Seiki Chiba

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.

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.

Electrostriction of polymer films for microactuators

The investigation of electrostrictive polymers (EPs) as a means of microactuation is described. EP materials are squeezed and stretched by electrostatic forces generated with compliant electrodes. This approach offers several advantages over existing actuator technologies, including high strains (>30%), good actuation pressures (1.9 MPa), and high specific energy densities (0.1 J/g). In addition, the actuation is fast, uses lightweight materials, and has the potential for high energy efficiencies. Although EP actuators are electrostatics based, they offer 5 to 20 times the effective actuation pressure of conventional air-gap electrostatics at the same electric field strength. The gain is due to replacing air with a higher dielectric material, and to using two orthogonal modes of electromechanical coupling (stretching and squeezing) rather than one. Analysis of the mechanism of EP actuation is discussed. We also discuss fabrication techniques such as spin coating, casting, and dipping, as well as polymer and electrode materials. We describe demonstrations of prototype mini- and microactuators in a variety of configurations such as stretched films, stacks, rolls, tubes, and unimorphs. Last, we suggest potential applications of the technology in areas such as microrobots, sound generators, and displays.

Current status and future prospects of power generators using dielectric elastomers

Electroactive polymer artificial muscle (EPAM), known collectively as dielectric elastomers in the literature, has been shown to offer unique capabilities as an actuator and is now being developed for a wide variety of generator applications. EPAM has several characteristics that make it potentially well suited for wave, water current, wind, human motion, and other environmental energy harvesting systems including a high energy density allowing for minimal EPAM material quantities, high energy conversion efficiency independent of frequency of operation and non-toxic and low-cost materials not susceptible to corrosion. Experiments have been performed on push-button and heel-mounted generator devices powered by human motion, ocean wave power harvesters mounted on buoys and water turbines. While the power output levels of such demonstration devices is small, the performance of these devices has supported the potential benefits of EPAM. For example, an electrical energy conversion efficiency of over 70% was achieved with small wave heights. The ability of EPAM to produce hydrogen fuel for energy storage was also demonstrated. Because the energy conversion principle of EPAM is capacitive in nature, the performance is largely independent of size and it should eventually be possible to scale up EPAM generators to the megawatt level to address a variety of electrical power needs.

Current status and future prospects of electric generators using electroactive polymer artificial muscle

The type of electroactive polymer known as dielectric elastomers has shown considerable promise for harvesting energy from environmental sources such as ocean waves, wind, water currents, human motion, etc. The high energy density and conversion efficiency of dielectric elastomers can allow for very simple and robust “DIRECT DRIVE” generators. Various types of energy harvesting generators based on dielectric elastomers have been tested. For example, buoy-mounted generators that harvest the energy of ocean waves were tested at sea for two weeks. Each generator uses a proof-mass to provide the mechanical forces that stretch and contract the dielectric elastomer generator. Those generators operated successfully during the sea trials. The buoy-mounted generators will be scaled up to produce larger amounts of power. The use of significantly larger amounts of dielectric elastomer material to produce generator modules with outputs in the MEGAWATT at range is being investigated for application to ocean wave power systems.

Innovative wave power generation system using electroactive polymer artificial muscles

As human population and the demands of better standards of life increase in the 21st century, a sudden surge in energy demand is predicted and the accompanying environmental problems will become a subject of discussion. The establishment of an energy system that uses renewable energy is attracting attention as a possible answer to these problems. This article presents a discussion on one energy harvesting method that has been the focus of attention recently: the generation system based on electroactive polymer artificial muscle (EPAM).

Electric Power from Artificial Muscles

In this work, as a novel process for use of renewable energy, the authors would like to discuss the possibility of an artificial muscle actuator based on a dielectric electroactive polymer (elastomer). This highly efficient actuator can transform electric energy into mechanical energy (theoretical transformation efficiency of 80 to 90%) with a high energy density of 1.0 W/g. Using the reverse operation for this actuator, it is possible, with current materials, to obtain a maximum output of 0.4 J/g. With this new material, it is not impossible to dream of having an output on the order of 2.0 J/g.

Extending Applications of Dielectric Elastomer Artificial Muscles to Wireless Communication Systems

Electro active polymers (EAPs) are used for actuators that can electrically control their motions to resemble those of actual muscles. Thus, they are called artificial muscles. In addition, since EAPs are often made of flexible materials, they have also come to be called “soft actuators” in recent years. There are many types of EAPs such as dielectric elastomers (Perline & Chiba, 1992a), ionic polymer-metal composites (Oguro et al., 1999), electroconductive Polymers (Otero & Sansinera, 1998), and ion polymer gels (Osada et al., 1992b). Figure 1 shows typical EAPs.

Electroactive Polymer “Artificial Muscle” Operable in Ultra-High Hydrostatic Pressure Environment

Transducers for high-power sonars, an important tool for undersea exploration and monitoring, may be required to work in deep water where pressures are higher than several tens of MPa. In contrast with the piezoelectric devices commonly used as high-power sonars for seabed resource exploration, electroactive polymers offer the benefits of high coupling efficiency, low cost, and the ability to form large area skins or other devices. One question about the use of electroactive polymers for sonar has been their ability to withstand the rigors of the deep-sea environment. In a recent experiment, we have verified that the dielectric elastomer type of electroactive polymer can maintain good operational characteristics even in an ultrahigh-pressure environment by showing that the electroactive strain response to an applied voltage was unaffected by externally applied pressures of up to 100 MPa.

Development of Wave Generation Module for Small Ships Using Dielectric Elastomer

From 2007 to 2015, we installed DE (dielectric elastomer) generators on a buoy, and succeeded in a demonstration of power generation at sea. In 2011, we also pointed out that DE generators could be useful for ships for the first time in the world. Using the know-how obtained at that time, we have recently developed an innovative wave-power generator for small ships, which can generate electric power by the rocking movement of the ship. Mounting this device on a model ship, we carried out a demonstration experiment of the power generation in a wave-generation water-tank to verify its feasibility for practical use on a real ship. And 48% of wave energy (gross value) can be converted to electric energy, suggesting the realization of fairly high efficiency power generation, compared with the efficiency of the existing wave generators.