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Brissaud M.,CNRS Laboratory of Electrical Engineering and Ferroelectricity
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control | Year: 2010

This paper deals with 3-D modeling of piezoelectric materials. The model is based on an exact description of the potential and electric field inside a material. Moreover, coherent piezoelectric equations are used. Modeling has been applied to rectangular and cylindrical elements. In each case, the exact equations of the displacements along the three coordinate axes and the corresponding electric impedance are calculated. The general resonance conditions are stated for these two geometries. It is shown that, contrary to the 1-D models, a unique equation describes lateral and thickness vibrations, or radial and thickness vibrations. These properties enable us to analytically calculate the frequency spectrum of rectangular elements, thick disks, or cylinders and also thick rings or hollow cylinders versus the width to thickness ratio. It is then very easy to determine the corresponding dispersion diagram related to each geometry sample. These resonance conditions are similar to those deduced from the 1-D model described in the IEEE standard but are more general and necessitate no cancelling out assumptions. In addition, contrary to 1-D models, the wave velocities and the permittivity are independent of the element geometry (parallelepiped or cylindrical). The wave velocities are equal to those stated for the wave propagation in infinite medium and measured with pulse-echo techniques. It is the coupling inside the material which modifies the resonance conditions and not the geometrical dimensions of the vibrating element. 3-D modeling and 1-D radial mode of the admittance of a thick disk are calculated and compared with experimental measurements. Theoretical and measured admittances are compared and discussed. © 2010 IEEE. Source

Lallart M.,CNRS Laboratory of Electrical Engineering and Ferroelectricity | Guyomar D.,CNRS Laboratory of Electrical Engineering and Ferroelectricity
Applied Physics Letters | Year: 2010

This letter reports a concept for enhancing the conversion abilities of piezoelectric materials based on initial energy injection, as well as its application to energy harvesting. Unlike conventional energy conversion approaches, this concept considers a pulsed bidirectional energy flow between the source and the storage stages. The presented technique shows an "energy resonance" effect that can bring up the gain in terms of harvested energy up to 40 (20 using typical components) compared to standard energy harvesting methods. Such a system thus allows a significant reduction in active materials required for the conception of autonomous devices supplied by ambient energy. © 2010 American Institute of Physics. Source

Wongtimnoi K.,CNRS Laboratory for Materials: Engineering and Science | Guiffard B.,CNRS Laboratory of Electrical Engineering and Ferroelectricity | Bogner-Van de Moortele A.,CNRS Laboratory for Materials: Engineering and Science | Seveyrat L.,CNRS Laboratory of Electrical Engineering and Ferroelectricity | And 2 more authors.
Composites Science and Technology | Year: 2011

The electrostrictive properties of a polyether-based polyurethane elastomer and its corresponding composites filled with conductive carbon black (CB) were studied by measuring the thickness strain SZ induced by external electric fields E. For films with thicknesses of approximately 50 μm, the apparent electrostrictive coefficient M was measured at low electric fields, E≤ 4. V/μm, and different CB contents (up to a volume fraction of 2%). Dielectric measurements in AC mode were performed in order to determine the percolation threshold fc, which was 1.25. v%. This optimal volume fraction yielded a remarkable threefold increase in M, associated with an increase of the dielectric constant by a factor 7, in comparison with pure PU. This enhancement of the electric field-induced strain and apparent electrostriction was mainly triggered by an increase of the dielectric constant, even if the intrinsic electrostriction coefficient Q was decreased. The nanocomposites thus seem to be very attractive for low-frequency electromechanical applications. Above fc, their conductivity was raised and their electrostrictive activity lost. Finally, there is a good agreement between the experimentally determined dependence on the CB content of the M coefficient and the theoretical estimation calculated from dielectric and mechanical measurements. © 2011 Elsevier Ltd. Source

Guyomar D.,CNRS Laboratory of Electrical Engineering and Ferroelectricity | Lallart M.,CNRS Laboratory of Electrical Engineering and Ferroelectricity
Micromachines | Year: 2011

This paper aims at providing an up-to-date review of nonlinear electronic interfaces for energy harvesting from mechanical vibrations using piezoelectric coupling. The basic principles and the direct application to energy harvesting of nonlinear treatment of the output voltage of the transducers for conversion enhancement will be recalled, and extensions of this approach presented. Latest advances in this field will be exposed, such as the use of intermediate energy tanks for decoupling or initial energy injection for conversion magnification. A comparative analysis of each of these techniques will be performed, highlighting the advantages and drawbacks of the methods, in terms of efficiency, performance under several excitation conditions, complexity of implementation and so on. Finally, a special focus of their implementation in the case of low voltage output transducers (as in the case of microsystems) will be presented. © 2011 by the authors. Source

Lallart M.,CNRS Laboratory of Electrical Engineering and Ferroelectricity | Wu Y.-C.,CNRS Laboratory of Electrical Engineering and Ferroelectricity | Guyomar D.,CNRS Laboratory of Electrical Engineering and Ferroelectricity
IEEE Transactions on Industrial Electronics | Year: 2012

Energy harvesting using piezoelectric elements received much attention as vibrations are widely available and as piezoelectric transducers feature high-power densities and promising integration potentials. It has also been shown that applying a nonlinear treatment on the output voltage of the piezoelectric material can significantly enhance the performance of the device. This process consists of inverting the piezoelectric voltage when the displacement is maximum, which therefore requires a way of synchronization. In practical applications, however, a delay may happen between the inversion and the actual occurrence of an extremum. The purpose of this paper is to investigate the effect of such a delay on the microgenerator performance and therefore to predict the power output that can be expected under real circumstances. Theoretical analysis validated through experimental measurements shows that the effect may not be the same for positive or negative delays. It is also demonstrated that the effect is not significant as long as the delay is small. The acceptable delay range also increases as the electromechanical system becomes more coupled and/or less damped. Under such configuration, the output power can even be slightly increased as the delay permits controlling the tradeoff between energy extraction and damping effect. © 2011 IEEE. Source

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