles is its communication
system. Devices such as radio and telephone produce significant
amounts of high frequency electromagnetic information. One can
detect radio waves using a sensor according to the present
invention with high signal to noise ratio. One can both measure the
frequency of the signal and possibly demodulate the signal and
determine the content of the communication.
[0095] Obtaining all of this information requires a fast and highly
efficient data collection scheme. Sensors according to the present
invention used in conjunction with computerized data collection and
analysis circuitry can operate at low power levels (.about.3 mw
when active) yet can collect data at 20 mHz. Such circuitry can fit
on a printed circuit board about the size of a quarter dollar, and
has been subjected to 100,000 g by firing on board a 40 mm round.
It is preferred to include a power management capability to reduce
power consumption to 0.3 microamps at 3 v by using one of the
sensors, such as a seismic sensor, to activate the circuitry,
permitting the magnetic field sensor system to remain functional
for over ten years using a single coin cell battery.
[0096] Sensor integration will be an important aspect of a sensor
system according to the invention. The information generated by
several magnetic field sensors can be analyzed using several
different techniques. Each sensor will produce information
concerning field amplitude, frequency and position of the source.
This independent information will provide information to decide the
type of vehicle being scanned. It can also be used to compare to a
magnetic field signature for known vehicles or types of vehicles.
It can also be used as nodes in a neural network. In the case of
biosensors, a neural network can be used to improve the selectivity
of the array for molecular analysis. For magnetoresistance sensors,
such analysis can be used to correlate frequency, amplitude and
phase data to produce high spatial information, three-dimensional
images of magnetic field sources.
[0097] A second aspect of sensor fusion is in improving power
management and the functional lifetime of the sensor. One approach
is to use data from the seismic sensors to activate the magnetic
sensors. Another approach is activating the magnetic field sensors
for a few microseconds each second (the sensors and circuit
activate in .about.1 ns) to determine the presence of a threat, and
the need to fully activate the entire system. The combination of
the data output from the different types of sensors in the system
will also improve the characterization of the vehicle and increase
the probability of it being able to perform as desired.
[0098] Magnetoresistance Sensors and Sensor Arrays For
Nondestructive Evaluation (NDE)
[0099] The magnetoresistance sensors and arrays of the present
invention can also be employed for NDE of conductive components
(see FIG. 19, sample results in FIG. 18). Sensors according to the
present invention can be used to detect, scan, and image eddy
currents in defective metallic components, such as sheet metal
parts or pipe welds. This is particularly valuable for evaluation
of items with small feature size such as printed circuit boards,
flip chips, and printed circuit tapes. An array of sensors with
dimensions on the order of 1 to 50 microns can detect defects that
are micron-sized or smaller.
[0100] Because magnetic fields pass through materials it is
possible to form three-dimensional images of materials. The depth
of penetration of an induced magnetic field is dependant on field
frequency and the electronic properties of the material. This
phenomena will provide depth information at any given magnetic
field induction frequency.
[0101] Using a variety of different frequencies enhances the
ability to perform depth analysis. When evaluating objects such as
printed circuit boards, images made at different frequencies will
obtain data at various depths in the material. It is possible to
use high frequencies to examine only the top layer(s) of the
printed circuit board because at sufficiently high frequencies the
field will not penetrate beyond the first layer of the printed
circuit board. Lower frequencies will allow analysis deeper into
the material. By collecting data at a variety of frequencies, it is
possible to separate the upper layers of a material (or printed
circuit board) from the lower layers. In this way depth analysis
can be performed. For example, it would allow non-destructive
evaluation of individual layers in a printed circuit board.
[0102] Tunnel junction GMR sensor arrays for NDE were developed.
The sensor elements developed were only 10 microns on a side, yet
delivered 7% (AR in a 2 Oe field with nominal resistance near 10
k). Signal conditioning and readout electronics for the sensors may
also be employed. Other types of GMR and CMR sensors can also be
used rather than the preferred tunnel junction type of GMR device.
The source of the magnetic field may be induced eddy currents,
electrical current flow through a trace, wire, or component, or
another source.
[0103] U.S. Pat. No. 6,150,809, entitled "Giant Magnetorestive
Sensors and Sensor Arrays for Detection and Imaging of Anomalies in
Conductive Materials" relates to magnetic and electromagnetic
nondestructive evaluation. This technology is based on a
synergistic combination of a traditional eddy-current coil or
permanent magnet and a unique magnetic sensor based on a class of
materials known as giant magnetoresistors. The result is a sensor
exhibiting substantially higher field sensitivity and spatial
resolution when compared with traditional methods. Since these
sensors directly sense the magnetic field, rather than changes in
the field as is the case for coils, they can be operated with high
sensitivity at very low frequencies and even with DC generated
fields.
