Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FAR FIELD MAGNET RESENSTI7ZER APPA.RATUS FOR
USE WITH ARTICLE SURVEILLANCE SYSTEMS
Technical Field
The present invention relates to electronic article surveillance (EAS) systems
of the type in which a dual status marker, affixed to articles to be
protected, causes a
detectable signal in response to an alternating magnetic field produced in an
interrogation
zone. More particularly, the present invention relates to an apparatus for
changing the state
of such markers.
Backaround
EAS systems of the type described above are described in
U.S. Pat. No. 4,689,590 and U.S. Patent No. 4,752,758. With such systems,
a dual status marker may comprise a
piece of a high permeability, low coercive force magnetic material and at
least one
permanently magnetizable control element. When the control element is
demagnetized, a
signal may be produced when the marker is in the zone, and when magnetized, a
different
signal corresponding to another state of the marker may be produced. These
dual status
markers may be sensitized (by demagnetizing the high-coercive force control
elements
thereof ) by applying an alternating magnetic field of diminishing amplitude.
Such a demagnetization operation may be effected
through the proper selection and arrangement of a series of permanent magnets
in which
adjacent magnets are oppositely polarized. By selecting the magnets to be of
different
strengths and by an~anging them in an order ranging from highest to lowest
(relative to the
direction of travel), the magnetic field will appear to diminish in amplitude
when an article
having a control element passes over the magnets.
The above-mentioned references describe an apparatus that creates a
magnetic field at or near the working surface on which an article having a
marker is placed.
One of the primary reasons for the development of the near field resensitizer
described in
U.S. Patent Nos. 4,689,590 and 4,752,758, was
to provide a safe way to resensitize magnetic markers affixed to the cover of
a magneticaIly
sensitive media such as audio cassettes or video cassettes without interfering
with the signals
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on the magnetically sensitive media. These solid state decaying magnetic
arrays take
advantage of the fact that similar magnets placed close together, with their
poles altennately
arrayed, tend to have their extemal fields cancel out when they are measured
much beyond a
distance of approximately the width of a magnetic pole face. Within about half
this distance,
the observed magnetic field is almost exclusively the result of the near pole
and the magnetic
fields from the other magnets can almost be ignored. However, at measured
distances from
the array, the measured field of the near magnet starts to be affected by the
other magnets in
the array. At a distance about two to three pole faces above the magnetic
array, all the
extennal magnetic vectors start to cancel each other out and the resulting
external field is very
low. As a result, there is little residual external magnetic field above the
magnet array to
cause hanm to magnetic media.
While a near field array of permanent magnets is useful in demagnetizing
control elements contained in anti-theft markers affixed to prerecorded
magnetic tapes
without affecting the prerecorded signals on such tapes, the near field array
is not as useful
on articles in which the markers cannot be positioned sufficiently close to
the surface of the
magnet array. As mentioned, at appreciable distances away from the near field
array, the
external field is very low. Therefore, the near field array may be ineffective
in resensitizing
markers at increased distances from the array. This may occur, for example
with articles in
which the marker is embedded within the article away from the surface such as
in the spine of
a book. Moreover, the distance from the array of a marker on articles such as
books may
vary depending on the size or shape of the article. Since optimal ring-down
occurs when the
alternating field decreases in an exponential envelope, it is necessary for
the magnetic marker
to experience an exponential decaying magnetic field as it is moved past the
array regardless
of its distance from the array. However, at distances above a given magnet in
the array there
is-an appreciable contribution from the other magnets in the array, and this
contribution
varies depending on the distance from the given magnet to the other array
magnets and the
distance the marker is above the given magnet. It can be seen then that there
exists a need
for a device that provides for sensitizing EAS markers on articles when the
location of the
marker on the article, and hence the distance of the marker from a sensitizing
apparatus, is
unknown.
The present invention provides solutions to these and other problems, and
offers other advantages over the prior art designs.
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Summary of the Invention
According to one broad aspect of the present
invention, there is provided an arrangement which in
movement relative to an article, having affixed thereto a
dual status electronic article surveillance marker including
at least one control element, demagnitizes the control
element to change the status of the marker, the arrangement
comprising: a housing having a working surface; and an
array of magnets coupled to the housing, wherein the array
defines a plane along the surface of the magnets, and
wherein the array produces an alternating magnetic field
having, after a most intense peak, a substantially constant
percentage decrease with each field reversal along a
plurality of substantially parallel paths at different
distances from the working surface.
