U.S. patent application number 15/154738 was filed with the patent office on 2017-11-16 for chemical sensors based on chipless radio frequency identification (rfid) architectures.
The applicant listed for this patent is XEROX CORPORATION. Invention is credited to George A. GIBSON.
Application Number | 20170330004 15/154738 |
Document ID | / |
Family ID | 58765659 |
Filed Date | 2017-11-16 |
United States Patent
Application |
20170330004 |
Kind Code |
A1 |
GIBSON; George A. |
November 16, 2017 |
CHEMICAL SENSORS BASED ON CHIPLESS RADIO FREQUENCY IDENTIFICATION
(RFID) ARCHITECTURES
Abstract
A method and structure for a radio frequency identification
(RFID) sensor that may be used to monitor various environmental
conditions. The environmental condition measured depends on a
sensor material used in the RFID sensor. The sensor material is
selected based on a flux in electrical conductivity relative to its
saturation of the environmental condition being monitored. The
sensor material is placed between adjacent electrically conductive
structures of the RFID sensor. Upon a change in the environmental
condition being measure, the electrical conductivity of the sensor
material changes, thereby increasing or decreasing an amplitude of
a response by the RFID sensor to an interrogation by an RFID
reader.
Inventors: |
GIBSON; George A.;
(Fairport, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
XEROX CORPORATION |
NORWALK |
CT |
US |
|
|
Family ID: |
58765659 |
Appl. No.: |
15/154738 |
Filed: |
May 13, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F 120/06 20130101;
G06K 7/10366 20130101; G06K 19/0677 20130101; C08G 73/0611
20130101; C08F 116/06 20130101; G06K 19/0672 20130101 |
International
Class: |
G06K 7/10 20060101
G06K007/10; C08F 116/06 20060101 C08F116/06; C08F 120/06 20060101
C08F120/06; C08G 73/06 20060101 C08G073/06 |
Claims
1. A radio frequency identification (RFID) device, comprising: a
receive antenna; a transmit antenna; a multiresonator comprising a
plurality of resonators, wherein the multiresonator is electrically
coupled between the receive antenna and the transmit antenna; and a
sensor material bridging two or more electrically conductive
structures of the RFID device, wherein: the sensor material has a
variable electrical conductivity that is configured to change
depending on an environmental condition to which the sensor
material is exposed; a resonation amplitude of the multiresonator
is configured to attenuate by a first amount dependent on a first
electrical conductivity of the sensor material to provide a first
response, and to output the first response having a first amplitude
from the RFID sensor, wherein the first amplitude is dependent on a
first state of the environmental condition; and the resonation
amplitude of the multiresonator is configured to attenuate by a
second amount dependent on a second electrical conductivity of the
sensor material to provide a second response, and to output the
second response having a second amplitude from the RFID sensor,
wherein the second amplitude is dependent on a second state of the
environmental condition.
2. The RFID device of claim 1, further comprising: a first arm of
the multiresonator; and a second arm of the multiresonator spaced
from the first arm by an interstitial space, wherein the sensor
material is positioned within the interstitial space and bridges a
width of the interstitial space between the first arm and the
second arm.
3. The RFID device of claim 2, wherein the sensor material
comprises at least one of polyvinyl alcohol, a filled polyvinyl
alcohol composite, polyacrylic acid, a semiconductor film, a
sputtered semiconductor film, a vapor-deposited semiconductor film,
polypyrrole, polyaniline, polyethylene amine,
poly(ethylene-co-acrylic acid), poly(vinyl alcohol) polypyrrole
ferric chloride (PVA PPy FeCl3) composite films, multi-walled
carbon nanotube (MWCNT)/poly(vinylidene fluoride) (PVDF),
polycaprolactam, Nylon-6,6, polyoxymethylene, high density
polyethylene, and combinations of two or more of these.
4. The RFID device of claim 2, wherein the sensor material
comprises polyvinyl alcohol and the RFID device is further
configured to monitor or measure relative humidity.
5. The RFID device of claim 2, wherein the sensor material
comprises polyacrylic acid and the RFID device is further
configured to monitor or measure a concentration of hydrogen ions
that result in a pH of from 1 to 12.
6. The RFID device of claim 2, wherein the sensor material
comprises polypyrrole and the RFID device is further configured to
monitor or measure temperature.
