U.S. patent application number 14/689626 was filed with the patent office on 2015-11-12 for elastomeric particle having an electrically conducting surface, a pressure sensor comprising said particles, a method for producing said sensor and a sensor system comprising said sensors.
The applicant listed for this patent is Swelling Solutions, Inc.. Invention is credited to Landy Toth, Johan Wallen.
Application Number | 20150320356 14/689626 |
Document ID | / |
Family ID | 37907032 |
Filed Date | 2015-11-12 |
United States Patent
Application |
20150320356 |
Kind Code |
A1 |
Toth; Landy ; et
al. |
November 12, 2015 |
ELASTOMERIC PARTICLE HAVING AN ELECTRICALLY CONDUCTING SURFACE, A
PRESSURE SENSOR COMPRISING SAID PARTICLES, A METHOD FOR PRODUCING
SAID SENSOR AND A SENSOR SYSTEM COMPRISING SAID SENSORS
Abstract
A compression treatment device includes a pressure sensor
system. The pressure sensor system includes at least one sensor
cluster positioned relative to a body part, wherein each sensor
cluster includes a plurality of pressure sensor elements. Further,
each sensor cluster includes at least one pressure sensor element
or group of pressure sensor elements connected in parallel with
another pressure sensor element or group of pressure sensor
elements, and at least one pressure sensor element or group of
pressure sensor elements connected in series with another pressure
sensor element or group of pressure sensor elements.
Inventors: |
Toth; Landy; (Doylestown,
PA) ; Wallen; Johan; (Linkoping, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Swelling Solutions, Inc. |
Minneapolis |
MN |
US |
|
|
Family ID: |
37907032 |
Appl. No.: |
14/689626 |
Filed: |
April 17, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12524312 |
Jan 22, 2010 |
9027408 |
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PCT/EP2007/000567 |
Jan 24, 2007 |
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14689626 |
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Current U.S.
Class: |
600/587 |
Current CPC
Class: |
A61B 2562/0247 20130101;
A61H 9/0078 20130101; G01L 1/205 20130101; H01C 10/106 20130101;
H01B 1/22 20130101; A61B 5/4848 20130101; H01C 10/12 20130101; G01L
9/02 20130101 |
International
Class: |
A61B 5/00 20060101
A61B005/00; A61H 9/00 20060101 A61H009/00; G01L 9/02 20060101
G01L009/02 |
Claims
1-150. (canceled)
151. A compression treatment device comprising: one or more layers
configured to apply pressure to a body part, wherein the one or
more layers comprise at least a carrier layer; and a pressure
sensor system, wherein the pressure sensor system comprises at
least one sensor cluster, wherein each sensor cluster comprises a
plurality of pressure sensor elements distributed over at least a
portion of the carrier layer, and further wherein each sensor
cluster comprises: at least one pressure sensor element or group of
pressure sensor elements connected in parallel with another
pressure sensor element or group of pressure sensor elements, and
at least one pressure sensor element or group of pressure sensor
elements connected in series with another pressure sensor element
or group of pressure sensor elements.
152. The compression treatment device of claim 151, wherein the one
or more layers comprise at least one layer associated with one or
more actuators configured to provide compression to the body
part.
153. The compression treatment device of claim 152, wherein the at
least one layer associated with the actuator comprises at least one
layer forming a part of an inflatable bladder configured to provide
compression to the body part.
154. The compression treatment device of claim 151, wherein the
device further comprises only two external connections for each
sensor cluster to provide signal information therefrom.
155. The compression treatment device of claim 151, wherein at
least the carrier layer comprises a flexible material to form about
the body part for measuring pressure applied thereto.
156. The compression treatment device of claim 151, wherein the
carrier layer forms a part of a laminated structure.
157. The compression treatment device of claim 151, wherein the one
or more layers comprise one or more smoothing layers positioned on
one or both sides of the carrier layer to smooth stresses occurring
at an interface between the plurality of pressure sensor elements
and surroundings thereof before such stresses reach the plurality
of pressure sensor elements.
158. The compression treatment device of claim 151, wherein the one
or more layers comprise at least one smoothing layer positioned
between the carrier layer and the body part when the compression
treatment device is worn by a user to smooth stresses occurring at
an interface between the plurality of pressure sensor elements and
the body part.
159. The compression treatment device of claim 158, wherein the at
least one smoothing layer comprises a layer formed of at least one
of microcellular foam structure, rubber, and non-woven fabric.
160. The compression treatment device of claim 158, wherein the at
least one smoothing layer is 5 to 10 times the thickness of the
carrier layer.
161. A compression treatment device to apply pressure to a body
part, wherein the compression treatment device comprises: at least
one layer of flexible material to form about the body part; and a
pressure sensor system, wherein the pressure sensor system
comprises at least one sensor cluster positionable relative to the
body part when the at least one layer of flexible material is worn
and forms about the body part, wherein each sensor cluster
comprises at least three spaced apart pressure sensor elements, and
further wherein each sensor cluster comprises: at least one
pressure sensor element or group of pressure sensor elements
connected in parallel with another pressure sensor element or group
of pressure sensor elements, and at least one pressure sensor
element or group of pressure sensor elements connected in series
with another pressure sensor element or group of pressure sensor
elements.
162. The compression treatment device of claim 161, wherein the
device further comprises at least one layer associated with one or
more actuators configured to provide compression to the body
part.
163. The compression treatment device of claim 162, wherein the at
least one layer associated with the actuator comprises at least one
layer forming a part of an inflatable bladder configured to provide
compression to the body part.
164. The compression treatment device of claim 161, wherein the
device further comprises only two external connections for each
sensor cluster to provide signal information therefrom.
165. The compression treatment device of claim 161, wherein the
device further comprises one or more smoothing layers positioned on
one or both sides of the plurality of pressure sensor elements to
smooth stresses occurring at an interface between the plurality of
pressure sensor elements and surroundings thereof before such
stresses reach the plurality of pressure sensor elements.
166. The compression treatment device of claim 161, wherein the
device further comprises at least one smoothing layer positioned
between the carrier layer and the body part when the compression
treatment device is worn by a user to smooth stresses occurring at
an interface between the plurality of pressure sensor elements and
the body part.
167. The compression treatment device of claim 166, wherein the at
least one smoothing layer comprises a layer formed of at least one
of microcellular foam structure, rubber, and non-woven fabric.
168. The compression treatment device of claim 161, wherein each
sensor cluster comprises pressure sensor elements forming a
circuit, a reduced equivalent circuit of which substantially
comprises a polygon network element.
Description
BACKGROUND OF THE INVENTION
[0001] The present disclosure relates to pressure sensors and
systems comprising such sensors. In particular, the present
disclosure is directed towards sensors and sensor systems that may
be used for measuring pressure on a body part.
[0002] Hence, the present disclosure relates to particles that may
form part of sensor elements, sensor systems, clusters of sensor
elements and devices for measuring pressure on a body part.
[0003] There are many applications in which it may be desirable to
measure pressure on a body part. As a non-limiting example, it may
be desirable to measure pressure on a body part in connection with
compression treatment of the body part. Compression therapies may
be used for treatment and/or prophylaxis of a number of conditions,
including, but not limited to, Deep Vein Thrombosis (DVT), vascular
disorders, circulatory disorders, edemas, heart conditions (treated
by counterpulsation), lymphedema, burns, injuries, and
embolisms.
[0004] Some devices for compression treatment are known in the art,
e.g., from US 2004/0073146 A1, US 2004/0073146 A1, US 2002/0173735
A1, U.S. Pat. No. 6,434,852 B1, U.S. Pat. No. 5,997,465, U.S. Pat.
No. 6,123,681, U.S. Pat. No. 6,198,204 B1, EP 1 324 403 A1, US
2004/0167375 A1, WO 2004/093763 A1 and US 2005/0043657 A1.
[0005] Presently available systems for measuring pressure on a body
part, however, suffer from a number of drawbacks. Major issues with
existing measurement systems have been identified on the areas of
mismatched mechanical properties (body/device impedance mismatches
and resulting interface stress modification), sensitivity (often
too high), quiescent impedance (often nearly infinite),
nonlinearity, poor repeatability (cycle to cycle and insertion to
insertion), creep, hysteresis, and sensitivity to curvature,
temperature-pressure-humidity, etc.
[0006] Generally existing sensors have excellent precision (which
is good) and perform well at high pressures in planar, mechanically
isolated spaces between well characterized surfaces. Such spaces
and surfaces are not available in the case of devices for measuring
pressure on a body part.
[0007] U.S. Pat. No. 2,951,817 discloses a variable resistance
material, comprising a body of elastomeric polyvinyl chloride with
a granular filler selected from a group assisting of precipitated
manganese dioxide and microphone carbon granules.
[0008] U.S. Pat. No. 3,629,774 discloses a progressively
collapsible variable resistance element, comprising an elastic
cellular structure of, e.g., elastomer foam. Examples given include
silicone rubber, natural rubber, latex and polyurethane rubber. The
element further comprises a conducting coating provided on the
inside of the cells in the structure. Examples of coaling materials
are carbon (graphitized, partially graphitized, carbon black),
sliver, gold, copper, tungsten, aluminum, and other metals.
[0009] U.S. Pat. No. 4,292,261 discloses a pressure sensitive
conductor and method of manufacturing the same. The conductor
comprises an isolating elastomer having electrically conductive
magnetic particles dispersed therein.
[0010] U.S. Pat. No. 6,388,556 B1 discloses a film pressure
sensitive resistor and pressure sensitive sensor. The film
comprises a binder, spherical elastomeric-particles and conductive
particles, such as carbon black. Examples of conductive particles
comprise graphite, carbon black, indium-doped tin oxide and the
like. Examples of elastic organic fillers comprise silicone
polymer, acrylic polymer, styrene polymer, urethane polymer and the
like. Examples of spherical elastomeric particles comprise nylon
particles. The binder may be a silicone rubber, polyurethane resin,
epoxy resin, phenol resin or polyester resin.
[0011] U.S. Pat. No. 6,291,558 B1 discloses a polymer composition
comprising an electrically conductive filler material selected from
a group consisting of powder-form metallic elements and alloys,
electrically conductive oxides of such elements or alloys and
mixtures thereof, mixed with a non-conductive elastomer.
[0012] The above described sensors are of a conductive elastomer
type, and constitute composites of an elastomeric matrix and a
conductive particle filler. When such composites are used in
practice, strain related damage occurs easily, and as such, creep,
hysteresis, and electrical aging are all increased significantly.
At such high loading levels so as to induce finite quiescent
impedance, the viscoelastic properties of the composite degrade
dramatically and their usefulness as "pressure sensors" is greatly
diminished.
[0013] U.S. Pat. No. 6,388,556 B1 discloses, as prior art for the
invention patented therein, a variable area type pressure sensor,
wherein a conduction path between first and second coplanar
electrodes is variable in response to a pressure applied on the
sensor. It is recognized that this type of sensor does not provide
a smooth resistance-load curve.
[0014] Such sensors do not provide the desired accuracy needed in
measuring pressure on a body part.
[0015] Hence, there is a need for improvements in sensors for
measuring pressure on a body part.
SUMMARY OF THE INVENTION
[0016] It is thus a general object of the present disclosure to
provide a sensor or sensors that overcome, or at least alleviate,
the problems associated with prior art sensors.
[0017] It is an object to provide a sensor or sensors that are
sufficiently accurate and have sufficiently high precision for
measuring pressures at an interface.
[0018] It is also an object to provide a sensor or sensors that are
suitable for measuring pressure, in particular contact pressure,
applied to a human or animal body.
[0019] It is also an object to provide a sensor or sensors that can
be produced at a sufficiently low cost.
[0020] The invention is defined by the appended independent claims.
Embodiments are set forth in the dependent claims, and in the
following description and drawings.
[0021] According to a first aspect, there is provided an
elastomeric particle, comprising a non-conducting elastomeric body
having an electrically conducting surface. The conducting surface
is organized such that the overall mechanical properties of the
particle are governed by the elastomeric body of the particle,
while the electrical properties are governed by the conducting
surface.
[0022] Such an elastomeric particle may be suitable for use in a
pressure sensor element, i.e., it may be sufficiently small, and
suitable for inclusion of a plurality of such elastomeric particles
in a matrix to provide a composite material, whose conduction
properties are variable in response to mechanical deformation of
the sensor element.
