METHOD AND APPARATUS FOR DETECTING AT A DISTANCE THE STATUS AND IDENTITY OF OBJECTS

• US 3,665,449 A
• Filed: 07/11/1969
• Issued: 05/23/1972
• 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): Caldwell, John W.
• Assistant Examiner(s): Partridge, Scott F.
• Application Number:
  US04/840,973
• Time in Patent Office: 1,047 Days
• Field of Search: 340/280,258,258C,149A 324/41
• US Class Current: 340/572.1
• CPC Class Codes: G01N 27/72 by investigating magnetic variables
• CPC Class Codes: G08B 13/2408 using ferromagnetic tags
• 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

A non-contact method of and system for distinguishing the presence, identity or status of an object. The system comprises a marker including a ferro-magnetic material to accompany each object to be detected, means for producing an alternating magnetic field within a zone through which the objects are to pass, means for monitoring magnetic flux changes within the zone and a circuit for detecting a flux change within the zone which corresponds to a signal characteristically produced by magnetization reversal of the marker ferro-magnetic material. The marker includes a relatively long, relatively thin, open-strip of a ferro-magnetic material and may include a remanently magnetizable control element to provide a sensitized and desensitized marker for demagnetized and magnetized states, respectively, of the control element. A plurality of magnetic field producing means are employed to produce in the zone magnetic fields of different orientations, virtually assuring production of a characteristic signal when a marker is passed into the zone.

Claims

1. A method for detecting the presence of an object within an interrogation zone, comprising a. securing a marker means to said object, which marker means comprises an open-strip of a ferro-magnetic material, which is sufficiently thin relative to its major dimension to produce a characteristic pulse of an external magnetic field when its magnetization is reversed by a sinusoidal alternating applied magnetic field having a maximum time rate of change in excess of 300 oersteds per second, wherein said characteristic pulse comprises a composite signal containing a band of frequencies having a lower bound exceeding 1,000 Hz. and a width at least 10 times the frequency of said applied field;

b. passing said object into said interrogation zone;

c. applying in said interrogation zone an alternating applied magnetic field having a maximum time rate of change in excess of 300 oersteds per second; and

d. detecting in the vicinity of said interrogation zone the presence of a signal comprising a band of frequencies whose lower bound exceeds 1,000 Hz. and whose width is at least 10 times the frequency of said applied field.

2. A method according to claim 1 wherein step (c) further comprises sequentially applying in said interrogation zone a plurality of alternatIng applied magnetic fields such that while said object is in said interrogation zone there is present in every direction at least one magnetic field component vector greater than a field sufficient to reverse the magnetization of said marker to thereby assure at least one magnetization reversal whenever said object is in said interrogation zone.

3. A method according to claim 1 wherein step (c) comprises applying a pulsed alternating applied magnetic field. 4 The method of claim 1 wherein said ferro-magnetic material has an aggregate saturation magnetic moment of at least 0.1 pole-centimeter, the magnetization of each strip when said strip is subjected over its full length of a 60 Hz. sinusoidally varying magnetic test field of a predetermined peak magnitude of less than 20 oersteds reversing for each alternation of said test field, wherein step (c) further comprises applying in said interrogation zone at least said applied alternating magnetic field having at least 3/4 oersted peak amplitude;

and wherein the method further comprises e. sensing the amplitude and time characteristics of at least one of said detected signals to verify the presence of a said object.

5. The method of claim 4 wherein step (e) further comprises producing a timing signal and comparing the time occurrences of said at least one said detected signal and said timing signal to verify the presence of a said object.

6. The method of claim 1 wherein said applied magnetic field is a modulated sinusoidally varying magnetic field.

7. The method of claim 4 wherein step (c) further comprises applying in said interrogation zone at least a second alternating magnetic field of a frequency at least 5 Hz. different from said first applied alternating magnetic field, wherein step (d) further comprises detecting the presence of at least one further signal comprising a said band of frequencies whose lower bound exceeds 1,000 Hz. and whose width is at least 10 times the frequency of said second alternating magnetic field;

and wherein step (e) further comprises sensing the amplitude and time characteristics of at least one of said detected further signals to verify the presence of a said object.

