U.S. patent application number 11/474775 was filed with the patent office on 2006-11-30 for optically encoded glass-coated microwire.
Invention is credited to Alexis G. Clare, Wesley A. King, William C. LaCourse, Howard H. Liebermann, James E. JR. O'Keefe.
Application Number | 20060266543 11/474775 |
Document ID | / |
Family ID | 36205154 |
Filed Date | 2006-11-30 |
United States Patent
Application |
20060266543 |
Kind Code |
A1 |
Clare; Alexis G. ; et
al. |
November 30, 2006 |
Optically encoded glass-coated microwire
Abstract
A drawn glass-coated metallic member has a thermal contraction
coefficient differential such that the thermal contraction
coefficient of the glass is less than that of the metallic member.
The thermal contraction coefficient differential is maintained
within a predetermined range during drawing. Drawn glass is placed
under residual compression, interfacial bonding between said glass
and said wire is substantially uniform, and surface cracking and
bond breaks between metal and glass are substantially prevented.
Optical properties of the glass coated microwire provide a basis
for enabling multi-bit encoding capability. Advantageously data
encoding is achieved optically, magneto-optically or using a
combined magnetic and optical encoding mechanism. The duplex
material constitution of the glass coated microwire permits
imparting of data thereon by selection and processing of the glass.
Data implantation is readily achieved in-line, during an initial
drawing operation, or as a separate post-draw process. Reading of
data on optically encoded glass coated microwire is readily
accomplished by optical or magnetic methodology, or a combination
thereof.
Inventors: |
Clare; Alexis G.; (Alfred
Station, NY) ; King; Wesley A.; (Almond, NY) ;
LaCourse; William C.; (Alfred, NY) ; Liebermann;
Howard H.; (Succasunna, NJ) ; O'Keefe; James E.
JR.; (Westwood, NJ) |
Correspondence
Address: |
ERNEST D. BUFF;ERNEST D. BUFF AND ASSOCIATES, LLC.
231 SOMERVILLE ROAD
BEDMINSTER
NJ
07921
US
|
Family ID: |
36205154 |
Appl. No.: |
11/474775 |
Filed: |
June 26, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10972549 |
Oct 25, 2004 |
7071417 |
|
|
11474775 |
Jun 26, 2006 |
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Current U.S.
Class: |
174/122G ;
29/825; 29/868 |
Current CPC
Class: |
Y10T 29/49117 20150115;
G06K 19/06018 20130101; Y10T 29/49194 20150115; G06K 19/06187
20130101 |
Class at
Publication: |
174/122.00G ;
029/825; 029/868 |
International
Class: |
H01B 7/00 20060101
H01B007/00; H01R 43/00 20060101 H01R043/00 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. A method for making a preform appointed for use in the
production of glass coated microwire, comprising the steps of: a.
forming a melt of base glass; b. pouring said molten glass into a
die having preselected dimensions; c. extruding said molten glass
through the die using a plunger; d. extruding a length of
solidifying glass; e. cutting a defined length of glass to be used
in a glass coated microwire drawing operation; f. closing one end
of a glass tube to complete the creation of a useable preform.
13. A method for making a preform to be used in the production of
glass coated microwire, comprising the steps of: a. forming a melt
of base glass; b. adding to the melt predetermined amounts of rare
earth oxides; c. pouring said molten glass into a die having select
dimensions; d. causing extrusion of said molten glass through said
die using a plunger; e. extruding a length of solidifying glass; f.
cutting a defined length of glass to be used in a glass coated
microwire drawing operation; g. closing one end of a glass tube to
complete the creation of a useable preform.
14. A method for making a preform to be used in the production of
glass coated microwire, comprising the steps of: a. mixing together
preselected glass components to form a solution; b. gelling said
mixed solution via sol-gel processing to obtain a tube-shaped
solid. c. drying said tube-shaped solid to remove residual water
therefrom; d. sintering said dried, tube-shaped solid at a
temperature well below its melting temperature to reduce its
surface area and minimize porosity, whereby said sintered solid
comprises a glass tube that provides a perform for use in the glass
coated microwire manufacturing process.
15. A method for making a preform to be used in a process for
manufacture of glass coated microwire, comprising the steps of: a.
depositing a coating comprising a film or layer of glass
constituents either inside or outside a glass tube via chemical
deposition, said glass tube and said glass constituents being
compatible; b. thermally treating the glass tube after deposition
to consolidate the coated glass tube to the desired geometry and
density, whereby said thermally treated glass tube comprises a
preform for use in said glass coated microwire manufacturing
process.
16. A method for producing glass coated microwire utilizing the
preforms recited in claims 12-15, comprising the steps of: a.
forming a melt of metallic alloy in a hollow glass perform; b.
drawing said glass preform to entrain and rapidly solidify said
molten alloy while simultaneously providing a glass coating; and c.
placing said glass coating under residual compression during said
drawing step, so that interfacial bonding between said glass and
said metallic alloy core is substantially uniform and surface
cracking and bond breaks between the metallic alloy and glass are
substantially prevented.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to glass-coated wire; and more
particularly, to a glass coated microwire (GCM) that is optically
encoded to provide an article having multi-bit data read/write
capability.
[0003] 2. Description of the Prior Art
[0004] Electronic Article Surveillance (EAS) systems are used to
electronically detect goods that have not been authorized when they
are removed from a retailer. The systems comprise a marker attached
to the goods and a sensor mechanism. The retailer can neutralize
the marker when he wishes to authorize the removal of the goods,
for example when the items have been legitimately purchased.
[0005] One type of EAS marker, termed harmonic or electromagnetic,
is disclosed by U.S. Pat. Nos. 4,484,184 and 5,921,583. Such a
marker comprises a plurality of strips or wire segments of
ferromagnetic amorphous magnetic material that resonate
electromagnetically and thereby generate harmonics in the presence
of an incident magnetic field that has a preselected frequency and
is applied within an interrogation zone. Generation of harmonics
under these conditions provides marker signal identity. An
unmagnetized permanent magnet in the vicinity of the resonating
plurality of strips or wire segments can be magnetized or
demagnetized to inactivate or re-activate said marker.