[0104] A handheld NDE instrument was developed. This system was
able to detect third layer (0.065" 2024T3 per layer) cracks without
the need for bench-top instrumentation. The present invention is a
handheld NDE unit along with a variety of sensors as shown in FIG.
11. This unit provides four different graphical data display modes
and is capable of resolving defects to a depth of approximately
0.2" using the smaller diameter probes and to a depth of
approximately 0.4" using the larger probe.
[0105] Current GMR detectors include several configurations. Most
are packaged using molded urethane. The process begins with a
sensor, coil and flux focusing (if applicable) alignment on a
metrology station. The aligned assembly, along with the electronics
subsystem, sapphire wear surface and electrical connector, is then
encased in color-coded urethane. This process provides a rugged and
compact package for the sensor and eliminates costly machining.
[0106] The sensors are typically driven with a constant-current AC
drive between 50 Hz and 25 kHz. At 1 kHz the 3/8" diameter sensors
can easily resolve EDM cuts less than 0.25" in length through
0.195" of 2024T3. A larger, 3/4"version of this sensor has be used
to image anomalies to over 0.4" in 6061T6.
[0107] Two-dimensional imaging arrays of GMR elements have been
designed and units have been fabricated. Functional arrays
consisting of 196 tunnel-junction sensors (14.times.14). The
individual sensors are only a few square microns in area and are
positioned on a grid with a sensor-to-sensor spacing of
approximately 210 microns. The active area of the entire
14.times.14 element array is less than 3 mm on a side (9 mm2). FIG.
12 shows a photo of one of the imaging array prototypes. In this
photo the magnetic field generation has been removed. Large
(4".times.4") arrays provide for real-time imaging of deeply
imbedded defects and corrosion.
[0108] High resolution images of magnetic fields were obtained by
performing raster scans of various test samples. FIG. 13 shows an
11 kHz scan of first and second layer rivet heads in an aluminum
sheet metal section simulating an aircraft wing. FIG. 14 shows 100
micron wide cuts in an aluminum sheet metal sample. This data
demonstrates the extremely high signal-to noise ratio obtainable
with the GMR sensor technology of the present invention.
[0109] FIG. 15 shows an image of a corrosion test sample provided
by the Federal Aviation Administration, Nondestructive Inspection
Validation Center (FAA/AANC). The sample is a 0.06" thick, 2024T3
plate with a nominal 10% uniform mass loss corrosion region on one
side. The image corresponds to a scan performed on the side
opposite the corroded region. The boundary of the corroded region,
as well as the pitting within the corroded region is sharply
defined in the image and the signal-to-noise ratio in excess of 100
for these features.
[0110] A fusion of magnetic vision (MV) and other types of machine
vision is useful for applications such as sorting metals or
locating defects. Information from both types of images, taken
together, can be the only effective way to provide the total amount
of information needed of complete analysis. The images from a MV
system and an optical system (for example) can be put together
(fused) in software. The optical image might, for example, detect
the full shape or color or differentiate plastic from metal. The MV
system might, for example, provide detailed information about the
metal parts, not possible with the optical vision system by itself.
The optical system would identify materials such as plastic that
the MV system would not be able to detect at all. The fusion of the
two data sets would provide more information than either alone, and
would be necessary for some applications.
[0111] Detection of Conductive Materials
[0112] The present invention also provides a magnetometer (see FIG.
16) for detecting conductive materials either on the surface or
underneath other materials such as earth or water (e.g., mines).
This sensor is handheld or operated from a vehicle or aircraft. It
operates in a DC detection mode or with oscillating magnetic
fields. Permanent magnets or flux concentrators are used to enhance
the signal detected by the sensor.
[0113] This type of sensor may be used to locate ships, submarines,
and other vessels. It can also be used to detect electrical
currents flowing through PCB traces or IC components. It can be
used to measure the amplitude of electrical currents. It can also
be used to detect breaks in electrical conductors which would
result in low or non-existent current flow. As such, it can be used
for inspection of many types of circuitry and wiring.
[0114] Impact Sensing
[0115] GMR sensors are magnetorestrictive. During impact such
sensors are compressed and will output a signal characteristic of
impact.
[0116] Magnetic Field Tracking for Guidance
[0117] GMR sensors according to the invention may also be used for
more sophisticated means of guidance of ordnance. A sensor can use
a map of local magnetic fields to determine position and direction
of a munition or any moving object such as an aircraft or truck.
Flying objects may be detected by looking for response to an
emitted electromagnetic field (active sensing) or looking for eddy
currents output by aircraft as they traverse the earth's magnetic
field (passive sensing).
[0118] Although the invention has been described in detail with
particular reference to these preferred embodiments, other
embodiments can achieve the same results. Variations and
modifications of the present invention will be obvious to those
skilled in the art and it is intended to cover in the appended
claims all such modifications and equivalents. The entire
disclosures of all references, applications, patents, and
publications cited above are hereby incorporated by reference.
* * * * *