U.S. patent number RE37,956 [Application Number 08/916,572] was granted by the patent office on 2003-01-07 for radio frequency identification tag and method.
This patent grant is currently assigned to C. W. Over Solutions, Inc.. Invention is credited to Michael J. Blama.
United States Patent |
RE37,956 |
Blama |
January 7, 2003 |
Radio frequency identification tag and method
Abstract
A method of and apparatus for identifying an item to or with
which a radio frequency identification tag is attached or
associated is provided. The tag is made of a nonconductive material
to have a flat surface on which a plurality of circuits are
pressed, stamped, etched or otherwise positioned. Each circuit has
a capacitance and an inductance. The capacitance is formed from the
capacitive value of a single capacitor. The inductance is formed
from the inductive value of a single inductor coil having two
conductive ends each connected to the capacitor. Each tag is
associated with a binary number established from a pattern of
binary ones and zeros which depend on the resonance or nonresonance
of each circuit, respectively and the circuits position with
respect to the binary table. The binary number may be converted to
a decimal number using the binary table for conversion.
Inventors: |
Blama; Michael J. (Baltimore,
MD) |
Assignee: |
C. W. Over Solutions, Inc.
(Aberdeen, MD)
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Family
ID: |
22657479 |
Appl.
No.: |
08/916,572 |
Filed: |
August 22, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
179664 |
Jan 11, 1994 |
05444223 |
Aug 22, 1995 |
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Current U.S.
Class: |
235/435; 235/487;
235/492; 361/765; 361/766; 361/821 |
Current CPC
Class: |
G06K
19/0672 (20130101) |
Current International
Class: |
G06K
19/067 (20060101); G06K 007/00 () |
Field of
Search: |
;235/435,492,494,487
;333/175,185,219 ;343/895 ;361/301.2,763,765,782,766,821 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2-195491 |
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Aug 1990 |
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JP |
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WO/83 04448 |
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Dec 1983 |
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WO |
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Primary Examiner: Frech; Karl D.
Attorney, Agent or Firm: Donner, Esq.; Irah H. Hale and Dorr
LLP
Claims
I claim:
1. A tag which uses radio frequency waves transmitted from a
scanning device in order to identify an item to which said tag is
attached or with which said tag is associated comprising: an
insulating layer having a top surface, a bottom surface, and side
surfaces; thin conductive metallic means adjacent either said top
surface or said bottom surface of said tag for forming a plurality
of circuits, wherein each circuit of said plurality of circuits has
a unique resonant frequency formed by one-to-one correspondence of
a capacitance made up of a single capacitor and an inductance made
up of a single inductor coil having two conductive ends with a
first conductive end being connected to said single capacitor in
order for said inductor coil to wind around said capacitor to end
in a second conductive end which crosses said single inductor coil
in a layer above said inductor coil so that said second conductive
end is above said inductor coil and separated from said inductor
coil by an insulated layer in order for said second conductive end
to connect to said capacitor to close each said circuit without
shorting out the circuit; and wherein said tag is associated with a
binary number established by a pattern of ones and zeros depending
on each circuits' resonance or nonresonance, respectively, and each
circuits' position on said tag with respect to a binary table.
2. The tag as in claim 1 wherein said capacitor is a dielectric
dot.
3. The tag as in claim 2 wherein said inductor coil is made from a
conductive material.
4. The tag as in claim 3 wherein said conductive ends of said
inductor coil are connected to said capacitor in such a way so as
to be in adjacent layers separated by an insulating material.
5. The tag as in claim 4 wherein said plurality of circuits are
located on a surface of said tag at spaced intervals of a distance
far enough apart so that adjacent circuits do not electronically
interfere with each other.
6. The tag as in claim 5 wherein said tag associates a bit of
information with each said circuit on said tag's surface.
7. The tag as in claim 6 wherein said tag is made of a
nonconductive material.
8. The tag as in claim 7 wherein said nonconductive material of
said tag is paper.
9. The tag as in claim 8 wherein said paper tag is disposable.
10. The tag as in claim 7 wherein said nonconductive material is
plastic.
11. The tag as in claim 10 wherein said plastic tag is
reusable.
12. The tag as in claim 7 wherein said pattern of binary ones and
zeros is established by varying numbers and positions of circuits
being left blank.