[0006] Another type of marker, described as being acoustomagnetic
or magneto-mechanical, is disclosed by U.S. Pat. No. 4,510,490. In
this system, a marker is adapted, when energized, to mechanically
resonate at preselected frequencies that are provided by an
incident magnetic field applied within an interrogation zone. The
marker has a plurality of elongated ductile strips of
magnetostrictive ferromagnetic material. Each of the strips is
disposed adjacent to a ferromagnetic element which, upon bring
magnetized, magnetically biases the strips and energizes them to
resonate at the preselected frequencies. A substantial change in
effective magnetic permeability of the marker at the preselected
frequencies provides the marker with signal identity.
[0007] The prior art technologies described hereinabove provide a
method and means for sensing the presence of an object to which a
marker is affixed.
[0008] In related technologies, multi-bit rather than single-bit
(on/off) markers have been described in the technical and patent
literature. For example, a publication by Zhukov et al., J. Mater.
Res. 15 No. 10 Oct. (2000), reports on the ability to produce a
multi-bit marker when utilizing multiple amorphous glass-coated
wire segments, each having a different dimension (length, alloy vs.
gross diameter, etc.) or magnetic property (coercive field, etc). A
multi-bit marker disclosed by U.S. Pat. No. 5,729,201 to Jahnes
describes a similar marker containing multiple wires; but wherein
all wires have the same chemistry and geometric dimensions. A
permanent magnet bias field element in the vicinity of an array of
amorphous metallic wires serves to differentiate the drive field,
at which harmonic response is obtained, by way of proximity of each
individual wire segment to the permanent magnet bias field element,
thereby providing multi-bit capability. PCT patent publication WO
01/29755 A1 to Antonenco et al. describes a multi-wire marker that
is capable of multi-bit performance. As with the Jahnes teaching,
each of the GCM segments utilized in the construction of the marker
have the same chemistry and geometric dimensions. Antonenco et al.
disclose arranging the GCMs in a manner similar to stripes in a
conventional optical bar code. Information concerning the Antonenco
et al. marker is read using a magnetic reading head.
[0009] Each of the encoded markers described in the technical and
the patent literature requires the use of a plurality of magnetic
elements (strips or wire segments). These multiple magnetic
elements must be carefully arranged with respect to each other.
They increase the size, weight and cost of the marker and, unless
accurately positioned thereon, decrease its identifying
characteristics.
[0010] There remains a need in the art for a glass-coated amorphous
or nanocrystalline alloy GCM marker that is lightweight, small,
inexpensive to construct and highly reliable in operation. In
addition, there has long remained a need for such a GCM marker that
can be optically encoded by any number of means. Finally, there
exists a long felt need for a GCM marker that is encoded both
magnetically and optically, and would provide redundant
authentication or complimentary functions, such as anti-theft
capability in conjunction with multi-bit authentication.
SUMMARY OF THE INVENTION
[0011] The present invention provides a multi-bit encoded glass
coated microwire and articles produced therefrom. Also provided by
the invention is a process for encoding of the amorphous or
nanocrystalline alloy GCM and article. Advantageously, the
invention obviates the need for multiple segments of GCM when
manufacturing an encoded article such as an EAS marker.
Surprisingly, it has been discovered that altering either the
ferromagnetic amorphous alloy core or the glass outer layer of a
GCM enables production of the GCM, as well as articles having
multi-bit encoding capability. This is the case even when the
encoded marker comprises a single segment of GCM. Encoding is
afforded either magnetically, or optically; or by a combination
thereof. This feature provides the additional advantage of enabling
either redundant or complementary systems to be operative in even a
single segment of GCM. A further advantage provided by the instant
invention is that encoding of the GCM and articles containing GCM
can be encoded either during their production process, at various
stages of downstream conversion, or even in the field by the end
user.
[0012] Advantageously, glass-coated amorphous or nanocrystalline
alloy GCM marker produced in accordance with the invention is
lightweight, small, inexpensive to construct and highly reliable in
operation. Optical encoding of the GCM is readily accomplished by
numerous means. When encoded both magnetically and optically, the
glass coated microwire of the invention provides redundant
authentication or complimentary functions, such as anti-theft
capability in conjunction with multi-bit authentication.
[0013] Numerous, highly advantageous uses for glass-coated articles
produced in accordance with the present invention are disclosed
hereinafter in greater detail.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention will be more fully understood and further
advantages will become apparent when reference is had to the
following detailed description and the accompanying drawings, in
which:
[0015] FIG. 1 is a schematic cross-sectional view of a GCM preform
showing constituent parts, including a coating at the periphery
that is separate and distinct from that of the base GCM;
[0016] FIG. 2 is a schematic representation of GCM having discrete
bands of an optically distinctive material;
[0017] FIG. 3 is a schematic representation of GCM having a
reflection grating;
[0018] FIG. 4 is a schematic representation of GCM having discrete
bands of a) selectively ablated glass coating, and b) selectively
ablated glass coating and back-filled contrast coating;
[0019] FIG. 5 is a perspective view showing a GCM produced by
drawing from a round glass tube;
[0020] FIG. 6 shows optical emission spectra of an alkali
borosilicate base glass and of the same base glass doped with 1
mole % of Europium in the form of Eu.sub.2O.sub.3;
[0021] FIG. 7 shows optical emission spectra of an alkali
borosilicate base glass of the same base glass doped with 1 mole %
of Terbium in the form Tb.sub.4O.sub.7; and
[0022] FIG. 8 shows optical emission spectra of an alkali
borosilicate glass with the addition of various amounts of Terbium
in the form Tb.sub.4O.sub.7 as well as Dy.sub.2O.sub.3.
DETAILED DESCRIPTION OF THE INVENTION
[0023] As used herein, the term "amorphous metallic alloy" means a
metallic alloy that substantially lacks any long-range order and is
characterized by x-ray diffraction intensity maxima that are
qualitatively similar to those observed for liquids or oxide
glasses. By way of contrast, the term "nanocrystalline metallic
alloy" pertains to those metallic alloys having constituent grain
sizes on the order of nanometers (nm).
[0024] The term "nanocrystalline alloy", as used herein, means an
alloy that has a grain size less than 100 nm. Preferably such an
alloy has a grain size ranging from about 10 nm to 100 nm, and most
preferably from about 1 nm to 10 nm.
[0025] The term "ferromagnetism", as used herein, refers to a
phenomenon by which a material can exhibit a net spontaneous
magnetization by the self-alignment of constituent magnetic
moments.
