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This paper investigates the use of elastomeric dielectric materials with compliant electrodes as a means of actuation. When a voltage is applied to the electrodes, the elastomeric films expand in area and compresses in thickness. The strain response to applied electric fields was measured for a variety of elastomers. A nonlinear, high-strain, Mooney–Rivlin model was used to determine the expected strain response for a given applied field pressure. Comparing this analytical result to with experimentally measured strains, we determined that the electrostatic forces between the free charges on the electrodes are responsible for the observed response. Silicone polymers have produced the best combination of high strain and energy density, with thickness strains up to 41% and elastic energy densities up to 0.2 MJ/m3. Response times of 2 ms have been experimentally measured. This paper also reports recent progress in making highly compliant electrodes. We have shown, for example, that gold traces fabricated in a zig-zag pattern on silicone retain their conductivity when stretched up to 80%, compared to 1–5% when fabricated as a uniform two-dimensional electrodelayer. Optimal loading of dielectric elastomers can have a significant impact on performance: and the paper describes techniques which that can increase output up to a factor of 5 compared to neutral loading conditions. Lastly, the paper briefly discusses the performance of various actuators that use dielectric elastomer materials. The technology appears to be well-suited to a variety of small-scale actuator applications.

A new type of loudspeaker that generates sound by means of the electrostrictive response of a thin polymer film is described. Electrostrictive polymer film (EPF) loudspeakers are constructed with inexpensive, lightweight materials and have a very low profile. The films are typically silicone and are coated with compliant electrodes to allow large film deformations. Acoustical frequency response measurements from 5 x 5 cm (planar dimensions) prototype EPF loudspeakers are presented. Measurements of harmonic distortion are also shown, along with results demonstrating reduced harmonic distortion achieved with square-root wave shaping. Applications of EPF loudspeakers include active noise control and general-purpose flat-panel loudspeakers.

This paper discusses a novel electroacoustic transducer that uses the electrostrictive response of a polymer film. The active element of the transducer is a thin silicone-rubber film, with graphite powder electrodes on each side, that forms an array of bubble-like radiating elements. In experiments, radiated acoustic pressure and harmonic distortion of the electrostrictive-film actuator were measured in the frequency band 50–2000 Hz. A simple acoustic model was also developed to study the effect of various design and operating parameters on the actuator performance. Preliminary results from the experiments and simulations show that the electrostrictive-polymer-film actuator has the potential to be an efficient, compact, and lightweight electroacoustic transducer.

Electroactive polymers (EAPs) that are suitable for actuators undergo changes in size, shape, or stress state upon the application of an electrical stimulus. Much research in the field of EAPs tends to focus on the development and understanding of the polymer materials themselves. However, practical devices require that changes in dimension and stress state be effectively exploited to produce the desired functionalities (e.g., driving the motion of a robot limb or simply changing appearance or surface texture). This chapter focuses on those issues that must be considered in implementing EAP materials in practical devices. For purposes of discussion we will focus on one particular type of electroactive polymer: dielectric elastomers. In the literature [e.g., Liu, Bar-Cohen, and Leary, 1999] and elsewhere in this book, dielectric elastomers are also known as electrostatically stricted polymers. Dielectric elastomers are a type of electronic EAPs as defined in Chapter 1 of this book - €”in that their operation is based on the electromechanical response of polymer materials to the application of an electric field. They have demonstrated good performance over a range of performance parameters and thus show potential for a wide range of applications. Dielectric elastomers were pioneered by SRI International, but several research groups around the world are actively investigating applications of this technology [e.g., Wingert et al., 2002; Sommer-Larsen et al., 2001; Jeon et al., 2001]. While the principle of operation of dielectric elastomer EAPs is not used with all EAPs, many of the issues we will discuss are common to all. These issues include the high compliance and large strains that EAPs can produce, as well as the necessity of simultaneous consideration of both the electrical properties and mechanical properties of materials. This chapter is organized as follows. First, we consider the specifications used to match actuation technologies with applications, and when it makes sense to consider EAPs. Next, we discuss the basic principles of dielectric elastomer technology. We then consider design issues that may affect the actuation performance of dielectric elastomer EAPs, as well as the operational characteristics of EAPs and how they may affect an application. We present several examples of dielectric elastomer actuators for a wide range of applications, highlighting both the potential advantages of EAPs and the challenges associated with their use. Finally, we conclude with a brief summary of the subchapter and a discussion of the future of EAP application.

Dielectric elastomer electroactive polymer (EAP) loudspeakers have been built and demonstrated at SRI International. Dielectric elastomer loudspeakers have the advantages of being very lightweight and able to conform to any shape or surface, making them attractive as low-profile, surface-mounted speakers in rooms or vehicle interiors, and for applications in active noise control. Loudspeaker performance depends on a number of mechanical factors, such as speaker shape and mechanical bias, as well as on electrical driving characteristics. This paper discusses important aspects of loudspeaker performance, including sound pressure level and directivity.

