Note: Descriptions are shown in the official language in which they were submitted.
CA 02615013 2007-12-06
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RADIO FREQUENCY AUTOMATIC IDENTIFICATION SYSTEM
This application is a divisional application of Canadian Patent Application
Serial
No. 2,191,778, entitled "Radio Frequency Automatic Identification System", and
having a filing
date of November 29, 1996.
Field of the Invention
This invention relates to automatic identification of items using radio
frequency
signals. More particularly, this invention relates to production of radio
frequency responsive
materials for use in such a system; to radio frequency responsive targets
using such materials; and to
systems for automatic radio frequency identification of items by such targets.
Background of the Invention
Automatic identification systems are widely used to input data into computer
systems and to control operation of equipment. Radio frequency operated
systems are often used in
automatic identification applications where identification of an object is to
be made without contact
and where the application may not permit line-of-sight communication between
the object and a
sensor. Radio frequency automatic identification ("RF/AID") systems are based
on "targets" which
generally function as transponders. Upon receipt of a radio frequency
interrogating signal, the target
responds by producing a detectable radio frequency response signal. Such
targets have taken the
form of tags or labels which are affixed to an object to be identified. As
used herein, a "target" is
any radio frequency responsive means which may be attached to, printed upon,
embedded in, or
otherwise associated with an object to be identified. Although the term "radio
frequency" is used
herein because that is the region of the electromagnetic spectrum which is
most frequently used for
such automatic identification, it will be understood that the invention
embraces any electromagnetic
radiation.
Automatic identification systems are presently used or contemplated for use in
a
wide variety of applications for monitoring of people, animals, locations, and
things. Such
applications include material handling, such as automatic storage and
retrieval; cargo handling, such
as baggage sorting and tracking; asset management, such as rental vehicles or
for retail theft control;
identification of persons, such as for facility access control or patient
tracking; and identification of
animals, such as for automatic feeding.
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One major attribute of presently available RF/AID systems which limits their
use is that the target cost is substantial. Situations in which this high cost
can be justified
include those where targets are removed from an item after purchase and reused
on other
items, those where the item to be identified is costly or important, and those
where an item is
likely to be misappropriated absent some effective control system. Another
attribute which
restricts use of present RF/AID systems is the target size. Targets are
typically several inches
long, which inhibits their use where small items are to be identified or where
it is desired that
the target be unobtrusive.
Both of these attributes result in large part from the structure typically
employed for RF/AID targets and the frequency at which they operate. Such
targets typically
contain an antenna for receiving an interrogating RF signal; radio frequency
processing means
for detennining whether an interrogating signal has been received; and radio
frequency
transmitting means responsive to the processing means for transmitting a
detectable RF
response signal from the target. Present systems typically operate at fairly
low frequencies.
One application for which existing RF/AID techniques have not been used, due
to the cost, size, and limited information content of prior art targets, is
identification of
documents including currency and financial instruments such as credit cards.
Counterfeiting of
currency has become a major problem, on scales and using technology ranging
from color
photocopying to altering of genuine currency printing operations. Credit card
fraud, involving
magnetic programming of counterfeit cards or reprogramming of genuine ones,
has become
epidemic. Existing techniques for identifyinng such items are obviously
deficient. Ordinary
business documents would desirably be protectable from unauthorized copying or
use and
verifiable as original or genuine, but no effective means for doing so are
available.
The present invention is directed to a new system for RF/AID which avoids the
foregoing drawbacks of the prior art and is suitable for use in a wide variety
of applications
which were not possible using prior art systems.
Summary of the Invention
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The present invention comprises several aspects which are useful together to
provide a new system for automatic identification.
In one aspect of the invention, a radio frequency target includes a plurality
of
resonant articles, resonating at a plurality of radio frequencies. The
resonant frequencies of the
articles are used to provide identification data. In a preferred embodiment of
this first aspect of
the invention, the resonant articles are passive solid state resonators. In a
particularly preferred
embodiment, the articles are materials in the quartz family, such as quartz
crystals, which may
be fabricated having various desired properties and shapes.
In another aspect of the invention, a method of making a target having
resonant
articles to provide identification data includes the step of measuring the
resonant frequencies of
the resonant articles. In a particularly preferred embodiment of this aspect
of the invention,
resonant articles for use in a particular target are selected according to
their resonant frequency
as previously measured.
In another aspect of the invention, items are identified by transmitting radio
frequency interrogating signals into a target field and evaluating the
response of the target field
to determine whether the field contains resonant articles. In a preferred
embodiment of this
aspect of the invention, the frequency of the interrogating signal is varied
so as to detenmine the
response of the target field to different frequencies. In a particular
preferred embodiment of
this aspect of the invention, the presence or identity of a target in the
target field is evaluated
according to the frequencies at which the target field response indicates the
presence within the
field of resonant articles.
In another aspect of the invention, a radio fiNuency target includes a
plurality
of resonant articles, which are located at spatially differentiable positions
in the target. The
spatial locations of the resonant articles are used to provide identification
data; the resonant
frequencies of the articles may also, but need not, provide identification
data. In accordance
with this aspect of the invention, items are identified by transmitting radio
frequency
interrogating signals into a target field and evaluating the radio frequency
response of the target
field to detenmine whether it contains such articles and the location thereof.
The spatial
locations of any resonators in the target field having appropriate resonant
frequencies, and
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perhaps the resonant frequencies of such resonators as well, are detennined in
order to evaluate
the information contained within the target.
In another aspect of the invention, various methods of malcing targets with
resonant articles at spatially differentiable locations are provided. In one
such method, the
articles are disposed at predetermined information-bearing locations during
the manufacture of
the target, to encode particular predetennined information. In a second such
method, the
articles are disposed at random locations during the manufacture of the
target, and information
is later attributed to the target by determining the locations at which
resonant articles are
positioned in it. In a preferred embodiment of this second method, an
automatically readable
translation code is subsequently generated based on the determined locations
of resonant
articles, whereby a standard identification system may produce information
which is desired to
be attributed to the target, in a standard format, by operating on the random
resonant article-
position infomiation and the information of the translation code. The
translation code may be
encoded in the target itself or stored separately.
In another aspect of the invention, a system is provided for automatically
acquiring information from a target containing information in the location in
the target of
resonant articles. In a preferred embodiment of this aspect of the invention,
a transceiver for
transmitting interrogating signals to and receiving response signals from a
target field includes a
resonant iris aperture which is adjacent to a location on a target to be
interrogated. The
presence, in the target location being interrogated, of a resonant article
having a resonant
frequency near that of the aperture, creates a large reflection of the
interrogating signal which
may easily be detected as an information-bearing response signal. In a
particularly prefenred
embodiment of this aspect of the invention, the transceiver apparatus includes
a plurality of
such apertures which are separated from one another, so that the acquisition
of infonnation
from separate target locations may take place simultaneously and the
identification process may
be performed quickly.
