Mikio Waki

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.

Innovative Elastomer Transducer Driven by Karman Vortices in Water Flow

A simple experimental model of a power generation system was tested in a flowing water tank in order to investigate the performance and feasibility of a small hydroelectric generation system using DE (dielectric elastomer) transducer. The mass of DE material in the power generator module was only 0.1 g. The electric energy generated with a stroke of 10 mm was 12.54 mJ. An electrical energy of approximately 1.5 J per cycle of DE generators can be expected to be generated by scaling up this system, which is capable of being equipped with up to about 100 units of DE transducers. The water velocity was set at 0.30 to 0.70 m/s. This is a small flow, about the same flow as the water in a Japanese garden. This system was driven by Karman vortices in the wake of a cylinder fixed in the water flow. The characteristics of DEs can be utilized to produce electric power effectively. A wing, which is an important part in the generation system to convert fluid energy into mechanical energy, was set behind the cylinder. The wing oscillated due to the pressure caused by Karman vortices, resulting in stretching and contracting of the DE transducers, thus producing electrical power. Experimental results show that an average output power of approximately 31 mW was produced with a generation efficiency of about 66%, when the diameter of the cylinder is 60 mm, the span and chord length of the wing are 120 mm and 30 mm, respectively, the distance between the cylinder and the wing is 170 mm, and the velocity of the water flow is 0.50 m/s.

Innovative Power Generation System for Harvesting Wave Energy

As a wave power generator utilizing dielectric elastomers can directly drive elastomers by the up and down motions of waves, the structure of the generator is simple and its size can be made small. Using a power generator set on a shore protection, we have proved that it can generate electric power even by fairly small-amplitude waves. Also, we have confirmed that this small-sized device can be utilized for stable hydrogen generation. 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.

An Experimental Study on the Motion of Floating Bodies Arranged in Series for Wave Power Generation

This paper considered the optimal arrangement on the assumption that multiple power generation systems are used in a row ahead of the realization of the wave power generation system using the DE (dielectric elastomer) which is expected to be popularized in the future. A power generation system using DEs was studied as a moored floating body, and tank tests were conducted. There are few studies on the influence of multiple moored floating bodies on each other. Those studies clarified the fluctuation, energy absorption efficiency, tension mooring force and quietness characteristics produced from differences in the arrangement of the floating bodies within the floating body group and so on utilizing the principle of double oscillating water columns. The purpose of this paper is to clarify the influence of floating body intervals and number of floating bodies on floating motion and mooring tension when a plurality of floating bodies are moored in a row perpendicular to the advancing wave direction. We also discuss the conditions of the large power generation system in actual sea areas using the DEs.