13. The tag as in claim 12 wherein said blank position on said tag
was created by not printing or etching a circuit in a position
where a circuit could have been printed or etched respectively.
14. The tag as in claim 13 wherein said pattern of binary ones and
zeros is established by disabling a circuit on said tag.
15. The tag as in claim 7 wherein said nonconductive material of
said tag is glass.
16. The tag as in claim 15 wherein said glass is located in a
window of an automobile or other vehicle.
17. A method of identifying an item to or with which a radio
frequency identification tag is attached or associated,
respectively, comprising the method steps of: providing said radio
frequency identification tag having a top surface, a bottom surface
and side surfaces with a plurality of circuits each having a
capacitance and an inductance both located on either said top
surface or said bottom surface of said tag to form a one-to-one
correspondence and to have a resonating frequency wherein said
capacitance comprises a single capacitor and said inductance
comprises a single inductor coil such that said inductor coil has
two conductive ends with a first conductive end connected to said
capacitor in order for said inductor coil to wind around said
capacitor and end in a second conductive end which crosses said
single inductor coil in a layer above said inductor coil so that
said second conductive end is above said inductor coil and
separated from said inductor coil by an insulated layer in order
for said second conductive end to connect to said capacitor to
close each said circuit without shorting out the circuit; using a
scanning device to interrogate said circuits by means of said
scanner transmitting varying radio frequency waves at which said
circuits may resonate; and interrogating said circuits to establish
a pattern of binary ones and zeros wherein a binary one is given to
a resonant circuit and a binary zero a nonresonant circuit.
18. The method as in claim 17 wherein said step of providing a
radio frequency identification tag with a plurality of circuits is
accomplished by etching said surface of said tag which has been
coated with a layer of conductive material.
19. The method as in claim 17 wherein said step of providing a
radio frequency identification tag with a plurality of circuits is
accomplished by printing onto or pressing into said surface of said
tag a conductive material..Iadd.
20. A resonant circuit including a single capacitor, a single
inductor coil electrically connected to said single capacitor, and
an insulating layer separating from each other portions of at least
one of said single capacitor and said single inductor coil that
cross over each other, and said single capacitor and said single
inductor disposed on a same surface of a
substrate..Iaddend..Iadd.
21. A resonant circuit as in claim 20, wherein said resonant
circuit is tuned by at least one of changing a mass of the single
capacitor and changing a length of the single inductor
coil..Iaddend..Iadd.
22. A resonant circuit as in claim 20, wherein said resonant
circuit is associated with a three-state system established by
resonating at a high quality level, resonating at a low quality
level, or not resonating..Iaddend..Iadd.
23. A resonant circuit as in claim 20, wherein said single inductor
coil includes first and second ends, and each of said first and
second ends are connected to said capacitor..Iaddend..Iadd.
24. A resonant circuit as in claim 20, wherein said single inductor
coil is of a first width substantially narrower than a second width
of said capacitor..Iaddend..Iadd.
25. A resonant circuit as in claim 24, wherein said single inductor
coil is of a first length substantially longer than a second length
of said capacitor..Iaddend..Iadd.
26. A resonant circuit as in claim 20, wherein said single inductor
coil is of a first length substantially longer than a second length
of said single capacitor..Iaddend..Iadd.
27. A resonant circuit having two opposing sides including a single
capacitor, and a single inductor coil electrically connected to
said single capacitor, and said capacitor and said single inductor
coil are located on the same side of a resonance tag and disposed
on a common surface of a substrate, wherein the substrate is
adjacent to one of said two opposing sides of said resonant
circuit..Iaddend..Iadd.
28. A resonant circuit as in claim 27, wherein said resonant
circuit is tuned by at least one of changing a mass of the single
capacitor and changing a length of the single inductor
coil..Iaddend..Iadd.
29. A resonant circuit as in claim 27, wherein said resonant
circuit is associated with a three-state system established by
resonating at a high quality level, resonating at a low quality
level, or not resonating..Iaddend..Iadd.
30. A resonant circuit as in claim 27, wherein said single inductor
coil includes first and second ends, and each of said first and
second ends are connected to said single
capacitor..Iaddend..Iadd.
31. A resonant circuit as in claim 27, wherein said single inductor
coil is of a first width substantially narrower than a second width
of said single capacitor..Iaddend..Iadd.
