Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1996-12-16
1999-11-23
Swann, Glen
Communications: electrical
Condition responsive indicating system
Specific condition
340551, 3405721, G08B 13187
Patent
active
059907924
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to amorphous tapes with improved properties for use in labels. The labels are used for the purpose of marking and identifying objects.
DESCRIPTION OF THE PRIOR ART
The type of labels mentioned above is described in, e.g., WO 88/01427 and EP-B-0 096 182. The labels in these patent specifications are provided with an internal cavity, in which at least one tape of an amorphous material resides. The tape material has a large magneto-mechanical coupling, i.e., a mechanical load on the tape also causes a change in the magnetic properties of the tape. The tape or strip is a kind of mechanically resonating element, the resonance frequency of which being located in different frequency bands depending on the length of the tape.
The magnetic properties of the tape are also influenced by its length and geometry. For instance, the demagnetizing effect present at the ends of a tape has a substantially different influence on the magnetization of the tape, depending on the length of the tape. This means that tapes with different lengths are magnetized to different degrees when exposed to an identical magnetic field.
With magneto-elastical resonance elements, such as amorphous tapes, the magneto-elastical coupling factor, which affects the signal strength of the tape, and the .DELTA.-E effect, which affects the resonance frequency of the tape, both depend on the magnetization of the tape. In the embodiment disclosed in EP-B-0 096 182, the above-mentioned factors have substantially no importance. In the embodiment according to WO 88/01427, on the other hand, certain problems are associated with adjusting a magnetic control field in the form of a bias field, if tapes with different lengths are used together in labels, which are read simultaneously. This is particularly true, if simultaneous signals are desired from many tapes at the same time, and if all tapes simultaneously are supposed to produce a high coupling factor and a strong frequency response. If, for instance, such a control field is used, that optimally magnetizes tapes with shorter lengths, longer tapes will already be over-magnetized beyond saturation. Thus, significant problems arise when it comes to detecting the tapes and keeping the signals within the desired part of the frequency band of the tapes. To some extent, the above-mentioned problem may be reduced by producing a control field in a considerably more complex and complicated way. However, the improvement does only occur to a minor degree, and a certain amount of time is lost at the label detection.
The label detection is done by exposing the tapes to a magnetic interference signal, whereby the tapes are forced into a state of mechanical oscillation. The tape resonance can be detected by the use of a magnetic detection coil. The tape resonance frequency is highly influenced by surrounding magnetic fields, and the above-mentioned bias field is used to vary the magnetic field in an interrogation zone, thereby making it possible to simultaneously detect identical tapes, which are exposed to magnetic fields of different strengths or different directions.
BRIEF SUMMARY OF THE INVENTION
An object with the present invention is to provide tapes, which are identically magnetized but which work within different frequency bands. This is accomplished by the use of tapes with identical geometries (length, width and thickness), which are exposed to an influence for changing the tape mass while preserving the magnetical properties of the tape. Functionally, these new resonance elements may be viewed upon as a spring, the spring constant of which being magnetically controllable through the .DELTA.-E effect, and which has a mass applied at each end. The resonance frequency then depends on the masses, the spring constant and the self-mass of the spring/tape.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail by way of preferred embodiments and with reference to the accompanying drawings, in which
FIG. 1 is a schematic persp
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RSO Corporation N.V.
Swann Glen
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