ELECTROMAGNETIC FIELD PRODUCING APPARATUS AND METHOD FOR SEQUENTIALLY PRODUCING A PLURALITY OF FIELDS

• US 3,697,996 A
• Filed: 12/17/1969
• Issued: 10/10/1972
• Est. Priority Date: 07/11/1969
• Status: Expired due to Term

• Current Assignee: Donald A. Wright, James T. Elder
• Original Assignee: Donald A. Wright, James T. Elder
• Inventors: Elder, James T., Wright, Donald A.
• Primary Examiner(s): Quarforth, Carl D.
• Assistant Examiner(s): Potenza, J. M.
• Application Number:
  US04/885,874
• Time in Patent Office: 1,028 Days
• Field of Search: 324/34,41 340/38L,258 343/101
• US Class Current: 324/260
• CPC Class Codes: G01N 27/72 by investigating magnetic variables
• CPC Class Codes: G08B 13/2437 Tag layered structure, processes for making layered tags
• CPC Class Codes: G08B 13/2442 Tag materials and material properties thereof, e.g. magnetic material details
• CPC Class Codes: G08B 13/2474 Antenna or antenna activator geometry, arrangement or layout loop antennae H01Q1/22
• CPC Class Codes: G08B 13/2477 Antenna or antenna activator circuit

Abstract

An apparatus and method for sequentially producing in a zone a plurality of electromagnetic fields. The lines of each field are produced to be generally curved and to have a direction at substantially every point in the zone substantially different from the direction of at least one other electromagnetic field line at that point. The apparatus comprises a plurality of field producing means each of which is responsive to applied electrical energy to produce an electromagnetic field. Means are provided for sequentially applying energy to the field producing means.

Claims

1. An apparatus for sequentially producing a plurality of electromagnetic fields within an interrogation zone comprising:

a plurality of field producing means, each being positioned for producing in response to electrical energy supplied thereto an electromagnetic field the lines of which in said interrogation zone are generally curved and have a direction at substantially every point in the zone substantially different from the direction of at least one electromagnetic field line produced by another of said field producing means at that point; and

means for sequentially applying electrical energy to each of said plurality of field producing means.

2. An apparatus according to claim 1 wherein said plurality of field producing means comprises:

a first means for producing a first electromagnetic field;

a second means for producing a second electromagnetic field each line of which has at substantially every point in the zone a direction substantially perpendicular to the direction of the line of the first field at that point.

3. An apparatus according to claim 2 wherein the first field producing means comprises a first long, straight conductor, and wherein the second field producing means comprises at least one other long, straight conductor parallel to and co-extensive with the first conductor.

4. An apparatus according to claim 3 wherein the first field producing means comprises at least two long, straight parallel conductors.

5. An apparatus according to claim 4 wherein the second field producing means comprises at least two long, straight parallel conductors and the conductors of at least one of the first and second field producing means comprise parallel segments of a generally rectangular planar loop.

6. An apparatus according to claim 5 wherein said loop comprises a generally rectangular figure-8 coil and said parallel segments comprise the end and center segments of the figure-8 coil.

7. An apparatus according to claim 6 wherein the conductors of the other of said first and second field producing means also comprise parallel segments of a generally rectangular planar loop, the loops of the first and second field producing means being closely spaced and lying in substantially parallel planes.

8. An apparatus according to claim 2 wherein the first field producing means comprises a first long, straight conductor and wherein the second field producing means comprises a second long, straight conductor orthogonal to and crossing the first conductor, the first and second conductors crossing far from their respective ends.

9. An apparatus according to claim 8 wherein at least one of the first and second field producing means further comprises at least one additional long, straight conductor positioned paralLel to the conductor comprising the same field producing means and lying in substantially the same plane as said first and second conductors.

10. An apparatus according to claim 9 wherein alternate ones of the conductors of said at least one field producing means are connected to said energizing means as a first group of conductors and wherein the other conductors of said at least one field producing means are connected to said energizing means as a second group of conductors, and wherein said energizing means energizes each of said groups in sequence.