According to another broad aspect of the present
invention, there is provided an apparatus which in movement
relative to an article, having affixed thereto a dual status
electronic article surveillance marker including at least
one control element, demagnetizes the control element to
change the status of the marker, the apparatus comprising:
(a) a housing having a working surface; and (b) an array of
magnets provided at a uniform distance from the working
surface, wherein the array exhibits an alternating magnetic
field having, after a most intense peak, a substantially
constant percentage decrease with each field reversal along
the working surface.
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In some embodiments, the apparatus provides a magnet array that produces
an altemating magnetic field optimized to decrease in intensity with every
field reversal inside
an exponential envelope, that is capable of demagnetizing high-coercive force
control
elements of a marker along paths at varying distances from the magnet array.
In addition, the
demagnetization apparatus of the present invention requires no power source,
sends out no
possibly harmful AC fields, and performs without dependence on the speed with
which the
marker is moved relative to the apparatus.
lo In some embodiments, the apparatus is adapted for use with an electronic
article surveillance (EAS) system for detecting a sensitized dual status anti-
theft marker
secured to an article. The apparatus may be adapted for use with books or
other articles to
which a marker is affixed but the distance of the marker from the surface of
the article cannot
be predicted. The marker in such a system includes a piece of low coercive
force, high-
permeability ferromagnetic material and at least one control element of a
permanently
magnetizable high coercive force material positioned proximate to the first
material. Such an
element, when demagnetized, results in the marker being in a first state, such
as, for example,
a sensitized state in which the marker may be detected when it is in the
interrogation zone.
Conversely, when the control element is magnetized, the marker is in a second
state, such as,
for example, a desensitized state in which the marker is not detected when it
is in the zone.
In some embodiments, the apparatus comprises a housing having a working
surface relative to which the article may be moved and an array of magnets
associated with
the housing. The magnets within the array are sized and positioned relative to
other magnets
in the array so as to exhibit along a plurality of paths at varying distances
above the working
surface of the housing a succession of fields of altemate polarity whose
intensities decrease
upon each field reversal within an exponential envelope. Each magnet extends
substantiaily
across the width of the housing and the succession of magnets extend along the
length of the
housing. Thus, movement of the article relative to the working surface from a
position
adjacent the most intense field past each successively weaker field of
opposite polarity will
expose the marker affixed thereto to fields of alternate polarities and
exponentially decreasing
intensities to substantially demagnetize the control element of the marker.
This will occur
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within a range of distances above the working surface so as to sensitize the
marker regardless
of the location of the marker on the article.
Brief Description of the Drawinsts
The various objects, features, and advantages of the present deactivating
device will be understood upon reading and understanding the following
detailed description
and accompanying drawings, in which:
FIG. 1 is a perspective view of one embodiment of the demagnetization
apparatus of the present invention;
FIG. 2 is an enlarged top view of FIG. 1, with the cover partially removed;
FIG. 3 is a cross sectional view of FIG. 2, taken along the lines 2-2;
FIG. 4 is a graph representing the field strength and polarity along a path at
a
distance of 0.32 cm (0.125 inches) above the surface of a magnet array such as
in FIGS. 1-2;
FIG. 5 is a graph representing the field strength and polarity along a path at
a
ls distance of 0.57 cm (0.225 inches) above the surface of a magnet array such
as in FIGS. 1-2;
FIG. 6 is a graph representing the field strength and polarity along a path at
a
distance of 0.83 cm (0.325 inches) above the surface of a magnet array such as
in FIGS. 1-2;
FIG. 7 is a graph representing the field strength and polarity along a path at
a
distance of 1.08 cm (0.425 inches) above the surface of a magnet array such as
in FIGS. 1-2;
FIG. 8 is a graph representing the field strength and polarity along a path at
a
distance of 1.59 cm (0.625 inches) above the surface of a magnet array such as
in FIGS. 1-2;
FIG. 9 is a semi-log graph illustrating field strength along portions of the
paths in FIGS. 48 for the demagnetization apparatus of the present invention;
and
FIG. 10 is a schematic representation of an enlarged section of the
embodiment of the magnetic array of FIG. 3, and the alternating magnetic field
produced by
each of the magnets in the array.
Detailed Description of the Drawings
As shown in FIG. 1, the demagnetization apparatus of the present invention
may be in the forrn of a counter top apparatus 10. The apparatus could also
take other forms
as will be recognized by those of sldll in the art. The counter top apparatus
10 includes a
housing 12 and an array of magnets (see FIGS. 2 and 3) mounted within the
housing 12.