8. The method of claim 1 including the step of sensing for a potential carrier of said object within said interrogating zone and initiating step (c) only when a said carrier is sensed.

9. A method for detecting the presence of an object within an interrogation zone, comprising a. securing a marker means to said object, which marker means comprises an open-strip of a ferro-magnetic material, which is sufficiently thin relative to its major dimension to produce a characteristic pulse of an external magnetic field when its magnetization is reversed by a sinusoidal alternating applied magnetic field having a maximum time rate of change in excess of 300 oersteds per second, wherein said characteristic pulse comprises a composite signal containing a band of frequencies having a lower bound exceeding 1,000 Hz. and a width at least 10 times the frequency of said applied field, and depending upon the particular composition, size and shape of said ferro-magnetic material, the peak amplitude of said composite signal will occur for an applied alternating field of a particular waveform a predictable time after each applied field alternation;

b. passing said object into said interrogation zone;

c. applying in said interrogation zone an alternating applied magnetic field having a maximum time rate of change in excess of 300 oersteds per second;

d. detecting in the vicinity of said interrogation zone the presence of a signal comprising a band of frequencies whose lower bound exceeds 1,000 Hz. and whose width is at least 10 times the frequency of said applied field; and

e. detecting in the vicinity of said interrogation zone whether the pEak amplitude of said composite signal occurs a predictable time after each applied field alternation.

10. A system for detecting the presence of an object within an interrogation zone, comprising a. marker means secured to said object, which marker means comprises an open-strip of a ferro-magnetic material, which is sufficiently thin relative to its major dimension to produce a characteristic pulse of an external magnetic field when its magnetization is reversed by a sinusoidal alternating applied magnetic field having a maximum time rate of change in excess of 300 oersteds per second, wherein said characteristic pulse comprises a composite signal containing a band of frequencies having a lower bound exceeding 1,000 Hz. and a width at least 10 times the frequency of said applied field, and depending upon the particular composition, size and shape of said ferro-magnetic material, the peak amplitude of said composite signal will occur for an applied alternating field of a particular waveform a predictable time after each applied field alternation;

b. means defining an interrogation zone;

c. means for applying in said interrogation zone an alternating applied magnetic field having a maximum time rate of change in excess of 300 oersteds per second;

d. means for detecting in the vicinity of said interrogation zone the presence of a signal comprising a band of frequencies whose lower bound exceeds 1,000 Hz. and whose width is at least 10 times the frequency of said applied field; and

e. means for detecting in the vicinity of said interrogation zone whether the peak amplitude of said composite signal occurs a predictable time after each applied field alternation.

11. A system for detecting the presence of an object within an interrogation zone, comprising a. marker means secured to said object, which marker means comprises an open-strip of a ferro-magnetic material, which is sufficiently thin relative to its major dimension to produce a characteristic pulse of an external magnetic field when its magnetization is reversed by a sinusoidal alternating applied magnetic field having a maximum time rate of change in excess of 300 oersteds per second, wherein said characteristic pulse comprises a composite signal containing a band of frequencies having a lower bound exceeding 1,000 Hz. and a width at least 10 times the frequency of said applied field;

b. means defining an interrogation zone;

c. means for applying in said interrogation zone an alternating applied magnetic field having a maximum time rate of change in excess of 300 oersteds per second; and

d. means for detecting in the vicinity of said interrogation zone the presence of a signal comprising a band of frequencies whose lower bound exceeds 1,000 Hz. and whose width is at least 10 times the frequency of said applied field.

12. A system according to claim 11 wherein the means of paragraph (c) further comprises means for sequentially applying in said interrogation zone a plurality of alternating applied magnetic fields such that while said object is in said interrogation zone there is present in every direction at least one magnetic field component vector greater than a field sufficient to reverse the magnetization of said marker to thereby assure at least one magnetization reversal whenever said object is in said interrogation zone. 13 A system according to claim 11, wherein the means of paragraph (c) comprises means for applying a pulsed alternating applied magnetic field.