[0026] The term "glass", as used throughout the specification and
claims, refers to an inorganic product of fusion that has cooled to
the solid state without crystallizing, or to glassy materials
formed by chemical means such as a sol-gel process, or by "soot"
processes, both of which are used to form glass preforms that are
used in fiber optic processing. These materials are not fused; but
rather are consolidated at high temperatures, generally below the
fusion temperatures of the constituents in question.
[0027] The term "preform", as used herein, refers to a vessel in
which alloy is melted and subsequently drawn into GCM.
[0028] The term "drawing", as used herein, refers to the extension
of a material using a tensile force, the extension resulting in a
permanent reduction of the material's cross-sectional area.
[0029] The term "microwire", as used herein, refers to a thin
element, which may be continuous or non-continuous, of circular or
non-circular cross-section, and which has a transverse dimension
less than about 50 .mu.m, and comprises at least one metallic
material.
[0030] The term "glass-coated microwire (GCM)", as used herein,
refers to a thin element, which may be continuous or
non-continuous, of circular or non-circular cross-section, and
which has a transverse dimension less than about 50 .mu.m, and
comprises at least one metallic material and at least one glassy
material.
[0031] The term "article", as used herein, refers to a geometric
body comprising, at least in part, ferromagnetic amorphous alloy
GCM.
[0032] The term "bundle", as used herein, refers to a multiplicity
of amorphous glass-coated GCMs that are bound together and act as a
single element, possibly carrying multi-bit digital data.
[0033] The term "multi-bit", as used herein, refers to numerous
occurrences of binary (on/off) switching capability.
[0034] The term "rare earth", as used herein, refers to any one of
a group of closely related metallic elements of atomic number 57 to
71 inclusive.
[0035] Glass-coated amorphous and nanocrystalline alloy microwire
and its production have been disclosed in the technical and patent
literature [see, for example, U.S. Pat. Nos. 6,270,591 and
5,240,066; Horia Chirac, "Preparation and Characterization of Glass
Covered Magnetic Wires", Materials Science and Engineering A304-306
(2001) pp. 166-171]. Continuous lengths have been produced by
melting either a pre-alloyed ingot or the required elemental
constituents in a generally vertically disposed glass tube that is
sealed at the bottom. Once the alloy is converted to a molten
state, using radio frequency ("r.f.") heating for example, the
softened bottom of the glass tube is grasped and drawn into
continuous microwire. Rapid reduction of alloy cross-section,
together with the use of secondary cooling means, causes the alloy
to become amorphous or nanocrystalline during drawing.
[0036] Ferromagnetic amorphous glass-coated microwires having
positive magnetostriction are based on Fe-based alloys. Such
Fe-based alloy microwires show outstanding magnetic properties due
to their specific magnetic domain structure and magnetoelastic
anisotropies. A general attribute of Fe-based alloy microwires is
the presence of a large Barkhausen effect, that is, an abrupt jump
of the magnetization almost to the saturation value at a certain
value of an applied magnetic field, called the switching field. The
switching field can be tailored to a particular value over a wide
range via the GCM drawing process through the resulting microwire
dimensions. In addition, the squareness of the magnetization loop
ensures the presence of higher order harmonics, which enables more
reliable performance in anti-theft applications, for example.
Ferromagnetic amorphous glass-coated microwire having positive
magnetostriction has an axially magnetized inner core and a
radially magnetized outer shell that result from the magnetoelastic
coupling between internal stresses and the positive
magnetostriction.
[0037] The stress sensitivity of ferromagnetic amorphous
glass-coated microwire can be used advantageously as the physical
basis for affecting magnetic domain structure. In fact,
ferromagnetic amorphous glass-coated microwire encoding can result
from a localized alteration of this domain structure. The
alteration is readily accomplished by imposition of localized
stresses or by selective crystallization of the amorphous alloy.
Such changes are affected by a number of means, including localized
heating via pulsed laser, chemical thinning of the glass coating,
coatings on the glass, and the like. Particularly important for
ferromagnetic amorphous glass-coated microwire is the fact that
localized modification of the glass coating can be used to
effectively produce controlled changes in the magnetic domain
structure of the amorphous alloy core in order to enable
encoding.
[0038] While the outstanding electromagnetic and mechanical
properties of amorphous glass-coated microwire (GCM) can be
optimized by tailoring the compositions of both core alloy and
glass coating and their respective thicknesses, and also through
careful process control both during and after the drawing process,
the glass coating itself enables one skilled in the art to apply
many of the encoding techniques used in optical fibers to GCM.
Optically encoding the glass coating provides a means of
information storage which can be the primary, a complimentary or a
redundant encoding function in relation to any magnetic encoding
present. Such functionality can be obtained by exploiting the
ability to controllably modify any number of properties of the
glass coating, including but not limited to: refractive index,
surface reflectivity, transmission, and fluorescence.
[0039] The means for detecting or "reading" optically encoding
information from glasses is already developed to one degree or
another for all of the techniques disclosed herein. Optical
detection devices typically consist of a light source of known
intensity, polarization, and spectrum and a detector element having
known sensitivity to one or more particular wavelengths of light. A
further refinement to such a device might include one or more
optical filters having intensity, wavelength, polarization or angle
dependencies, which allow for increased signal to noise ratio and
an improved detection accuracy or reliability. Clearly, device
complexity and specificity can be increased through the use of
multiple source, filter or detector components to address a
particular application. In addition, further sensitivity or
accuracy may be obtained by independent or coupled scanning or
pulsed operation of the source, the detector, the filter elements
or any combination thereof. The fundamental principle underpinning
any optical information detection or reading method is that an
incoming light signal is modified through its interaction with the
glass and that the modification discernible by the detector
element. As such, optical detection methods are invariably
line-of-sight techniques, whereby the input light signal is
directed to the interrogated surface or volume, and the modified,
output light signal must then be directed to the detector
element.
[0040] Amorphous or nanocrystalline microwire technology will have
a significant impact in brand protection and anti-forgery
applications, thereby saving domestic retailers billions of dollars
in shrinkage and grey market losses. These products will address a
number of homeland/national security needs.
Optical Encoding of GCM for Enhanced EAS, Security and
Authentication Applications
[0041] Information storage can be achieved through optical
encoding, which exploits the spectroscopic properties of glass.
Optical encoding can be accomplished by harnessing the fluorescent
and/or color and refractive properties of glass and will provide an
independent and complimentary encoding strategy for achieving
multi-functionality GCM.