7. A radio frequency identification (RFID) system, comprising: an
RFID reader; and an RFID sensor device configured to receive an
interrogation from the RFID reader and to output a response to the
RFID reader upon receipt of the interrogation, wherein the RFID
sensor device comprises: a receive antenna; a transmit antenna; a
multiresonator comprising a plurality of resonators, wherein the
multiresonator is electrically coupled between the receive antenna
and the transmit antenna; and a sensor material bridging two or
more electrically conductive structures of the RFID device,
wherein; the sensor material has a variable electrical conductivity
that is configured to change depending on an environmental
condition to which the sensor material is exposed; a resonation
amplitude of the multiresonator is configured to attenuate by a
first amount dependent on a first electrical conductivity of the
sensor material to provide a first response, and to output the
first response having a first amplitude from the RFID sensor,
wherein the first amplitude is dependent on a first state of the
environmental condition; and the resonation amplitude of the
multiresonator is configured to attenuate by a second amount
dependent on a second electrical conductivity of the sensor
material to provide a second response, and to output the second
response having a second amplitude from the RFID sensor, wherein
the second amplitude is dependent on a second state of the
environmental condition.
8. The RFID system of claim 7, further comprising an RFID
controller comprising the RFID reader and further comprising memory
configured to store data corresponding to an amplitude of the
response received by the RFID reader.
9. The RFID system of claim 8, further comprising: a first arm of
the multiresonator; and a second arm of the multiresonator spaced
from the first arm by an interstitial space, wherein the sensor
material is positioned within the interstitial space and bridges a
width of the interstitial space between the first arm and the
second arm.
10. The RFID system of claim 9, wherein the sensor material
comprises at least one of polyvinyl alcohol, polyacrylic acid, a
filled polyacrylic acid composite, polyarylene, and a filled
polyarylene composite.
11. The RFID system of claim 9, wherein the sensor material
comprises polyvinyl alcohol and the RFID device is further
configured to monitor or measure relative humidity.
12. The RFID system of claim 9, wherein the sensor material
comprises polyacrylic acid and the RFID device is further
configured to monitor or measure a concentration of hydrogen
ions.
13. The RFID system of claim 8, wherein the sensor material
comprises polypyrrole and the RFID device is further configured to
monitor or measure temperature.
14. A method for sensing an environmental condition, comprising:
receiving a first interrogation from a radio frequency
identification (RFID) reader using an RFID sensor, wherein the RFID
sensor comprises: a receive antenna; a transmit antenna; a
multiresonator comprising a plurality of resonators, a first arm of
the multiresonator, and a second arm of the multiresonator spaced
from the first arm by an interstitial space, wherein the
multiresonator is electrically coupled between the receive antenna
and the transmit antenna; and a sensor material within the
interstitial space and bridging a width of the interstitial space
between the first arm and the second arm, wherein the sensor
material has a variable electrical conductivity that is configured
to change depending on the environmental condition to which the
sensor material is exposed; attenuating a resonation amplitude of
the multiresonator by a first amount dependent on a first
electrical conductivity of the sensor material to provide a first
response; outputting the first response having a first amplitude
from the RFID sensor, wherein the first amplitude is dependent on a
first state of the environmental condition; receiving a second
interrogation from the RFID reader using the RFID sensor;
attenuating the resonation amplitude of the multiresonator by a
second amount dependent on a second electrical conductivity of the
sensor material to provide a second response, wherein the first
amount is different than the second amount; and outputting the
second response having a second amplitude from the RFID sensor,
wherein the second amplitude is different from the first amplitude
and is dependent on a second state of the environmental
condition.
15. (canceled)
16. The method of claim 14, wherein the sensor material comprises
at least one of polyvinyl alcohol, a filled polyvinyl alcohol
composite, polyacrylic acid, a semiconductor film, a sputtered
semiconductor film, a vapor-deposited semiconductor film,
polypyrrole, polyaniline, polyethylene amine,
poly(ethylene-co-acrylic acid), poly(vinyl
alcohol)-polypyrrole-ferric chloride (PVA-PPy-FeCl3) composite
films, multi-walled carbon nanotube (MWCNT)/poly(vinylidene
fluoride) (PVDF), polycaprolactam, Nylon-6,6, poly oxymethylene,
high density polyethylene, and combinations of two or more of
these, and the method comprises monitoring or measuring at least
one of relative humidity, concentration of hydrogen ions, and
temperature.
17. The method of claim 14, wherein the sensor material comprises
polyvinyl alcohol and the method comprises monitoring or measuring
relative humidity.
