Deactivatable/reactivatable magnetic marker having a step change in magnetic flux

An electronic article surveillance system for detecting the presence of an article in an interrogation zone comprising:

• means for generating an applied alternating magnetic interrogation field in the interrogation zone, the magnitude of said interrogation field in said interrogation zone exceeding a predetermined threshold value;
• and
• a marker secured to the article, the marker comprising:
• a) a marker element including first and second integral components, said first component comprising a soft magnetic material and said second component comprising a hard a semi-hard magnetic material;
• b) said marker element having an active state wherein said marker element exhibits a hysteresis characteristic upon being subjected to said applied alternating magnetic field such that the magnetic flux of said marker element undergoes substantially no change during the time from when the applied field passes through a preselected offset field value toward and until the applied field reaches a predetermined threshold value, undergoes a regenerative step change at the time when the applied field reaches the predetermined threshold value and undergoes a gradual change during the time from when the applied field passes through the predetermined threshold value toward and until the applied field reaches the preselected offset field value;
• c) said marker element having a deactivated state wherein said marker element exhibits a different hysteresis characteristic from the hysteresis characteristic exhibited by said marker element in the active state;
• d) said second component of said marker element having an activating state which places said marker element in said active state and a deactivating state which places said marker element in said deactivated state;
• whereby the marker element is switched between said active state and said deactivated state by switching said second component between said activating state and said deactivating state, respectively;
• and receiver means for detecting the presence of the marker when the marker element is in the interrogation zone and while the marker element is in the active state by detecting perturbations of the interrogation field.

A method of making a marker for use in an article surveillance system, the marker comprising:

• a) a marker element including first and second integral components, said first component comprising a soft magnetic material and said second component comprising a hard or semi-hard magnetic material;
• b) said marker element having an active state wherein said marker element exhibits a hysteresis characteristic upon being subjected to an applied alternating magnetic field such that the magnetic flux of said marker element undergoes substantially no change during the time from when the applied field passes through a preselected offset field value toward and until the applied field reaches a predetermined threshold value, undergoes a regenerative step change at the time when the applied field reaches the predetermined threshold value and undergoes a gradual change during the time from when the applied field passes through the predetermined threshold value toward and until the applied field reaches the preselected offset field value;
• c) said marker element having a deactivated state wherein said marker element exhibits a different hysteresis characteristic from the hysteresis characteristic exhibited by said marker element in the active state;
• d) said second component of said marker element having an activating state which places said marker element in said active state and a deactivating state which places said marker element in said deactivated state;
• whereby the marker element is switched between said active state and said deactivated state by switching said second component between said activating state and said deactivating state, respectively, the method comprising the steps of:
• processing one or more materials in a first step to form said first and second components such that said second component is in said activating state;
• and processing said formed first and second components in a second step to establish said hysteresis characteristic exhibited when the second component is in the activating state.

A method for detecting the presence of an article in an interrogation zone comprising the steps of:

• generating an applied alternating magnetic interrogation field in the interrogation zone, the magnitude of said interrogation field in said interrogation zone exceeding a predetermined threshold value;
• securing a marker to said article, the marker comprising:
• a) a marker element including first and second integral components, said first component comprising a soft magnetic material and said second component comprising a hard or semi-hard magnetic material;
• b) said marker element having an active state wherein said marker element exhibits a hysteresis characteristic upon being subjected to said applied alternating magnetic field such that the magnetic flux of said marker element undergoes substantially no change during the time from when the applied field passes through a preselected offset field value toward and until the applied field reaches a predetermined threshold value, undergoes a regenerative step change at the time when the applied field reaches the predetermined threshold value and undergoes a gradual change during the time from when the applied field passes through the predetermined threshold value toward and until the applied field reaches the preselected offset field value;
• c) said marker element having a deactivated state wherein said marker exhibits a different hysteresis characteristic from the hysteresis characteristic exhibited by said marker element in the active state;
• d) said second component of said marker element having an activating state which places said marker element in said active state and a deactivating state which places said marker in said deactivated state;
• whereby the marker element is switched between said active state and said deactivated state by switching said second component between said activating state and said deactivating state, respectively;
• and detecting the presence of said marker when said marker is in the interrogation zone while the marker element is in the active state by detecting perturbations of the interrogation field.

A method of making a deactivatable reactivatable electronic article surveillance system marker comprising:

• a) heating a marker element comprising a soft amorphous magnetic material to form a part of said soft amorphous magnetic material into a hard or semi-hard component;
• b) applying a sufficient DC magnetic field to the marker element to place the hard or semi-hard component in a first magnetic state;
• and
• c) heating the marker element to cause the marker element, when said hard or semi-hard component is in the first magnetic state, to exhibit a hysteresis characteristic upon being subjected to an applied alternating magnetic interrogating field, such that the magnetic flux of said marker element undergoes substantially no change during the time from when the magnitude of the applied field passes through a preselected offset field value toward and until the magnitude of the applied field reaches a predetermined threshold value, undergoes a regenerative step change at the time when the applied field reaches the predetermined threshold value, and undergoes a gradual change during the time from when the applied field passes through the predetermined threshold value toward and until the applied field reaches the preselected offset field value;
• whereby the marker is deactivated by placing the hard or semi-hard component in a second magnetic state and reactivated by returning said hard or semi-hard component to the first magnetic state.

A marker for use in an electronic article surveillance system in which an applied alternating magnetic field is established in a surveillance zone and an alarm is activated when a predetermined perturbation to the field is detected, said marker comprising:

• a) a marker element including first and second integral components, said first component comprising a soft magnetic material and said second component comprising a hard or semi-hard magnetic material;
• b) said marker element having an active state wherein said marker element exhibits a hysteresis characteristic upon being subjected to an applied alternating magnetic field such that the magnetic flux of said marker element undergoes substantially no change during the time from when the applied field passes through a preselected offset field value toward and until the applied field reaches a predetermined threshold value, undergoes a regenerative step change at the time when the applied field reaches the predetermined threshold value and undergoes a gradual change during the time from when the applied field passes through the predetermined threshold value toward and until the applied field reaches the preselected offset field value;
• c) said marker element having a deactivated state wherein said marker element exhibits a different hysteresis characteristic from the hysteresis characteristic exhibited by said marker element in the active state;
• d) said second component of said marker element having an activating state wherein said second component is substantially demagnetized which places said marker element in said active state and a deactivating state wherein said second component is substantially magnetized which places said marker element in said deactivated state;
• whereby said marker element is switched from said active state to said deactivated state by switching said second component from said activating state to said deactivating state.

A method of making a marker for use in an EAS system comprising the steps of

• a) selecting a marker element comprising a soft amorphous magnetic material as a base material;
• b) heating the base material at a temperature in a range from about 350.degree. C. to about 450.degree. C. for a time in a range from about 2 minutes to 120 minutes to form an integral hard or semi-hard crystallized layer on the soft amorphous magnetic material;
• c) applying a DC magnetic field of sufficient magnitude to at least substantially magnetize the crystallized layer in a longitudinal direction;
• and
• d) heating the marker element at a temperature in a range of about 400.degree. C. to 420.degree. C. for a time in a range of about 1 minute to 5 minutes to cause said marker element, when in an active state and subjected to an applied alternating magnetic field, to exhibit a hysteresis characteristic such that the magnetic flux of said marker element undergoes substantially no change during the time from when the applied field passes through a preselected offset field value toward and until the applied field reaches a predetermined threshold value, undergoes a regenerative step change at the time when the applied field reaches the predetermined threshold value and undergoes a gradual change during the time from when the applied field passes through the predetermined threshold value toward and until the applied field reaches the preselected offset field value.