Data processing: measuring – calibrating – or testing – Measurement system – Orientation or position
Reexamination Certificate
2002-11-26
2004-01-06
Nghiem, Michael (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Orientation or position
Reexamination Certificate
active
06675123
ABSTRACT:
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or for the United States Government for Governmental purposes without the payment of any royalties.
TECHNICAL FIELD
The present invention generally relates to magnetic sensors. The present invention also relates generally to the tracking of magnetic objects, and more particularly, to a computer-implemented algorithm that permits tracking of magnetic objects.
BACKGROUND OF THE INVENTION
Numerous opportunities exist for tracking objects that generate magnetic fields. All types of land vehicles, ships, and aircraft have structural and power systems capable of generating substantial magnetic signatures. Even small inert objects may exhibit sufficient magnetization to be observed from a distance. For example, the ability to determine the location of a metallic object on a person can be crucial. These applications include covert handgun detection to protect buildings and their occupants; pinpointing unexploded ordnance at converted military bases; and locating the position and depth of underground pipes prior to construction activities. The ability to track magnetic objects is also crucially important in other areas, such as medicine. For example, in the field of surgery, there exists a continuing need to control the orientation, forces, and/or motion of internally implanted devices. Clearly, both operation time and risk to a patient could be reduced if an apparatus and method were available to more accurately and rapidly guide or move a magnetic surgical implant.
A variety of magnetic sensor data processing algorithms, methods, systems and devices thereof capable of localizing, quantifying, and classifying objects based on their magnetic fields and magnetic signatures have been developed. To date, the prior art has been primarily concerned with detecting, locating, and classifying magnetic objects based on a large set of measurements distributed over space and/or time. Some techniques involve using measurements of an object's magnetic dipole moment. Metal objects such as firearms, automobiles, ships, submarines, and airplanes, for example, have magnetic dipole moments that can be utilized in their detection.
These techniques are based on dipole detection and localization algorithms, which assume that the field of a magnetic source object is well represented as the field of a magnetic dipole moment at distances far removed from the source. The location of the dipole is determined by maximizing an objective function over a grid of search points that spans the search volume. Two known limitations of this method are the assumption of a linear array of sensors and the need to search over all possible dipole orientations if the orientation is unknown.
Several other magnetic object tracking methods, systems and algorithms and devices thereof are also known in the art. For example, some magnetic object tracking techniques are based on electromagnetic anomaly detection technology, which senses an electromagnetic anomaly and pinpoints it at close to real time. Such a technique can measure how close a target is located to a sensor head, while locating the target or magnetic object in three dimensions and thereafter evaluating its orientation.
One of the problems associated with such prior art techniques for tracking magnetic objects is that they are generally based on the utilization of three components of a detected magnetic field. If measurements of the vector magnetic field are made, great care must be taken to minimize rotational vibrations. Because the earth's magnetic field is so large (i.e., on an order 50,000 nT), it is difficult to differentiate rotational vibrations from signals from an object.
Programs and algorithms based on such techniques require the inversion of a matrix and additionally require a great deal of processing time. Such programs and algorithms also usually require obtaining measurements from several sensors simultaneously. In order to perform several measurements on nearby weak sources and to avoid rotational vibrations, the sensors should be placed close to one another on a rigid frame. If the sensors are configured in this manner, the difference between the signals from strong distant sources is generally small. Additionally, obtaining accurate measurements of these small differences requires expensive sensors and the use of gradiometer algorithms. Such techniques are time consuming and also inefficient.
The present inventor has concluded that a need exists for improved methods and systems for tracking magnetic objects, which not only provider greater efficiency than prior art magnetic tracking techniques but can also process much more quickly and also in near real time on a fairly simple computer. Further, such sensing techniques should be able to utilize less accurate and lower cost sensors.
BRIEF SUMMARY OF THE INVENTION
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is, therefore, one aspect of the present invention to provide methods and systems for detecting magnetic objects.
It is another aspect of the present invention to provide methods and systems for tracking magnetic objects.
It is yet another aspect of the present invention to provide improved methods and systems for detecting and tracking magnetic objects based on data collected from one or more magnetic sensors.
It is still another aspect of the present invention to provide methods and systems for tracking magnetic objects based on the total magnetic field measured at a position of closest approach to a magnetic sensor.
The above and other aspects can be achieved as will now be summarized. Methods and systems for tracking a magnetic object are disclosed herein. A plurality of line segments can be compiled based on data received from a plurality of magnetic sensors. The line segment that minimizes an error thereof can then be determined. The path of a magnetic object can then be established based on the compiled line segments and calculated error thereof, thereby permitting the magnetic object to be tracked according to the data received from the magnetic sensors, which can be based on a measurement performed at the point of closest approach of one or more magnetic sensors to the magnetic object. The aforementioned error can be calculated, wherein the variable E
r
represents such an error. The error E
r
is generally determined according to following mathematical formula:
E
r
=
∑
i
(
S
i
S
imax
-
C
i
C
imax
)
2
In this mathematical formulation, the variable S
i
represents the total magnetic field measured by the i
th
magnetic sensor among the plurality of magnetic sensors, while the variable S
imax
represents a maximum of S
i
. The variable C
i
represents the total magnetic field calculated at a position of the i
th
magnetic sensor based on a set of assumptions regarding the magnetic object, which are described in greater detail herein. Finally, the variable C
imax
represents the total magnetic field calculated at a position of a magnetic sensor among a group of magnetic sensors at which the variable S
i
attains a maximum value.
As indicated herein, the present invention can thus permit a magnetic object to be tracked utlizing the total magnetic field measured at the position of closest approach by the magnetic object to at least one magnetic sensor from among a group of magnetic sensors. These measurements do not have to be performed simultaneously. Generally, the field measured at different sensors will be different in magnitude. Thus, less accurate, lower cost sensors can be utilized in accordance with the invention described herein.
REFERENCES:
patent: 5239474 (1993-08-01), Eaton, Jr. et al.
patent: 5381095 (1995-01-01), Andrews
patent: 5684396 (1997-11-
Nghiem Michael
Stolarun Edward L.
The United States of America as represented by the Secretary of
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