U.S. patent application number 11/463960 was filed with the patent office on 2006-12-28 for electronic devices and systems.
Invention is credited to Stuart Colin Littlechild, Graham Alexander Munro Murdoch.
Application Number | 20060290475 11/463960 |
Document ID | / |
Family ID | 27810050 |
Filed Date | 2006-12-28 |
United States Patent
Application |
20060290475 |
Kind Code |
A1 |
Murdoch; Graham Alexander Munro ;
et al. |
December 28, 2006 |
Electronic Devices and Systems
Abstract
A device having a switched impedance that can be switched
between a first state and a second state wherein, in the first
state, the device acts as a voltage multiplier and, in the second
state, the device acts as a rectifier.
Inventors: |
Murdoch; Graham Alexander
Munro; (Wollstonecraft, AU) ; Littlechild; Stuart
Colin; (Stanmore, AU) |
Correspondence
Address: |
Jenkens & Gilchrist, a Professional Corporation
Suite 3200
1445 Ross Avenue
Dallas
TX
75202
US
|
Family ID: |
27810050 |
Appl. No.: |
11/463960 |
Filed: |
August 11, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10525408 |
Apr 17, 2006 |
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PCT/AU03/01072 |
Aug 23, 2003 |
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11463960 |
Aug 11, 2006 |
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Current U.S.
Class: |
340/10.42 |
Current CPC
Class: |
G06K 19/0715 20130101;
G06K 19/0701 20130101; G06K 19/0712 20130101; G06K 19/0709
20130101; G06K 19/0723 20130101; G06K 7/10366 20130101; G06K
7/10009 20130101 |
Class at
Publication: |
340/010.42 |
International
Class: |
H04Q 5/22 20060101
H04Q005/22 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 22, 2002 |
AU |
2002950973 |
Claims
1. A device having a switched impedance that can be switched
between a first state and a second state wherein, in the first
state, the device acts as a voltage multiplier and, in the second
state, the device acts as a rectifier.
2. A device as claimed in claim 1 wherein the device includes
receiving means for receiving a signal, the device being configured
for selectively controlling the amount of current in the receiving
means by switching between the first state and the second
state.
3. A device as claimed in claim 2 wherein the current drawn through
the receiving means in the first state is greater than the current
drawn through the receiving means in the second state.
4. A device as claimed in claim 2 or 3 wherein the receiving means
is connected to one or more voltage input terminals of the
device.
5. A device as claimed in claim 2 wherein the receiving means
comprises a coil in an antenna circuit.
6. A device as claimed in claim 2 wherein the receiving means has a
impedance of substantially 200 ohms.
7. A device as claimed in claim 1 wherein a load is connected
between one or more output voltage terminals of the rectifier.
8. A device as claimed in claim 7 wherein the load comprises an
integrated circuit.
9. A device as claimed in claim 1 wherein the first state is an
operational state and the second state is a standby state.
10. A device as claimed in claim 1 wherein the switched impedance
comprises a switch in series with a capacitor.
11. A device as claimed in claim 10 wherein the switch of the
switched impedance comprises a MOSFET.
12. A device as claimed in claim 1 wherein the switched impedance
is connected between a first input terminal and a first output
terminal of the rectifier.
13. A device as claimed in claim 1 wherein the device includes a
series regulator for controlling an operating voltage by varying
resistance when the device is switched between the first and second
states.
14. A device as claimed in claim 13 wherein the device includes
receiving means in series with the series regulator, the receiving
means being configured for receiving a signal.
15. A device as claimed in claim 1 wherein the device includes a
load in series with the series regulator.
16. A device as claimed in claim 1 wherein the device includes a
shunt regulator to control the operating voltage when the device is
switched between the first and second states.
17. A device as claimed in claim 1 wherein the voltage multiplier
transforms the load impedance by a factor of 8.
18. A device as claimed in claim 1 wherein the rectifier transforms
the load impedance by a factor of 2.
19. A device as claimed in claim 1 wherein the device is configured
for controlling current and wherein there is a relatively smaller
amount of current, relative to the first state, when the device is
in the second state.
20. A device as claimed in claim 19 wherein in the first state the
current is hundreds of microamperes and in the second state the
current is tens of microamperes.
21. A device as claimed in claim 19 or 20 wherein in the second
state the relatively smaller amount of current is less than
approximately 50 .mu.A.
22. A device as claimed in claim 19 or 20 wherein in the second
state the relatively smaller amount of current is less than
approximately 30 .mu.A.
23. A device as claimed in claim 19 wherein in the second state the
relatively smaller amount of current is less than approximately 15
.mu.A.
24. A device as claimed in claim 19 or 20 wherein in the second
state the relatively smaller amount of current is between
approximately 1 .mu.A and approximately 4.99 .mu.A.
25. A device as claimed in claim 19 wherein in the second state the
relatively smaller amount of the first current is less than 50% of
the relatively larger amount of the first current.
26. A device as claimed in claim 1 wherein the switched impedance
is configured to select the second state more frequently than the
first state.
27. A device as claimed in claim 1 wherein the switch is used to
select the first or second states according to an algorithm.
28. A device as claimed in claim 1 wherein in the second state the
device acts as a full wave bridge rectifier.
29. A device as claimed in claim 1 wherein the voltage multiplier
provides as increased output voltage.
30. A device as claimed in claim 1 wherein in the first state the
device acts as a voltage doubler.
31. A device as claimed in claim 1 wherein the device is utilized
in a radio frequency identification device.
32. A device as claimed in claim 1 wherein the radio identification
frequency device is passive.
33. A device as claimed in claim 1 wherein in the second state
current is used to maintain RAM data stored in CMOS memory, and
operate logic functions.
34. A device as claimed in claim 1 including an onboard energy
storage device.
35. A method of selectively controlling current, the method
comprising: providing a device operable in one of a first state or
a second state, coupling an impedance to the device to enable
switching of the device between a first state and a second state
wherein, in the first state, the device acts as a voltage
multiplier and, in the second state, the device acts as a
rectifier.
36. A method as claimed in claim 35 wherein the method includes
using a receiving means to receive a signal, and selectively
controlling the amount of current in the receiving means by
switching between the first state and the second state.
37. A method as claimed in claim 36 wherein the current drawn
through the receiving means in the first state is greater than the
current drawn through the receiving means in the second state.
38. A method as claimed in claim 36 or 37 wherein the receiving
means is connected to one or more voltage input terminals of the
device.
39. A method as claimed in claim 36 wherein the receiving means
comprises a coil in an antenna circuit.
40. A method as claimed in claim 36 wherein the receiving means has
a impedance of substantially 200 ohms.
