Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-04-08
2001-07-10
Lee, Benjamin C. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S572300
Reexamination Certificate
active
06259368
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an element for electronically securing articles or for sensor technology, comprising a striplike or wirelike Barkhausen material of given length, which in an external alternating magnetic field is excited to emit a characteristic signal, and a soft magnetic material which is associated with the Barkhausen material.
BACKGROUND OF THE INVENTION
Elements of Barkhausen material—also known as pulse wires—are used both for electronically securing articles and for so-called pulse wire sensors in sensor technology. They are distinguished by a virtually rectangular hysteresis curve; that is, the reversal of magnetization in an outer alternating magnetic field takes place virtually abruptly as soon as the exciter field has reached the predetermined threshold value. Elements suitable for electronically securing articles are described for instance in U.S. Pat. Nos. 4,247,601 and 4,660,025 and European Patent Disclosures EP 0 309 679 B1 and EP 0 762 354 A1.
The abrupt reversal of magnetization of wirelike or striplike Barkhausen materials in an external alternating field is the consequence of a pronounced monoaxial anisotropy along the longitudinal axis of the wire or strip. This anisotropy suppresses not only disruptive rotational processes during the magnetization reversal but also the formation of terminal domain structures before the switching field intensity is attained. After all, the formation of such structures would cause a rounding off of the hysteresis curve and thus would worsen the switching characteristics.
The anisotropy required to form a markedly rectangular hysteresis curve can have various causes. Methods have become known from the patent literature that utilize voltage-induced anisotropy (U.S. Pat. No. 4,660,025) or magnetic field-induced anisotropy (EP 0 762 354 A1). However, it is common to all these methods that to support the induced anisotropies, a pronounced formal anisotropy, in order to attain the pronounced switching behavior is necessary. Shortening the strips or wires, which as a rule are elongated, causes a decrease in the formal anisotropy and an increase in the demagnetization effect, which reduces the rectangular shape of the hysteresis curve.
Increasing the intrinsic anisotropy, as proposed for instance in EP 0 762 354 A1 for labels of short length, would indeed at least partly compensate for the decrease in formal anisotropy or the increase in the demagnetization factor; however, at the same time it would lead to an increase in the switching field intensity, which is undesired for the application in systems for electronically securing articles.
From the patent literature, alternative ways have already become known for how the demagnetizing field in the end regions of the Barkhausen material, which after all causes the undesired magnetization reversal processes, can be suppressed. For instance, in European Patent Disclosure EP 0 710 923 A2, a magnetic marking element is described, which comprises a thin magnetic wire of Barkhausen material, in the two end regions of which two soft magnetic chips are disposed that have a lower coercive force than the Barkhausen material wire. To increase the pulse height, the chips cover the ends of the strips and preferably protrude past the ends to all sides.
From EP 0 762 354 A1, it has become known to use an amorphous band or an amorphous wire of Barkhausen material as a securing element for electronically securing articles. To increase the pulse height, at least one further strip of soft magnetic material is associated with the amorphous material and preferably protrudes past the ends of the amorphous material.
Both of these versions in the prior art have the disadvantage of being unsuitable for continuous production of bands from which labels of varying length are later stamped out. The reason for this is that the soft magnetic strips must be positioned at the ends of the labels, yet as a rule the position cannot be determined during production.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an economical element for electronically securing articles or for sensor technology that does not have the above disadvantages.
This object is attained in that the portions of soft magnetic material are positioned relative to the Barkhausen material such that the magnetic stray fields they generate couple with the magnetization of the Barkhausen material.
By means of the stray field coupling, a stabilization of the prestressed wirelike or striplike Barkhausen material is brought about. By disposing the soft magnetic portions along the striplike or wirelike Barkhausen material, the internal field of the element is reduced, and not only—as described in the prior art—in the end regions. As a result—as will be described in further detail below—the actual switching range is stabilized in a targeted way until the intrinsic switching field intensity is reached, which is finally determined by induced anisotropies and thus by the domain wall mobility.
Since in accordance the present invention it is unnecessary for the ends of the wirelike or striplike Barkhausen material to be covered, the corresponding securing elements can be manufactured in the form of continuous bands. From the bands, labels with a length needed for the particular application can then be stamped out.
An especially favorable method for producing the securing elements according to the present invention is described in German Patent Disclosure DE 196 31 852 A1. Although the method disclosed in this prior art relates to the production of deactivatable soft magnetic strip elements, nevertheless if the activatable soft magnetic material of this Published, Unexamined German Patent Application is replaced by striplike or wirelike Barkhausen material, and if the semihard or hard magnetic deactivator material is replaced with soft magnetic material, then the method that has been disclosed can be adopted analogously to the production of the securing elements of the present invention. The disclosure content of DE 196 31 852 A1 is hereby expressly incorporated into the description of the present invention.
It is understood that the element according to the invention for securing articles or for sensor technology can also be made by any other methods that have become known for producing deactivatable strip elements. One example that can be mentioned in particular is the production method described in European Patent Disclosure EP 0 690 011 A1.
To optimize the coupling of the portions of the soft magnetic material with the Barkhausen material, it is proposed that the portions of the soft magnetic material be disposed on the Barkhausen material.
In a preferred feature of the element of the present invention, it is provided that the portions of the soft magnetic material and the Barkhausen material have substantially the same width. It is also proposed that the portions of the soft magnetic material are distributed substantially uniformly over the length of the Barkhausen material.
For use as pulse wires in sensors, the element according to the present invention has the advantage that the ends are not covered.
It thus becomes possible to keep the spacing between the actual sensor and the field source slight. Precisely in such sensors but to an increasing extent also in elements for electronically securing articles (especially small articles), one feature of the switch element according to the present invention can be considered especially favorable, in which—as already noted—the length of the striplike or wirelike Barkhausen material is selected to be relatively short. By adapting the length, spacing and permeability of the portions of the soft magnetic material, the characteristic signal of the element can be optimized for the applicable length of the Barkhausen material. Thus the version according to the present invention makes it possible to shorten the length of the Barkhausen elements, known from the prior art, by approximately one-half, without drastically increasing the switching field intensi
Jones Tullar & Cooper P.C.
Lee Benjamin C.
Meto International GmbH
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