In another aspect of the invention, the resonant articles are conductive
structures which are printed on, or embedded in, or otherwise applied to a
dielectric substrate
to form a target. The geometry of each structure determines the frequencies at
which it
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provides a detectable radio frequency response; such frequencies, and/or the
spatial locations of
the conductive structures, provides the target with information. This aspect
of the invention is
useful for identifying documents, and in a particularly preferred embodiment,
the conductive
structures include structures having the shape of ordinary human-readable
alphanumeric
characters.
Other aspects of the invention will become apparent upon review of the
following specification and the drawings.
Brief Descriytion of the DrawinPs
Figure 1 is a block diagram generally illustrating the functional elements of
an
RF/AID system.
Figure 2 is a block diagram illustrating in greater detail the radio frequency
responsive means shown in Figure 1.
Figure 3 illustrates a preferred radio frequency responsive means.
Figure 4 is a graph illustrating a method whereby numerical data may be
attributed to frequency.
Figure 5 is a graph showing a distribution of resonant frequencies in a
process
for producing resonators.
Figure 6 is a flow diagram of a process for producing targets in accordance
with the invention.
Figure 7 is a flow diagram of another process for producing targets in
accordance with the invention.
Figure 8 is a graphical illustration of a preferred method of radio frequency
signal generation and processing.
Figure 9 is a block diagram illustrating a resonator whose resonant
characteristics may be altered to alter information in a target.
Figure 10 is a schematic illustration of a document having information which
is
encoded by location of resonators.
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Figure 11 is a flow diagram of a process for reading and writing infonnation
which is encoded in a document by resonator spatial location.
Figure 12, comprising Figures 12A, 12B and 12C, is a flow diagram of other
processes for reading and writing information which is encoded in a document
by resonator
spatial location.
Figure 13 is a block diagram illustrating the functional elements of a
document
reader in accordance with the invention.
Figure 14 is an illustration of a document interfacing surface useful with the
document reader of Figure 13.
Figure 15 is front elevation and Figure 16 is side elevation of another
document
which has information encoded by the spatial location of resonators.
Figure 16 is a diagram of another document reader, which may be used to read
the document of Figure 15.
Figure 17 is an illustration of various signals which may be generated by
reading the document of Figure 15.
Figure 18 is an illustration of a tag or target in which a plurality of RF
responsive articles are disposed on a substrate.
Figure 19 is a block diagram illustrating the function of a near field radio
frequency reading system in accordance with the invention.
Figure 20 is an illustration of a microwave reading system embodiment of the
system of Figure 19.
Figure 21 is an iflustration of a diskette encoded with radio frequency
readable
infonnation.
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Detailed Descrintion
The system of the present invention provides automatic item identification in
a
manner which, like existing RF/AID systems, can be free from the constraints
of line-of-sight
detection imposed by barcode systems and short range detection imposed by
magnetic
encoding systems. Unlike existing RF/AID systems, the system of the present
invention is
operable with inexpensive targets which may be of smafl size and/or large
information density.
The system is operable at great distances as well as in confined areas. The
information-
containing components of the invention may be fashioned into targets which are
easily applied
to a wide variety of items to be identified. Such items may be reliably
identified using versatile,
low-cost interrogating systems.
Figure 1 generally illustrates the functional elements of an RF/AID system.
The system includes a target 10 which includes and serves as a carrier for
radio frequency
responsive means 12. Such a target 10 may be affixed to or incorporated in an
item to enable it
to be detected and/or identified by a system, often referred to as a scanner
or reader, which
includes a radio frequency transmitter 20 and a radio frequency receiver 30.
Transmitter 20
includes a signal generator 22 coupled to an antenna 24 for generating radio
frequency
interrogating signals 26 in a desired target field. Receiver 30 receives radio
frequency response
signals 36 at antenna 34 coupled to signal processor 32. Signal processor 32
produces an
output 38 indicative of the presence of a target 10 within the target field in
response to the
response signals 36 received by antenna 34. Output 38 may be supplied to a
computer or other
identification information processing system 39. Transmitter 20 and receiver
30 may be
physically associated in a single transceiver unit, and the functions of
antennas 24 and 34 may
be performed by a single antenna. A system as shown in Figure 1 may be
designed to detect
radio frequency responses means in the near field of the antenna(e), in the
far field of the
antenna(e), or both.
Figure 2 functionally illustrates in greater detail the preferred radio
frequency
responsive means 12 shown in Figure 1. Responsive means 12 includes a
plurality of devices
which are resonant at radio frequency. Figure 2 shows resonant means or
resonators 12a, 12b,
12c ... 12n which are resonant at frequencies fs, fb, fc ... fn. These
frequencies represent a subset
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of possible resonant frequencies which may be provided by resonators in target
10. In some
aspects of the invention, the resonators may have the same resonant frequency
or resonant
frequencies which are not intended to provide identifying information; in
other aspects of the
invention, the resonators may have different resonant frequencies, and the
particular
frequencies present provide the target with identification data.
Figure 3 illustrates a preferred embodiment of a resonator 12n. The resonator
comprises a piece of solid material having dimensions, electromagnetic
properties, and/or
mechanical properties rendering it resonant at radio frequency. Although
depicted as a
rectangular prism, it will be understood that a large variety of shapes may be
used in devices
having suitable radio frequency response characteristics.
One preferred resonator 12n is a quartz crystal. Such crystals have electrical
and mechanical properties which enable them to be used as accurate, rugged,
reliable, and
stable frequency determining elements. While a resonator suitable for use in
the present
invention may consist merely of a quartz crystal, it may be desirable to
tailor its properties for
particular applications by modifying it to alter its characteristics such as
by improving its Q.
For instance, it may be desirable to dope the quartz with another material,
such as gallium. It
may also be desirable to couple the crystal to auxiliary structures such as
metallizations forming
antennas to improve coupling of incident radio frequency energy to the crystal
or to control the
mode of operation of the crystal, for instance such as is done in a surface
acoustic wave device.
Although quartz crystals are preferred resonators, useful solid resonators may
no doubt be
made from other crystalline materials or from non-crystalline solids. For
instance, other
preferred resonators include thin dipoles, materials operating in electron
paramagnetic
resonance, and ferrite materials operating in the ferroelectric mode.
Moreover, as will be
discussed with respect to certain embodiments of the invention, other
properties of such
resonators besides their resonance may be detected to obtain identification
information; for
instance, the short circuiting effect of a thin dipole or similar resonant
conductive structure may
be detected by a suitable transceiver.
Such a resonator 12n may be resonant at several frequencies and may be
structured so that several such frequencies are used to provide identification
information in a
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target. At any rate, the resonator is configured so that it resonates at least
at one resonant
frequency which in certain embodiments is an information-catrying frequency in
the system.
While a variety of frequency ranges may be used in systems according to the
present invention, high frequencies are believed preferable for a variety of
reasons including
availability for use, size of resonator required, identification range, and
ability to control the
interrogating signal. Thus, for instance, frequencies in excess of about I GHz
are preferred,
particularly frequencies in excess of about 10 GHz. Frequencies may be used up
to and even
above 500 GHz, near visible light frequency.
