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Publication Number
US-7545140-B2
Publication Date
2009-06-09
Expiration Date
Abstract
A metal object detecting apparatus comprising, a transmitter for generating a primary magnetic field having a resultant magnetic field direction which varies along any substantially linear path through a surveillance volume such that at three locations along said path the resultant magnetic field points in three mutually substantially orthogonal directions; a detector for measuring a secondary magnetic field at a plurality of positions as a function of time due to the presence of a metal object within the surveillance volume as it passes a plurality of measurement points there-through; and a processor for determining from the measured secondary magnetic fields a track through the surveillance volume comprising a plurality of locations of the metal object and a magnetic moment thereof at each location, the processor being adapted in use to derive there-from a magnetic signature that is characteristic of the metal object and independent of the orientation and track of the metal object.
Core Innovation
The invention provides a metal object detecting apparatus that generates a time varying primary magnetic field within a surveillance volume, with the magnetic field having a non-zero magnitude throughout substantially all of the surveillance volume. Along any substantially linear path through the surveillance volume, the resultant magnetic field direction varies such that at three locations along the path the resultant magnetic field points in three mutually substantially orthogonal directions. This arrangement supports measurement of a secondary magnetic field caused by a metal object passing through the surveillance volume.
A detector measures the secondary magnetic field at a plurality of positions as a function of time due to the presence of a metal object within the surveillance volume. The detector is arranged to substantially reject the primary magnetic field. A processor determines, from the measured secondary magnetic fields, a track through the surveillance volume comprising a plurality of locations of the metal object within the surveillance volume and a magnetic moment thereof at each location.
From the determined plurality of locations and the corresponding magnetic moment at each location, the processor derives a magnetic signature that is characteristic of the metal object and independent of the orientation and track of the metal object through the surveillance volume. The derived signature is based on the magnetic polarizability tensor, including eigenvalues and eigenvalue components, and the resultant signature can be used to classify or identify the metal object by database matching against predetermined classes.
Claims Coverage
Two independent claims are provided: one to an apparatus and one to a method. Across these, the core inventive features revolve around generating a specific primary-field directional property, measuring a time-dependent secondary field while substantially rejecting the primary field, determining a 3D track with magnetic moments, and deriving an orientation- and track-independent magnetic signature characteristic of the metal object.
Primary field with orthogonal directions at three locations along a path
A time varying primary magnetic field within a surveillance volume has non-zero magnitude throughout substantially all of the surveillance volume and a resultant magnetic field direction that varies along any substantially linear path such that at three locations along the path the resultant magnetic field points in three mutually substantially orthogonal directions.
Secondary-field measurement while substantially rejecting the primary field
A detector measures a secondary magnetic field at a plurality of positions as a function of time due to the presence of a metal object within the surveillance volume as it passes through measurement points there-through, the detector being arranged to substantially reject the primary magnetic field.
Track determination with magnetic moments at multiple locations
A processor determines a track through the surveillance volume comprising a plurality of locations of the metal object within the surveillance volume and a magnetic moment thereof at each location, based on the measured secondary magnetic fields.
Orientation- and track-independent magnetic signature
The processor derives from the plurality of locations and the magnetic moment thereof a magnetic signature that is characteristic of the metal object and independent of the orientation and track of the metal object through the surveillance volume.
The independent claims collectively require a time-varying primary magnetic field whose resultant direction yields three mutually orthogonal resultant directions along any substantially linear path at three locations, time-dependent secondary magnetic-field measurement at multiple positions while substantially rejecting the primary field, processor-based determination of a track with magnetic moments at multiple locations, and derivation of an orientation- and track-independent magnetic signature characteristic of the metal object.
Stated Advantages
Discrimination into threat/non-threat classes.
Optional imager/visual/audible warning outputs.
Simultaneous tracking of multiple objects passing simultaneously.
Documented Applications
An imager/visual/audible warning use case for detecting and indicating where a metal object is relative to an occupant.
Tracking and classification for multiple metal objects passing simultaneously.
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