18. The method of claim 14, wherein the sensor material comprises
polyvinyl alcohol and the method further comprises monitoring or
measuring a concentration of hydrogen ions.
19. The method of claim 14, wherein the sensor material comprises
polyacrylic acid and the method further comprises monitoring or
measuring relative humidity.
Description
TECHNICAL FIELD
[0001] The present teachings relate generally to chipless radio
frequency identification (RFID) tags and, more particularly, to a
chemical sensor based on chipless RFID architectures.
BACKGROUND
[0002] Radio frequency identification (RFID) technology has become
increasingly commonplace for use in inventory tracking, loss
prevention, and other uses. An RFID system may include a
transponder or tag that is placed on an object and an interrogator
or reader that wirelessly receives information transmitted by the
tag. RFID tags may be broadly classified as active tags that
include a local power source such as a battery, or passive tags
that are activated by electromagnetic waves generated by the reader
that induce a current in an antenna within the tag.
[0003] RFID tags can include an electronic circuit that may be in
the form of an chip or integrated circuit (IC). The chip may store
data that is communicated to the reader. In contrast, a chipless
RFID tag has neither an integrated circuit nor discrete active
electronic components, and may be printed directly onto a substrate
resulting in a lower cost than a chipped RFID tag.
[0004] A chipless RFID tag may include a receive antenna that
intercepts interrogator output, a transmit antenna that broadcasts
data that is received by the interrogator, and a plurality or array
of resonators (i.e., a multiresonator) electrically coupled between
the receive antenna and the transmit antenna. During use, the
reader may output a broad band or spectrum of radio frequencies.
Depending on the configuration of the multiresonator, one or more
of the radio frequencies may include a frequency-dependent antenna
load that is intercepted by the receive antenna and causes the
multiresonator to resonate. The resonation modifies the signal that
is transmitted by the transmit antenna and may be received by the
interrogator. Each RFID tag may be encoded by etching a conductive
film to result a specific set of patterned resonant structures that
form the multiresonator. For unique identification of a particular
tag from a set of tags, each transponder must be made to include a
unique multiresonator design, which is an expensive process.
[0005] The receive antenna, the transmit antenna, and resonators
may be prepared using one or more patterning techniques to pattern
a conductive layer, for example a metal layer. Various patterning
techniques may be used, for example, stamping, chemical etching,
mechanical etching, laser etching, direct writing of a metal layer,
vapor deposition, etc.
[0006] As a practical matter, RFID technology uses radio
frequencies that have much better penetration characteristics to
material than do optical signals, and will work under more hostile
environmental conditions than bar code labels. Therefore, the RFID
tags may be read through paint, water, dirt, dust, paper, human
bodies, concrete, or through the tagged item itself. RFID tags may
be used in managing inventory, automatic identification of cars on
toil roads, security systems, electronic access cards, keyless
entry and the like.
[0007] Sensors for detecting various environmental conditions such
as temperature, relative humidity, concentration of hydrogen ions
(pH), the presence of various chemicals, as well as other
conditions are well known and based on various different
technologies. These sensors can include a substantial number of
electronic components that may require manual assembly, and are
there for costly. In many instances it is desirable to be apprised
of the state of a remote environment or an environment that may not
be easily inspected (e.g., the inside of a package).
[0008] A sensor for detecting various environmental conditions that
is less expensive than conventional sensors would be a welcome
addition to the art.
SUMMARY
[0009] The following presents a simplified summary in order to
provide a basic understanding of some aspects of one or more
embodiments of the present teachings. This summary is not an
extensive overview, nor is it intended to identify key or critical
elements of the present teachings, nor to delineate the scope of
the disclosure. Rather, its primary purpose is merely to present
one or more concepts in simplified form as a prelude to the
detailed description presented later.
[0010] In an embodiment, a radio frequency identification (RFID)
device according to an embodiment of the present teachings may
include a receive antenna, a transmit antenna, a multiresonator
comprising a plurality of resonators, wherein the multiresonator is
electrically coupled between the receive antenna and the transmit
antenna, and a sensor material bridging two or more electrically
conductive structures of the RFID device, wherein the sensor
material has a variable electrical conductivity that is configured
to change depending on an environmental condition to which the
sensor material is exposed.