Figure 4 illustrates generally how identification information is provided in
accordance with one aspect of the present invention. Figure 4 is a graph of
attributed
numerical value versus frequency. The frequency domain is divided up into a
plurality of bands
or "windows", each representing a binary digit or bit value. Thus an n-bit
number requires n
distinguishable frequency bands. One or more "start" bits may be required in a
target. Thus,
for instance, an identification band of 60.0-60.1 GHz may be partitioned into
10 windows each
of which is 10 MHz wide including any "stop" bands between adjacent windows
which may be
desired. These windows may be defined in the system to represent a start bit
and a 9-bit data
word. In the terms of Figure 2, any resonators 12 present would be required to
fall into one of
the 10 frequency windows defined in the system of this example, and 10
resonators would be
required to provide a target with a start bit and all 9 available data bits.
Referring to Figure 3, it is noted that although one such solid resonator is
necessary and sufficient to provide one bit of information by resonance, it
may be desirable to
use a number, perhaps even a very large number, of individual resonators such
as ciystals to
form each identifying resonant means of Figure 2. Increasing the number of
individual
resonators can provide a cheap and reliable way of increasing the target's
responsiveness to a
given intensity of interrogating signal at the target. Thus, a large number of
crystals each
having a frequency in a certain window will enable the presence of the
corresponding data bit in
the target to be detected at long range, with low power interrogation, andJor
with a low gain
receiver, any of which may be highly desirable in a given application.
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An important part of the present invention lies in the ability to provide
resonant
devices for use in targets which are cheap, accurate, and stable. As noted
above, preferred
resonant devices include quartz crystals fomiing solid state passive
resonators. Although
quartz crystals are currently produced in large numbers for use in frequency
determirnng
applications, existing techniques for production would probably be too
expensive for
economical use in the RF/AID system of the present invention. Such crystals
presently are
carefully cut to precise dimensions to produce products meeting very tight
frequency tolerance
requirements.
To avoid the limitations of existing production techniques, so as to provide a
method for inexpensively producing crystals in large numbers for use in the
system of the
present invention, a novel method for manufacturing is provided, comprising
generally two
parts. The first part is a method of inexpensively producing solid resonators
such as quartz
crystals in large numbers, with each resonator having resonant characteristics
reasonably likely
to fall within the system's identification band. The second part is
determining the resonant
characteristics of individual resonators by measuring their as-produced
characteristics.
The preferred method of providing solid resonators is to fabricate resonators
of
a solid material in approximately desired size and to select resonators
according to their
measured resonant characteristics. Applicant believes that the following
method would satisfy
the requirements of the invention.
When quartz is heated sufficiently, it softens somewhat prior to liquefying.
It is
believed that such heated softened quartz may be easily cut and/or molded into
dimensions and
shapes suitable for use as radio frequency resonators. Thus, it is believed
that a mass of quartz
may be softened by heating, passed through a forming die in a process in the
nature of
extrusion, and cut into individual crystals, which are then cooled, such as by
quenching.
Quenching may be performed by immersion in a liquid such as water, oil,
petroleum based
liquids, or other hydrogen, oxygen, or carbon based liquid. Crystals so
produced may then be
collected for further processing. Other methods of providing a number of
crystals or other
resonators having approximately proper characteristics may no doubt be
provided.
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Desirably, the process used for manufacturing resonators of approximately
correct resonant characteristics would produce a distribution of
characteristics exactly
corresponding to the need for resonators in each window. More likely, a
manufacturing
process will produce resonators with another distribution, such as a norntal
distribution of
resonator frequencies. Such a distribution desirably substantially coincides
with the range for a
particular identification band or bands to be used for RF/AID. For instance,
Figure 5 shows an
approximately normal distiibution centered around 60.05 GHz, which might be
produced in a
process to make resonators in approximately equal numbers in each window of
the 60.0-60.1
GHz band described with respect to Figure 4.
Once a process is developed for producing resonators differing in
characteristics, resonators so produced may be fabricated into information-
canying targets.
Figures 6 and 7 show two methods for producing targets which are identifiable
by frequency
for use in RF/AID systems.
Figure 6 is the presently preferred method for producing such targets. In step
40, a set of resonators is produced by a process or processes designed to
yield resonators
having differing resonant frequencies approximating a desired value. The
frequency of each
resonator is measured in step 42, and in step 44 the resonators are sorted by
frequency in
accordance with the measurement made in step 42. For instance, quartz crystal
resonators may
be fabricated as described above, conveyed to a measuring system which may be
sirnilar to the
system in Figure 1, and each crystal sorted by identifiably marking it or
preferably by
segregating it with other crystals of the same or similar frequency. Thus,
with reference to
Figure 4 and 5, upon completion of sorting step 44, one might have 10
containers, each of
which contains crystals from only one frequency window representing only one
bit of
information. A set of crystals having frequencies which represent the bits of
an identifying
digital word are selected in step 46, and a target is made using the selected
crystals in step 48.
The method of Figure 6 pemiits one to make a target containing predetermined
identifying
data.
In contrast, Figure 7 shows a method for making targets which contain random
or uncontrolled identifying data rather than predetermined identifying data.
After fabrication of
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resonators having differing frequencies in step 50, a set of resonators is
randomly selected in
step 52 and incorporated into a target in step 54. A measurement is made in
step 56 to
determine the frequencies of the resonators which were incorporated into the
target. Measured
data is stored in step 58 so that the target can be identified as valid when
it is interrogated in
actual use.
Figure 8 illustrates a preferred method of generating and processing radio
frequency signals in accordance with the present invention. In accordance with
this method,
the target field is interrogated for possible resonant articles by varying the
transmitted
frequency in a range which includes the applicable information-bearing band of
the system.
Figure 8 is a pair of graphs, the top showing interrogating signal frequency
with respect to time and the bottom illustrating a possible RF response from
the target field
over the same time interval. As shown in the top graph, the frequency of
interrogating signal is
varied from a lower limit to an upper limi.t, which are designated fs and fn
to correspond with
Figure 4. After reaching the upper frequency f,, at time T, the variation may
be repeated
starting again at f, either immediately or after a delay period. Desirably and
as shown the
frequency sweep is substantially linear and continuous, but other
predetermined variations may
be used. The lower graph of Figure 8 illustrates a response signal which might
be produced by
the target field and detected in signal processor 32. This signal shows
differences from the
background signal, which are illustrated as spikes but might take a variety of
forms. The lower
graph illustrates a significant feature of the swept-frequency measurement,
namely that
identifying data may be easily detected by measuting the time at which the
spikes or other
resonant effects occur in the response.
In the terms of the Figure 4, if the frequency band is partitioned into 10
windows, with the low frequency window representing a start bit and 9 data
bits ranging from
a low order bit at f, to a high order bit at f9, the data word represented by
the response in
Figure 8 is 100001000. Such a serial data structure can be easily and
inexpensively evaluated.