[0023] Such particles may thus be utilized to form a composite
material having pressure sensitive electrical properties and
reduced creep, hysteresis and/or electrical aging, as compared with
prior art composite materials.
[0024] According to a second aspect, reduced creep, hysteresis
and/or electrical aging, as compared with prior art composite
materials there is provided a pressure sensor element, comprising a
plurality of particles having at least conducting surfaces, said
particles being arranged as at least one particle layer on a
non-conducting elastomeric portion.
[0025] Such a pressure sensor element may be used to form in situ a
composite of particles and a matrix material.
[0026] The particles may be elastomeric particles as set forth
above. Alternatively, the particles may be non-elastomeric.
[0027] According to a third aspect, there is provided composite
material comprising particles having a first modulus of elasticity
and electrically conductive surface; and an elastomeric matrix
material having a second modulus of elasticity, wherein said first
modulus of elasticity is different from said second modulus of
elasticity, and wherein the particles are elastomeric.
[0028] Such a composite material may be used to form a pressure
sensor element. In particular, such a soft conducting particle
composite may be used to better manage damage, electrical impedance
and strain sensitivity within the composites by improving stresses
at interfaces between conducting particles and matrix and within
the matrix. Furthermore, hysteresis and strain related damage
within composite are reduced, and finite quiescent impedance can be
set during fabrication via alignment, volumetric ratios of
constituents and fabrication conditions (solvents, compression,
temperature profile during curing, etc). Also, pressure sensitivity
may be determined primarily by the equivalent hardnesses and the
structure of the sensor built from the composite, in terms of
geometry, field orientation, electrode placement, etc.
[0029] According to a fourth aspect, there is provided a printable
compound for forming the composite material as described above, the
compound comprising said particles and a composition or
compositions for forming the matrix material.
[0030] Such a printable compound may be applied in a desired
pattern for forming portions of the composite material according to
the third aspect.
[0031] According to a fifth aspect, there is provided a pressure
sensor element comprising a composite material as described
above.
[0032] According to a sixth aspect, there is provided a sensor
system comprising at least one sensor element as described above,
and means for receiving a sensor signal from said sensor
element.
[0033] According to a seventh aspect, there is provided a pressure
sensor element, comprising a resistive element providing a
conduction path, a first electrode, connected to the resistive
element, a second electrode, which in a quiescent state is spaced
from said first electrode, wherein the second electrode, when the
pressure sensor element is subjected to a pressure, is arranged to
contact said first electrode or said resistive element.
[0034] Such a sensor element may have improved mechanical response
and aging characteristics, immunity to EMI, and the ability to be
used for inline calibration of compression systems. Such a pressure
sensor element may be used individually, or in combination with
sensors or sensor clusters according to the other aspects, to
provide an accurate pressure value, and/or for calibration
purposes.
[0035] According to an eight aspect, there is provided a sensor
system comprising at least one pressure sensor element as described
above and means for receiving a sensor signal from said sensor
element.
[0036] According to a ninth aspect, there is provided a sensor
cluster, comprising at least three sensor elements wherein the
sensor cluster comprises at least one sensor element or group of
sensor elements, which is connected in parallel with-another sensor
element, or group of sensor elements, and at least one sensor
element or group of sensor elements, which is connected in series
with another sensor element, or group of sensor elements. The
cluster may be an organized collection of miniature sensory
elements and electrical traces.
[0037] Such a sensor cluster may be used to provide an average
pressure value over an area, based on a plurality of sensor
elements, without having to handle values from each individual
sensor element. The sensor cluster also provides a means of
measuring pressure with thinner sensors then an equivalently sized
sensor of the prior art. It also provides a means of measuring
characteristics of the applied pressure over the entire cluster in
a fast, simple and economical way. The cluster also decreases
sensitivity to curvature, thereby improving sensor performance on
non-planar or uneven surfaces.
[0038] Such a sensor cluster may also comprise sensor elements
forming a circuit, a reduced equivalent circuit of which
substantially comprises a polygon network element.
[0039] A polygon network element of order N is a network consisting
of N+I separate nodes, one of which may be termed "main node" and N
of which may be termed "minor nodes", wherein each minor node is
connected to the main node by a circuit element, and is connected
to two other minor nodes by circuit elements.
[0040] By "substantially a polygon network element", is understood
that circuit elements may be missing or added from the perfect
polygon network element, however, not to such an extent as to
seriously impair the effect of the polygon network element. As
non-limiting examples, there may be one or a few circuit elements
may be missing as compared to the perfect polygon network element
or there may be one or a few circuit elements added as compared to
the perfect polygon network element.
[0041] According to a team aspect, there is provided a sensor
system comprising at least one sensor cluster as described above
and means for receiving a sensor signal front said sensor
element.
[0042] According to an eleventh aspect, there is provided a sensor
system, comprising at least one first pressure-sensor element
according to either or both of the second or fifth aspects and at
least one second pressure sensor element according to the seventh
aspect.
[0043] Such a sensor system may be used for measuring pressure on a
body part.
[0044] According to an eleventh aspect, there is provided a device
for measuring pressure on a body part, comprising a sensor system
as described above.
[0045] According to a twelfth aspect, there is provided a method
for producing a sensor element, comprising providing a substrate,
dispensing, in a first desired pattern on the substrate, a primer,
and dispensing, at least in said desired pattern, particles having
a conducting surface.
[0046] According to a thirteenth aspect, there is provided a method
for producing a sensor element, comprising providing a substrate,
dispensing, in a desired pattern on the substrate, a compound
according to the fourth aspect, and allowing said compound to set,
whereby said composite material is formed.
[0047] According to a fourteenth aspect, there is provided a method
for producing a sensor element, comprising providing a first
substrate, providing a resistive element on the substrate by a
first patterning operation, providing a first electrode on the
substrate by a second patterning operation, providing a spacer
element on the substrate, and providing a second substrate
comprising a second electrode, such that said spacer element is
between the first electrode and the second electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] FIGS. 1a-1b are schematic cross-sectional views of different
embodiments of a particle according the present disclosure.
[0049] FIGS. 2a-2h are schematic cross-sectional views of further
embodiments of a particle according the present disclosure.
[0050] FIG. 3 is a schematic view of a compound according to the
present disclosure.
[0051] FIG. 4 is a schematic cross-sectional view of a sensor
element according to a first type of embodiment of 5 the present
disclosure.
[0052] FIG. 5 is a schematic cross-sectional view of a sensor
element according to the first type of embodiment of the present
disclosure.
[0053] FIGS. 6a and 6b are schematic cross-sectional views of a
sensor element according to the first type of embodiment of the
present disclosure.
[0054] FIG. 7 is a schematic cross-sectional view of a sensor
element according to the first type of embodiment of the present
disclosure.
[0055] FIG. 8 is a schematic cross-sectional view of a sensor
element according to the first type of embodiment of the present
disclosure.
[0056] FIG. 9 is a schematic cross-sectional view of a sensor
element according to the first type of embodiment of the present
disclosure.
[0057] FIG. 10 is a schematic cross-sectional view of a sensor
element according to the first type of embodiment of the present
disclosure.
[0058] FIGS. 11 -14 are schematic views of layers forming part of a
sensor element according to a second type of embodiment of the
present disclosure.
[0059] FIGS. 15 and 16 are cross-sectional views of the sensor
element of FIGS. 11-14.
[0060] FIGS. 17-18 are diagrams illustrating the behavior of the
sensor element of FIGS. 11-16.
[0061] FIGS. 19a-19c illustrate alternative embodiments of the
sensor element of FIGS. 11-16.
[0062] FIGS. 20a, 20b, 21a, 21b, 22a, and 22b illustrate yet
further embodiments of the sensor element of FIGS. 11-16.
[0063] FIGS. 23a-23b illustrate generic connection schemes for a
pair of sensor elements.
[0064] FIGS. 24-26 illustrate connection schemes for a plurality of
sensor elements.
[0065] FIG. 27 is a diagram illustrating the behavior of the
connection schemes of FIGS. 24-26.
[0066] FIGS. 28-33 illustrate further connection schemes equivalent
circuits.
[0067] FIGS. 34-36 schematically illustrate devices for measuring
pressure on a body part.
[0068] FIG. 37 schematically illustrates a sensor cluster forming
part of a sensor system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0069] Referring to FIGS. 1a-2b, an elastomeric particle 1, 1', 1''
according to the first aspect will now be described. Such an
elastomeric particle 1, 1', 1'' comprises an elastomeric body 2 and
a conducting surface layer 4a, 4b, 6. The conducting surface layer
4a, 4b, 6 may be formed by a plurality of conducting particles 7a,
7b, by deposition of a conducting material 6 (e.g., metal or
conducting polymer), or by modifying the conducting properties of
the surface of the elastomeric body 2 (e.g., interpenetrating
polymer networks with electrically conducting polymer
constituents). In the case of conducting particles 7a, 7b, these
may be adhered to the elastomeric body 2 by a primer 3. One or more
further conductive layers 4b may be provided (as indicated in FIGS.
1a and 2a). and preferably attached to the previous layer 4a by a
binder 5.
[0070] The size of the elastomeric particle 1, 1', 1'' may be in
the range of 0.1-250 .mu.m, more preferably in the range of 1-10
.mu.m. The elastomeric particle may have a shape that is regular or
irregular. As non-limiting examples, the elastomeric particles may
be rod-like, ellipsoidal, spherical, platelets, granules, fibers,
porous shells, scaffolding, etc. The elastomeric particles may be
hollow or solid. Generally, spherical elastomeric particles may be
produced by emulsion or suspension polymerization. Other shapes may
be produced by, e.g., cryogenic pulverization or other breakdown
processes, such as grinding.
[0071] Another way of producing such elastomeric particles is
through seed polymerization, which is described in, e.g., JP-A
58-106554 and JP-A 63-191818. Yet another way of producing such
elastomeric particles is through emulsion polymerization With
additional conditions for creating larger, crosslinked, elastomeric
particles, such as is described in U.S. Pat. No. 6,914,100, JP-A
83-191805, JP-A 4323213 and JP-A 10-310603. The polymerization
process corn be of any type, including radical, polyaddition or
polycondensation reactions.
[0072] The elastomeric particles may be cross-linked to ensure
suitable mechanical properties. It is noted that the references
above demonstrate creation of particles that are crosslinked.
[0073] in a practical case, it may be convenient to purchase
elastomeric particles, which do not have a conducting surface, in
wet or dry form from various suppliers, examples of which include
Dow Corning, Shin Etsu Chemical and Rohm and ideas for small
particles, and several chemical suppliers for larger particles.
Naturally, it is also possible to purchase pellets that are to be
pulverized or atomized. For example, commercially available
thermoplastic elastomer pellets can be heated and spray dried to
create smaller particles, or alternatively cryogenically pulverized
to produce the same.
[0074] The elastomeric body 2 and/or the matrix 11, as will be
discussed below, may, as non-limiting examples comprise silicone
elastomers, polyurethanes, polybutadiene (specifically high cis
polybutadiene), natural rubber, polyisoprene,
ethylene-propylene-diene, thermoplastic elastomers, segmented block
copolymers, etc. In particular, silicone elastomers have excellent
compression set, creep and temperature stability, and can be
formulated with excellent fatigue properties, while polyurethanes
and polybutadienes can be formulated with excellent dynamic
properties (low hysteresis, high resilience, long fatigue life,
etc.). Specifically useful are chain-extended PU elastomers with
amide chain extenders, with excellent temperature/frequency
stability of mechanical properties.
[0075] An example of a suitable material is provided in van der
Schuur, M, Noordover B, Gaymans R J, 2006, Polyurethane elastomers
with amide chain extenders of uniform length. Polymer, 47;
1091-1100.
[0076] There are also biomaterials with excellent resilience, such
as elastin and resilin, see Elvin C M, Carr A G, Huson M G, Maxwell
J M, Pearson R D, Vuocolo T. Liyou N E, Wong D C, Merritt O J,
Dixon M E. 2005. Synthesis and properties of crosslinked
recombinant pro-resilin. Nature. 437(7061): 999-1002.
