Note: Descriptions are shown in the official language in which they were submitted.
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SURFACE DEFORMATION ELECTROACTIVE POLYMER
TRANSDUCERS
This application is a division of application number 2,537,244, filed in
Canada on September 1, 2004.
U.S. GOVERNMENT RIGHTS
This application was made in part with government support under contract
number MDA972-02-C-0001 awarded by the United States Defense Advanced
Research Project Agency. The government has certain rights in the invention.
BACKGROUND OF THE INVENTION
The present invention relates generally to electroactive polymers that convert
between electrical energy and mechanical energy. More particularly, the
present
invention relates to electroactive polymers and their abilities and
applications related
to surface deformation, surface texturing and surface geometry control.
In many applications, it is desirable to convert between electrical energy and
mechanical energy. Common technologies that convert electrical energy to
mechanical work include motors and piezoelectric ceramics for example. Most
conventional electrical to mechanical technologies provide limited mechanical
output
abilities. Motors provide continuous rotary output - and generally require
additional
and bulky coupling to provide discontinuous output or low-frequency motion.
Piezoelectric ceramics are typically limited to in-plane strains between the
rigid
electrodes below about 1.6 percent and are not suitable for applications
requiring
greater strains or out-of plane deformations.
New high-performance polymers capable of converting electrical energy to
mechanical energy, and vice versa, are now available for a wide range of
energy
conversion applications. One class of these polymers, electroactive elastomers
(also
called dielectric elastomers, electroelastomers, or EPAM (Electroactive
Polymer
Artificial Muscle)), is gaining wider attention. Electroactive elastomers may
exhibit
high energy density, stress, and electromechanical coupling efficiency. To
date,
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electroactive polymer transducers and devices have been directed towards in-
plane
strains for conversion between electrical and mechanical energy.
Many applications demand a light-weight, scaleable device that converts
between electrical and mechanical energy in out-of plane directions.
SUMMARY OF THE INVENTION
The present invention provides electroactive polymer transducers that produce
out-of-plane deflections. The transducers form a set of surface features based
on
deflection of an electroactive polymer. The set of surface features may
include
elevated polymer surface features and/or depressed electrode surface features.
Actuation of an active area may produce the polymer deflection that creates
one or
more surface features. In one embodiment, a passive layer operably connects to
a
polymer and augments out-of-plane deflections. The passive layer may comprise
a
thicker and softer material to amplify thickness changes and increase surface
feature
visibility.
In one aspect, the present invention relates to an electroactive polymer
transducer. The transducer comprises an electroactive polymer including an
undeflected thickness for a surface region on a first surface of the polymer.
The
transducer also comprises a first electrode disposed on a portion of the first
surface of
the electroactive polymer. The transducer further comprises a second electrode
disposed on a portion of a second surface of the electroactive polymer. The
electroactive polymer is configured to include a polymer surface feature above
the
undeflected thickness after deflection of an active area. The first electrode
is
configured to include an electrode surface feature below the undeflected
thickness
after deflection of the active area
In another aspect, the present invention relates to an electroactive polymer
transducer. The transducer comprises an electroactive polymer including an
undeflected thickness for a surface region on a first surface of the polymer.
The
transducer also comprises a first electrode disposed on the first surface of
the
electroactive polymer and a second electrode disposed on a second surface of
the
electroactive polymer. The electroactive polymer and first electrode are
configured to
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produce a set of surface features on the first surface after deflection of an
active area.
The set of features includes a) a polymer surface feature that is elevated
above the
undeflected thickness and outside the first electrode on the first surface or
b) an
electrode surface feature that is depressed below the undeflected thickness.
In yet another aspect, the present invention relates to an electroactive
polymer
transducer. The transducer comprises an electroactive polymer including an
undeflected thickness for a surface region on a first surface of the polymer.
The
transducer also comprises a first electrode disposed on a portion of the first
surface of
the electroactive polymer. The transducer further comprises a second electrode
disposed on a portion of a second surface of the electroactive polymer. The
electroactive polymer and first electrode are configured to produce a set of
surface
features on the first surface after deflection of an active area. The set of
surface
features includes a polymer surface feature above the undeflected thickness on
the
first surface or an electrode surface feature below the undeflected thickness.
The
transducer additionally comprises a passive layer that neighbors the first
surface and
is configured to deflect with the deflection of the electroactive polymer such
that a
surface of the passive layer opposite to the electroactive polymer forms a set
of
passive layer surface features that resembles the set of surface features on
the first
surface
In still another aspect, the present invention relates to a method of
actuating an
electroactive polymer transducer. The method comprises actuating a first
portion of
the electroactive polymer including an undeflected thickness for a first
surface region
on a first surface of the polymer before actuation of the first portion to
create a first
surface feature on the first surface. The method also comprises actuating a
second
portion of the electroactive polymer including an undeflected thickness for a
second
surface region on the first surface of the polymer before actuation of the
second
portion to create a second surface feature on the first surface.
These and other features and advantages of the present invention will be
described in the following description of the invention and associated
figures.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIGs. 1A and 1B illustrate a top perspective view of a transducer before and
after application of a voltage in accordance with one embodiment of the
present
invention.
FIG. 1C illustrates a side view of transducer including a surface region
before
actuation in accordance with one embodiment of the present invention.
FIG. 1D illustrates a side view of transducer including surface region after
actuation in accordance with one embodiment of the present invention.
FIG. lE illustrates a transducer comprising a rigid layer in accordance with
one embodiment of the present invention.
FIG. IF illustrates a monolithic transducer comprising a plurality of active
areas in accordance with one embodiment of the present invention.
FIG. 1G illustrates an electroactive polymer transducer before deflection in
accordance with a specific embodiment of the present invention.
FIG. 1H illustrates the transducer of FIG. 1G after deflection.
FIG. 2A illustrates a transducer including a passive layer that enhances out-
of-
plane deflection in accordance with one embodiment of the present invention.
FIG. 2B illustrates the transducer of FIG. 2A in an actuated state.
FIG. 2C illustrates a transducer comprising an electroactive polymer between
two passive layers in accordance with a specific embodiment of the present
invention.
FIG. 3A shows a top elevated view of crossing common electrodes for a
transducer in accordance with a specific embodiment of the present invention.
FIGs. 3B-3C show top elevated photos for a transducer including a passive
layer in accordance with another specific embodiment of the present invention.
FIG. 3D illustrates a top elevated view of a transducer in accordance with a
specific embodiment of the present invention.
FIG. 3E illustrates a top elevated view of the transducer of FIG. 3D with
actuation of a letter.
FIG. 3F illustrates a side view of grid surface features electrodes for a
transducer in accordance with another specific embodiment of the present
invention.
FIG. 4 illustrates a process flow for using an electroactive polymer
transducer
in accordance with one embodiment of the present invention.
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FIG. 5A illustrates a method for moving two objects relative to each other
using stepwise deflection of multiple active areas in accordance with a
specific
embodiment.
FIG. 5B illustrates surface deforming electroactive polymer transducers
mounted to a surface of a wing and a flap in accordance with a specific
embodiment
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is described in detail with reference to a few preferred
embodiments as illustrated in the accompanying drawings. In the following
description, numerous specific details are set forth in order to provide a
thorough
understanding of the present invention. It will be apparent, however, to one
skilled in
the art, that the present invention may be practiced without some or all of
these
specific details. In other instances, well known process steps and/or
structures have
not been described in detail in order to not unnecessarily obscure the present
invention.
1. GENERAL STRUCTURE OF ELECTROACTIVE POLYMERS
The transformation between electrical and mechanical energy in transducers
and devices of the present invention is based on elasticity of an
electroactive polymer
and energy conversion of one or more portions of an electroactive polymer
(EAP).
To help illustrate the performance of an electroactive polymer in converting
electrical energy to mechanical energy, FIG. IA illustrates a top perspective
view of a
transducer portion 10 in accordance with one embodiment of the present
invention.
While electroactive polymer transducers will now be described as structures,
those
skilled in the area will recognize that the present invention encompasses a
methods
for performing the actions as described below.
