This article reviews the developments in electrostrictive polymers for energy harvesting. Electrostrictive polymers are a variety of electroactive polymers that deform due to the electrostatic and polarization interaction between two electrodes with opposite electric charge. Electrostrictive polymers have been the subject of much interest and research over the past decade. In earlier years, much of the focus was placed on actuator configurations, and in more recent years, the focus has turned to investigating material properties that may enhance electromechanical activities. Since the last 5 years and with the development of low-power electronics, the possibility of using these materials for energy harvesting has been investigated. This review outlines the operating principle in energy scavenging mode and conversion mechanisms behind this generator technology, highlights some of its advantages over existing actuator technologies, identifies some of the challenges associated with its development, and examines the main focus of research within this field, including some of the potential applications. KEYWORDS: actuators; dielectric properties; electrostrictive polymers; energy harvesting; ferroelectricity; nanoparticles INTRODUCTION The performance of energy harvesters is directly linked to the efficiency of the mechanical-electrical conversion within the active materials. For piezoelectric materials, the efficiency of the conversion can be estimated with the help of the coupling coefficient. For a given vibration mode, this coefficient expresses the ratio of the converted energy to the input one. Another key point for electroactive materials concerns the easiness of their integration within the whole structure.
The harvesting of energy from ambient environments is an emerging technology with potential for numerous applications, including portable electronic devices for renewable energy. Most of the current research activities refer to classical piezoelectric ceramic materials, but more recently the development of electrostrictive polymers has generated novel opportunities for high-strain actuators. At present, the investigation of using electrostrictive polymers for energy harvesting (a conversion of mechanical to electrical energy) is beginning to show potential for this application. This paper discusses the development of a model that is able to predict the energy harvesting capabilities of an electrostrictive polymer composite (EPC). An equivalent electrical scheme has been developed by using the model of current that was recently developed by our group. After the validation of the model on a macroscopic level, an empirical relationship was established to predict the value of power from the electrostriction coefficient, the dielectric permittivity, and the compliance of the material. Finally, results indicated that the dielectric permittivity was the crucial parameter for energy harvesting.
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