Papers by Author: C.J. Dias

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Authors: Rosa Marat-Mendes, C.J. Dias, José N. Marat-Mendes
Authors: Paulo Inácio, José N. Marat-Mendes, C.J. Dias
Authors: Paulo Inácio, C.J. Dias, José N. Marat-Mendes
Authors: A. Basílio, Rui Igreja, Paulo Inácio, C.J. Dias, José N. Marat-Mendes
Abstract: Ultrasonic motors are of great interest since their operation is not affected by a magnetic field. On this work the development of a prototype of a smart ultrasonic motor and its characteristics will be presented. The stator of the motor is formed by a cantilever made of PZT ceramic plate sandwiched between two unidirectional CFRP composite sheets. The composite sheets are oriented to 45º and -45º in the longitudinal direction. By application of a sinusoidal electric field to the piezoelectric ceramic plate, it vibrates. The anisotropy of the CFRP composite sheets induces an expansion/torsion movement. This effect is transformed into rotation by friction. The study of adequate voltages and frequencies of the applied electric field allows the optimization of the rotating motor performance.
Authors: M. Carmo Lança, C.J. Dias, D.K. Das Gupta, José N. Marat-Mendes
Authors: Bogdan Neagu, Eugen R. Neagu, Rui Igreja, C.J. Dias
Abstract: Information about the spatial distribution of the electric field can be obtained by measuring the electrode impedance as a function of the diameter of the electrolyte surrounding the electrode. The non-uniform distribution of the electric field around the electrode is supported by the variation of the geometry factor (GF) with the electrical conductivity and geometry of the volume conductor. A comparison of the values obtained for the GF from experimental data, from model calculations and simulations help to understand the non-uniform distribution of the electric field. The GF calculated from four-electrode-measurements is significantly higher. GF should be used with caution in calculations of the deep brain stimulation (DBS) electrode impedance.
Authors: Eugen R. Neagu, C.J. Dias, M.C. Lança, Paulo Inácio, José N. Marat-Mendes
Abstract: For the characterization of the new materials and for a better understanding of the connection between structure and properties it is necessary to use more and more sensible methods to study molecular movement at nanometric scale. This paper presents the experimental basis for a new electrical method to study the fine molecular movements at nanometric scale in dielectric materials. The method will be applied for polar and non-polar materials characterization. Traditionally, the electrical methods used to study the molecular movements are based on the movements of the dipoles that are parts of the molecules. We have proposed recently a combined protocol to analyze charge injection/extraction, transport, trapping and detrapping in low mobility materials. The experimental results demonstrate that the method can be used to obtain a complex thermogram which contains information about all molecular movements, even at nanoscopic level. Actually during the charging process we are decorating the structure with space charge and during the subsequent heating we are observing an apparent peak and the genuine peaks that are related to charge de-trapping determined by the molecular movement. The method is very sensitive, very selective and allows to determinate the parameters for local and collective molecular movements, including the temperature dependence of the activation energy and the relaxation time.
Authors: Paulo Inácio, José N. Marat-Mendes, C.J. Dias
Abstract: Most piezoelectric biosensors normally use crystals, as in the quartz crystal microbalances or surface acoustic wave devices. A new system is described in which piezoelectric polymer films (made of polyvinylidene fluoride, PVDF, and Immobilon, a porous type of PVDF) are used to produce a mass sensitive oscillatory resonant device. Recent results demonstrated that this system successfully detects the binding between bovine IgG (immunoglobulin G) and anti bovine IgG. In order to improve the performance of the biosensor the electromechanical behaviour of such film-membrane is being studied. Miniaturization is also a desirable trend which will be pursued. Thus reports on the dependence on the electrical, mechanical and biological properties with the size of the film will be presented.
Authors: Rui Igreja, H. Domingos, João P. Borges, C.J. Dias
Abstract: Chemocapacitors are polymer coated Interdigital electrodes (IDE) where the transducer mechanism relies on the permittivity changes and swelling of the coating polymer (sensitive layer), usually in a form of a thin film, when exposed to an volatile organic compound (VOC). Despite several synthetic and natural polymers have already been produced by electrospinning, there have been fewer studies on rubbery polymers with low glass transition temperature (e.g. Poly(dimethyl siloxane) – PDMS). In this work we produce PDMS:PMMA 3:1 nanofiber (NF) layers by electrospinnig to be used as chemical sensitive layers on IDE chemocapacitors. The results show an enhanced response from the sensors with NFs with respect with sensors prepared with the same sensitive layers in the form of a homogeneous film.
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