Optical Encoding Applied to GCM
Uniform Color Methods (i.e. Binary "On/Off", Simple
Authentication)
[0042] Uniformly colored glass: The glass coating of GCM can
possess a specific and identifiable coloration (spectroscopic
property). This coloration can be achieved through various methods
and can be classified as either intrinsic coloration or
light-activated fluorescence.
[0043] Intrinsic coloration: The optical properties of a glass are
determined by the chemical composition; the base glass components,
which determine the major physical and thermal properties, lend a
certain base coloration. The optical properties may then be altered
significantly through the incorporation of small amounts of
specific species called dopants. Dopants are commonly selected from
the Rare Earth elements, which are classified as the lanthanides
and actinides, respectively, in Periods 6 & 7 of the periodic
table of elements. These elements possess partially shielded
f-level electrons, resulting in particularly well-defined
electronic transitions that cause interesting optical properties of
the Rare Earths. Elements from the transition metals (Groups 4-12)
also contribute coloration to the glass. Particular combinations of
dopant elements can result in a unique spectroscopic signature that
is detectable.
[0044] Light-activated fluorescence: In addition to its intrinsic
optical appearance, a glass might also possess a fluorescent
nature. The phenomenon of fluorescence occurs when incident light
of a given energy (E.sub.1) or wavelength (.lamda..sub.1) falls on
the glass surface, causing the emission of light of a lower energy
(E.sub.2) or wavelength (.lamda..sub.2>.lamda..sub.1). Certain
components lend a fluorescent quality to the glass, and careful
control of glass chemistry will result in a desired
fluorescence.
[0045] Uniform colored coating: A uniform colored coating, whereby
the coloration is achievable through intrinsic coloration or
light-activated fluorescence, can also be applied to the exterior
of the glass coating on GCM to provide a desired spectroscopic
quality. The glass and colored coating must be matched to ensure
adequate bonding, which normally requires the glass surface to be
treated or functionalized to accept the coating. Such coatings are
often of the organic or polymeric type, but they might also consist
of a separate layer of glass, being distinguishable somehow from
the base glass either by chemistry, properties or both.
[0046] Color shifting: Another example of a colored coating is one
which shifts either the reflected or transmitted color or both
depending upon the angle of observation and/or the angle of
incident light. This behavior is sometimes termed "dichroic" and
can be caused by a set of optically distinct layers on the glass
surface, comprising an interference filter
(http://www.techmark.nl/ocj/filters.htm). The layers themselves may
consist of inorganic oxides, metallic films or organic films and
may be applied singly to the drawn GCM through a variety of
methods, including chemical vapor deposition, thermal evaporation,
sputtering, dip-coating, and spray-coating. Another method for
obtaining the layers is to make a preform already incorporating the
desired layer structure in the glass portion and then draw the
preform into the GCM. In this case, the layers comprising the
components of the filter on the GCM start as concentric,
thermo-mechanically similar, optically distinct glass regions in
the preform glass tube. A schematic representation is given in FIG.
1.
[0047] Another means of obtaining "dichroic" behavior is to add
certain components to the glass, for example the rare earths
elements Praseodymium and Neodymium. A glass containing these
elements as dopants will have a coloration that depends on the
wavelength of the light that is used to view the glass.
Multi-Bit Optical Encoding
[0048] Spatially modified surface color methods ("optical
barcode"): Intentional modulation of the detectable coloration of
the GCM exterior will allow for the formation of an optical
"barcode", retaining stored information that can be retrieved.
Three variations on this same theme are presented below, where
"color" refers to a particular spectroscopic signature, whether an
intrinsic (passive) color or a fluorescent (activated) color, that
is distinctive and can be detected. It is presumed that the
detection of the optical bar code can be accomplished using
currently available equipment (e.g. red laser scanners), or the
detection may be tuned to a particular optical frequency or
frequencies, providing further security and increasing the
difficulty for fraud and counterfeiting. [0049] Non-colored, opaque
coating on colored glass: The coating forms a pattern in which
coated regions block the underlying glass color and uncoated
regions show the glass color, as depicted schematically in FIG. 2.
[0050] Colored coating on non-colored glass: The coating forms a
periodic pattern in which coated regions exhibit a detectable
coloration and the uncoated regions show the glass, which is a
different, unspecific (and not detected) color. [0051] Colored
coating on a differently-colored glass: The coating forms a
periodic pattern in which coated regions exhibit a particular,
detectable coloration and the uncoated regions show the glass,
which is has a different, specific detectable coloration. These
colors may be detectable in a part of the spectrum that is not
visible to the human eye. This method allows for some signal
redundancy during detection as the bar code pattern may be
determined by scanning for color matching either the outside
coating or the underlying glass. Processes for Optical Encoding
Technique of optical bar code formation: All of the variants
described above rely upon forming a spatially modulated coating on
the GCM resulting in an optically detectable signal. Optical
detection for the bar code forming methods described below can
consist of either the normal reflective detection of a scanned
laser beam or the comparison of a captured digital image with a
database of stored digital images. [0052] Technique 1: High speed
printing methods, whereby the coating is in the form of a liquid or
powdered ink or toner, can be applied in-line to the external
surface of the GCM. The ink can be cured using heat or UV light
methods. [0053] Technique 2: Laser-induced modification of a
writeable layer present on the outside surface of the GCM. Examples
include metallic films, dye-polymer films, bubble forming films,
magneto-optical films, and amorphous-to-crystalline phase
transition films (U.S. Pat. No. 6,442,296). Upon exposure to the
laser light, the reflectivity of the affected film area changes
from its initial state, providing a means for spatial
differentiation reading [0054] Technique 3: A uniform coating is
applied to the surface of the GCM, subjected to a curing step,
which "fixes" or cures the coating, and the uncured or "unfixed"
portion of the coating subsequently is removed. Curing of the
coating may be accomplished locally using a laser or a sharply
focused, broad spectrum light source or heat source. Further, a
combination of a broad spectrum source coupled with a lithographic
mask may be used to cure a portion of the "coded" surface or its
entirety. This method is a particular variant of the previous
method described. Another variant of this method would be the
laser-induced removal of portions of the applied film or layer,
enabling the formation of an optically readable bar code
(http://www jpsalaser.com/page.asp?page_id=20). [0055] Technique 4:
Certain glass compositions are prone to photo-induced structural
changes that, with subsequent heat treatment, lead to
crystallization (M. F. Barker, P. F. James and R. W. Jones, J.
