Hybrid energy harvesting systems, using piezoelectric elements and dielectric polymers

cited By 0International audienceInterest in energy harvesting applications has increased a lot during recent years. This is especially true for systems using electroactive materials like dielectric polymers or piezoelectric materials. Unfortunately, these materials despite multiple advantages, present some important drawbacks. For example, many dielectric polymers demonstrated high energy densities; they are cheap, easy to process and can be easily integrated in many different structures. But at the same time, dielectric polymer generators require an external energy supply which could greatly compromise their autonomy. Piezoelectric systems, on the other hand, are completely autonomous and can be easily miniaturized. However, most common piezoelectric materials present a high rigidity and are brittle by nature and therefore their integration could be difficult. This paper investigates the possibility of using hybrid systems combining piezoelectric elements and dielectric polymers for mechanical energy harvesting applications and it is focused mainly on the problem of electrical energy transfer. Our objective is to show that such systems can be interesting and that it is possible to benefit from the advantages of both materials. For this, different configurations were considered and the problem of their optimization was addressed. The experimental work enabled us to prove the concept and identify the main practical limitations. � 2016 IOP Publishing Ltd

High performance material based carbon nanotube buckypaper actuation

cited By 0; Conference of Composites and Advanced Materials Expo: Combined Strength. Unsurpassed Innovation., CAMX 2014 ; Conference Date: 13 October 2014 Through 16 October 2014; Conference Code:111496International audienceThe materials used in many branches of engineering for actuation applications are typically heavy, nonflexible and require high driving power, so their practicality for creating biomimetic systems is limited. Due to their unique combination of electrical and mechanical properties, carbon nanotubes have attracted a great deal of interest for use as electromechanical actuators. Individual carbon nanotubes combine excellent electrical and thermal conductivities with remarkable mechanical properties. They are also currently considered the strongest and stiffest materials known. However, these properties have yet to be effectively transferred when the nanotubes are attempted to be assembled into useful macroscopic forms. A practical approach to manufacture manageable structures of carbon nanotubes for engineering applications is to assemble them into buckypapers. Buckypapers are sheets of highly entangled single- or multiwalled nanotubes held together by entanglement and van der Waals interactions. These structures provide sufficient mechanical and good electrochemical properties to study their actuator performance and applications. To incorporate buckypaper actuators into engineering systems, it is of high importance to understand their material property-actuation performance relationships in order to model and predict the behavior of these actuators. The electromechanical actuation of macroscopic buckypaper structures and their actuators, including single and multi-walled carbon nanotube buckypapers and aligned single-walled nanotube buckypapers, were analyzed and compared. From the experimental evidence, this paper discusses the effects of the fundamental material properties, including Young modulus and electrical double layer properties, on actuation performance of the resultant actuators

Analytical modeling of curved piezoelectric, Langevin-type, vibrating transducers using transfer matrices

cited By 3International audienceThis paper describes a relatively general method based on a transfer matrices approach, for modeling piezoelectric Langevin-type transducers presenting a curved geometry. The obtained equations are simple enough to be solved for a vast number of configurations and be easily implemented in a program. The paper explains how they were obtained and how they can be solved using a method involving transfer matrices. The model was also employed to simulate a real transducer and a good agreement was found between calculated and measured data. Also the results given by model were compared with those obtained with FEM software ANSYS, again the model proved to work well. © 2014 Elsevier B.V

Scale-like compliant gold electrode: Towards high strain capacitive devices for energy harvesting

cited By 2International audienceHighly compliant electrodes are of primary importance for high strain capacitive energy harvesting. Herein, we present a compliant gold sputtered electrode on a natural rubber substrate. Electrical conductivity remained remarkably good even at strains of 500%. The robustness of the electrodes has been assessed in fatigue tests and resistivity of less than 25 Ω cm -1 were observed after 1500 cycles between 200% and 300% strain. These electrodes were then used in harvesting energy for large strains and experimental energy densities up to 3.3 mJ cm-3 cycle-1 have been recorded, showing the capabilities of such electrodes for efficiently ensuring electrical contact under high strain for converting mechanical energy into electricity. © 2014 Elsevier B.V

