Method and apparatus for detecting at a distance the status and identity of objects

Claim 2

A marker capable of producing magnetic pulses which can be unambiguously detected by unsophisticated apparatus out of direct contact with said marker, said marker comprising ''''n'''' sections of ferromagnetic material, said sections having an aggregate saturation magnetization of at least 0.1 pole-centimeters and each section differing from the other sections in A.C. coercivity such that when subjected to a periodically varying magnetic field which increases at a predetermined time rate of change, the magnetization of the sections reverses sequentially at equal intervals of time, each interval being less than or equal to T/4n where ''''T'''' is equal to the period of said varying magnetic field and wherein each alternation and set of said sequential reversals produced in response thereto results in a magnetic pulse train.

Claim 3

A marker according to claim 1 wherein said ferromagnetic sections comprise ''''n'''' open-strips.

Claim 4

A multi-status marker capable of producing magnetic pulses which can be unambiguously detected by unsophisticated apparatus out of direct contact with said marker, said marker further capable of being deactivated to prevent production of said magnetic pulses upon interrogation, comprising: a. ''''n'''' sections of ferromagnetic material, said sections having an aggregate magnetization of at least 0.1 pole-centimeters and each section differing from the other sections in A.C. coercivity such that when subjected to a periodically varying magnetic Field which increases at a predetermined time rate of change, the magnetization of the sections reverses sequentially at equal intervals of time, each interval being less than or equal to T/4n where ''''T'''' is equal to the period of said varying magnetic field, and wherein each alternation and set of said sequential reversals produced in response thereto results in magnetic pulses; and b. at least one control element of a ferromagnetic material having a coercivity of at least 5 oersteds producing when remanently magnetized a static external magnetic field of at least three-fourths oersted over at least a portion of each section to at least partially magnetize each said portion whereby the amplitude and time characteristics of a signal produced by said sections in response to said applied magnetic field differs distinguishably from the corresponding signal when the control element is demagnetized.

Claim 5

A multi-status marker capable of producing magnetic pulses which can be unambiguously detected by unsophisticated apparatus out of direct contact with said marker, said marker further capable of being deactivated to prevent production of said magnetic pulses upon interrogation, comprising: a. ''''n'''' sections of ferromagnetic material, said sections having an aggregate magnetization of at least 0.1 pole-centimeters and each section differing from the other sections in A.C. coercivity such that when subjected to a periodically varying magnetic Field which increases at a predetermined time rate of change, the magnetization of the sections reverses sequentially at equal intervals of time, each interval being less than or equal to T/4n where ''''T'''' is equal to the period of said varying magnetic field, and wherein each alternation and set of said sequential reversals produced in response thereto results in magnetic pulses; and b. at least one control element of a ferromagnetic material having a coercivity of at least 5 oersteds producing when remanently magnetized a static external magnetic field of at least three-fourths oersted over at least a portion of each section to at least partially magnetize each said portion whereby the amplitude and time characteristics of a signal produced by said sections in response to said applied magnetic field differs distinguishably from the corresponding signal when the control element is demagnetized.

Claim 6

A marker according to claim 3 wherein said ferromagnetic sections comprise ''''n'''' open-strips.

Claim 7

A marker according to claim 4 having at least two control elements which when remanently magnetized produce a static external magnetic field over at least two portions of each section.

Claim 8

A marker according to claim 4 having one control element which produces a static external magnetic field of at least 3/4ths oersted over the entire length of each of said ''''n'''' sections of open-strips.

Claim 11

A system according to claim 7 further comprising means for desensitizing said marker to render said marker incapable of producing said magnetic pulses when subjected to said varying magnetic field.

Claim 12

The system of claim 8 wherein said desensitizing means when in operation is out of contact with said marker.

Claim 13

The system of claim 8 further comprising means for altering said marker from a desensitized to a sensitized state to render said marker capable of producing said magnetic pulses when subjected to said varying magnetic field.

Claim 14

The system of claim 10 wherein each marker further comprises at least one control element of a ferromagnetic material having coercivity of at least five oersteds capable of producing when remanently magnetized a static external magnetic field of at least three-fourths oersted over at least a portion of said sections to at least partially magnetize said portion whereby the amplitude and time characteristics of a signal produced by said sections in response to said varying magnetic field differs distinguishably from the corresponding signal when the control element is demagnetized, and wherein said desensitizing means includes means for remanently magnetizing said control element; and said altering means includes means for demagnetizing said control element.

Claim 15

An object to which is secured a marker which can be detected without direct contact comprising ''''n'''' open-strips where ''''n'''' is an integral number greater than one, of ferromagnetic material as herein defined with an aggregate saturation magnetic moment of at least 0.1 pole-centimeter, the magnetization of each of said open-strips when subjected to a 60 Hz. sinusoidally varying magnetic test field of a predetermined peak magnitude of less than 20 oersted reversing at each field alternation to in turn produce a pulse of external polar magnetic field having appreciable flux components within the range of 1,000 to 16,000 Hz., the gross time rate of change of which flux components defines a signal having a width at half amplitude less than 0.1 millisecond, said strips selected to sequentially reverse their magnetization following a said applied field alternation at equal intervals of time, each interval being less than or equal to T/4n where ''''T'''' is equal to the period of said applied field, said sequential reversals producing a magnetic pulse train which can be unambiguously detected by unsophisticated apparatus.

Claim 16

An object to which is secured a marker which can be detected without direct contact comprising ''''n'''' open-strips where ''''n'''' is an integral number greater than one, of ferromagnetic material as herein defined with an aggregate saturation magnetic moment of at least 0.1 pole-centimeter, the magnetization of each of said open-strips when subjected to a 60 Hz. sinusoidally varying magnetic test field of a predetermined peak magnitude of less than 20 oersted reversing at each field alternation to in turn produce a pulse of external polar magnetic field having appreciable flux components within the range of 1,000 to 16,000 Hz., the gross time rate of change of which flux components defines a signal having a width at half amplitude less than 0.1 millisecond, said strips selected to sequentially reverse their magnetization following a said applied field alternation at equal intervals of time, each interval being less than or equal to T/4n where ''''T'''' is equal to the period of said applied field, said sequential reversals producing a magnetic pulse train which can be unambiguously detected by unsophisticated apparatus.