41. A method as claimed in claim 35 wherein a load is connected
between one or more output voltage terminals of the rectifier.
42. A method as claimed in claim 41 wherein the load comprises an
integrated circuit.
43. A method as claimed in claim 35 wherein the first state is an
operational state and the second state is a standby state.
44. A method as claimed in claim 35 wherein the switched impedance
comprises a switch in series with a capacitor.
45. A method as claimed in claim 44 wherein the switch of the
switched impedance comprises a MOSFET.
46. A method as claimed in claim 35 wherein the switched impedance
is connected between a first input terminal and a first output
terminal of the rectifier.
47. A method as claimed in claim 35 wherein the device includes a
series regulator for controlling an operating voltage by varying
resistance when the device is switched between the first and second
states.
48. A method as claimed in claim 47 wherein the device includes
receiving means in series with the series regulator, the receiving
means being configured for receiving a signal.
49. A method as claimed in claim 35 wherein the device includes a
load in series with the series regulator.
50. A method as claimed in claim 35 wherein the device includes a
shunt regulator to control the operating voltage when the device is
switched between the first and second states
51. A method as claimed in claim 35 wherein the voltage multiplier
transforms the load impedance by a factor of 8
52. A method as claimed in claim 35 wherein the rectifier
transforms the load impedance by a factor of 2.
53. A method as claimed in claim 35 wherein the device is
configured for controlling current and wherein there is a
relatively smaller amount of current, relative to the first state,
when the device is in the second state.
54. A method as claimed in claim 53 wherein in the first state the
current is hundreds of microamperes and in the second state the
current is tens of microamperes.
55. A method as claimed in claim 53 or 54 wherein in the second
state the relatively smaller amount of current is less than
approximately 50 .mu.A.
56. A method as claimed in claim 53 or 54 wherein in the second
state the relatively smaller amount of current is less than
approximately 30 .mu.A.
57. A method as claimed in claim 53 or 54 wherein in the second
state the relatively smaller amount of current is less than
approximately 15 .mu.A.
58. A method as claimed in claim 53 or 54 wherein in the second
state the relatively smaller amount of current is between
approximately 1 .mu.A and approximately 4.99 .mu.A.
59. A method as claimed in claim 53 wherein in the second state the
relatively smaller amount of the first current is less than 50% of
the relatively larger amount of the first current.
60. A method as claimed in claim 35 wherein the switched impedance
is configured to select the second state more frequently than the
first state.
61. A method as claimed in claim 35 wherein the switch is used to
select the first or second states according to an algorithm.
62. A method as claimed in claim 35 wherein in the second state the
device acts as a full wave bridge rectifier.
63. A method as claimed in claim 35 wherein the voltage multiplier
provides as increased output voltage.
64. A method as claimed in claim 35 wherein the voltage multiplier
is a voltage doubler.
65. A method as claimed in claim 35 wherein the device is utilized
in a radio frequency identification device.
66. A method as claimed in claim 35 wherein the radio
identification frequency device is passive.
67. A method as claimed in claim 35 wherein in the second state
current is used to maintain RAM data stored in CMOS memory, and
operate logic functions.
68. A method as claimed in claim 35 including an onboard energy
storage device.
69. A method as claimed in claim 35 wherein the coupling of the
impedance is enabled by a switch.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a continuation of, and
incorporates by reference the entire disclosure of, U.S. patent
application Ser. No. 10/525,408, which has been accorded a filing
date of Apr. 17, 2006. U.S. patent application Ser. No. 10/525,408
is a national-stage filing of PCT/AU2003/001072, filed Aug. 23,
2003.
FIELD OF INVENTION
[0002] In arrangements the invention has been developed primarily
as a radio frequency identification ("RFID") tag for a parcel,
document or postal handling system and will be described
hereinafter with reference to these applications. However, the
invention is not limited to those particular fields of use and is
also suitable to inventory management, stock control systems, and
other applications.
[0003] The present invention provides novel and inventive
electronic devices.
BACKGROUND ART
[0004] Passive RFID tags are known, and generally include a
resonant tuned antenna coil electrically connected to an integrated
circuit (IC). Examples of such RFID tags include: U.S. Pat. No.
5,517,194 (Carroll et al); U.S. Pat. No. 4,546,241 (Walton); U.S.
Pat. No. 5,550,536 (Flaxel); and U.S. Pat. No. 5,153,583
(Murdoch).
[0005] Systems that employ RFID typically include an interrogator
that generates a magnetic field at the resonant frequency of the
tuned antenna coil. When the coil is located within the magnetic
field, the two couple and a voltage is generated in the coil. The
voltage in the coil is magnified by the coil's Q factor and
provides electrical power to the IC. With this power, the IC is
thereby able to generate a coded identification signal that is
ultimately transmitted to the interrogator.
[0006] Limitations arise because the resonant current that flows in
the tuned antenna coil also generates a magnetic field in the
region of the coil. That is, if there is an object--such as a
second tag with a second coil--disposed near the first coil, the
voltage generated by the first coil (and the second coil as well)
will be reduced by the partial cancellation--or even complete
cancellation--of these respective fields. In turn, this
consequential reduction in power will not allow the first tag (and
likely the second tag as well) to reliably provide an
identification signal to the interrogator.
[0007] In this light, many fields that employ such tags--such as
baggage handling services, letter carrying services, inventory
management systems, etc.--cannot be processed in "dense"
configurations. In other words, such articles must be sufficiently
spread apart for the tags--and systems incorporating such tags--to
operate reliably. Such "density" limitations thus tend to result in
speed and efficiency restrictions.
[0008] In order to address these problems several inventive
arrangements have been developed. As mentioned above and whilst
these arrangements have been developed with particular regard to
radio frequency identification systems that clearly also have
advantageous application in a number of other applications.
[0009] The discussion of the prior art within this specification is
to assist the addressee understand the invention and is not an
admission of the extent of the common general knowledge in the
field of the invention.
SUMMARY OF INVENTION
[0010] According to a first aspect of the invention there is
provided a device having a switched impedance that can be switched
between a first state and a second state wherein, in the first
state, the device acts as a voltage multiplier and, in the second
state, the device acts as a rectifier.
[0011] Preferably in the first state the device acts as a voltage
doubler and in the second state the device acts as a full wave
bridge rectifier. Furthermore the switched impedance preferably
comprises a switch in series with a capacitor.
[0012] In preferred embodiment, the full wave bridge rectifier
comprises a Wheatstone bridge diode arrangement having a first and
a second input and a first and a second output, with the switched
impedance being connected between a first input terminal and a
first output terminal of the diode arrangement. As such the
switched impedance may be connected between a first input terminal
and a first output terminal of the rectifier.
