US4890115A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Magnetic antenna
Assignee: Sensormatic Electronics Corp
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Filing: 1988-02-10
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Granted: 1989-12-26
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Expires: 2008-02-10
Abstract
Abstract A magnetic antenna particularly usable for deactivating electronic article surveillance tags that are attached to articles of merchandise to prevent unauthorized removal from a protected area. The antenna comprises a driven element in the form of a transmitting loop, preferably a pair of loops driven in opposite phase, and shield grids disposed on opposite sides of the driven elements. The shield grids serve to prevent electric field radiation from the driven element from propagating past the shield, but permit the passage of magnetic field radiation therethrough. The antenna may also be used at a protected exit to detect the presence of a tag.
Inventors
- 👤 Michael F. Hartings
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 15:50
CPC Classifications
H; H01; H01Q; H01Q7/00; H01Q7/04
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
120 words
A magnetic antenna, comprising: means including an active element having two loops disposed adjacent each other in a generally coplanar relationship for generating a strong field that has a limited propagation distance near the antenna, said loops being connected together in a parallel connection; means connected to the parallel connection of said loops for applying signals to said parallel connection to thereby cause currents to flow in opposite directions in said loops; and means including a shield structure having a pair of generally planar shields disposed on opposite sides of said active element in a generally parallel relationship therewith for preventing the passage of the electric field of an electromagnetic radiation therethrough while permitting the passage of magnetic field radiation.
Claim 2
Dependent Claim
120 words
A magnetic antenna, comprising: means including an active element having two loops disposed adjacent each other in a generally coplanar relationship for generating a strong field that has a limited propagation distance near the antenna, said loops being connected together in a parallel connection; means connected to the parallel connection of said loops for applying signals to said parallel connection to thereby cause currents to flow in opposite directions in said loops; and means including a shield structure having a pair of generally planar shields disposed on opposite sides of said active element in a generally parallel relationship therewith for preventing the passage of the electric field of an electromagnetic radiation therethrough while permitting the passage of magnetic field radiation.
Claim 3
Dependent Claim
22 words
A magnetic antenna as recited in claim 1 wherein said shield comprises a structure fabricated from a plurality of individual spaced conductors.
Claim 4
Dependent Claim
21 words
A magnetic antenna as recited in claim 1 further including means for connecting the shield to a source of common potential.
Claim 5
Dependent Claim
41 words
A magnetic antenna as recited in claim 1 wherein said generally planar shields have portions thereof that extend beyond said loops, and the portions of the generally planar shields that extend beyond the loops are turned to extend toward the loops.
Claim 6
Dependent Claim
22 words
A magnetic antenna as recited in claim 1 wherein said loops and said shields are fabricated from a plurality of self-supporting members.
Claim 7
Dependent Claim
16 words
An antenna as recited in claim 5 wherein said self-supporting members are spaced approximately 1/4" apart.
Claim 8
Dependent Claim
29 words
An antenna as recited in claim 6 wherein said shields have horizontal and vertical dimensions of approximately 9 inches for an antenna designated to operate at approximately 8 MHz.
Claim 9
Dependent Claim
121 words
A magnetic antenna, comprising: means including an active element having two single loops disposed adjacent each other in a generally coplanar relationship for generating a strong field that has a limited propagation distance near the antenna, said loops being connected together in a parallel connection; means connected to the parallel connection of said loops for applying signals to said parallel connection to thereby cause currents to flow in opposite directions in said loops; and means including a shield structure having a pair of generally planar shields disposed on opposite sides of said active element in a generally parallel relationship therewith for preventing the passage of the electric field of an electromagnetic radiation therethrough while permitting the passage of magnetic field radiation.
Claim 10
Dependent Claim
121 words
A magnetic antenna, comprising: means including an active element having two single loops disposed adjacent each other in a generally coplanar relationship for generating a strong field that has a limited propagation distance near the antenna, said loops being connected together in a parallel connection; means connected to the parallel connection of said loops for applying signals to said parallel connection to thereby cause currents to flow in opposite directions in said loops; and means including a shield structure having a pair of generally planar shields disposed on opposite sides of said active element in a generally parallel relationship therewith for preventing the passage of the electric field of an electromagnetic radiation therethrough while permitting the passage of magnetic field radiation.
Claim 11
Dependent Claim
129 words
A magnetic antenna, comprising: means including an active element having two loops disposed adjacent each other in a generally coplanar relationship for generating a strong field that has a limited propagation distance near the antenna, said loops being connected together in a parallel connection at a point generally centrally located on the antenna; means connected to the parallel connection of said loops for applying signals to said parallel connection to thereby cause currents to flow in opposite directions in said loops; and means including a shield structure having a pair of generally planar shields disposed on opposite sides of said active element in a generally parallel relationship therewith for preventing the passage of the electric field of an electromagnetic radiation therethrough while permitting the passage of magnetic field radiation.
Claim 12
Dependent Claim
129 words
A magnetic antenna, comprising: means including an active element having two loops disposed adjacent each other in a generally coplanar relationship for generating a strong field that has a limited propagation distance near the antenna, said loops being connected together in a parallel connection at a point generally centrally located on the antenna; means connected to the parallel connection of said loops for applying signals to said parallel connection to thereby cause currents to flow in opposite directions in said loops; and means including a shield structure having a pair of generally planar shields disposed on opposite sides of said active element in a generally parallel relationship therewith for preventing the passage of the electric field of an electromagnetic radiation therethrough while permitting the passage of magnetic field radiation.
Claim 13
Dependent Claim
18 words
A magnetic antenna as recited in claim 9 wherein each of said two loops is a single loop.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1992-12-25 | 1993-06-26 | 1993-12-26 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1996-12-25 | 1997-06-26 | 1997-12-26 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2000-12-25 | 2001-06-26 | 2001-12-26 | $7700.00 | Window Closed / Lapsed |