Note: Descriptions are shown in the official language in which they were submitted.
COUNTERFEIT PREVENTION STRUCTURE AND COUNTERFEIT PREVENTION
MEDIUM
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The
present invention relates to a counterfeit
prevention structure capable of preventing counterfeiting and
a counterfeit prevention medium including the counterfeit
prevention structure.
2. Description of the Related Art
[0002]
Conventionally, a counterfeit prevention structure
that prevents counterfeiting is arranged in a sheet-like
valuable medium such as a banknote (paper currency), a stock
certificate, a bond, a check, a coupon, and the like. For
example, Japanese Patent Application Laid-Open No. 2016-000498
discloses a technique of using a conductive layer, in which
split ring resonators (SRRs) are formed, as the counterfeit
prevention structure. The
SRRs, each of which an outer
diameter is around several hundred micrometers, have effect on
terahertz electromagnetic waves. Metamaterial formed by the
minute SRRs is used for counterfeit prevention.
[0003]
Specifically, a conductive layer, in which SRRs of
a predetermined shape are arranged in a matrix layout at
regular intervals, is formed such that transmittance of a
predetermined value is obtained when the SRRs are irradiated
with terahertz electromagnetic waves of a specific frequency.
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Such a conductive layer is arranged inside or on a medium as
the counterfeit prevention structure. The
counterfeit
prevention structure is irradiated with the terahertz
electromagnetic waves, and the authenticity of the medium can
be determined based on the obtained value of the transmittance.
[0004] The
transmittance of the terahertz electromagnetic
waves penetrating the conductive layer changes depending on
the relation between a polarization direction of the terahertz
electromagnetic waves and directions of open parts of the SRRs.
The conductive layer is divided in a plurality of areas, and
the open part directions of the SRRs in each area are different.
By this structure, a counterfeit prevention structure in which
the transmittance in each area is different can be obtained.
The transmittance is measured while scanning each of the areas
of the counterfeit prevention structure with the terahertz
electromagnetic waves, and the authenticity of the medium is
determined based on whether the change in the measured
transmittance matches with a transmittance and a scan width of
each of the areas.
[0005] In the
conventional technique, however, the
authenticity of a medium in which the counterfeit prevention
structure is arranged may not be determined with a high
accuracy. For example, positions of a transmitting unit that
transmits the terahertz electromagnetic waves and a receiving
unit that receives the terahertz electromagnetic waves are
fixed in an apparatus, and when measuring the transmittance of
the terahertz electromagnetic waves, the medium is transported
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such that the counterfeit prevention structure thereof passes
between the transmitting unit and the receiving unit. As the
medium is transported, when the counterfeit prevention
structure made by the SRRs blocks the terahertz electromagnetic
waves between the transmitting unit and the receiving unit,
different transmittance is obtained depending on the directions
of the open parts of the SRRs. At this time, if the transported
medium inclines (skewed transport state), an angle between the
polarization direction of the terahertz electromagnetic waves
and the directions of the open parts changes, and the
transmittance also changes. For
example, in a certain
counterfeit prevention structure that is designed such that
the angle between the polarization direction of the terahertz
electromagnetic waves and the directions of the open parts are
60 degrees, the value of the transmittance changes between 30%
and 60% when the medium is inclined by between -15 degrees and
15 degrees. The authenticity is determined by comparing the
value of the transmittance with a threshold value. However,
if the threshold value is set so as to permit such a huge
change in the transmittance, the authenticity cannot be
determined with a high accuracy.
[0006] A range
of variation of the transmittance due to
the inclination of the medium varies according to the
directions of the open parts of SRRs. In the
conventional
technique, the counterfeit prevention structure is divided in
a plurality of areas, and the directions of the open parts in
each of the areas are set in different directions. In this
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case, when the medium is inclined, the transmittance of each
of the areas changes in a different range of variation
depending on the directions of the open parts. Therefore, the
change in the transmittance obtained by scanning the
counterfeit prevention structure is different from the original
change so that the authenticity may not be determined with a
high accuracy.
SUMMARY OF THE INVENTION
[0007] The
present invention has been made to solve the
problems in the conventional technique. One object of the
present invention is to provide a counterfeit prevention
structure and a counterfeit prevention medium that allow highly
accurate determination of the authenticity.
[0008] To
solve the above problems and to achieve the
above object, a counterfeit prevention structure according to
one aspect of the present invention is provided on a medium to
determine authenticity of the medium. The
counterfeit
prevention structure includes a hybrid area in which a
plurality of types of split ring resonators is formed in a
mixed state in a predetermined ratio. Each
split ring
resonator includes an open part. A direction of the open part
of each type of the split ring resonators is different from
each other.
[0009] A
counterfeit prevention medium according to
another aspect of the present invention is a counterfeit
prevention medium including the above counterfeit prevention
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structure.
[0010] The
above and other objects, features, advantages
and technical and industrial significance of this invention
will be better understood by reading the following detailed
description of presently preferred embodiments of the invention,
when considered in connection with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0011]
FIG. 1 is a view indicating one embodiment of a
counterfeit prevention structure.
FIG. 2 is a view for explaining a shape of a split ring
resonator.
FIGS. 3A to 3C are views indicating examples of patterns
formed by using a plurality of types of the split ring
resonators.
FIG. 4 is a view indicating an example of frequency
characteristics of transmittance obtained when an area in which
the split ring resonators are arranged is irradiated with
terahertz electromagnetic waves.
FIG. 5 is a view indicating an example of another pattern
formed by using a plurality of types of the split ring
resonators.
FIG. 6 is a view for explaining an example of the
transmittance of the counterfeit prevention structure.
FIG. 7 is a view of an example of the counterfeit
prevention structure in which a plurality of types of the
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patterns is combined.
FIG. 8 is a view indicating another pattern obtained by
rotating one of the patterns shown in FIGS. 3A to 30.
FIG. 9 is a view for explaining a change in the
transmittance of the terahertz electromagnetic waves observed
in a counterfeit prevention medium provided with the
counterfeit prevention structure shown in FIG. 7.
FIG. 10 is a view for explaining change in the
transmittance obtained when a secondary resonance frequency is
used.
FIG. 11 is a schematic diagram indicating a schematic
internal configuration of an authenticity determination
apparatus seen from a side thereof.
FIGS. 12A and 12B are schematic diagrams of the
configuration shown in FIG. 11 when seen from above.
FIG. 13 is a block diagram indicating a schematic
functional configuration of the authenticity determination
apparatus.
FIG. 14 is a schematic cross section indicating another
structural example of the counterfeit prevention structure.
FIG. 15 is a view indicating an example of a counterfeit
prevention structure having split ring resonators in which
directions of open parts are different.
FIG. 16 is a view indicating another example of the
counterfeit prevention structure that is divided in a plurality
of areas.
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EMBODIMENTS
[0012]
Exemplary embodiments of a counterfeit prevention
structure and a counterfeit prevention medium according to the
present invention are explained below in detail by referring
to the accompanying drawings. One
feature of the present
invention is that a plurality of types of split ring resonators
(SRRs) is used to obtain a predetermined value of transmittance
when terahertz electromagnetic waves penetrate a counterfeit
prevention structure.
[0013] The SRR
has a ring-like shape and has an open part
(Split). For example, the shape of the SRR can be substantially
like the English character C in which an open part is provided
in a circular ring shape. Alternatively, the shape of the SRR
can be rectangular in which an open part is provided in a
rectangular ring shape. For example, SRRs each having an open
part in a ring-like shape are formed with conductive material
on a sheet of insulating material. When irradiating the SRRs
with a terahertz electromagnetic wave, depending on the
frequency and the polarization direction of the terahertz
electromagnetic wave, the transmittance of the terahertz
electromagnetic wave changes. Specifically, the transmittance
of the terahertz electromagnetic wave that resonates with the
SRRs is lower than the transmittance of the terahertz
electromagnetic wave that does not resonate with the SRRs.
[0014]
Alternatively, for example, an SRR can be formed
by carving a sheet of conductive material into a ring-like
shape having an open part.
Particularly, an SRR formed by
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carving conductive material is called a complementary split
ring resonator (CSRR). Even in
a complementary split ring
resonator, when irradiating the SRR with the terahertz
electromagnetic wave, depending on the frequency and the
polarization direction of the terahertz electromagnetic wave,
the transmittance of the terahertz electromagnetic wave
penetrating the sheet changes. Specifically, the transmittance
of the terahertz electromagnetic wave that resonates with the
SRR is higher than the transmittance of the terahertz
electromagnetic wave that does not resonate with the SRR.