The expense of detection equipment may be reduced by use of a start bit
frequency as
described or other data structure which similarly permits evaluation by
relative rather than
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' . . '
absolute frequency determination. This avoids the difficulty and expense of
making high
resolution, high precision frequency measurements at high frequencies.
The lower graph of Figure 8 shows a response signal with identification
information present in the form of spikes having greater amplitude than the
received signal at
other frequencies. It should be noted that the response signal may provide
troughs or notches
at particular frequencies, such as where the resonator absorbs energy at the
resonant frequency.
All that is required is that the resonator provide a detectable difference in
response signal at an
identifiable frequency, whether the response is greater or less than at other
frequencies.
It should be noted that low average power levels can be maintained while using
larger measuring signals by transmitting a high power inten: ogating signal
with a small duty
cycle. For instance, an interrogating signal which is swept from the low
frequency to the high
frequency in a 1 millisecond interval and then turned off for 9 milliseconds,
to yield a 10% duty
cycle, will increase by a factor of 10 the response signal level available
from a given average
transniitted power level.
System according the foregoing are applicable to a wide range of target and
identification applications. For instance, the resonators may be extremely
small, on the order of
the wavelength of the interrogating signal. Resonators of one-half wave
dimensions at
frequencies on the order of 10-100 GHz are quite small, and large numbers of
them may be
used to provide high density identifying data, far greater than the 9 bits
used as illustrations in
connection with the above descriptions of drawing figures. A particularly
desirable mode of
application of an identifying set of resonators is in a matrix of adherent
radio frequency
transparent material, forming an encoded "ink". Such an ink may be applied to
a wide variety
of types of materials to target them for identification. One application which
deserves
particular mention is in identifying documents. An ink comprising radio
frequency resonators
may be applied to a wide variety of dor.uments to tag or identify them.
Applications range
from substitutes for barcodes or printed indicia, such as on checks and
carency, to inclusion in
toner to perniit monitoring and/or identification of xerographically copied
documents, laser-
printed documents, or other documents whether printed by thermal set
techniques or
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otherwise. Crystals or sets of identifying crystals may also be
microencapsulated, or included
in the bulk of a material to be identified.
Another application area which deserves particular mention is modification of
target response characteristics. This is done in the prior art, for instance
in deactivation of
retail theft control tags and labels. The system of the present invention
likewise pernuts
modification of target response characteristics, for instance to deactivate a
target or otherwise
alter the information it contains. A system for modifying target response
characteristics is
shown in Figure 9. A resonator 60 is coupled to a resonance characteristic
modifying means
64 by a coupling means 62 which may be altered by external influences to vary
the coupling
between the resonator and the resonance modifying means. Upon application of
the
appropriate stimulus to the coupling means 62, the resonance characteristics
of the entire
system of Figure 9 are altered to change the information provided. One or more
such systems
may be included in a target to provide the capability of changing the target
information.
One possible example of a system according to Figure 9 is a quartz crystal
which is microencapsulated in a heat-deformable medium functioning both as a
coupling means
and a resonance altering means. At low RF power levels, the mechanical
coupling between the
encapsulation and the resonator affects the natural resonance characteristics
of the resonator.
Application of RF power levels suff ciently high to generate heat due to
movement of the
resonator can result in deformation of the encapsulation medium and thereby
change the
coupling and resulting effects of the enca.psulation medium on resonance
characteristics. This
change can be interpreted as a change in information. Another example of an
alterable
resonator is a pair of crystal resonators which are mechanically coupled by a
heat deformable
medium. When united, the resonators together provide a first resonant
frequency. When high
power levels are applied at resonant frequency, resulting heat can deform the
coupling medium
and permit the component resonators each to resonate at their own resonant
frequencies, thus
providing a change in information contained in a target.
Figure 10 illustrates various aspects of the invention, in accordance with
which
the spatial locations of resonant articles in a target provide the target with
information and are
detected in order to obtain information from targets. These aspects are
particularly useful for
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~
.
identification of items comprising or consisting of a target which may be
easily brought into a
closely adjacent relationship with a transceiver reading device to facilitate
spatial differentiation
of the resonator locations within the target. An example of such an
application is the
identification of documents, which provide a two-dimensional area that may be
encoded with
resonators and that may be discretely handled using known document handling
techniques.
Another example is credit cards and like card-size instruments which have
traditionally been
fabricated of plastic and encoded by magnetic means, which can be handled by
known card
handling apparatus. Labels or tags which may be applied to the surface of an
article to identify
it may also be spatially encoded with resonant aracles. All of such specific
embodiments may
be referred to herein by the generic term "document". As has been noted, the
resonant
frequencies of the resonators may also be used to impart information to the
target in these
aspects of the invention.
Figure 10 illustrates a document 70 which has been encoded with information
in the form of the location of a set 72 of resonant articles 72a-72n which are
affixed to the
document. The resonant articles 72 are depicted as line segments in that a
preferred type of
article is a thin dipole such as an elongated metal or metallized article in
the nature of chaff.
Such a dipole is resonant at an interrogating frequency at which the dipole
is'/Z wavelength in
length. Metallized glass fibers may be used as the thin dipoles; the fibers
may be on the order
of.001" diameter. A wide variety of lengths may be used depending on the
resonant frequency
desired and the nature of the reader, but lengths for example on the order
of'/. inch may be
used.
Figure 10 illustrates, by dotted lines, a rectangular array of rows 1, 2, 3
... m
and columns 1, 2, 3, ... n. This m x n array is not necessarily an attribute
of the document 70,
although it may be; in general, it is established by the encoding/decoding (or
"coding") scheme
and defined by the scanner or reader with which the document 70 is to be read.
While it is
possible to precisely measure the spatial location of each resonator present
in the document, in
one preferred embodiment this difficult task is avoided by detecting the
presence of resonators
within spatial "windows". That is, under a particular coding scheme, the
preferred reader will
interpret the presence or absence of a resonator anywhere within a
predetermined area of the
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CA 02615013 2007-12-06
' = '
document 70 comprising the array element (m, n) as a bit of informa.tion. The
bits of
information may be organized as a single data word, or as a plurality of words
(for example,
each row or column may be considered a byte). As described more fully below
with respect to
the reader, the origin of the array may be determined with respect to the
location of resonators
in the document containing "start" data or with respect to the document
itself, e.g. with respect
to the document edges.
Figure 11 and Figure 12 (comprising Figures 12A, 12B, and 12C) illustrate
two alternative general methods of providing a document having information
encoded by the
spatial location of resonators in it. Each of these figures is divided by a
horizontal dotted line
into an upper portion comprising steps to "write" or create the encoded
document and a lower
portion comprising steps to "read" a document and, if it is readable, to
decode the encoded
information therein. In the method of Figure 11, the document is encoded by
disposing
resonators at predetermined locations; in the methods of Figure 12, the
document is encoded
by disposing resonators at random locations.
In the flow diagram of Figure 11, resonators are first fabricated in step 80
to
provide a supply of resonators suitable for inclusion in a document to be
identified. In step 81,
a coding system is determined which is to be used in encoding the document.