[0011] In another embodiment, an RFID system according to an
embodiment of the present teachings may include an RFID reader and
an RFID sensor device configured to receive an interrogation from
the RFID reader and to output a response to the RFID reader upon
receipt of the interrogation. The RFID sensor device may include a
receive antenna, a transmit antenna, a multiresonator comprising a
plurality of resonators, wherein the multiresonator is electrically
coupled between the receive antenna and the transmit antenna, and a
sensor material bridging two or more electrically conductive
structures of the RFID device. The sensor material may include a
variable electrical conductivity that is configured to change
depending on an environmental condition to which the sensor
material is exposed.
[0012] In another embodiment, a method for sensing an environmental
condition may include receiving a first interrogation from a radio
frequency identification (RFID) reader using an RFID sensor,
wherein the RFID sensor includes a receive antenna, a transmit
antenna, a multiresonator comprising a plurality of resonators,
wherein the multiresonator is electrically coupled between the
receive antenna and the transmit antenna, and a sensor material
bridging two or more electrically conductive structures of the RFID
sensor, wherein the sensor material has a variable electrical
conductivity that is configured to change depending on the
environmental condition to which the sensor material is exposed.
The method may further include outputting a first response having a
first amplitude from the RFID sensor, wherein the first amplitude
is dependent on a first state of the environmental condition,
receiving a second interrogation from the RFID reader using the
RFID sensor, and outputting a second response having a second
amplitude from the RFID sensor, wherein the second amplitude is
different from the first amplitude and is dependent on a second
state of the environmental condition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The accompanying drawings, which are incorporated in, and
constitute a part of this specification, illustrate embodiments of
the present teachings and, together with the description, serve to
explain the principles of the disclosure. In the figures:
[0014] FIG. 1 is a plan view of an in-process radio frequency
identification (RFID) device in accordance with an embodiment of
the present teachings.
[0015] FIG. 2 is a cross section along 2-2 of the FIG. 1
structure.
[0016] FIG. 3 is a cross section of an in-process multiresonator in
accordance with an embodiment of the present teachings.
[0017] FIG. 4 is a cross section of an in-process multiresonator in
accordance with an embodiment of the present teachings.
[0018] FIG. 5 is a cross section of an in-process multiresonator in
accordance with an embodiment of the present teachings.
[0019] FIG. 6 is a cross section of an in-process multiresonator in
accordance with an embodiment of the present teachings.
[0020] FIG. 7 is a schematic depiction of an RFID sensor system
attached to an article in one exemplary use.
[0021] FIG. 8 is a flow diagram of a method for sensing an
environmental condition using an RFID device according to an
embodiment of the present teachings.
[0022] It should be noted that some details of the FIGS. have been
simplified and are drawn to facilitate understanding of the present
teachings rather than to maintain strict structural accuracy,
detail, and scale.
DETAILED DESCRIPTION
[0023] Reference will now be made in detail to exemplary
embodiments of the present teachings, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers will be used throughout the drawings to
refer to the same or like parts.
[0024] As used herein, unless otherwise specified: the term
"chipless" describes a radio frequency identification (RFID)
transponder that has neither an integrated circuit nor discrete
electronic components, such as a transistor or coil; the term
"resonator" or "resonant structure" refers to a structure having an
associated resonance corresponding to a characteristic frequency;
the term "spectral signature" refers to at least one identifying
resonance associated with an applied excitation frequency; the term
"tag" refers to a transponder or a combination of a transponder and
other structures that may include a carrier on which the
transponder is disposed or device package within which the
transponder is disposed. A tag may be attached to an article; the
term "transponder" refers to a device such as a tag that receives
signals, such as those transmitted by an interrogator, and sends
one or more response signals in response to the received signals;
the term "etched" refers to a process by which portions of a
material are removed, such as a chemical etch, a mechanical etch, a
laser etch or ablation, etc.; the term "security overlayer" refers
to a layer that, when tampered with, damages, destroys or otherwise
modifies a structure on which the security overlayer is disposed;
the term "generic RFID transponder" means an RFID transponder that
has an associated resonant structure for each frequency domain
applied by a transmitter, such as an interrogator.
[0025] FIG. 1 is a top view, and FIG. 2 is a magnified cross
section along 2-2 of FIG. 1, depicting a portion of a transponder
100 that is part of an RFID tag. Transponder 100 can include a
receive antenna 102, a multiresonator 104 including a plurality of
resonators 104A-104D, and a transmit antenna 106. As depicted in
FIG. 1, each resonator 104A-104D has a unique spiral pattern that
causes each resonator to resonate at a different frequency. In an
embodiment, an interstitial space, area, or region 110 between
adjacent arms of the spirals within a resonator may have a width
"W" as depicted in FIG. 2 of about 0.5 times a linewidth of the
conductive line that forms or provides the arms of the
multiresonator spiral. The multiresonator and, more particularly,
each resonator spiral and interstitial space, is designed such that
the interstitial space 110 does not cause an unintended resonance.