[0015] By
arranging a large number of SRRs in an area, the
transmittance of the terahertz electromagnetic wave of a
specific frequency in this area can be controlled. For example,
the large number of SRRs are arranged in a matrix layout in
which the SRRs are arranged in a longitudinal direction and a
lateral direction at regular intervals. Alternatively, the
SRRs are arranged in a checkered pattern layout or in a
honeycomb pattern layout.
[0016] One
method of forming an area having a
predetermined transmittance is to form the ring-like SRR by
using conductive material on a sheet of insulating material.
Another method is to form the SRR by carving a sheet of
conductive material into a ring-like shape. An area, in which
the transmittance of terahertz electromagnetic wave is a
predetermined value, can be formed by using any of the above
methods; however, a case of forming the SRR by carving a sheet
of conductive material is explained as an example in the
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present embodiment.
[0017] The
counterfeit prevention structure according to
the present embodiment includes a conductive layer. When the
prevention structure is irradiated with the terahertz
electromagnetic wave that has a predetermined frequency and a
predetermined polarization direction, the conductive layer
shows a transmittance of a predetermined value. At least two
types of the SRRs of which the directions of the open parts
differing by 90 degrees are arranged in the conductive layer.
Coordinate axes are shown in each of the drawings to facilitate
understanding of the correspondence of the polarization
direction of the terahertz electromagnetic waves used for
measuring the transmittance, the direction of the open part of
the SRR, and the like. The predetermined direction used in the
context of the terahertz electromagnetic waves is a direction
selected as the polarization direction of the terahertz
electromagnetic waves used in the measurement of the
transmittance. The predetermined frequency in the context of
the terahertz electromagnetic waves is a frequency (resonance
frequency) at which the terahertz electromagnetic waves
resonate with the SRRs, and it is the frequency selected as
the frequency of the terahertz electromagnetic waves used in
the measurement of the transmittance. To detect a difference
in the transmittance depending on the types of the SRRs, it is
desirable that the predetermined frequency of the terahertz
electromagnetic wave is the frequency at which the
transmittance greatly changes when the direction of the open
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part of the SRR is changed with respect to the predetermined
direction (polarization direction).
Specifically, it is
desirable that the terahertz electromagnetic wave has a
frequency band including the central frequency corresponding
with the peak frequency at which the transmittance has a peak
value. If the
peak frequency is stable in the counterfeit
prevention structures, the terahertz electromagnetic wave
having a single frequency can be also used. If it is possible
to accommodate the variation in the transmittance, the
terahertz electromagnetic wave can have the predetermined
frequency that is not the peak frequency.
[0018] FIG. 1
is a view indicating one embodiment of a
counterfeit prevention structure 10. A plan
view of the
counterfeit prevention structure 10 is shown in the upper left
part of FIG. 1 and a partially enlarged view of a partial area
of the counterfeit prevention structure 10 is shown in the
upper right part of FIG. 1. Moreover, a plurality of types of
SRRs 20 to 23 included in the counterfeit prevention structure
is shown in the bottom part of FIG. 1. This counterfeit
prevention structure 10 is arranged in a counterfeit prevention
medium (hereinafter, "medium") to prevent counterfeiting of
the medium. The
medium is, for example, a sheet valuable
medium. Such a medium includes a banknote (paper currency), a
stock certificate, a bond, a check, and a coupon.
[0019] FIG. 1
shows an example of the counterfeit
prevention structure 10 in which the plurality of types of the
SRRs 20 to 23 are arranged in a matrix layout. The SRRs have
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open parts in different directions from each other. The
plurality of types of the SRRs 20 to 23 is mixed in a
predetermined ratio. In such
a structure, transmittance of
the terahertz electromagnetic wave of a specific frequency that
penetrates the counterfeit prevention structure 10 can be
maintained to a predetermined value.
[0020] The
counterfeit prevention structure 10 includes a
conductive layer 16 in which the plurality of types of the SRRs
20 to 23 are formed in the matrix layout at regular intervals.
Each of the SRRs 20 to 23 has a shape substantially like the
English character C in which a part of a circular ring is cut
to form open part 20a to 23a. As shown in FIG. 1, when seen
from a center of the ring part, the SRR 20 has the open part
20a in the positive X-axis direction. When
seen from the
center of the ring part, the SRR 21 has the open part 21a in
the positive Y-axis direction. When seen from the center of
the ring part, the SRR 22 has the open part 22a in the negative
X-axis direction. When seen from the center of the ring part,
the SRR 23 has the open part 23a in the negative Y-axis
direction. The shape of the SRR 20 matches with the shape of
the SRR 21 when the SRR 20 is rotated clockwise by 90 degrees,
the shape of the SRR 21 matches with the shape of the SRR 22
when the SRR 21 is rotated clockwise by 90 degrees, and the
shape of the SRR 22 matches with the shape of the SRR 23 when
the SRR 22 is rotated clockwise by 90 degrees. That is, the
directions of the open parts of the SRRs 20 to 23 vary by 90
degrees from each other. The
direction of the open part
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mentioned in the present embodiment is the direction when see
from the center of the ring part of the SRR having the open
part.
[0021] As shown in the partially enlarged view in the
upper right part of FIG. 1, the four types of the SRRs 20 to
23 are arranged at regular intervals and form a predetermined
pattern. Specifically, a basic pattern of a two-by-two matrix
is formed by arranging the four SRRs 20 to 23 in two rows and
two columns. In the basic pattern, the SRR 21 is arranged on
the right side (in the positive Y-axis direction) of the SRR
20, the SRR 23 is arranged below (in the negative X-axis
direction) the SRR 20, and the SRR 22 is arranged on the right
side of the SRR 23. The four types of the SRRs 20 to 23 are
arranged at regular intervals by repeating this basic pattern.
The details about the basic pattern formed by using the four
SRRs 20 to 23 will be explained later.
[0022] The SRRs 20 to 23 are formed by carving the
conductive layer 16 made of conductive material into a shape
substantially like the English character C. The four SRRs 20
to 23 have the same structure except that the directions
(position in the ring part) of the open parts 20a to 23a thereof
are different. The SRRs 21 to 23 can be obtained by rotating
the SRR 20 and therefore the specific structure of the SRRs 20
to 23 will be explained below by using the SRR 20 as an example.
[0023] FIG. 2 is a view for explaining the shape of the
SRR 20. A plan view of the SRR 20 is shown in the upper part
of FIG. 2 and a cross-section along a line AA shown in the plan
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view is shown in the lower part of FIG. 2. The counterfeit
prevention structure 10 includes a base member 17 made of
insulating material and a thin conductive layer 16 formed on a
surface of the base member 17. The base member 17 is made of
insulating material, such as paper and resin, through which
the terahertz electromagnetic waves can penetrate. On the
other hand, the conductive layer 16 is made of conductive
material, such as Al, Fe, Au, Cu, Ag, Mg, Zn, and Sn, that
blocks the terahertz electromagnetic waves.
[0024] The SRR
20 is formed by carving from the conductive
layer 16, which is formed on the base member 17, an area having
the shape substantially like the English character C.
Specifically, the SRR 20 is formed by carving the ring-shaped
conductive layer 16 having a predetermined width in the
diameter direction while leaving behind only the open part 20a.
The area corresponding to the ring part having the shape
substantially like the English character C is a groove and a
surface of the base member 17 is exposed at the bottom of the
groove. In an area other than the ring part, including the
open part 20a, the surface of the base member 17 is covered
with the conductive layer 16. Each of other SRRs 21 to 23 can
be formed by changing the area that is left behind as the open
part 21a to 23a when forming the groove having the shape
substantially like the English character C. The
machining
method to form the SRR in the conductive layer, the functions
of the SRR, and the like are disclosed, for example, in Japanese
Patent Application Laid-Open No. 2016-000498.
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[0025] A
length and a width of the sheet-like counterfeit
prevention structure 10 are, for example, 20 mm. An
inner
diameter d of the SRR 20, shown in the upper part of FIG. 2,
is a few hundred pm and a width g of the open part 20a is a
few ten pm. A width W of the SRR 20, shown in the lower part
of FIG. 2, in a diameter direction thereof is a few ten pm.