32. A resonant circuit as in claim 31, wherein said single inductor
coil is of a first length substantially longer than a second length
of said single capacitor..Iaddend..Iadd.
33. A resonant circuit as in claim 27, wherein said single inductor
coil is of a first length substantially longer than a second length
of said single capacitor..Iaddend..Iadd.
34. A resonant circuit which resonates radio frequency waves
transmitted from a scanning device and having a resonant frequency
associated therewith, comprising: a first insulating layer having a
top surface and a bottom surface; a capacitance and an inductance
having first and second ends and formed on one of the top surface
and the bottom surface of said first insulating layer, the first
and second ends of the inductance connected to the capacitance, and
a first portion of the first end traversing a second portion of the
inductance; and a second insulating layer disposed between and
separating the first portion of the first end and the second
portion of the inductance, thereby electrically closing without
shorting out said resonant circuit and while the capacitance and
the inductance formed on the one of the top and bottom surfaces of
said first insulating layer..Iaddend..Iadd.
35. A method of producing or manufacturing one or more resonant
circuits disposed on a substrate of a radio frequency
identification tag, comprising sequential, non-sequential or
independent steps of: disposing a single capacitor on the
substrate; disposing a single inductor coil having first and second
ends on the substrate; disposing an insulating layer between
portions of the single capacitor and the single inductor coil that
cross over each other, thereby separating the portions of the
single capacitor and the single inductor coil that cross over each
other; and electrically connecting the first and second ends of the
inductor coil to the single capacitor with the insulating layer
disposed between the portions, thereby electrically closing the one
or more resonant circuits without shorting out
same..Iaddend..Iadd.
36. The method as in claim 35, wherein at least one of said
disposing steps is accomplished by etching the substrate of the
radio frequency identification tag which has been coated with a
layer of conductive material..Iaddend..Iadd.
37. The method as in claim 35, wherein at least one of said
disposing steps is accomplished by printing onto or pressing into
the substrate of the radio frequency identification tag a
conductive material..Iaddend..Iadd.
38. A method of producing or manufacturing one or more resonant
circuits including a single capacitor and a single inductor coil
having first and second ends and each disposed on a same side of a
substrate of a radio frequency identification tag, comprising
sequential, non-sequential or independent steps of: disposing an
insulating layer between portions of the single capacitor and the
single inductor coil that cross over each other, thereby separating
the portions of the single capacitor and the single inductor coil
that cross over each other; and electrically connecting the first
and second ends of the inductor coil to the single capacitor with
the insulating layer disposed between the portions, thereby
electrically closing the one or more resonant circuits without
shorting out same..Iaddend..Iadd.
39. The method as in claim 38, wherein at least one of said
disposing steps is accomplished by etching the substrate of the
radio frequency identification tag which has been coated with a
layer of conductive material..Iaddend..Iadd.
40. The method as in claim 38, wherein at least one of said
disposing steps is accomplished by printing onto or pressing into
the substrate of the radio frequency identification tag a
conductive material..Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates generally to electronic items
identification systems and more particularly, to a radio frequency
(RF) identification tag and method for identifying an item to or
with which the tag is attached or associated, respectively, wherein
each tag includes a plurality of circuits having a capacitance made
up of a single capacitor and an individual made up of a single
inductor coil which capacitor and inductor coil are in one-to-one
correspondence such that each capacitor and inductor coil pair have
a unique frequency at which the circuit resonates.
BACKGROUND OF THE INVENTION
Currently, electronic item identification systems are in widespread
use today to identify a variety of items. A first type of
electronic item identification system commonly used in industry is
one in which bar code labels are used to identify items. These
types of electronic item identification systems are typically used
by supermarkets, distributors, shipping services and clothing
retailers to scan the bar code labels for quick retrieval of an
item's price or other information.
The way conventional bar code identification systems work is as
follows. Bar codes labels are made up of a series of lines of
varying widths or thicknesses to establish a code which can be read
by a scanner. A bar code label is usually read by a laser scanner.
The data from the scanner is electronically fed to a receiver which
determines the identification code or number associated with the
bar code label. The identification code or number is then sent to a
central processing unit or computer where each code or number is
matched to data stored on a master list such as item price or other
information. The central processing unit or computer then
electronically sends the stored data associated with the
identification code or number to the cash register or other
tabulator to arrive at a final total or tabulated result.