Non-Cryst. Solids, Vol. 104, 1988, 1-16). The photo-induced
structural changes alter the appearance for the affected regions,
providing one mechanism for forming an optically readable bar code.
Furthermore, these affected regions, once crystallized, undergo
much faster etching rates compared to the unaltered glass when
exposed to the appropriate etchant, for example HF (hydrofluoric
acid). Selective crystallization of well-defined spatial regions on
the GCM surface, followed by an etching step, could result in a
physical pattern of relative depressions on the surface. The
contrasting appearance of these regions may enable optical reading,
or a substance allowing greater optical contrast could be filled
into these depressions thereby facilitating optical detection.
[0056] Technique 5: (1) A glass contains a metal oxide component(s)
that can be reduced in oxidation state by suitable heat treatment.
(2) After the GCM is formed, a metallic film (aluminum, copper,
nickel, etc.) is applied to the GCM such that some areas are left
uncoated. It is preferable to have a metal coating which is easily
removable by etching. (3) The coated GCM is heat-treated in a
reducing atmosphere, the hydrogen being unable to diffuse quickly
through the metal-coated regions. (4) The hydrogen will cause
oxidation state reduction for the heavy metal component in uncoated
regions. (5) The metal coating is chemically etched to remove it.
(6) The reduced regions will possess an altered optical
reflectivity relative to unreduced regions. This modification will
in essence result in a permanent, localized removal of the GCM
glass coating. [0057] Technique 6: A color-coded pattern may be
created by combining several GCM lengths together into an article,
said article having a unique and designed optical signature that
results from a particular geometric arrangement. [0058] Technique
7: An optical bar code pattern may be formed on the surface of the
GCM using the laser direct writing method. See D. B. Chrisey et
al., Appl. Surf. Sci. 154-155, 593 (2000); J. M. Fitz-Gerald et
al., Appl. Phys. Lett. 76, 1386 (2000). In this method, material is
deposited by a beam of a high-repetition-rate, 355-nm ultraviolet
(UV) laser, which is focused through a transparent support having a
coating that absorbs the laser light on its opposite side. The
coating is transferred to the intended substrate and forms an
adherent film upon subsequent heat treatment. The heat treatment
conditions required will depend upon the material that comprises
the film Techniques of Modifying GCM Glass Refractive Index to
Result in Refraction Gratings Reflection gratings on the outside
surface of the GCM can be used as a further security or
authentication feature. The grating structure will cause selective
enhanced reflection of a certain wavelength or wavelengths for
broadband incident light. This is schematically shown FIG. 3. Owing
to the relatively short length needed to make a
wavelength-selective grating, it is possible to place several
identical gratings in a sequence to provide built-in redundancy,
which will reduce the possibility for reading errors. UV writing of
gratings using photosensitivity: Gratings can be created by using a
UV laser to induce permanent changes in the refractive index of an
illuminated glass region. This is possible because of the
interaction between certain glass components and the UV light,
which is termed photosensitivity. There are several methods for
obtaining these gratings in glass objects, including glass fibers.
Direct laser written (Interference): By interfering two UV lasers,
one can obtain an interference pattern of alternating strong and
weak intensity regions or fringes. If this fringe pattern is
directed onto the side of a GCM, the strong regions of the
interference pattern can induce permanent refractive index changes
via the photosensitivity of the glass coating. This technique is
referred to as side-writing, and the angle at which the two laser
beams are combined or interfered directly affects the grating
spacing or period, which in turn determines the wavelengths
affected by the grating. Lithography/masking: A second method for
side-writing a grating involves use of a single UV laser beam and a
mask, which is placed adjacent to the GCM. The mask modulates the
laser beam to produce the periodic intensity variation on the GCM
glass coating, which in turn creates the grating via the
photosensitivity mechanism. Laser-induced modification
(femtosecond-pulsed UV lasers): Very fast UV laser pulses have been
shown to cause permanent changes in the refractive index of silica
glass. The precise mechanism is still being investigated; however,
this method has been used to create 3-D wave guides in solid silica
forms. (K. Hirao and K. Miura, J. Non-Cryst. Solids, 239, 1998, pp.
91-95). It is likely this technique can also be used to write
gratings in non-telecommunications glass compositions (not high
purity silica) that are more normally used for GCM applications. A
recent paper has reported refractive index modifications to
non-silica glass (Foturan.RTM.) using a femtosecond pulsed, near
infrared laser (.lamda.775 nm). (M. Masuda et al., SPIE Proc. 4830,
576-80, 2002). UV laser ablation (physical grating): Using a UV
laser, portions of the glass coating can physically be removed from
the GCM surface. [http://wwwjpsalaser.com] If the procedure is
properly carried out, the resulting surface structure will have a
unique reflectivity when exposed to incident light, thereby
providing a means for encoding information on the GCM. This
technique may also be used to remove outer layers from GCM glass
coating to form an optically detectable bar code, as previously
described herein. Additionally, a coating could be applied to the
GCM after this physical grating is formed whereby the optical
contrast is enhanced, easing detection. This concept is shown
schematically in FIG. 4. Techniques Based Upon Combined Effects
Field-induced heating: The glass-alloy composite structure of GCM
permits a variety of additional encoding/detection combinations.
One interesting approach is to use thermal imaging of the GCM,
wherein an external magnetic field is applied, causing the alloy of
the GCM core to heat. Infrared measurement of the temperature rise
is one detection method. Another technique would be to dope the
glass with the Rare Earth element Europium, which has a highly
temperature-sensitive fluorescence emission spectrum, and sense the
temperature increase by observing the shift in the Europium
emission peak. Simultaneous magnetic and optical encoding: The
magnetic properties of the GCM can be used to alter the detectable
optical properties of the external glass coating. Certain elements,
when incorporated into a glass, exhibit magneto-optical properties,
whereby polarized light passing through the glass will undergo a
rotation in the plane of polarization when the glass is exposed to
a magnetic field. Examples of potential dopants include several
elements in the Rare Earth family, which could be incorporated into
the glass coating of the GCM. In addition, a separate coating,
containing a magneto-optical substance, could be placed onto the
outside surface of the GCM immediately after drawing. In either
case, the operating principle is for the underlying magnetic domain
structure of the GCM alloy core, having been magnetically encoded,
to alter the polarization plane of polarized light passing through
the glass coating of the GCM. Such alterations will be detectable
optically, thereby providing a means of information storage that is
either redundant or complimentary to magnetically stored
information. Reading this type of optical encoding requires the
measurement of normal (at 90.degree. to the surface) reflectance of
a polarized incident light source in each of the magnetically
encoded regions, and one could envision detecting the normal
reflection of a laser source as it is scanned along the GCM.