It will be appreciated that an RFID tag can include other
structures that are not depicted for simplicity, while various
depicted structures may be removed or modified.
[0026] In use, the interrogator outputs a broad spectrum of
frequencies that may be received by the receive antenna 102, and
that may cause one or more of the resonators 104A-104D to resonate.
The number of resonators 104A-104D that resonate and the amplitude
(e.g., magnitude and/or phase) at which they resonate results in an
output frequency that is translated into an analog signal that is
transmitted as a response signal by the transmit antenna 106 to the
interrogator. For example, and without limitation to the
frequencies specified, resonator 104A may resonate at 2.97
gigahertz (GHz), resonator 104B may resonate at 2.66 GHz, resonator
104C may resonate at 24 GHz, and resonator 104D may resonate at
24.3 GHz. Because the analog signal generated during an
interrogation and transmitted by the transmit antenna 106 is unique
to the specific tag from a plurality of tags as a result of the
unique pattern of resonators 104A-104D, the interrogator can
identify the specific tag from the plurality of tags. The
transponder 100 may be disposed on a carrier 108 such as directly
on an article or on an intermediate adhesive backing for attaching
onto an article. The carrier 108 may be a substrate on which the
RFID transponder is initially fabricated or may be a carrier on
which an RFID transponder is transferred onto after it is
fabricated. A carrier 108 having an adhesive backing may allow the
RFID transponder to be easily attached (i.e., tagged) onto an
article.
[0027] An embodiment of the present teachings can include an RFID
device that may be used as a sensor to detect one or more
environmental conditions, as well as a method for forming the RFID
device.
[0028] As depicted in FIG. 3, after forming the multiresonator 104
of FIG. 2, a sensory or sensor material 300 is disposed at least
within the interstitial spaces 110 between adjacent arms of each
resonator 104A-104D. The sensor material 300 is a material that
changes electrical conductivity with changes in the environmental
condition being measured. Various sufficient materials and methods
of formation are discussed below.
[0029] In one embodiment, the sensor material 300 may be deposited
or otherwise dispensed over the multiresonator 104 as depicted in
FIG. 3. FIG. 3 further depicts a patterned mask 302 that may be
formed over the carrier 108 to expose first regions where the
sensor material 300 is to be formed and to cover second regions
where the sensor material 300 is to be excluded. In one embodiment,
the sensor material 300 may be a solid such as a powder or a gel
that is dispensed over the mask 302 and over the multiresonator
104, and then removed from the masked regions. The removal from the
masked regions may be performed, for example, using a blade such
blade manufactured, for example, from a polymer such as silicone,
or other suitable material.
[0030] In another embodiment, the sensor material 300 may be
dispensed as a liquid solution including a solute suspended within
a solvent. In this embodiment, the solution may be dispensed over
the resonators 104A-104D using the mask 302 to contain the solution
to the regions of the multiresonator 104. The solvent may then be
removed using an appropriate curing process, leaving the solute as
a solid.
[0031] In either of these processes, after dispensing and
performing any necessary curing of the sensor material 300, the
mask 302 may be removed to result in a structure similar to that
depicted in FIG. 4.
[0032] It will be appreciated that, for the FIG. 4 structure, the
resonators 104A-104D have a first thickness extending from the
lower surface contacting the carrier 108 to the top surface that is
substantially parallel with the carrier 108. Further, the sensor
material 300 has a second thickness extending from the lower
surface contacting the carrier 108 at the interstitial spaces 110,
wherein the second thickness is greater than the first thickness.
This results in the sensor material 300 being formed over the top
of the multiresonators 104, such that the sensor material 300 is
not confined to only the interstitial spaces 110. Depending on
various design characteristics of the multiresonator 104 and the
chemical composition, density, and flexibility or rigidity of the
sensor material 300, the sensor material 300 formed over a top
surface the resonators 104A-104D may have a relatively large
dampening effect on the resonation of the multiresonator 104 in
response to an interrogation (i.e., interrogation signal or
"chirp"). In some uses and/or RFID designs, this dampening may be
desired or acceptable. In other uses and/or RFID designs, this
dampening may be excessive or not desired. Therefore, in some uses,
the thickness of the sensor material 300 may be reduced. The
reduction in thickness may be performed after forming the FIG. 4
structure, for example, by performing a vertical planarization or
buffing process to result in the structure of FIG. 5. In another
embodiment, a smaller quantity of the sensor material 300 may be
dispensed at FIG. 3, such that the sensor material is not dispensed
over the top surface of the resonators 104A-104D. The amount of
sensor material 300 dispensed, however, should be sufficient to
bridge the interstitial spaces 110 and physically contact the arms
of the resonators 104A-104D on either side of the interstitial
spaces 110 as depicted in FIG. 5 subsequent to any curing
process.
