Elaboration et caractérisation de céramiques ferroélectriques de type PZT flurore.

Les céramiques ferroélectriques de formulation générale Pb(ZrxTi1-x)O3 (PZT) sont massivement utilisées dans de nombreux domaines comme la médecine ou l\u27aéronautique en raison de leurs propriétés diélectriques et électromécaniques. L\u27objet de l\u27étude est la recherche de céramiques PZT dur possédant des caractéristiques stables et reproductibles en fonction de la température et de la contrainte et sans comportement hystérétique. Ces spécificités sont requises pour des dispositifs tournant à grande vitesse comme les gyromètres et les gyroscopes vibrants qui peuvent être soumis à des variations de température importantes et dans lesquels les céramiques subissent des contraintes mécaniques élevées. Pour cette application particulière, le matériau doit également présenter une faible permittivité diélectrique relative (er < 1000) ainsi qu\u27un coefficient de surtension mécanique élevé (Qm ³ 2000). Pour atteindre ces objectifs, nous avons élaboré par voie liquide et caractérisé de nouveaux matériaux PZT fluoré. La s

Piezoelectric response of a PZT thin film to magnetic fields from permanent magnet and coil combination

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High curvature sensors based on flexoelectric effect in soft semi-conducting polymer films

International audienceA sensor based on the flexoelectric effect capable of measuring large curvature variations is proposed. The flexoelectric effect is defined as the coupling between the strain gradient and polarization in solid dielectrics and semiconductors. It can be considered as an alternative transduction mechanism to the piezoelectric effect to directly measure curvature without the need to apply a large electric field to induce a macroscopic piezoelectric-like effect.In this study, the process for obtaining a bending sensor from a semiconducting solution of commercial (3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) deposited as a free standing thin film in the thickness range : 18 μm - 50 μm is presented. Owing to its specific properties, PEDOT:PSS films are mechanically fragile and sensitive to water. An encapsulation step in a polyethylene terephthalate (PET) polymer increases the robustness of the device while maintaining its flexibility.The flexoelectric characterization showed a coefficient much higher than those reported in the literature for PEDOT:PSS polymers with a coefficient that reaches 76 μC/m at 0.5 Hz (3 orders of magnitude higher than insulating polymers). In the case of PEDOT:PSS which is a mixed ionic/electronic semi-conductor, flexoelectric response might be mainly attributed to short range PEDOT+-PSS- dipole motion rather than pure ionic polarization mechanism (flexoionic effect).It was also demonstrated that with the acquisition of the output current signal at the sensor terminals it is possible to determine the curvature of the sensor used in cantilevered beam bending configuration. The demonstration of their efficiency in converting a strain gradient into electrical energy, combined with their robustness and flexibility, makes these devices very attractive for wide range curvature sensing

Large Curvature Sensors Based on Flexoelectric Effect in PEDOT:PSS Polymer Films

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Commercial piezoelectric unimorph diaphragm as a magnetic energy harvester

International audienceA magnetoelectric coupling in a low-cost and commercially available piezoelectric unimorph diaphragm is demonstrated by measuring magnetically induced AC voltage from the sample. Such a magnetoelectric effect could be achieved only because of the combination of magnetic forces within the electrodes and piezoelectric effect, without any magnetic constituent. Harvested magnetic power density across an optimal resistive load is found to be 0.12 mW/Oe.cm3 at the bending mode resonance frequency. The proposed transduction mechanism opens new and simple ways for producing electricity from stray magnetic fields

High curvature sensors based on flexoelectric effect in soft semi-conducting polymer films

A sensor based on the flexoelectric effect capable of measuring large curvature variations is proposed. The flexoelectric effect is defined as the coupling between the strain gradient and polarization in solid dielectrics and semiconductors. It can be considered as an alternative transduction mechanism to the piezoelectric effect to directly measure curvature without the need to apply a large electric field to induce a macroscopic piezoelectric-like effect.In this study, the process for obtaining a bending sensor from a semiconducting solution of commercial (3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) deposited as a free standing thin film in the thickness range : 18 μm - 50 μm is presented. Owing to its specific properties, PEDOT:PSS films are mechanically fragile and sensitive to water. An encapsulation step in a polyethylene terephthalate (PET) polymer increases the robustness of the device while maintaining its flexibility.The flexoelectric characterization showed a coefficient much higher than those reported in the literature for PEDOT:PSS polymers with a coefficient that reaches 76 μC/m at 0.5 Hz (3 orders of magnitude higher than insulating polymers). In the case of PEDOT:PSS which is a mixed ionic/electronic semi-conductor, flexoelectric response might be mainly attributed to short range PEDOT+-PSS- dipole motion rather than pure ionic polarization mechanism (flexoionic effect).It was also demonstrated that with the acquisition of the output current signal at the sensor terminals it is possible to determine the curvature of the sensor used in cantilevered beam bending configuration. The demonstration of their efficiency in converting a strain gradient into electrical energy, combined with their robustness and flexibility, makes these devices very attractive for wide range curvature sensing