Conversely, combined magnetic and optical encoding can be achieved
through the application of a spatially varying, permanent magnetic
film to the surface of the GCM (i.e. magnetic film or ink bar
code). Such a film could be chosen such that its reflectivity
contrasts sufficiently from the uncoated GCM surface to enable bar
code reading. Furthermore, being a permanent magnetic material, the
film will affect the Barkhausen response of the underlying alloy
core of the GCM, thereby altering the magnetically detected
signal.
[0059] GCM of the instant invention having an amorphous or
nanocrystalline core can readily be tailored for use with an
extensive variety of distinct applications through the appropriate
selection of metal alloy and glass chemistries, and the control of
alloy and glass dimensions. The ability to magnetically and/or
optically store information in or on the microwire by multi-bit
encoding/reading capabilities enables a multitude of additional
applications in which information exchange is required. Among other
benefits, magnetically and/or optically encoded GCM is a passive
device. It requires no internal power source, with the result that
device size and cost are reduced relative to non-passive devices.
An additional benefit resides in the ability to store information
using either or both magnetic and optical encoding. This feature
allows for complimentary functionality and/or redundancy in which
the reading of each encoding type can be independent. Reading of
information stored either magnetically or optically can be
accomplished either at close proximity or from a distance. Optical
reading is a line-of-sight process, whereas magnetically stored
information has the additional benefit of not being limited as a
line-of-sight process. Some optical and magnetic encoding
techniques must be practiced while the glass-coated amorphous or
nanocrystalline microwire is manufactured. This approach provides
additional benefits in those applications requiring brand
authentication, security and anti-counterfeiting functionality.
Other types of optical and magnetic encoding can be carried out
either during GCM manufacture or at the point-of-use, thereby
providing flexibility for many end-use applications. In addition,
the encoding of the GCM of the instant invention provides a
critical link to establishing low-cost systems wherein multi-bit
information storage media is read remotely. Further advantages of
encoded GCM are its small size and continuous nature, which provide
the benefits of unobtrusiveness and high-speed incorporation,
respectively, to certain applications. The remarkable physical
properties of the GCM facilitates its incorporation as a component
onto or into a vast variety of materials, including paper,
paperboard, foils, corrugated papers, converted paper products,
cardboard, paper laminations, plastics, polymers, and textiles,
which includes yarns, threads, woven products, ribbons and the
like, and combinations of these materials. Having been incorporated
onto or into any of the above materials or by itself, the GCM may
be used to make composite structures comprising alloys, ceramics,
plastics, glasses and liquids.
[0060] Applications for the aforementioned systems include enhanced
inventory control, cradle to grave tracking of livestock and
related food products, designer product authentication, tracking
and anti-diversion, for example cigarette products, driver's
licenses, identification cards, passports, and various other
documentation of import, including currency, commercial instruments
and the like. Additional applications where special functionality
derives from the incorporation of encoded glass-coated amorphous or
nanocrystalline microwire include credit cards, retail
gift/merchandise cards, smart labels and smart packaging for the
retail, industrial and government markets, all forms of ticketing,
for example event and transportation ticketing, identification and
tracking of biomedical items and living organisms. One specific use
of the combined optical and magnetic capabilities of the GCM is to
facilitate retail customer self-checkout. This device combines both
EAS (electronic Article Surveillance) simultaneously with the
ability to optically/magnetically scan data. The low cost ease of
application and combined features of EAS, inventory data management
and checkout scanning make this ideal for food and grocery stores.
The use of optical and magnetic capabilities of GCM will also be
applied as an item level interface that will transmit and
communicate information to RFID tags. GCM may also be used in the
technology of smart antennas. Specifically, such GCMs find use as
the on-off elements of phased array systems.
[0061] The following examples are presented to provide a more
complete understanding of the invention. The specific techniques,
conditions, materials, proportions and reported data set forth to
illustrate the principles and practice of the invention are
exemplary and should not be construed as limiting the scope of the
invention.
EXAMPLE 1
[0062] An ingot composed of an amorphous-forming metallic alloy is
prepared by loading the appropriate weights of constituent elements
into a quartz tube that is sealed at one end. The other end of this
quartz tube is connected to a pressure-vacuum system to allow
evacuation and back-filling with Ar gas several times to ensure a
low oxygen Ar atmosphere within the quartz tube. Next, the closed
end of the quartz tube in which the elements reside is introduced
into a high frequency induction-heating coil. With the application
of radio frequency ("r.f.") power, the elements inside the tube are
caused to heat and melt into a stirred, homogeneous metallic alloy
body. When the r.f. power is shut off, the alloy body is allowed to
cool to room temperature in the Ar atmosphere. Once cooled, the
same metallic alloy body is inserted into the bottom of a
vertically disposed glass tube 1 (preform), having 6-mm diameter
that is sealed at the lower end, as depicted in FIG. 5. The upper
end of this preform is connected to a pressure-vacuum system to
allow evacuation and back-filling with Ar gas several times to
ensure a low oxygen Ar atmosphere within the quartz tube. A
specially built inductor 2 at the bottom of the preform is
energized with r.f. power in order to heat and then melt the
metallic alloy body 3 within the tube. Once the metallic alloy body
is molten and heated above its liquidus temperature by some 20 to
50.degree. C., a solid glass rod is used to touch and bond to the
bottom of the sealed glass preform in which the molten metallic
alloy resides. The heat of the molten metallic alloy softens the
glass preform allowing it to be drawn by pulling on the glass rod
to which it is attached. Molten metallic alloy is entrained in the
drawn glass capillary 4 that results. The drawn capillary is then
pulled and guided onto a spinning take-up spool, which provides
both winding tension to ensure continuous drawing at a rate of
about 5 meters/second and a systematically wound article
(microwire) package.
[0063] Amorphous glass-coated microwire about 30 .mu.m in diameter
is produced using the procedure described above. The microwire has
an Fe.sub.77.5B.sub.15Si.sub.7.5 amorphous alloy core that is under
axial tensile stress. The glass from which the preform was made,
and which coats the microwire, is similar to a commercially
available alkali borosilicate glass (PYREX.RTM.) composition,
having optical properties as shown in FIG. 6. The use of this basic
glass in making the GCM does not afford any outstanding, intense
optical behaviors that might be exploited for optical
authentication or encoding purposes.