Another system of electronic item identification uses radio
frequency (RF) identification tags to identify items. Radio
frequency (RF) identification tags can be used to identify a
variety of items to which the tags are attached or otherwise
associated. In particular, radio frequency (RF) identification tags
are currently used to identify passengers, luggage, library books,
inventory items and other articles. Radio frequency (RF)
identification tags will allow electronic identification of people
or objects, moving or stationary, at distances of several feet.
In recent years, radio frequency identification tags have been
manufactured using silicon chips. The silicon chips have been
revolutionary because in the area of the size of the head of a pin,
a silicon chip can hold a myriad of components and information. The
problem with silicon chip radio frequency item identification tags
is that silicon is very expensive and cannot be produced in the
quantities necessary in industries such as the airline industry to
make the tags feasible. Furthermore, the silicon chip
identification tags are disadvantageous in having a limited range
of approximately two feet and using a scanner that sends out only
one signal which the chip alters by means of a phase shift. It
would be desirable to develop a radio frequency identification tag
that could be manufactured in mass quantities on a less expensive
material than silicon such as paper or plastic and that could be
used without having to alter the circuits on the tags in any
way.
Other types of currently available radio frequency (RF)
identification tags have the disadvantage that only recognition and
surveillance functions can be performed. The radio frequency (RF)
identification cards presently available in these types of systems
do not to have the electronic properties necessary to allow for
interrogation and identification functions.
For example, U.S. Pat. No. 4,694,283 to Reeb and U.S. Pat. No.
4,910,499 to Benge et al. both teach electronic identification
systems which use multilayered radio frequency (RF) identification
tags. The tags taught by the Reeb and Benge et al. patents each
have conductive layers separated by a layer of di-electric material
in order to form a resonant circuit. However, the Reeb patent
teaches an electronic surveillance device and the Benge et al.
patent teaches an anti-theft device, both of which are only usable
for recognition and do not have the electronic properties necessary
to allow for identification.
This is because the recognition function requires only one
possibility, i.e., either resonant or not resonant. The
identification function requires that the resonant frequency of the
tag be read and then compared to another frequency to which it will
match to achieve identification. It would be desirable for a radio
frequency (RF) identification card to have the proper electronic
properties to allow both recognition and identification functions
to be performed with the card on an inexpensive material.
Some presently available radio frequency (RF) identification cards
operate on the principle of establishing a code through the use of
a pattern of binary numbers such as "ones" and "zeros". These type
of electronic item identification systems have the disadvantage
that the radio frequency (RF) identification tag includes a
circuitry for initially establishing a resonant circuit having a
first resonating frequency which tag is activated by changing the
resonating frequency of the resonant circuit to a second resonating
frequency.
For instance, U.S. Pat. No. 5,218,189 to Hutchinson discloses a
binary encoded multiple frequency RF identification tag and U.S.
Pat. No. 5,103,210 to Rode et al. discloses an
activatable/deactivatable security tag. The tags of both patents
are used for identifying an item to which the tag is attached or
with which the tag is associated. The tags both include an
inductance connected in parallel with a capacitance wherein the
capacitance is made up of a plurality of individual capacitors. The
Hutchinson patent teaches individual capacitors which each have a
predetermined different capacitance and which are connected in
series and the Rode et al. patent teaches two capacitance branches
which each have a predetermined different capacitance wherein the
individual capacitors of each branch are connected in series.
In other words, according to the teachings of the Hutchinson and
Rode et al. patents, the binary number generated from the circuit
needs to be detected by varying the circuit's total capacitance in
order to check for resonance at a predetermined frequency. It would
be desirable to develop an electronic item identification system
using a radio frequency (RF) identification tag wherein each
circuit on the tag has a constant inductance and capacitance and
thus the circuit itself does not have to be changed to check for
the resonating frequency.
The devices of the Hutchinson and Rode et al. patents short out
capacitors during interrogation and thus the circuit can never be
restored to its original frequency to be read over again. It would
be desirable to develop an electronic item identification system in
which the radio frequency (RF) identification tag can be read any
number of times while still generating the same binary number as
was read the first time and in this manner the tag can be
reused.
The Hutchinson and Rode et al. patents teach a device where the
binary number to be obtained from the tag must be predetermined.