Other SRRs 21 to 23 are formed with the same size as that of
the SRR 20. In the counterfeit prevention structure 10, the
SRRs 20 to 23 are arranged vertically and horizontally at
regular intervals and form the matrix layout. A
distance
between adjacent SRRs 20 to 23 is a few ten pm. For example,
in 10 mm long, several tens of SRRs 20 to 23 is arranged at
regular intervals. The shape of each SRRs 20 to 23 and the
layout of the SRRs 20 to 23 are determined such that, resonance
occurs when the SRRs 20 to 23 are irradiated with the terahertz
electromagnetic wave of the predetermined frequency, and the
terahertz electromagnetic wave penetrate the SRRs 20 to 23 at
predetermined transmittance. The frequency of the terahertz
electromagnetic wave is set, for example, between 0.1 THz and
1 THz. A
dimension of an area of the conductive layer 16
irradiated with the terahertz electromagnetic wave is
determined based on the SRRs 20 to 23 as the target for
irradiation and is about 1 mm to about 5 mm in a diameter in a
half-band width.
[0026] A
minimal configuration of the counterfeit
prevention structure 10 is shown in FIG. 2. As long as the
properties of the conductive layer 16 with respect to the
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terahertz electromagnetic wave are not affected, another layer
may be provided on the conductive layer 16 and/or below the
base member 17.
Moreover, another layer may be provided
between the conductive layer 16 and the base member 17.
[0027] The
thin counterfeit prevention structure 10 can
be embedded in the medium, such as the coupon, that is the
target of counterfeit prevention.
Alternatively, the
counterfeit prevention structure 10 can be affixed to the
medium. For example, as the counterfeit prevention structure
10, both the conductive layer 16 and the base member 17 are
newly arranged in the medium such as the coupon. For another
example, the medium, such as the coupon, itself is used as the
base member 17, and the conductive layer 16 is formed on the
medium.
[0028] FIGS.
3A to 30 are views indicating examples of
patterns formed by using the SRRs 20 to 23. A pattern that
functions as a basic unit is shown in the left part of FIGS.
3A to 30. A
partial area of the counterfeit prevention
structure 10 formed by repeatedly arranging these basic pattern
in a matrix layout is shown in the right part of FIGS. 3A to
3C. Each
pattern constitutes a hybrid area in which the
plurality of types of the SRRs 20 to 23 are mixed in a
predetermined ratio.
[0029] A
first pattern 31 shown in FIG. 3A is a two-by-
two matrix pattern. In the first pattern 31, the SRR 20 is
arranged in the upper left corner, the two SRRs 22 are arranged
on the right side of and below the SRR 20, and the other SRR
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20 is arranged on the right side of the lower SRR 22. The
first pattern 31 is the hybrid area in which two types of the
SRRs, that is, the SRRs 20 and 22, are mixed in the
predetermined ratio. The first pattern 31 is constituted by
only the SRRs 20 and 22 that have the open parts 20a and 22a
in the X-axis direction.
[0030] When
the first pattern 31 is irradiated with the
terahertz electromagnetic wave of the predetermined frequency
(primary resonance frequency), which has the polarization
direction in the X-axis direction, the transmittance of the
SRRs 20 and 22, of which the open parts 20a and 22a are arranged
in the X-axis direction that is the polarization direction,
will be maximum. Therefore, when the counterfeit prevention
structure 10 constituted by the first pattern 31 is irradiated
with the terahertz electromagnetic wave having the polarization
direction in the X-axis direction, the transmittance will be
maximum.
[0031] About
the order of the resonance frequency will be
explained next. FIG. 4
is a view indicating an example of
frequency characteristics of transmittance obtained when the
area in which the SRRs are arranged is irradiated with the
terahertz electromagnetic wave. The frequency characteristics
shown in FIG. 4 is obtained when, as shown in FIGS. 3A to 3C,
a large number of the SRRs having the open parts are arranged
at regular intervals in a sufficiently wider area than the area
irradiated with the terahertz electromagnetic wave.
[0032] When
the polarization direction of the emitted
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terahertz electromagnetic wave and the directions of the open
parts of the SRRs formed in the area irradiated with the
terahertz electromagnetic wave match, that is, when both the
directions are parallel, the frequency characteristics shown
with a solid line in FIG. 4 is obtained. On the other hand,
when the polarization direction of the emitted terahertz
electromagnetic wave and the directions of the open parts of
the SRRs formed in the area irradiated with the terahertz
electromagnetic wave are orthogonal, the frequency
characteristics shown with a dotted line in FIG. 4 is obtained.
Specifically, for example, when the directions of the open
parts of the SRRs are in the X-axis direction, the frequency
characteristics as shown with the solid line will be obtained
if the polarization direction of the terahertz electromagnetic
wave matches with the X-axis direction, and the frequency
characteristics shown with the dotted line will be obtained if
the polarization direction of the terahertz electromagnetic
wave matches with the Y-axis direction.
[0033] As
shown with the solid line in FIG. 4, two peaks
P1 and P2 are clearly observed when the directions of the open
parts of the SRRs and the polarization direction of the
terahertz electromagnetic wave match. On the other hand, as
shown with the dotted line in FIG. 4, one peak V1 is clearly
observed when the directions of the open parts of the SRRs and
the polarization direction of the terahertz electromagnetic
wave are orthogonal. The frequencies at which the peaks are
obtained are referred to as P1, V1, and P2 sequentially from
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the low frequency side.
[0034] As has
been mentioned above, it is desirable that
the frequency (predetermined frequency) of the emitted
terahertz electromagnetic wave is the resonance frequency at
which the transmittance greatly changes when the directions of
the open parts of the SRRs are changed with respect to the
polarization direction (predetermined direction) of the
emitted terahertz electromagnetic wave. When comparing a ratio
of the dotted line showing transmittance with respect to Y-
polarization to the solid line showing transmittance with
respect to X-polarization at each peak P1, V1, and P2, the
ratios at P1 and V1 are bigger than the ration at P2. To
compare the difference in each of the transmittance obtained
when the SRRs are irradiated with the terahertz electromagnetic
waves having different polarization directions, it is
preferable to adopt the peak P1 and the peak Vi. Accordingly,
the present embodiment is explained by taking the frequency of
the peak P1 as a primary resonance frequency and by taking the
frequency of the peak V1 as a secondary resonance frequency.
As has been mentioned above, it is allowable to take the
frequency band including the frequency of the peak P1 as the
primary resonance frequency, and take the frequency band
including the frequency of the peak V1 as the secondary
resonance frequency.
[0035] A
second pattern 32 shown in FIG. 3B is a two-by-
two matrix pattern. In the second pattern 32, the SRR 20 is
arranged in the upper left corner, the SRR 21 is arranged on
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the right side of the SRR 20, the SRR 22 is arranged below the
SRR 20, and the other SRR 20 is arranged on the right side of
the lower SRR 22. The
second pattern 32 is obtained by
replacing the upper right SRR 22 of the first pattern 31 with
the SRR 21. The second pattern 32 is the hybrid area in which
three types of the SRRs, that is, the SRRs 20 to 22, are mixed
in the predetermined ratio. The
second pattern 32 is
constituted by three SRRs 20 and 22 having the open parts 20a
and 22a in the X-axis direction and one SRR 21 having the open
part 21a in the Y-axis direction. A ratio of the number of the
SRRs 20 and 22 having the open parts 20a and 22a thereof
parallel to the X-axis direction and the number of the SRR 21
having the direction of the open part 21a thereof orthogonal
to the X-axis direction is 3:1. When four SRRs arranged in the
two-by-two matrix pattern are selected from the area in which
the SRRs of the second pattern 32 are arranged successively as
shown in the right part of FIG. 3B, a ratio of the number of
the SRRs having the open parts parallel to the X-axis direction
and the number of the SRRs having the open parts orthogonal to
the X-axis direction is 3:1. That
is, when a desired area
having the same shape as the second pattern 32 is selected,
the ratio of the number of the SRRs 20 and 22 and the number
of the SRRs 21 will always be the same.
[0036] When
the SRRs are irradiated with the terahertz
electromagnetic wave of the predetermined frequency (primary
resonance frequency) having the polarization direction in the
X-axis direction, the transmittance of the SRRs 20 and 22
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having the open parts 20a and 22a parallel to the polarization
direction (X-axis direction) will be maximum. On the other
hand, the transmittance of the SRRs 21 and 23 having the open
parts 21a and 23a orthogonal to the polarization direction (X-
axis direction) will be minimum.
[0037] When
the counterfeit prevention structure 10 having
the plurality of types of the SRRs, of which the open parts
have different directions, is irradiated with the terahertz
electromagnetic wave, the transmittance will be a value between
a transmittance Tx and Ty. The value Tx is a transmittance
obtained when all the SRRs have the open parts in a direction
parallel to the polarization direction of the terahertz
electromagnetic wave. The value Ty is a transmittance obtained
when all the SRRs have the open parts in a direction orthogonal
to the polarization direction of the terahertz electromagnetic
wave.