[0013] In the ideal the voltage doubler has a voltage gain of two,
and transforms the load impedance by a factor of 8. In contrast,
the full wave rectifier, in the ideal, has a voltage gain of one,
and transforms the load impedance by a factor of 2. Thus, in
arrangements, when embodied in the form of a RFID device with an
antenna coil, the voltage doubler circuit is arranged to draw a
significantly larger current from the antenna coil, and acts as the
normal current state rectifier whilst, in contrast, when the full
wave rectifier is switched "on" during a low current state
significantly less current is drawn.
[0014] Other aspects and preferred aspects are disclosed in the
specification and/or defined in the appended claims, forming a part
of the description of the invention.
[0015] For example according to a second aspect of the invention
there is provided a method of selectively controlling current, the
method comprising providing a device operable in one of a first
state or a second state, coupling an impedance to the device to
enable the switching of the device between a first state and a
second state wherein, in the first state, the device acts as a
voltage multiplier and, in the second state, the device acts as a
rectifier. The method may include using a receiving means to
receive a signal, and selectively controlling the amount of current
in the receiving means by switching between the first state and the
second state. Further preferred features of the invention will
become apparent.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Preferred embodiments of the invention will now be
described, by way of example only, with reference to the
accompanying drawings, in which:
[0017] FIG. 1 is a symbolic circuit diagram of a preferred
embodiment of the invention;
[0018] FIG. 2 is a symbolic circuit diagram of the embodiment shown
in FIG. 1;
[0019] FIG. 3 is a symbolic circuit diagram of a voltage doubler
circuit associated with the embodiment of the invention shown in
FIGS. 1 and 2;
[0020] FIG. 4 is a schematic representation of a device according
to another preferred embodiment of a related invention;
[0021] FIG. 5 is a plan view of the embodiment of FIG. 4;
[0022] FIG. 6 is a symbolic circuit diagram in one form
illustrating a typical prior art tag;
[0023] FIG. 7 is a symbolic circuit diagram of an RFID device
according to the embodiment shown in FIG. 4;
[0024] FIG. 8 is a circuit model for the device of FIG. 7;
[0025] FIG. 9 is a symbolic circuit diagram of another embodiment
of the invention that includes a voltage multiplier;
[0026] FIG. 10 is a symbolic circuit diagram of a further
alternative embodiment of the invention that includes a circuit for
changing the current collection efficiency of the antenna;
[0027] FIG. 11 is a symbolic circuit diagram of a further
embodiment of the invention where the circuit for changing the
current collection efficiency is on the DC side;
[0028] FIG. 12 is a symbolic circuit diagram of another embodiment
of the invention that includes a circuit for changing the operating
voltage;
[0029] FIG. 13 is a symbolic circuit diagram of a further
embodiment of the invention that includes a series voltage
regulator circuit;
[0030] FIG. 14 is an alternative symbolic embodiment of that of
FIG. 7, where the antenna coil is substituted with a generic
interrogation signal-receiving device;
[0031] FIG. 15 is an alternative symbolic embodiment of that of
FIG. 7; where the antenna coil is substituted with a dipole
antenna;
[0032] FIG. 16 is an alternative symbolic embodiment of that of
FIG. 7; where the antenna coil is substituted with a capacitive
antenna;
[0033] FIG. 17 is a circuit model for the prior art circuit of FIG.
6;
[0034] FIG. 18 is a perspective view of a plurality of stacked
envelopes, each of which contains a device according to FIG. 7;
[0035] FIG. 19 is a perspective cut-away view of a parcel according
to another embodiment; and
[0036] FIG. 20 is a schematic representation of a system according
to a further embodiment.
DETAILED DESCRIPTION
FIGS. 1 to 3
[0037] It is to be noted at the outset that FIGS. 1 to 3 are
"symbolic" or models of a preferred embodiment of the
invention.
[0038] Referring to FIG. 1 there is provided a device 100 having a
switched impedance 101 that can be switched between a first state
and a second state wherein, in the first state, the device 100 acts
as a voltage multiplier and, in the second state, the device 100
acts as a rectifier. In this particular embodiment the voltage
multiplier, in the first state of operation, is a voltage doubler
and the rectifier, in the second state of operation, is a full wave
bridge rectifier.
[0039] In the device 100 there is provided a switched impedance 101
comprising a switch T1 in series with a capacitor C3. The switch T1
is able to be moved between on and off states so as to switch the
device 100 between the first and second states. In the first state
the switch T1 is closed while in the second state the switch T1 is
open.
[0040] With T1 open no current can flow through capacitor C3
causing the device 100 to act as a full wave bridge rectifier. The
full wave bridge rectifier includes four diodes D1 to D4 arranged
in a Wheatstone bridge formation. In the formation as shown in FIG.
1 the tails of D1 and D4 extend from a first output terminal 102 of
the bridge to respective first and second input terminals 104, 106,
from which the tails of D1 and D4 respectively extend to a second
output terminal 108 of the bridge. This formation is known as a
Wheatstone bridge.
[0041] With T1 closed the operation of the device 100 is best
understood by recasting FIG. 1 into the form shown in FIG. 2.
Taking the effort to recast FIG. 1 and with subsequent circuit
analysis, with switch T1 closed, there is provided a voltage
doubler in which the diodes D3 and D4, effectively, can be thought
of being reversed biased so as to conduct no current. Removing D3
and D4 from FIG. 2 consequently results in a voltage doubler
arrangement. Moreover, as is know, a voltage doubler of this type,
in the ideal, transforms the load impedance by a factor of 8. With
switch T1 open, the full wave bridge rectifier will transform the
load impedance by a factor only 2. The advantageous nature of this
construction for RFID devices is discussed below.
[0042] The importance of another feature of the device 100 is that
with the switched impedance 101 being connected between the input
terminal 106 and the output terminal 102 of the bridge, there is
provided for the effective reuse of diodes D1 and D2 in the second
state of operation as a voltage doubler.
FIG. 4
[0043] It will now become apparent that the device 100 includes
both a voltage doubler circuit and a full wave rectifier circuit,
and finds particular application in RFID devices.
[0044] In the arrangement schematically represented in FIG. 4 the
present invention is embodied as a radio frequency identification
device 200. The device 200 comprises a receiver portion 235; an
integrated circuit 237 with one or more functionalities; a
connection 239 between the two; and a state selection means 241
that determines whether the device is in a first state or a second
state; and a transmission means 245--preferably in the form of an
antenna 247. These components are reflected symbolically in the
following Figures.