This is because the device teaches the "dimpling" of capacitors
which to be accurate must be done with expensive, precision
equipment. It would be desirable to develop an electronic item
identification system in which a radio frequency (RF)
identification tag having numerous circuits made up of
capacitor/inductor coil pairs at evenly spaced intervals on the
surface of the tag so that the presence or absence of a circuit or
the circuit's functionability could be programmed at the point of
use with inexpensive equipment.
SUMMARY OF THE INVENTION
The present invention provides a radio frequency (RF)
identification tag for identifying an item attached to or
associated with the tag. The tag includes numerous circuits,
C.sub.1 through C.sub.N, each having a capacitance and an
inductance. The capacitance is formed by a single capacitor and the
inductance is formed by a single inductor coil. The inductor coil
is preferably wound around the capacitor to form a capacitor and
inductor coil pair each of which have a unique resonant frequency.
A scanner is used to transmit a frequency to the circuits. If any
of the circuits located on the tag are resonant at the frequency
transmitted, a binary number "1" is recorded for that circuit's
location. A circuit that is not resonant within the frequency range
of the transmitted signal is given a binary number "0" and that
circuit's location is recorded. Once all circuits from C.sub.1 to
C.sub.N have been scanned and assigned a binary "1" or "0", a
decimal number is calculated through the use of the binary
table.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIGS. 1(a) and 1(b) are perspective views of the radio frequency
(RF) identification tag of the present invention showing paper and
plastic tags, respectively, having numerous circuits, C.sub.1
through C.sub.N.
FIG. 2 is a top plan view of one the circuits, C.sub.1 through
C.sub.N, of the radio frequency (RF) identification tag.
FIG. 3 is a schematic of the one of the circuits of the radio
frequency (RF) identification tag.
FIGS. 4(a) and 4(b) are perspective views of a radio frequency (RF)
identification tag showing paper and plastic tags, respectively,
having unprinted circuits.
FIGS. 5(a) and 5(b) are perspective views of a radio frequency (RF)
identification tag showing paper and plastic tags, respectively
having disabled circuits.
FIG. 6 is an example of a binary table used to convert a binary
number of "1"'s and "0"'s to a decimal number.
FIGS. 7(a) and 7(b) and FIGS. 7(c) and 7(d) are perspective views
of paper and plastic radio frequency identification tags,
respectively, having down-sized circuits.
FIG. 8 is a schematic of a radio frequency identification tag and
scanner.
FIG. 9 shows an automobile having a radio frequency identification
tag on the front windshield.
DETAILED DESCRIPTION OF THE INVENTION
The drawing figures illustrate features of the radio frequency (RF)
identification tag 10 of the present invention which allows for
electronic identification of people or objects, either stationary
or moving, at distances of several feet. The identification tag 10
can be placed on merchandise, carried by people or animals, or even
placed in automobile windshields, and interrogated by a scanning
device or unit in order to establish an unique binary number for
identification purposes from which a decimal number can be
calculated using a binary table for conversion. The radio frequency
(RF) identification tag 10 is passive in that it needs no power
supply, but instead uses absorbed energy from the scanning
unit.
Referring to FIGS. 1(a) and 1(b), paper and plastic radio frequency
(RF) identification tags 10, respectively, having numerous
circuits, C.sub.1 through C.sub.N, is shown. Each of the numerous
circuits, C.sub.1 through C.sub.N, are located at spaced intervals
on the surface of the tag 10 at a distance far enough apart so that
there is no electronic interference between adjacent circuits. The
exact number of circuits, C1 through CN, on any individual tag 10
will vary depending on the tag's 10 application or use to determine
the number of "bits" of information needed to be stored on the tag
10 which in turn determines the physical size and configuration of
the tag 10 itself.
Even though FIGS. 1(a) and 1(b) show the circuits, C1 through CN,
as being arranged in a system of columns and rows, the physical
arrangement of the circuits, C1 through CN, on the tag is not
limiting to the invention. The circuits, C1 through CN, may be
positioned in any physical arrangement which allows the
identification tag 10 to function in a manner within the spirit and
scope of the invention.
The radio frequency (RF) identification tag 10 may range in size
from as large as a typical 6 inch by 9 inch business envelope for
practicality, although larger tags are certainly possible, to as
small as 1 square inch. In other words, the individual tag 10
having N circuits may be down-sized from 6 inches by 9 inches to a
tag 10 as small as 1 square inch still having N circuits, except
that each circuit itself is smaller in size, in order to hold more
circuits and bits of information in a smaller surface area.
