Method and apparatus for generating alternating magnetic fields to produce harmonic signals from a metallic strip
Patent 4300183 Issued on November 10, 1981. Estimated Expiration Date: 
March 27, 2000. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
March 27, 2000. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.Patent References Re29610 3665449 3758849 3820103 InventorApplicationNo. 06/134684 filed on 03/27/1980US Classes:361/152, Including particular drive circuit340/572.1, Detectable device on protected article (e.g., "tag")361/203With oscillatorExaminersPrimary: Moose, Harry E. Jr.International ClassG08B 13/24 (20060101)AbstractA system (10) produces an alternating magnetic field in a detection zone between a pair of doorways (346, 348) to produce harmonic signals from a marker (330) when the marker (330) is activated and located in the detection zone. Each of the doorways (346, 348) is provided with a trapezoidally shaped coil which is in a resonant circuit. The coils in the doorways (346, 348) are driven at periodic time periods with in-phase currents to produce aiding magnetic fields perpendicular to doorways in the detection zone. At alternate time periods the coils in the doorways are driven with out-of-phase signals which produce opposing magnetic fields perpendicular to the doorways (346, 348) and aiding magnetic fields parallel to the planes of the doorways. The magnetic fields thus produced in the detection zone cause the marker (330) when activated to produce harmonic signals despite the orientation of the marker (330) as it passes through the detection zone. | |
