Dual-status, magnetically imagable article surveillance marker

DETAILED DESCRIPTION Like certain of the markers discussed in the references cited above, the marker of the present invention is intended for use in an electronic article surveillance system having within an interrogation zone an alternating magnetic field.
Also likewise, the marker comprises at least one piece of low coercive force, high permeability material and at least one piece of remanently magnetizable material.
It is at this point, however, that all similarities between prior art markers and the marker of the present invention cease.
Every such prior art marker has heretofore utilized at least one piece of high permeability material which is physically dimensioned, such as by being very long and thin, so as to produce a characteristic response upon which an alarm may be based when the magnetization of the entire, magnetically unbiased, piece is reversed by the alternating field in the interrogation zone.
In direct contrast, the piece of high permeability material used in the marker of the present invention is physically dimensioned so that it does not work (i.
e.
, produce a response upon which an alarm may be based) when the magnetization of the entire piece is reversed upon exposure to such an alternating field.
Thus, the present marker comprises at least one substantially two dimensional piece of low coercive force, high permeability material having overall dimensions such that when the marker is exposed to the alternating field no characteristic response is produced.
As noted above, the marker of the present invention also includes at least one piece of remanently magnetizable material adjacent to at least a portion of the piece of low coercive force material.
It has now been found that portions of this piece may be magnetized in a predetermined pattern, i.
e.
, to be magnetically "imaged", so that the field associated with the magnetic image biases only the adjacent portions of the piece of low coercive force material.
This bias inhibits magnetic flux changes in those adjacent portions when the marker is exposed to the alternating field such that those portions are magnetically inactive