Electroactive polymer (EAP) transducers are an emerging technology with many features that are desirable for MEMS devices. These advantages include simple fabrication in a variety of size scales, and ruggedness due to their inherent flexibility. Dielectric elastomer, a type of EAP transducer that couples the deformation of a rubbery polymer film to an applied electric field, shows particular promise because it can produce high strain and energy density, high efficiency and fast speed of response, and inherent environmental tolerance. A variety of proof-of-principle dielectric elastomer actuator configurations have been demonstrated at the small size scales needed for MEMS devices, including rolled "artificial muscle" actuators for insect-inspired microrobots, framed and bending beam actuators for efficient opto-mechanical switches, diaphragm and enhanced-thickness-mode actuators for microfluidic pumps, and valves and arrays of diaphragms for haptic displays. Several challenges remain for EAPs, including integration with driving electronics, and operational lifetime.

'Drummond, J. P., and Hussaini, M. Y., "A Detailed Numerical Model of a Supersonic Reacting Mixing Layer," AIAA Paper 861427, June 1986. Riggins, D. W., and McClinton, C. R., "A Computational Investigation of Flow Losses in a Supersonic Combustor," AIAA Paper 90-2093, July 1990. Eklund, D. R., Northam, G. B., andHartfield, R. J., "ADetailed Investigation of Staged Normal Injection into a Mach 2 Flow," 27th J ANNAF Combustion Meeting, F. E. Warren Air Force Base, Cheyenne, WY, Nov. 1990. Eklund, D. R., Northam, G. B., and Fletcher, D. G., "A Validation Study of the SPARK Navier-Stokes Code for Nonreacting Scramjet Combustor Flowfields," AIAA Paper 90-2360, July 1990. Drummond, G. B., "A Two-Dimensional Numerical Simulation of a Supersonic, Chemically Reacting Mixing Layer," NASA TM 4055, Dec. 1988. Hitch, B. D., and Senser, D. W., "Reduced H2-O2 Mechanisms for Use in Reacting Flow Simulation," AIAA Paper 88-0732, Jan. 1988.

Electroactive polymers (EAPs) can overcome many limitations of traditional smart material and transducer technologies. A particularly promising class of EAP is dielectric elastomer, also known as electroelastomer. Dielectric elastomer transducers are rubbery polymer materials with compliant electrodes that have a large electromechanical response to an applied electric field. The technology has been developed to the point where exceptional performance has already been demonstrated: for example, actuated strains of over 300 percent. These strains and the corresponding energy densities are beyond those of other field-activated materials including piezoelectrics. Because of their unique characteristics and expected low cost, dielectric elastomer transducers are under development in a wide range of applications including multifunctional (combined actuation, structure, and sensing) muscle-like actuators for biomimetic robots; microelectromechanical systems (MEMS); smart skins; conformal loudspeakers; haptic displays; and replacements for electromagnetic and pneumatic actuators for industrial and commercial applications. Dielectric elastomers have shown unique performance in each of these applications; however, some further development is required before they can be integrated into products and smart-materials systems. Among the many issues that may ultimately determine the success or failure of the technology for specific applications are durability, operating voltage and power requirements, and the size, cost, and complexity of the required electronic driving circuitry.

Dielectric elastomer actuators, based on the field-induced deformation of elastomeric polymers with compliant electrodes, can produce a large strain response, combined with a fast response time and high electromechanical efficiency. This unique performance, combined with other factors such as low cost, suggests many potential applications, a wide range of which are under investigation. Applications that effectively exploit the properties of dielectric elastomers include artificial muscle actuators for robots; low-cost, lightweight linear actuators; solid- state optical devices; diaphragm actuators for pumps and smart skins; acoustic actuators; and rotary motors. Issues that may ultimately determine the success or failure of the actuation technology for specific applications include the durability of the actuator, the performance of the actuator under load, operating voltage and power requirements, and electronic driving circuitry, to name a few.

This paper investigates the use of elastomeric dielectric materials with compliant electrodes as a means of actuation. When a voltage is applied to the electrodes, the elastomeric films expand in area and compress in thickness. The strain response to applied electric fields was measured for a variety of elastomers. A nonlinear high-strain Mooney-Rivlin model was used to determine the expected strain response for a given applied field pressure. Using this model, we determined that the electrostatic forces between the free charges on the electrodes are responsible for the observed response. Silicone polymers have produced the best combination of high strain and energy density, with strains exceeding 30% and energy densities up to 0.15 MJ/m3. Based on the electrostatic model, the electromechanical coupling efficiency is over 50%. This paper also reports recent progress in making highly compliant electrodes. We have shown, for example, that gold traces fabricated in a zig-zag pattern on silicone EPAM retain their conductivity when stretched up to 80% compared to 1 - 5% when fabricated as a uniform 2-dimensional electrode. Lastly, the paper presents the performance of various actuators that use EPAM materials. The technology appears to be well-suited for a variety of small-scale actuator applications.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Described herein are compliant electroactive polymer transducers for use in acoustic applications. A compliant electroactive polymer transducer includes a compliant electroactive polymer at least two electrodes. For sound production, circuitry in electrical communication with the transducer electrodes is configured to apply a driving signal that causes the electroactive polymer to deflect in the acoustic range.