Seajin Oh

Dielectric elastomers: generator mode fundamentals and applications

Dielectric elastomers have shown great promise as actuator materials. Their advantages in converting mechanical to electrical energy in a generator mode are less well known. If a low voltage charge is placed on a stretched elastomer prior to contraction, the contraction works against the electrostatic field pressure and raises the voltage of the charge, thus generating electrical energy. This paper discusses the fundamentals of dielectric elastomer generators, experimental verification of the phenomenon, practical issues, and potential applications. Acrylic elastomers have demonstrated an estimated 0.4 J/g specific energy density, greater than that of piezoelectric materials. Much higher energy densities, over 1 J/g, are predicted. Conversion efficiency can also be high, theoretically up to 80-90%; the paper discusses the operating conditions and materials required for high efficiency. Practical considerations may limit the specific outputs and efficiencies of dielectric elastomeric generators, tradeoffs between electronics and generator material performance are discussed. Lastly, the paper describes work on potential applications such as an ongoing effort to develop a boot generator based on dielectric elastomers, as well as other applications such as conventional power generators, backpack generators, and wave power 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.

Ultrahigh strain response of field-actuated elastomeric polymers

Extremely large strains were achieved with elastomeric polymer films that are subject to high electric fields. The films were coated on both sides with complaint electrode material. When voltage was applied, the film compressed in thickness and expanded in area. The strain response is dominated by the electrostatic forces produced by the charges on the compliant electrodes. Actuated strains up to 117% were demonstrated with silicone elastomers, and up to 215% with acrylic elastomers. A key to achieving these large strains is to introduce a high prestrain to the film. Specific energy densities were much greater than those of other field-actuated materials. Because the response is electrostatic in nature, the actuation mechanism is predicted to be fast. Response speeds in excess of 2000 Hz have ben demonstrated in silicones. Acrylic response speeds are more than an order of magnitude slower, although the reason for this difference is not yet known. Measurement of material viscoelastic and electrical properties predicts that high efficiencies (> 80%) may be achieved with efficient driver circuits. A variety of actuators, including electrooptical devices, diaphragm pumps, and muscle like linear actuators, have been demonstrated with these materials, suggesting that this technology is well suited to small-scale electromechanical devices and robots.

Controlled Continuous Patterning of Polymeric Nanofibers on Three-Dimensional Substrates Using Low-Voltage Near-Field Electrospinning

We report on a continuous method for controlled electrospinning of polymeric nanofibers on two-dimensional (2D) and three dimensional (3D) substrates using low voltage near-field electrospinning (LV NFES). The method overcomes some of the drawbacks in more conventional near-field electrospinning by using a superelastic polymer ink formulation. The viscoelastic nature of our polymer ink enables continuous electrospinning at a very low voltage of 200 V, almost an order of magnitude lower than conventional NFES, thereby reducing bending instabilities and increasing control of the resulting polymer jet. In one application, polymeric nanofibers are freely suspended between microstructures of 3D carbon on Si substrates to illustrate wiring together 3D components in any desired pattern.

Dielectric elastomer artificial muscle actuators: Toward biomimetic motion

To achieve desirable biomimetic motion, actuators must be able to reproduce the important features of natural muscle such as power, stress, strain, speed of response, efficiency, and controllability. It is a mistake, however, to consider muscle as only an energy output device. Muscle is multifunctional. In locomotion, muscle often acts as an energy absorber, variable-stiffness suspension element, or position sensor, for example. Electroactive polymer technologies based on the electric-field-induced deformation of polymer dielectrics with compliant electrodes are particularly promising because they have demonstrated high strains and energy densities. Testing with experimental biological techniques and apparatus has confirmed that these dielectric elastomer artificial muscles can indeed reproduce several of the important characteristics of natural muscle. Several different artificial muscle actuator configurations have been tested, including flat actuators and tubular rolls. Rolls have been shown to act as structural elements and to incorporate position sensing. Biomimetic robot applications have been explored that exploit the muscle-like capabilities of the dielectric elastomer actuators, including serpentine manipulators, insect-like flapping-wing mechanisms, and insect-like walking robots.