Flexoelectric energy harvester based on soft semi-conducting polymer films

A flexoelectric micro generator able to harvest mechanical energy from large localized curvature variations along multilayer polymer films is proposed. The energy conversion is based on direct flexoelectricity, which is a universal effect in all solid dielectrics that corresponds to the appearance of an electrical polarization induced by a deformation gradient. This “flexoelectric technology” is a potential alternative to energy harvesting with piezoelectrics without the need for applying large electric field for inducing macroscopic piezoelectric effect and thus eliminates associated problems such as leakage and breakdown. The micro-generators are made from a solution of semi-conducting (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) deposited as a free-standing thin film. This material is lead-free and biocompatible, ideal for applications in the medical field. The developed thin films exhibit a very large flexoelectric coefficient > 50 μC/m (1000 times higher than insulating polymer films) and a high flexibility which allows them to withstand large deformation. The electrical characterization of the films was performed using a mechanical roller to apply a low frequency bending radius to the micro-generator and recovering the output flexoelectric current. We were able to obtain a current density of about 2.2 μA/cm2 at 2 Hz for a curvature of 62 m-1. The electrical characterization under slow air flow (< 6 m/s) was also carried out in wind tunnel in order to demonstrate the aero-electric potentialities of the micro-generators. The combination of flexibility and flexoelectricity allows the integration of these films into devices for low frequency (<20 Hz) mechanical energy conversion

Flexoelectric energy harvester based on soft semi-conducting polymer films

International audienceA flexoelectric micro generator able to harvest mechanical energy from large localized curvature variations along multilayer polymer films is proposed. The energy conversion is based on direct flexoelectricity, which is a universal effect in all solid dielectrics that corresponds to the appearance of an electrical polarization induced by a deformation gradient. This “flexoelectric technology” is a potential alternative to energy harvesting with piezoelectrics without the need for applying large electric field for inducing macroscopic piezoelectric effect and thus eliminates associated problems such as leakage and breakdown. The micro-generators are made from a solution of semi-conducting (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) deposited as a free-standing thin film. This material is lead-free and biocompatible, ideal for applications in the medical field. The developed thin films exhibit a very large flexoelectric coefficient > 50 μC/m (1000 times higher than insulating polymer films) and a high flexibility which allows them to withstand large deformation. The electrical characterization of the films was performed using a mechanical roller to apply a low frequency bending radius to the micro-generator and recovering the output flexoelectric current. We were able to obtain a current density of about 2.2 μA/cm2 at 2 Hz for a curvature of 62 m-1. The electrical characterization under slow air flow (< 6 m/s) was also carried out in wind tunnel in order to demonstrate the aero-electric potentialities of the micro-generators. The combination of flexibility and flexoelectricity allows the integration of these films into devices for low frequency (<20 Hz) mechanical energy conversion

Polyurethane membranes for flexible centimeter-wave patch antennas

International audienceIn this paper, we present the original use of a recyclable and low cost soft polymer, polyurethane (PU) (εr ≈ 3.5 at 10 GHz), as part of a dielectric substrate of a microstrip patch antenna. The combination of simple membrane manufacturing process and the low Young's modulus of PU (EPU ≈ 30 MPa) are employed in an X-band antenna application in this study. The PU dielectric characterizations indicate the high loss tangent value (tan δ ≈ 0.1 at 10 GHz). Membrane supported technology is used to reduce the influence of this high loss and increase the antenna efficiency. The measurement of antenna performances such as efficiency (η ≈ 31.7%) confirms the viability of the technological process and the specific patch antenna design developed in this work. Besides, the potential of the PU-based soft patch antenna for frequency agility (3.88%) via mechanical reconfiguration is also shown