1,721,053 research outputs found
Energy Harvesting Based on Bistable Shape Memory Film Actuation
Get PDFMost microsensors, microdrivers, and low-power devices for wearable devices require continuous power supply through batteries. However, with the increase in the number and density of electronic devices, the demand for the number of batteries will increase rapidly, which brings many severe problems such as battery recycling and waste battery pollution. In order to overcome these drawbacks, it is of practical significance to develop micro-energy technology to harvest energy from the surrounding environment. Among the different energy sources, thermal energy is widely present in industrial production but often neglected and not effectively used. Direct thermoelectric conversion requires large temperature gradients and it is difficult to sustain sufficient temperature gradients for practical applications. Besides, miniaturization is necessary to enable thermoelectric energy harvesting technology to be more competitive compared to batteries. There are still many difficulties in the miniaturization of current thermoelectric technology. When the volume is miniaturized to a certain extent, heat dissipation by air convection will not be able to meet the cooling demand and large heat sinks are needed, thus limiting the miniaturization. Thermoelastic materials that can produce work by heating or cooling open up new approaches to overcome the limitations of miniaturized thermal energy harvesting systems.
Shape memory alloy (SMA) microactuators enable the conversion of modest heat quantities into usable work output within a limited temperature range due to high power/weight ratio, low cost and easy machining. Additionally, SMA film becomes an attractive candidate for thermal energy harvesting, since the SMA film produces substantial stress on heating and promises efficient heat transfer property due to the high surface-to-volume ratio. At a certain critical temperature, the SMA undergoes a phase transformation dominated by shear distortions of the crystal lattice, which can be utilized to drive mechanical systems or generate electrical energy through oscillation induced by the shape memory effect.
This work presents a SMA-based bistable actuator and a miniature-scale thermal energy harvester, which can be applied in a low-grade temperature range for waste heat recovery. The starting material is an unstructured free-standing TiNiCu film of 15µm thickness, which has been prepared by magnetron sputtering followed by crystallization by rapid thermal annealing. The bistable SMA film actuator consists of two antagonistically coupled pre-deflected SMA beams, a spacer and two heat sources. The antagonistic coupling beams achieve a bi-directional snapping motion by alternately heating, which results in an oscillatory snapping motion. The stationary force-displacement characteristics of monostable actuators consisting of single buckling SMA beams and bistable actuators are characterized with respect to their geometrical parameters. The dynamic performance of bistable actuation is investigated by selectively heating the SMA beams via direct mechanical contact with a heat source below the temperature of 190°C. The bistable actuation is characterized by a large stroke up to 3.65 mm, corresponding to more than 30% of the SMA beam length. Operation frequencies are in the order of 1 Hz depending on geometrical parameters and heat source temperature.
When the bistable SMA actuator is located in the magnetic field induced by a miniature permanent magnet and the spacer is replaced with a miniature coil, the pick-up coil can convert the mechanical oscillation to electricity according to Faraday\u27s law. After optimization of the magnet position, the heat source position, the heat source temperature, the distance between two beams, and the turns of the pick-up coil, thermal energy harvesting demonstrated a maximum output voltage of 57 mV with a thermal actuation frequency of 1.2 Hz. By reducing the number of turns of the pick-up coil to 100 turns, the oscillation frequency of the bistable energy harvester can be increased to 1.56 Hz, an improvement of 30%. After optimizing the external resistor, the maximum peak power density reaches 16.2 μW/cm2. In addition to actuators, SMA beams can also be used as electrodes for triboelectric nanogenerators (TENG). The SMA beams are able to contact and separate from a Kapton film attached to the heat source during selective heating of the bistable actuator. Relying on the principles of contact initiation and electrostatic induction, the contact-separation mode TENG generates a peak power density of 2.4 μW/cm2. Different energy harvesting units can either work independently and simultaneously or be connected in series or parallel to increase the power density, which can increase the total output of the energy harvesting device.