Microstructure evolution and gas sensitivities of Pd-doped SnO2-based sensor prepared by three different catalyst-addition processes

Abstract We have investigated three ways of impregnating PdO on an SnO 2 gas sensor to achieve a simple and reliable sensor-fabrication process. These impregnating processes are: (1) coprecipitation of SnO 2 and Pd compounds in the solution; (2) addition of PdCl 2 to SnO 2 gel, followed by precipitation; and (3) infiltration of PdCl 2 into calcined SnO 2 powder. Processes (1) and (2) introduce Pd into SnO 2 particles before particle growth is completed. The phase and microstructures of particles have been analysed by X-ray diffraction, scanning and transmission electron microscopes, and an energy-dispering X-ray spectroscope. The presence of Pd in the process of SnO 2 precipitation restrains the growth of SnO 2 particles and enhances a uniform distribution of fine PdO powder on the SnO 2 grains. SnO 2 gas sensors have been fabricated and tested for response to CH 4 , C 2 H 6 and CO. Processes (1) and (2) show many possibilities of improving SnO 2 gas-sensor sensitivity with a simplified fabrication process.

Biologically inspired hexapedal robot using field-effect electroactive elastomer artificial muscles

Small, autonomous mobile robots are needed for applications such as reconnaissance over difficult terrain or internal inspection of large industrial systems. Previous work in experimental biology and with legged robots has revealed the advantages of using leg actuators with inherent compliance for robust, autonomous locomotion over uneven terrain. Recently developed field-effect electroactive elastomer artificial muscle actuators offer such compliance as well as attractive performance parameters such as force/weight and efficiency, so we developed a small (670 g) six-legged robot, FLEX, using AM actuators. Electrically, AM actuators are a capacitive, high-impedance load similar to piezoelectrics, which makes them difficult to rive optimally with conventional circuitry. Still, we were able to devise a modular, microprocessor-based control system capable of driving 12 muscles with up to 5,000 V, operating form an on- board battery. The artificial muscle actuators had excellent compliance and peak performance, but suffered from poor uniformity and degradation over time. FLEX is the first robot of its kind. While there is room for improvement in some of the robot systems such as actuators and their drivers, this work has validated the idea of using artificial muscle actuators in biologically inspired walking robots.

Development and testing of a solid-state CO2 gas sensor for use in reduced-pressure environments

Abstract A planetry instrument called the thermal and evolved analyzer (T/EGA) is currently being developed, consisting of a combined differential scanning calorimeter (DSC) and evolved gas analyzer (EGA) to subject regolith samples to a temperature ramp and monitor gas-evolution events. This paper reports the development and testing of a miniature carbon dioxide (CO 2 ) solid-state electrochemical gas sensor (SSEGS) for use in the EGA portion of the instrument. A miniature potentiometric CO 2 sensor has been developed that is configured in a planar geometry. The sensor uses solid-state reference and measuring electrodes co-located one one side of a beta alumina electrolyte substrate, and a thick-film platinum heater on the opposite side. Experiments are performed under reduced-pressure conditions to characterize the sensor response in terms of heater power, sensor temperature, total pressure, and gas-composition parameters. The sensor response to carbon dioxide (CO 2 ) is found to be a complex function of these variables, and to act through two separate and independent mechanisms to influence the sensor output. The sensor oxygen sensitivity is also measured in the presence of CO 2 . A sensor temperature of 530°C is found to result in an oxygen-response slope coefficient of zero. Operation of the sensor at this temperature results in selective carbon dioxide response, and an output that is independent of oxygen partial pressure.

In Situ Electrochemical Sensor for Measurement in Nonconductive Liquids

The principle of an in situ oil-quality sensor based on extraction electrochemistry has been proven. The sensor consists of a silver/silver chloride reference electrode in contact with a polar electrolyte contained in a housing and a thin film iridium oxide sensing electrode coated on a porous membrane which allows diffusion of electroactive polar species into the housing. An increase in the concentration of acidic compounds was observed when the oil degraded

Multilayer ionic devices fabricated by the plasma-spray method

Abstract Using the plasma spray method, ceramic films can be easily and quickly coated onto a substrate. Zirconia-based oxygen sensors, both potentiometric-mode and amperometric-mode, were fabricated by the plasma-spray method and their oxygen sensing ability was demonstrated. Stabilized zirconia films had sufficient ionic conductivity for use in oxygen sensors. The film permeability was controlled by changing spray conditions, providing flexibility in the design of amperometric-mode sensors. Combined with other thin- and thick-film techniques, and shadow mask technologies, the plasma spray method has great potential in the fabrication of multilayered ceramic devices, especially in batch processes.