The transducer portion 10 comprises an electroactive polymer 12 for
converting between electrical energy and mechanical energy. In one embodiment,
an
electroactive polymer refers to a polymer that acts as an insulating
dielectric between
two electrodes and may deflect upon application of a voltage difference
between the
two electrodes. Top and bottom electrodes 14 and 16 attach to electroactive
polymer
12 on its top and bottom surfaces, respectively, to provide a voltage
difference across
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a portion of the polymer 12. Polymer 12 deflects with a change in electric
field
provided by the top and bottom electrodes 14 and 16. Deflection of the
transducer
portion 10 in response to a change in electric field provided by the
electrodes 14 and
16 is referred to as actuation.
FIG. 1B illustrates a top perspective view of the transducer portion 10
including deflection in response to a change in electric field. In general,
deflection
refers to any displacement, expansion, contraction, bulging, torsion, linear
or area
strain, or any other deformation of a portion of the polymer 12. The change in
electric
field corresponding to the voltage difference applied to or by the electrodes
14 and 16
produces mechanical pressure within polymer 12. In this case, the unlike
electrical
charges produced by electrodes 14 and 16 attract each other and provide a
compressive force between electrodes 14 and 16 and an expansion force on
polymer
12 in planar directions 18 and 20, causing polymer 12 to compress between
electrodes
14 and 16 and stretch in the planar directions 18 and 20.
After application of the voltage between electrodes 14 and 16, polymer 12
expands (stretches) in both planar directions 18 and 20. In some cases,
polymer 12 is
incompressible, e.g. has a substantially constant volume under stress. For an
incompressible polymer 12, polymer 12 decreases in thickness as a result of
the
expansion in the planar directions 18 and 20. It should be noted that the
present
invention is not limited to incompressible polymers and deflection of the
polymer 12
may not conform to such a simple relationship.
Application of a relatively large voltage difference between electrodes 14 and
16 on the transducer portion 10 shown in FIG. 1A thus causes transducer
portion 10
to change to a thinner, larger area shape as shown in FIG. 1B. In this manner,
the
transducer portion 10 converts electrical energy to mechanical energy.
As shown in FIGs. IA and 1B, electrodes 14 and 16 cover the entire portion
of polymer 12 as shown. More commonly, electrodes 14 and 16 cover a limited
portion of polymer 12 relative to the total surface area of the polymer. For
the present
invention, this is done to utilize incompressibility of the polymer and
produce surface
features and deformations on one or more of the polymer surfaces. This may
also be
done to prevent electrical breakdown around the edge of polymer 12. Electrodes
may
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also be patterned with special shapes to achieve customized surface
deflections, as
will be described in further detail below.
As the term is used herein, an active area refers to a portion of a transducer
comprising polymer material 12 and at least two electrodes. When the active
area is
used to convert electrical energy to mechanical energy, the active area
includes a
portion of polymer 12 having sufficient electrostatic force to enable
deflection of the
portion. When the active area is used to convert mechanical energy to
electrical
energy, the active area includes a portion of polymer 12 having sufficient
deflection
to enable a change in electrostatic energy. As will be described below, a
polymer of
the present invention may have multiple active areas.
FIG. 1C illustrates an extended side view of a transducer 10 outside the
portion shown in FIG. IA and including a surface region 21 before actuation in
accordance with one embodiment of the present invention. As the term is used
herein,
a surface region 21 generally refers to a surface portion of interest for an
electroactive
polymer transducer that includes at least a part of the polymer surface
covered by an
electrode (or electrode portion) and polymer surface outside the electrode (or
portion)
that is affected by deflection of an active area including the electrode (or
portion). For
the planar polymer 12 and rectangular electrode 14 of FIG. 1C, surface region
21
comprises the surface area of polymer 12 covered by electrode 14 and
neighboring
surface portions 23 of polymer 12 perimetrically surrounding electrode 14 on
the top
surface of polymer 12. In one embodiment, surface region 21 comprises all
surface
portions of an electroactive polymer transducer affected by elastic and
electrostatic
forces resulting from actuation of an active area of polymer 12, including
polymer
and electrode material surface portions of a driven active area and polymer
and
electrode material surface portions proximate to the driven active area.
Before actuation, transducer 10 can be described by an undeflected thickness
22 over surface region 21. The undeflected thickness 22 refers to the
approximate
thickness of polymer 12 before deflection to produce a surface feature.
Thickness 22
may be measured from one surface of polymer 12 to the other surface of polymer
12
over the surface region 21. Typically, polymer 12 is relatively flat on both
its top and
bottom surfaces and has a relatively constant thickness 22 across the polymer
surface
and surface region 21. Electrodes 14 and 16 often include a minimal or
negligible
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depth and add little to thickness 22 and in these cases undeflected thickness
22 may
include electrodes 14 and 16. The undeflected thickness 22 thus corresponds to
the
thickness of the polymer in cross section. For commercially available
polymers, the
undeflected thickness 22 may roughly correspond to the thickness of the
polymer as
manufactured and received. In one embodiment, polymer 12 is pre-strained, as
will be
described in further detail below, and thickness 22 refers to the undeflected
thickness
in surface region 21 after pre-straining. It is understood that the thickness
of polymer
12 and electrodes 14 and 16 between top and bottom surfaces over the surface
region
21 may vary slightly, say by 1-20 percent in some cases. Here, undeflected
thickness
22 may refer to an average or arithmetic representation of the varying
thicknesses
across surface region 21. It is understood that some polymers may not include
perfectly consistent thicknesses and that an undeflected thickness for a
surface region
21 may better describe the thickness of surface region 21 before actuation. In
one
embodiment, transducer 10 is substantially flat before deflection. In another
embodiment, transducer 10 is configured on a curved surface and with a
generally
consistent thickness for the polymer on the curved surface. While deflection
as
described herein will mainly be described via an actuation using electrodes 14
and 16,
it is understood that generation and sensing functions as described below may
also
lead to deflections and surface features.
FIG. ID illustrates a side view of transducer 10 including surface region 21,
after deflection of an active area, in accordance with one embodiment of the
present
invention. Polymer 12 material outside an active area typically resists active
area
deflection. While the amount of resistance may vary based on how the entire
polymer
is held or configured by a frame for example, polymer 12 material outside an
active
area commonly acts as a spring force, based on elasticity of the material.
Since the
polymer 12 material is compliant, the material may deform and bulges out-of-
plane in
the thickness direction (orthogonal to the plane) in response to deflection or
actuation
of an active area.
The polymer 12 and one or both electrodes 14 and 16 of transducer 10 are
configured to produce polymer surface features 17a-b form on the top surface
of
polymer 12 above the undeflected thickness 22 after deformation of the active
area.
The polymer surface features 17 refer to portions of an electroactive polymer
elevated
above the undeflected thickness 22 as a result of deflection, electrostatic
forces and/or
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elastic response in the polymer. In this case, elevated surface features 17a-b
are
created around the edges of an active area corresponding to the surface shape
of
electrode 14 (and to a lesser extent, electrode 16 on the opposite surface).
The surface
features 17a-b may be distinct bulges as shown in Figure ID, or they may be
more
distributed increases in thickness outside the electrode region 14, depending
on the
films tension and elasticity. Similarly, bottom polymer surface features 17c-d
are
formed on the bottom side of polymer 12 around the edges of an active area
corresponding to the surface shape of electrode 16 (and to a lesser extent,
electrode
14). The polymer surface features 17 generally result from the fact that while
the
actuated polymer 12 increases in surface area over an active area proximate to
electrodes 14 and 16, the polymer often (depending on design) decreases in
area over
the inactive regions of the polymer. The bulging polymer surface features 17
then
include displaced polymer material, typically located at the edges of an
electrode for
an active area. Surface region 21 for the top surface of transducer 10 in this
case then
includes the planar area of electrode 14 and polymer surface features 17a-b.
In addition to the elevated polymer surface features 17, polymer 12 and one or
both electrodes 14 and 16 of transducer 10 are configured to produce a lowered
electrode portion 27 that rests below the undeflected thickness 22 after the
deflection
due to actuation. In this case, all of electrode 14 on the top surface is
depressed below
the undeflected thickness 22 after deflection. The depressed electrode portion
27 also
acts as an electrode surface feature 19a created by actuation and deflection
of
polymer 12 and thinning of polymer 12 around electrodes 14 and 16. For
example, if
electrode 14 is shaped as a circle, then the electrode surface feature 19a
will be a
depressed circle when viewed from the top, while polymer surface feature 17
will
comprise an elevated '0' or ring about the depressed circle. As will be
described in
greater detail below, electrodes 14 and 16 can be patterned or designed to
produce
customized polymer surface features 17 and electrode surface features 19, such
as
letters (e.g., a, n, y, 1, e, t, r) or more complex patterns and shapes.