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The housing 12 includes a non-magnetic cover plate 18 which both covers and
protects the
array of magnets. In addition, the cover plate 18 provides a working surface
19 relative to
which an article 20 having a marker 22 affixed thereto may be moved during use
of the
apparatus. Such a cover plate 18 may comprise a strip of non-magnetic
stainless steel having
a thickness in the range of 20 mils (0.50 mm). The use of a metallic cover
plate 18 is further
desired because such a surface resists wear from scratching or chipping as may
otherwise
occur with cover plates having a polymeric or painted surface, and it thereby
remains
aesthetically acceptable even over many cycles of use. While the apparatus 10
may be used
with the working surface 19 established by the cover plate 18 in a horizontal
position, such
that an article 20 may be moved across the horizontal surface, the apparatus
may also be
positioned to have the working surface 19 vertical.
The housing 12 further includes sidewalls 21 and ends 34 that attach to the
sidewalls 21 with, for example, a bolt or screw 35 such as shown in FIGS. 2
and 3. In one
embodiment, the sidewalls 21 are aluminum rails having dimension of 0.95 cm x
3.81 cm
with a length of 63.98 cm (0.375 x 1.5 inches with a length of 25.1875
inches). The portions
of the housing 12 are also preferably constructed of non-magnetic materials.
Also, beveled
faces (not shown) may be provided on the housing 12 to carry appropriate
legends,
manufacturer identification, instructions, and the like.
In using the apparatus of FIG. 1, it will be recognized that the article 20 is
to
be moved in the direction shown by arrow 24, thus causing the marker 22
affixed to one
surface of the article to be moved so that the marker 22 is passed over the
array of magnets
positioned directly beneath the cover plate 18. Thus, for example, if the
article 20 is a book
such as illustrated in FIG. 1, the marker 22 could be affixed within the
spine, and the book
held so as to be positioned on the cover plate 18 and passed along the working
surface 19 in
the direction of the arrow 24. The demagnetization of the control element 32
is effected
upon exposure to the fields produced by the array of magnets when the control
element 32 is
brought into close proximity with the magnetic fields associated with the
magnet array above
the working surface 19.
The marker 22 is typically constructed of a strip of a high perrneability, low
coercive force magnetic material such as a peffnalloy, certain amorphous
alloys, or the like as
disclosed, for example, in U.S. Pat. No. 3,790,945 (Fearon). The marker 22 is
further
provided with at least one control element 32 of high coercive force
magnetizable material as
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disclosed, for exaacple, in U.S. Pat. No. 3,747,086 (Peterson). The control
element 32 is
typically fomied of a material such as vicalloy, magnetic stainless steel or
the Iike, having a
predetermined value of coercive force in the range of 50 to 240 oersteds. When
such an
element 32 is magnetized, it prevents the marker 22 from being detected by the
system when
5' the marker 22 is present in the interrogation zone. Further examples of
dual status markers
for use with elearomagnetic article surveillance systems are disclosed in U.S.
Pat. No.
5,432,499 (Montean), U S. Pai. No. 5,331,313 (Koning), U.S. Pat. No. 5,083,112
(Piotrowski), U S. Pat. No. 4,967,185 (Montean), U.S. Pat. No. 4,884,063
(Church), U.S.
Pat. No. 4,825,197 (Church), U.S. Pat. No. 4,745,401 (Montean), and U.S. Pat.
No.
4,710,754 (Montean).
The details of the magnet array of the apparatus in FIG. I are shown in
FIGS. 2 and 3. In the disclosed embodiment, the array includes thirty discrete
magnets 100.
As shovir, grooves are formed within the sidewalls 21. A groove formed within
the first
sidewall has a corresponding groove directly across on the other sidewa1121.
Each of the
magnets 100 in the magnet array is positioned within the housing 12 by sliding
the magnet
100 within a pair of the corresponding grooves within the sidewalls 21. The
magnets 100 are
to be secured in position within the grooves with suitable epoxy, or
a}tematively, mechanical
fasteners. As seen in FIG. 3, each of the magnets extend within the grooves
into the housing
12 until the top face of the magnet 100 is approximately level with the top of
the sidewalls
21. When the cover plate 18 is positioned on the housing 12 to rest on the
sidewalls 21, the
face of the ma.gnet 100 contacts or is positioned directly beneath the cover
plate 18. As
suck the faces of the magnets 100 in the array are positioned at approximately
the same
distance relative to the marker 22 on an article 20 placed on the cover plate
18 as the marker
22 is from the woridng surface defined by the top surface of the cover plate
18.