FIG. 5
[0045] A radio frequency identification ("RFID") device or tag 1,
is symbolically illustrated in FIG. 5. The tag 1 includes a
multi-turn coil 303 for receiving an interrogation signal. A
transceiver, in the form of an integrated circuit (IC) 304, is
connected to the coil 303 and is responsive to the interrogation
signal. In other embodiments, other devices are used as the
transceiver; such devices will be readily apparent to those skilled
in the art. In this embodiment, coil 303 and the circuit 304 are
mounted on a common generally rectangular substrate 302. The IC
includes a memory 306. The device 100 is included in the tag 1.
FIG. 6
[0046] FIG. 6 includes a tuning capacitor C1. This Figure is
discussed below in relation to a specific example.
FIG. 7
[0047] As schematically illustrated in FIGS. 7 the circuit 304
toggles between a first state and a second state, wherein the
current drawn from the coil 303 by the circuit 304--in the presence
of the interrogation signal--during a first state is greater than
the current drawn during a second state. A noted above device 100
is employed within circuit.
FIG. 8
[0048] FIG. 8 illustrates a circuit model for circuit 304.
Particularly: [0049] (a) the voltage V1 is induced in the antenna
coil L1 by the interrogation field. [0050] (b) Impedance Z1
represents the series impedance of the antenna coil and any other
series--connected impedance. [0051] (c) R4 symbolically represents
the equivalent AC resistance of circuit 304. [0052] (d) Current I2
flows from the antenna coil into R4. [0053] (e) Voltage V4 across
R4 symbolically represents the voltage of the antenna terminals of
L1 and circuit 304, which is rectified and stored on a DC storage
capacitor C2 as shown in FIG. 3.
[0054] Accordingly, V4 equals V1 minus the volt drop in L1 and Z1
due to the current I2 flowing through L1 and Z1. That is:
V4=V1-I2.(Z1+jwL1)
[0055] Where jw is the complex frequency in radians per second.
This equation can be rearranged into the following two forms.
I2=(V1-V4)/(Z1+jwL1) and I2=V1/(R4+Z1+jwL1) Adjusting I2
[0056] In light of the above, assuming that the voltage V1 and the
inductance L1 is fixed, then current I2 is adjusted by varying
either V4, R4 or Z1. For instance: [0057] 1. I2 is varied by
changing V4. That is, by increasing the output voltage more voltage
appears at the coil terminals and less current is drawn from the
antenna coil. [0058] 2. I2 is varied by changing R4. That is, by
increasing the AC resistance of the circuit 4 less current is drawn
from the antenna coil. And, [0059] 3. I2 is varied by changing Z1.
That is, by inserting an extra impedance in series with Z1, a
larger voltage is dropped in the antenna coil impedance and less
current is drawn from the antenna coil.
[0060] Embodiments incorporating such techniques have in fact
already been described in the context of device 100 represented in
FIGS. 1 to 3.
Resonant Tuning
[0061] As described with T1 closed in device 100 there is provided
a voltage doubler of the form illustrated in FIG. 3. With reference
to the embodiment shown in FIG. 7 this state of operation can be
viewed as comprising a voltage multiplier as shown in FIG. 9. This
is advantageous, since in the absence of resonant tuning, the coil
voltage is relatively low because it is not magnified by Q. To
compensate, circuit 8 increases the voltage supplied to circuit 7
and allows the circuit to operate with a lower coil voltage; the
lower coil voltage also requiring a lower interrogation field.
[0062] In other related devices use is made of other types of
voltage multipliers, such as triplers or quadruplers. Since the
impedance level of the coil used in many preferred embodiments is
low--in the order of 200 ohms--it is, therefore, ideally suited to
a connection with a voltage multiplier.
Load Impedance
[0063] As discussed above the voltage doubler has a voltage gain of
two, and transforms the load impedance of the chip by a factor of
8. In contrast, the full wave rectifier has a voltage gain of one,
and transforms the load impedance by a factor of 2. Thus, since the
voltage doubler circuit draws a significantly larger current from
the antenna coil, it acts as the normal current state rectifier. In
contrast, the full wave rectifier is switched "on" during the low
current state.
[0064] In the case of the full wave rectifier, for an AC input
voltage of Vac peak (2Vac peak to peak) the DC output voltage Vdc
equals Vac. For a DC load resistance Rdc the output power Pout
equals Vdc 2/Rdc and the input power Pin equals Vac 2/2.Rac where
Rac is the input impedance. Again, from energy conservation the
input power Pin must equal the output power requiring that Vdc
2)/Rdc=Vac 2/2.Rac. Substituting Vdc=Vac gives (Vac 2)/Rdc=Vac
2/2.Rac and rearranging gives 2.Rac equalling Rdc. Thus the input
AC resistance is 1/2 of the DC load resistance.
[0065] The switch T1 is provided in the form of a MOSFET transistor
and as would now be apparent, is used to select either the normal
current state or the low current state. (T1's drive is provided by
the transceiver.) When transistor T1 is closed and opened, the
circuit respectively acts as a voltage doubler and a full wave
rectifier.
[0066] In the present embodiment circuit 304, has a current cycle
during which the circuit randomly selects either the first or the
second state for the duration of the cycle. The random selection of
state during the cycle by each individual tag reduces the risk of
two adjacent radio frequency identification tags simultaneously
operating in the first state.
[0067] Moreover, in this embodiment, the selection of the second
state by circuit 4 is about 16 times more probable then the
selection of the first state. That is, the probability of the
circuit 4 drawing a high current--and thereby jeopardizing the
performance of an adjacent tag, and itself, by their mutual
coupling is 1/16. Accordingly, the tags may operate at a much
smaller spatial separation than could be achieved by prior art
tags.
[0068] The state selection means is implemented with digital
circuits. These circuits are designed to select the current state
according to the chosen algorithm or method. There are several
methods which can be used to implement the state selection
circuits. Logic gates can be used to create a dedicated logic
circuit for determining the state selection. A state engine
consisting of logic arrays can be designed to implement the state
selection function. A microcontroller or processor can execute
software instructions that code for the chosen algorithm or method.
The preferred embodiment is a logic array controlled by a
microcontroller. The microcontroller software executed the slower
parts of the chosen algorithm or method while the logic array
performs the faster parts of the chosen algorithm or method.
A. Embodiments with an Extra Impedance
[0069] In FIG. 10, circuit 11 includes a sub-circuit 12 that
provides an extra impedance Z2 in series with the antenna coil L1
when circuit 11 is in the low current state. Z2 can be a
resistance, capacitance, inductance or a combination of any, or
all, of these. The extra impedance causes a drop in voltage across
itself and reduces I2. This is advantageous for reducing the
current drawn from the antenna during the low current state.