Bottom electrode 16 similarly expands in the plane and thins to create an
electrode surface feature I 9b on the bottom side of transducer 10. Electrode
surface
feature 19b rests below the undeflected thickness 22 for the bottom side of
transducer
10. Elastic resistance in polymer 12 to expansion of polymer 12 in an active
area
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between electrodes 14 and 16 also creates polymer surface features 17c-d on
the
bottom side of transducer 10.
While out-of-plane surface features 17 are shown relatively local to the
active
area, the out-of-plane is not always localized as shown. In some cases, if the
polymer
is pre-strained, then the surface features 17a-b are stretched or smoothed out
over the
inactive polymer material. The magnitude of out-of-plane deformation may vary
with
the exact geometry, pre-strain, etc. However, regardless of whether it is
described as a
local bulge or distributed, the inactive regions generally become thicker in
cross
section.
In general, the transducer 10 (polymer 12 and electrodes) continues to deflect
until mechanical forces balance the electrostatic forces driving the
deflection. More
specifically, polymer 12 between electrodes 14 and 16 and in the active area
continues to expand and thin, while polymer surface features 17 continue to
elevate
from the surfaces of polymer 12 and electrode surface feature 19 continue to
form by
the thinning of polymer 12, until mechanical forces balance the electrostatic
forces
driving the deflection. The mechanical forces include elastic restoring forces
of the
polymer 12 material inside and outside the active area, the compliance of
electrodes
14 and 16, and any external resistance provided by a device and/or load
coupled to
the transducer portion 10, etc. The deflection of the transducer portion 10 as
a result
of the applied voltage may also depend on a number of other factors such as
the
polymer 12 dielectric constant and the size of polymer 12.
FIG. 1E illustrates a transducer 60 comprising a rigid layer 62 in accordance
with one embodiment of the present invention. Transducer 60 comprises rigid
layer
62, electroactive polymer 64, top surface electrode 66, bottom surface
electrode 68,
polymer surface features 63 and electrode surface features 65.
Rigid layer 62 attaches to a bottom surface of polymer 64 and prevents the
bottom surface of polymer 64 from deflecting. As a result, only the top
surface of
polymer 64 includes polymer surface features 63 and electrode surface feature
65.
Rigid layer 62 may comprise a rigid structure such as a stiff metal or non-
metal plate, for example. In one embodiment, rigid layer 62 comprises a non-
compliant electrode material such as a suitably stiff metal, which then doubly
acts as
an electrode for the surface it attaches to and a rigid layer 62. The rigid
layer 62
CA 02821442 2013-07-17
electrode may be any type of conductive material. For instance, the rigid
layer 62
electrode may be a metal, such as copper, aluminum, gold, silver, etc. In
another
specific embodiment, the rigid layer 62 electrode may comprise a conductive
ceramic-based composite material.
Polymer 64 may be bonded to rigid layer 62 using a bonding agent. Partially
bonding between polymer 64 and the structure, i.e. the area of the bonding
agent is
less than the area of contact between polymer 64 and rigid layer 62, permits
customized deflections of polymer 64. For example, for a rectangular polymer
64 and
rigid layer 62, polymer 64 may be bonded to rigid layer 62 along two edges of
the
rectangle. In this case, polymer 64 expands relative to rigid layer 62 in the
un-bonded
direction. During expansion of polymer 64, a lubricant may be disposed between
rigid
layer 62 and polymer 64 to reduce friction between the two surfaces. An
optional
passive layer may also be disposed between rigid layer 62 and polymer 64. The
passive layer is selected so that it deflects as polymer 64 deflects. This
specific
embodiment allows polymer 64 to expand more as compared to when it is directly
bonded to rigid layer 62.
Generally, polymers that are suitable for use with transducers of this
invention
include any substantially insulating polymer or rubber (or combination
thereof) that
deforms in response to an electrostatic force or whose deformation results in
a change
in electric field. Preferably, the polymer's deformation is reversible over a
wide range
of strains. Many elastomeric polymers may serve this purpose. In designing or
choosing an appropriate polymer, one should consider the optimal material,
physical,
and chemical properties. Such properties can be tailored by judicious
selection of
monomer (including any side chains), additives, degree of cross-linking,
crystallinity,
molecular weight, etc.
Polymer 12 may assume many different physical and chemical states. For
example, the polymer may be used with or without additives such as
plasticizers. And
they may be monolithic polymeric sheets or combinations of polymers such as
laminates or patchworks. Further, the polymers may exist in a single phase or
multiple phases. One example of a multiphase material is a polymeric matrix
having
inorganic filler particles admixed therewith.
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Regardless of the ultimate chemical and physical state of the transducer
polymer, it will include a polymer matrix. That matrix may be a homopolymer or
copolymer, cross-linked or uncross-linked, linear or branched, etc. Exemplary
classes
of polymer suitable for use with transducers of this invention include
silicone
elastomers, acrylic elastomers, polyurethanes, thermoplastic elastomers,
copolymers
comprising PVDF, pressure-sensitive adhesives, fluoroelastomers, polymers
comprising silicone and acrylic moieties, and the like. Obviously,
combinations of
some of these materials may be used as the polymer matrix in transducers of
this
invention. Copolymers and blends fall within the class of suitable polymers.
One
example is a blend of a silicone elastomer and an acrylic elastomer.
One suitable commercially available polymer is NuSil CF19-2186 as provided
by NuSil Technology of Carpenteria, CA. An example of a suitable silicone
elastomer
is Dow Corning HS3 as provided by Dow Corning of Wilmington, Delaware. One
example of a suitable fluorosilicone is Dow Corning 730 as provided by Dow
Corning of Wilmington, Delaware. Examples of suitable acrylics include any
acrylic
in the 4900 VHB acrylic series as provided by 3M Corp. of St. Paul, MN.
Suitable actuation voltages for electroactive polymers, or portions thereof,
may vary based on the material properties of the electroactive polymer, such
as the
dielectric constant, as well as the dimensions of the polymer, such as the
thickness of
the polymer film. For example, actuation electric fields used to actuate
polymer 12 in
Figure 1A may range in magnitude from about 0 V/m to about 440 MV/m. Actuation
electric fields in this range may produce a pressure in the range of about 0
Pa to about
10 MPa. In order for the transducer to produce greater forces, the thickness
of the
polymer layer may be increased. Actuation voltages for a particular polymer
may be
reduced by increasing the dielectric constant, decreasing the polymer
thickness, and
decreasing the modulus of elasticity, for example.
In one embodiment, polymer 12 is compliant and selected based on its
elastance. A modulus of elasticity for polymer 12 less than about 100 MPa is
suitable
for many embodiments. In one specific embodiment, electroactive polymer 12
includes an elastic modulus less than 40 MPa. In another specific embodiment,
electroactive polymer 12 is relatively compliant and includes an elastic
modulus less
than 10 MPa.
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In one embodiment, electroactive polymer 12 is pre-strained. The
performance of many polymers is notably increased when the polymers are pre-
strained in area. For example, a 10-fold to 25-fold increase in area
significantly
improves performance of many electroactive elastomers. Pre-strain of a polymer
may
be described, in one or more directions, as the change in dimension in a
direction
after pre-straining relative to the dimension in that direction before pre-
straining. The
pre-strain may comprise elastic deformation of polymer 12 and be formed, for
example, by stretching the polymer in tension and holding one or more of the
edges
while stretched. The pre-strain may be imposed at the boundaries using a rigid
frame
or may also be implemented locally for a portion of the polymer. In another
embodiment, portions of the polymer are cured or otherwise stiffened to
increase their
rigidity and hold pre-strain on a polymer. This allows pre-strain to be held
without an
external frame. For many polymers, pre-strain improves conversion between
electrical and mechanical energy. The improved mechanical response enables
greater
mechanical work for an electroactive polymer, e.g., larger deflections and
actuation
pressures. In one embodiment, prestrain improves the dielectric strength of
the
polymer. In another embodiment, the pre-strain is elastic. After actuation, an
elastically pre-strained polymer could, in principle, be unfixed and return to
its
original state.