[0038] In the
counterfeit prevention structure 10
according to the second pattern 32, a ratio of the number of
the SRRs having the open parts parallel to the polarization
direction (X-axis direction) and the number of the SRRs having
the open parts orthogonal to the polarization direction (X-
axis direction) is 3:1.
Therefore, when the counterfeit
prevention structure 10 of the second pattern 32 is irradiated
with the terahertz electromagnetic wave of the predetermined
frequency (primary resonance frequency) having the
polarization direction in the X-axis direction, the
transmittance will be a value near (3xTx+Ty)/4. The above-
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mentioned dimension of the area irradiated with the terahertz
electromagnetic wave is determined so as to be at least larger
than the area occupied by the SRRs arranged in the two-by-two
matrix pattern.
[0039] A
third pattern 33 shown in FIG. 3C is a two-by-
two matrix pattern. In the third pattern 33, the SRR 20 is
arranged in the upper left corner, the SRR 21 is arranged on
the right side of the SRR 20, the SRR 23 is arranged below the
SRR 20, and the SRR 22 is arranged on the right side of the
SRR 23. The third pattern 33 is obtained by replacing the
lower left SRR 22 of the second pattern 32 with the SRR 23 and
replacing the lower right SRR 20 of the second pattern 32 with
the SRR 22. The third pattern 33 is the hybrid area in which
four types of the SRRs, that is, the SRRs 20 to 23, are mixed
in the predetermined ratio. The
third pattern 33 is
constituted by two SRRs 20 and 22 having the open parts 20a
and 22a in the X-axis direction and two SRRs 21 and 23 having
the open parts 21a and 23a in the Y-axis direction. A ratio
of the number of the SRRs 20 and 22 having the open parts 20a
and 22a parallel to the X-axis direction and the number of the
SRRs 21 and 23 having the open parts 21a and 23a orthogonal to
the X-axis direction is 1:1. When four SRRs arranged in the
two-by-two matrix pattern are selected from the area in which
the SRRs of the third pattern 33 are arranged successively as
shown the right part of FIG. 30, a ratio of the number of the
SRRs having the open parts parallel to the X-axis direction
and the number of the SRRs having the open parts orthogonal to
21
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the X-axis direction is 1:1. That
is, when a desired area
having the same shape as the third pattern 33 is selected, the
ratio of the number of the SRRs 20 and 22 and the number of
the SRRs 21 and 23 will always be the same. The third pattern
33 shown in FIG. 30 is used in the counterfeit prevention
structure 10 shown in FIG. 1.
[0040] When
the counterfeit prevention structure 10 of the
third pattern 33 is irradiated with the terahertz
electromagnetic wave of the predetermined frequency (primary
resonance frequency) having the polarization direction in the
X-axis direction, the transmittance will be a value between
the transmittance Tx obtained when all the SRRs having the open
parts in a direction parallel to the polarization direction
(X-axis direction) and the transmittance Ty obtained when all
the SRRs having the open parts in a direction orthogonal to
the polarization direction (X-axis direction). In the third
pattern 33, a ratio of the number of the SRRs having the open
parts parallel to the polarization direction (X-axis direction)
and the number of the SRRs having the open parts orthogonal to
the polarization direction (X-axis direction) is 1:1.
Therefore, the transmittance will be a value near (Tx+Ty)/2.
The above-mentioned dimension of the area irradiated with the
terahertz electromagnetic wave is determined so as to be at
least larger than the area occupied by the two-by-two matrix
pattern SRRs.
[0041] The
pattern formed with the four types of the SRRs
20 to 23 is not limited to the two-by-two matrix pattern. FIG.
22
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is a view indicating an example of another pattern formed by
the SRRs 20 to 23. FIG. 5 shows, in the left part, a fourth
pattern 34 that functions as a basic unit. A partial area of
the counterfeit prevention structure 10 formed by repeatedly
arranging the fourth pattern 34 in the matrix layout is shown
in the right part of FIG. 5.
[0042] In the
fourth pattern 34 shown in FIG. 5, nine SRRs
20 to 23 are arranged in a three-by-three matrix pattern. The
SRR 22 is arranged at the center, the two SRRs 20 arranged
adjacent to the central SRR 22 in the diagonal direction are
in the upper left and the lower left of the SRR 22, and the
two SRRs 22 arranged adjacent to the central SRR 22 in the
diagonal direction are in the upper right and the lower right
of the SRR 22. The two SRRs 23 are arranged on the left side
and the right side of the central SRR 22, and the two SRRs 21
are arranged above and below the central SRR 22. The fourth
pattern 34 is the hybrid area in which four types of the SRRs,
that is, the SRRs 20 to 23, are mixed in the predetermined
ratio. The fourth pattern 34 is constituted by five SRRs 20
and 22 having the open parts 20a and 22a in the X-axis direction
and the four SRRs 21 and 23 having the open parts 21a and 23a
in the Y-axis direction. A ratio of the number of the SRRs 20
and 22 having the open parts 20a and 22a parallel to the X-
axis direction and the number of the SRRs 21 and 23 having the
open parts 21a and 23a orthogonal to the X-axis direction is
5:4. When SRRs forming a three-by-three matrix are selected
from the area in which the SRRs of the fourth pattern 34 are
23
CA 3018059 2018-09-20
arranged successively, a ratio of the number of the SRRs having
the open parts parallel to the X-axis direction and the number
of the SRRs having the open parts orthogonal to the X-axis
direction is 5:4. That is, when a desired area having the same
shape as the fourth pattern 34 is selected, the ratio of the
number of the SRRs 20 and 22 and the number of the SRRs 21 and
23 will always be the same.
[0043] When the counterfeit prevention structure 10 of the
fourth pattern 34 is irradiated with the terahertz
electromagnetic wave of the predetermined frequency (primary
resonance frequency) having the polarization direction in the
X-axis direction, the transmittance will be a value between
the transmittance Tx obtained when all the SRRs having the open
parts in a direction parallel to the polarization direction
(X-axis direction) and the transmittance Ty obtained when all
the SRRs having the open parts in a direction orthogonal to
the polarization direction (X-axis direction). In the fourth
pattern 34, a ratio of the number of the SRRs having the open
parts parallel to the polarization direction (X-axis direction)
and the number of the SRRs having the open parts orthogonal to
the polarization direction (X-axis direction) is 5:4.
Therefore, the transmittance will be a value near (5xTx+4xTy)/9.
The above-mentioned dimension of the area irradiated with the
terahertz electromagnetic wave is determined so as to be at
least larger than the area occupied by the SRRs arranged in
the three-by-three matrix pattern.
[0044] In this manner, a basic patter is formed by
24
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selecting the SRRs from the four types of the SRRs 20 to 23
having the open parts 20a to 23a parallel to or orthogonal to
the X-axis direction. The
transmittance of the terahertz
electromagnetic wave can be changed by changing the type and
the number of the SRRs. By using this technique, the first
pattern 31 to the fourth pattern 34 are formed such that each
gives a different transmittance. Moreover, the basic pattern
set by using the SRRs 20 to 23 is successively arranged in a
matrix layout thereby forming the counterfeit prevention
structure 10. By this
structure, the variation in the
transmittance due to an inclination of the counterfeit
prevention structure 10 can be suppressed.
[0045] FIG. 6
is a view for explaining an example of the
transmittance of the counterfeit prevention structure 10. The
frequency characteristics shown in the lower part of FIG. 6 is
a schematic representation of the change in the transmittance
when the counterfeit prevention structure 10 of the first
pattern 31 to the fourth pattern 34 is irradiated with the
terahertz electromagnetic wave having the polarization
direction in the X-axis direction. The
horizontal axis
represents the frequency of the emitted terahertz
electromagnetic wave and the vertical axis represents the
transmittance value. As shown in the upper part of FIG. 6, an
angle of an inclination of the counterfeit prevention structure
is taken as (1. The
frequency characteristics of the
transmittance shown with a dotted line in the lower part of
FIG. 6 is obtained when the counterfeit prevention structure
CA 3018059 2018-09-20
is not inclined (a=0 degree). On the
other hand, the
frequency characteristics of the transmittance shown with a
solid line is obtained when the counterfeit prevention
structure 10 is inclined by 15 degrees (a=15 degrees). A range
of variation of the transmittance of the primary resonance
frequency fl (THz) that can occur when the counterfeit
prevention structure 10 is inclined is shown with "r" in FIG.
