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J. G. Rocha

Bio: J. G. Rocha is an academic researcher from University of Minho. The author has contributed to research in topics: Photodetector & Detector. The author has an hindex of 24, co-authored 113 publications receiving 2141 citations.


Papers
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Journal ArticleDOI
TL;DR: The use of piezoelectric polymers in order to harvest energy from people walking and the fabrication of a shoe capable of generating and accumulating the energy is described.
Abstract: In the last few years, there has been an increasing demand for low-power and portable-energy sources due to the development and mass consumption of portable electronic devices. Furthermore, the portable-energy sources must be associated with environmental issues and imposed regulations. These demands support research in the areas of portable-energy generation methods. In this scope, piezoelectric materials become a strong candidate for energy generation and storage in future applications. This paper describes the use of piezoelectric polymers in order to harvest energy from people walking and the fabrication of a shoe capable of generating and accumulating the energy. In this scope, electroactive s-polyvinylidene fluoride used as energy harvesting element was introduced into a bicolor sole prepared by injection, together with the electronics needed to increase energy transfer and storage efficiency. An electrostatic generator was also included in order to increase energy harvesting.

247 citations

Journal ArticleDOI
TL;DR: In this paper, the energy harvesting efficiency of electrospun poly(vinylidene fluoride), its copolymer vinylidene fluoride-trifluoroethylene and composites of the later with barium titanate ceramic fillers on interdigitated electrodes has been investigated.
Abstract: The energy harvesting efficiency of electrospun poly(vinylidene fluoride), its copolymer vinylidene fluoride-trifluoroethylene and composites of the later with barium titanate ceramic fillers on interdigitated electrodes has been investigated. Ceramic fillers of 500 (tetragonal), 100 (cubic) and 10 nm (cubic) have been used. Further, a study of the influence of the electrospinning processing parameters on the average size of the composites fibers has been performed. It is found that the best energy harvesting performance was obtained for pure poly(vinylidene fluoride) fibers, with power outputs up to 0.02 μW and 25 μW under low and high mechanical deformation. The copolymer and the composites show reduced power output mainly due to increased mechanical stiffness, the power output of the composites being better for the nonpiezoelectic smaller fillers. The obtained values, among the largest found in the literature, the easy processing and the low cost and robustness of the polymer, demonstrate the applicability of the developed system.

130 citations

Journal ArticleDOI
TL;DR: In this paper, the authors report on the piezoresistive behavior of polymer based nanocomposites, composed of poly(vinylidene fluoride) and carbon nanotubes (CNTs).
Abstract: This paper reports on the piezoresistive behavior of polymer based nanocomposites, composed of poly(vinylidene fluoride) – PVDF and carbon nanotubes (CNTs). The samples were prepared by hot pressing with CNT sample concentrations up to loadings of 10 wt.%. The phase present in the polymer was the α-phase. The correlation between the electrical resistivity and mechanical solicitations is presented in this work for the different composites and for varying mechanical solicitations. The values of the gauge factor, ranging up to 6.2, and the linearity of the response over a wide strain range shows the viability of these materials to be used as piezoresistive sensors. The stability of the signal, the time response and the temperature behavior were also evaluated. The observed electrical and electromechanical behavior can be explained in the framework of the percolation theory.

123 citations

Journal ArticleDOI
01 Sep 2009-Carbon
TL;DR: In this article, VGCNF/PVDF composites prepared by solution casting were studied and it was shown that the incorporation of the carbon nanofibres/poly(vinilidene fluoride) matrix increases the degree of crystallinity of the polymer composites for concentrations lower than ∼1%, remaining stable for higher concentrations.

116 citations

Journal ArticleDOI
TL;DR: In this paper, the influence of the processing methods in the thermal stability of polyvinylidene fluoride (PVDF) samples was studied by UV-VIS spectroscopy and thermogravimetric analysis.
Abstract: Poly(vinylidene fluoride), PVDF, in its β-phase is an electroactive polymer with many technological applications. There are two main ways to prepare this polymer in its electroactive β-phase: by high temperature stretching from the α-phase and directly from solution. In this paper, the influence of the processing methods in the thermal stability of the samples was studied by UV–VIS spectroscopy and thermogravimetric analysis. The number of chain defects was measured by 1 H NMR. The results obtained were compared to a commercial β-PVDF sample. The number of head to head defects in the different samples is found to be between 6% and 9%. The onset temperature for thermal degradation and the average activation energy (∼76.5 kJ mol −1 ) of the process are approximately equal for the α-phase sample and the β-phase obtained from it. Larger values of the onset temperature and average activation energy (∼100 kJ mol −1 ) are found for the β-phase sample directly obtained from the solution and for the commercial β-phase sample. The thermal degradation of the samples occurs in two steps, independently of the phase of the sample, the degree of crystallinity and the processing method.

110 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the main characteristics of the electroactive phases of polyvinylidene fluoride and copolymers are summarized, and some interesting potential applications and processing challenges are discussed.

2,242 citations

Journal ArticleDOI
TL;DR: In this article, the recent developments and the characteristics of membrane separators for rechargeable lithium-ion batteries are reviewed and the outlook and future directions in this research field are also given.
Abstract: In this paper, the recent developments and the characteristics of membrane separators for lithium-ion batteries are reviewed. In recent years, there have been intensive efforts to develop advanced battery separators for rechargeable lithium-ion batteries for different applications such as portable electronics, electric vehicles, and energy storage for power grids. The separator is a critical component of lithium-ion batteries since it provides a physical barrier between the positive and negative electrodes in order to prevent electrical short circuits. The separator also serves as the electrolyte reservoir for the transport of ions during the charging and discharging cycles of a battery. The performance of lithium-ion batteries is greatly affected by the materials and structure of the separators. This paper introduces the requirements of battery separators and the structure and properties of five important types of membrane separators which are microporous membranes, modified microporous membranes, non-woven mats, composite membranes and electrolyte membranes. Each separator type has inherent advantages and disadvantages which influence the performance of lithium-ion batteries. The structures, characteristics, manufacturing, modification, and performance of separators are described in this review paper. The outlook and future directions in this research field are also given.

1,077 citations

Journal ArticleDOI
TL;DR: In this article, the authors present the past and current efforts with a brief description on the featured properties of hydrogel membranes fabricated from biopolymers and synthetic ones for wound dressing applications.

1,059 citations

Journal ArticleDOI
TL;DR: In this article, a review of recent research in the field of phosphor and scintillator materials and related detectors is presented, where the fundamental issues regarding the interaction of x-ray radiation with a solid state are explained.
Abstract: Recent research in the field of phosphor and scintillator materials and related detectors is reviewed. After a historical introduction the fundamental issues are explained regarding the interaction of x-ray radiation with a solid state. Crucial parameters and characteristics important for the performance of these materials in applications, including the employed measurement methods, are described. Extended description of the materials currently in use or under intense study is given. Scintillation detector configurations are further briefly overviewed and selected applications are mentioned in more detail to provide an illustration.

741 citations

Proceedings Article
01 Jan 2009
TL;DR: This paper summarizes recent energy harvesting results and their power management circuits.
Abstract: More than a decade of research in the field of thermal, motion, vibration and electromagnetic radiation energy harvesting has yielded increasing power output and smaller embodiments. Power management circuits for rectification and DC-DC conversion are becoming able to efficiently convert the power from these energy harvesters. This paper summarizes recent energy harvesting results and their power management circuits.

711 citations