Piezoceramic actuators, presently used in commercial Braille displays, are limited by the material's relatively small
strain and brittle nature. For this reason, it is a challenge to develop full page, compact, graphic Braille displays that are
affordable. A newly developed material composed of P(VDF-TrFE-CFE) terpolymer blended with 5% P(VDF-CTFE)
electrostrictive actuators exhibits large strains (~5% at 150V/μm), fast actuation (>5 mm/s), and has a relatively high
elastic modulus (1.2 GPa). This material exhibits more than double the elastic energy density and a 50% higher modulus
of the original electrostrictive terpolymer. Hence, the potential for viable actuators in compact, full page Braille displays
is greater than ever, provided actuators can be manufactured reliably in quantity. This talk presents recent work in
scaling production of such rolled actuators. Actuators extend .5 mm, are confined to the 2.5 mm grid spacing of
conventional Braille text, generate >0.5 N force and operate at less than 200V, thus meeting the primary requirements
for a commercialized Braille display. To manufacture these actuators, cast films are stretched using a roll-to-roll zone
drawing machine that is capable of producing quantities of 2 μm thick film with high quality. What follows is a
discussion of this machine, the roll-to-roll film stretching process and an assessment of the resulting stretched film for
use as linear strain actuators, like those used in our Braille cell.
Traditional ionic polymer/conductor network composite (IPCNC) electromechanical actuators exhibit low actuation
speed and efficiency. In order to improve these parameters while still maintaining low voltage operation, we investigated
IPCNC with a range of composite layer (active layer) and middle ionomer layer (passive layer) thicknesses. We show
that it is the slow ion transport in the porous composite electrode layer that limits the actuation speed of IPCNCs. By
reducing the thickness of the composite electrode layers, both the actuation speed and efficiency can be improved.
Moreover, we show that the IPCNC actuator speed and efficiency are intimately related to the morphology of the
composite electrode layer and the conductor network composites fabricated by ionic self-assembled layer-by-layer
(LBL) exhibit higher strain response compared with that from the traditional IPCNC. For example, LBL composites
show very high intrinsic strain of about 7%. Detailed device analysis points out directions of further improvement of
these actuators.
Although the Ionic Polymer-Metal Composite (IPMC) actuators developed up to date are in the form of bending
actuators, development of extensional actuators based on IMPC is highly desirable from practical applications and
fundamental understanding points of view. This talk presents the design, fabrication and characterization of a recent
work on an extensional Ionic Polymer-Metal Composite actuator. The extensional actuator consists of the Nafion
ionomer as the matrix and the sub-micron size RuO2 particles as the conductive filler for the conductor/ionomr
composites. In this investigation, several ionic liquids (IL) were investigated. For a Nafion/RuO2 composite with 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf) IL, it was found that as the ions are driven into the
ionomer/RuO2 composite (the composite under negative voltage), an extensional strain of 0.9% was observed; while as
the ions were expelled from the ionomer/RuO2 composite (under positive voltage), a contraction of -1.2% was observed.
The results indicate that multiple ions are participating in charge transport and actuation process. In this paper, we also
discuss several design considerations for future extensional actuators with fast response, much improved strain and stress
level. Especially an actuator based on multilayer configuration can significantly increase the electric field level in the
actuator and consequently significantly improve the actuator speed. The extensional actuator investigated here provides a
unique platform to investigate various phenomena related to ion transport and their interaction with the
ionomer/conductor matrix to realize high electromechanical performance.
KEYWORDS: Actuators, Ferroelectric polymers, Reflectors, Control systems, Antennas, Polymers, Electrodes, Control systems design, Finite element methods, Electroactive polymers
Extremely large, lightweight, in-space deployable active and passive microwave antennas are demanded by future
space missions. This paper investigates the development of PVDF based piezopolymer actuators for controlling the
surface accuracy of a membrane reflector. Uniaxially stretched PVDF films were poled using an electrodeless
method which yielded high quality poled piezofilms required for this applications. To further improve the
piezoperformance of piezopolymers, several PVDF based copolymers were examined. It was found that one of
them exhibits nearly three times improvement in the in-plane piezoresponse compared with PVDF and P(VDF-TrFE)
piezopolymers. Preliminary experimental results indicate that these flexible actuators are very promising in
controlling precisely the shape of the space reflectors. To evaluate quantitatively the effectiveness of these PVDF
based piezopolymer actuators for space reflector applications, an analytical approach has been established to study
the performance of the coupled actuator-reflector-control system. This approach includes the integration of a
membrane reflector model, PVDF piezopolymer actuator model, solution method, and shape control law. The reflective Newton method was employed to determine the optimal electric field for a given actuator configuration and loading/shape error.
The large strain, high elastic modulus, and easy processing of P(VDF-TrFE-CFE) electrostrictive terpolymer make it
very attractive to replace low strain piezoceramics and piezopolymers in many applications with much improved
performance. In this paper, a compact polymer actuator is developed utilizing the electrostrictive terpolymer, which
is suitable for full page Braille Display and graphic display. Key issues related to the reliability of electroactive
polymers used in the compact actuators and for the mass fabrication of these polymer actuators are investigated.
Making use of a recently developed conductive polymer, a screen printing deposition method was developed which
enables direct deposition very thin conductive polymer electrode layer (< 0.1 &mgr;m) with strongly bonding to the
terpolymer surface and short fabrication time. It was observed that the thin conductive polymer electrodes lead to the
self-healing of the polymer after electric breakdown. An EAP compact Braille actuator was designed and fabricated
with these terpolymer films wound on a spring core. The test results demonstrate that the EAP Braille actuator meets
all the functional requirements of actuators for refreshable full Braille display, which offers compact size, reduced
cost and weight.
In this work, an investigation of the tuning characteristics of electrically tunable long-period gratings (LPGs) is
presented. A precise four-layer model is used to quantitatively analyze the tuning potential of the gratings and
experimental data is provided to support the analysis. The four-layer model includes a silica core layer with an inscribed
LPG, a thin silica cladding layer (~40 μm), an ultra-thin (~ 50 nm) high refractive index indium-tin dioxide (ITO) inner
electrode layer, and a tunable electro-optic polymer layer. It has been found that the inner electrode layer, made of high
refractive index ITO, can be modeled as a high index overlay and causes the forward propagating modes in the thin silica
cladding to reorganize as the ambient refractive index changes. This reorganization effect can lead to a significant
increase (10 plus fold) in the tuning range of LPG tunable filters. Moreover, the required specifications of the tunable
polymer layer are quantitatively analyzed. Finally, the required characteristics of the electro-optic polymer are realized
by using a nano-composite of zinc sulfide and ferroelectric relaxor poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) terpolymer.
We demonstrate an widely electrically tunable long-period fiber grating with ultrathin first cladding and ferroelectric relaxor poly(vinylidene fluoride - trifluoroethylene - chlorofluoroethylene) terpolymer as the second cladding. Large Kerr effect is found in the terpolymer where a refractive index change of -2.6% can be induced under an electric field of 80MV/m. Simulations and experiments show that electrodes and the index matching between terpolymer and fiber have significant effect on the tuning range. An 18nm resonant wavelength shift is achieved by the terpolymer when electric field of 50MV/m is applied. On the other hand, over 100nm shift is observed by index matched terpolymer/PMMA blend as the temperature changes from 25oC to 100oC (temperature tuning). To realize this index matching condition, ZnS/terpolymer nanocomposite was developed which allowed the index of the composite to be varied over a large range while maintaining large electro-optical response. A simulation result predicts that large electrical tuning of the resonance band can be realized by the the index matched nanocomposite.
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