The coding
system associates predetermined information with predetermined spatial
locations in the
document, and may be selected from a set of coding systems which are available
for use. In
step 82, the information which is to be encoded in the document is determined.
In step 83, the
spatial locations in the document are detennined which will encode the
particular information
to be encoded (as determined in step 82) in accordance with the particular
coding system to be
used (as determined in step 81). In step 84, resonators are disposed in the
document at the
locations determined in step 83. Step 84 may be effectuated by disposing the
resonators in the
document as the document base material is being fabricated, as for instance by
dispensing
resonators from a supply into a web of paper pulp (e.g. for cuirency) or soft
plastic (e.g. for
cards) while it is in a somewhat fluid-like condition as it is being formed,
and prior to
application of printing or magnetic coding materials. Step 84 may also be
effected by applying
and adhering the resonators to the document after the base material has been
fully formed,
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either before or after any printing, magnetic material, or other non-resonant
information-
bearing materials have been applied to the documents. After completion of step
84, the
document has been "written" by providing resonators at information-bearing
predetermined
spatial locations.
The reading steps 86 and 88 of Figure 11 may be performed using a reader
such as that described below with respect to Figure 13. In step 86, the
locations of resonators
in a document are determined. This may include a discriminating step, in which
the
characteristics of each resonator are determined to determine whether it is
genuine or to
discem further information, e.g. from the frequency of the resonator. In step
88, the coding
system which should apply to the document (if it is genuine and was properly
encoded) is used
to decode the information present in the document, if any, under the coding
system based on
the resonator locations determined in step 88.
Because it may be difficult or expensive to control the location at which
resonators are disposed in perfornvng step 84 of the method of Figure 11, in
such
circumstances the methods of Figure 12 may be preferred. In step 90,
resonators are fabricated
to provide a supply of resonators. In step 92, resonators are disposed in the
document at
random or uncontrolled locations. Step 92 may be effected during or after
formation of the
document base material, and before or after application of other information-
bearing materials
such as printing or magnetic materials. In step 94, the locations of the
randomly-disposed
resonators in the document are determined, such as by passing it through the
reader of Figure
13. In step 95, the information which is desired to be encoded in the document
(i.e. the
informa.tion which is to be represented by the resonator location) is
determined. In step 96, this
determined information is attributed to the spatial locations of the
resonators which were
deterniined in step 94.
Step 96 may be effected in several ways; one such way is illustrated in Figure
12B, and another is illustrated in Figure 12C. Each of these figures includes
the reading steps
which are appropriate to the particular information attribution method
illustrated.
In Figure 12B, the information attribution step 96B is to store data which
relates the resonator locations in the document to the information which is to
be attributed to
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the document. This may be done, for instance, in a digital memory which
comprises the reader
or which receives information from the reader. Such data may be organized as a
lookup table.
The associated document reading process first is to determine in step 98 the
locations of
resonators in a document to be read. Then in step 98 the stored data is
examined for data
representing the determined locations, and if such location data is found, the
associated
information is extracted from the stored data to decode the document. In a
simple example,
where the only information of interest is genuineness, the stored data may
merely consist of the
locations of resonators in each genuine document created using the writing
steps. During the
reading process, if a data entry is found for such locations, the document is
detemiined to be
genuine or authentic; if not, it is determined to be a forgery or non-
authentic. The method of
Figure 12B requires that the reader contains or has access to the stored data
generated during
the writing process.
The method of Figure 12C may be preferred when it is desired to output the
information obtained from the document by the reader in a particular format,
without the
necessity of storing location and infocmation data for each genuine document
(as is done in
step 96B). Thus, in step 96C, a translation code is generated. The translation
code is an
algorithm or data for use in a predetermined algorithm which, when applied to
the location
information of a document, provides in a predetermined format the information
desired to be
attributed to the document. The translation code is thus unique for each
different set of
document resonator locations and each different piece of formatted information
to be attributed
to a document. In step 102, the translation code is stored to complete the
writing process. In
step 104, where the reading process commences, the resonator locations in a
document to be
read are determined. In step 106, the stored translation code is read. In step
108, the
information in the document (if any) is determined by applying the translation
code to the
determined resonator locations to decode the infon:nation.
An example illustrating the differences between the methods of Figures 12B
and 12C is credit card validation. A system may be provided including readers
at a large
number of disparate locations, such as merchant facilities, each of which
desires the capability
to determine if a card presented is a genuine card. The validation method
might be to present
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CA 02615013 2007-12-06
information to the merchant in a format which can be compared with that
printed on the card -
for instance, card number and expiration date in arabic numerals, cardholder
name in English
characters, and the like. In the method of Figure 12B the merchant, upon
reading the resonator
location of a card, would require access to the database comprising stored
data for all valid
credit cards in order to look up the location information from the presented
card and obtain
the formatted attributed information. Such a large amount of inforrnation may
be impractical
to store in a merchant's reader, and accordingly resonator location
information and decoded
information would have to be interchanged between the merchant used and a
large central
database. In the method of Figure 12C, the translation code storing step 102
may be effected
by storing the code on the card itself. While the translation code might be
stored in resonators
disposed in the card, difficulties in placing resonators at predetermined
locations may be
avoided by storing the translation code in another format and medium, such as
by printing, bar
coding, or magnetic encoding. Each merchant reader need only be provided with
a means for
applying a translation code to the detemuned resonator location data (and
perhaps also means
for automatically reading the translation code) in order to decode the
resonator information and
present it to the merchant in the desired format. This can be done
autonomously by the
merchant's reader, without any access to a central database.
Figure 10 illustrates a translation code associated with the document 74. The
translation code is disposed in an area 76 within the document; this area may
be an integral part
of the document itself or it may comprise a label or the like which is
generated and applied to
the document 74. The translation code may be encoded in alphanumeric
characters 76a, bar
code symbols 76b, a magnetic stripe 76c, radio frequency responsive articles
76d, or other
formats. Such formats may be used individually, or a combination of them may
be used.
Figure 13 is a schematic illustration of a document reader 110 which may be
used to read documents such as that shown in Figure 10 by methods such as
those shown in
Figures 11 and 12. The reader components are contained within a housing 111
which includes
an entrance 112 for receiving a document to be read, and conveying means 116
for conveying
the document along a path P from entrance 112 to exit 114. A radio frequency
source 122 is
coupled to a resonant iris aperture 120 which is disposed adjacent the path P.
