Electrostriction of polymer dielectrics with compliant electrodes as a means of actuation
TL;DR: Electrostrictive polymer (EP) dielectric actuators have been shown to produce 5 to 20 times the effective actuation pressure of conventional air-gap electrostatics at the same electric field strength as mentioned in this paper.
Abstract: The electrostriction of elastomeric polymer dielectrics with compliant electrodes is potentially useful as a small-scale, solid-state actuator technology. Electrostrictive polymer (EP) materials are capable of efficient and fast response with high strains (> 30%), good actuation pressures (up to 1.9 MPa), and high specific energy densities (up to 0.1 J g−1). In this article, the mechanism of electrostriction is shown to be due to the electrostatic attraction of free charges on the electrodes. Although EP actuators are electrostatics based, they are shown to produce 5–20 times the effective actuation pressure of conventional air-gap electrostatics at the same electric field strength. The thin uniform dielectric films necessary for fabrication of EP actuators have been fabricated by techniques such as spin coating, casting, and dipping. A variety of materials and techniques have been used to produce the compliant electrodes, including lift-off stenciling techniques for powdered graphite, selective wetting of ionically conductive polymers, and spray coating of carbon blacks and fibrils in polymeric binders. Prototype actuators have been demonstrated in a variety of configurations such as stretched films, stacks, rolls, tubes, and unimorphs. Potential applications of the technology in areas such as microrobots, sound generators, and displays are discussed in this article.
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TL;DR: It is shown that prestraining the film further improves the performance of electrical actuators made from films of dielectric elastomers coated on both sides with compliant electrode material.
Abstract: Electrical actuators were made from films of dielectric elastomers (such as silicones) coated on both sides with compliant electrode material. When voltage was applied, the resulting electrostatic forces compressed the film in thickness and expanded it in area, producing strains up to 30 to 40%. It is now shown that prestraining the film further improves the performance of these devices. Actuated strains up to 117% were demonstrated with silicone elastomers, and up to 215% with acrylic elastomers using biaxially and uniaxially prestrained films. The strain, pressure, and response time of silicone exceeded those of natural muscle; specific energy densities greatly exceeded those of other field-actuated materials. Because the actuation mechanism is faster than in other high-strain electroactive polymers, this technology may be suitable for diverse applications.
2,969 citations
TL;DR: An exceptionally high electrostrictive response was observed in electron-irradiated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer, suggesting that the electron irradiation breaks up the coherent polarization domain in normal ferroelectric P( VDF- TrFE)Copolymer into nanopolar regions that transform the material into a relaxor ferroElectric.
Abstract: An exceptionally high electrostrictive response ( approximately 4 percent) was observed in electron-irradiated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer. The material exhibits typical relaxor ferroelectric behavior, suggesting that the electron irradiation breaks up the coherent polarization domain (all-trans chains) in normal ferroelectric P(VDF-TrFE) copolymer into nanopolar regions (nanometer-size, all-trans chains interrupted by trans and gauche bonds) that transform the material into a relaxor ferroelectric. The expanding and contracting of these polar regions under external fields, coupled with a large difference in the lattice strain between the polar and nonpolar phases, generate an ultrahigh strain response.
1,451 citations
TL;DR: In this paper, the authors focus on the important role and challenges of high-k polymer-matrix composites (PMC) in new technologies and discuss potential applications of highk PMC.
Abstract: There is an increasing need for high-permittivity (high-k) materials due to rapid development of electrical/electronic industry. It is well-known that single composition materials cannot meet the high-k need. The combination of dissimilar materials is expected to be an effective way to fabricate composites with high-k, especial for high-k polymer–matrix composites (PMC). This review paper focuses on the important role and challenges of high-k PMC in new technologies. The use of different materials in the PMC creates interfaces which have a crucial effect on final dielectric properties. Therefore it is necessary to understand dielectric properties and processing need before the high-k PMC can be made and applied commercially. Theoretical models for increasing dielectric permittivity are summarized and are used to explain the behavior of dielectric properties. The effects of fillers, fabrication processes and the nature of the interfaces between fillers and polymers are discussed. Potential applications of high-k PMC are also discussed.
