Method and apparatus for the promotion of selected harmonic response signals in an article detection system
First Claim
1. Apparatus for detecting the presence of an article in an interrogation zone, said apparatus comprising a target formed of a strip of a saturable ferromagnetic material and adapted to be carried on said article, an enlarged, flat, planar interrogation antenna coil positioned adjacent to and extending along said interrogation zone, so that targets carried through said zone must pass through magnetic interrogation fields produced by said coil, electrical oscillator and drive means constructed and arranged to produce an interrogation signal at a first frequency, said interrogation antenna coil being electrically coupled to said electrical oscillator and drive means to produce a varying magnetic interrogation field at said first frequency throughout said interrogation zone, said varying magnetic field having a characteristic magnetic field pattern, magnetic bias means constructed and arranged to produce, throughout said interrogation zone a magnetic biasing field having a characteristic magnetic field pattern essentially the same as the characteristic magnetic field pattern of said varying magnetic interrogation field said magnetic bias means including a bias coil of substantially the same configuration as said interrogation antenna coil and positioned adjacent said interrogation antenna coil and means for supplying electrical current to said bias coil, said drive means, said interrogation antenna coil, and said magnetic bias means further being arranged such that the net magnetic fields produced thereby are capable, at each location throughout said interrogation zone, of causing said target to produce target signals in the form of magnetic fields which vary at frequencies harmonically related to said first frequency and receiver means constructed and arranged to detect the presence, in said interrogation zone of said target signals.
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Accused Products
Abstract
An electromagnetic article detection system of the type wherein a saturable magnetic target generates harmonics of an alternating magnetic interrogation field. A magnetic bias means is provided along with the magnetic interrogation field to promote the production of target response particularly at even harmonics, throughout the interrogation region.
45 Citations
27 Claims
- 1. Apparatus for detecting the presence of an article in an interrogation zone, said apparatus comprising a target formed of a strip of a saturable ferromagnetic material and adapted to be carried on said article, an enlarged, flat, planar interrogation antenna coil positioned adjacent to and extending along said interrogation zone, so that targets carried through said zone must pass through magnetic interrogation fields produced by said coil, electrical oscillator and drive means constructed and arranged to produce an interrogation signal at a first frequency, said interrogation antenna coil being electrically coupled to said electrical oscillator and drive means to produce a varying magnetic interrogation field at said first frequency throughout said interrogation zone, said varying magnetic field having a characteristic magnetic field pattern, magnetic bias means constructed and arranged to produce, throughout said interrogation zone a magnetic biasing field having a characteristic magnetic field pattern essentially the same as the characteristic magnetic field pattern of said varying magnetic interrogation field said magnetic bias means including a bias coil of substantially the same configuration as said interrogation antenna coil and positioned adjacent said interrogation antenna coil and means for supplying electrical current to said bias coil, said drive means, said interrogation antenna coil, and said magnetic bias means further being arranged such that the net magnetic fields produced thereby are capable, at each location throughout said interrogation zone, of causing said target to produce target signals in the form of magnetic fields which vary at frequencies harmonically related to said first frequency and receiver means constructed and arranged to detect the presence, in said interrogation zone of said target signals.
- 13. A method of detecting the presence of an article in an interrogation zone, said method comprising the steps of attaching to said article a target of a saturable ferromagnetic material, carrying said article, with said target attached, through a magnetic interrogation field produced in an interrogation zone by an enlarged, flat planar interrogation antenna coil positioned adjacent to and extending along said interrogation zone while energizing said interrogation antenna coil to generate throughout said interrogation zone said magnetic interrogation field at a predetermined interrogation frequency, simultaneously driving electrical current through a bias coil which is of substantially the same configuration as and is positioned adjacent to said interrogation antenna coil to generate throughout said interrogation zone a magnetic biasing field, said magnetic biasing field having a configuration throughout said interrogation zone which is essentially the same as the configuration of said magnetic interrogation field, the combined interrogation and biasing fields being capable, at each location throughout said interrogation zone, of causing said target to produce target signals in the form of magnetic fields which vary at frequencies harmonically related to said predetermined frequency, monitoring said interrogation zone for the presence of said target signals at a selected harmonic of said predetermined frequency, and generating an alarm signal upon the detection of said target signals.
Specification