[0070] In other embodiments, such as that shown in FIG. 11, circuit
I2 is placed on the DC side of the rectifier and a resistor R3 is
used to reduce I2.
B. Embodiments with a Shunt Regulator
[0071] The embodiment shown in FIG. 12 includes a circuit 15 that
utilises a shunt regulator 16 for controlling the operating voltage
provided to the integrated circuit. A detailed explanation of the
operation of the shunt circuit is given in U.S. Pat. No.
5,045,770.
[0072] In essence, the IC's operating voltage is changed such that
the low current state's operating voltage, VA+VB, is higher than
the normal current state's operating voltage, VB. When the IC's is
at the higher operating voltage, the transceiver portion of the
device operates at a lower current--therefore, less current is
drawn from the antenna.
[0073] The low current state operating voltage is set as high as is
possible given the limitations of the IC technology. In this
embodiment, for example, VA+VB=4.2 volts and VB=2.1 volts.
C. Embodiments with a Series Regulator
[0074] The embodiment of FIG. 13 includes a circuit that utilises a
series regulator for controlling the operating voltage. The input
voltage to the regulator increases when the circuit toggles into
the low current state.
Dimensions
[0075] Returning to FIG. 5 the substrate 302 is about 80 mm by 50
mm, and includes a plurality of layers that are laminated together
to encapsulate the coil 303 and the circuit 304. In this
embodiment, the thickness of the tag 1 is about 0.3 mm. In other
embodiments, the dimensions of tag 1 are bigger or smaller. That
is, it is generally preferable for the tag to be sized such that it
may be unobtrusively incorporated into packaging and other
articles.
Devices Used to Transmit the Identification Signal
[0076] In the preferred embodiment, the coil 303 transmits an
identification signal generated by the transceiver. In other
embodiments, a second separate antenna coil is used to transmit the
identification signal.
Devices Used to Receive the Interrogation Signal
[0077] While in this embodiment, the antenna is the coil 303, other
devices may be employed to receive the interrogation signal.
Examples of such alternative devices are shown in FIGS. 14, 15 and
16. In FIG. 14, the interrogation signal is received by a
non-specific or generic receiving device 31. As shown in FIG. 15
includes a dipole antenna 32 is used for receiving a radiated
interrogation signal. In other embodiments (not shown), device 31
is a monopole. In still further embodiments, such as that
illustrated in FIG. 18, device 31 includes a capacitive antenna 33
for receiving an electric, capacitive, or interrogation signal.
Further, it will be understood by the skilled addressee from the
teaching herein that the invention is applicable to still other
receiving devices, and is not limited by the choice of antenna or
the specific form of interrogation signal.
The Typical Operation of Prior Art Tags
[0078] Before further describing the embodiments of the invention,
the operation of a typical prior art tag will be examined. A
typical tag includes a circuit 6 illustrated schematically in FIG.
6. Particularly, the voltage V1 is induced in antenna coil by the
interrogation field, and the antenna coil L1 is tuned by a tuning
capacitor C1. Accordingly, L1 and C1 form a resonant tuned circuit,
which magnifies the voltage V1 by the loaded Q factor of the
antenna coil. The AC voltage generated across the tuned circuit is
rectified by a rectifier 6a, and the DC output voltage is stored on
a storage capacitor C2. The DC load of the IC is represented by
R1.
[0079] FIG. 17 shows a circuit model for the RFID circuit 5 where
corresponding features are denoted by corresponding notations The
antenna coil is represented by inductance L1 and the coil losses by
series resistance R5. The tuning capacitance and circuit stray
capacitance are represented by C1, and the losses of the rectifier
and IC circuit by R3. The resonant currents circulating in the
tuned circuit formed by L1 and C1 are I1; and the output current
into R3 is I2.
[0080] The capacitor Q factor (Qc=w.R3.C1) normally dominates the
total resonant Q factor. Typically, Qc has a value of between 10
and 40. Since the ratio of I1/I2=Q, the resonant current I1 is much
larger than the output current I2.
[0081] In light of the above, when tags of this type are in close
proximity the magnetic field generated by the resonant current
couples--through mutual inductance--with proximate tags and,
therefore V1 is diminished. In other words, once the tags are in
close proximity--that is, within about 50 mm of each other--such
"interference" compromises the reliable operation of the tags.
The Removal of the Resonant Capacitor
[0082] In a related aspect it has been appreciated by the inventors
that for tags operating in close proximity to each other it is
important that these resonant currents are eliminated. Given this,
the inventors have found that it is possible to eliminate these
resonant currents by disconnecting the resonant capacitor from the
antenna coil. However, even with the resonant capacitor removed
from prior art devices like that shown in FIG. 7, the antenna
current drawn by circuit 7 is still too large to allow a plurality
of tags to be closely stacked. Specifically, even without a
resonant capacitor, if such tags are placed within a few
millimetres of each other, the tags will not operate reliably.
Minimising the Current in the Second State
[0083] When the antenna coil current becomes very small or, as in
some cases zero, the coil becomes transparent to the interrogation
field. In this state the antenna coil has (a) no effect upon the
interrogation field and (b) those tags in the low current state do
not interfere with the operation of those tags in the normal
current state.
[0084] In low current state, tag 1 is not fully functional. That
is, the current drawn from the coil is reduced such that only
necessary circuit functions are viable. In a preferred embodiment,
the current is in order of 30 .mu.A. Ideally, the current is zero;
or at least minimised as much as possible.
[0085] In other embodiments, the minimising of current is realised
by one or more of a variety of methodologies, including: [0086] 1.
Minimising the required functions to be performed by the circuitry.
[0087] 2. Utilising low power circuitry. Low power circuitry, while
widely understood, are much more difficult to design than
conventional circuitry. Low power circuits require less current to
operate and consequently draw less current. Using low power
circuits for those circuits that must remain operational in the low
current state reduces the current drawn during the low current
state. [0088] 3. The use of onboard energy storage devices and in
particular a capacitive device. On board storage devices can
provide the current required to operate the circuits in the low
current state. For example, a capacitive device can charge up
during the normal current state and use the stored charge during
the low current state so as to minimise the current drawn from the
antenna. Alternatively, a battery can be used to supply the low
current state current.
[0089] More generally, the impedance seen by the antenna coil
should be as large as possible. This is particularly so in the low
current state. That is, the quantum of the antenna current is
proportional to the quantum of the resistive and/or the reactive
load as seen by the coil. When the amount of the coil current is
too high, coil-to-coil magnetic interference will cause the tags to
stop operating reliably.
Operation
[0090] In the FIG. 7 embodiment--which does not include a
resonating capacitor--voltage V1 is induced in the antenna coil L1
by the interrogation field. Further, the antenna voltage is
rectified and stored on a DC storage capacitor C2. The generated
current is managed by symbolic switch SW1.