[0033] In another embodiment, the sensor material 300 may be
dispensed directly into only the interstitial spaces 110 such that
a mask is not required. For example, the sensor material 300 may be
dispensed using a dispensing tip 600 in fluid communication with a
sensor material supply 602 as depicted in FIG. 6. An amount of
sensor material 604 from the sensor material supply 602 may be
dispensed from an opening 606 in the dispensing tip 600 as
depicted. The sensor material 604 may be dispensed as a solid, for
example a powder, as a liquid, or as a gel. A carrier gas may be
used to improve dispensing of the sensor material 604, particularly
if the sensor material 604 is dispensed as a powder. The sensor
material 604 may be dispensed from the opening under a pressure
sufficient to expel the sensor material 604 at a desired flow rate
for a given speed of the dispensing tip 600 across the
multiresonator 104.
[0034] After dispensing the sensor material, the sensor material
300 within the interstitial spaces 110 is cured using an
appropriate curing process. For example, the sensor material 300
may be heated to remove a solvent or to flow and solidify a powder
such that the sensor material 300 becomes physically stable within
the interstitial space to prevent the material from dislodging
during subsequent processing or use.
[0035] After forming the sensor material 300, any additional
processing of the RFID device may be completed to form the final
RFID device that is suitable for use.
[0036] As discussed above, the sensor material 300 is a material
having a variable electrical conductivity. The electrical
conductivity of the sensor material 300 is a function of an
environmental condition that is being measured, for example,
relative humidity (RH), pH, temperature, the presence of certain
gaseous components, etc. As the electrical conductivity of these
films increases, the attenuation of a broad band interrogation
signal received by the antenna increases in the region of the
frequency of the resonant structure. In other words, the resonation
amplitude of a resonator in response to an interrogation is
inversely proportional to the electrical conductivity of the sensor
material 300. Accordingly, the strength of the attenuation can be
correlated with the environmental condition (RH, pH, etc.) within
which the tag is located.
[0037] A sensor for detecting RH may be formed by filling the
interstitial spaces 110 with a sensor material 300 that changes
electrical conductivity with a change in relative humidity. For
example, the electrical conductivity of polyvinyl alcohol (PVA) is
proportional to relative humidity, with the electrical conductivity
increasing as the PVA moistens from the absorption of moisture from
surrounding air, and decreasing as the PVA dries or desiccates with
decreasing humidity. In this case, the resonation of the
multiresonator 104 in response to an interrogation decreases with
increasing humidity.
[0038] An RFID device design manufactured as an RH sensor using PVA
may be correlated during testing. For example, data relative to the
correlation of RH percentage with resonation amplitude (response
amplitude) in response to an interrogation may be determined during
testing, where the response amplitude is measured over a range of
known RH percentages that may be encountered by the sensor during
use.
[0039] Similar devices may be constructed using other films
including those sensitive to pH, the presence of other chemicals,
temperature, light exposure, radiation exposure, or another
environmental condition. Various materials suitable for use as an
environmental sensor are discussed below.
[0040] For example, polyacrylic acid is known to change electrical
conductivity with a flux in pH. As the pH of the medium becomes
more acidic, the electrical conductivity of the film increases
decreases. Similarly, materials such as polyvinyl alcohol, and
filled compounds thereof, can be used for the measurement of RH,
strain, temperature, and the presence of hazardous materials. The
sensor material may include polypyrrole to monitor or measure
temperature. The sensor material may include at least one of
polyarylene, a filled polyarylene composite, polyvinyl alcohol, a
filled polyvinyl alcohol composite, polyacrylic acid, a filled
polyacrylic acid composite, a semiconductor film, a sputtered
semiconductor film, a vapor-deposited semiconductor film,
polypyrrole, polyaniline, polyethylene amine,
poly(ethylene-co-acrylic acid), poly(vinyl
alcohol)-polypyrrole-ferric chloride (PVA-PPy-FeCl.sub.3) composite
films, multi-walled carbon nanotube (MWCNT)/poly(vinylidene
fluoride) (PVDF), polycaprolactam, Nylon-6,6, poly oxymethylene,
high density polyethylene, and combinations of two or more of
these. The sensor may measure or monitor a concentration of
hydrogens resulting in a pH of from 1 to 12.