[0077] In general, the elastomeric body 2 and the matrix 11 may be
made from the same family of elastomer, with different degrees of
crosslinking or fillers to achieve variations in hardness. One
example of an easy to use system is the three-component, variable
mix ratio polyurethane system from Crosslink Technology Inc.
(disclosed in US 2006/0058456), or their CLC system. Examples of
hardening filler materials include quartz, silica, mica, carbon
black, etc. These materials are especially suitable for use as
fillers in silicone systems.
[0078] For the conducting layer 4a, 4b, 6, a range of materials may
be used, including metallic or metal oxide conducting species,
carbon and structures thereof, conducting polymers etc.
Combinations of these materials may also be used.
[0079] In case alignment, is desirable, the conducting layer 4a,
4b, may include materials from the known groups of paramagnetic,
super paramagnetic, or ferromagnetic materials.
[0080] In one embodiment, the particles 1, 1', 1'' may be
constructed by layer-by-layer self assembly (LbL-SA) or
layer-by-layer covalent self assembly (LbL-CSA) approaches, which
produces stronger interlayer bonding than LbL-SA. In this case, the
conductive materials (e.g., metallic, metal-oxide, semiconductive
or organic) forming the conducting layers 4a, 4b will generally be
nanoparticulates 7a, 7b with useful examples being nanoparticles of
(including core shell particles) gold, silver, platinum, palladium,
copper, nickel, aluminum, chromium, etc. In particular,
nanoparticles of gold are easy to produce, and can be stored in a
stable configuration before the deposition process.
[0081] As one alternative, the conducting layer 4a, 4b, 6 may be
provided by electroless deposition, which is a well known method
wherein a seed layer (catalyst), such as palladium, is applied to
the particles, and further conducting material is deposited via
reduction of a metal salt onto the surface of the elastomeric
particles. Such a method is described in Mallory G O, Hajdu J B,
Electroless plating: fundamentals and applications, American
Electroplaters and Surface Finishers Society, Florida, 1990. In
such cases a primer 3 may be applied prior to the deposition of the
conducting layer.
[0082] The elastomeric particles may be somewhat swollen during the
application of the conducting layer 4a, 4b, 6, regardless of which
type of application technique is selected so that when they are
dried, the surface will take on a microscopic texture, in addition
the particles will be more suitable for undergoing strain as their
surfaces will be wrinkled rather than smooth, since when smooth and
too thick, the conductive layers will interfere with the mechanical
properties of the particles and can also crack, thereby losing
their conductive properties.
[0083] As another option, conducting polymers can be
electrochemically deposited on the surface of the elastomeric body
2. For example, a thin conducting polymer layer can be deposited so
as to produce an inherently conducting layer over the elastomeric
particles using in situ oxidization. Such techniques are described
within U.S. Pat. No. 5,240,644, U.S. Pat. No. 6,899,829, Gregory R
V, Kimbrell W C, Kuhn H H, Synthetic Metals, 28 (1989), pg 823, and
Hansen T S, West K, Hassager O, Larsen N B, Synthetic Metals, 158
(2006), pg 1203.
[0084] In the case of LbL-SA or LbL-CSA produced layers, the
conductivity of the layers is a combination of quantum tunneling
and physical contact between the tightly packed conductive
nanoparticles 7a, 7b arranged within the layers over the surfaces
of the elastomeric particles 1, 1', 1''. This tight knit structure
minimally affects the mechanical properties of the elastomeric
particle 1, 1', 1''. This arrangement also allows the elastomeric
particles to maintain surface conductivity even when the entire
composite structure is strained.
[0085] The fluid environment in which the conductive particles 7a,
7b are constructed must be compatible with the elastomeric
particles so that they are not damaged during the assembly process
and may be easily transferred from one layering environment to the
next wilt rout overly demanding intermediate washing and/or drying
steps. As mentioned earlier, optimization of the fluid environment
can cause advantageous swelling of the elastomeric particles during
deposition of the conductive layers.
[0086] LbL-CSA or LbL-SA can also be used to form a monolayer on
the elastomeric particles, which would be a seed layer, whereupon
further conducting material is deposited electrochemically, e.g. by
electroless deposition.
[0087] Examples of methods for depositing the conducting
nanoparticles 7a, 7b onto a surface by self assembly are known
from, e.g. US2005/0064204, U.S. Pat. No. 6,025,202, U.S. Pat. No.
6,624,886, U.S. Pat. No. 6,242,264, U.S. Pat. No. 6,458,327, U.S.
Pat. No. 6,592,945.
[0088] The process of building up multiple conducting layers onto a
surface is achieved through repetition of deposition steps, as is
disclosed in US2005/0064204 and U.S. Pat. No. 6,458,327. Yet
another option for forming the conducting layer 4a, 4b, 6 involves
physical vapor deposition processes, a variety of which are known,
including vacuum evaporation, sputtering and chemical vapor
deposition. Deposition via such methods is considered straight
forward, except that one may need to continually mix the
elastomeric particles to ensure adequate coverage with the thin
conducting material.
[0089] The thickness of the conducting layer 4a, 4b, 6 should be as
thin as possible, so as not to add to the overall mechanical
stiffness of the final particle. This is especially important when
using methods that form continuous layers onto the elastomeric
particles.
[0090] Preferably, the conducting layer thickness may be less than
10% of the diameter of the elastomeric particle. More, the
thickness may be less than 5%, less than 1% or less than 0.1% of
the diameter of the elastomeric particle.
[0091] Expressed differently, the thickness may preferably be jess
than 500 nm, more preferably less than 100 nm, of less than 50
nm.
[0092] For a sensor type embodiment, the layers on the elastomeric
body 2 collectively should have an overall quiescent sheet
resistance of 0.1-100 k.OMEGA./.quadrature., and more preferably a
sheet resistance of 1-10 k.OMEGA./.quadrature..
[0093] For an electrical interconnect application, the layers on
the elastomeric body 2 should have an overall quiescent sheet
resistance of less than 10.OMEGA./.quadrature., more preferably
less than 1.OMEGA./.quadrature., and most preferably less than
0.10.OMEGA./.quadrature..
[0094] The primer 3 on the surface of the elastomeric body 2 is
selected to initiate the deposition process onto the elastomeric
body surface, improve bonding between the elastomeric body and the
first conducting layer, and/or to improve bonding of the completed
particles to the matrix material. The primer 3 is generally chosen
from the known organosilanes and organosiloxanes with examples
provided below.
[0095] The organosilane compounds include compounds having alkyl
and alkoxide groups in one molecule such as hexyltrimethoxysilane,
octyltrimethoxysilane, cyclopentyltrimethoxysilane and
cyclohexyltrimethoxysilane; organosilane compounds having vinyl and
alkoxide groups in one molecule such as vinyltrimethoxysilane;
organosilane compounds having amino and alkoxide groups in one
molecule such as (N,N-dimethylaminopropyl)trimethoxysilane,
(N,N-diethylaminopropyl) trimethoxysilane,
aminopropyltrimethoxysilane, N-(6-aminohexyl)
aminopropyltrimethoxysilane, and
(aminoethylaminomethyl)-phenethyltrimethoxysilane; compounds having
ammonium and alkoxide groups in one molecule such as
N,N,N-trimethylammonio-propyltrimethoxysilane; organosilane
compounds having heteroaromatic ring and alkoxide groups in one
molecule such as 2-(trimethoxysilethyl)pyridine; organosilane
compounds having fluoroalkyl and alkoxide groups in one molecule
such as (3,3,3-trifluoropropyl)trimethoxysilane and
(decafluoro-1,1,2,2-tetrahydr-ooctyl) triethoxy silane;
organosilane compounds having polyethyleneglycol and alkoxide
groups in one molecule such as
N-(triethoxysilylpropyl)-O-polyethyleneoxide-urethane; organosilane
compounds having thiocyanate and alkoxide groups in one molecule
such as 3-thiocyanoatepropyltriethoxysilan-e; organosilane
compounds having ether and alkoxide groups in one molecule such as
3-methoxypropyltrimethoxysilane; organosilane compounds having
thiol and alkoxide groups in one molecule such as
3-mercaptopropyltrimethy-oxysilane; organosilane compounds having
halogen atom and alkoxide groups in one molecule such as
3-iodopropyltrimethoxysilane and 3-bromo-propyltrimethoxysilane;
organosilane compounds having epoxy and alkoxide groups in one
molecule such as 5,5-epoxyhexyl-triethoxysilane; organosilane
compounds having sulfide and alkoxide groups in one molecule such
as bis[3-(triethoxysilyl)propyl]tetrasulfide; organosilane
compounds having hydroxyl, amino and alkoxide groups such as
bis(2hydroxyethyl)-3-amino-propyltriethoxysilane; organosilane
compounds having an amino group and groups derived by hydrolysis of
alkoxide groups in one molecule such as aminopropylsilane triol;
oganosilane compounds having alkyl group and chlorine atoms in one
molecule such as octyltrichlorosilane,
cyclotetramethylenedi-chlorosilane,
(cyclohexylmethyl))trichlorosilane, cyclohexyl-trichlorosilane, and
tert-butyltrichlorosilane; organosilane compounds having
fluoroalkyl group and chlorine atoms in one molecule such as
(decafluoro-1,1,2,2-tetrahydrooctyl)tri-chlorosilane and
(3,3,3-trifluoropropyl)trichlorosilane; organosilane compounds
having heteroaromatic ring and chlorine atoms in one molecule such
as 2[2-(trichlorosilyl)-ethyl]pyridine; and organosilane compounds
having an aromatic ring and chlorine atoms in one molecule such as
phenethyltrichlorosilane. See, e.g., US 2005/0064204.
[0096] Organosiloxane compounds generally include alkoxy-silanes
such as methyltrimethoxysilane, vinyltrimethoxy silane,
3-glycidoxypropyltrimethoxysilane,
3-methacryloxypropyltrimethoxysilane, dimethyldimethoxysilane,
trimethylmethoxysilane, trimethylethoxysilane, tetramethoxysilane,
and tetraethoxysilane; siloxane oligomers such as
silanol-endblocked dimethylsiloxane oligomers, silanol-endblocked
dimethylsiloxane/methylvinylsiloxane cooligomers,
silanol-endblocked methylvinylsiloxane oligomers,
silanol-endblocked methylphenylsiloxane oligomers,
1,3,5,7-tetramethylcyclotetrasiloxane, and
1,3,5,7,9-pentamethylcyclopentasiloxane; polyorganosiloxanes
ranging from low-viscosity liquids to gums, and including but not
limited to trimethylsiloxy-endblocked polydimethylsiloxanes,
trimethylsiloxy-endblocked dimethylsiloxane/methylvinylsiloxane
copolymers, trimethylsiloxy-endblocked
dimethylsiloxane/methylphenylsiloxane copolymers,
trimethylsiloxy-endblocked polymethylhydrogensiloxanes,
trimethylsiloxy-endblocked dimethylsil oxane/methylhydrogensiloxane
copolymers, silanol-endblocked polydimethylsiloxanes,
silanol-endblocked dimethylsiloxane/methylvinylsiloxane copolymers,
silanol-endblocked dimethylsiloxane/methylphenylsiloxane
copolymers, silanol-endblocked polymethylhydrogensiloxanes,
silanol-endblocked dimethylsiloxane/methylhydrogensiloxane
copolymers, dimethylvinylsiloxy-endblocked polydimethylsiloxanes,
dimethylvinylsiloxy-endblocked dimethylsiloxane/methylvinylsiloxane
copolymers, dimethylvinylsiloxy-endblocked dimethylsiloxane/methyl
phenylsiloxane copolymers, dimethylhydrogensiloxyendblocked
polymethylhydrogensiloxanes, and dimethylhydrogensiloxy-endblocked
dimethylsiloxane/methylhydrogensiloxane copolymers; and silicone
resins, including but not limited to resins composed of
R.sub.3SiO.sub.1/2 and SiO.sub.4/2 units, silicone resins composed
of the RSi(.sub.3/2 unit, resins composed of the R.sub.2SiO.sub.2/2
and RSiO.sub.3/2 units, and resins composed of the
R.sub.2SiO.sub.2/2, RSiO.sub.3/2, and SiO.sub.4/2 unit. See, e.g.,
U.S. Pat. No. 7,074,849.
