Richard Heydt

High-field deformation of elastomeric dielectrics for actuators

Abstract 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.

Electroelastomers: applications of dielectric elastomer transducers for actuation, generation, and smart structures

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.

Acoustical performance of an electrostrictive polymer film loudspeaker

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.

High-field electrostriction of elastomeric polymer dielectrics for actuation

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.

Applications of dielectric elastomer actuators

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.

Sound radiation properties of dielectric elastomer electroactive polymer loudspeakers

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.