Mr. Hassen Ben Ammar Profile

Hassen Ben Ammar

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Proceedings Article | 22 March 2021 Presentation + Paper

Contribution of flexoelectricity in piezoelectric PVDF films for EH applications

Lars Seyfert, Hassen ben Ammaa, Norbert Schwesinger

Proceedings Volume 11588, 115880E (2021) https://doi.org/10.1117/12.2581560

KEYWORDS: Ferroelectric polymers, Polymers, Polymer thin films, Dielectrics, Temperature metrology, Piezoelectric effects, Energy harvesting, Dielectric polarization, Capacitance, Thermoelectric materials

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A new branch of research in energy harvesting is flexoelectricity of solids. The flexoelectric effect is an electromechanical conversion mechanism that occurs in all dielectric materials. This can lead to new applications especially due to the larger number of possible materials. Therefore, investigation of properties of dielectric materials and specific conversion conditions are of great importance. Of importance is also finding out the significance of flexoelectric in relation to the piezoelectric energy conversion and possible other conversion mechanisms. This paper seeks to verify the flexoelectric effect in solid piezoelectric materials and to discover the usability for energy harvesting purposes. It follows earlier studies in this area only proving the flexoelectricity in non-piezoelectric materials. In our investigations, PolyVinylidene DiFluoride (PVDF) polymer films were used in a plate capacitor configuration. A measurement setup was built to enable the evaluation of polymer films under different temperature levels. Thereby, the pure flexoelectric behavior above the Curie temperature could be separated from the combined piezoelectric and flexoelectric effect at room temperature. In this way, an impression of the contribution of the flexoelectric effect in the energy conversion should be gained. As main parameters we used the change of electrical voltage and drift current in a differential measurement setup by means of a Lock-In Amplifier. The strain gradients in the material were generated by needles of steel with a vertical oscillation of the polymer film in relation to the needle tip. The results clearly show the presence of the flexoelectric effect and in this way also its contribution for energy conversion. The relative voltage and current drift response of the samples offer a great contribution of flexoelectric energy conversion under inhomogeneous mechanical loads.

Proceedings Article | 19 May 2020 Presentation + Paper

Verification of the flexoelectric effect in PET polymer films for EH applications

Lars Seyfert, Lukas Moritz, Hassen ben Ammar, Norbert Schwesinger

Proceedings Volume 11376, 113761T (2020) https://doi.org/10.1117/12.2558027

KEYWORDS: Electrodes, Polymers, Polymer thin films, Dielectrics, Actuators, Amplifiers, Dielectric polarization, Ferroelectric polymers, Piezoelectric effects, Energy harvesting

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The flexoelectric effect of solids represents a new branch of research. As an electromechanical conversion mechanism, it occurs in all dielectric materials. This offers new applications based on a large number of possible materials. Based on that, an investigation of properties and conversion conditions are of great importance. It is important to find out the significance of flexoelectric energy conversion in relation to other conversion mechanisms. This paper attempts to verify the flexoelectric effect in simple dielectric materials and to investigate the applicability in the area of energy harvesting (EH). In our studies, dielectric Polyethylene-Terephthalate (PET) polymer films were used in two different plate capacitor configurations. Two different measurement setups were built to enable the evaluation of polymer films under changing conditions. Main verification parameter of the energy conversion is the electrical voltage change in a differential measurement setup. Changing strain gradients, the basis of the flexoelectric conversion, were generated in two separate ways in thin PET-films. First results clearly show the presence of flexoelectric conversion. The height of the voltage pulses by mechanical loading of the samples cannot be explained by capacitive energy conversion only. Another effect is required to explain the electrical response - FLEXOELECTRICITY

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