A. The Symbolic Switch
[0091] The two states can be symbolically reflected by a switch SW1
and resistors R1 and R2. Importantly, these are employed to reflect
the two states and are not, in fact, part of the invention.
[0092] In other words, switch SW1 reflects the device's operation
in the two different "states". In essence, this is further
symbolically implemented by resistors R1 and R2--which are
representative of the load provided by circuit 4 in the low current
state and the normal current state respectively.
[0093] With the benefit of the teaching herein, it will be
appreciated by those skilled in the art that there are many well
known methods for disabling circuits and reducing their current
consumption--all of which are applicable to achieve the
functionality required. For example, there are various hardware and
software methods for putting a microprocessor into a "standby" or a
"sleep" state. The present invention does however provide a
solution whereby the device includes a switched impedance that can
be switched between a first state and a second state wherein, in
the first state, the device acts as a voltage multiplier and, in
the second state, the device acts as a rectifier.
B. Current Input by the Symbolic Switch
[0094] The change in the current drawn by circuit 304 in the low
current and the normal current state corresponds to a change in the
antenna coil's current. In the low current state that antenna
current is tens of microamperes and in the normal current state the
antenna current is hundreds of microamperes. Specifically, typical
values are 70 .mu.A in the low current state and 300 .mu.A in the
normal current state.
[0095] In FIG. 7, the low current state is symbolically represented
by switch SW1 being open and the current Iq being drawn through R2.
In the low current state, the quiescent current Iq is symbolically
drawn. The current Iq is very small and is typically a few tens of
microamperes. In this embodiment, Iq symbolically represents the
current used to: maintain RAM data stored in CMOS memory, operate
logic functions, and power analogue circuitry.
[0096] Further, the normal current state is symbolically
represented by SW1 being closed and reflects activation of all of
circuit 4's functionality. In the normal current state, currents Ic
and Iq are drawn. The total current drawn by circuit 304 in the
normal current state (Iq+Ic) is typically about 300 .mu.A, although
this does vary considerably between embodiments.
Systems Incorporating the Device
[0097] FIG. 18 illustrates an application of an embodiment of the
invention as an inventory system for jewels. Previously, this
process has been achieved manually, and is therefore both time
consuming and prone to error.
[0098] In this embodiment, 100 small envelopes are horizontally
stacked in a cardboard box; each envelope storing a jewel and a
report on the characteristics of the jewel. As is evident from FIG.
18, a plurality of RFID tags 1 may be placed within a few
millimetres of each other without impacting on the devices'
reliability.
[0099] Since each tag 1 is programmed with the contained jewel's
characteristics, its uniquely coded identification signal will
provide the interrogator with data this is indicative not only of
the identity of each tag in the box, but also of the jewel
contained within each envelope. Accordingly, the whole box of
jewels is accounted for in one automatic process. There is no need
to take the envelopes out of the box and separate them to "safe"
distances from each other.
[0100] In this way, security is more easily maintained as well. For
instance, the interrogator may be placed at a passage (through
which the box is placed) between a safety deposit storage area and
a customer service area. Preferably, the personnel progressing the
box also carries a tag so that their identity may be
determined.
The Determination of "State"
[0101] As mentioned earlier, to maximise the reliability of the
operation of closely stacked or spaced tags, such as those used in
FIG. 18, the tags operate in either of two current states. At any
one time, a small proportion of the tags are in a normal current
state where the tags are responsive to the interrogator, and the
remainder of the tags are in a low current state where they are not
fully functional. Accordingly, in the FIG. 18 embodiment, where the
tags must operate within a few millimetres of each other, the
probability of an individual tag being in the normal state is
1/16.
[0102] Generally speaking, the longer the tags are disposed within
the interrogation field, the lower the normal state probability may
be. In other embodiments having only a few tags, the probability of
the tags being in the normal state can also be decreased. In such
instances, the spacing between tags can thereby be further
decreased as well.
[0103] The selection of state is made using a predetermined
algorithm. An example of a preferred algorithm is a random or a
pseudo-random number algorithm.
A. Autonomous Selection
[0104] In a preferred embodiment, the tags randomly select their
current state autonomously. That is, the tags randomly choose a
current state; receive commands and/or data, and/or transmit
replies; and then randomly choose a new current state.
B. Responsiveness to Interrogation Signals
[0105] In alternative embodiments, the interrogation signals are
used to direct tags to select a new current state, and the tags
randomly choose their current state. These interrogation signals,
in some embodiments, take the form of short breaks in the
interrogation field. Example of such breaks include a single break
and a coded break (where the codes are sequences of breaks
directing the tags to perform to various current state
selection).
[0106] In further alternative embodiments, other forms of
modulation of the interrogation field are used to direct tags in
their selection of current state. Examples of such modulations
include amplitude, phase, and frequency modulation.
C. Probabilities
[0107] The precise proportion of tags selecting the normal state is
not critical, except in so far that the coupling between tags is
reduced sufficiently to allow reliable operation. The probabilities
or proportion of operating tags should be selected to suit the
number and spacing of tags and can be determined by experiment.
[0108] Moreover, the algorithm may be structured so that a tag will
be guaranteed to have been in the normal current state at least
once every "n" state selections, where "n" is the reciprocal of the
probability of selecting the normal state. A simple method of
ensuring this is to force the selection of the normal current state
if it has not been selected after a fixed number of selections. The
value of this fixed number can be selected to suit the number and
spacing of tags.
D. Use of Unique Tag Number
[0109] Alternatively, each tag selects a current state dependent
upon a fixed number, such as a unique number. In such preferred
embodiments, the tag uses a portion of that number to choose a
current state. More particularly, in the FIG. 18 embodiment, each
tag's unique number includes a 4-bit mask value. The 4-bit value
represents the number of interrogator breaks, or commands, received
before the tag enters the normal current state. The field
transmitted by the interrogator can be modulated to transmit
commands to the tags. Various methods of modulating the field such
as pulse, amplitude, frequency and phase are widely used and
understood.
[0110] In further embodiments, the mask may be altered each time
the tag exits the normal state. In this way, adjacent tags with
similar numbers are prevented from moving to the normal current
state at the same time.
[0111] Larger and smaller probabilities can be selected by using
smaller and longer masks. The mask can also be reduced or increased
in length so that probabilities of 1, 1/2, 1/4, 1/8, 1/16, and 1/32
can be selected by employing masks of 0, 1, 2, 3, 4 and 5 bits
respectively.