Referring to FIGS. 7(a) and 7(b) and FIGS. 7(c) and 7(d), in order
to electronically down-size the paper and plastic identification
tags 10, respectively the frequency of each circuit may have to be
increased to a higher frequency range.
Referring to FIG. 2, a single circuit C representative of each
circuit, C.sub.1 through C.sub.N, from the radio frequency (RF)
identification tag 10 of the present invention is shown. The
circuit C has an inductance "i" and a capacitance "c". The
inductance "i" is preferably formed from the inductive value of a
single inductor coil 12 and the capacitance "c" is preferably
formed from the capacitive value of a single capacitor 14.
The inductor coil 12 has two conductive ends 16, 18 each of the
which are connected to the capacitor 14. The inductor coil 12 may
be either wound around the capacitor 14 as shown in FIG. 2 or not
wound around the capacitor 14 as is shown in the schematic in FIG.
3.
In the preferred embodiment of the present invention, the inductor
coil 12 is a made from wire, foil, conductive ink or other
conductive material which is etched, pressed, glued or printed onto
a non-metallic surface such as paper, plastic, glass etc. The
materials used for the inductor coil 12 and the identification tag
10 do not limit the invention nor does the method of attachment of
the coil 12 to the tag 10.
As shown in FIG. 2, in the preferred embodiment of the invention
one conductive end 18 of the inductor coil 12 is attached to the
capacitor 14 so as to be contained in a layer below the layer of
the main coil 20. The conductive end 16 is separated from contact
with the main coil 20 by means of an insulating material place
between the layers.
In the preferred embodiment of the present invention, the
capacitance "c" of each circuit, C.sub.1 through C.sub.N, is formed
from the capacitive value of a single capacitor 14. The capacitor
14 is preferably a small dot of dielectric material. The capacitor
14 may be formed by etching or trimming of the dielectric material
electronically, or with a laser to exact specifications from a
surface completely covered with dielectric material. Such
dielectric surfaces can be manufactured in advance and then
programmed to exact bit configurations upon demand.
Another method of forming the capacitor uses a machine, such as a
laser printer, to etch the circuit's inductor coils 12 onto a paper
or plastic surface that has been covered with a layer of dielectric
material. In the same printing process, the printer would etch the
capacitor 14. Although two separate methods of capacitor 14
formation have been described, it is understood that the type of
material used for the capacitor 14 or the method of forming the
capacitor 14 is not limiting to the invention and that any material
or method within the spirit and scope of the invention may be
used.
The theory of operation of each circuit, C.sub.1 through C.sub.N,
is the simple electronic law of resonance. When an inductor coil
and capacitor 14 are connected together, the resulting circuit C is
a "tank" circuit which becomes resonant at a particular frequency
f.sub.R. The frequency f.sub.R is determined by the mathematical
value of the inductor 12, i.e., the inductance "i" and the
mathematical value of the capacitor 14, i.e., the capacitance "c".
The resonance of a circuit, C.sub.1 through C.sub.N, can be
detected by an interrogating or scanning device 22.
Referring to FIG. 8, the interrogator or scanner 22 used is a
simple oscillator that generates and transmits or oscillate a
frequency. If any of the capacitor 14 and inductor coil 12
circuits, C.sub.1 through C.sub.N, are found resonant at the
particular frequency transmitted by the scanner, a "bit" of
information is recorded in the form of a binary number "1" being
located at a particular position on the tag 10. On the other hand,
if resonance is not detected, that "bit" of information is
interpreted as a binary number "0" being located at a particular
position on the tag 10. This process of transmitting a frequency to
check for resonance is repeated for as many times as there are
number N of circuits, C.sub.1 through C.sub.N, and the whole
process of interrogating a tag 10 having a plurality of circuits
takes place in a very short time period.
A single circuit may have either 2 or 3 states. In a two state
system, the circuit is simply resonant or nonresonant. This allows
only 2 possible numbers, i.e., either a binary "1" or "0",
respectively, at each circuit, C.sub.1 through C.sub.N. In a three
state system, the circuit is not simply resonant or nonresonant but
instead has high quality resonance, low quality resonance or is
nonresonant.