[0097] Further organosilanes with functional groups including:
epoxy, amino, ketimino, vinyl methacryloxy, acryloxy, mercapto,
polysulfido, isocyanato, styryl and hydrolysable groups including
chloro, methoxy, and ethoxy functional groups. See Shin Etsu
Chemical silane coupling agent brochure for similar listings.
[0098] In practice, a particular agent is generally selected based
on consultation of the literature, and simple adhesion trials. In
general, the coupling agents are selected such that the coupling
agents have organic functional groups that match the reactivity of
the polymer surface in question.
[0099] Known examples include aminopropyltriethoxysilane or
mercaptopropyltrimethoxysilane (depends on the base material being
bonded to), as disclosed in US2005/0064204 or U.S.Pat. No.
6,458,327 for glass substrates, but groups can be selected for the
appropriate elastomer materials in question.
[0100] There are also proprietary, commercially available primers
available from such companies as Dow Corning, Shin Etsu Chemical,
Nusil, among others.
[0101] The binding layer 5 is used to bond together subsequently
deposited conducting layers. As examples of binders for LbL-SA,
materials containing two functional groups such as hydroxyl groups,
amino groups, carboxyl groups, carboxylic acid anhydride groups,
mercapto groups, hydrosilicon groups and combinations thereof may
be used, as described in US2005/0064204. The selected material
should have at least one functional group that can covalently or
non-covalently bond to the desired molecule, such as the
nanoparticle or the elastomer.
[0102] Another name for these materials are ligands, containing one
or more amino groups, thiol groups, and are chosen from the the
group comprising mercaptoalkylsilanes, aminoalkylsilanes,
dimercaptoalkanes, diaminoalkanes, hydroxy-alkanes,
carboxy-alkanes, dihydroxy alkanes, and dicarboxyalkanes, as
disclosed in U.S. Pat. No. 6,458,327.
[0103] As an example for polyurethane/gold nanocomposites,
mercaptoethanol may be used as the binding agent.
[0104] As an example for a polysiloxane/silver nanocomposite,
polysiloxane may be used as the binding agent. Specifically,
poly(dimethyl-co.methylhydrido-co-3cyanopropyl,methyl)siloxane. The
same polysiloxane as used for the elastomeric materials of the
composite may be used directly as the binder (without primer), so
as to reduce the overall number of materials in the composite.
[0105] As an example for building up multiple gold nanoparticle
layers, 2-mercaptoethanol or 2mercaptoethylamine may be used, see
US2005/0064204.
[0106] Another example for building up multiple layers of gold
nanoparticles with dodecylamine stabilizing ligands would be
mercaptoalkylsilanes, aminoalkylsilanes, dimercaptoalkanes,
diaminoalkanes, or polyfunctionalized polymers, as disclosed in
U.S. Pat. No. 6,458,327.
[0107] Referring to FIGS. 4-6b. the above described elastomeric
particles having a conducting surface may be used to provide a
pressure sensor element.
[0108] FIG. 4 schematically illustrates a first embodiment of a
pressure sensor element 20. The drawing is magnified, and the
vertical direction V is greatly exaggerated. The measurement side
is indicated by reference numeral 310. The sensor element 20 is
based on a substrate 21, upon which a pair of electrodes 22a, 22b
are arranged. The electrodes may, but do not need to, be co-planar.
Electrodes 22a, 22b may be provided by patterning a conducting
material onto the substrate/first elastomeric portion in any known
manner. A first nonconducting elastomeric portion 23 is arranged
between the electrodes. The first elastomeric portion 23 may cover
opposing edge portions of the electrodes 22a, 22b and it may have a
maximum thickness which is larger than that of the electrodes. The
thickness of the first elastomeric portion 23 may taper or
otherwise diminish towards its edges.
[0109] On the first elastomeric portion 23, one or more conducting
layers 24 may be arranged. Such conducting layers may comprise
elastomeric particles as described above, which are arranged in a
matrix comprising a primer and/or a binder as described above. The
conducting layers 24 are in contact with the electrodes 22a, 22b.
In particular, a primer 3, such as the ones mentioned above, may be
used between the first elastomeric portion 23 and the first
conducting layer 24, and a binder 5, such as the ones mentioned
above, may be used between the first conducting layer 4a and
further conducting layers 4b.
[0110] A second non-conducting elastomeric portion 25 may be
arranged on top of the conducting layers 24, such that the
conducting layers 24 are enclosed by the first and second
elastomeric portions 23, 25 with only edge portions of the
conducting layers 24 being exposed to the electrodes 22a, 22b.
Another primer or binder may be used between the conducting layers
24 end the second elastomeric portion 25. The elastomeric portions
23, 25 may be formed from any material mentioned above with respect
to the elastomeric body 2.
[0111] The sensor element, including the elastomeric portions 23,
25, the electrodes and the conducting layers 24 may be enclosed in
an isolation coating 26, which may be non-conducting. The isolation
coating 26 may be made from an elastomeric material and may
optionally be foamed.
[0112] In one embodiment, the elastomeric portions 23, 25 are made
from elastomeric materials having different modulus of elasticity.
In another embodiment, the elastomeric portions 23,25 are made from
elastomeric materials having substantially the same modulus of
elasticity.
[0113] When the sensor element 20 is subjected to pressure
(typically compression in the vertical direction V), the relative
positions of the particles present in the conducting layers 24 will
change, thereby changing the impedance of the sensor element, as
measured over the electrodes 22a, 22b.
[0114] The sensor element 20 may be produced according to the
following.
[0115] A substrate 21 with electrodes 22a, 22b is prepared and
possibly cleaned. Such a substrate may, e.g., be a fabric or a
polymer film. A primer may be applied to the surface where the
first elastomer layer 23 is to be deposited. A first elastomer
layer 23 with a first hardness is deposited. A primer layer, with a
primer as described above, may then be deposited. Conductive layers
24 are deposited to bridge the electrodes 22a, 22b and to extend
out past the first elastomer 23. Binder layers 5 as described above
may be arranged between the conductive layers 24. Another primer
may be used to coat the conductive layers 24. A second elastomer
layer 25 with a second hardness is deposited. This second elastomer
layer 25 can also function as a mechanical isolation layer.
Optionally, an isolation coating 26 is deposited, and optionally
foamed. This isolation coating 26 also may function as a stress
filtering layer to smooth out contact stresses applied to the
sensor element in the vicinity of the first and second elastomer
layers 24, 25.
[0116] FIG. 5 illustrates an alternative embodiment of a sensor
element 20', wherein the first elastomer 23' has been dispensed on
the substrate 21 prior to the forming of the conducting layer 24
and the electrodes 22a', 22b'. The conducting layers 24 and/or the
electrodes 22a', 22b' may be patterned, e.g., dispensed, printed or
jetted, onto the substrate and onto the first elastomer 23'.
[0117] FIG. 6a illustrates another alternative embodiment of a
sensor element 20'', wherein the first elastomer 23'' has been
molded onto the substrate. Subsequently, the conducting layers 24
have been formed, and thereafter the electrodes 22a'', 22b'' have
been printed.
[0118] Referring to FIG. 6b, there is illustrated a detail on how
the conducting layer 24 may be formed. In one embodiment, the
conducting layer 24 comprises one, two or more layers of the
elastomeric particles 1, 1', 1'' described above with reference to
FIGS. 1a-2b. The conducting layer 24 according to this embodiment
may be produced by applying a primer 3 in a desired pattern where
the conducting layer 24 is to be formed. Thereafter, conducting
particles 1, 1', 1'' are applied so as to form a first conducting
layer 4a. A binder 5 is thereafter applied in a desired pattern,
after which further conducting particles 1, 1', 1'' may be applied
so as to form a second conducting layer 4b. This method may be used
to provide the conducting layer of any of the embodiments
illustrated in FIGS. 4-6b..
[0119] In another embodiment, the conducting layer 24 of FIGS. 4-6b
may be formed in the any of the manners described with reference to
the conducting surface of the elastomeric particles 1, 1', 1'' of
FIGS. 1a-2b. Thus, the conducting layer 24 may be formed using
primer 3 and/or binders 5 as described with reference to FIGS.
1a-2b to provide one, two or more layers 4a, 4b of non-elastomeric
conducting particles 7a, 7b. The technology disclosed in US
2005/0064204A1 may be used to provide the conducting layer.
[0120] It is noted that alternatively, the conducting layer 24 may
be formed by patterning a compound for forming the composite
material described below, possibly after deposition of a
primer.
[0121] FIG. 3 schematically illustrates a composite material 10
comprising elastomeric particles 1, 1', 1'' as described above and
a matrix material 11.
[0122] The above described elastomeric particles 1, 1', 1'' may
thus be used to provide a composite material 10, which in turn may
be used for forming pressure sensor elements. Such a composite
material may be formed by mixing the elastomeric particles with a
matrix material 11, which may also be an elastomeric material.
[0123] In practice, the matrix material may be substantially the
same as that of the elastomeric body 2 of the particles, however,
with a different hardness or modulus of elasticity. Examples of
suitable matrix materials are thus given above with reference to
the elastomeric particle 2.
[0124] By using a composite comprising soft elastomeric particles
1, 1', 1'', it is possible to better manage strain related damage,
quiescent electrical impedance and strain sensitivity of the
electrical impedance within the composites by improving and
managing stresses at interlaces between matrix and particles, and
within the matrix.
[0125] The composite material thus comprises soft particles 1, 1',
1'' (elastomeric in nature) of a first modulus of elasticity, the
surfaces of which are made conductive (as described above), mixed
with a binder material (elastomeric in nature) of a second modulus
of elasticity into a composite structure. The composite material
may also contain coupling agents, compatibilizing agents and other
particulates, etc. to fine tune the final composite properties.
[0126] The coupling agents or compatibilizing agent may be chosen
from the known organosilanes and organosiloxanes with examples
mentioned above.
[0127] Interfacial stresses and strain related damage may be
minimized when the first and second moduli of elasticity are chosen
to be substantially equivalent to each other. Such an arrangement
produces a composite with low mechanical hysteresis, and low
impedances strain sensitivity while further improving the cycle
life of the composite and improving linearity of the
strain-impedance relationship of the composite.
[0128] Finite quiescent impedance can be set during fabrication via
alignment, volumetric ratios of constituents and fabrication
conditions (solvents, compression, temperature profile, during
curing, etc).
[0129] Pressure sensitivity may be determined primarily, by the
equivalent modulus of elasticity, the strain-impedance relationship
of the composite, and the structure of the sensor built from the
composite (geometry, field orientation, electrode placement,
etc.).
[0130] Strain sensitivity can be increased in a controlled manner
by changing the ratio between the first and second moduli of
elasticity.
[0131] The soft elastomeric particles 1, 1', 1'' can be mixed
randomly with a matrix-forming material (and other particles) or
used in conjunction with preferential alignment (see below).
[0132] Alignment, as will be further discussed below, can be used
to further affect strain sensitivity of the electrical impedance of
the composite.
[0133] The mechanical properties of the overall system are
primarily related to the mechanical properties of the constituent
components (particles, matrix, and the difference between the two),
the mix ratios, alignment configurations, as well as the strength
of the bonds between the particles and the matrix.
[0134] The pressure sensitivity of the electrical impedance is than
a function of the strain sensitivity and the mechanical properties
of the composite.
[0135] A mixture or compound 10 (see FIG. 3) comprising elastomeric
particles 1, 1', 1'' and matrix-fencing material 11 may be
provided. The compound may be in the form of a paste. The
matrix-loaning material may be allowed to harden or set into any of
the materials mentioned above as being suitable for the elastomeric
body 2 or matrix 11, or similar/equivalent materials. Such a
compound may be, e.g., printed or deposited in order to provide
sensor elements as illustrated in FIGS. 4-10 and then allowed to
harden or set. Curing may be facilitated in anyway known to the
skilled person, such as by influence of radiation, etc.
[0136] In the composite material arranged with generally randomly
distributed soft elastomeric particles, the volume percent of
coated particles into a matrix, for randomly distributed particle
systems, will generally be in the range of 10-75% by volume. This
is in line with the volume percent of prior art sensory
materials.