[0112] Another application is illustrated in FIG. 19, where tag 1
is shown disposed between two cut-away layers 21 and 22 of a
laminated envelope 23. While tag 1 is shown in the Figure as
protruding from between the layers, that is for purposes of
illustration only. It will be appreciated that, in use, tag 1 is
completely enclosed by the layers. Importantly, since tag 1 is
operable, even when in close proximity to a number of like tags, it
is possible to reliably interrogate the tags.
Further Applications
[0113] FIG. 20 depicts a system 50 according to a preferred
embodiment of the invention. As shown, an interrogator 43
integrates a plurality of devices 1.
[0114] For postal envelopes, the user is able to pre-program the
tags 1 to include address and content information to facilitate the
sorting of the envelope. Moreover, in some embodiments, the tag is
pre-programmed with an encrypted message for the intended
recipient. For courier envelopes, the courier may pre-program the
tag to include data about the intended recipient, the contents of
the envelope, the priority of the required delivery, and other
data.
[0115] Although the tag 1 is shown sandwiched between two layers of
the envelope of FIG. 19, in other embodiments it is attached by
other means. For example, one embodiment makes use of a plastics
pocket formed on the exterior layer of the envelope for selectively
receiving the tag. In another embodiment, the tag is simply placed
within the envelope with the other contents. Further, attached to
parcels, the invention is particularly advantageous because loosely
packed parcels will often lie directly adjacent to one
another--without any separation. Other alternatives will also be
apparent to the skilled addressee in light of the teaching
herein.
[0116] In another embodiment of the invention, a tag is disposed
within the packaging for a saleable item. Following the placement
of the item into the packaging the tag is programmed to include
data indicative of the quantity or quality of the contents. This
allows ease of distribution and inventory control from the point of
packaging to the ultimate point of sale. This embodiment is
particularly advantageous when applied to packaging for computer
software. However, it is also applicable to other items such as
compact disc's, toys, integrated circuits, books, and any other
goods that are packed closely together for storage or
transportation.
[0117] In more complex embodiments, a number of tags are associated
with a single article. In the case of an envelope for courier use,
one of the tags contains data readable only by the courier
organisation, while another tag includes data only readable by the
sender and recipient of the envelope.
The Interrogator
[0118] The interrogator 43 is either a fixed installation device
or, in other embodiments, a handheld device. In any event, the
interrogator provides an interrogation signal--preferably in the
form of a RF field--that is detected by, and selectively responded
to, by each tag in its field.
Reusability and Reliability
[0119] The RFID tags of the preferred embodiments provide a
re-usable resource, as the tags are re-programmable. Moreover,
unlike bar codes, they will not be so easily disabled through
physically rough handling.
Other Benefits Associated with the Present System
[0120] Since prior art system, tags are used to identify items such
as baggage and are designed to operate at ranges up to 1 metre, the
application of such technology is thereby limited to circumstances
where tags are well spaced apart. In sharp contrast, the preferred
embodiments of the invention are able to be stacked closely and
continue to reliably operate.
[0121] A typical application is the identification of RFID tags
attached to bundles of letters where the tag data is used to
control the automatic sorting of each letter. However, the
invention is not limited to this particular field of use. For
example, various aspects of the invention are applicable to systems
used for identification or inventory management of items such as
shoe uppers, shoe soles, diamonds, and jewellery.
[0122] Moreover, in addition to allowing ease of inventory control,
the invention facilitates the automated sorting of those articles.
This is well illustrated in the context of the jewel handling
system and also in the context of mail handling systems--where each
piece of mail includes a tag.
[0123] Accordingly, the preferred embodiments may be applied
advantageously to various uses such as item identification, stock
control, and inventory management. By having the ability to
reliably operate in "close" ranges, such as when stacked, the
application's tag and system allow these processes to be done in
bulk and automatically--without the need for manual intervention.
Accordingly, the preferred embodiments of the invention provide
many significant advantages over prior art systems.
[0124] It is to be appreciated that the present invention may be
provided a radio frequency identification ("RFID") device, the
device including: an antenna for receiving an interrogation signal;
and a transceiver connected to the antenna and being responsive to
the interrogation signal, whereby the transceiver selectively draws
current from the antenna.
[0125] The transceiver may toggle between a first state and a
second state, wherein the current drawn by the transceiver during
the first state is greater than the current drawn during the second
state. The transceiver may select the second state more frequently
than the first state. More preferably, the probability of selecting
the second state is at least twice the probability of selecting the
first state.
[0126] In a preferred embodiment, the transceiver has an operating
cycle wherein, during that cycle, the transceiver is in either the
first or the second state. Preferably, the transceiver selects the
first state with a probability of less than 1/2. More preferably,
the probability is less than 1/4.
[0127] Even more preferably, the probability is less than or equal
to 1/16. Accordingly, the first state is not necessarily selected
in each cycle. In signal use, the interrogation signal is generated
in a predetermined area by an interrogator. Preferably, the device
is maintained within the signal field for more than one cycle. More
preferably, the device is maintained within the field for at least
the number of cycles equal to the reciprocal of the probability of
the first state being selected.
[0128] In a preferred form, the selection of the first state and
the second state is based upon a predetermined algorithm. An
example of a preferred algorithm is a random or a pseudo-random
number.
[0129] Preferably, the antenna and the transceiver are mounted to a
common substrate. More preferably, the antenna is a coil and the
current generated in the coil is in response to the interrogating
signal.
[0130] Preferably, during the first state, the current drawn by the
transceiver is to allow its operation. That is, the first state is
a normal state, while the second state is a standby state. For
example, in the normal state the current supplies the relevant
clock circuits, the signal processing circuit, and the like. In
this state, the current also allows the transceiver to generate an
identification signal.
[0131] More preferably, the transceiver relies upon the current to
drive the antenna to transmit the identification signal. In other
embodiments, the device includes a separate transmission antenna
and the transceiver drives that separate antenna to transmit the
identification signal. In both cases, the current drawn from the
antenna is the source of power for the generation and transmission
of the identification signal.
[0132] The device is preferably passive in that it does not have an
onboard power source.
[0133] However, the invention is also applicable to active devices
wherein the life of the onboard power source is prolonged.
[0134] The present invention may be provided as a radio frequency
identification ("RFID") device, the device including: an antenna
for receiving an interrogation signal and being responsive to the
signal for supporting an antenna current; a coupling connected to
the antenna for toggling the antenna current between a first state
and a second state, wherein the antenna current in the first state
is greater than the antenna current in the second state; and a
transceiver connected to the coupling and drawing an operational
current that is derived from the antenna current, whereby the
transceiver is selectively responsive to the interrogation signal
to generate an identification signal.
