Patent Application
20070290857
The advantages of this invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein:
Referring to
Conventional practice utilizes semi-hard magnetic material as the bias piece in the disposable labels so that the bias material will not be deactivated in the standard detection apparatus. By setting a minimum DC coercivity, and, therefore, using semi-hard magnetic material in the formation of the semi-hard magnetic bias piece 15, the bias material would not be in danger of becoming demagnetized by the interrogation field of the detection apparatus. The concern was that the interrogation field could have a peak as high as 12.5 Oe in a real security label detection system. As is noted in greater detail below, the 58Hz AC coercivity is the final important property to see if the bias material can be stable or not in the interrogation field, not DC coercivity as referred in all prior arts documents relating to this subject.
Semi-hard magnetic material is manufactured by carefully controlled manufacturing parameters to provide a material having consistent DC Hc and DC Br properties. The material must be heat treated within very strict temperature controls to provide satisfactorily operable material for the bias pieces. As a matter of fact, most final heat treatments to form a semi-hard magnetic material for use as a bias material in prior AM labels are irreversible. Namely, it is a “hit or miss” process with great risk involved. If a final heat treatment cannot reach a targeted combination of DC Hc and DC Br to provide a good bias function for prior AM labels, the strip will no longer be salvageable by any other means. Consequently, a failed final heat treatment will result in scraping the entire lot being processes at final thin gauge after enormous process from melting. In contrast, the soft magnetic bias material can be manufactured very easily. For example, by using Fe-based or Ni-based cold rolled strip or wire with big cold reduction (e.g. >90%) without heat treatment needed, we will get high consistency properties from lot-to-lot in the manufacturing process. No uncertainty to produce every qualified lot of this bias material. More particular examples are: a Fe—Ni alloy (the commercial example is 49Ni—Fe) strip material, as well as low carbon Fe strip, is widely used as soft magnetic strips. These alloys have single phase and easy cold formability.
Although they have never been considered for using as AM label's bias material, these soft magnetic alloys are widely available materials with manufacturing experience spanning several decades and were available long before the existence of the semi-hard bias materials as well as the AM labels. In contrast, current semi-hard bias materials always are patented special material compositions with complicated processes. The as-rolled DC coercivity and DC remenance of soft magnetic alloys become insensitive to the process parameters and become uniformly consistent after a heavy cold reduction such as >90%. No further heat treatment is needed after cold rolling the material at finished thickness for use as bias material for AM labels. The homogenity of the whole batch, as well as the batch to batch consistency is superior, compared to the semi-hard magnetic materials that go through various low temperature heat treatments under controlled atmospheres with difficult handling on annealed thin gage strip.
The reduced DC Hc of soft magnetic bias materials enables a significantly longer deactivation distance. Unlike the detection system operated at high frequency at 58 kHz, the AC deactivation field frequency can be designed as low as power line frequency such as 50-60 Hz. In such low frequency, the eddy current is low and the material has AC coercivity close to DC coercivity, which is at about or below 12.5 Oe. Therefore, the lower deactivation peak field at 12.5 Oe is enough to deactivate the soft magnetic bias material, while semi-hard bias material cannot be deactivated with DC Hc greater than 20 Oe at same distance.
The lower DC coercivity of the soft magnetic bias piece 25 provides just enough bias field without excess magnetic force to clamp the flat resonator piece 24. Prior AM security label 10 incorporated many measures to reduce such clamping effect: such as making resonator piece 14 with a transversely curled shape, as depicted in
The magnetically softer bias material has much less or nearly zero “clamping” effect on the resonator pieces compared to a same size (e.g. 0.05 mm thick) semi-hard magnetic material. Therefore, the resonator pieces 24 can be flat instead of being curled shape resonator piece 14 across width. The fact that 49Ni—Fe soft magnetic material can be used in AM label also overthrow the conventional notion that the bias material has to be high in DC Br in order to get enough flux level at thin gage such as 0.05 mm. All known prior semi-hard materials have a higher DC Hc (>12.5 Oe) as well as high DC Br (e.g. about 12-18 kGs). In contrast, our one specific example showing that the 49Ni—Fe soft magnetic bias piece with its DC Br is less than 7 kOs but showing acceptable bias function, when the strip is same thin thickness of 0.05 mm, to make an active and detectable AM label in commercially available Ultramax detection system. This clearly demonstrated that high DC Br is not necessary which combined with higher DC Hc could cause adverse “clamping” effect.