[0137] In cases of alignment, as described below, generally the
required volume percent of particles may be reduced by a factor of
10 to 100. This will further benefit the mechanical properties of
the resulting composite, as the reduced amount of Interfaces will
further reduce mechanical hysteresis during use.
[0138] Referring to FIGS. 7-10, the description will now be focused
on sensor elements using a composite material as described
above.
[0139] FIG. 7 schematically illustrates a first embodiment of a
sensor element 30, wherein a substrate 31 is provided with
electrodes 32a, 32b. A conductive composite 33, such as the one
described above, is then provided on the substrate and in contact
with the electrodes. Optionally, an isolation coating 34, such as
the ones described with respect to FIGS. 4-6b, may be provided to
encapsulate the sensor element 30.
[0140] FIG. 8 schematically illustrates a second embodiment of a
sensor element 30', which is similar to the one of FIG. 7, but
provided with a second substrate 31a, with a third electrode 32c.
The second substrate is spaced from the first substrate, and may be
"floatingly" arranged in the composite material 33. The second
substrate 31a with its associated electrode may be produced in the
same way as the first substrate 31. The third electrode 32c can be
used to facilitate preferential alignment within the composite
material 33 during fabrication, augment the electrical impedance of
the sensor element. 30, provide more suitable area within the
composite material 33 where impedance measurements can be taken,
preferentially spread applied stress over the composite material
33, provide a means of measuring pressure gradients applied to the
sensor element 30, or electrically shield the sensor element 30
from the surroundings.
[0141] FIG. 9 schematically illustrates a third embodiment of a
sensor element 30'', wherein a non-conducting elastomeric portion
35 is provided between the electrodes 32a, 32b in a manner similar
to that of FIGS. 4 or 5, e.g., in order to reduce stress
concentrations around the edges of the electrodes, to control
stresses in the composite material 33', to separate the stress and
field concentrations within the composite material 33' and/or to
facilitate preferential alignment in the composite materiel 33'
during fabrication of the sensor element 30''. The elastomeric
portion 35 may be further foamed to alter the hardness and the
Poisson's ratio of this portion of the sensor element 30'' . This
provides a further means of controlling pressure sensitivity of the
sensor element 30''.
[0142] Furthermore, in FIG. 9, the portion of the composite
material 33' extending between the electrodes 32a, 32b may be
structured, e.g., made narrower, so as to further control
sensitivity of the electrical impedance of the composite material
33' to applied pressure, and locally alter the mechanical
properties of the composite material 33'.
[0143] In the embodiment of FIG. 9, a third electrode with
substrate as described with reference to FIG. 8 may be
included.
[0144] FIG. 10 schematically illustrates a fourth embodiment of a
sensor element 30'', which is arranged in a through hole 38 in the
substrate 31. Such a substrate may, e.g., be a fabric or a polymer
film. The composite material 33'' may be symmetrically arranged in
relation to the substrate 31. Electrodes 32a', 32b' may be provided
by a wire embedded in or arranged on the substrate 31, or as a
conductive yarn provided in a fabric. Electrodes 32a', 32b' may
also be provided by patterning a conducting material onto the
substrata in any known manner. In the latter case, the wires
loading to the electrodes may be provided with an isolating
coating, which is removed to expose the conducting part to thereby
provide the electrodes 32a', 32b'. Such removal may be achieved by,
e.g., etching, solvent, mechanical ablation, etc. This embodiment
is particularly suitable for creating very thin sensor systems.
[0145] In this embodiment, isolation coatings 34a, 34b may be
provided on both sides of the substrate 31, such as to encapsulate
the sensor element.
[0146] In the embodiment of FIG. 10, the third electrode with or
without associated substrate, as described with respect to FIG. 8
may be provided.
[0147] In the embodiments of FIGS. 7-10, the composite material may
optionally be foamed, in a per se known manner.
[0148] A production process for providing the sensor element of
FIGS. 7-10 may include providing a suitable substrate material;
providing electrodes on the substrate, e.g., by a patterning
process; depositing a mixture for forming the composite material
(including elastomeric particles and matrix material); optionally
providing a field application fixture and apply the requisite
fields (AC, DC, ramp-up, hold, ramp-down) for alignment; curing the
matrix material (e.g., by application of UV light, heating, etc.);
removing any alignment field; optionally post curing the matrix
material; and removing any remaining alignment field. If not
removed early in the curing process. Optionally, conductive bridges
between sensors and external electronics may be provided, e.g., by
printing, lithographic patterning, etc.
[0149] It is recognized that there are many electrode and magnet
arrangements for alignment as well as mechanical layouts that may
be optimized for this type of sensor.
[0150] It is noted that for the embodiments described with
reference to FIGS. 4-10, the electrodes may be a conducting
compound, metal or conducting organic material. Application methods
include PVD, CVD, electrochemical methods, inkjetting, printing
etc., followed by any necessary sintering or drying steps.
[0151] Substrate materials for providing the substrate of the
embodiments disclosed with reference to FIGS. 4-10 include films
(preferably biaxially oriented polymer films including polyethylene
terephthalate, polyethylene naphthalate, but also polymer films
including polycarbonate, polyamide, polyimide, nylon,
polyethersulfone, aromatic fluorine-containing polyarylates, etc.),
fabrics (both woven and nonwoven), felts, apertured films and foams
(such as PU foam).
[0152] As indicated above, in the embodiments illustrated with
reference to FIGS. 4-10, it is possible, and sometimes desirable,
to preferentially align the elastomeric particles of the composite
between the electrodes during fabrication. Motives for so doing
include reducing the volume fraction of particulate in the
conducting elastomer composite. This process may improve two
important aspects of the sensor properties: (i) hysteresis is
improved due to the fact that fewer interfaces are present to form
stress concentrations throughout the composite material, and (ii)
the elastomeric particles may be localized only to the regions of
the sensor where they are needed. Furthermore, alignment allows for
the monitoring and control of the quiescent impedance of the
sensors during fabrication and aging (post fabrication), thereby
increasing yield and more tightly controlling the final properties
of the sensors.
[0153] In the same regard, alignment can allow individual sensors
within a cluster or garment to be adjusted so as to be similar to
each other within each final product. It may also allow flexibility
in terms of calibrating some sensors within a garment to behave
with different quiescent impedance than others for various
applications.
[0154] For example, it may be possible to provide a composite,
where all sensor elements are tuned to have a quiescent impedance
of 10 kohm under application-like test conditions.
[0155] As another example, some sensor elements may be tuned to
believe more like switches with high sensitivity (for determining
garment state, e.g., donned, removed), while others maintain lower
sensitivity (for making accurate measurements during
treatments).
[0156] The alignment discussed above may most easily be performed
using B-fields, E-Fields, or combinations thereof during the
fabrication of the sensor element.
[0157] Of course, to use B-fields, the particles should have a
suitably high magnetic permeability, such that they can move within
the composite upon the application of an external field.
[0158] E-field systems will work for any particle types, it may be
preferable that an AC field is used and that the application
frequency is sufficiently high, such that the field does not
collapse (breakdown) if a solid chain of particles is formed
between the electrodes. Field collapse is not good in general, as
it prevents surrounding particles from forming chains within the
composite of the sensor, i.e., without control of E-field collapse,
one gets only a single connection between electrodes that is very
fragile in practice.
[0159] For E-field systems, it is also possible to use a soft
barrier layer around the elastomeric particles, such that the
breakdown effect will not be as dramatic, i.e., as particles come
together into chains, the impedance drops more gradually and
therefore breakdown of the field does not occur suddenly as can
happen with purely conducting fillers. Such a barrier layer can be
formed by a primer layer applied to the external surface of the
particles before mixing them with the matrix. For some matrix
material, and conducting layer combinations, such a barrier layer
is formed naturally such as is the case for silicone matrices and
nickel conducting layers.
[0160] For both types of fields, in situ stirring is possible using
rotating fields. This can be useful for slowly guiding particles
into position without creating strong single chains and will
generally result in more particles forming along the desired
pathway than with only one field element applied between the
requisite electrodes.
[0161] The electrodes applying the field may be the sensor
electrodes themselves, but they may also be separate electrodes
provided in a manufacturing fixture or mold.
[0162] Combination of fields may be useful as the presence of one
field can significantly reduce the requirements for the other
field. For example, permanent magnets may establish a B-field in
the vicinity of the sensor element electrodes, whereby particles
begin movement towards the electrodes due to the presence of the
B-field. Then an E-field applied at the electrodes may be used to
finish the alignment process with much lower voltage requirements,
e.g., dropping the voltage requirement by a factor of 10-100
times.
[0163] Passive structures can also be printed onto the sensor to
guide the particle traces and further assist with the alignment
process. For example, a printed elastomer layer, between
electrodes, with different hardness than the conducting elastomer
blend, may be printed such that when an E-field is applied to the
electrodes, particles align primarily from the centers of the
electrodes rather than the edges. This prevents collocation of
field concentrations between the test E field and stress fields in
the sensor during operation, thus improving repeatability within
the sensor element. An example of such an elastomer is shown in
FIG. 9.
[0164] Referring to FIGS. 11-22, another type of sensor element 40
will now be described. This type of sensor element may be used on
its own or in combination with the sensor elements 20, 30 described
above.
[0165] The sensor element 40, 40', 40'', 40''', 40.sup.IV,
40.sup.V, 40.sup.VI, 40.sup.VII and associated embodiments as
described in the following are advantageous as sensor elements in
that they have improved mechanical response and aging
characteristics, immunity to EMI, and the ability to be used for
inline calibration of compression systems.
[0166] This type of sensor can be most basically be characterized
as an array of contact switches with pressure defined switching
levels.
[0167] Referring to FIGS. 11-16, the sensor element 40 comprises a
first substrate 41 with patterned metallic electrodes 43a, 43b,
42a-1, 42a-2, 42a-3, 42a-4, 42a-5, 42a-6, a spacer 45, and a second
substrate 47 with patterned metallic electrodes 42b, wherein the
first electrodes comprises an array of electrode elements 42a-1,
42a-2, 42a-3, 42a-4, 42a-5, 42a-6, which are separated from each
other by a spacing S. A resistive element 44 forming a conduction
path is arranged on the first substrate 41, such that the electrode
elements 42a-1, 42a-2, 42a-3, 42a-4, 42a-5, 42a-6 contact the
resistive element 44 at different portions along the conduction
path. Connector electrodes 43a, 43b are provided at spaced apart
portions of the resistive element 44, typically at end portions of
the conduction path.
[0168] The second substrate 47 is arranged substantially parallel
with the first substrate 41, and spaced from the first substrate 41
by the spacer 45. On the second substrate 47, there is a second
electrode 42b, which is spaced from and faces the first electrode
42a. The second electrode 42b may be formed as a continuous sheet,
the extent of which substantially coincides with an effective
overall extent of the first electrode 42a-1, 42a-2, 42a-3, 42a-4,
42a-5, 42a-6.
[0169] The spacer 45 forms a cavity 43 between the first and second
substrates 41, 47. This cavity may be vented, so as to equalize air
pressure inside and outside the sensor element.
[0170] The cavity 48 need not be rectangular or circular in shape.
It can be formed info many shapes including, rectangles, circles,
ellipses, dumb-bell like shapes, polygons, and perturbations
thereof. Circles are useful for minimizing stresses at the edges of
the cavity 48, while rectangles are easily patterned by standard
manufacturing processes.
[0171] In one embodiment, the resistive element is arranged outside
or adjacent the cavity. Hence, the resistive element need not
contact the movable parts of the electrode(s), which decreases its
sensitivity to wear.
[0172] When the sensor element 40 is subjected to pressure, the
first and second substrates 41, 47, and thereby also the first and
second electrodes 42a-1, 42a-2, 42a-3, 42a-4, 42a-5, 42a-6, 42b,
are pressed towards each other, so that an area of contact between
the first and second electrodes 42a-1, 42a-2, 42a-3, 42a-4, 42a-5,
42a-6, 42b is provided. The area of contact will increase
continuously, as more pressure is applied. As the area of contact
increases, more and more of the first electrode elements 42a-1,
42a-2, 42a-3, 42a-4, 42a-5, 42a-6 will become "short circuited" by
the second electrode 42b, thereby providing a shunt path past the
conduction path provided by the resistive element 44. Hence, the
impedance of the sensor element 40 will decrease stepwise as a
function of the applied pressure. This is illustrated in FIG. 17,
which illustrates a behavior of an embodiment with a number of
first electrode elements 42a-1, 42a-2, 42a-3, 42a-4, 42a-5, 42a-6
that successively contact the second electrode 42b, so as to shunt
the resistive element 44 to decrease the overall impedance of the
sensor 40.
