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An approach to harvesting electrical energy from a mechanically excited piezoelectric element has been described. The topic of this paper studies the most important properties of piezoelectric polymer polyvinylidene fluoride (PVDF) in energy harvesting. We have chosen to develop a recovery application within the clothes. By the use of a piezoelectric energy harvester capable to convert the mechanical energy produced by the knee during walking to an electrical energy. This will be achieved by replacing the traditional textile of the kneepad with the one that is made of the technical textile based on acrylic knitted and PVDF as a patch stuck on the textile. Furthermore, PVDF has many unique features, such as excellent mechanical behavior, large strain without structure fatigue, which enables it to act strongly as the load bearing member, and corrosion resistance. The technical textile, functioning as multifunctional wearable human interfaces, is considered today as a useful tool in several energy fields. In this paper, a smart structure based on piezoelectric polymer (PVDF) has been presented, which a power analytical model, based on the frequency, the geometrical parameters and other factors were investigated. Furthermore, the set of numerical results illustrating the harvested power for a given size of the device has been performed and discussed and how this harvested power may be used as a source for a wearable device. Finally, the theory presented in this study can be used for the realization of other optimal designs, for a wearable sensor with low consumption and so on.

Electroactive polymers have been widely used as smart material for actuators in recent years. Electromechanical applications are currently focused on energy harvesting and actuation, including the development of wireless portable electronic equipment autonomous and specific actuators such as artificial muscles. The problem to be solved is to make its devices the most efficient, as possible in terms of harvested energy and action. These two criteria are controlled by the permittivity of the electrostrictive polymer used, the Young’s modulus, and their dependence on frequency and level of stress. In the present paper, we presented a model describing the mechanical behaviour of electrostrictive polymers with taking into account the mechanical losses. Young’s modulus follows a linear function of strain and stress. However, when the elongation becomes higher, the data obtained from this strain linear trend and significant hysteresis loops appear the reflections on the existence of mechanical losses. In this work, to provide the analysis of the experimental observations, we utilized a theoretical model in order to define a constitutive law implying a representative relationship between stress and strain. After detailing this theoretical model, the simulation results are compared with experimental ones. The results show that hysteresis loss increases with the increase of frequency and strain amplitude. The model used here is in good agreement with the experimental results.

The use of piezoelectric nanocomposite in detection and actuation applications for the development of electromechanical microsystems (MEMS) has become quite common over the last decade. In this paper, we present a flexible piezoelectric nanocomposite films, composed of lead zirconate titanate (PZT) nanoparticles, embedded in poly(vinylidene-difluoride hexafluoro propylene) (PVdF-HFP) matrix. Piezoelectric and ferroelectric properties evolution is proportional to the evolution of the crystalline β-phase. The evaluation of the interactions between PZT and PVdF- HFP, performed by Fourier transform infrared spectroscopy (FTIR), revealed a dramatic improvement in these characteristics over pure PVdF-HFP, and attributed to a better crystallinity of the PVdF-HFP matrix and uniform distribution of nanoparticles. These films nanocomposites were done by solvent casting method, with various concentrations of PZT. Results of these experiments indicate that the investigated thin films nanocomposites are appropriate for various applications in energy storage and energy harvesting application.

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Modal synchronized switch damping on inductor control is a vibration damping technique that combines the advantages of both semiactive and active control techniques based on a modal strategy. This method allows targeting any unwanted vibration mode of a structure while using a semiactive autonomous synchronized switch damping on inductor damping technique. This article presents a performance analysis of an improved modal synchronized switch damping on inductor approach called ''SSDI-Max.'' The particularity of this new approach is to maximize the self-generated voltage amplitude by a proper definition of the switch instants (voltage inversion) according to the chosen targeted mode. Following the basic modal synchronized switch damping on inductor technique, the switch is synchronized with the chosen modal coordinate extremum. In the investigated approach, the voltage is increased by waiting for the next voltage extremum following immediately any targeted modal coordinate extremum in a given time window. This article presents simulations performed on a model representative of a clamped plate. The damping results are given in the case of multimodal, pulse, or noise excitations. This article analyzes the performance of the observer used to focus on a given mode and the influence of the control time window on the damping performance of the system. The results show that substantial damping increase can be obtained with a very slight modification of the control architecture and the same control energy.

The harvesting energy with electrostrictive polymers has great potential for remote applications such as invivo sensors, embedded micro-electro-mechanical systems devices, and distributed network instruments. A majority of current research activities in this field refers to classical piezoelectric ceramics, but electrostrictive polymers offer promise of energy harvesting with few moving parts; power can be produced by simply stretching and contracting a relatively low-cost rubbery material. The use of such polymers for energy harvesting is a growing field, which has great potential from an energy density viewpoint. The output power is inversely proportional to the harvester's frequency bandwidth. Consequently, it is much harder to efficiently harvest power from low-frequency sources with a large frequency band response and with a very small system size than from a stabilized high-frequency vibration source. This paper presents a new structure that is able to predict mechanical frequency excitation in order to increase power-harvesting capabilities of electrostrictive polymers. An equivalent structure scheme has been developed by using current and electrical schemes models. With a transverse strain of 0.5% and a bias field of 10 V/μm, such a process rendered it possible to increase the converted power by 80% with a low-frequency mechanical excitation. This study contributes to provide a framework for developing an innovative energy-harvesting technology that collects vibrations from the environment and converts them into electricity to power a variety of sensors.

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