1,412 citations
TL;DR: A number of materials have been explored for their use as artificial muscles, but dielectric elastomers appear to provide the best combination of properties for true muscle-like actuation, and widespread adoption of DEs has been hindered by premature breakdown and the requirement for high voltages and bulky support frames.
Abstract: A number of materials have been explored for their use as artificial muscles Among these, dielectric elastomers (DEs) appear to provide the best combination of properties for true muscle-like actuation DEs behave as compliant capacitors, expanding in area and shrinking in thickness when a voltage is applied Materials combining very high energy densities, strains, and efficiencies have been known for some time To date, however, the widespread adoption of DEs has been hindered by premature breakdown and the requirement for high voltages and bulky support frames Recent advances seem poised to remove these restrictions and allow for the production of highly reliable, high-performance transducers for artificial muscle applications
1,299 citations
TL;DR: In this article, a flexible piezoelectric foil stave was used to harness sole-bending energy and a reinforced PZT dimorph to capture heel-strike energy.
Abstract: Decreasing size and power requirements of wearable microelectronics make it possible to replace batteries with systems that capture energy from the user's environment. Unobtrusive devices developed at the MIT Media Lab scavenge electricity from the forces exerted on a shoe during walking: a flexible piezoelectric foil stave to harness sole-bending energy and a reinforced PZT dimorph to capture heel-strike energy.
975 citations
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TL;DR: In this article, it was shown that a large acoustic thickness response might be obtained by application of high dc bias fields, approx. 20 MV/rn, to a film while driving the film with an ac signal to access the high slope region of the electrostrictive strain vs. applied field curve.
Abstract: : It is well known that electrostrictive strains are proportional to the square of the applied electric field. It therefore appeared reasonable to assume that for some polymeric materials, a large acoustic thickness response might be obtained by application of high dc bias fields, approx. 20 MV/rn, to a film while driving the film with an ac signal to access the high slope region of the electrostrictive strain vs. applied field curve. Previous studies of crystallizing poly(vinylidene fluoride) (PVF2) from solution under high electric fields have demonstrated that gel-like samples of PVF2 with high content of the plasticizer tricresyl phosphate (TCP) could he subjected to electric fields as high as approx. 100 MV/m. Using this type of heavily plasticized PVF2, d sub T values approx. 4 Angstrom/V were obtained. Values of 9 Angstrom/V were obtained for a certain class of thermoplastic elastomer (i.e., a polyurethane). These d sub T values are considerably greater than those obtained from conventional piezoelectric ceramic materials. In addition, large elastic strains (> 3%) were observed as a function of applied dc field. (MM)
232 citations
"Electrostriction of polymer dielect..." refers background or methods in this paper
...In addition to doubling the effective pressure using compliant electrodes, Eq. ( 6 ) also indicates that the pressure is proportional to the relative dielectric constant of the material....
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...p=coeE’ ( 6 ) The effective pressure in Eq. (6) is exactly twice the pressure in a parallel-plate capacitor....
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...The pressure is given by Eq. ( 6 )) but the strain depends on a number of factors such as boundary conditions, modulus of elasticity, and loading....
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...The effective pressure in Eq. ( 6 ) is exactly twice the pressure in a parallel-plate capacitor....
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...If the electrostatic pressure from Eq. ( 6 ) is balanced by the elastic pressure of the film, the thickness strain can be written as...
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26 Jan 1997
TL;DR: In this article, the pull-in time of an electrostatically-actuated micromechanical fixed-fixed beam is shown to be a sensitive, and nearly linear function of ambient air pressure in the measured range of 0.1 mbar to 1013 mbar (1 atm or 760 Torr).
Abstract: The squeezed-film damping component of the pull-in time of an electrostatically-actuated micromechanical fixed-fixed beam is shown to be a sensitive, and nearly linear function of ambient air pressure in the measured range of 0.1 mbar to 1013 mbar (1 atm or 760 Torr). Pull-in time simulations, based on a one-dimensional macromodel using a damping constant proportional to pressure, are in good agreement with measured data. The data and simulations show that pull-in type devices will make excellent microelectromechanical systems (MEMS) sensors for broad-range absolute pressure measurements and for in situ leak monitoring of hermetically scaled packages containing other sensors or IC's. The pull-in sensors are compatible with any MEMS fabrication processes that allow out-of-plane electrostatic actuation, including surface micromachining and silicon wafer-bonding, and they do not require a cavity sealed at vacuum or at a reference air pressure.