At least one, and
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.~..,... ,
preferably a plurality, of such resonant irises 120 are included. When a
plurality of irises 120 is
used, the resonant frequencies thereof may be the same or different. An RF
detector 124 such
as an envelope detector is disposed so as to detect the radio frequency energy
emitted by
source 122 as preselected by iris 120. When a dipole taggant covers the
aperture of'nis 120 as
the taggant-containing document is moved along the path P, it creates a low
impedance, which
may be near a short circuit, at the aperture. This condition creates a large
reflection of the
illuminating RF energy and greatly reduces the RF voltage in the aperture
while the energy
remains constant. This condition may be detected by placing the detector on
the source side of
the path P (as shown in Figure 13) and detecting the energy reflected from the
iris, or by
placing the detector on the opposite side of the path P from the source 122
and detecting the
energy transmitted through iris 120. The operation of the reader 110 is
controlled, and the
information extracted from a document is processed, by a controller-processor
126. This
functional block may be implemented by a variety of microprocessor-based
systems, the
construction of which is believed to be a straightforward matter for those
skilled in that art. A
suitable system may include a microprocessor, a memory containing a stored
program for
operating the system in accordance with this invention, and suitable interface
devices to
interface the microprocessor with other functional blocks shown in Figure 13.
The longitudinal position of a resonator in a document being scanned may be
determined by correlating the maximum low-impedance effect detected by RF
detector 124
with the position of the document along the path P. For instance, in the
embodiment shown in
Figure 13, an edge detector 118 is provided which outputs a signal to
controller/processor 126
when a document edge passes the edge detector 118. Such an edge detector may
for instance
be made from a light source and photodetector arranged so that a light path
from the source to
the photodetector is occluded by a document being conveyed along path P. The
controller/processor 126 niay detemnine the document edge position with
respect to edge
detector 118 at any time by integrating the document speed along path P from
an edge
detection event to a time of interest. The document speed may be detenmined by
the
controller/processor either in response to a speed signal transmitted from the
conveying means
116 to the controller/processor 126, or from control signals transmitted to
the conveying
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means 116 if its speed is controlled by the controller/processors 126. The
position of the
document edge with respect to iris 120 may be computed in accordance with the
iris-edge
detector separation.
As has been indicated, the edge detector 116 may be dispensed with-and other
means employed to establish a spatial frame of reference for determining the
position of
taggants in the document. Such other means include using RF detector 124 to
detect a "start"
taggant in the document, or using other types of detectors (such as optical
detectors) to detect
printing or other features which provide one or more spatial reference points
on the document.
In the preferred embodiment of reader 110, each iris is fixed in position, and
thus is capable of reading one column of the document when it is inserted into
entrance 112
and conveyed with edge 74 leading. A plurality of irises 120 (with associated
sources 122 and
detectors 124) is thus preferably provided, each of which is laterally
disposed along path P so
as to be capable of reading one column of the document. Such an arrangement is
illustrated in
Figure 14, which is discussed later. However, it will be recognized that other
methods and
types of apparatus may be used to detect the spatial locations of taggants
over a two
dimensional area of the document. For instance, a single iris 120 may be moved
laterally back
and forth to sweep or scan each row as the document is advanced along path P,
or the
document may be maintained at a fixed position in reader 110, and a single
iris 120 moved both
laterally and longitudinally, over the entire surface of the document, thus
dispensing with the
need for document conveying means 114. While such readers would minimize the
RF
apparatus needed, it is believed that the mechanical complexities would render
them less
preferable than a reader such as is shown in Figure 13. On the other hand,
mechanical
complexities may be minimized by eliminating the need for relative movement
between the
document and the iiises 120, by providing one iris (with associated RF source
and detector) for
each grid element (i,j) where a taggant might be disposed in the document
coding system.
However, except for systems using only a small number of possible taggant
positions, the
expense and complexity of providing many RF systems is believed to render such
an approach
less preferable.
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CA 02615013 2007-12-06
. y ,
Once a spatial reference for the document in the reader 110 has been
established, the longitudinal positions of taggants 72 in the document can be
determined by
controller/processor 126 based on the times at which RF detector 124 detects
impedance
minima in iris 120, and the speed of movement of the document along path P.
In general, the surface of the document is mapped in software in
controller/processor 126 to grid or array coordinates (i,j). Each grid element
(ij) is assigned a
binaiy value (1 or 0) in accordance with whether an impedance minimum was
detected in the
document in a position corresponding to that grid element. The assignment of
data bits to grid
elements may be effected in a variety of ways. For instance, the times of
impedance minima
may be measured and compared with limits of time "windows" applicable to the
spatial
boundaries of the grid elements. Altennatively, a data storage device such a
latch may be
provided for each grid element and enabled for a predetermined time interval
corresponding to
the time interval when the grid element is over the iris; a comparator coupled
to the data
storage element may provide a logical output in accordance with whether the
iris impedance
crosses a threshold value, which logical value is stored in the data storage
element.
The reader 110 includes an output 128 for local output of information obtained
by reading a document; for instance, output 128 niay be an alphanumeric visual
display. The
reader 110 also includes an 1/0 port 130, such as a modeni, by which
information obtained by
reading a document may be transmitted to a remote location over communication
channel 132.
It will generally be preferable to output information obtained from the
document in a
predetermined and convenient format, rather than as a binary string or series
of binaiy words
comprising the raw data of whether or not a taggant is present in each grid
element. Thus, the
controller/processor 126 preferably includes means such as a data processing
algorithm for
performing the decoding steps 88, 100, or 108 of Figures 11, 12B, and 12C,
respectively. If
the method of Figure 12C is to be employed, the reader 110 preferably includes
a translation
code reader 134 for automatically reading the translation code of a document
and supplying the
translation code for use in performing step 108. A light source 144, such as
an LED, forms
part of an edge detector 118 along with a photodetector (which typically would
be disposed
above the path P and is not shown).
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Figure 14 shows a plan view of a document-interfacing surface which may be
used in a document reader such as that shown in Figure 13. While the reader
110 in Figure 13
is shown in block form, the plan view of Figure 14 corresponds to a view
downwardly from the
path P toward the iris 120, edge detector 118, and conveying means 116 shown
in Figure 13.
A plurality of feed rollers 142, driven by suitable means (not shown) such as
a motor, comprise
conveying means 116 and are disposed to convey a document along surface 140 in
contact
with or closely adjacent surface 140. Each such feed roller 142 may be
disposed adjacent a
cooperating driven or idling roller (above the path P and therefore not shown)
to define a nip
through which the document passes and is conveyed by rotation of the rollers
142. Other well-
known document-conveying techniques, such as belt systems, may be employed.
Disposed in
surface 140 are a pluraGty of RF apertures each provided with a resonant iris
aperture and
illuminated from below by an RF source, not shown. At least one such aperture
and iris is
provided for each column of the grid array (see Figure 10) which is defined in
the coding
system to be used. Preferably, and as shown in Figure 14, two irises are
provided for each
column: a vertically polarized aperture 146 and iris 148, and a horizontally
polarized aperture
150 and iris 152. Use of both horizontally and vertically polarized components
is preferable
whenever the orientation of taggants in the document is variable. For
instance, as shown in
Figure 10, the dipoles 72 are disposed at a variety of angles ranging from 0
to 360 . This may
result from either random disposition of dipoles or from purposeful
disposition at
predetennined angles. The detection of a dipole is generally a cosine function
of the dipole
angle with respect to the polarization axis of the iris. Thus, the dipole 72a
of Figure 10 would
have a maximum short circuiting effect when adjacent iris 148 and a minimum
impedance effect
when adjacent iris 152; the converse would be true for dipole 72c. Thus, the
orientation of
dipole taggants in the document may be used in addition to the grid location
to encode
information in the document, and the use of both horizontally and vertically
polarized antenna
elements enables deterrnination of the angle of orientation of the dipole to
decode such
infonnation. Where the dipole orientation is not used to encode information,
the use of both
horizontally and vertically polarized antenna elements ensures that a
detectable impedance
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CA 02615013 2007-12-06
change occurs in at least one of the irises, so that dipoles may reliably be
detected regardless of
their orientation.