[0173] The elements of the first electrode 42a-1, 42a-2, 42a-3,
42a-4, 42a-5, 42a-6 are patterned such that they are shunted at the
appropriate pressure levels. For example, for an application which
requires that the patient is subjected to 10 mmHg.+-.3 mmHg for
some time period, followed by 50 mmHg.+-.5 mmHg, and the overall
pressure applied should not exceed 70 mmHg, the traces could be
arranged such that shunting occurs at 7 mmHg, 13 mmHg, 45 mmHg, 55
mmHg, and 70 mmHg. Another alternative would be that the traces are
arranged such that shunting occurs at 10 mmHg, 50 mmHg and 70
mmHg.
[0174] Hence, points of discontinuity between the pressure and
impedance relationship of the pressure sensor element 40 may be
determined by the number of first electrode elements 42a-1, 42a-2,
42a-3, 42a-4, 42a-5, 42a-6, their size and relative position with
respect to each other and within the cavity 48, as well as the
thickness of the spacer 45, the mechanical properties of the first
and second substrates 41, 47 and the overall dimensions of the
cavity 48. In embodiments with a large number of first electrode
elements, the sensor element 40 will more closely approximate an
analog relationship between impedance of the conduction path and
the applied pressure.
[0175] The resistive element 44 may be formed as a patterned
resistive trace (e.g., by means of printing, vacuum evaporation,
thermal transfer printing, etc.) or as an array of discrete
elements. This resistive element may be arranged outside the
flexible part of the sensor element 40. The resistive element 44
may most easily be provided by printing using traditional resistive
inks or pastes. The resistive element 44 will generally be
encapsulated or covered by the spacer layer 45, such that it is not
subjected to significant pressure application during typical
operations, and thus the resistance of the resistive element 44
will not vary significantly during operation. Stiff, well
characterized inks and pastes can be used for the resistive element
44 to ensure that suitable properties are maintained during use. In
addition, due to the discontinuous nature of the pressure-impedance
relationship for such a sensor, moderate variations in the
resistance of the resistive element 44 can be easily tolerated over
the life of the sensor 35 element 40 without degradation of
performance.
[0176] The manner in which the elements of the first electrode
42a-1, 42a-2, 42a-3, 42a-4, 42a-5, 42a-6 are connected to the
resistive element 44 can be a serial connection, parallel or any
combination thereof. Full advantage of connection possibilities can
be used to optimally shape The pressure-impedance relationship of 5
the sensor element 40.
[0177] In addition, in the case where the resistive element 44 is
made from several Individual resistor elements, these need not be
equal to one another. For example, in the above case, the
resistance change for the shunt at 7 mmHg may be significantly
smaller than that at 13 mmHg, so as to most clearly define the
output resistance around the desired operating point. This may the
useful when the device is operated in very hostile electromagnetic
environments.
[0178] The sensor element 40, 40', 40'', 40''', 40.sup.IV,
40.sup.V, 40.sup.VI, 40.sup.VII may be built from structurally
sound materials, such as biaxially oriented films, and metallic,
carbon, or metal oxide layers, which are thin and deposited from
pure materials (no particulate based inks, etc, are needed). The
spacer may be attached directly to the adjacent membranes without
pressure sensitive adhesives or other creep prone materials, e.g.,
by welding. This ensures that the creep and other undesirable
mechanical effects are minimized within the flexible components of
the sensor element 40, 40', 40'', 40''', 40.sup.IV, 40.sup.V,
40.sup.VI, 40.sup.VII.
[0179] The substrates 41, 47 may be in the form of membranes of
biaxially oriented films of engineering polymers. Primarily,
biaxially oriented polymer films, such as polyethylene
terephthalate, polyethylene naphthalate and also polymer films
including polycarbonate, polyamide, polyimide, nylon,
polyethersulfone, aromatic fluorine-containing polyarylates may be
used. Membrane thickness is generally less than 25 micron,
preferably less than 10 micron, most preferably 2-5 micron.
[0180] Electrodes 42a-1, 42a-2, 42a-3, 42a-4, 42a-5, 42a-6, 42b,
43a, 43b may be formed by patterning onto the substrate 41, 47
using physical or chemical vapor deposition techniques. Typical
conducting materials for electrodes may be silver, gold, copper,
aluminum, titanium, chromium, nickel, etc. Alternatively,
electrodes may be provided by conductive films and may be patterned
using electroless deposition, electrochemical deposition, LbL self
assembly and other techniques known in the art. It may be
advantageous if the electrodes are at least partially composed of
multiple layers. A base layer may be a compatibilizing layer, such
as Cr, Ti, NiCr to improve adhesion to the substrate 41, 47, a
second layer may be a highly conducting layer, and an upper layer
may be a protective layer.
[0181] It is possible to deposit a thin overcoating layer 301, to
protect one or both of the electrodes from damage due to repeated
contact during operation. One example of a suitable material for an
overcoating layer would be graphite, another would be chrome or
chrome alloys. Such top layers can be applied via PVD, CVD,
electrochemical or self assembled means.
[0182] The electrodes may preferably be patterned using
lithographic techniques to ensure that smooth lines are patterned
and finely spaced onto the substrates 41, 47.
[0183] It is preferable that the thickness of the electrodes are
maintained at less than 1 .mu.m, more preferably less than 500 nm,
so that the influence of the mechanical properties of electrodes on
the performance of the sensor element 40, 40', 40'', 40''',
40.sup.IV, 40.sup.V, 40.sup.VI, 40.sup.VII is minimized.
[0184] Alternatively, if the electrodes are being placed onto a
substrate that does not flex significantly, a thin film type ink
can be used to provide the electrode. Such films can be patterned
using printing techniques such as inkjet, pad, and offset printing,
among others.
[0185] Nanoparticulate conducting inks can be employed for this
layer. In order to improve the mechanical robustness of the ink, it
may be sintered after deposition. Low temperature sintering of the
nano-ink is only suitable when depositing conductors onto films
with high temperature resistance, such as fluorene polyarylates,
polycarbonate, polyethersulfone, polyimide or heat stabilized
biaxially oriented films of PET or PEN.
[0186] Another suitable alternative, which is known per se, may be
to apply an LbL self assembled wear resistant layer to the
electrodes.
[0187] The spacer 45 should be selected so as to present low creep
and good bonds to the substrates 41, 47. For example, it can be a
biaxially oriented film, that is to be laminated together with the
adjacent substrates. Such lamination should be performed using the
thinnest possible adhesive layers (preferably thermosetting
adhesives), as the presence of adhesive may adversely affect creep.
Many films are commercially available with suitable adhesive
surface layers.
[0188] The spacer 45 can also be provided in the form of a
patterned printed layer of a curable epoxy resin, a high
performance polyurethane resin or alternative, that may be further
cured and used both as the spacer 45 and to bond together adjacent
substrates 41, 47. In this case, care must be given to creeping of
the spacer 46 during use, and reinforced resin systems may be used
for the spacer 45 to further improve its mechanical properties.
[0189] The spacer may include both an extension of the cavity 48
within the sensor (air reservoir) as well as a vent 45 or series of
vents to equalize pressures between the sensory element and the
ambient environment.
[0190] External connections to the sensor element 40 may be
provided in the form of printed silver traces or the like.
Alternatively, it may be advantageous to use the electrode
patterning technique everywhere, i.e., both for the electrodes and
for the external connections. The trace thickness away from the
sensing area may be increased by masking the sensor regions, and
using on electrochemical technique to add conductor thickness to
the traces leading from the sensor elements to the electronics.
[0191] Reel-to-reel techniques are suitable for mass production of
the sensor element 40, 40', 40'', 40''', 40.sup.IV, 40.sup.V,
40.sup.VI, 40.sup.VII.
[0192] An isolation material 49a, 49b may be provided in the form
of, e.g., a foamed polymer, which may generally be very sot, with
small pores. The isolation material 49a, 49b should be
significantly softer than the substrate materials 41, 47, so as not
to interfere with the function of the sensor element 40, 40', 40'',
40''', 40.sup.IV, 40.sup.V, 40.sup.VI, 40.sup.VII, but so as to
also provide a thin, but smooth interface with the surrounding
surfaces.
[0193] FIG. 18 illustrates the behavior of an embodiment wherein
the electrodes 42a-1, 42a-2, 42a-3, 42a-4, 42a-5, 42a-6, 42b have
been made from a poorly conducting material, i.e. resistive
material such resistive materials may be provided from, e.g.,
nickel-chrome, tantalum, tantalum-nitride, chromium, titanium,
silicon-chromium, cermet, carbon. Such materials can be deposited
by evaporation, sputtering, cvd, etc.
[0194] By using such materials for the electrodes, it is possible
to create sheet resistance on the electrodes 42a-1, 42a-2, 42a-3,
42a-4, 42a-5, 42a-6, 42b in a range similar to that of the
resistive element 44.
[0195] In addition, thin film inks can also be used, as they are
sufficiently thin so as to not adversely affect the mechanical
properties of the flexible substrate 41, 47 materials. Generally,
silver loaded inks are satisfactory for this purpose. Other inks
based on particles of the above materials can also be used to
achieve particular sheet resistance or improve mechanical strength
of the contact interface between membranes. The equivalent sheet
resistance of the electrode 42b can also be adjusted by patterning
of the deposited electrode materials.
[0196] Furthermore, the sheet resistance can be modified by rising
nanoparticulate layered thin films as producible using LbL-CSA, or
LbL-SA.
[0197] FIGS. 19a-19c illustrate alternative embodiments of the
resistive element 44 and the connectors 43a, 43b. Such embodiments
are useful for tailoring the pressure impedance response of the
sensor element 40, 40', 40'', 40''', 40.sup.IV, 40.sup.V,
40.sup.VI, 40.sup.VII.
[0198] Specifically, they are useful for controlling the height of
the various discontinuities shown in FIGS. 17 and 18.
[0199] In FIG. 18a, the resistive element 44 is formed as a
substantially rectangular elongate structure, while the connectors
43a', 43b' are arranged at respective ends of the resistive
element.
[0200] In FIG. 19b, the resistive element 44' presents a varying
width and/or thickness, being elongate and concave, while the
connectors 43a', 43b' are arranged at respective ends of the
resistive element More generally the resistive element 44' is
shaped in a continuous fashion without discontinuities in width
along the conducting path.
[0201] In FIG. 19c, the resistive element 44'' presents a varying
width and/or thickness, including broader end portions and a
broader middle portion, spaced apart by respective narrower
intermediate portions. More generally, the width of the resistive
element 44'' may be varied along the conductive path in a step wise
fashion to tailor the step height of discontinuities in the
pressure-impedance response of the sensor element 40''. This form
of adjustment of the resistive element 44'' is a simple way of
tailoring the sensor response to distinguish critical pressure
transitions when used in hostile environments with significant
EMI.
[0202] FIGS. 20a and 20b illustrates an embodiment of an electrode
configuration, wherein the increase in contact area between the
first electrode 42a-1, 42a-2 and the second electrode 42b' alters
the slope of the pressure impedance relationship of the sensor
element 40.sup.IV around the point P1. Such an embodiment may be
provided by using poorly conducting electrodes. The effect may be
achieved by the first electrode elements 42a-1, 42a-2 being of a
varying width and/or a reduction in gap spacing between two
elements at some point along their length. This may be useful for
enhancing the sensitivity of the sensor to pressure in a particular
range. This can be especially useful for adjusting the sensitivity
of the sensor element 40, 40', 40'', 40''', 40.sup.IV, 40.sup.V,
40.sup.VI, 40.sup.VII at higher pressure levels where it is very
important to remain below a maximum pressure limit while performing
a therapy.
[0203] FIG. 20b illustrates the behavior such an embodiment: the
slope of the pressure-impedance curve is discontinuous at the point
P1.