[0041] The amplitude of the response by the RFID sensor device to
an interrogation will change (either increase or decrease)
depending on the amount of saturation of the sensor material to the
condition being measured. In some cases, the electrical
conductivity may be proportional to the saturation, and in other
cases the electrical conductivity may be inversely proportional to
the saturation.
[0042] FIG. 7 is a schematic illustration of an RFID sensor system
700 attached to an article 702. The RFID sensor system 700
incorporates the use of an RFID sensor 704, such as an RFID sensor
as described above. The RFID sensor system 700 may include a
substrate 706 that provides a base for the RFID sensor system 700.
The RFID sensor 704 and an RFID controller 708 may be formed upon,
or otherwise attached, to the substrate 706. The RFID controller
708 may include an RFID reader 710 in electrical communication with
memory 712 through a data bus 714.
[0043] It will be appreciated that, during transport, storage, or
use of the article 702, the environmental conditions being
monitored by the RFID sensor 704 are likely to change and thus
continuous monitoring of the condition may be required. The RFID
controller 708 may be programmed to interrogate the RFID sensor 704
via a chirp 716 either continuously or at preprogrammed intervals.
The amplitude of a response 718 from the RFID sensor 704 to the
RFID controller 708 will depend on the saturation of the RFID
sensor 704 and, more particularly, the sensor material 300 (FIG. 3)
of the RFID sensor 704.
[0044] During use, the RFID controller 708 sends out an
interrogation to the RFID sensor 704 via the chirp 716. The RFID
sensor 704 issues a response 718 that is received by the RFID
controller 708. Data corresponding to the amplitude of the response
718 received by the RFID controller 708 is written, for example by
the RFID reader 710, to the memory 712 through the data bus 714.
Subsequently, the monitoring data may be downloaded from the
memory, either wirelessly or through a wired connector 720 of the
RFID sensor system 700, for analysis.
[0045] FIG. 8 is a flow chart of a method for sensing an
environmental condition that may employ the use of the RFID device
described above. In an embodiment, an RFID reader outputs a first
interrogation signal to an RFID device that includes a sensor
material as shown at 802. As described above, the RFID sensor can
include the receive antenna, the transmit antenna, and the
multiresonator that includes a plurality of resonators, wherein the
multiresonator is electrically coupled between the receive antenna
and the transmit antenna. The RFID sensor may further include the
sensor material bridging two or more electrically conductive
structures of the RFID device, wherein the sensor material has a
variable electrical conductivity that is configured to change
depending on the environmental condition to which the sensor
material is exposed.
[0046] At 804, the RFID sensor receives a first interrogation from
the RFID reader. At 806, a first response is output from the RFID
sensor to the RFID reader, which is received by the RFID reader at
808. The first response has a first amplitude that is dependent on
a first state of the environmental condition. A resonation
amplitude of, for example, the multiresonator, the transmit
antenna, the receive antenna, or another RFID sensor structure may
be attenuated by a first amount during the first response dependent
on a first electrical conductivity of the sensor material to
provide the first response.
[0047] Data corresponding to the first amplitude of the first
response may be stored in memory at 810. Subsequently, the RFID
reader may output a second interrogation at 812 that is received by
the RFID sensor at 814, and a second response may be output from
the RFID device at 816 that is received by the RFID reader at 818.
A resonation amplitude of, for example, the multiresonator, the
transmit antenna, the receive antenna, or another RFID sensor
structure may be attenuated by a second amount during the second
response dependent on a second electrical conductivity of the
sensor material to provide the second response.
[0048] Data corresponding to the second amplitude of the second
response may be stored in memory at 820. It will be appreciated
that the second amplitude may be different than the first amplitude
if the environmental condition surrounding the RFID sensor has
changed.
[0049] The amplitudes of the responses are thus variable and
dependent on the state of the environmental condition that
surrounds the RFID sensor, and by a second amount during the second
response dependent on a second electrical conductivity of the
sensor material to provide the second response.