The soft magnetic bias material does not require curled resonator pieces, and operates satisfactorily with flat ones. With a bias piece formed as a flat strip, a wire or other elongated shape, the anti-theft AM security label can be manufactured thinner. Another embodiment of the bias piece would be to place multiple wires in a parallel array, for example on a piece of pressure sensitive tape or double tape. Still another embodiment of the instant invention utilizes a triangle shape bias material with acceptable performance. This embodiment can effectively reduce the half weight of the bias strip needed for the same function. This is half cost reduction for making an equivalent or better AM label. In summary, the thin soft magnetic bias piece (e.g. 0.05 mm) has nearly zero “clamping” effect. Therefore, all previously utilized complicated measures to offset “clamping” effect become unnecessary. More favorably, the soft magnetic bias piece 25 can now be placed inside the resonating cavity of the house together with the resonator pieces 24, which much simplified the label production process.
One of the major advantages of using low DC coercivity bias material is that we can use cheaper resonator material. In Anderson's '489 patent, Fe—Si—B amorphous was listed as having the highest magneto-elastic exchange factor k, which is listed as suitable for AM label application. However, the bias field needed to get the maximum coupling is lower compared to that for a cobalt-contained amorphous resonator. Prior semi-hard magnetic materials give a higher bias field that is suitable for the cobalt-contained resonators that need higher bias field to reach maximum coupling exchange. Therefore, the semi-hard bias materials are not suitable for Fe—Si—B resonator that needs much lower bias field. Now, the soft magnetic bias materials, with its lower bias field, make it possible to use much cheaper Fe—Si—B amorphous as the resonator material.
One example to manufacture soft magnetic bias pieces, start with a coil of 100 mm wide, 0.5 mm thick 49Ni—Fe strip, which is widely available in the marketplace, cold roll with a four-high rolling mill directly down to 0.05 mm thick with cold reduction rate greater than 80%, preferably greater than 90%, but maintaining the DC Hc still below 12.5 Oe. In our specific case, the DC Hc is about 8.5 Oe for 49Ni—Fe soft magnetic bias material as manufactured. The coil is then slit into strips about 7 mm wide, which are then cut into 32-35 mm long pieces with a high speed shear utilizing an automatic feeder. The soft magnetic bias pieces do not need any heat treatments at 0.05 mm final thickness.
As a test of the soft magnetic biased AM security labels, a narrow deactivator commercially available from SEC under the name of“Scanmax Slim-Pad Pro” was employed by placing activated AM labels with the elongated direction thereof oriented parallel to the surface of the deactivator at various distances from the deactivator, as listed in Table I below. The deactivator was triggered with a permanent AM security tag to release the AC demagnetization field. The exposed soft magnetic biased AM security labels were then checked with a label detector (commercially available under the name of “Double Checker” made by SEC) to check the deactivation performance. The test was duplicated using semi-hard magnetic biased security labels (DR labels) commercially available from SEC for comparison purpose.
As is reflected in Table I below, the soft magnetic biased AM security labels incorporating the principles of the instant invention demonstrated significantly better deactivation performance when compared to the presently commercially available semi-hard magnetic biased AM security labels. The soft magnetic biased AM security labels increased effective deactivation distance to 24 cm compared to the corresponding distance of 15 cm for the semi-hard magnetic biased AM security labels. The instant invention greatly enhances the deactivation reliability to big articles or whole box of articles attached with AM labels (i.e. “source tagging”).
Referring now to
Table II below shows the effect of different locations of the soft magnetic bias piece 25 on the detection performance of the AM security labels 20. Samples A and B of the soft magnetic biased security label, incorporating a 49Ni—Fe 32×7×0.05 mm bias piece 25 placed inside the resonating cavity 23 of the housing 22 with a resonator piece formed of FeNiMoB amorphous strip, were tested using a commercially available label detector (Double Checker manufactured by SEC) to determine the detection distance. The results of this test show that the exact position of soft magnetic bias piece 25 inside the resonating cavity 23 does not affect the label detection performance significantly. Accordingly, a significant advantage of the instant invention is that no specific requirement for the exact position of the soft magnetic bias piece 25 is mandated. As a result, production and equipment costs can be substantially reduced.
Referring now to
The utilization of the soft magnetic bias piece in an AM security label enables the configuration of the housing 22, and arrangement of the soft magnetic bias piece 25 and the resonator piece(s) 24 within and outside the resonating cavity, as are described above with respect to
It will be understood that changes in the details, materials, steps and arrangements of parts which have been described and illustrated to explain the nature of the invention will occur to and may be made by those skilled in the art upon a reading of this disclosure within the principles and scope of the invention. The foregoing description illustrates the preferred embodiment of the invention; however, concepts, as based upon the description, may be employed in other embodiments without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200610052012.4 | Jun 2006 | CN | national |