14. A system according to claim 11 wherein the system further comprises A. a plurality of markers, at least one of which markers is to be secured to each object, each marker comprising at least one open-strip of a ferro-magnetic material with an aggregate saturation magnetic moment of at least 0.1 pole-centimeter, the magnetization of a said marker when the marker is subjected over its entIre length to a test field of a 60 Hz. sinusoidal magnetic field of a predetermined peak magnitude of less than 20 oersteds reversing at each field alternation to in turn produce a said characteristic pulse of external polar magnetic field having appreciable flux components within the range of 1, 000 Hz. to 16,000 Hz., the gross time rate of change of which flux components defines a signal having a width at half amplitude of less than 0.1 millisecond;

and B. means for applying throughout said zone at least one alternating magnetic field of a predetermined frequency having a peak magnitude of at least 3/4 oersted.

15. A system according to claim 11 wherein said alternating magnetic field applying means comprises a set of magnetic field producing means including a first substantially linear electromagnet;

a second substantially linear electromagnet orthogonal to said first linear electromagnet; and

an air core loop for producing a magnetic field, said linear electromagnets and said air core loop disposed in mutually parallel planes and the perimeter of the air core loop passing adjacent the magnetic poles of said first and said second linear electromagnets.

16. The system of claim 11 further comprising means for desensitizing said marker to render said marker incapable of producing said characteristic pulse when subjected to said applied field.

17. The system of claim 16 wherein said desensitizing means when in operation is out of contact with said marker.

18. The system of claim 16 further comprising means for altering said marker from a desensitized to a sensitized state to render said marker capable of producing said characteristic pulse when subjected to said applied field.

19. The system of claim 18 wherein each marker further comprises a control element of a ferro-magnetic material having a coercivity of at least 5 oersteds and capable of producing, when remanently magnetized, a static external magnetic field of at least 3/4 oersted over at least a portion of said open-strip to at least partially magnetize said portion wherein the disposition of said control element with respect to said open-strip is such that an electrical signal generated while the control element is demagnetized differs distinguishably from an electrical signal generated while the control element is magnetized and wherein said desensitizing means include means for remanently magnetizing said control element;

and said altering means includes means for demagnetizing said control element.

20. An automated checkout system employing the apparatus of claim 16 and further comprising machine readable indicia associated with each object, which indicia identifies said object;

means for encoding said indicia and for providing a signal for recording said indicia; and

means, responsive to sensing a machine readable user'"'"''"'"'s identity card and a said indicia, for actuating said desensitizing means and for making a record of the contents of said identity card and said indicia.

21. The system of claim 11 for detecting the presence, identity, or status of an object within an interrogation zone, wherein each marker comprises at least two open-strips, each open-strip having a different AC coercivity;

wherein the magnetization of each of said open-strips reverses during a different time interval following each said field alternation to produce flux changes defining a characteristic signal for each said open-strip, each said characteristic signal occurring a different time interval after a said field reversal; and

wherein said detecting means produces a status indication in response to detecting at least one of each of said characteristic signals during a time interval between successive field alternations.

22. The system according to claim 21 wherein the system comprises n groups of markers, each open-strip of all markers in a particular group having the sAme AC coercivity but the AC coercivity of each group being different;

wherein the magnetization of the strips of each group reverses during substantially the same time interval after each said field alternation but the magnetization of strips of different groups reverse during different time intervals to produce flux changes defining signals respectively characteristic of each said group; and

wherein said detecting means produces an indication in response to detecting a said characteristic signal and wherein the indication produced is different for each characteristic signal to provide an indication of which group the characteristic signal corresponds to.

23. The system according to claim 21 wherein the system comprises n groups of markers, where n is an integral number greater than 1, each said marker in said group comprising m open-strips, wherein m is an integral number, each of the m open-strips of a said marker having different AC coercivities, all of said markers of a said group having the same combination of said open-strips but different groups having different combinations of open-strips, each marker of a said group producing a set of magnetic field pulses characteristic of said group when said each marker is passed into said applied field, and wherein said detecting means produces an indication representative of a said group in response to detecting a set of said pulses characteristic of said group.