11. An apparatus according to claim 8 wherein at least one of the first and the second field producing means comprises a center segment of a figure-8 coil.

12. An apparatus according to claim 2 wherein the first field producing means comprises a first substantially linear electromagnet;

and wherein the second field producing means comprises a second substantially linear electromagnet disposed close to and substantially orthogonal to the first electromagnet, the first and second electromagnets crossing near their mid-points.

13. An apparatus according to claim 2 wherein the first field producing means comprises a substantially linear electromagnet and wherein the second field producing means comprises a substantially planar air core loop having a diameter approximately equal to the separation of the magnetic poles of said first substantially linear electromagnet and wherein the electromagnet and air core loop are close-spaced with the periphery of the air core loop passing proximate the magnetic poles of the electromagnet.

14. An apparatus according to claim 2 further comprising:

third means for producing a third electromagnetic field the lines of which have a direction substantially mutually perpendicular to the directions of the first and second field lines at substantially every point in the interrogation zone.

15. An apparatus according to claim 14 wherein said first and third field producing means each comprise a generally rectangular figure-8 coil, each coil comprising a generally rectangular figure-8 winding which forms two generally rectangular portions of nearly equal size, each portion having substantially parallel top and bottom lengths and a top and a bottom length of the two portions being substantially coincident to form a center segment of the figure-8 coil and the other of said top and bottom lengths of said portions forming end segments of the figure-8 coil, the figure-8 coils being oriented so that their center segments are orthogonal and cross near their mid-points;

wherein said second field producing means comprises parallel segments of a generally rectangular o coil;

wherein said figure-8 and o coils are closely spaced and lie in substantially parallel planes and wherein each of the parallel segments of the o coil are parallel to and lie between the center segment and one end segment of one figure-8 coil.

16. An apparatus according to claim 15 wherein the means for sequentially applying energy comprises a source of electrical energy;

an energy transfer section coupled between each of said field producing means and the source of electrical energy, each energy transfer section including a switch responsive to a control signal to enable the transfer section to pass a pulse of energy from the energy source to the field producing means; and

a control signal generator for providing a control signal to each of the switches in a predetermined sequence.

17. An apparatus according to claim 16 wherein each field producing means is a coil having appreciable electrical inductance;

wherein said source of energy is a DC voltage; and

wherein each energy transfer section includes a capacitor and wherein the energy transfer section and field producing means form an inductive-capacitive circuit, the capacitor of the transfer section acting to store said pulse of energy upon actuatiOn of said switch and to pass the energy to the field producing means as a damped pulse of energy.

18. An apparatus according to claim 17 wherein said inductive-capacitive circuit is an overdamped electrical circuit to produce an overdamped electromagnetic field pulse.

19. An apparatus according to claim 17 wherein said inductive-capacitive circuit is an underdamped circuit to produce an underdamped electromagnetic field pulse.

20. A method of sequentially producing a plurality of electromagnetic fields within an interrogation zone comprising the steps of providing a plurality of field producing means, each of said means being positioned for producing in response to electrical energy supplied thereto an electromagnetic field the lines of which in an interrogation zone are generally curved and have a direction at substantially every point in the zone substantially different from the direction of at least one electromagnetic field line produced by another of said field producing means at that point;

and sequentially applying electrical energy to each of said plurality of field producing means;

thereby producing as a pulse sequence in the interrogation zone a plurality of pulses of electromagnetic field, the lines of each field being generally curved and having respective directions at substantially every point in the zone substantially different from the direction of at least one other electromagnetic field line produced by another of said field producing means at that point.

21. A method according to claim 20 wherein said step of producing comprises producing the pulse sequence during a sequence period comprising:

producing at least one continuous period of at least 1.0 seconds during which no field is produced; and

, producing said pulse sequence during an interval of not longer than 0.4 seconds.