The Characterisation of the harvesting capabilities of an electrostrictive polymer composite
Introduction
During the last decade, and due to the constantly growing demand for highly integrated, low-power autonomous electronic systems, scientists have been forced to search for new power sources that are able to recover energy from the environment [1]. Moreover, great advances in the field of new active materials, also called “smart materials” because of their sensor and actuator capabilities, have given rise to research into the power harvesting capabilities of these materials.
Energy harvesting systems are systems capable of converting residual environmental energy into useable electrical energy. Great effort is being put into research concerning systems that convert strain energy, induced by mechanical vibration, into electrical energy. A significant amount of research has been devoted to understanding power harvesting systems using piezoelectric materials.
Advances in the field of new smart materials have suggested the investigation of their capabilities as energy converters [2]. One of the most promising type of new materials is represented by electrostrictive polymer composites, EPCs belonging to the family of electro-active polymers, EAPs. For instance, polyurethane is an electrostrictive polymer capable of generating strains above 10% under a moderate electric field, thus leading to them being considered as potential actuators [3]. Furthermore, these materials are lightweight, very flexible, have low manufacturing costs and are easily moulded into any desired shapes [4]. With the intention of increasing the capacity of the polyurethane, particles (carbon black coated or solicon-carbide nanowires) can be added to a polyurethane matrix. In addition, other polymer hosts such as nylon and polyethylene, require investigation in their neat form.
This article reports on measurements of the electrostrictive coefficient in newly developed copolymers. One of the challenges in characterising the electrostrictive response in polymer films is to measure the electrostrictive coefficient. In general, the experimental methods for carrying out electrostrictive coefficient measurements can be grouped into two categories: contact methods and non-contact methods [5]. The contact methods include those with a strain gauge and a linear variable differential transformer, whereas in the non-contact methods, the interferometer principle can be employed. This latter procedure is very difficult, particularly with regard to sample holding.
The electromechanical properties and energy harvesting capacities of EPCs are important both from the points of view of application and fundamental understanding. Thus, the present contribution describes the development of a new technique or setup for characterising the electromechanical behaviour of materials. This setup was simple, convenient to use and capable of measuring the harvested power, and its performance was evaluated on a variety of materials.
Section snippets
The setup
The setup developed for characterizing the electrostrictive coefficient in polymer film is shown schematically in Fig. 1a and b. The key part of the setup was a metal cantilever on which the polymer film was attached. As seen from Fig. 2, the polymer film was clamped in one end at a solid base (fixed) whereas the other end was attached to the free end of the metal cantilever (the EPC film was glued to the clamped end of the beam in order to obtain the maximum strain for conversion energy).
The
Results and discussion
The following section judges the accuracy of the measured output current and displacement, the validity of the modelling of the current, the adhesive layer effect but also the characteristics of the polymers.
Results
Measurements were performed at 20 Hz and the results are summarised in Table 2. The equivalent piezoelectric coefficient d31 is provided to facilitate the comparison between the electromechanical activity of the EPC and PVDF. The theoretical value of d31 is calculated usingwhere E3 is the bias electric field. The pseudo-piezoelectric coefficient of the studied polymers and EPCs is lower than that PVDF. However, one should keep in mind that the d31 coefficient is directly
Conclusion
In this paper, we report on the harvesting capabilities of an electrostrictive polymer composite. In order to evaluate the capabilities of the polymer for harvesting electrical energy, a dedicated bench has been built for the measurement of the apparent transverse electrostrictive coefficient and of the harvested current. The modelling of the harvested current has also been developed and has shown that the figure of merit which represents the capacity to extract electrical energy was equal to
Acknowledgments
This work was supported by the DGA (Délégation Générale pour l’Armement). The authors wish to thank LMI Labaratory of Lyon 1 University for providing the SiC nanowires. They also will to thank MATEIS Labaratory of INSA de Lyon for DMA Analysis.
L. Lebrun graduated from the Ecole Nationale Supérieure d’Ingénieurs de Caen, France, in 1991. He received a PhD degree in Acoustics in 1995 from the Institut National des Sciences Appliquées de Lyon (INSA) France for his thesis on piezoelectric motors. During 2001, he was a visiting scientist at the Materials Research Institute of Pennsylvannia State University, State College, PA, in the group of Prof. Tom Shrout. Currently, he is a professor at INSA de Lyon, with research interests concerning
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L. Lebrun graduated from the Ecole Nationale Supérieure d’Ingénieurs de Caen, France, in 1991. He received a PhD degree in Acoustics in 1995 from the Institut National des Sciences Appliquées de Lyon (INSA) France for his thesis on piezoelectric motors. During 2001, he was a visiting scientist at the Materials Research Institute of Pennsylvannia State University, State College, PA, in the group of Prof. Tom Shrout. Currently, he is a professor at INSA de Lyon, with research interests concerning electroactive materials (ceramics, single crystals and polymers) and smart structures.
D. Guyomar received a degree in physics from Amiens University, Amiens, France, an engineering and a doctor-engineer degree in acoustics from Compiègne University, France, as well as a PhD degree in physics from Paris VII University, Paris, France. In 1982–1983 he worked as a research associate in fluid dynamics at the University of Southern California, Los Angeles, CA. He was a National Research Council Awardee (1983–1984) detached at the Monterey Naval Postgraduate School, California, to develop transient wave propagation modelling. He was hired by Schlumberger in 1984 to lead several projects dealing with borehole imaging; and then moved to Thomson Submarine activities in the field of underwater acoustics. In 1992, Dr Guyomar co-created the Techsonic company, which is involved in research, development, and production of piezoelectric and ultrasonic devices. He is presently full-time university professor at Institut National des Sciences Appliquées de Lyon (INSA), Lyon, France, where he manages the Laboratoire de Génie Electrique et Ferroélectricité (LGEF). He also works as a consultant for several companies. His present research interests include the field of piezo-material characterization, piezo-actuators, acoustics, power ultrasonics, vibration control, and energy harvesting.
B. Guiffard graduated from the Ecole Nationale Supérieure de Chimie de Rennes, France in 1995. He joined the Laboratoire de Génie Electrique et Ferroélectricité (LGEF) at the Institut National des Sciences Appliquées (INSA), Lyon, France in 1996, where he obtained his PhD in Inorganic Chemistry in 1999. He became an associate professor at INSA in 2000 at which time he started to work on the doping of piezoelectric materials (ceramics, single crystals). His present research interests include the development of electroactive polymer composites exhibiting multiferroic behaviour for enhanced sensing capability and external field induced strain. In this topic, he is currently involved in the optimization of actuation performances of nano-objects filled semi-crystalline elastomers and the investigation of magneto-electric composite films loaded with magnetic nanoparticles.
P.-J. Cottinet received the MSc degree in electrical engineering from the INSA de Lyon, France in 2008. He is currently PhD student at INSA working on electroactive polymers and their applications for actuators and energy harvesting.
C. Putson was born in Thailand in 1978. He received a BSc degree in physics from the Prince of Songkla University in 2000, which was followed by an MSc degree, also in physics, at Chulalongkorn University in 2004. Currently, he is a PhD student at INSA in Lyon, France. His research interests involve the energy conversion of electrostrictive polymers for energy harvesting.