79 research outputs found

    EWOD using nonaqueous liquids

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    Electrowetting on Dielectric (EWOD) has been studied for more than a decade and used for different applications but still there are few works on non-aqueous liquids such as mixtures of polyols. We have found that significant contact angle change can be achieved at voltages of 10 V and bellow and that the recovery, when the voltage is withdrawn, exceeds 92% in all the cases. The dynamic change of contact angle has been measured applying 2 Hz and 5 Hz square 10 V amplitude signal. The operation is stable but has a cut-off frequency in the range of frequency explored. Those results have been achieved using a glass substrate covered by an ITO electrode followed by a thin alumina layer and by a Teflon layer. We have also observed that the use of an HMDS layer followed by an ALD alumina layer prior to Teflon deposition provides better initial contact angle value, and that it can be achieved a significant contact angle change at lower voltages. Up to 1000 switch cycles have been performed and the contact angle change when using DI water rapidly becomes insignificant whereas with the polyol mixtures, although we have observed contact angle change degradation, it gets to a stable value thereafter.Peer ReviewedPostprint (updated version

    Effect of dielectrophoretic force in the self-assembly process of electrosprayed nanoparticles

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    In this work the effect of the dielectrophoretic force (DEP) in the self-assembly process of nanoparticles electrosprayed onto a substrate, is examined. DEP force is originated by the electric field created by the electrospray gun and by the distortion of the field created by the effective dipole of each nanoparticle. It is also shown that the modulus of this force is large when the distance between particles is few times its diameter, provided the medium is wet and the electric field is not switched off. The directional nature of DEP In this wet phase, is shown to chain nanoparticles aligned with the main electric field direction. Although there is a repulsive force between chains in the orthogonal direction to the field, it is minimum when the beads align with the voids in the nearby chains. DEP is a dominant force in the close distances of nanoparticles compared to double layer, van der Waals, electrophoretic retardation, weight and buoyancy.Preprin

    Capacitance study of a polystyrene nanoparticle capacitor using impedance spectroscopy

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    In this study, a metal-insulator-metal capacitor structure is fabricated using polystyrene nanoparticles. Impedance spectroscopy is used to evaluate the performance of this capacitor in which we found a significant magnitude increment in capacitance and loss tangent compared with an equivalent ideal capacitor with continuous polystyrene layer and same geometry. Capacitance values up to 11.7 and loss tangent values up to 387 (at 0.1 Hz) larger than the expected for a continuous polystyrene MIM capacitor are achieved. The capacitor shows a good stable capacitive behaviour in the frequency range from 0.1 Hz to 100 kHz at room temperature, 30 °C, 40 °C and 50 °C without an effective relaxation process. Nyquist, capacitance, loss tangent and normalized powers curves are analysed by modified Randles model. Also, a slight decrease in the capacitance value at 50 °C is observed, which that may be attributed to space charge localized at the nanoparticles interface and that are affected by the temperature changes.Peer ReviewedPostprint (author's final draft

    Acceleration of the measurement time of thermopiles using sigma-delta control

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    This work presents a double sliding mode control designed for accelerating the measurement of heat fluxes using thermopiles. The slow transient response generated in the thermopile, when it is placed in contact with the surface to be measured, is due to the changes in the temperature distributions that this operation triggers. It is shown that under some conditions the proposed controls keep the temperature distribution of the whole system constant and that changes in the heat flux at the thermopile are almost instantaneously compensated by the controls. One-dimensional simulations and experimental results using a commercial thermopile, showing the goodness of the proposed approach, are presented. A first rigorous analysis of the control using the Sliding Mode Control and Diffusive Representation theories is also made.Peer ReviewedPostprint (published version

    A miniaturized 3d heat flux sensor to characterize heat transfer in regolith of planets and small bodies

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    The objective of this work is to present the first analytical and experimental results obtained with a 3D heat flux sensor for planetary regolith. The proposed structure, a sphere divided in four sectors, is sensible to heat flow magnitude and angle. Each sector includes a platinum resistor that is used both to sense its temperature and provide heating power. By operating the sectors at constant temperature, the sensor gives a response that is proportional to the heat flux vector in the regolith. The response of the sensor is therefore independent of the thermal conductivity of the regolith. A complete analytical solution of the response of the sensor is presented. The sensor may be used to provide information on the instantaneous local thermal environment surrounding a lander in planetary exploration or in small bodies like asteroids. To the best knowledge of the authors, this is the first sensor capable of measuring local 3D heat fluxThis work was supported in part by the Spanish Ministerio de EconomĂ­a y Competividad under Projects RTI2018-098728-B-C31 and RTI2018-098728-B-C33Peer ReviewedPostprint (published version

    Towards photovoltaic powered artificial retina

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    The aim of this article is to provide an overview of current and future concepts in the field of retinal prostheses, and is focused on the power supply based on solar energy conversion; we introduce the possibility of using PV minimodules as power supply for a new concept of retinal prostheses: Photovoltaic Powered Artificial Retina (PVAR). Main characteristics of these PV modules are presented showing its potential for this application.Peer ReviewedPostprint (published version

    Correlation study between the access mark and the performance in project-based and standard courses

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    The access mark to engineering studies is often used as an a priori success estimator. In our institution, we have observed that the correlation of the access mark with the grades obtained in project-based courses (R=0.52) is slightly lower than the one obtained with the average of the other non-project-based courses (R=0.58), and is especially low in capstone projects (R=0.31). Project-based and Challenge-based courses are one of the most acknowledged ways of promoting the learning of transversal skills, specifically innovation and entrepreneurship skills. In our institution, ICT engineering bachelor students perform a project-courses path, with three subjects of growing complexity in the 2nd, 3d and 4th year. While the first two are partially guided and with challenges proposed by the faculty members, the 3d one is a 12 ECTS capstone project with challenges proposed by industry or external institutions. In this study, we have analyzed the performance of the students along 10 academic years (2011-2012 to 2020-2021). Not only the correlation with the access mark in these courses is lower but the prediction interval is also different. While it is almost impossible that a student with a low access mark gets an outstanding average mark in the bachelor and vice-versa, there are students with a low access mark which have an outstanding performance in the capstone project and students with a very high access mark and with high results in analytical courses but with a poor performance in capstone projects. Therefore, a different kind of skills are promoted in these courses

    Design and smart control of sensors for optimal performance: a application to wind sensing in Mars

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    Sensor performance in terms of time response and sensitivity can be dramatically enhanced by operating sensors under what may be called a “constant state operation”. This means that any change in the sensor due to external factors (including the ones to be measured) is compensated by the smart control, so that state of the sensor does not change with time. This idea has been applied to thermal anemometry in Mars (for REMS, TWINS and MEDA) by using constant temperature operation and differential thermal conductance estimators. In the case of our miniature spherical wind sensor for future missions, this principle requires a careful thermal design ensuring that single time constant operation is ensured, [1-3]. Experiments show that it is possible to obtain response times (1s) well below the open loop time constants. Additionally, the performance of the sensor at the Aarhus Martian wind tunnel are presented, as well as experiments in the Reynolds regime 1000-10e4, with equivalent Mars wind velocities in the range 100-150m/s.Peer ReviewedPostprint (published version
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