6. , Even
when the counterfeit prevention structure 10 is
inclined, the range r of variation of the transmittance is very
small and it is only few percent of the absolute value of the
transmittance.
[0046]
Specifically, when the counterfeit prevention
structure 10 that is not inclined (a=0 degree) is irradiated
with the terahertz electromagnetic wave of the primary
resonance frequency fl (THz) having the polarization direction
in the X-axis direction, the transmittance of the counterfeit
prevention structure 10 of the first pattern 31 is about 40%.
Moreover, the transmittance of the counterfeit prevention
structure 10 of the second pattern 32 is about 35%, the
transmittance of the counterfeit prevention structure 10 of
the third pattern 33 is about 30%, and the transmittance of
the counterfeit prevention structure 10 of the fourth pattern
34 is about 30%. On the
other hand, when a conventional
counterfeit prevention structure, in which the angle between
the polarization direction of the terahertz electromagnetic
wave and the directions of the open parts of all the SRRs is
60 degrees, is similarly irradiated with the terahertz
26
CA 3018059 2018-09-20
electromagnetic wave, the transmittance is about 30%.
[0047] When
the counterfeit prevention structure 10 of the
first pattern 31 inclines in a range of -15 degrees to 15
degrees (-15 degrees a 15
degrees) while irradiating with
the terahertz electromagnetic wave, the transmittance varies
between about 40% and about 38%. The range of variation of the
transmittance is about 2% in the counterfeit prevention
structure 10 of the first pattern 31. Similarly, the range of
variation of the transmittance is about 1% in the counterfeit
prevention structure 10 of the second pattern 32, the range of
variation of the transmittance is almost 0% in the counterfeit
prevention structure 10 of the third pattern 33, and the range
of variation of the transmittance is about 0.3% in the
counterfeit prevention structure 10 of the fourth pattern 34.
In a case where the conventional counterfeit prevention
structure, in which the angle between the polarization
direction of the terahertz electromagnetic wave and the
directions of the open parts are 60 degrees, inclines in a
range of -15 degrees to 15 degrees, the angle varies in a range
of 45 degrees to 75 degrees and the range of variation of the
transmittance is about 20%.
[0048] When
the counterfeit prevention structure 10 is not
inclined, the transmittance in the counterfeit prevention
structure 10 of the third pattern 33, the counterfeit
prevention structure 10 of the fourth pattern 34, and the
conventional counterfeit prevention structure is almost the
same and it is about 30%. On the
other hand, when the
27
CA 3018059 2018-09-20
counterfeit prevention structure is inclined in the range of -
15 degrees to 15 degrees, while the range of variation of the
transmittance of the conventional counterfeit prevention
structure is about 20%, the range of variation of the
transmittance of the counterfeit prevention structure 10 of
the third pattern 33 and the counterfeit prevention structure
of the fourth pattern 34 remains less than 1%. This means
that, in the counterfeit prevention structure 10 according to
the present embodiment, the range of variation of the
transmittance with respect to the inclination thereof can be
suppressed in comparison with the conventional structure.
[0049] The reason why the range of variation of the
transmittance is suppressed in the counterfeit prevention
structure 10 of the first pattern 31 is because the range of
variation arising from the inclination is less when the
directions of the open parts of the SRRs are parallel to the
polarization direction of the terahertz electromagnetic wave.
[0050] The reason why the range of variation of the
transmittance is suppressed in the counterfeit prevention
structure 10 of the second pattern 32 to the fourth pattern 34
is because of the use of a mixture of a plurality of types of
the SRRs 20 to 23 in which the directions of the open parts
differ by 90 degrees unit. Specifically, for example, if the
SRRs are inclined while the terahertz electromagnetic wave of
the primary resonance frequency is emitted, the transmittance
of the SRRs having the open parts parallel to the polarization
direction of the terahertz electromagnetic wave decreases, but
28
CA 3018059 2018-09-20
the transmittance of the SRRs having the open parts orthogonal
to the polarization direction increases.
Therefore, the
increase and the decrease in the transmittance are offset and
the range of variation of the transmittance can be suppressed.
[0051] There
is a mixture of the SRRs for which the
transmittance increases and the SRRs for which the
transmittance decreases when the counterfeit prevention
structure 10 is inclined with respect to the polarization
direction of the terahertz electromagnetic wave, an effect of
suppressing the range of variation of the transmittance due to
the inclination can be achieved. The types of the SRRs used
to make the counterfeit prevention structure 10 are not limited
to the SRRs in which the directions of the open parts are
different by 90 degrees. However, by using the SRRs in which
the directions of the open parts are different by 90 degrees,
irrespective of the polarization direction of the terahertz
electromagnetic wave, there will be a mixture of the SRRs for
which the transmittance increases and the SRRs for which the
transmittance decreases when the counterfeit prevention
structure 10 is inclined.
Accordingly, an effect of
suppressing the range of variation of the transmittance due to
the inclination of the counterfeit prevention structure 10 can
be achieved irrespective of the polarization direction of the
terahertz electromagnetic wave.
[0052] In
FIGS. 3A, 3B, 3C, and 5 is shown an example of
the counterfeit prevention structure 10 formed by successively
arranging in a matrix layout one pattern of the SRRs selected
29
CA 3018059 2018-09-20
from the four types of the SRRs 20 to 23; however, the
counterfeit prevention structure can be obtained by combining
a plurality of types of the patterns.
[0053] FIG. 7
is a view of an example of a counterfeit
prevention structure 50 in which a plurality of types of the
patterns is combined. In the left part of FIG. 7 is shown a
plan view of the counterfeit prevention structure 50 including
a first area 11 (11a and 11b), a second area 12, and a third
area 13 (13a and 13b), and in the right part is shown an
enlarged view of a partial area 15 containing these three areas
11 to 13. The first area 11 has the shape substantially like
the English character L. The third area 13 has a shape obtained
by rotating the first area 11 by 180 degrees. An
area
surrounded by the first area 11 and the third area 13 is the
second area 12. The
sheet-like counterfeit prevention
structure 50 is, for example, a square of a length and a width
20 mm. The
second area 12 arranged at the center of the
counterfeit prevention structure 50 is a square of a length
and a width 10 mm.
[0054] As
shown in the partially enlarged view in the
right part of FIG. 7, the first pattern 31 shown in FIG. 3A is
successively arranged into a matrix layout in the first area
11. In the third area 13, the third pattern 33 shown in FIG.
3C is successively arranged into a matrix layout.
[0055] The
second area 12 is constituted by a fifth
pattern 35 obtained by rotating the first pattern 31 in the
counterclockwise direction by 90 degrees. FIG. 8 indicates a
CA 3018059 2018-09-20
configuration of the fifth pattern 35. The fifth pattern 35
that functions as a basic unit is shown in the left part of
FIG. 8. A part of the second area 12 formed by repeatedly
arranging the fifth pattern 35 in a matrix layout is shown in
the right part of FIG. 8. The fifth pattern 35 is a two-by-
two matrix pattern in which the SRR 21 is arranged in the upper
left corner, the SRRs 23 are arranged on the right side of and
below the SRR 21, and the SRR 21 is arranged on the right side
of the lower SRR 23. The fifth pattern 35 is constituted by
only the SRRs 21 and 23 that have the open parts 21a and 23a
in the Y-axis direction.
[0056] FIG. 9
is a view for explaining a change in the
transmittance of the terahertz electromagnetic wave observed
in a medium 100 on which the counterfeit prevention structure
50 shown in FIG. 7 is provided. A plan view of the medium 100
having the counterfeit prevention structure 50 is shown in the
upper part of FIG. 9. The counterfeit prevention structure 50
of the square shape is arranged such that each edge thereof is
parallel to the corresponding edge of the rectangular medium
100. A scanning position and a scanning direction when the
counterfeit prevention structure 50 is scanned with the
terahertz electromagnetic wave are shown with an arrow 200 in
the central part of FIG. 9. A waveform of the transmittance
of the terahertz electromagnetic wave obtained at the scanning
position is shown in the lower part of FIG. 9. This
transmittance waveform is a schematic representation of the
change in the transmittance of the counterfeit prevention
31
CA 3018059 2018-09-20
structure 50 when scanned with the terahertz electromagnetic
wave of the primary resonance frequency.