The results of this work provide the basis for the design of novel waste-heat thermal actuators operating at low-temperature differences. The bistable thermoelastic energy harvester presents an environmentally friendly approach for converting waste heat energy from the surrounding environment into reusable electrical energy
Propiedades mecánicas y calóricas de cintas elaboradas por solidificación rápida de aleaciones ferromagnéticas con memoria de forma base Níquel
Get PDF127 p.Se presentan estudios de efecto magnetocalórico (MCE) y elastocalórico (eCE) en cintas con memoria de forma Ni50-xMn40Sn10Fex. Se encontró que la adición de Fe genera un incremento de la red cristalina y de la interacción ferromagnética. MCE es mayor al aumentar la adición de Fe. La contribución magnética genera un aumento del cambio de entropía total. -Efecto de la rapidez de enfriamiento sobre la transformación martensítica y MCE en las cintas de Ni50Mn35In15. La rapidez de enfriamiento genera un cambio de orden químico. Un mayor orden químico (L21) genera mayores valores de MCE y menor interacción antiferromagnética. Se reportan medidas directas de cambio de temperatura adiabática realizadas en cintas. -Propiedades mecánicas y eCE de las cintas elaboradas por solidificación rápida de aleaciones ferromagnéticas con memoria de forma base Ni-Fe-Ga y Ni-Mn-Sn. La existencia de un efecto a anómalo en las curvas de deformación-temperatura genera un eCE convencional e inverso en el material originado por esfuerzos internos. -Comportamiento de la transformación martensítica y efectos calóricos inversos en la aleación con memoria de forma magnética Ni44-xCuxCo6Mn39Sn11. Se reportan EMC y eCE inverso y convencional. La adición de Cu genera una disminución de las temperaturas de TM y un aumento en la histéresis térmica. Se reporta que los esfuerzos internos generan eCE inverso.Instituto Potosino de Investigación Científica y Tecnológic
Energy Harvesting Based on Bistable Shape Memory Film Actuation
Get PDFThis work presents a SMA-based bistable actuator and a miniature-scale thermal energy harvester. The dynamic performance of bistable actuation is investigated by selectively heating. Different energy harvesting units can either work independently and simultaneously or be connected in series or parallel to increase the power density. The results of this work provide the basis for the design of novel waste-heat thermal actuators operating at low-temperature differences
“Propiedades mecánicas y calóricas de cintas elaboradas por solidificación rápida de aleaciones ferromagnéticas con memoria de forma base Níquel”
Get PDFTesis (Doctorado en Nanociencias y Nanotecnología)"La refrigeración en estado sólido basada en efectos calóricos es una tecnología amigable con el medio y con una eficiencia energética mayor respecto a la convencional. Un efecto calórico es la respuesta térmica de un material al aplicar o remover una carga uniaxial o un campo magnético, por lo que se clasifican en elasto (eCE) y magnetocalórico (MCE), respectivamente. En el presente trabajo se presentan los resultados de dichos efectos mediante mediadas directas de cambio de temperatura adiabática (Tad) e indirectas (Siso) realizadas en cintas de cuatro diferentes estudios: en el primer estudio se estudia el efecto de la adición de Fe en Ni-Mn-Sn sobre el MCE, donde la adición de Fe genera una disminución de las temperaturas de transformación martensítica (TM) y un incremento en el cambio de entropía magnética relacionado con el volumen de la celda cristalina. En el segundo estudio, se ha reporta el efecto de la rapidez de enfriamiento en el sistema Ni-Mn-In sobre la TM y el MCE. La rapidez de enfriamiento modifica el orden químico de la fase austenita, modificándose así las propiedades magnéticas. Cuando la rapidez de enfriamiento es menor, la fase mayoritaria tiene una estructura cristalina tipo L21 y el MCE es mayor que cuando el material presenta una estructura B2. Además, se presentan por primera vez medidas directas del MCE en cintas. En el tercer estudio, se estudió el eCE de las cintas de aleaciones Ni-Mn-Sn y Ni-Fe-Ga, las cuales muestran un aparente eCE inverso a bajos esfuerzos. Se concluyó que este se debe a los esfuerzos internos que se generan en la solidificación rápida. Por último, se presentan los resultados de la adición de Cu en el sistema Ni-Mn-Sn-Co, donde la adición de Cu genera una disminución de las temperaturas de TM y un incremento en la histéresis térmica. Durante la TM el material presenta un MCE y eCE inversos."Financial support from CONACYT Mexico (project No. CB-2010-01-157541)