The faces of the magnets 100 directed toward the cover plate 18 are poles
that create a magneac field extending upward from the cover plate 18.. Each of
the magnets
are sized and positioned relative to adjacent magnets so as to create along
multiple paths,
within a range above the cover plate 18, a magnetic field of alternating
polarity and of
suitable intensity that decreases within an exponential envelope from one end
of the elongated
ma.gnetic aray to the other. One of skil! in the art will appreciate that such
fields may be
created along a plurality of paths at varying distances above the cover plate
18 by methods
which include providing appropriate shielding to alter the effective strength
of each magnet
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100 as well as adjusting positions of the magnets 100 relative to the cover
plate 18 and to the
other magnets 100 within the magnet array. In the embodiment shown in FIGS. 2
and 3,
each of the magnets (and hence the poles that are defined by the face of the
magnet
contacting the cover plate) extends across the width of the housing, and the
succession of
thirty magnets in the magnet array extends along the length of the housing 12.
Although the
magnets 100 are shown as generally decreasing in size, this is
representational of decreasing
strength only and not necessarily of actual physical size. The important
factor regarding the
strength of the magnets is that the strength of each magnet is preferably
determined so that
the fields created along multiple paths above and parallel to the worlcing
surface decrease
within an exponential envelope along the length of the magnet array. For the
counter top
apparatus 10 of FIG. 1, the field produced along the paths above the cover
plate 18
decreases within an exponential envelope in the direction of the arrow 24.
The magnets 100 within the magnet array may be made of any suitable
magnetic materials including, but not limited to, any combination of the
following: (1) an
injection molded permanent magnet material, such as type B-1060 "Plastiform"
Brand sold
by Arnold Company ofNorfolk, Nebraska, which is magnetized after molding and
subsequently arranged with appropriately; (2) a sheet material magnetized with
alternating
poles, such as type B-1013 "Plastiform" Brand, type 2002-B "Plastiform" Brand,
or type
1030-B "Plastifornm" Brand, all sold by Arnold Company ofNorfolk, Nebraska; or
(3) a
machineable metallic material such as Nd 35 or Nd 40 or other NdFeB alloy such
as sold
under the brand name Magnaquench by MagStar Technologies, St. Anthony,
M'umesota.
Other appropriate materials will also be recognized by those of skill in the
art.
FIGS. 4- 8 illustrate alternating magnetic fields of exponentially decreasing
intensity along paths within the range of 0.32 to 1.59 cm (0.125 inches to
0.625 inches)
above the working surface that are produced by one embodiment of a magnet
array set forth
below in Table 1. FIG. 4 shows the alternating magnetic field along a path at
a distance of
0.32 cm (0.125 inches) above the surface of the magnet array. FIG. 5 shows the
alternating
magnetic field along a path at a distance of 0.57 cm (0.225 inches) above the
surface of the
magnet array. FIG. 6 shows the alternating magnetic field along a path at a
distance of 0.83
cm (0.325 inches) above the surface of the magnet array. FIG. 7 shows the
alternating
magnetic field along a path at a distance of 1.08 cm (0.425 inches) above the
surface of the
magnet array. FIG. 8 shows the alternating magnetic field along a path at a
distance of 1.59
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an (0.625 tnciies) above the surrace of the magnet array. 1 he range oi
distanees in FiGS. 4-
8 represents the range of distances for which a marker on, for example, a book
wil! lt7cely be
positioned from the cover of the apparatus of FIG. 1. The corresponding peaks
and valyeys
in FIGS. 4- 8 represent the field intensity at that location along the path.
In order to demagnetize a marker, the marker should pass along a path that
has a field strength that decreases from approxamately 300 gauss to 70 gauss.
Anything
geater than 300 gauss wdl typical}y completely megnetize the magnetic control
elements of the
marker in question, and anything less than 70 gauss wdl typically have no
effect on the
magnetic control elements. Referring again to FIGS. 4-8, it can be seen that a
magnetic marker
passing along the enfire magnet array wiIl experience this correct exponential
decaying field
regardless of a distance from the array. However, it can be seen that the
location within the
array in which the marker passes through the decaying range of 300 gauss to 70
gauss di;ff'ers
depending on the distance of the marker from the surface of the magnet array.