In one embodiment, pre-strain is applied uniformly over a portion of polymer
12 to produce an isotropic pre-strained polymer. By way of example, an acrylic
elastomeric polymer may be stretched by 200 to 400 percent in both planar
directions.
In another embodiment, pre-strain is applied unequally in different directions
for a
portion of polymer 12 to produce an anisotropic pre-strained polymer. In this
case,
polymer 12 may deflect greater in one direction than another when actuated.
While
not wishing to be bound by theory, it is believed that pre-straining a polymer
in one
direction may increase the stiffness of the polymer in the pre-strain
direction.
Correspondingly, the polymer is relatively stiffer in the high pre-strain
direction and
more compliant in the low pre-strain direction and, upon actuation, more
deflection
occurs in the low pre-strain direction. In one embodiment, the deflection in
direction
108 of transducer portion 10 can be enhanced by exploiting large pre-strain in
the
perpendicular direction 110. For example, an acrylic elastomeric polymer used
as the
transducer portion 10 may be stretched by 10 percent in direction 108 and by
500
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percent in the perpendicular direction 110. The quantity of pre-strain for a
polymer
may be based on the polymer material and the desired performance of the
polymer in
an application. Pre-strain suitable for use with the present invention is
further
described in commonly owned, copending U.S. Patent Application No. 09/619,848.
Edges of polymer 12 may be fixed to one or more objects. The polymer may
be fixed to the one or more objects according to any conventional method known
in
the art such as a chemical adhesive, an adhesive layer or material, mechanical
attachment, etc. Transducers and polymers of the present invention are not
limited to
any particular geometry or type of deflection. For example, the polymer and
to electrodes may be formed into any geometry or shape including tubes and
rolls,
stretched polymers attached between multiple rigid structures, stretched
polymers
attached across a frame of any geometry - including curved or complex
geometry's,
across a frame having one or more joints, etc. Deflection of a transducer
according to
the present invention includes linear expansion and compression in one or more
directions, bending, axial deflection when the polymer is rolled, deflection
out of a
hole provided in a substrate, etc. Deflection of a transducer may be affected
by how
the polymer is constrained by a frame or rigid structures attached to the
polymer. In
one embodiment, a flexible material that is stiffer in elongation than the
polymer is
attached to one side of a transducer induces bending when the polymer is
actuated.
2. ELECTRODES
As electroactive polymers of the present invention may deflect at high
strains,
electrodes attached to the polymers should also deflect without compromising
mechanical or electrical performance. Generally, electrodes suitable for use
with the
present invention may be of any shape and material provided that they are able
to
supply a suitable voltage to, or receive a suitable voltage from, an
electroactive
polymer. The voltage may be either constant or varying over time. In one
embodiment, the electrodes adhere to a surface of the polymer. Electrodes
adhering to
the polymer may be compliant and conform to the changing shape of the polymer.
The electrodes may be only applied to a portion of an electroactive polymer
and
define an active area according to their geometry. As will be described below,
the
electrodes may also be patterned to achieve a desired shape for a surface
feature
created by deflection of the polymer.
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CA 02821442 2013-07-17
In one embodiment, electrodes 14 and 16 are compliant and conform to the
shape of an electroactive polymer to which they are attached. Referring back
to FIG.
lA and 1B, the configuration of polymer 12 and electrodes 14 and 16 provides
for
increasing polymer 12 response with deflection. More specifically, as the
transducer
portion 10 deflects, compression of polymer 12 brings the opposite charges of
electrodes 14 and 16 closer and the stretching of polymer 12 separates similar
charges
in each electrode. In one embodiment, one of the electrodes 14 and 16 is
ground.
Various types of electrodes suitable for use with the present invention are
described in commonly owned, copending U.S. Patent Application No. 09/619,848.
Electrodes described therein and suitable for use with the present invention
include
structured electrodes comprising metal traces and charge distribution layers,
textured
electrodes, conductive greases such as carbon greases or silver greases,
colloidal
suspensions, high aspect ratio conductive materials such as carbon fibrils and
carbon
nanotubes, and mixtures of ionically conductive materials.
The present invention may also employ metal and semi-flexible electrodes. In
one embodiment, a rigid electrode comprises a metal disposed in a thick layer
that is
not capable of significant bending or planar stretching. In another
embodiment, a
semi-flexible electrode comprises a metal disposed in thin sheets such that
the metal
layer, like tin foil for example, is flexible out-of-plane but relatively
rigid in plane.
Thus, the polymer may deflect out-of-plane as described above but deflections
in
plane are limited to elastic strain of the metal sheet. Another flexible out-
of-plane but
relatively rigid in plane electrode may comprise a sheet of aluminized mylar.
In
another embodiment, the metal is disposed in thick sheets such that the metal
layer is
rigid and restrains the polymer from deflection on the attached surface.
Materials used for electrodes of the present invention may vary. Suitable
materials used in an electrode may include graphite, carbon black, colloidal
suspensions, thin metals including silver and gold, silver filled and carbon
filled gels
and polymers, gelatin, and ionically or electronically conductive polymers. In
a
specific embodiment, an electrode suitable for use with the present invention
comprises 80 percent carbon grease and 20 percent carbon black in a silicone
rubber
binder such as Stockwell RTV60-CON as produced by Stockwell Rubber Co. Inc. of
Philadelphia, PA. The carbon grease is of the type such as NyoGel 756G as
provided
CA 02821442 2013-07-17
by Nye Lubricant Inc. of Fairhaven, MA. The conductive grease may also be
mixed
with an elastomer, such as silicon elastomer RTV 118 as produced by General
Electric of Waterford, NY, to provide a gel-like conductive grease.
It is understood that certain electrode materials may work well with
particular
polymers and may not work as well for others. For most transducers, desirable
properties for the compliant electrode may include one or more of the
following: low
modulus of elasticity, low mechanical damping, low surface resistivity,
uniform
resistivity, chemical and environmental stability, chemical compatibility with
the
electroactive polymer, good adherence to the electroactive polymer, and the
ability to
form smooth surfaces. In some cases, a transducer of the present invention may
implement two different types of electrodes, e.g., a different electrode type
for each
active area or different electrode types on opposing sides of a polymer.
Electronic drivers are typically connected to the electrodes. The voltage
provided to an electroactive polymer will depend upon specifics of an
application. In
one embodiment, a transducer of the present invention is driven electrically
by
modulating an applied voltage about a DC bias voltage. Modulation about a bias
voltage allows for improved sensitivity and linearity of the transducer to the
applied
voltage. For example, a transducer used in an audio application may be driven
by a
signal of up to 200 to 1000 volts peak to peak on top of a bias voltage
ranging from
about 750 to 2000 volts DC.
In accordance with the present invention, the term "monolithic" is used herein
to refer to electroactive polymers, transducers, and devices comprising a
plurality of
active areas on a single polymer. FIG. 1F illustrates a monolithic transducer
150
comprising a plurality of active areas in accordance with one embodiment of
the
present invention. The monolithic transducer 150 converts between electrical
energy
and mechanical energy. The monolithic transducer 150 comprises an
electroactive
polymer 151 having two active areas 152a and 152b.
Active area 152a has top and bottom electrodes 154a and 154b that are
attached to polymer 151 on its top and bottom surfaces 151c and 151d,
respectively.
The electrodes 154a and 154b provide a voltage difference across a portion
151a of
polymer 151. The portion 151a deflects with a change in electric field
provided by the
electrodes 154a and 154b. More specifically, portion 151a expands in the plane
and
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thins vertically ¨ or orthogonal to the plane - with a suitable voltage
difference across
a portion 151a. The portion 151a comprises the polymer 151 between the
electrodes
154a and 154b and any other portions of the polymer 151 having sufficient
stress
induced by the electrostatic force to enable deflection and thinning upon
application
of voltages using the electrodes 154a and 154b.