Spanish Ministry of Economy and Competitiveness (MAT2014-56116-C4-3-4-R
Development of Heusler-alloy. based magnetocaloric inks for 2D - 3D printing
No full text206 p.This doctoral thesis explores sustainable cooling technologies through the magnetocaloric effect. Focusing on NiMn-based Heusler alloys, the research investigates the impact of composition and annealing effect on magnetic and magnetocaloric properties. Melt-spun ribbons undergo a systematic heat treatments, and a refined powder preparation from the ribbons seeks the preservation of magnetocaloric properties. The implementation in additive manufacturing of magnetocaloric materials is done developing a cost-effective 3D printing technique and using cellulose as an environmentally friendly polymeric alternative exploring the novel cold extrusion 3D printing technique.Post-printed structures undergo a meticulous heat treatments for obtaining fully metallic structures, balancing mechanical integrity with magnetocaloric effects. The objective is to demonstrate sustained retention of magnetocaloric properties throughout alloy fabrication, heat treatment, grinding, additive manufacturing, and sintering. The findings contribute insights into practical applications of Heusler alloys and advance materials with enhanced magnetocaloric functionalities in additive manufacturing, offering a significant contribution to the quest for energy-efficient cooling solutions.bcmaterials: basque center for materials, applications & nanostructure
Development of new Ni-Mn-Ga based high temperature shape memory alloys.
Get PDF146 p.Desarrollo de aleaciones con memoria de forma, tanto como convencional, SMAs, como magnética, FSMAs, para aplicaciones a alta temperatura. Estudio de las propiedades magnéticas, estructurales y mecánicas de las aleaciones tipo Heusler con base Ni2MnGa. En esta tesis se desarrollaron SMAs monocristalinos, con actuación a 670 K, mostrándose deformaciones del 4%. Se estudiaron sistemas de FSMAs multicomponentes policristalinos de Ni-Mn-Ga-Fe-Co-Cu, y se determinándose la relación existente entre la composición y las distintas propiedades. De entre los sistemas estudiados se obtuvieron 3 composiciones que mostraban temperaturas de transformación por encima de los 373 K y temperaturas de Curie mayores de 423 K. El estudio de neutrones realizado en las muestras multicomponentes ha permitido dilucidar el orden atómico presente en estas aleaciones y correlacionarlo con el aumento de la imanación de saturación mediante la variación de las interacciones entre manganesos. Por último, se ha analizado la relación entre la composición y la estructura con los parámetros críticos para la obtención de memoria de forma magnética, en monocristales de FSMAs de alta temperatura
Development of new Ni-Mn-Ga based high temperature shape memory alloys.
Get PDF146 p.Desarrollo de aleaciones con memoria de forma, tanto como convencional, SMAs, como magnética, FSMAs, para aplicaciones a alta temperatura. Estudio de las propiedades magnéticas, estructurales y mecánicas de las aleaciones tipo Heusler con base Ni2MnGa. En esta tesis se desarrollaron SMAs monocristalinos, con actuación a 670 K, mostrándose deformaciones del 4%. Se estudiaron sistemas de FSMAs multicomponentes policristalinos de Ni-Mn-Ga-Fe-Co-Cu, y se determinándose la relación existente entre la composición y las distintas propiedades. De entre los sistemas estudiados se obtuvieron 3 composiciones que mostraban temperaturas de transformación por encima de los 373 K y temperaturas de Curie mayores de 423 K. El estudio de neutrones realizado en las muestras multicomponentes ha permitido dilucidar el orden atómico presente en estas aleaciones y correlacionarlo con el aumento de la imanación de saturación mediante la variación de las interacciones entre manganesos. Por último, se ha analizado la relación entre la composición y la estructura con los parámetros críticos para la obtención de memoria de forma magnética, en monocristales de FSMAs de alta temperatura
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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