[0057] A
substantially central part in the X-axis
direction of the counterfeit prevention structure 50 is scanned
in the direction shown with the arrow 200 with the terahertz
electromagnetic wave of the predetermined frequency having the
polarization direction in the X-axis direction. The medium
100 is scanned in a where that the medium 100 namely the
counterfeit prevention structure 50 is not inclined. The
transmittance in the first area 11 constituted by the first
pattern 31, the transmittance in the second area 12 constituted
by the fifth pattern 35, and the transmittance in the third
area 13 constituted by the third pattern 33 show different
values corresponding to the respective pattern.
[0058] For
example, for the primary resonance frequency,
the transmittance in the first area 11 shows a high value
(about 40%), and the transmittance in the second area 12 shows
a very low value (about 2%). The transmittance in the third
area 13 shows a value (about 20%) between the transmittance in
the first area 11 and the transmittance in the second area 12.
Therefore, as shown in the lower part of FIG. 9, after a
waveform 71 indicating a substantially constant and high
transmittance is obtained in the first area 11 on the right
side of FIG. 9, the transmittance decreases in the central
second area 12. After a waveform 72 indicating a substantially
constant transmittance is obtained in the second area 12, the
transmittance increases again in the third area 13 on the left
32
CA 3018059 2018-09-20
side of FIG. 9. A
waveform 73 indicating a substantially
constant transmittance lower than the waveform 71 is obtained
in the third area 13. In
this manner, if the counterfeit
prevention structure 50 is constituted by a plurality of areas
each of which indicates a different transmittance when
irradiated with the predetermined terahertz electromagnetic
wave, a characteristic waveform in which the transmittance
changes while scanning the counterfeit prevention structure 50
can be obtained. The authenticity of the medium 100 can be
determined based on the feature of the obtained transmittance
waveform.
[0059] Even
when the counterfeit prevention structure 50
is inclined by 15 degrees, the range of variation of the
transmittance of the first area 11 constituted by the first
pattern 31 and the range of variation of the transmittance of
the second area 12 remain as low as 2%.
Moreover, the
transmittance of the third area 13 constituted by the third
pattern 33 almost does not vary.
Therefore, even when the
counterfeit prevention structure 50 is inclined, as shown in
the lower part of FIG. 9, a stepped waveform in which the
transmittance decreases from the waveform 71 to the waveform
72 and the transmittance increases from the waveform 72 to the
waveform 73 is obtained.
Moreover, the relation of the
magnitudes of the waveform 71, the waveform 72, and the
waveform 73 does not change even when the counterfeit
prevention structure 50 is inclined. Therefore, even when the
inclined medium 100 namely the inclined counterfeiting
33
CA 3018059 2018-09-20
prevention structure 50 is scanned for measuring the
transmittance, a characteristic waveform in which the
transmittance changes in three phases can be obtained. The
authenticity of the medium 100 can be determined based on the
feature of the obtained transmittance waveform.
[0060] A case
of irradiating the counterfeit prevention
structures 10 and 50 with the terahertz electromagnetic wave
of the primary resonance frequency (P1 of FIG. 4) having the
polarization direction in the X-axis direction is mainly
explained above; however, different
transmission
characteristics will be obtained with the secondary resonance
frequency (V1 of FIG. 4). FIG. 10 is a view for explaining a
change in the transmittance obtained when the secondary
resonance frequency is used. A plan view of the medium 100,
which is the same as that shown in FIG. 9, having the
counterfeit prevention structure 50 is shown in the upper part
of FIG. 10, and a scanning position and a scanning direction
when the counterfeit prevention structure 50 is scanned with
the terahertz electromagnetic wave are shown with the arrow
200 in the central part. A transmittance waveform obtained
when the counterfeit prevention structure 50 is scanned with
the terahertz electromagnetic wave of the secondary resonance
frequency at the scanning position is shown in the lower part
of FIG. 10.
[0061] A
substantially central part in the X-axis
direction of the counterfeit prevention structure 50 is scanned
in the direction shown with the arrow 200 with the terahertz
34
CA 3018059 2018-09-20
electromagnetic wave of the predetermined frequency having the
polarization direction in the X-axis direction. The medium
100 is scanned in a state where the medium 100 namely the
counterfeit prevention structure 50 shown in FIG. 7 is not
inclined. The transmittance waveform shown in the lower part
of FIG. 9 is obtained when the scanning is performed by using
the terahertz electromagnetic wave of the primary resonance
frequency, and the transmittance waveform shown in the lower
part of FIG. 10 is obtained when the scanning is performed by
using the terahertz electromagnetic wave of the secondary
resonance frequency. The
relation between the polarization
direction of the terahertz electromagnetic wave, the directions
of the open parts of the SRRs 20 to 23 and the transmittance
value varies depending on a resonance mode. For the primary
resonance frequency, the transmittance becomes maximum when
the directions of the open parts of the SRRs are parallel to
the polarization direction of the terahertz electromagnetic
wave. On the other hand, for the secondary resonance frequency,
the transmittance becomes maximum when the directions of the
open parts of the SRRs are orthogonal to the polarization
direction of the terahertz electromagnetic wave.
[0062] Even
for the secondary resonance frequency,
different transmittance can be obtained in each of the first
area 11 to the third area 13; however, the transmittance in
the first area 11 shows a very low value of a few percent and
the transmittance in the second area 12 shows a high value.
The transmittance in the third area 13 shows a value between
CA 3018059 2018-09-20
the transmittance in the second area 12 and the transmittance
in the first area 11. Therefore, as shown in the lower part
of FIG. 10, after a waveform 81 indicating a substantially
constant and low transmittance is obtained in the first area
11 on the right side of FIG. 10, the transmittance increases
in the central second area 12. After a waveform 82 indicating
a substantially constant transmittance is obtained in the
second area 12, the transmittance decreases again in the third
area 13 on the left side of FIG. 10. A waveform 83 indicating
a substantially constant transmittance higher than the waveform
81 is obtained in the third area 13. The authenticity of the
medium 100 can be determined based on the feature of the
obtained transmittance waveform.
[0063] Even
when the counterfeit prevention structure 50
is inclined by 15 degrees, like in the case of the primary
resonance frequency, each of the range of variation of the
transmittance of the first area 11, the range of variation of
the transmittance of the second area 12, and the range of
variation of the transmittance of the third area 13 remains as
low as 4%. Therefore, even when the counterfeit prevention
structure 50 is inclined, a stepped waveform in which the
transmittance increases from the waveform 81 to the waveform
82 is obtained as shown in the lower part of FIG. 10. There
is a difference of about 15% between the transmittance of the
second area 12 shown with the waveform 82 and the transmittance
of the third area 13 shown with the waveform 83. Even when the
counterfeit prevention structure 50 is inclined by 15 degrees,
36
CA 3018059 2018-09-20
the range of variation of the transmittance of the second area
12 remains as low as about 4%, and the transmittance of the
third area 13 almost does not vary. Therefore, even when the
counterfeit prevention structure 50 is inclined, a stepped
waveform in which the transmittance decreases from the waveform
82 to the waveform 83 is obtained as shown in the lower part
of FIG. 10. Moreover, the relation of the magnitudes of the
waveform 81, the waveform 82, and the waveform 83 does not
change even when the counterfeit prevention structure 50 is
inclined. Even when measuring the transmittance by scanning
the inclined medium 100 namely the inclined counterfeit
prevention structure 50, a characteristic waveform in which
the transmittance changes in three phases can be obtained. The
authenticity of the medium 100 can be determined based on the
feature of the obtained transmittance waveform.
[0064] As
explained by referring FIGS. 9 and 10, the
counterfeit prevention structure 50 provided in the medium 100
is scanned with the terahertz electromagnetic wave. Such a
scanning can be implemented by an authenticity determination
apparatus. In the
authenticity determination apparatus, a
position from which the terahertz electromagnetic wave is
emitted and a position at which the emitted terahertz
electromagnetic wave is received are fixed. The medium 100 is
scanned by being transported inside the authenticity
determination apparatus. Such an authenticity determination
apparatus is explained below by taking the measurements
corresponding to FIG. 9 as an example.
37
CA 3018059 2018-09-20
[0065] FIG. 11
is a schematic diagram indicating a
schematic internal configuration of the authenticity
determination apparatus seen from a side thereof. A transport
unit 63 transports the medium 100 in a direction shown with an
arrow 201. A terahertz electromagnetic wave transmitting unit
61 is arranged above the transport unit 63. A
terahertz
electromagnetic wave receiving unit 62 is arranged below the
transport unit 63. The
terahertz electromagnetic wave
transmitting unit 61 transmits the terahertz electromagnetic
wave of the predetermined frequency having the polarization
direction in the X-axis direction in a lower direction as shown
with an arrow 202. The counterfeit prevention structure 50
provided on the medium 100 being transported by the transport
unit 63 is irradiated with the terahertz electromagnetic wave.