For example,
as shown in the seni-log plot in FIG. 9, along a path 0.32 cm (0.125 inches)
above the
magnet array a marker passes through this rangc in the disclosed embodimcnt
magnct array
between the nineteenth and thirtieth magnets in the magnet array, whereas
along a path 1.59
an (0.625 inches) above the magnet array a marker would pass through this
range when
passing between the second and twelfth magnets of the magnet acray. "nerefore,
because
the location of a marker on an article is unknown, it is important that a user
who is
demagnetizing a marker on an article passes the article along the entire
length of the cover
plate 18 of the apparatus.
Providing an exponentially decaying field along paths at varying distances
above the magnet array is necessary because there is no way to predict the
distance or
orientation of the magnetic marker in, for example, a book or similar device
as it is used in
this invention. As shown, this invention will sensitize a magnet marker at any
distance
from 0.32 to 1.59 cm (0.125 to 0.625 inches) above the surface of the magnet
array. It can
be appreciated by those of skill in the art that the size, strength and
positioning of the
magnets within the array can be altered to increase or decrease that range.
Such alterations
are within the scope of this invention.
The r, etic field intensity and polarity at a given position P along a path
above the surface of the magnet array is govemed by the algebraic sum of the
intensity and
polarity of each magnet reduced approptiately according to its distance from
the positionP.
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Thus, the field contribution of any given magnet is affected by the field
contribution of its
adjacent magnets, its next nearest magnets, and so on. The magnets positioned
at each end
of the magnet array, however, are adjacent to only one other magnet and thus
may have an
undesirably large contribution to the magnetic field along the path in the
region above these
end magnets. For this reason, the end magnets must be carefully selected and
adjusted so
that their contribution to the field intensity along the path is not so large
so as to deviate from
the exponential envelope of the entire magnet array. It will be appreciated by
one of skill in
the art that the selection and adjustment of the end magnets may be properly
affected by
partial shielding of the end magnets, adjusting the spacing of the end magnets
relative to the
worlcing surface and to the other magnets, adjusting the magnet strength by
material or size
of the magnet, by adequately trimming the end magnets, or by offsetting the
end magnets
relative to the worlcing surface.
It is preferred that the most intense peak or valley seen by the control
element is strong enough to initiate the demagnetization process by ensuring
that all magnetic
domains in the control element are oriented in one direction parallel with the
initial field. In
order to initiate the demagnetization process, it has been found that the most
intense pole is
preferably at least approximately one and one half times the predetemined
value of coercive
force of the control elements. Subsequent to the most intense pole, each field
reversal ends
preferably in a peak or valley whose intensity is decreased by approximately
the same
percentage from the previous peak or valley. It has been found that
demagnetization will
occur if on the average the field intensity associated with each successive
pole changes by 5
to 20 percent between any two adjacent poles. Preferably, the field intensity
associated with
each successive pole changes by approximately 15 percent between any two
adjacent poles.
It is also preferred that the last peak or valley seen by the control element
is weaker than all
previous poles so that the control element is not left with an undesirable net
magnetization.
Thus, as illustrated by the final peak shown in each of FIGS. 4-8, the final
pole is preferably
chosen so that the field falls off to zero in concert with the exponential
envelope.
When an alternating magnetic field decreases within an exponential envelope,
the percent decrease between any two adjacent magnets remains constant. The
rapidity with
which the field decreases in such a magnetic circuit may be described as its Q
value, defined
by:
Q = -mt/ln(f L/fQ
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wherein
I-L = field at the working distance associated with any given pole; and
H. = field at the working distance associated with a pole located n poles away
from
the given pole.
A magnetic section with an exponentially decreasing field along the working
distance is thus
defined by a constant Q value. An alternating field that decreased
approximately 15 percent
between adjacent poles would thus have a Q value of approximately 9.5.
A series of poles establishing a magnetic field with a constant Q value
ensures that a control element moved relative to the magnetic field in the
direction of
decreasing field strength will be incrementally demagnetized, undergoing a net
demagnetization by the same percent with each field reversal. A magnetic field
that does not
decrease exponentially will necessarily have regions where the incremental
demagnetization
occurs too rapidly, too slowly, or both, resulting in the control element not
being completely
demagnetized or an apparatus that is larger than necessary to achieve full
demagnetization.