Active area 152b has top and bottom electrodes 156a and 156b that are
attached to the polymer 151 on its top and bottom surfaces 151c and 151d,
respectively. The electrodes 156a and 156b provide a voltage difference across
a
portion 151b of polymer 151. The portion 151b deflects with a change in
electric field
provided by the electrodes 156a and 156b. More specifically, portion 151a
expands in
the plane and thins vertically ¨ or orthogonal to the plane - with a suitable
voltage
difference across a portion 151a. The portion 151b comprises polymer 151
between
the electrodes 156a and 156b and any other portions of the polymer 151 having
sufficient stress induced by the electrostatic force to enable deflection upon
application of voltages using the electrodes 156a and 156b.
Polymer surface features may be formed about the perimeter of top and
bottom electrodes 154a and 154b during actuation of each active area 151a. The
polymer surface features would include aggregated polymer 151 material that
bulges
vertically from the plane of polymer 151 on the top and bottom surfaces. When
viewed from the top, the top polymer surface feature resembles a rectangle
that
borders the rectangular dimensions of top electrode 154a. When viewed from the
bottom, the bottom polymer surface feature resembles a rectangle that borders
the
rectangular dimensions of bottom electrode 154b.
Electrode surface features may be formed corresponding to the shape and size
of electrodes 154a and 154b during actuation of each active area 151a. In this
case,
the top and bottom electrode surface features resemble a rectangle with
dimensions
corresponding to the dimensions of electrodes 154a and 154b when actuated,
respectively.
Active areas 152a and 152b permit independent control via their respective
electrodes. Thus, in conjunction with suitable control electronics, active
areas 152a
and 152b may be actuated individually, simultaneously, intermittently, etc. to
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independently create polymer surface features and electrode surface features
for each
active area 151.
So far, electrodes on opposite surfaces of an electroactive polymer described
so far have been symmetrical in size, shape and location. Electrodes on
opposite sides
of a transducer of the present invention are not limited to symmetrical
designs or
layouts and may have different sizes, shapes, types, and/or locations on
opposite
surfaces of an electroactive polymer. Electrodes on a polymer may be patterned
as
desired. For example, one or more electrodes may be sprayed onto a surface of
a
polymer in the shape determined by a stencil. Different stencils may be used
for each
polymer surface Control of electrodes for each active area then allow each
active area
to be activated on the polymer surface individually, simultaneously,
intermittently,
etc. Further description and examples of customized surface features are
described
below.
FIG. 1G illustrates an electroactive polymer transducer 70 before deflection
in
accordance with a specific embodiment of the present invention. Transducer 70
comprises an electroactive polymer 72, electrode 74 and electrode 76. Polymer
72 is
characterized by an undeflected thickness 22 before deflection for a surface
region 80
of interest. Undeflected thickness 22 for either surface is measured from a
surface
opposite to the surface of polymer 72 being deformed, before deflection.
Electrode 74
adheres to a bottom surface of polymer 72, comprises a metal, and is thick and
rigid.
Electrode 76 adheres to a top surface of polymer 72, comprises a compliant
electrode
and conforms in shape to polymer 72. Electrode 76 also includes a different
size,
lateral location and shape than electrode 74.
FIG. 1H illustrates transducer 70 after actuation using electrodes 74 and 76
and deflection of a portion of polymer 72. Rigid electrode 76 prevents the
bottom
surface 72b of polymer 72 from deflecting. In this case, only a portion of
polymer 72
deflects and expands in the plane where electrodes 74 and 76 laterally
overlap, as
shown. After deflection, a polymer surface feature 82 is created above the
undeflected
thickness 22 after deflection. In addition, only a left portion of compliant
electrode 76
is below the undeflected thickness 22 and forms an electrode surface feature
85. The
remainder of compliant electrode 76 remains substantially at the same
elevation
relative to the undeflected thickness 22. Thus, in some cases, it is possible
for an
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electrode to include portions in an active area that contribute to an
electrode surface
feature and portions outside an active area or electrode surface feature that
do not
contribute.
In some cases, an electrode may elevate above the undeflected thickness, t.
For example, if a second active area were patterned over polymer 72 at polymer
surface feature 82, it is possible for this electrode from a second active
area to rise
above the undeflected thickness 22 for deflection of another portion of the
polymer.
Thus, the polymer surface feature refers to polymer material above the
undeflected
thickness after the deflection regardless of whether an electrode has been
pattered
over the polymer surface feature.
In another embodiment, an electroactive polymer comprises a common
electrode. A common electrode is an electrode that is capable of electrically
communicating with more than one active area of an electroactive polymer. In
many
cases, a common electrode allows monolithic transducers to be implemented with
less
complexity (see FIG. 3C). For example, multiple electrodes may be patterned on
one
surface of a polymer while the entire second surface includes a common
electrode.
Alternatively, a common electrode may be used to sequentially actuate multiple
active areas according to a propagation of the electrical charge through the
common
electrode.
3. PASSIVE LAYER
For some electroactive polymer transducers, in absolute terms, the change in
polymer thickness during deflection or actuation may be small relative to the
change
in the planar area dimensions. For instance, for a thin polymer film, area
changes may
be of the order of square centimeters and changes in planar dimensions may be
of the
order of centimeters, while thickness changes may be of the order of microns
(thousandths of a millimeter). However, although the absolute change in
thickness for
the polymer film in an electroactive polymer device in this instance is small,
the
percentage change is still significant (e.g., 50% or greater).
In one embodiment, transducers and devices of the present invention comprise
a passive layer to amplify out-of-plane deformations and create more visible
polymer
and electrode surface features. FIGs. 2A-2B illustrate an electroactive
polymer
transducer 51 comprising a passive layer 50 in accordance with one embodiment
of
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the present invention. FIG. 2A illustrates transducer 51 in an undeflected
state
without polymer deflection. As shown in FIG. 2A, polymer surfaces 52a and 52b
and
a passive layer surface 50a opposite to polymer 52 are all substantially flat
before
deflection of polymer 52. FIG. 28 illustrates the transducer 51 in an actuated
state.
Compliant electrodes 54a and 54b are attached to a central portion 56 of
polymer 52
on its top and bottom surfaces 52a and 52b, respectively. For actuation, an
electric
field with a voltage, V, is applied via electrodes 54 across polymer 52 to
actuate a
portion 56 of polymer 52.
Passive layer 50 neighbors top surface 52a of polymer 52 and is configured to
to deflect with deflection of the electroactive polymer such that a surface
50a of passive
layer 50 opposite to electroactive polymer 52 forms a set of passive layer
surface
features 57 that resembles the set of surface features 59 on top surface 52a
of polymer
52. Passive layer 50 is passive in that it conforms in cross sectional shape
and
dimensions to the forces applied onto it by polymer 52. In another embodiment,
passive layer 50 may also be considered passive relative to the electroactive
polymer
52 in that it does not respond to the application of an electric field, with
an area
change and thickness change, like polymer 52.
For transducer 51, passive layer 50 couples directly to electroactive polymer
52 such that changes in polymer 52 surface area and thickness during actuation
at
least partially transfer to passive layer 50. When passive layer 50 couples to
electroactive polymer 52, surface area and thickness changes in electroactive
polymer
52 induce shearing forces in passive layer 50 that change the surface area and
thickness of passive layer 50. Since passive layer 50 is thicker than polymer
52, or at
least increases the combined thickness of passive layer 50 and polymer 52, a
change
in surface area and thickness in passive layer 50 may be used to amplify, in
absolute
terms, a displacement produced by the change in thickness of polymer 52.
In one embodiment, passive layer 50 contacts polymer 52 and coupling
between passive layer 50 and polymer 52 may include direct attachment, an
adhesive,
or bonding of passive layer 50 onto polymer 52 (or portion thereof), etc.
Alternatively, each passive layer 50 may be applied to electroactive polymer
52 as a
surface coating. In another embodiment, passive layer 50 does not contact
polymer 52
and one or more intermediate rigid structures are disposed between passive
layer 50
CA 02821442 2013-07-17
and polymer 52. The rigid structures, such as metal posts, attach to both
passive layer
50 and polymer 52 and are configured to transfer forces from the electroactive
polymer to passive layer 50. The intermediate rigid structures then
mechanically
couple passive layer 50 and polymer 52 and transmit forces upon polymer 52
deflection.