The terahertz electromagnetic wave receiving unit 62 receives
the terahertz electromagnetic wave that penetrates the
counterfeit prevention structure 50. A position from which
the terahertz electromagnetic wave is emitted and a position
at which the terahertz electromagnetic wave is received are
fixed. The terahertz electromagnetic wave receiving unit 62
detects intensity of the received terahertz electromagnetic
wave, and obtains a transmittance from the detected intensity.
The transmittance is a ratio of the detected intensity to
intensity of the terahertz electromagnetic wave that is
detected in a state where there is no medium 100 being
transported by the transport unit 63. As shown in FIG. 11, the
medium 100 is transported by the transport unit 63 in the
38
CA 3018059 2018-09-20
direction shown with the arrow 201. The
medium 100 passes
through the position at which the terahertz electromagnetic
wave is emitted and received. While the medium 100 passes
through the position, the counterfeit prevention structure 50
is scanned in the direction shown with the arrow 200 and the
waveform of the transmittance is obtained as shown in FIG. 9.
Instead of calculating the transmittance in the terahertz
electromagnetic wave receiving unit 62, the transmittance can
be calculated by a control unit 64. In this case, the terahertz
electromagnetic wave receiving unit 62 outputs the intensity
of the received terahertz electromagnetic wave to the control
unit 64, and the control unit 64 calculates the transmittance.
[0066] FIGS.
12A and 12B are schematic diagrams of the
configuration shown in FIG. 11 when seen from above. FIG. 12A
shows a case in which the medium 100 is transported without
inclining. FIG. 12B shows a case in which the medium 100 is
transported while the medium 100 is inclined by an angle cy.
The transmittance of the terahertz electromagnetic wave
penetrating the counterfeit prevention structure 50 is
different for the state shown in FIG. 12A and the state shown
in FIG. 12B, however, the range of variation of the
transmittance is small. Therefore, the authenticity of the
medium 100 can be determined with a high accuracy based on the
value of the transmittance, the waveforms of the transmittance
obtained by scanning the counterfeit prevention structure 50,
and the like.
[0067] FIG. 13
is a block diagram indicating a schematic
39
CA 3018059 2018-09-20
functional configuration of an authenticity determination
apparatus 1. The
authenticity determination apparatus 1
includes the control unit 64 and a memory 65 in addition to
the configuration shown in FIG. 11. The
memory 65 is a
nonvolatile storage device constituted by a semiconductor
memory and the like. In the
memory 65, reference data is
previously prepared. The reference data includes the values
of the transmittance, the waveforms of the transmittance, the
characteristic features of the waveforms, and the like to be
obtained by irradiating the counterfeit prevention structure
50 with the predetermined terahertz electromagnetic wave.
[0068] The
control unit 64 controls the transport of the
medium 100 by the transport unit 63, the transmission of the
terahertz electromagnetic wave by the
terahertz
electromagnetic wave transmitting unit 61, the receiving of
the terahertz electromagnetic wave by the terahertz
electromagnetic wave receiving unit 62, and the like. Moreover,
the control unit 64 acquires the values of the transmittance
of the terahertz electromagnetic wave that penetrates the
counterfeit prevention structure 50, the waveforms of the
transmittance, and the like. The control unit 64 determines
the authenticity of the medium 100 by comparing with the
reference data prepared previously in the memory 65 at least
one among the values of transmittance, the waveforms of the
transmittance, the characteristic features of the waveforms,
and the like. The control unit 64 outputs the determination
result of the authenticity to a not-shown external apparatus.
CA 3018059 2018-09-20
For example, the determination result of the authenticity is
output to a display apparatus to be displayed and alarmed.
[0069] The
present embodiment explained an example in
which the counterfeit prevention structures 10 and 50 includes
the base member 17 and the conductive layer 16 in which the
SRRs 20 to 23 are formed; however, the structure of the
counterfeit prevention structures 10 and 50 is not limited to
this. FIG. 14 is a schematic cross section indicating another
structural example of the counterfeit prevention structures 10
and 50. In the counterfeit prevention structures 10 and 50
shown in FIG. 14, the conductive layer 16 shown in FIGS. 1 and
7 is adhered to a surface of the medium 100 via an adhesive
layer 41. A hologram layer 42 is arranged on the conductive
layer 16, and a release layer 43 is arranged on the hologram
layer 42. For example, after the release layer 43, the hologram
layer 42, the conductive layer 16, and the adhesive 41 are
sequentially formed on a predetermined base material, the
layers above and including the release layer 43 are separated
from the base material, the top and bottom of the separated
structure is reversed, and the configuration shown in FIG. 14
is obtained by sticking the released structure to the medium
100 via the adhesive 41. The
release layer 43 is made of
material such as transparent resin. Under the visible light,
when the counterfeit prevention structures 10 and 50 shown in
FIG. 14 is seen from above, a three-dimensional image recorded
in the hologram layer 42 can be seen. The SRRs 20 to 23 each
having the shape substantially like the English character C
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are minute structures formed in the thin conductive layer 16
having a thickness of few pm and therefore, it is difficult to
see with the naked eyes. Moreover, because the predetermined
design recorded in the hologram layer and the like arranged on
the conductive layer 16 is seen, it becomes more difficult to
notice the SRRs 20 to 23 whereby the effect of the counterfeit
prevention is enhanced.
[0070] The
present embodiment explained an example in
which the directions of the open parts of the SRRs are either
parallel or orthogonal to the polarization direction of the
terahertz electromagnetic wave; however, the direction of open
part is not limited to this. FIG. 15 is a view indicating an
example of the counterfeit prevention structure 10 having SRRs
120 to 123 of which the open parts are in different directions.
The SRRs 120 to 123 shown in FIG. 15 have a shape obtained by
rotating each of the SRRs 20 to 23 shown in FIG. 1 in the
clockwise direction by 45 degrees. The
directions of open
parts 120a to 123a of the SRRs 120 to 123 make an angle of 45
degrees to the X-axis direction and the Y-axis direction. Even
when the SRRs 20 to 23 constituting the first pattern 31 to
the fifth pattern 35 are replaced with the SRRs 120 to 123
shown in FIG. 15, respectively, an area in which the
transmittance of the terahertz electromagnetic wave shows a
predetermined value can be realized as explained above.
[0071] In the
example explained with reference to FIGS. 9
and 10, the medium 100 provided with the counterfeit prevention
structure 50 is rectangle, and the directions of the open parts
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of the SRRs and the orientations of the edges of the medium
100 are parallel or orthogonal; however, the angle between the
directions of the open parts and the edges of the medium 100
can be 45 degrees. Specifically, for example, the medium 100
shown in FIG. 9 can be kept as it is and only the counterfeit
prevention structure 50 can be rotated in the clockwise
direction by 45 degrees. Alternatively, for example, the SRRs
of the counterfeit prevention structure 50 can be replaced with
the SRRs 120 to 123 shown in FIG. 15. Even in this case, a
waveform having different transmittance of the terahertz
electromagnetic wave can be obtained in the first area 11 to
the third area 13 as explained above.
[0072]
Moreover, a structure different from that shown in
FIG. 7 can be adopted as the structure in which the
transmittance changes in various areas while scanning the
counterfeit prevention structure 50 of the medium 100 being
transported. FIG. 16 is a view indicating another example of
a counterfeit prevention structure 150 that is divided in a
plurality of areas. The counterfeit prevention structure 150
having a square shape shown in FIG. 16 is divided into eight
areas at regular intervals in the diagonal direction. These
eight areas make an angle of 45 degrees to the edges of the
counterfeit prevention structure 150. The
areas are
constituted by two types of areas, a first area 111 and a
second area 112, and the two types of areas are arranged
alternately. For example, a desired one of the first pattern
31 to the fifth pattern 35 can be selected for each of the
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CA 3018059 2018-09-20
first area 111 and the second area 112 thereby obtaining areas
having different patterns. Moreover, for example, the first
area 111 can be an area made of insulating material through
which the terahertz electromagnetic wave can penetrate or can
be made of conductive material that blocks the terahertz
electromagnetic wave, and that does not include the SRRs. In
this example, the second area 112 can be an area constituted
by a pattern selected among the first pattern 31 to the fifth
pattern 35, and that includes the SRRs. With
this
configuration, when a substantially central in the X-axis
direction of the counterfeit prevention structure 150 is
scanned in the Y-axis direction with the predetermined
terahertz electromagnetic wave, the transmittance changes in
the first area 111 and the second area 112. The authenticity
determination can be performed based on the transmission
characteristics of the counterfeit prevention structure 150.
