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Formulation of electrostrictive materials for vibrational energy recovery and development of high sensitivity stress sensors

Abstract : The goal of this thesis is to leverage soft matter for the development of electrostrictive composite materials for use in vibrational energy recovery and high sensitivity pressure sensors. An emulsion approach is proposed for making composites and incorporating conductive particles such as grapheme foils or carbon black particles into an elastic polymeric matrix made of polydimethylsiloxane (PDMS). This original approach allows controlling the dispersion of the charges and the microstructure of the composites. The dielectric properties of these materials are controlled by the type of charges, their concentration, and their dispersion path. Optimization of formulation levers makes it possible to achieve very high dielectric permittivity values (ε_r^'≈182 at 100 Hz) for polymer composites. The materials developed during this work have been used successfully in vibrational energy recovery devices. In combination with an insulating layer, the studied structures have a high effective relative dielectric permittivity with a very low effective conductivity (up to 2,53 10-8 S.m-1). We have developed an experimental device to measure the electrostriction of materials and to quantify the generation of electrical energy in response to mechanical vibrations. A power density of 0.38 W m-3 was measured for mechanical excitations of 100 Hz. For real-life use of electrostrictive materials and their use as an ambient mechanical energy harvester, we incorporated them into vibrating beam structures cantilevered. Thanks to the flexibility of these structures and their low resonance frequency, we managed to recover 0.4 W.m-3 for a mechanical excitation of 25 Hz. In the last part of our work, we focused our attention on high sensitivity pressure sensors, necessary for long-term cardiac monitoring and for the natural interaction of robots with humans. We demonstrate that our electrostrictive composite materials can be integrated into these flexible pressure sensors. The reported performance in terms of pressure sensitivity is above that of the literature. We illustrate the performance of our materials by successfully using them to continuously and non-invasively record the pulse waves of a radial artery.
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Mickaël Pruvost. Formulation of electrostrictive materials for vibrational energy recovery and development of high sensitivity stress sensors. Chemical Physics [physics.chem-ph]. Université Paris sciences et lettres, 2018. English. ⟨NNT : 2018PSLET027⟩. ⟨tel-02506398⟩



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