EXAMPLE 2
[0064] GCM for use in optical-based authentication is produced
using the methods, materials and apparatuses of Example 1, except
that the borosilicate composition used to form the glass coating of
the GCM now contains a small amount of the rare earth element
Europium (Eu). The incorporation of Eu into the glass composition
results in the optical behavior shown in FIG. 6, wherein the
detectable emission of light at 611 nm occurs when the glass is
illuminated by broadband light having wavelengths between 420-600
nm. Note the dramatically increased output signal from the glass of
this example, when compared to that of Example 1. Furthermore, the
sensitive effect of Eu concentration on the resultant emission
strength is shown thereby, providing a complementary means for
providing authentication.
EXAMPLE 3
[0065] GCM for use in optical-based authentication is produced
using the methods, materials and apparatuses of Example 1, except
that the borosilicate composition used to form the glass coating on
the GCM now contains a small portion of any one of the rare earth
elements: Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Samarium
(Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium
(Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), and
Lutetium (Lu). Each individual rare earth element lends its own
unique contribution to the host glass' intrinsic optical signature,
which can then be exploited for authentication purposes. As for the
Eu in Example 2, the unique optical signature due to the rare earth
component is a function of the concentration. FIG. 7 shows optical
emission spectra of an alkali borosilicate base glass of the same
base glass doped with 1 mole % of Terbium in the form
Tb.sub.4O.sub.7. Note how output increases rapidly with the
addition of Tb.sub.4O.sub.7.
EXAMPLE 4
[0066] GCM for use in optical-based authentication is produced
using the methods, materials and apparatuses of Examples, except
that the borosilicate composition used to form the glass coating on
the GCM now contains a small portion of two or more of the rare
earth elements: Cerium (Ce), Praseodymium (Pr), Neodymium (Nd),
Samarium (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb),
Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium
(Yb), and Lutetium (Lu). Each individual rare earth element lends
its own unique contribution to the host glass' optical signature,
allowing one skilled in the art to construct an infinite variety of
unique optical signatures through various combinations of rare
earths at different concentrations. In addition, certain
synergistic optical effects can be obtained through direct
interaction between different rare earth components. FIG. 8
illustrates an example to the interactive output resulting from
having both Tb.sub.4O.sub.7 and Dy.sub.3O.sub.3 present as small
amounts in the base alkali borosilicate glass. It is the overall
unique and controllable optical signature, with virtually an
infinite number of predetermined combinations, which is then
utilized for authentication purposes.
EXAMPLE 5
[0067] GCM for use in optical-based authentication is produced
using the methods, materials and apparatuses of Examples 1, except
that the glass composition used to form the glass coating on the
GCM and which contains a small portion of one or more of the rare
earth elements (Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and
Lu), is not limited to the borosilicate family. Rather, the glass
used to produce the GCM and which acts as the host matrix for the
rare earth elements can be any composition possessing the physical,
thermal and chemical properties consistent with microwire
production (Liebermann et. al., U.S. patent application Ser. No.
10/746,784, filed: Dec. 26, 2003.) Regardless of the glass host,
each individual rare earth element lends its own unique
contribution to the host glass' intrinsic optical signature, which
can then be exploited for authentication purposes.
EXAMPLE 6
[0068] GCM for use in optical-based authentication is produced
using the methods, materials and apparatuses of Example 1, wherein
a film or coating, having a specific and detectable optical nature,
preferably different from the GCM surface, is applied to the drawn
microwire. This coating can be a polymer, metal, and ceramic and
can be coated onto the microwire using any method, including but
not limited to vapor deposition, dip coating, and laser direct
writing. [0069] One variant is to coat the GCM during its drawing
by passing it through a bath of molten aluminum that will coat the
external glass surface. [0070] A second variant involves printing a
specifically-colored coating onto the GCM using a high speed ink
printer, as it is currently done with electrical wire. In this
case, the ink must be cured by exposing the GCM to a high intensity
UV light source. The intensity required is a function of the ink,
its thickness, and the GCM drawing speed. The printed and cured
pattern can then provide the basis for optical identification.
Further variants involve a coating/ink that must be cured using one
or more of the following: heat, oxidation, laser or electron beam
radiation, and ultrasonic energy. [0071] A further variant involves
dip-coating the GCM through a sol-gel solution containing any of a
number of fluorescent or specially colored pigments. The coated GCM
is then passed through an oven heated to a temperature sufficient
to cure the sol-gel coating, given the composition and GCM drawing
rate. The special color properties imparted to the GCM by the
sol-gel coating then become the basis for optical authentication.
[0072] Yet another variant involves the vapor deposition of a
metallic film onto the outside surface of the GCM via sputtering,
also known as physical vapor deposition. In this case, the metal to
be coated onto the GCM is first fashioned into a "target", which
when impacted by ionized argon gas molecules, will contribute
ejected atoms from its surface. The ejected or "sputtered" atoms
will travel to and bond with the intended substrate, in our example
the GCM, thereby forming the film. Metallic films obtainable using
this method may include any of the following elements constituting
from 0% to 100% of the film: B, C, Na, Mg, Al, Si, P, S, Ca, Sc,
Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb,
Mo Ru, Tb, Pd, Ag, Cd, In Sn, Sb, Te, Ba, La, Hf, Ta, W, Re, Os,
Ir, Pr, Au, Ti, Pb, Bi. [0073] Methods practiced in conjunction
with the previous variant include other vapor deposition methods,
including chemical vapor deposition (CVD), thermal evaporation
deposition, electron beam evaporation deposition, plasma vapor
deposition, plasma-assisted CVD, atomic layer deposition (ALD),
laser-assisted vapor deposition, and the like. [0074] Structures
associated with the practice of the previous two variants include
non-metallic films formed on the GCM using any of the vapor
deposition-based techniques available and appropriate for a given
film composition.