[0135] Preferably, during the first state the transceiver is
responsive to the interrogation signal to generate the
identification signal. More preferably, in the second state the
device is responsive to the interrogation signal only for the
purpose of toggling the antenna current between the first and
second states. That is, the first state is a normal current state,
whereas the second state is a low current or standby state.
[0136] Preferably also, the antenna is responsive to the
transceiver for transmitting the identification signal. In other
embodiments, however, the device includes a separate antenna that
is responsive to the transceiver for transmitting the
identification signal.
[0137] The present invention may be provided as a system for
identifying articles that are collocated with an RFID tag of the
first aspect, the system including: an interrogator for providing
an interrogating field; a plurality of identification devices
mounted to the respective articles, the devices including:
respective antennas for being contemporaneously disposed within the
field and being responsive to that field for providing antenna
currents; respective transceivers that are connected to the
antennas for selectively toggling the currents between an
operational state and a standby state such that not all the
currents are simultaneously in the operational state, whereby the
transceivers are responsive to the currents for providing
identification signals that include identification data unique to
the respective articles; and a receiver for processing the
identification signals to extract the identification data and
thereby identify the respective articles.
[0138] Preferably, the current drawn by the transceiver during the
operational state is greater than the current drawn during the
standby state. More preferably, the transceiver selects the standby
state more frequently than the operational state. Even more
preferable, the probability of selecting the second state is at
least twice the probability of selecting the first state.
[0139] In the preferred embodiments, the transceiver has an
operating cycle with a start and a finish wherein, during that
cycle, the transceiver is in either the first or the second
state.
[0140] Preferably also, the transceiver selects the first state
with a small probability of less than 1/2.
[0141] More preferably, the probability is less than 1/4. Even more
preferably, the probability is less than or equal to 1/16.
[0142] In a preferred form, the selection of state is based upon a
predetermined algorithm. An example of a preferred algorithm is a
random or a pseudo-random number used to determine the state
selection of the transceiver.
[0143] Preferably, the identification signals are transmitted while
the respective transceivers are in the first state. More
preferably, the transceivers use the respective antennas to
transmit the identification signals. In other embodiments, however,
the devices include respective second antennas that are used by the
transceivers to transmit the identification signals.
[0144] The present invention may be provided as a radio frequency
identification("RFID") device including: an antenna that is
responsive to an interrogation signal for providing an antenna
current; and a transceiver for selecting between a normal state and
a standby state wherein, during the normal state, the transceiver
is responsive to the interrogation signal for generating an
identification signal and, during the standby state, the
transceiver is only responsive to the interrogation signal for
selecting between the normal and standby states.
[0145] Preferably, in the absence of the interrogation signal the
device is inactive. Conversely, in the presence of an interrogation
signal, the device is either in the normal state or the standby
state. Preferably, the normal state has a short duration and,
therefore, the device is predominantly in the standby state in the
presence of an interrogating signal. Preferably, during the standby
state, the device is only responsive to the interrogation signal
for the purpose of selecting between normal and standby states.
[0146] The present invention may provided as a voltage regulator
for a radio frequency identification ("RFID") device; the device
having: an antenna for receiving an interrogation signal and for
transmitting an identification signal and a transceiver for being
responsive to the interrogation signal to generate the
identification signal. The regulator including: a current coupling
for providing a supply voltage to the transceiver, the current
coupling, in the first state, drawing a first current from the
antenna and, in the second state, drawing a second current from the
antenna that is less than the first current.
[0147] The present invention may provided as an identification
device for receiving a first signal and transmitting a second
signal, the device including: a receiving means for receiving the
first signal and employing the first signal to generate a voltage;
wherein the receiving means generates a first current from the
voltage; an integrated circuit that selectively controls the amount
of the first current in the receiving means; a connection between
the receiving means and the integrated circuit; a transmission
means for generating the second signal; a state selection means for
selecting whether the device is in a first state or a second state;
wherein-relative to the second state-a relatively larger amount of
the first current flows through the receiving means when the device
is in the first state; and wherein-relative to the first state-a
relatively smaller amount of the first current flows through the
receiving means when the device is in the second state.
[0148] The present invention may provided as system for identifying
articles, the system including: a signal generator for generating a
first signal; a plurality of articles; a plurality of
identification devices, each individual device being respectively
associated with each individual article; wherein each device
includes: a receiving means for receiving the first signal and
employing the first signal to generate a voltage; wherein the
receiving means generates a first current from the voltage; an
integrated circuit that selectively controls the amount of the
first current in the receiving means; a connection between the
receiving means and the integrated circuit; a transmission means
for generating the second signal; a state selection means for
selecting whether the device is in a first state or a second state;
wherein-relative to the second state-a relatively larger amount of
the first current flows through the receiving means when the device
is in the first state; and wherein-relative to the first state-a
relatively smaller amount of the first current flows through the
receiving means when the device is in the second state.
[0149] Although the invention has been described with reference to
a number of specific examples, it will be appreciated by those
skilled in the art that the invention can be embodied in many other
forms.
[0150] While this invention has been described in connection with
specific embodiments thereof, it will be understood that it is
capable of further modification(s). This application is intended to
cover any variations uses or adaptations of the invention following
in general, the principles of the invention and including such
departures from the present disclosure as come within known or
customary practice within the art to which the invention pertains
and as may be applied to the essential features hereinbefore set
forth.
[0151] As the present invention may be embodied in several forms
without departing from the spirit of the essential characteristics
of the invention, it should be understood that the above described
embodiments are not to limit the present invention unless otherwise
specified, but rather should be construed broadly within the spirit
and scope of the invention as defined in the appended claims.
Various modifications and equivalent arrangements are intended to
be included within the spirit and scope of the invention and
appended claims. Therefore, the specific embodiments are to be
understood to be illustrative of the many ways in which the
principles of the present invention may be practiced. In the
following claims, means-plus-function clauses are intended to cover
structures as performing the defined function and not only
structural equivalents, but also equivalent structures. For
example, although a nail and a screw may not be structural
equivalents in that a nail employs a cylindrical surface to secure
wooden parts together, whereas a screw employs a helical surface to
secure wooden parts together, in the environment of fastening
wooden parts, a nail and a screw are equivalent structures.
[0152] "Comprises/comprising" when used in this specification is
taken to specify the presence of stated features, integers, steps
or components but does not preclude the presence or addition of one
or more other features, integers, steps, components or groups
thereof." Thus, unless the context clearly requires otherwise,
throughout the description and the claims, the words `comprise`,
`comprising`, and the like are to be construed in an inclusive
sense as opposed to an exclusive or exhaustive sense; that is to
say, in the sense of "including, but not limited to".
* * * * *