FIG. 9 schematically illustrates the decrease in peak to peak field intensity
with distance along portions of the paths in FIGS. 4-8 for the demagnetization
apparatus of
the present invention. FIG. 9 represents a semi-log plot of the envelope in
which the
alternating fields decrease in the apparatus of the present invention along
several paths at
distances between.125 and .625 inches above the surface of the magnet array.
Each of lines
90, 88, 86, 84 and 82 in FIG. 9 corresponds to the paths in FIGS. 4-8,
respectively. As can
be seen, an exponentially decreasing alternating magnetic field such as
embodied in the
present invention yields straight lines for each of the paths on the semi-log
plot, thus denoting
a constant Q value and a constant percent decrease along each of the paths.
When a
demagnetization apparatus comprises a magnetic field that deviates from
constant percentage
decrease, there will be regions in which the magnetic field decreases too
rapidly, thus risking
a residual magnetization of the control element, and there will be regions in
which the
magnetic field decreases too slowly, thus requiring a longer magnetic section
than would be
required for an alternating field that decreases by a constant percentage with
each field
reversal.
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One embodiment of the present invention includes a calibrated array of
discrete magnets each comprising a length of permanently magnetized material
sandwiched
between two flux collectors. In this embodiment, the magnetic polarity of each
discrete
magnet alternates from magnet to magnet so that the line drawn from the north
pole to the
south pole for each discrete magnet lies along the length of the magnet array.
The array is
preferably calibrated by choosing the magnet material for each discrete magnet
and adjusting
the size of the magnet so that when it is positioned in its proper place in
the array the
magnetic array will display an alternating field of exponentially decreasing
intensities. FIG.
schematically illustrates from a cross sectional view the preferred
construction of each
10 discrete magnet 108 in the magnet array of the present invention. Each
magnet 108 is
constructed from a length of pennanently magnetized material 106 and
positioned so that its
magnetic pole is aligned along the length of the array as indicated by arrow
104. The size of
each permanent magnet 106 and the material from which it is made is chosen so
that the
magnetic field produced along multiple paths above the surface of the array
for the entire
array altennates and decreases at a constant percentage with each field
reversal. The flux
collectors 102 that sandwich each permanent magnet 106 gather the flux lines
produced by
the permanent magnet so that the field on the path above the surface of the
array above each
magnet is parallel to the particular path. These flux collectors 102 are
preferably made from
a mild steel. While the detailed magnetic properties of the flux collectors
102 is not critical,
the flux collectors 102 should preferably be designed to absorb at least as
much of the
magnetic flux produced by its associated permanent magnet.
The discrete magnets 108 of the magnetic array of the present invention are
preferably arranged in one of two ways in order to generate a series of
altennating poles, as
illustrated in FIG. 10. The upper series of magnets 117 shows a section of an
array in which
each magnet 106 has a polarity 104 that is counter parallel (parallel and in
the opposite
direction) to the polarities of its adjacent magnets. Such an arrangement
produces an
altemating magnetic field 116 that successively reaches a maximum positive
intensity and a
maximum negative intensity directly above the center of each magnet 106 and
reaches zero
intensity above the midpoint between two adjacent magnets as shown by waveform
116. In
such an arrangement, the number of discrete magnets 108 in the array equals
the total
number of field maxima and minima. The arrangement of the polarities of the
upper series of
magnets 117 is the arrangement used in the exemplary embodiment magnet array
in Table 1.
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The lower series of magnets 115 shows a section of an array in which each
magnet 106 has a
polarity 104 that is paraIlel and in the same direction to the polarity of its
adjacent magnet.
Such an arrangement produces flux lines ninning from north to south for each
individual
magnet 106, but it also creates induced poles 105 that produce flux lines
running in the
opposite duection between magnets from the north of one magnet to the south of
the
a,dacent mapet. In such a manner, an alternating magnetic field 114 is
produced that
successrvdy reaches a maximum posttive intensity direcdy above each magnet,
and a
maximum negative itrtensity above the midpoint between adjacent magnets. In
this
anangement, there are twice as many total mmxama and minima as there are
discrete magnets
108 in thearray.
The two arrays 117 and 115 both create alternating magnetic fields, but with
different periodicities. FIG. 10 illustrates that between the points 110 and
112 the field
produced by array 117 has two field reversals whereas the field produced by
the array 115
has four field reversals and each array uses the same number of magnets 106.