The radio frequency (RF) identification tag 10 of the present
invention will hold any number of "ganged" tuned circuits, C.sub.1
through C.sub.N, on its surface. Each circuit, C.sub.1 through
C.sub.N, will be tuned to a unique frequency for detection of
numerous N bits of information. In the preferred embodiment of the
present invention, each circuit may be tuned to a unique frequency
by either changing the length of the inductor coil 12 or changing
the mass or value of the capacitor 14. These bits of information
are assembled and converted into a decimal number by use of a
binary table as shown in the example in FIG. 6.
Referring to FIG. 6, the example given is for a two state system
where each of the circuits, C.sub.1 through C.sub.N, is either
resonant at the frequency transmitted by the scanner 22 and thus,
given a binary number "1" or nonresonant at the frequency
transmitted by the scanner 22 and thus, given the binary number
"0". The scanner interrogates all N circuits in the system to
determine the circuit's binary number. From the resulting pattern
of binary "1"'s and "0"'s established, a corresponding decimal
value may be arrived at through the use of a binary table for
conversion.
Because circuits, C.sub.1 through C.sub.N, may be either two state
or three state, there are two possible methods of interrogation. A
first possible method of interrogation is where each tuned circuit,
C.sub.1 through C.sub.N, will represent a bit of information,
either resonant, i.e., binary number "1", or not resonant, i.e.,
binary number "0". For instance, if there are to be 30 tuned
circuits, C.sub.1 through C.sub.30, positioned on the radio
frequency (RF) identification tag 10, 30 bits of information and 30
unique frequencies will be needed.
A second possible method of interrogation may be where each tuned
circuit, C.sub.1 through C.sub.N, will be interrogated for
resonance by interpreting high or low circuit "Q" which is the
quality factor of the resonant circuit or its degree of resonance.
This method would allow us 3 states or combinations, i.e., high
resonance, low resonance or nonresonant, thus reducing the number
of circuits and frequencies needed and the physical size of the
radio frequency (RF) identification tag 10.
There are several methods of producing a circuit. The circuit can
be etched or printed with conductive ink onto paper, plastic, glass
or any non-metallic surface. In the preferred embodiment of the
present invention, the circuits, C.sub.1 through C.sub.N, would be
printed onto a piece of paper such as airline bag tags. The use of
paper as the material for making the radio frequency (RF)
identification tag 10 would make it extremely inexpensive, easy to
manufacture in mass quantities and disposable.
Referring to FIGS. 4(a) and 4(b), one way of programming a
particular decimal number onto the paper or plastic tags,
respectively, would be to suppress printing of a "bit" of
information or circuit, C.sub.1 through C.sub.N. In other words, a
blank space would be left on the surface of the identification tag
10 where a circuit might otherwise have been printed or placed. The
scanner would not detect that "bit" of information and would thus,
interpret it as a binary "0".
Referring to FIGS. 5(a) and 5(b), another way to program the radio
frequency (RF) identification tag 10 of the present invention is to
mass produce paper or plastic tags with all circuits, C.sub.1
through C.sub.N, intact and disable the circuits needed to arrange
the bit pattern for the number being programmed. The disablement of
the circuit would preferably be accomplished by the disconnection
of the conductive end 18 of the inductor coil 12 from the capacitor
14 although other methods of disablement may be used.
In operation, the scanning unit 22 will transmit a first frequency
and wait for detection of resonance of one of the identification
tag's 10 associated circuits, C.sub.1 through C.sub.N. After a
sufficient time interval, the scanner will transmit or scan a
second frequency and so on. The scanner will repeat these steps
throughout all frequencies, depending on the number N of circuits,
C.sub.1 through C.sub.N, until all N circuits have been
interrogated. Then, for redundancy, the scanner may repeat all
scans again to insure that the active bits have been detected by
comparing them to the first scan results.
If the tap 10 is scanned for redundancy, after 2 of 3 successful
compares, the bit pattern is sent to a simple binary to decimal
conversion circuit for display or transmission to another device
such as a personal computer or PC, mainframe computer, or other
calculating or data storage device.
The present invention has been shown in the drawing figures and
described in detail in its preferred embodiment for the purposes of
illustration, however, variations and departures can be made
therefrom by one of ordinary skill in the art without departing
from the spirit and scope of the invention.
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