[0204] FIGS. 21a-21b illustrates another embodiment of an electrode
configuration, wherein the increase in contact area between the
first electrode element 42a-1, 42a-2, 42a-3 and the second
electrode 42b'' alters the slope of the pressure-impedance
relationship of the sensor element 40.sup.V around point P2 while
also introducing a discontinuity around P2. In this embodiment, the
lengths of the elements 42a-1, 42a-2, 42a-3 do not extend across
the entire sensor area. Then, as the contact region between the
first and second electrodes 42a, 42b expands with increasing
applied pressure, more or less elements will come into contact.
[0205] This will cause both a change In sensitivity similar to the
example of FIGS. 20a-20b, but will also produce a jump
discontinuity at the point P2 of contact with the shorter element.
This point can then be more easily used as a pressure calibration
point for the sensory array.
[0206] FIG. 22a illustrates another embodiment of a sensor element
40.sup.VI, wherein the resistive element 44''', providing the
conductive path, is substantially circular, and the "fingers" of
the first electrode 42a-1, 42a-2, 42a-3, 42a-4, 42a-5, 42a-5,
42a-7, 42a-8 extend substantially radially from the resistive
element and towards the center of the sensor element 40.sup.VI.
[0207] Connectors 43a'' and 43b'' are arranged at the respective
ends of the resistive element 44'''. The elements of the first
electrode 42a-1, 42a-2, 42a-3, 42a-4, 42a-5, 42a-6, 42a-7, 42a-8
may present different lengths, and the spacer 45a may ha provided
as a ring around me sensor element 40.sup.VII. The second electrode
42b' is spaced from the first electrode element 42a-1, 42a-2,
42a-3, 42a-4, 42a-5, 42a-6, 42a-7, 42a-8 in a manner similar to
that described with respect to FIGS. 11-16.
[0208] Sensor element 40.sup.VI is advantageous in that its
circular form allows for uniform stress at the spacer 45a, thereby
providing a sensor element 40.sup.VI with improved fatigue
life.
[0209] FIG. 22b illustrates another embodiment of a sensor element
40.sup.VII, comprising a pair of resistive elements 44a, 44b, each
forming a respective conduction path. The resistive elements 44a,
44b have respective connectors 43a''', 43b''', which may also
interconnect the resistive elements 44a, 44b, as illustrated, such
that they are connected in parallel. A number of first electrode
elements 42a are connected to the first resistive element 44a at a
respective position along the conduction path of the first
resistive element 44a. Similarly, a number of first electrode
elements 42a are connected to the second resistive element 44b at a
respective position along the conduction path of the second
resistive element 44b. Thus, first electrode elements 42a extend
from the respective resistive element 44a, 44b and into an active
area of the sensor, which may generally coincide with the cavity of
the sensor element 40.sup.VII. The cavity is defined by the
patterned shape of the spacer 45a. in this example, the cavity is
defined by a spacer 45a comprising a circular hole as shown in FIG.
22b.
[0210] Extra ventilation and air reservoirs are not shown in FIG.
22b but may be added as previously discussed.
[0211] The first electrode elements of this embodiment may, but do
not need to, present mutually different lengths. This embodiment
increases the maximum possible switch levels available from the
sensor without significantly increasing the size of the sensor. It
also adds flexibility in terms of optimizing the pressure-impedance
response of the sensor element.
[0212] In FIGS. 11-13, 16 and 22a-22b, the characteristic length L,
characteristic width Wand overall sensor thickness T (including
isolating layers 49a, 49b) are indicated. Also, in FIG. 16, there
is indicated the sensor body thickness S.
[0213] Generally, the sensor body thickness R should be very small,
preferably less than 50 pm, more preferably less than 25 .mu.m or
less than 20 .mu.m. The overall sensor thickness T is preferably
less than 1.5 mm, more preferably less than 1 mm, more preferably
less than 0.5 mm or 0.2 mm. The ratio between Land/or Wand T may be
about 1.
[0214] Referring to FIGS. 4-10, the same ratios between sensory
region length/width and thickness, and between sensor body
thickness and isolation layer thickness, apply.
[0215] It is not a requirement that the electrode elements be
arranged as lines in an array (as shown in FIGS. 11-14, 19a-19c, or
22b), or as racial spokes (as shown in FIG. 22a). It is quite
possible to attain useful sensors by providing sensor elements
comprising first electrode elements with rectangular, linear,
elliptical, circular, spiral, or exotic-shapes and perturbations
thereof.
[0216] It is also possible to mix and match differently shaped
electrode elements and cavities to suicide particular needs of a
given application.
[0217] One example that can be particularly useful is a combination
of rectangular-shaped electrode elements in a grid-like formation
(easily patterned) with a circular-shaped cavity (minimized edge
stress). Such a circular-shaped cavity can be easily provided by a
perforated film spacer 45. An example of this configuration is
exemplified by FIG. 22b.
[0218] The description will now focus on schemes for connecting and
arranging the above-discussed sensor elements. In particular, these
schemes address the problem of variations in pressure within the
measuring device. Contact pressures between surfaces can vary
widely, and often in a periodic manner, over short distances
between two surfaces in contact. Such variations occur due to the
random nature of contact mechanics and the texture of the materials
at the contact interface. These variations are further exaggerated
when light pressures are applied between textured surfaces (such as
fabric layers pressed against a body for example). In these cases,
pressure is primarily transmitted through apexes at the interface
between the surfaces during initial contact and tends to settle out
as the interface materials creep under continued contact
pressure.
[0219] If a sensor system is to adequately measure the contact
pressures between two surfaces, it should preferably be able to
cope with these unavoidable aspects of contact mechanics.
[0220] The geometric issues of measuring representative stresses
between two surfaces can be remedied by using sufficiently thick
isolation layers between the sensor elements and the surfaces in
question to alleviate pressure variations in the vicinity of the
pressure sensor. This task is not easy to accomplish when measuring
pressures applied to body parts as overly thick isolation layers
make the device uncomfortable for the patient, and curvature makes
use of such layers Impractical. Instead, the sensor elements should
be made sufficiently small such that a thin isolation layer is
suitable for averaging out the microscopic stress variations
present in the immediate vicinity of a single sensor element.
Unfortunately, the randomness of contact mechanics prevents a lone
sensor from recovering the overall characteristics of stress
between the contact surfaces.
[0221] One way of handling this problem is to provide a large
number of miniature sensors, and to analyze the signals from each
of the sensors in order to provide a useful result, which may be an
average pressure estimate over the area of the sensor array.
However, this would require a large number of sensors to be
individually connected to a processing unit. The processing unit
would also need sufficient processing power to perform the analysis
from such a large number of sensors, and under realistic operating
conditions with associated cost, power, and time constraints.
[0222] This task is further complicated in that pressure sensor
elements are nonlinear by nature. Therefore, the processing unit
would require an array of individually calibrated lookup-tables, or
configurable algorithms to convert sensor singles into "pressure
estimates", and further analyze the results mathematically under
real-time conditions. As sensor elements will also age during use,
a means of updating the lookup-tables in the processing unit would
be required.
[0223] Instead, the present disclosure provides connectivity
schemes to naturally recover useful pressure related information
directly from groupings of pressure sensor elements, regardless of
sensor nonlinearities and in a real-time fashion, without the need
for large numbers of routed traces or hefty computational
requirements.
[0224] Such pressure related information includes (but is not
limited to) the average pressure, the pressure gradient vector, the
magnitude of the pressure gradient, and higher order spatial
derivatives of the pressure applied to the cluster or portion of
the cluster.
[0225] For clarity, FIGS. 23a and 23b illustrate generic connection
schemes for a pair of two part sensor elements. A two port sensor
element is simply a sensor element with only two electrodes. FIG. 8
shows a sensor element 30' with more than two electrodes.
[0226] FIG. 23a illustrates a pair 50 of sensor elements 53a, 53b,
which via first and second conductors 52a, 52c are connectable to
an external circuit and which via a third conductor 52b are
interconnected in a serial manner. External connections are
provided at 51a and 51b.
[0227] FIG. 23b illustrates a pair 50' of sensor elements 53a, 53b,
which via first and second conductors 52a, 52d are connectable to
an external circuit and which are interconnected in a parallel
manner. External connections are provided at 51a and 51b.
[0228] The solution of the problem of recovering pressure related
information over an area of the surface is to provide a cluster
50'', 50''', 50.sup.IV, 50.sup.V, 50.sup.VI of sensor elements,
which are interconnected in such a manner as to provide a minimum
of external connections, ideally only two, whereby an impedance
value is provided between these two external connections that is
representative of the desired pressure related information. The
cluster should contain at least one sensor element which is
connected in series with one or more other sensor elements, and at
least one sensor element which is connected in parallel with one or
more further sensor elements.
[0229] FIG. 24 schematically illustrates an example of a cluster
50'' of sensor elements. The cluster is provided as an n.times.m
array of sensor elements 53, with a first electrode 52a providing a
first external connection 51a, a final electrode 53d providing a
second external connection 51b, and a plurality of m columns of
sensor elements 53, each column consisting of n sensor elements 53
connected along the conduction path between the first electrode 52a
and a final electrode 52d by a plurality of generally placed
internal electrodes 52. The internal electrodes of the cluster are
generally arranged to connect small groups of sensor elements 53 in
adjacent columns to each other. Hence, the infernal electrodes 52
may extend vertically in FIG. 24 so as to contact two or more of
the sensor elements 53. The connections are established such that
the required pressure related information can be obtained from the
external connections 51a, 51b. For a cluster with only two external
connections, this pressure related information is most commonly the
representative of the average pressure applied to the cluster.
[0230] To achieve a representation of the average pressure applied
to the cluster, the connections within the cluster should
preferably contain at least one polygon network element. The
details am described below in more detail with examples.
[0231] The sensor elements included in the cluster need not have
the same properties, nor must they connect only two electrodes. It
is also not necessary that every position in the cluster be
populated with either sensor element or an electrode element (e.g.,
clusters may contain regions free from sensor elements or
electrodes).
[0232] FIG. 25 illustrates another embodiment of a cluster 50''
wherein the sensor elements 53 are in contact with three or four
different electrodes 52, thus providing a more complex
connectivity. Sensor elements with more than two electrodes are
capable of resolving pressure gradients internally and thus produce
a higher effective resolution than sensor elements with only two
electrodes. Such sensor elements can also have reduced
susceptibility to temperature and humidify fluctuations when
properly connected into clusters.
[0233] FIG. 26 illustrates yet another embodiment of a cluster
50.sup.IV, wherein four sensor elements 53', 53'' each contact two
electrodes, and wherein external connectors are provided at 51a,
51b, 51c, 51d. A cluster with more than two external connections is
capable of resolving higher order pressure related information from
the cluster, such as the pressure gradient magnitude and direction,
and higher order spatial derivatives of the pressure over the
cluster. Such arrangements also provide natural compensation for
changes in the sensor properties due to aging and
temperature-humidity fluctuations.
[0234] The embodiment demonstrated by the cluster 50.sup.IV is
particularly useful when sensor elements 53' and sensor elements
53'' are provided with different pressure sensitivities. In this
case, if a voltage is applied across external connectors 51c, 51d,
then the differential voltage between electrodes 51a, 51b will be
representative of the average pressure applied to the cluster
50.sup.IV.
[0235] FIG. 27 schematically illustrates a signal P.sub.par from a
sensor cluster comprising only parallel connected sensor elements,
a signal P.sub.ser from a sensor cluster comprising only serial
connected sensor elements and a composite signal P.sub.comp from a
cluster comprising both serial and parallel connected sensor
elements, in a situation with a maximum measured pressure
P.sub.max, a minimum measured pressure P.sub.min and a actual
average pressure P.sub.avg over the entire area. It is demonstrated
that an optimally connected cluster will give rise to pressure
estimates P.sub.comp which have values centered around those of the
average applied pressure P.sub.avg with a variance that is much
smaller than that of the overall applied pressure. General
connections depicted by P.sub.ser and P.sub.par fail to attain a
similar correlation.
[0236] FIG. 28 illustrates another embodiment of a cluster
50.sup.V, comprising both serial and parallel connected sensor
elements. This embodiment is a specific example of a 4.times.4
cluster. This example cluster 50.sup.V composes first and second
axes of symmetry A1, A2. The cluster also comprises a quadrilateral
polygon network of sensory elements. This polygon connection is
clarified in more detail by FIGS. 29-30.