In the cross section shown in FIG. 2B, elevated passive layer surface features
57a and 57b are created around the edges of top electrode 54a corresponding to
the
displaced top and elevated polymer surface features 59a and 59b, respectively,
at the
edges of top electrode 54a. Passive layer surface features 57a and 57b
generally result
in passive layer 50 from the fact that while the passive layer 50 increases in
area over
portion 56 corresponding to the shape of electrodes 54a and 54b and active
area
created by electrodes 54, passive layer 50 typically (depending on design)
decreases
in area over the inactive regions 55 of polymer 52 outside the electrodes 45
and active
area. Since passive layer 50 generally keeps a substantially constant total
volume
(with the exception when passive layer 50 includes a compressible foam), if
its
surface area decreases during actuation or polymer deflection in the inactive
regions,
then the passive layer 50 thickness typically increases and forms the surface
features
57. The location of thickness increase and surface features is typically
predictable
based on stress build up in the passive layer 50. In many cases, the thickness
increase
is enhanced in regions of high strain, such as those immediately bordering the
electrodes 54 and active area of transducer 51.
In this manner, passive layer 50 forms a set of passive layer surface features
57 that resembles the set of surface features 59 on the top surface of polymer
52. The
set of surface features 59 on the top surface of polymer 52 includes both
elevated
polymer surface features and depressed electrode surface features. Thus, a set
of
passive layer surface features 57 may include both elevated and depressed
portions
relative to the original thickness of passive layer 50. For transducer 51, the
set of
passive layer surface features 57 includes elevated portions 57a and 57b
corresponding to top polymer surface features 59a and 59b and a depressed
potion
57c corresponding to thinning of polymer 52 in central portion 56. It is
understood
that passive layer surface features 57 may not exactly mimic the spatial
arrangement
and size of polymer surface features and recessed electrode surface features
on
polymer 52 and may include spatial offsets, relative variations and minor
quantitative
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differences. In general, however, the set of passive layer surface features 57
resembles the set of surface features 59 on the top surface of polymer 52 in
approximate spatial configuration, relative size, etc. The number of surface
features
57 for passive layer 50 will generally correspond to the number of surface
features 59
on the top surface of polymer 52, and each set may include from 1 to 200
surface
features, or more, depending on the number, complexity and layout of
electrodes on
polymer 52.
FIG. 2C illustrates a transducer 51 comprising an electroactive polymer 52
between two passive layers 50 and 58 in accordance with a specific embodiment
of
the present invention.
Actuation of polymer 52 in portion 56 via electrodes 54 causes polymer 52 in
portion 56 to increase in planar area and reduce in thickness.
Correspondingly, when
portion 56 of polymer 52 is actuated, the passive layers 50 and 58 in this
surface
region both increase in area. Actuation of polymer 52 thus causes top and
bottom
passive layers 50 and 58 to reduce in thickness about portion 56 in the area
where
polymer 52 thickness has contracted. The reduction in thicknesses of the top
passive
layer 50 and the bottom layer 58 are distances, D1 and D4, respectively, as
measured
from their thickness. The change in thickness of polymer 52 at its contact
with the top
passive layer 50 and the bottom passive layer 58 are, D2 and D3, respectively.
Top
and bottom passive layers 50 and 58 are each thicker than polymer 52. Hence,
the
change in thickness of top and bottom passive layers 50 and 58 is greater than
the
change in thickness of polymer 52 in portion 56, i.e., D1>D2 and D4>D3. In
this
manner, each passive layer 50 and 58 amplifies the absolute displacement
(change in
thickness) as compared to an electroactive polymer transducer without passive
layers.
The magnitude of forces generated by actuation of portion 56 in polymer 52
limits the thickness and stiffness of each passive layer 50. As one of skill
in the art
will appreciate, the amount of forces generated by actuation of portion 56 is
affected
by the size of portion 56, polymer 52 material, dielectric constant, and
actuation
voltage, for example. As the thickness or stiffness of each passive layer 50
increases,
the required shear forces to displace it also increases. Thus, as the
thickness for
passive layer 50 increases, deflection of passive layer 50 decreases for a
constant
force from the polymer. Also, if passive layer 50 is relatively compliant but
thick,
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then actuation of portion 56 may still displace the passive layer but the
resulting
thickness change in passive layer 50 and definition of passive layer surface
features
may be smoothed out and not have sharp edge definition relative to portion 56.
The stiffness of the passive layers 50 and 58 may thus be selected depending
on a desired absolute displacement. In one embodiment, passive layer 50
comprises a
modulus of elasticity less than a modulus of elasticity for electroactive
polymer 52.
This reduces the elastic resistance provided by passive layer 50 onto
transducer 51
and increases the magnitude and definition of passive layer surface features
for a
given electrical input. In another embodiment, passive layer 50 comprises a
modulus
to of elasticity less than one tenth than the modulus of elasticity for
electroactive
polymer 52.
The thickness of the passive layers 50 and 58 may also be selected depending
on a desired absolute displacement. In one embodiment, passive layer 50
comprises a
thickness greater than a thickness for electroactive polymer 52. This
increases visual
output of surface features produced by actuation of portion 56. In another
embodiment, passive layer 50 comprises a thickness greater than double the
thickness
for polymer 52.
Multiple layers the polymer (plus electrodes) and/or the passive layers may
also be employed. This also allows actuation of surface features on top of
other
surface features, e.g. one layer actuates a broad bowl shape and another layer
actuates
a small bump within the bowl.
In general, passive layer 50 may comprise any material suitable for amplifying
the vertical profile and/or visibility of surface features in electroactive
polymer 52.
Exemplary passive layer 50 materials include silicone, a soft polymer, a soft
elastomer (gel), a soft polymer foam, or a polymer/gel hybrid, for example.
The
material used in passive layer 50 may be selected for compatibility with a
particular
electroactive polymer 52, depending on such parameters as the modulus of
elasticity
of polymer 52 and the thickness of passive layer 50. In a specific embodiment,
passive layer 50 comprises a compressible foam including a non-linear elastic
modulus with strain of the passive layer. In this case, elastic response of
passive layer
50 not linear and thus provides varying output (gets thinner or thicker at
varying
rates) based on the non-linear stress/strain curve.
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Deflections, surface features and thickness changes for top and bottom layers
50 and 58 may be asymmetric. As shown in FIG. 2B, top layer 50 includes a
smaller
thickness change than bottom layer 58. Displacement asymmetry may be achieved
via
several techniques, such as using different materials with different stiffness
for the
top and bottom passive layers 50 and 58, using the same passive layer material
but
with different thicknesses for the top and bottom layers 50 and 58, by placing
different pre-strains on the top and bottom layer, combinations of the above
techniques, etc. Alternatively, using substantially identical materials and
similar
actuation conditions between top and bottom passive layers 50 and 58 may
generate
substantially symmetrical displacements for top and bottom passive layers 50
and 58.
In some cases, larger or more defined surface features 57 may be desirable
and methods may be implemented to increase the height of surface features 57.
For
example, the thickness of passive layer 50 may be increased, more layers may
be
added or used, electrode 54 geometry changed, polymer 52 geometry changed,
passive layer 50 geometry or material changed, or the distribution of charge
across
electrodes 54 changed to increase the height of surface features 57.
Alternatively, if
desired, surface features 57a and 57b may be reduced in height by such methods
as
placing passive layer 50 under strain, by using a surface coating on passive
layer 50,
by changing electrode 54 geometry, changing polymer 52 geometry, changing
passive
layer 50 geometry, or by changing the distribution of charge across electrodes
54.
4. GEOMETRIC SURFACE FEATURE EXAMPLES
Transducers of the present invention may create wide variability in a set of
surface features ¨ both in number and specific shape or geometry for
individual
features. The surface features may include one or more elevated surface
features
based on polymer deformation out of the polymer plane and/or one or more
lowered
surface features based on the electrode and polymer thinning about an active
area.
Described below are several illustrative examples.
FIG. 3A shows a top elevated view of crossing common electrodes for a
transducer 220 in accordance with a specific embodiment of the present
invention. In
this case, a set of horizontal top surface common electrodes 222 are linked
together
and disposed on the top surface of a transparent electroactive polymer 221. In
addition, a set of vertical bottom surface common electrodes 224 are linked
together
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and disposed on the bottom surface of transparent electroactive polymer 221.