Thus, half as
many magnets are required when using the principle behind array 115 to design
a magnet
arcay to aclueve the same nurpber of field reversals as with array 117. This
may be important
when the size of the array is important. By fabricating an elongated magnetic
section using a
n'agnet array such as array 115, a much shorter magnetic section will be
attained so that a
housing with much smaller dimensions can be used.
In addition to having the advantages of more reliable demagnetization
performance and smaller size of the magnet array, the performance of ihe
demagnetization
apparatus of the present invention is not speed dependent. The demagnetization
of the
control element 32 does not depend on the speed with which the control element
32 is
moved relative to the magnet array because the control element 32 wUl
experience an
alternating magnetic field that decreases by a constant percentage with each
field reversal
without regard to the rate of movement. Thus, the only limitation on the speed
with which
the control element 32 may be moved relative to the magnet array is
deterinined by the
response rate of the magnetic domains of the control element material.
However, typical
rates of movement during human usage of the demagnetization apparatus of the
present
invention are in the range of 400 to 700 Hz, which is well below the rate
limitation due to
magnetic domain response times to magnetic fields.
CA 02344709 2001-03-20
WO 00/22587 PCT/US99/03635
-13-
As mentioned, one exemplary preferred embodiment configuration of the
magnet array with respect to material, length, width, thickness, and
orientation of each
permanent magnet 106, the width of the flux collectors 102, the distance
between adjacent
magnets and the total number of magnets within the array is tabulated in Table
1. The
magnet orientation data in Table 1 are represented by arrows which indicate
the north to
south orientation of each magnet. It can be appreciated that other embodiments
which
achieve the objectives of this invention are within the scope of this
invention.
CA 02344709 2001-03-20
WO 00/22587 PCT/US99/03635
-14-
Table 1
magnet lvlagnet Magnet Magnet Flux Distance
ma~et magnet metmial orientat'n I.ength Width Height collector frrnn pre.wi~s
ll cm cm cm width cm
Nd 35 10.16 0.274 1.27 0.152
1
2 Nd 35 10.16 0.475 1.27 0.152 2.54
3 Nd 35 10.16 0.419 1.27 0.152 2.54
4 Nd 35 10.16 0.356 1.27 0.152 2.54
Nd 35 10.16 0.404 0.841 0.152 2.54
6 Nd 35 10.16 0.318 0.945 0.152 2.54
7 20028 Amold Plastiforni 10.16 0.582 1.27 0.152 2.54
8 2002B Amold Plastiform 10.16 0.516 1.27 0.152 2.54
9 2002B Amold Plastiform 10.16 0.434 1.27 0.152 2.54
2002B Amold Plastifora- 10.16 0.371 1.27 0.152 2.54
11 2002B Amold Plastiform 10.16 0.328 1.27 0.152 2.54
12 2002B Amold Plastifocm 10.16 0.318 0.945 0.152 2.54
13 2002B Amold Plastifotm 10.16 0.318 0.737 0.152 2.54
14 2002B Amold Plestiform 10.16 0.318 0.594 0.122 2.54
2002B Amold Plastiform 10.16 0.318 0.465 0.122 2.54
16 2002B Amold Plastifam 10.16 0.318 0.366 0.122 2.54
17 2002B Amold Plastifarm 10.16 0.318 0.559 0.122 2.54
18 B1030 Amold PlasNfom- 10.16 0.318 0.790 0.122 2.54
19 B 1030 Amold Plastifotm 10.16 0.318 0.673 0.122 2.54
B1030 Amold Plastifonn 10.16 0.335 0.467 0.122 2.54
21 B1030 Amold Plestifonn 10.16 0.229 0.570 0.122 2.54
22 B 1030 Amold Plastifoan 10.16 0.229 0.401 0.122 2.54
23 B1030 Amold Plastifornt 10.16 0.229 0.310 0.122 1.27
24 B1030 Amold Plastifoan 10.16 0.229 0.259 0.122 1.27
B1030 Acnold Plastiform 10.16 0.152 0.318 0.122 1.27
26. B1030 Arnold Plastiform 10.16 0.152 2.489 0.122 1.27
27 B1030 Amold Plastifonn 10.16 0.152 1.905 0.122 1.27
28 B1030 Amold Plestiform 10.16 0.076 0.455 0.122 1.27
29 B 1030 Ainold Plastiform 10.16 0.076 0.310 0.122 1.27
B1030 Amold Plastifonn 10.16 0.076 0.239 0.122 1.27