123 citations
TL;DR: In this paper, a reluctance motors with bipolar microelectronics were constructed by using deep X-ray lithography and metal plating with a modified LIGA process and the rotor was assembled onto the stator shaft with submicron tolerances.
Abstract: Planar micromotors have the potential for high-speed control applications. These systems require closed loop control and therefore involve not only the motor but also associated high-speed control circuitry. Electrostatic devices with submicron gaps and CMOS controllers offer one possible construction technique. Magnetic motors with bipolar microelectronics are an attractive alternative. Magnetic micromotors have been constructed by using deep X-ray lithography and metal plating with a modified LIGA process. The devices are designed as reluctance motors and consist of a stator that is rigidly attached to the substrate and a rotor that is fabricated as a fully released, free part. Both pieces are formed from nickel and are typically 100 mu m in thickness. The rotor is assembled onto the stator shaft with submicron tolerances. The structure is driven by an external rotating magnet or a fixed electromagnet. Rotational speeds of up to 8000 rpm have been obtained and maintained for several days.
107 citations
TL;DR: In this paper, a polyvinyl alcohol-fluid gel was demonstrated to actuate at a much faster rate than those reported on conventional gel actuators in air and to flap a wing of 12.5 cm at a rate of 2 Hz with a span of 10 cm by periodically applying electric field.
Abstract: A gel of poly(vinyl alcohol) highly swollen with dimethyl sulfoxide was demonstrated to actuate at a much faster rate (more than 1000 times) than those reported on conventional gel actuators in air and to flap a wing of 12.5 cm at a rate of 2 Hz with a span of 10 cm by periodically applying electric field. The action (8% in length) induced by the electric field reached several hundreds times larger than those reported on the conventional ferroelectric solid materials. The electrostrictive gel was, thus, found to be a promising candidate material as a novel type of actuator or artificial muscle by having overcome some difficulties in responding time, electrochemical reactions on the electrodes, and magnitude of action in conventional methods or materials. © 1994 John Wiley & Sons, Inc.
81 citations
"Electrostriction of polymer dielect..." refers background in this paper
...p=( l/A)dU/dz=Q’/E& ( 5 ) Finally, noting that the electric field E is given by-E= &/E,+A, we can express the effective pressure aC...
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IBM1
TL;DR: In this article, an array-driven ultrasonic microactuator consisting of many distributed modules, using a concept similar to that of the distributed micro-actuators array, is presented.
Abstract: The authors present the design of an array-driven ultrasonic microactuator. Unlike a conventional ultrasonic motor, the array-driven ultrasonic microactuator consists of many distributed modules, using a concept similar to that of the distributed microactuator array. With a conventional ultrasonic motor, it is difficult to control an object locally and to obtain sufficient resolution of the rotor position and orientation without closed-loop control, since the motion of the rotor is produced by traveling waves on the whole diaphragm. However, an array-driven ultrasonic microactuator can control the motion with high accuracy even in open-loop control, because it can control the motion of each distributed module. It uses perpendicular motion, which is suitable for an electrostatic-force-type actuator. Perpendicular motions produced by two transducers in each module are mechanically transformed into circular motion, and a set of circular motions of the micromodules induces motion in the object. >
49 citations
"Electrostriction of polymer dielect..." refers background in this paper
...dU= (0.5Q’/~&)&- (OSQ’z/+4)dA/A ( 3 ) Applying the constraint in Eq. ( l), we find that dA/A = - dz/z; therefore, we can rewrite Eq. (3) as...
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...Applying the constraint in Eq. ( l), we find that dA/A = - dz/z; therefore, we can rewrite Eq. ( 3 ) as...
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...The difference is explained by the presence of the second term in Eq. ( 3 )) the dA term....
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