A modification of the invention which is particularly desirable for use with
credit cards and similar documents is illustrated in Figures 15-17. Figure 15
shows the "back"
side of a card 172 such as a credit card, and Figure 15A illustrates a side
view of the card
which is, for convenience, exaggerated in thickness. The card is generally of
conventional
construction and includes a pair of inner plastic layers 160, 162 which may
for instance be
made of .012" thick opaque PVC sheet and a pair of outer plastic layers 164,
166 which may
for instance be made of .0005" thick transparent PVC sheet. Printing may be
disposed
between the inner and outer layers, and the outer layers serve to protect the
printing while
maintaining it visible. Card 172 may have conventional data storage means such
as magnetic
stripe 168.
Card 172 differs from conventional cards in that it includes a plurality of
resonant articles which encode informa.tion by their positions in the card.
Preferred resonant
articles are thin dipoles 170 of the sort which have been previously
describeri, i.e. metal or
metallized fibers. The resonant articles may also comprise metal or conductive
structures
which are disposed on a nonconductive substrate, as described below with
respect to Figure
18. Dipoles 170 may be disposed at any location in the card, but a preferred
location is
between the inner layers 160, 162; they may be placed there during manufacture
prior to
lamination of the inner layers, either by being disposed at predetenmined
locations to encode
particular information, or by being randomly disposed. They may be generally
uniformly
distributed over the card area, or as shown be generally confined to a
predeternrined area. A
particularly preferred location for data-encoding resonators 170 is the area
adjacent the
magnetic stripe 168, as shown in Figures 15 and 16. This location is preferred
for several
reasons, including making it difficult to attempt to duplicate a card but
primarily so that the
card may be read both magnetically and at radio frequency by "swipe"-type
credit card readers.
Such a card reader which can read both types of encoded data is illustrated in
schematic form
in Figure 16.
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_ + .
The reader includes means for reading both magnetic data included in a
magnetic stripe upon the card, and for reading RF data from the card. The
apparatus may be
built as a swipe-type reader, in which a person grasps the card along one
edge, places the
opposite edge in a slot or reading track in a card reader, and moves the card
manuali'y along the
slot past stationary reading devices disposed in the slot walls. The slot or
reading track 182 in
Figure 17 includes a pair of side walls 184 and 186, and a magnetic detector
190, such as a
magnetic stripe read head, is disposed along one of the walls so as to be
adjacent the magnetic
stripe when a card is "swiped" through the slot. The output of the magnetic
detector 190 is
provided to a controller/processor 188, which can process received data,
generate outputs on a
local output device 202 such as a visual display, and communicate with other
devices if desired
by means of an UO port 200. In addition to these nonmal functions of a
magnetic card reader,
the apparatus of Figure 16 also includes RF reading apparatus. The preferred
apparatus shown
in Figure 16, includes an RF source 192 which feeds a radiating aperture 196
through a
circulator 194. The aperture 196 is disposed in a wall 186 of the slot 182. RF
energy
propagates from source 192 through circulator 194, through antenna aperture
196, and
through the space in the slot to the opposite wall 184 of the slot. The slot
wall 184 reflects
energy back to antenna aperture 196, where an appreciable amount of the energy
is collected
and propagates back through circulator 194 to RF detector 198, which may be a
diode
functioning as an envelope detector. The apparatus functions as a transmission
line with a
standing wave.
The RF reading apparatus is mechanically positioned to peak the power at the
detector 198 when there is nothing in the slot 182. This can be effected by
making the gap
between detector 198 and opposing wall 184 1/4 wavelength at the frequency of
operation,
which may be on the order of 25 GHz. When a card containing thin dipoles is
passed through
the slot 182, the dipoles nearly short the aperture and shift by approximately
90 the phase of
the standing wave in the transmission line. The resultant drop in energy is
detected by RF
detector 198, and the detected signal is provided to controller/proce,ssor
188. The spatial
positions along the card where such drops in energy occur can be very
precisely measured
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CA 02615013 2007-12-06
because the detection system detects the nulling of the standing wave in the
RF transmission
line. This pennits very dense packing of RF articles and a large data
capacity.
The combination of magnetic data and RF data in a single card which can be
read by a single reader provides several advantages. First, the magnetic
stripe may be used to
store translation code data, for use in the encoding systems as previously
described. Second,
magnetic stripes in common use in credit cards contain clocking data which can
be used to
establish an appropriate spatial frame of reference for the RF measurement.
While the reader
of Figure 13 includes document conveying means which permit controlling or
measuring the
speed of the document as it is moved past the RF detectors, in order to
corollate spatial
position with detected RF data, a swipe-type card reader lacks document
conveying means. In
order to account for variations in the speed with which a card is moved
through the slot, with
the apparatus of Figure 16 the detected RF signals may be time correlated with
detected
magnetic signals including magnetic clocking signals. These can be used to
establish a spatial
framework for the encoded RF information.
Figure 17 is a graph illustrating various signals which may occur in the
reader
of Figure 16. The horizontal axis is positioned along a card being read, and
the vertical axis is
signal amplitude. Waveform 214 illustrates a clocking signal which may be
stored in the
magnetic stripe. Waveform 212 illustrates an RF signal provided by detector
198, including
drops in energy caused by the presence of three dipoles at different spatial
locations along the
card. Such a signal may result from dipole placement as illustrated on the
left side of the card
of Figure 15, in which the dipoles are placed so as to be separately
distinguishable. When
dipoles instead are randomly distributed, as for instance is shown in the
right side of the card of
Figure 15, then the multiple reflections created by plural, randomly oriented
dipoles in the
antenna field, result in a smoother RF amplitude versus position waveform as
illustrated in
waveform 210 of Figure 18. The amplitude versus position characteristics of
this waveform
may be used to uniquely identify the card. Moreover, information may be
attributed to the data
obtained by sampling the detected RF amplitude at predetennined spatial
locations and
attributing information to the detected amplitudes.
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~ . .
While reader apparatus is illustra.ted in Figure 16 with a single RF detection
system and a single magnetic detection system, it will be understood that a
plurality of RF
systems can be included, including systems which are differently polarized,
operate at different
frequencies, and the like. A plurality of magnetic detectors may be provided,
so that the card is
never being moved past an RF head without magnetic data being simultaneously
obtained so
as to permit position determination. Finally, it will be understood that the
magnetic and RF
heads may be located along either slot wall at any position which is suitable
for carrying out the
necessary measurements.