[0073] The
present embodiment explained an example in
which each area of the counterfeit prevention structure 50
shown in FIG. 7 is constituted by one of the first pattern 31
and the third pattern 33 shown in FIGS. 3A and 3C and the fifth
pattern 35 shown in FIG. 8; however, the patterns used to form
the areas are not particularly limited. For
example, the
second pattern 32 and the fourth pattern 34 can be used.
Moreover, the counterfeit prevention structure 50 can be
divided in two areas or can be divided in four or more areas.
Moreover, it is explained to use the fifth pattern 35 obtained
by rotating the first pattern 31 by 90 degrees as the basic
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CA 3018059 2018-09-20
pattern; however, it is allowable to use a pattern obtained by
rotating the second pattern 32, the third pattern 33, and the
fourth pattern 34 by 90 degrees.
[0074] The
present embodiment explained an example in
which the first pattern 31 to the fifth pattern 35 are taken
as the basic pattern; however, the basic patterns are not
limited to this. The shape of the basic pattern, and the type,
the number, the layout, and the like of the SRRs that constitute
the basic pattern are not particularly limited as long as, in
an area which has the same shape as the basic pattern and is
selected from a desired position of an area in which the basic
patterns are repeatedly arranged in a matrix layout, the ratio
of the number of the SRRs having the open parts parallel to
the polarization direction of the terahertz electromagnetic
wave to the number of the SRRs having the open parts orthogonal
to the polarization direction of the terahertz electromagnetic
wave is the same as that of the basic pattern. Specifically,
for example, regarding the layout of the SRRs in the basic
pattern, other than the matrix layout, in which the SRRs are
arranged repeatedly vertically and horizontally, the SRRs can
be arranged in the checkered pattern layout or in the honeycomb
pattern layout. Regarding the layout of the basic patterns in
each area, other than arranging the basic patterns in the
matrix layout, a block pattern layout, a honeycomb pattern
layout, or a layout in which the basic patterns are repeated
as desired can be used. The shape of the SRRs is also not
limited as long as the desired transmittance can be obtained
CA 3018059 2018-09-20
when the terahertz electromagnetic wave of predetermined
frequency is emitted. For example, the ring part can have a
rectangle shape. Moreover, as long as the resonance frequency
is the same, it is not necessary that all of the types of the
SRRs are of the same shape. It is
allowable that the SRRs
having different shapes, such as the rectangle shape, the
circular shape, are mixed.
[0075] The
present embodiment explained an example in
which the polarization direction of the terahertz
electromagnetic wave used for the authenticity determination
is mainly along the X-axis direction; however, the terahertz
electromagnetic wave having the polarization direction in the
Y-axis direction can be used. The transmittance in each of the
basic patterns changes when the polarization direction of the
terahertz electromagnetic wave changes, however the
authenticity determination can be performed as explained above
by previously acquiring the transmittance corresponding to the
polarization direction.
[0076] The
present embodiment explained an example in
which the transmittance of the terahertz electromagnetic wave
is used for the authenticity determination of the counterfeit
prevention structure; however, it is allowable to use
reflectivity of the terahertz electromagnetic wave. The
transmittance and the reflectivity of
terahertz
electromagnetic wave have such a relation that when one of them
increases the other decreases. For
example, the terahertz
electromagnetic wave transmitting unit 61 and the terahertz
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CA 3018059 2018-09-20
electromagnetic wave receiving unit 62 are arranged across the
transported medium 100 in FIG. 11; however, these two units
can be arranged on the same side of the medium 100. The
reflectivity can be measured by receiving the terahertz
electromagnetic wave, which is emitted by the terahertz
electromagnetic wave transmitting unit 61 and reflected from
the medium 100, in the terahertz electromagnetic wave receiving
unit 62. Accordingly, the characteristics of the counterfeit
prevention structure can be obtained based on the reflectivity
of the terahertz electromagnetic wave and the authenticity
determination of the counterfeit prevention structure can be
performed by using the transmittance in the same manner as
explained above.
[0077] As
explained above, when the authenticity
determination apparatus according to the present embodiment is
used, it is possible to irradiate the counterfeit prevention
medium, such as the banknote or the coupon, provided with the
counterfeit prevention structure with the terahertz
electromagnetic wave and determine the authenticity of the
counterfeit prevention medium based on the transmission
characteristics, such as the frequency and the transmittance,
of the emitted terahertz electromagnetic wave.
[0078] To
allow determination of the authenticity, the
plurality of types of the split ring resonators that constitute
the counterfeit prevention structure include, for example, the
open parts in the direction that is parallel or orthogonal to
the polarization direction of the emitted terahertz
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CA 3018059 2018-09-20
electromagnetic wave. By adjusting the ratio of the number of
the split ring resonators having the open parts parallel to
and the number of the split ring resonators having the open
parts orthogonal to the polarization direction, the counterfeit
prevention structure through which the terahertz
electromagnetic wave of the predetermined frequency penetrates
at the predetermined transmittance can be realized. Moreover,
by using the split ring resonators having the open parts
parallel and orthogonal to the polarization direction of the
terahertz electromagnetic wave, the variation in the
transmittance of the counterfeit prevention structure when the
counterfeit prevention structure is inclined with respect to
the polarization direction of the terahertz electromagnetic
wave can be suppressed.
Therefore, the authenticity
determination can be performed with a high accuracy by using
the counterfeit prevention structure.
[0079] The
counterfeit prevention structure according to
one aspect of the present invention is a counterfeit prevention
structure provided on a medium to determine authenticity of
the medium. The counterfeit prevention structure includes a
hybrid area in which a plurality of types of split ring
resonators is formed in a mixed state in a predetermined ratio.
Each split ring resonator includes an open part. A direction
of an open part of each type of the split ring resonators is
different from each other.
[0080] In the
above counterfeit prevention structure, the
plurality of types of the split ring resonators resonates with
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a terahertz electromagnetic wave having the same frequency.
[0081] In the above counterfeit prevention structure, the
hybrid area is formed by repeatedly arranging a basic pattern
that includes at least two types of the split ring resonators.
[0082] In the above counterfeit prevention structure, when
the counterfeit prevention structure is irradiated with a
terahertz electromagnetic wave of a predetermined frequency
having a polarization direction in a predetermined direction,
a transmittance of the terahertz electromagnetic wave in the
hybrid area indicates a value depending on a ratio of mixed
types of the split ring resonators.
[0083] In the above counterfeit prevention structure, the
plurality of types of the split ring resonators includes at
least two types of the split ring resonators having the open
parts of which respective opening directions are different by
90 degrees.
[0084] The above counterfeit prevention structure
includes a plurality of types of areas each of which indicates
a different transmittance when irradiated with a terahertz
electromagnetic wave of a predetermined frequency having a
polarization direction in a predetermined direction. At least
one of the plurality of types of the areas is the hybrid area.
[0085] In the above counterfeit prevention structure, the
plurality of types of the areas includes a plurality of types
of the hybrid areas. Each of the plurality of types of the
hybrid areas has a different mixed ratio of the plurality of
types of the split ring resonators and a different
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CA 3018059 2018-09-20
transmittance.
[0086] The above counterfeit prevention structure
includes a hologram layer operable to generate a predetermined
design under visible light.
[0087] The above counterfeit prevention structure is
formed on a banknote.
[0088] A counterfeit prevention medium according to
another aspect of the present invention is a counterfeit
prevention medium including the above counterfeit prevention
structure.
[0089] In the counterfeit prevention structure according
to the present invention, the range of variation of the
transmittance due to the inclination thereof can be suppressed
and the authenticity determination can be performed with a high
accuracy in comparison with the counterfeit prevention
structure in which all the sprit ring resonators have the same
directions of the open parts.
[0090] As explained above, the counterfeit prevention
structure and the counterfeit prevention medium according to
the present invention are useful in determining the
authenticity of the counterfeit prevention medium provided with
the counterfeit prevention structure with a high accuracy.
CA 3018059 2018-09-20
[0091]
Although the invention has been explained with
respect to specific embodiments for a complete and clear
disclosure, the appended claims are not to be thus limited but
are to be construed as embodying all modifications and
alternative constructions that may occur to one skilled in the
art that fairly fall within the basic teaching of the claims.
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