Top
surface electrodes 222 may be activated commonly, as can bottom surface
electrodes
224.
FIGs. 3B-3C show top elevated photo of actuation patterns for a transducer
240 in accordance with another specific embodiment of the present invention.
Transducer 240 includes a passive layer 242 disposed over a top surface of an
electroactive polymer (not shown). The passive layer 242 enhances thickness
changes
in the polymer and visualization of surface features on the surface of passive
layer
242. In FIG. 3B, a voltage is not applied to the electroactive polymer and the
surface
of the passive layer 242 is essentially smooth and substantially flat. In FIG.
3C,
voltage is applied to common electrodes and a set of depressed square surface
features 246 are created. Also shown is a set of three depressed parallel line
surface
features 248 above the set of square surface features 246.
Displacements may also be asymmetric across a passive layer. For instance,
an electroactive polymer may include a plurality of active areas coated with a
passive
layer where the displacements may vary from one active area to another active
area
across the layer based on varying passive layer thicknesses for the different
active
areas.
In one embodiment, one or more electrodes are patterned or configured in
surface area to affect a surface shape and appearance for a surface feature.
FIG. 3A
illustrates a top elevated view of a transducer 200 in accordance with a
specific
embodiment of the present invention (without a passive layer). Transducer 200
comprises electrodes 202a-g disposed on a top surface 204 of electroactive
polymer
206 and a common electrode disposed on the bottom side (not shown). Each
electrode
202a-g resembles a letter, as shown.
Actuation of an active area corresponding to each electrode 202a-g causes
surfaces features 210 on surface 204 to become visible. FIG. 3E illustrates
actuation
of one letter. More specifically, actuation of an active area corresponding to
electrode
202a causes the letter 'a' to increase in planar size and depress into polymer
206
corresponding to the thinning of polymer 206, thus created an electrode
surface
feature 210a below the polymer thickness. In addition, actuation of an active
area
corresponding to electrode 202a causes the letter 'a' -shaped electrode 202a
to
CA 02821442 2013-07-17
increase in planar size and forces polymer 206 bordering the expanded
electrode 202a
to elevate and create a ridge polymer surface feature 212a about the electrode
202a.
Electrode 202a is thus configured in surface area to affect a surface shape
for recessed
electrode surface features 210a and elevated surface feature 212a.
Electrodes 202a-g and their corresponding active areas and surfaces features
may be independently controlled. Thus, in conjunction with suitable control
electronics, electrodes 202a-c and their respective active areas and surface
features
may be actuated simultaneously to create polymer surface features that spell a
word.
Other letters may be patterned to create customized visual words and outputs.
The present invention is not limited to simple square or rectangular geometric
shapes. Other shapes (circles, triangles, etc.) or complex patterns may be
generated
with the present invention. For instance, electrodes may be patterned for
logos, line
drawings, etc. In another embodiment the squares of FIG. 3A may be
individually
patterned and controlled to generate different surface feature outputs.
FIG. 3F illustrates a side view of grid surface features for a transducer 260
in
accordance with another specific embodiment of the present invention. A non-
compliant electrode 262 is mounted to a rigid structure 264. A passive layer
266 is
mounted on top surface of polymer 268. On a top surface of polymer 268 is a
grid of
thin conductive strips 270, such as a metal wires. When polymer 268 is
actuated, the
conductive wires 270 cut into polymer 268 causing polymer 268 to bulge around
the
wires 270. Bulging surface polymer features 269 in polymer 268 cause
corresponding
bulging surface features 267 in passive layer 266. For instance, in one
embodiment,
the metal wires 270 are laid out in a grid in a diamond pattern like a quilt
and when
the polymer 268 is actuated the passive layer 266 exhibits a quilted pattern
on the
surface of passive layer 266.
5. MULTIFUNCTIONALITY
Electroactive polymers may convert between electrical energy and mechanical
energy in a bi-directional manner. Sensing electrical properties of an
electroactive
polymer transducer also permits sensing functionality.
FIGs. 1A and 1B may be used to show one manner in which the transducer
portion 10 converts mechanical energy to electrical energy. For example, if
the
transducer portion 10 is mechanically stretched by external forces to a
thinner, larger
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area shape such as that shown in FIG. 1B, and a relatively small voltage
difference
(less than that necessary to actuate the film to the configuration in Fig. 1B)
is applied
between electrodes 14 and 16, the transducer portion 10 will contract in area
between
the electrodes to a shape such as in FIG. lA when the external forces are
removed.
Stretching the transducer refers to deflecting the transducer from its
original resting
position ¨ typically to result in a larger net area between the electrodes,
e.g. in the
plane defined by directions 18 and 20 between the electrodes. The resting
position
refers to the position of the transducer portion 10 having no external
electrical or
mechanical input and may comprise any pre-strain in the polymer. Once the
transducer portion 10 is stretched, the relatively small voltage difference is
provided
such that the resulting electrostatic forces are insufficient to balance the
elastic
restoring forces of the stretch. The transducer portion 10 therefore
contracts, and it
becomes thicker and has a smaller planar area in the plane defined by
directions 18
and 20 (orthogonal to the thickness between electrodes). When polymer 12
becomes
thicker, it separates electrodes 14 and 16 and their corresponding unlike
charges, thus
raising the electrical energy and voltage of the charge. Further, when
electrodes 14
and 16 contract to a smaller area, like charges within each electrode
compress, also
raising the electrical energy and voltage of the charge. Thus, with different
charges on
electrodes 14 and 16, contraction from a shape such as that shown in FIG. 1B
to one
such as that shown in Figure IA raises the electrical energy of the charge.
That is,
mechanical deflection is being turned into electrical energy and the
transducer portion
10 is acting as a generator.
In some cases, the transducer portion 10 may be described electrically as a
variable capacitor. The capacitance decreases for the shape change going from
that
shown in FIG. 1B to that shown in FIG. IA. Typically, the voltage difference
between electrodes 14 and 16 will be raised by contraction. This is normally
the case,
for example, if additional charge is not added or subtracted from electrodes
14 and 16
during the contraction process. The increase in electrical energy, U, may be
illustrated
by the formula U = 0.5 Q2/C, where Q is the amount of positive charge on the
positive electrode and C is the variable capacitance which relates to the
intrinsic
dielectric properties of polymer 12 and its geometry. If Q is fixed and C
decreases,
then the electrical energy U increases. The increase in electrical energy and
voltage
can be recovered or used in a suitable device or electronic circuit in
electrical
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communication with electrodes 14 and 16. In addition, the transducer portion
10 may
be mechanically coupled to a mechanical input that deflects the polymer and
provides
mechanical energy.
Electroactive polymers of the present invention may also be configured as a
sensor. Generally, an electroactive polymer sensor detects a "parameter"
and/or
changes in the parameter. The parameter is usually a physical property of an
object
such as strain, deformation, velocity, location, contact, acceleration,
vibration,
pressure, size, etc. In some cases, the parameter being sensed is associated
with a
physical "event". The physical event that is detected may be the attainment of
a
particular value or state for example. An electroactive polymer sensor is
configured
such that a portion of the electroactive polymer deflects in response to the
change in a
parameter being sensed. The electrical energy state and deflection state of
the
polymer are related. The change in electrical energy or a change in the
electrical
impedance of an active area resulting from the deflection may then be detected
by
sensing electronics in electrical communication with the active area
electrodes. This
change may comprise a capacitance change of the polymer, a resistance change
of the
polymer, and/or resistance change of the electrodes, or a combination thereof.
Electronic circuits in electrical communication with electrodes detect the
electrical
property change. If a change in capacitance or resistance of the transducer is
being
measured for example, one applies electrical energy to electrodes included in
the
transducer and observes a change in the electrical parameters.
For ease of understanding, the present invention is mainly described and
shown by focusing on a single direction of energy conversion. More
specifically, the
present invention focuses on converting electrical energy to mechanical
energy.
However, in all the figures and discussions for the present invention, it is
important to
note that the polymers and devices may convert between electrical energy and
mechanical energy bi-directionally. Thus, any of the exemplary transducers
described
herein may be used with a generator or sensor. Typically, a generator of the
present
invention comprises a polymer arranged in a manner that causes a change in
electric
field in response to deflection of a portion of the polymer. The change in
electric
field, along with changes in the polymer dimension in the direction of the
field,
produces a change in voltage, and hence a change in electrical energy.