EXAMPLE 7
[0075] GCM for use in optical-based authentication is produced
using the methods, materials and apparatuses of Examples 1, wherein
a film or coating, having a specific and detectable optical nature,
different from that of the GCM surface, is applied to the drawn
GCM, thereby forming an optically readable bar code. The means for
defining and forming this optical bar code include but are not
limited to the following variants: [0076] Masking--Specified
regions of the GCM are masked prior to film deposition. After
deposition, the mask elements are removed, exposing the uncoated
GCM surface. For example, one could form a pattern using balsam wax
on the GCM immediately prior to coating with a sol-gel. At
temperatures well below that used to cure the sol-gel, the wax will
melt, thereby being removed from the GCM and taking the uncured
sol-gel coating with it from those specified regions. A
predetermined and well-defined, optically readable pattern results.
[0077] Selective removal: One variant is to coat the GCM during its
drawing by passing it through a bath of molten aluminum that will
coat glass fibers. A commercially available UV laser, used for
precision machining and operating at a wavelength of 157 nm, can
then be used to remove the aluminum coating in selected regions,
thereby forming an optically detectable bar code on the surface of
the GCM. One skilled in the art could envision achieving this
result by employing any of a number of metal, non-metal, ceramic
and plastic materials to form the film using any one of a variety
of deposition methods, while the selective removal is done using
any of a number of lasers in the UV, Visible and Infrared portions
of the spectrum. A further example of this scenario would be to
coat the GCM with a UV-curable ink, then pass the GCM through a UV
source where a well-defined mask, having a pattern of slits, is
held between the GCM and the UV light source. After this selective
curing, the GCM is passed through a rinse station, where the
uncured ink is removed, leaving the intended, permanent pattern.
Optionally, a UV laser source effects curing of intended regions,
leaving other ink-covered regions uncured and subject to removal
during the rinse step. The cured ink regions provide the basis for
optical identification/reading. [0078] Selective
deposition/patterning--One example involves the printing of
specifically-colored rings onto the GCM using a high speed ink
printer, as it is currently done with many products including
electrical wire and food containers. In this case, the ink rings
would then be cured by exposure to a high intensity light source,
an electron beam, radiant heat, an oxidizing atmosphere, or an
ultrasonic environment. The curing methodology required is a
function of ink chemical composition, its thickness, GCM drawing
speed, and the desired form of the pattern. The printed and cured
pattern can then provide the basis for optical identification.
Another example of this type involves the use of a laser direct
write method. In this case, the material to be deposited is lightly
bonded to one side of a sheet of transparent material, typically a
polymer film. A pulsed laser source, to which the sheet material is
transparent and the deposition material is not, is directed to be
incident upon the uncoated side of the sheet, which is situated
between the pulsed laser and the GCM to be patterned. As the laser
is pulsed, the coating material is ejected from the backside of the
sheet and onto the GCM. Both the sheet and the GCM substrate are
moved, such that the pulsed laser beam strikes a new spot on the
sheet with each pulse, and the desired pattern is formed on the GCM
using the ejected coating material. After the pattern is deposited,
the coated GCM is then subjected to a heat treatment appropriate to
cure the patterned coating material. The result is an optically
readable pattern on the GCM.
EXAMPLE 8
[0079] GCM for use in optical-based authentication is produced
using the methods, materials and apparatuses of Example 1, wherein
a readable optical bar code is created by ablation methods. Ablated
regions have a greater surface roughness compared to the as-formed
GCM glass surface, which is very smooth. The surface roughness in
turn alters the reflection of incident light back to a detection
device, thereby providing the means for optical discrimination
between the ablated and unablated regions (i.e. optical reading).
Hereunder are disclosed some ablation methods that include but are
not limited to the following variants: [0080] Borofloat.TM. glass
(Corning 7740) is ablated using a Ti:sapphire laser
(.lamda.=780-800 nm) operating with femtosecond pulses (100-200
fs). By focusing the laser using a long working distance objective
lens, a small spot size is situated onto the target surface. The
ablated volume (i.e. removal thickness) is controlled by varying
the number of laser pulses incident upon a given region. Further,
by passing the laser through a diffractive grating or mask, a
specific pattern can be ablated into the GCM glass surface (Adela
Ben-Yakar et al., Applied Physics Letters 83, No. 15, 3030-32
(2003)). [0081] Another example involves the use of lasers
operating in the ultraviolet spectral region (UV) to ablate
glasses. Pulsed UV lasers (10 ns), operating at 157 nm and 266 nm,
are used to machine fused silica, soda lime silica and zinc
borosilicate glasses. (Michael Argument et al., Photons 1, No. 2,
15-17 (2004)). [0082] Yet another example is demonstrated by the
commercial usage of excimer UV lasers operating at 193, 248, 308
and 351 nm wavelengths to micro-machine and mark ceramic and
inorganic glass materials (http://www.resonetics.com/). [0083]
Finally, lasers operating in the infrared spectral region are also
used commercially to mark and machine ceramics and glasses.
CO.sub.2 lasers, operating at a wavelength of 10.6 .mu.m are used
for this purpose (http://www.resonetics.com/).
EXAMPLE 9
[0084] GCM for use in optical-based authentication is produced
using the methods, materials and apparatuses of Examples 8, wherein
a readable optical bar code is enhanced by methods that involve the
application of select substances to the GCM in the formerly ablated
regions, which will in turn alter the optically reflective
properties (e.g. color or reflectance) of those regions. The
application of an ink or coating to the GCM, followed by a wiping
step, which removes the ink from the unablated GCM surfaces
preferentially, leaves the ink remaining in the previously ablated
regions. The composition of the ink can be designed to impart a
color to the previously ablated regions. One example is an ink or
coating containing fluorescent pigments that strongly reflect at
specific wavelengths when subjected to UV illumination. Another
example is a black ink, the reflection from which will be easily
discernible from the shiny, unablated, uncoated GCM glass surface.
In both of these cases, the increased optical contrast between the
formerly ablated, coated regions and the unablated, uncoated
regions provides the means to enable optical reading. The ink or
coating can contain particles having specific optical or magnetic
properties. One example is an ink containing BASF 025 or BASF 340
magnetic pigments, which contain magnetizable iron and iron oxide
particles, respectively. Such pigments provide an enhanced optical
contrast between previously ablated and unablated regions, as well
as providing an external magnetic bias field that will interact
with the intrinsic magnetic domain structure of the GCM, thereby
altering the electromagnetic signal of the GCM.
[0085] Having thus described the invention in rather full detail,
it will be understood that such detail need not be strictly adhered
to but that various changes and modifications may suggest
themselves to one skilled in the art, all falling within the scope
of the present invention as defined by the subjoined claims.
* * * * *
References