Figure 18 illustrates a type of target which can be advantageously used in
many
RF/AID applications. The target consists of a substrate 220 upon which a
plurality of resonant
structures are disposed. A preferred form of target substrate is a thin
plastic sheet, for instance,
.0005" thick polyester or PVC $lm. The RF responsive structures which are
disposed upon the
substrate are preferably metal structures, for instance, made of aluminum.
Figure 19 shows a
substrate 220 upon which several types of RF responsive metal structures are
disposed. Thin
dipoles can be disposed on the substrate; dipoles 224 and 226 shown are
resonant at different
frequencies because of their different lengths. More complicated structures
can advantageously
be used; these include structures 222 having the shape of letters, numbers, or
other characters
or symbols. Such structures, in addition to conveying information which can be
determined by
visual inspection, also have radio frequency resonances associated with the
size and shape of
the character. Thin films with aluminumized characters, such as shown in
Figure 19, are in use
in U.S. currency as an anti-counterfeiting measure and such structures per se
are not a part of
this invention. However, in accordance with the invention, such structures can
be read at radio
frequency and authenticated by correlating the actual radio frequency response
with the
expected response for such a predetetmined character set. When the character
set is
predetenmined, as with present wtrently, then a reader can be provided in
advance with
information as to the expected RF characteristics of the character set. When
the information to
be included in the target is not uniform and predetermined, then the resonant
structures can be
read optically and at radio frequency, and the results correlated in order to
authenticate the
target. Other structures which are sized and shaped to provide specific RF
resonant responses
-27-
CA 02615013 2007-12-06
. ~ .
can be disposed upon the substrate 220. For instance, the metallizations 228
provide both
resonant frequency and phase information.
A given target may contain one or several different types of RF responsive
structures, as appropriate to the application. Depending on the type of
resonators iricluded in
the target and the information-containing aspects of the resonators, they may
be read by a wide
variety of reader devices, including a far-field frequency-responsive reader,
or a near-field
reader such as is shown in Figure 13 or 17. The target of Figure 19 may thus
function as the
target 12 of Figure 2, or the document of Figure 10, or may be laminated
between the layers of
the card of Figure 15 to provide the RF responsive data component.
The target of Figure 19 may be manufactured by a variety of techniques.
These include coating a plastic film substrate with a thin layer (e.g. 300
Angstroms) of metal by
vapor deposition or the like; areas where metal is to remain in a finished
target are protected by
a printed resist or an exposed and developed photo resist, and the remaining
metal areas are
removed by chemical etching.
Figure 19 is a block diagram illustrating the general function of a preferred
radio frequency reading system in accordance with the invention. A radio
frequency source
240 is coupled to a transmission line 242 and generates radio frequency
signals which are
conveyed along the transmission line. Transnlission line 242 includes at least
one radiating
aperture 246 from which radio frequency signals are radiated into space. A
radio frequency
detector 248 is disposed so as to receive radio frequency signals which are
affected by the
presence of radio frequency responsive articles in the near field region of
radiating aperture
246. Radio frequency reading devices may be built with RF detector 248 in a
variety of
different physical positions which will fulfill the function of providing
output signals 249 having
signal components which are responsive to the radio frequency conditions in
the near field
region of radiating aperture 246. Detection of signals which are responsive to
radio frequency
conditions in the near field region enable the positions and other
characteristics of radio
frequency responsive articles such as resonators to be determined. The readers
illustrated in
Figures 13, 14 and 16 include embodiments of the general system shown in
Figure 19.
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CA 02615013 2007-12-06
~
Figure 20 is an illustration of a preferred microwave reading system having
the
functions illustrated generally in Figure 19 and suitable for use in the
readers of Figures 13, 14
and 16. In Figure 20, a radio frequency source such as a Gunn diode supplies
signals to a
waveguide 250. The signals are directed from waveguide 250 to waveguide 252 by
a fenite
circulator 262. Waveguide 252 terminates in an aperture 254 where signals are
radiated into a
near field region. The aperture indicated in Figure 20 is aperture 254 in an
iris 256. Use of an
iris 256 is often desirable for a variety of reasons, but it need not be
provided and the
waveguide 252 may simply terminate to provide a radiating aperture. Signal
returning to the
apparatus from the aperture through waveguide 252 are directed by circulator
262 through
waveguide 258 to a detector diode where they are detected. Circulator 262 thus
acts as a
duplexer enabling both the source and detector to be coupled to an aperture.
Rather than providing a conventional antenna to direct the radio frequency
radiation from the aperture to a beam in the far field, in accordance with the
present invention
the apparatus may be used without such an antenna to read targets in the near
field of the
aperture. Thus, a target guide may be provided to position and/or guide a
target for movement
adjacent the aperture so that the radio frequency response characteristics of
the target can be
observed in small areas of the target, and thus the detected radio frequency
response
characteristics can be correlated with the position in the target having those
characteristics, to
read identifying data from the target. The signal path through waveguide 250,
circulator 262,
and waveguide 252 corresponds to and embodies the transmission line 242 of
Figure 19. The
signal path in Figure 20 from the aperture 254 to the detector diode is not
indicated as a
separate functional block in the general diagram of Figure 19.
Figure 21 shows another application of the invention. Figure 21 illustrates a
microfloppy diskette of the type typically used as a removable read/write
medium in computer
applications. Mounted for rotation within the shell 272 of diskette 270 is a
disk 276 having a
thin layer of magnetic material which is disposed on the surface of a plastic
substrate "cookie".
In accordance with the invention, radio frequency responsive articles such as
thin dipoles 278
may be incorporated on or in the disk 276 to provide identifying information.
The diskette of
Figure 21 is in many respects similar to the card of Figure 15, and may be
tagged with
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CA 02615013 2007-12-06
identifying articles in the same manner. Thus, the radio frequency responsive
articles may
include thin dipoles in the nature of "chaff' or metallizations on the plastic
disk substrate itself;
they may be randomly deposited or disposed in predetermined spatial locations;
and the
resonant frequencies of the articles, in addition to their spatial positions,
may be used to
provide identification data. The articles may be disposed in the magnetic
material itself as well
as on the disk. Identifying data which may be provided in such a diskette 270
includes security
data for purposes of preventing unauthorized copying of programs or data
stored in the
magnetic material on the diskette; for instance, radio frequency readable data
may be used in an
encryption algorithm which is used to encrypt and decrypt the information
stored magnetically
on the diskette. To use such a diskette, a drive having both radio frequency
and magnetic read
heads is required; such a drive can be made generally similar to those
illustrated in Figures 14
and 16 with mechanical and other variations as necessary to suit the
application. Application of
the invention to computer diskettes is facilitated by the fact that diskette
drives already include
means for moving the diskette past a reading head. It is believed to be a
relatively simple
matter to provide a diskette drive with the additional capacity to read radio
frequency encoded
information.
While particular embodiments of the invention have been described, variations
will no
doubt occur to those skilled in the art without departing from the spirit and
scope of the
invention.
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