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As the terms are used herein, a transducer refers to an electroactive polymer
with at least two electrodes; an electroactive polymer device refers to a
transducer
with at least one additional mechanical coupling or component; an
electroactive
polymer actuator refers to a transducer or device configured to produce
mechanical
output of some form; an electroactive polymer generator refers to a transducer
or
device configured to produce electrical energy; and an electroactive polymer
sensor
refers to a transducer or device configured to sense a property or event.
Thus, polymers and transducers of the present invention may be used as an
actuator to convert from electrical to mechanical energy, a generator to
convert from
mechanical to electrical energy, a sensor to detect changes in the mechanical
or
electrical state of the polymer, or combinations thereof. Mechanical energy
may be
applied to a transducer in a manner that allows electrical energy to be
removed or
electrical changes to be sensed. Many methods for applying mechanical energy,
removing electrical energy and sensing electrical changes from the transducer
are
possible. Actuation, generation and sensing devices may require conditioning
electronics of some type. For instance, at the very least, a minimum amount of
circuitry is needed to apply or remove electrical energy from the transducer.
Further,
as another example, circuitry of varying degrees of complexity may be used to
sense
electrical states of a sensing transducer.
In one embodiment, an electroactive polymer transducer active area may be
electrically controlled via suitable electronic control (e.g., a processor
configured to
control an active area) to provide a variable surface feature height and
displacement
depth in a passive layer that varies with time. For instance, a microprocessor
that
controls the actuation of electroactive polymer transducer may be connected to
a
sensor. The displacement depth may be varied in time by the microprocessor
according to measurements taken by the sensor.
6. METHODS OF USE
The present invention also incorporates methods of using an electroactive
polymer transducer. FIG. 4 illustrates a process flow 300 for using an
electroactive
polymer transducer in accordance with one embodiment of the present invention.
While electroactive polymer transducers will now be described as a method,
those
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skilled in the area will recognize that the present invention encompasses a
transducers
and devices capable of performing the actions as described below.
Process flow 300 begins by actuating a first portion of the electroactive
polymer (302). The first portion includes an undeflected thickness for a first
surface
region on a first surface of the polymer before actuation of the first
portion. Actuation
creates a first surface feature on the first surface. The surface feature may
comprise a
polymer surface feature that elevates above the undeflected thickness after
the
actuation or an electrode portion below the undeflected thickness for the firs
surface
region after the deflection. Exemplary feature shapes and arrangements are
described
above.
Process flow 300 proceeds by actuating a second portion of the electroactive
polymer (304). The second portion includes an undeflected thickness for a
second
surface region on the first surface of the polymer. The second actuation
creates a
second surface feature on the first surface. In one embodiment, the first and
second
FIG. 5A illustrates a method for moving two objects relative to each other
using stepwise deflection of multiple active areas in accordance with a
specific
embodiment. An object 322 is shown sliding over a surface 324. A surface
deforming
7. APPLICATIONS
A few additional exemplary applications will now be described. These
applications are provided for illustrative purposes and are not meant to the
limit the
CA 02821442 2013-07-17
such as speakers, or in microscopic applications, such as an actuator
fabricated on a
semi-conductor device.
Creation of letters as described above is well suited for used in
reconfigurable
displays. For example, a dashboard in a car may include a surface deforming
electroactive polymer transducer that includes multiple states. One state
might be
clean in which little or no surface features are visible. Upon initiation by a
user,
various menus and controls are then created on the dashboard. Combing the
sensing
ability of the polymers allows a driver or passenger to input commands and
interface
with a processor or affect one or more controlled systems in the car. The
dashboard
surface features may include letters, logos, symbols and other features
related to
control of systems in a car such as climate control, an audio system, a
navigation
system, etc. Other than dashboards, such reconfigurable actuators and sensors
are
useful to produce calculators, keyboards, handheld electronics devices, etc.
In one embodiment, surface deformation transducers and devices may be used
for sound generation applications, such as speakers. Further description of
sound
generation using a an electroactive polymer is described in U.S. Patent No.
6,343,129.
In another embodiment, a surface deforming electroactive polymer transducer
device may be actuated to increase or decrease the friction coefficient
between an
object and a surface. In one embodiment, the surface deforming transducer
device
may be mounted across the bottom of the object an actuated in a manner to
provide a
variable coefficient of friction across the bottom of the object. The variable
coefficient of friction may be used to generate frictional steering. One
application
where friction control may be applied is on the bottom of skis or snowboards.
The
friction control may be used for aiding in the braking or turning of the skis
or
snowboard.
FIG. 5B illustrates surface deforming electroactive polymer transducers 340
and 342 mounted to a surface of a wing 343 and a flap 345, respectively, in
accordance with a specific embodiment of the present invention. The actuation
of
transducers 340 and 342 changes a property of airflow over the wing 343 and
flap
345. For instance, active areas on transducer 340 may be actuated to increase
or
decrease lift and drag on the wing depending on the operating conditions of
the wing,
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e.g., actuated to increase surface roughness and turbulence of airflow passing
thereover. In other embodiments, the actuation of transducers 340 and 342 may
be
used to change the radar cross-sectional properties of the wing surface.
Other exemplary applications for surface deforming electroactive polymer
transducers include 1) Braille devices, 2) touch sensitive devices, such as
key boards
or other interfaces, where the surface deforming transducers are actuated to
provide
tactile feedback, 3) massagers, 4) vibration devices, 5) pumps and 6) linear
actuators.
In the Braille device, the surface deforming transducers may be used to create
a
surface texture that is readable by touch as Braille. In another related
application,
surface deforming transducers may be used in a 3-D topography display where
the
surface texture is representative of surface topography of a geographic
region.
In one specific embodiment, a transducer with a passive layer on each
opposing surface is sandwiched between two rigid conductive layers, such as
two
metal layers, to generate a variable capacitance capacitor. By actuating the
polymer
and the passive layers to vary the distance between the two metal layers, the
capacitance of the capacitor may be varied when the metal layers are charged.
Changing the texture of a surface is also desirable in military applications
such as 'active' military camouflage materials that alter their reflectance.
In one embodiment, actuators and transducers of the present invention are
employed for performing thermodynamic work on a fluid in a fluid system or
controlling a fluid. Fluid systems are ubiquitous. The automotive industry,
plumbing
industry, chemical processing industry and aerospace industry are a few
examples
where fluid systems are widely used. In fluid systems, it is often desirable
to control
properties of a fluid flow in the fluid system to improve a performance or
efficiency
of the fluid system or to control the fluid in the fluid system in manner that
allows the
fluid system to operate for a specific purpose. One method of control of a
fluid is
through control of a fluid-surface interface. The present invention may then
include
devices and methods for controlling a fluid surface interface using one or
more
electroactive polymer actuator devices and surface interfaces. In a specific
embodiment, surface deforming transducers are mounted to an inner surface of a
fluid
conduit. The surface deforming transducers may be actuated to generate wave
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patterns in the conduit. For instance, the wave patterns may be used to
promote
mixing. Alternatively, the surface deforming transducers may be actuated to
reduce
friction in the conduit.
In another specific application, a passive layer connects to a mechanical
output or linkage so that thickness displacements generated by a polymer are
transferred to the linkage. Deflection of the polymer then controls a state
for the
mechanical output, namely, the mechanical output has a first state before
deflection
and a second state after deflection. For example, a surface deforming
transducer (or
portion thereof) may be used to control a position of the mechanical output or
an
object that is connected to the mechanical linkage. Alternatively, a surface
deforming
transducer (or portion thereof) may be used to control a shape of the
mechanical
output. For example, the mechanical output may include a mirrored surface that
is
disposed on the passive layer and deflection of the polymer is used to change
the
shape or position of the mirror to vary light reflected by the mirror.
8. CONCLUSION
While this invention has been described in terms of several preferred
embodiments, there are alterations, permutations, and equivalents that fall
within the
scope of this invention which have been omitted for brevity's sake. By way of
example, although the present invention has been described in terms of several
polymer materials and geometries, the present invention is not limited to
these
materials and geometries. It is therefore intended that the scope of the
invention
should be determined with reference to the appended claims.
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