[0237] FIG. 29 illustrates an equivalent circuit diagram of the
embodiment of FIG. 28, illustrating, by the dotted boxes, the
serial connected pairs 50 of sensor elements and the parallel
connected pairs 50' of sensor elements.
[0238] FIG. 30 illustrates a reduced equivalent circuit diagram of
the embodiment of FIG. 28. The reduced equivalent circuit diagram
is achieved by merging all (purely) serial and parallel connected
pairs into equivalent circuit elements. Such a process is continued
until there are no remaining purely serial or parallel connected
pairs to further reduce. The reduced equivalent circuit clearly
demonstrates that the cluster 50.sup.V is electrically equivalent
to a polygon network element as described in March R H, Polygons of
resistors and convergent series. American Journal of Physics,
61(10), 1993, pg. 900. Faces F1 and faces with internal connections
F2 are illustrated. In this case, the cluster 50.sup.V comprises a
single quadrilateral polygon network element wherein two faces F1
have one impedance element while the other two faces are faces with
internal connections F2, or "tapped faces".
[0239] The impedance of the cluster 50.sup.V as measured between
the external connections 51a, 51b is representative of the average
pressure applied to the cluster 50.sup.V.
[0240] FIG. 31 illustrates a further embodiment of a cluster
50.sup.VI, composing both serial and parallel connected sensor
elements. This embodiment is another specific example of a
4.times.4 cluster. This embodiment comprises a first set of
external connections 51c, 51d and also a second set of external
connections 51a, 51b, which may be used to garner further
information about pressure distribution inside the cluster. For
example, such a second set of external connections may be used to
determine if the pressure is lower or higher in any quadrant of the
cluster, i.e., it can obtain 1st order information regarding the
macroscopic derivative of the pressure distribution applied to the
sensor cluster. The cluster 50.sup.VI is electrically equivalent to
a connection of two triangular polygon network elements with a
shared face F3. This equivalence is further clarified by FIGS.
32-33.
[0241] FIG. 32 illustrates an equivalent circuit diagram of the
embodiment of FIG. 31, illustrating the serial connected pairs 50
of sensor elements and the parallel connected pairs 50' of sensor
elements.
[0242] FIG. 33 illustrates a reduced equivalent circuit diagram of
the embodiment of FIG. 31. The equivalent circuit demonstrates that
equivalent circuit for the 20 cluster 50.sup.VI comprises a group
of polygon network elements. Faces F1 and shared face F3 are
illustrated. In this case, cluster 50.sup.VI comprises a connection
of two triangular polygon network elements with a shared face
wherein Faces F1 have a single impedance element while shared face
F3 is missing an impedance element.
[0243] The impedance of the cluster 50.sup.VI as measured between
the first set of external connections 51c, 51d is representative of
the average pressure applied to the cluster 50.sup.VI.
Alternatively, if a voltage is applied across the first set of
external connections 51c, 51d, then the voltages and voltage
difference measured between the second set of external connections
is representative of the pressure gradient applied to the cluster
50.sup.VI.
[0244] In the above described clusters, the overall impedance of
the cluster can be further tailored to achieve values that are most
suitable for the external electronics. To achieve this end, the
optimum connectivity is a combination of serial and parallel
connections with weight to more serial or more parallel depending
on the desired overall impedance of the cluster.
[0245] As FIGS. 23-33 depict connections in a schematic fashion, it
is to be understood that connectivity plays no bearing on the
actual geometric layout of the cluster. It is not a requirement
that the clusters be formed in rectangular arrays of sensor
elements. Furthermore, it is possible that the sensor elements be
printed on two sides of a substrate with connectivity between them
forming a single cluster.
[0246] It is also understood that connectivity of sensor elements
scattered over a wide area can be equivalent to the connectivity of
sensor element in a tight packed arrangement, and that a sensor
elements arranged in a grid can have equal connectivity to sensor
elements arranged randomly over an area.
[0247] It is not a requirement that sensor elements be connected
only to adjacent electrodes. Higher order connectivity, achievable
by multi-layered connections, is advantageous for some applications
such as measurement of temporal pressure events with related
spatial heterogeneity throughput the cluster (e.g., pressure
waves).
[0248] It is further understood that many physical connectivities
within a cluster can lead to the same representative reduced
equivalent circuit. As an example, the reduced equivalent circuit
of FIG. 33 could represent a cluster of ten sensor elements 53
connected precisely as shown in FIG. 33.
[0249] It is further understood that each sensor element 53 within
the clusters could equally represent a nested cluster. As an
example, the sensor element 53' as shown in FIG. 26 may actually
represent a cluster with two external connections such cluster
50.sup.VI while sensor element 53'' as shown in FIG. 26 may
represent a different cluster with two external connections such as
cluster 50.sup.V.
[0250] The sensor clustering principle, as exemplified with
reference to FIGS. 24-33 is mainly useful for analog sensors, such
as those described with reference to FIGS. 4-10.
[0251] In one embodiment, a sensor system may contain a cluster of
a plurality-sensor elements of the type described with reference to
FIGS. 4-10, and one or more sensors of the type described with
reference to anyone of FIGS. 11-22.
[0252] A cluster 70 comprising a plurality of sensor elements 40 as
described with reference to FIGS. 11-22, can be arranged such that
the pressure-impedance behavior of the cluster 70, as measured
between the external connections 51a, 51b, is demonstrated by FIG.
17. Similar behavior can be obtained from clusters comprise
different sensor elements as demonstrated in the following two
examples.
[0253] In the first example, a cluster 70 consists of five sensor
elements 40 as described with reference to FIGS. 11-22, each having
only two first electrodes 42a, which are connected together
serially. The size of the cavity 48, positioning of the first
electrode elements 42a with respect to the cavity 48, and/or
spacing S between the first electrode elements 42a are individually
adjusted for each sensor such that the sensor element provides a
corresponding switching pressure P1, P2, P3, P4 or P5.
[0254] In the second example, a cluster 70 comprising two sensor
elements 40 as described with reference to FIGS. 11-22, one sensor
element having three first electrode elements 42a, and a second
sensor element having four first electrode elements 42a, wherein
the sensor elements 40 are connected serially end the size of the
cavity 48, positioning of the first electrode elements 42a with
respect to the cavity 48, and/or spacing S between the first
electrode elements 42a, are individually adjusted for each sensor
element such that the first sensor element provides switching
pressures P1 and P2, and the second sensor element provides
switching pressures P3, P4 and P5.
[0255] In another embodiment, a sensor system may contain a first
cluster of a plurality sensor elements of the type described with
reference to FIGS. 4-10, and a second cluster of sensors of the
type described with reference to anyone of FIGS. 11-22.
[0256] In particular, the second cluster may compose sensors having
resistive electrodes, e.g., as discussed with reference to FIG.
18.
[0257] The sensor clusters and/or systems may be enclosed within a
common enclosure, such as the one designated by reference numerals
26, 34, 49a or 49b.
[0258] Individual sensor elements, sensor clusters or sensor
systems may be connected to a measuring device for measuring
pressure.
[0259] Referring to FIGS. 34-36, the sensor elements, sensor
clusters or sensor systems may be used for measuring pressure on a
body part 60, which in FIGS. 34-36 is illustrated by a lower leg. A
plurality of sensor devices 62, 62', 62'', each being in the form
of a sensor element, sensor cluster or sensor system, may be
distributed over a carrier 61, 61', which may be in the form of a
flexible sheet, in order to conform to the body part on which
measurements are to be made.
[0260] The sensor devices 82 may be connected via conductor devices
66 (cables, wires, conducting traces, etc.) to a central point 63,
wherein connectors for connection to external equipment may be
provided, or wherein the electronics itself may be provided. The
carrier 61, 61' may thus be the substrate (c.f. reference numerals
21, 31, 41, 47) on which the sensor element is arranged. The sensor
devices 62 may be distributed over an area of the carrier 61, such
as is illustrated in FIG. 34. Alternatively, or as a complement,
sensor devices 62' or substantially along a line, such as is
illustrated in FIG. 35.
[0261] Alternatively, the sensor devices 62'' may be distributed
over the entire carrier 61', with interconnection buses 65a, 65b,
65c provided, e.g., at the edges (65a, 65c) of the carrier 61,
and/or along the length of the carrier 61 (65b).
[0262] The carrier may be in the form of a flexible sheet of
garment or film, which optionally may be breathable. The carrier 61
may form the substrate as illustrated in FIGS. 4-22. In order to
form a measuring device for measuring pressure on a body part, the
carrier 61 with the sensors may be part of a laminated structure,
which may contain one or more pressure smoothing layers, arranged
on one or both sides of the carrier 61. The smoothing layers may be
intimately laminated or printed onto either side of the carrier 61,
such that the stresses at the interface between the sensor element
and its surroundings can be sufficiently smoothed before they reach
the surface of the sensing element.
[0263] Such smoothing layer way be in the form of a microcellular
foam structure. In other embodiments, it may be a printed layer of
rubber, a laminated non-woven fabric etc.
[0264] The mechanical properties and thickness ratios between the
smoothing layer and transverse sensor moduli and dimensions may be
selected so as to ensure that pressure is effectively smoothed upon
reaching the sensor element surface. The total sensor and smoothing
layer thickness should preferably be less than 1.5 mm, more
preferably less than 1.0 mm, even more preferably less than, 0.5 mm
and most preferably less than 0.2 mm, and therefore the sensor
element should be extremely thin to accommodate a sufficiently
thick smoothing layer into the small amount of space provided. The
smoothing layer may be chosen such that it is preferably 5-10 times
the thickness of the sensor element.
[0265] In order for the smoothing layer to be effective, it is also
preferable that the length, width or diameter of the sensing area
of the sensor element be roughly of the same order of magnitude as
the thickness of the total sensor and smoothing layer
thickness.
[0266] The carrier 61 may be included in a device for compression
treatment of the body part. Hence, the device may comprise further
layers 200 (FIG. 37) housing actuators etc., for providing the
compression movement.
[0267] As one example, the layer 200 may form part of an inflatable
bladder, which is used to provide a pressure to a body part in a
per se known manner.
[0268] In yet another embodiment, the substrate 21, 31, 41, 61,
61', upon which the sensor element is arranged, may be a wall of
such a bladder, i.e., the substrate may be integrated with the wall
of the bladder.
[0269] In other embodiments, the compression device may, as
non-limiting examples, be of the type described in any one, or a
combination of, US 2004/0073146A1, US 2002/0173735A1, EP 1 324 403
A1, U.S. Pat. No. 5,997,455, WO 2004/093763 A1, US 2005/0043657 A1,
U.S. Pat. No. 6,123,681, U.S. Pat. No. 6,494,852 B1, U.S. Pat. No.
6,198,204 B1 or US 2004/067375 A1.
[0270] Referring to FIG. 37, there is illustrated a detail of a
carrier 61, upon which a sensor device 62 is provided, and
connected via a conductor device 66 to a measuring device 100. The
sensor device comprises at least one, preferably more/pressure
sensor element 20, 30 of the first type as described with reference
to FIGS. 4-10, or clusters 50'', 50''', 50.sup.IV, 50.sup.V,
50.sup.VI of such pressure sensor elements, and at least one
pressure sensor element 40 of the second type, or cluster 70
thereof, as described with reference to FIGS. 11-22.
[0271] In one embodiment, the sensor device 62 may comprise a
plurality of sensor elements of the first type, which are arranged
as a sensor cluster 50'', 50''', 50.sup.IV, 50.sup.V, 50.sup.VI, as
described with reference to FIGS. 24-33, and optionally one or more
sensor elements of the second type.
[0272] In another embodiment, the sensor device 62 may also
comprise a plurality of sensor elements of the second type, which
are arranged as a sensor cluster as described with reference to
FIGS. 24-33.
[0273] The sensor elements may be arranged within a common
encapsulation 26, 34, 49a, 49b.
[0274] As indicated, the sensors and sensor systems described
herein may be used for measuring contact pressure between a body
part and a compression device, between two body parts, between a
body part and some external device, such as a steering wheel (e.g.,
when arranged in/on a glove or in/on the steering wheel), a
surgical tool, a floor (e.g., when arranged in/on a shoe).
* * * * *