Plasticized relaxor ferroelectric terpolymer: Toward giant electrostriction, high mechanical energy and low electric field actuators

cited By 18International audienceEnhancing the electrostrictive strain under low electric field of a dielectric electroactive polymer (EAP) is essential in soft actuators applications. Conventional electrostrictive polymers suffer of the high electric fields usually required to reach sufficient strain. Here we report a new approach that greatly enhanced the strain under electric field and the mechanical energy density of fluorinated terpolymer EAP. A new all organic composite based on poly(vinylidene fluoride-trifluoroethylene- chlorofluoroethylene) terpolymer (P(VDF-TrFE-CFE)) doped with bis(2-ethylhexyl) phthalate (DEHP) was synthesized. DEHP molecule acts as a plasticizer that leads to large dipolar interfacial effects. This chemical modification allows a 28-fold increase of the electrostrictive strain and a 215-fold increase of the mechanical energy density. As a consequence, this new approach permits the uses of the exceptional properties of the fluorinated terpolymer for an electric field nearly 5 times lower and represents a simple and effective solution to this technological barrier. © 2013 Elsevier B.V. All rights reserved

Buckypaper actuators: Material properties and performance relationships

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Revolutionary all-organic composite ferroelectric-relaxor P(VDF-TrFE-CFE) for low electric field actuators

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Mechanical energy harvesting via a plasticizer-modified electrostrictive polymer

cited By 3International audienceA plasticizer-modified electrostrictive terpolymer with improved electromechanical properties was investigated for mechanical energy harvesting via a pseudo-piezoelectric cycle. Experimental results indicate that the modified terpolymer exhibited improved energy harvesting performances in contrast with the pure terpolymer. A maximum generated short-circuit current of 3.635 μA (much higher than the leakage current) and a power density of 607 μW/cm3 were observed for modified terpolymer. Based on the quadric relationship between the energy conversion efficiency and the DC bias electric field, an energy conversion efficiency as high as 34% and a corresponding electrical power density of 4.31 mW/cm3 could be achieved for the modified terpolymer working at a DC bias electric field of 30 MV/m. © 2016 AIP Publishing LLC

Revolutionary all-organic composite ferroelectric-relaxor P(VDF-TrFE-CFE) for low electric field actuators

cited By 0; Conference of Composites and Advanced Materials Expo: Combined Strength. Unsurpassed Innovation., CAMX 2014 ; Conference Date: 13 October 2014 Through 16 October 2014; Conference Code:111496International audienceThe various types of natural muscle are incredible material systems that enable the production of large deformations by repetitive molecular motions. Electroactive Polymer technologies are being developed that produce similar strains and higher stresses using electrostatic forces, electrostriction, ion insertion, and molecular conformational changes. Materials used include elastomers, conducting polymers, ionically conducting polymers, and carbon nanotubes. These polymers reach large strain response to an electric field, making them good candidates as low frequency active actuators. Fluorinated terpolymer P(VDF-TrFE-CFE) is a semi-crystalline polymer which shows the highest level of conversion from electrical to mechanical energy thanks to its high dielectric permittivity (εΓ ∼ 50) and high mechanical modulus. However, large electrical field are required (E > 100V/μm) to reach sufficient strain levels (> 2%). In this work, fluorinated terpolymer P(VDF-TrFE-CFE) was doped with (2-ethylhexyl) phthalate (DEHP). Such modified terpolymer leads to 28-fold increase of the electrostrictive strain under low applied electric field and 233-fold increase of the mechanical energy compared to the neat polymer. This simple chemical doping allows the use of the exceptional properties of the terpolymer at an electric field 5.5 times lower than that of the pure terpolymer. In addition, the proposed structure in this paper is relatively cheap, industrially used and could potentially break a technological lock as the performance recorded at low electric field are greater than any conventional electroactive polymer

Converse electrostrictive effect in dielectric polymers

cited By 9International audienceThis paper aims at exposing a physical model for converse dielectric electrostrictive effect using Debye/Langevin formalism through the use of Boltzmann's statistics. The principle of the proposed approach consists of considering the electric field orientability of dipoles within the polymer matrix as a function of the applied strain, allowing the derivation of the polarization or electric displacement as a function of the electric field and strain or stress. The proposed model also permits taking into account the saturation effect that occurs in the polarization and that limits the mechanical to electrical conversion in electrostrictive dielectric polymers. © 2013 Elsevier B.V