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In last decades, using fibrous piezoelectric materials as energy harvesters and sensors attracted huge attention. Ductile behaviors and biocompatibility are the most beneficial characteristics of polymer-based materials, particularly poly vinylidene fluoride which is used for fabrication of wearable energy harvesters and sensors. Evaluation of piezoelectric properties, especially fiber and nanofiber piezo-polymers, is one of the most important inconveniences mode, particularly to quantify the sensitivity performance of fabricated devices, i.e. output voltage divided by the applied pressure. Conventional methods mostly are indirect, irrelevant and predominantly measure a related parameter instead of the main factor; they are also time consuming, expensive, constrained and have a high error rate. In this study, based on direct effect of piezoelectric, a novel universal system (PiezoTester) is presented to characterize piezoelectric properties and sensitivity of sensors and energy harvesters, especially flexible polymeric devices. This system was used to test three samples that are different in ZnO nanoparticle percentage in poly vinylidene fluoride/ZnO electrospun mats and its results compared by other measuring methods such as XRD, FTIR and differential scanning calorimeter as indirect methods and criterion piezoelectric method as a direct method to validate its performance. Promising evidence inferred PiezoTester could be used as a reliable system to evaluate piezoelectric properties of flexible energy harvesters and sensors as well as wearable gadget and smart textiles. [ABSTRACT FROM AUTHOR]

Piezoelectrics are one of the most important materials used for harvesting energies. Several piezoelectric nanostructures have been used to construct nanogenerators (NGs). Nanofibers made by piezo-polymers, especially polyvinylidene fluoride (PVDF) because of their high flexibility, biocompatibility, and low cost, have shown wonderful growth as the key materials for NGs. Despite these favorable properties, fabricated nanofibrous devices still has low efficiency and many studies have been conducted to characterize and improve the performance of the PVDF nanofibers. Here we tried to fabricate PVDF NG device based on align nanofibers to improve the NGs output, using two different methods rotary collector and applying magnetic field. Characteristics of these structures are evaluated utilizing X-ray diffraction, Fourier transform infrared, differential scanning calorimetry, and scanning electron microscopy. Electrical response of fabricated samples is measured through utilization of an impedance analyzer at room temperature. Results demonstrate that crystalline structure increases in both methods but sample fabricated by rotary collector in magnetic field has more improvement in their outputs. This result shows that in addition to the crystalline structure, nanofibers alignment and arrangement play important roles in piezoelectric properties of sample, as well as NG efficiency. These results teach us to establish engineering design rules for wearable power harvesting devices. [ABSTRACT FROM AUTHOR]

Lithium batteries have been widely used to power up implantable medical devices such as pacemakers that are often designed to treat, diagnose, and prevent different diseases. However, due to their limited capacity and lifetime, patients have to undergo a surgical procedure to replace the discharged battery. Recently, nanogenerators have been emerged and are broadly accepted since they can convert tiny biomechanical forces, such as heartbeats, into electrical energy. This study aims to manufacture a biocompatible and high-performance piezoelectric energy harvester (PEH) that is capable to be charged by the energy received from the heartbeat and store the generated voltage. In this research, a hybrid structure of poly (vinylidene fluoride) (PVDF) coupling with polyamide-11 (PA-11) was fabricated using dual electrospinning to enhance the piezoelectric properties of the intended PEH. The piezoelectric test results show an acceptable increase in nanofibers' piezoelectric sensitivity from 62.87 mV/N to 75.75 mV/N by adding 25% (v/v) of PA-11 to PVDF, indicating the synergistic effect of PVDF and PA-11. The specimen PVDF (75% v/v)-PA-11 (25% v/v) also showed the highest mechanical strength and consequently is suggested as the optimum sample. To further enhance the efficacy and sensitivity of PEH to convert the small mechanical forces into an acceptable voltage, 15% (w/w) of barium titanate (BaTiO3) nanoparticles were added to the hybrid structure. The crystallinity and mechanical strength were noticeably increased by incorporating BaTiO3 nanoparticles into the fibrous structure, leading to a piezoelectric sensitivity of 107.52 mV/N. This result lays the groundwork for producing an effective piezoelectric patch that could be used as pacemaker batteries. [ABSTRACT FROM AUTHOR]

In this paper, in order to identify the lifetime of energy scavenging devices, the effect of a cyclic compressive load on the performance of polyvinylidene fluoride micro-nano fibrous nanogenerators was investigated, and the electrical output of layers was measured at different cycles and frequencies. Results showed that as the number of cycles increased at the constant frequency, the electrical output initially largely increased and then reached to a maximum level with a very gentle slope. Moreover, the crystalline structure and β -phase of the PVDF nanofibrous mats improved by applying a periodic compressive force. This study showed that, although the PVDF electrospun micro-nano fibers have suitable piezoelectric properties, it is necessary to make some post-treatment to fabricate an energy harvester with constant performance. Results also showed that when the number of cycles at a constant frequency increased, mechanical properties also improved. These results enable us to have an idea about the expected lifetime of a fibrous nanogenerator exposed to cyclic compressive pressure. [ABSTRACT FROM AUTHOR]