[0050] The present teachings thus allow for an environmental sensor
designed using RFID device technology. An RFID tag that allows
monitoring of environmental conditions may be processed using
automated manufacturing techniques, and may be manufactured at a
low cost. These remote environmental sensors may be used in
packaging, for example, to monitor environmental conditions such as
RH, temperature, etc. In one technique, layers of materials that
change conductivity in response to environmental conditions may be
placed in the interstitial regions of resonant structures etched in
a microwave antenna, resonator(s), receive antenna, transmit
antenna, etc. In one embodiment, the interstitial regions in a
meander antenna may be filled with polyvinyl alcohol (PVA), which
is known to vary in conductivity with RH.
[0051] It will be appreciated that the sensor material 300 may be
located at a single resonator, or two or more resonators but less
than all of the resonators, or all of the resonators, of a
plurality of resonators that make up the RFID multiresonator.
Additionally, the sensor material may be located at RFID locations
other than, or in addition to, the multiresonator, for example, the
transmit antenna, the receive antenna, or at another location, that
provides a flux in the response to an interrogation, where the
response correlates with an environmental change being that is
being measured.
[0052] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the present teachings are
approximations, the numerical values set forth in the specific
examples are reported as precisely as possible. Any numerical
value, however, inherently contains certain errors necessarily
resulting from the standard deviation found in their respective
testing measurements. Moreover, all ranges disclosed herein are to
be understood to encompass any and all sub-ranges subsumed therein.
For example, a range of "less than 10" can include any and all
sub-ranges between (and including) the minimum value of zero and
the maximum value of 10, that is, any and all sub-ranges having a
minimum value of equal to or greater than zero and a maximum value
of equal to or less than 10, e.g., 1 to 5. In certain cases, the
numerical values as stated for the parameter can take on negative
values. In this case, the example value of range stated as "less
than 10" can assume negative values, e.g. -1, -2, -3, -10, -20,
-30, etc.
[0053] While the present teachings have been illustrated with
respect to one or more implementations, alterations and/or
modifications can be made to the illustrated examples without
departing from the spirit and scope of the appended claims. For
example, it will be appreciated that while the process is described
as a series of acts or events, the present teachings are not
limited by the ordering of such acts or events. Some acts may occur
in different orders and/or concurrently with other acts or events
apart from those described herein. Also, not all process stages may
be required to implement a methodology in accordance with one or
more aspects or embodiments of the present teachings. It will be
appreciated that structural components and/or processing stages can
be added or existing structural components and/or processing stages
can be removed or modified. Further, one or more of the acts
depicted herein may be carried out in one or more separate acts
and/or phases. Furthermore, to the extent that the terms
"including," "includes," "having," "has," "with," or variants
thereof are used in either the detailed description and the claims,
such terms are intended to be inclusive in a manner similar to the
term "comprising." The term "at least one of" is used to mean one
or more of the listed items can be selected. As used herein, the
term "one or more of" with respect to a listing of items such as,
for example, A and B, means A alone, B alone, or A and B. The term
"at least one of" is used to mean one or more of the listed items
can be selected. Further, in the discussion and claims herein, the
term "on" used with respect to two materials, one "on" the other,
means at least some contact between the materials, while "over"
means the materials are in proximity, but possibly with one or more
additional intervening materials such that contact is possible but
not required. Neither "on" nor "over" implies any directionality as
used herein. The term "conformal" describes a coating material in
which angles of the underlying material are preserved by the
conformal material. The term "about" indicates that the value
listed may be somewhat altered, as long as the alteration does not
result in nonconformance of the process or structure to the
illustrated embodiment. Finally, "exemplary" indicates the
description is used as an example, rather than implying that it is
an ideal. Other embodiments of the present teachings will be
apparent to those skilled in the art from consideration of the
specification and practice of the disclosure herein. It is intended
that the specification and examples be considered as exemplary
only, with a true scope and spirit of the present teachings being
indicated by the following claims.
[0054] Terms of relative position as used in this application are
defined based on a plane parallel to the conventional plane or
working surface of a workpiece, regardless of the orientation of
the workpiece. The term "horizontal" or "lateral" as used in this
application is defined as a plane parallel to the conventional
plane or working surface of a workpiece, regardless of the
orientation of the workpiece. The term "vertical" refers to a
direction perpendicular to the horizontal. Terms such as "on,"
"side" (as in "sidewall"), "higher," "lower," "over," "top," and
"under" are defined with respect to the conventional plane or
working surface being on the top surface of the workpiece,
regardless of the orientation of the workpiece.
* * * * *