1,721,057 research outputs found
A novel high-power density, low-frequency electromagnetic vibration energy harvester based on anti-phase motion
No full textThe paper proposes a novel electromagnetic vibration energy harvester based on the concept of anti-phase vibration. Anti-phase motion is desirable in electromagnetic vibration energy harvesting applications as it results in a higher power output due to the increase in the relative velocity between the coil and the magnet components. The proposed device achieves anti-phase motion at any driving frequency due to a developed new design. The harvester was experimentally tested under a base input of 0.49 g, 0.38 g and 0.36 g, recording a power density of 765.3 Wm−3, 420.8 Wm−3 and 587.2 Wm−3 respectively under a resonant frequency of 11.8 Hz. Although the device has not yet been optimised, these values obtained are already comparable, if not higher than the recent previous works on vibration energy harvesting. In addition, the observed experimental results have well agreed with the results obtained through the mathematical model, derived in this study. The original design was then optimised to determine the optimum load resistance, mechanical arm length and component dimensions that would result in the maximum power output. Considering a base input of 0.36 g and the same friction and damping forces as obtained from the experiment, a power density of 1708.5 Wm−3 could theoretically be achieved under the same natural frequency
Important considerations in optimising the structural aspect of a SDOF electromagnetic vibration energy harvester
Full text linkThis study investigates several important considerations to be made when optimising the structural aspects of a single-degree-of-freedom (SDOF) electromagnetic vibration energy harvester. Using the critically damped stress method, the damping and power output of the harvester were modelled and verified, displaying an excellent agreement with the experimental results. The SDOF harvester was structurally optimised under a certain set of constraints and it was found that under the fixed beam's thickness condition, the harvester displayed an insignificant increase in power output as a function of volume when the device's size was relatively larger. This highlights the importance of considering a smaller practical volume for this case. Additionally, when optimising the device using a low stress constraint and a low damping material, it was observed that considering the load resistance as an input parameter to the objective function would lead to a higher power output compared to the optimum load resistance condition. Further analysis indicated that there exists a power limit when the electromagnetic coupling coefficient approaches infinity. For the case of a high electromagnetic coupling coefficient value and a small volume constraint, it is possible to achieve approximately 80.0% of the harvester's power limit. Finally, it was demonstrated that a high power output can be achieved for a SDOF electromagnetic harvester by considering a high-density proof mass centred at the free end of the beam
A two-stage electromagnetic coupling and structural optimisation for vibration energy harvesters
No full textThis paper demonstrates a two-stage optimisation for a single-degree-of-freedom (SDOF) electromagnetic vibration energy harvester under a harmonic base excitation vibration. In this paper, a designed cantilever beam was used to verify the optimisation methods. The dynamics of the beam was modelled using the Euler-Bernoulli beam theory. By deriving the exact expression of the power output under the optimum load resistance condition, the correct electromagnetic coupling coefficient was determined. The first optimisation stage involves maximising this coefficient by considering several coils and magnet parameters, allowing at this stage to define the electrical efficiency of the harvester which is described as the ratio of the harvester's power output to its power limit. The experimentally determined power output for this stage was 3.51 mW. The structural aspects of the harvester were then optimised by considering the addition and placement of proof masses and the structural dimensions of the harvester. This part represents the second optimisation and determines the power limit of the harvester. An experimental power output of 7.95 mW was achieved in this stage. All experimental results displayed a good agreement with the derived theoretical model, recording an error of less than 10.0%, hence validating the theoretical model. The first optimisation stage presented here can be applied to any linear electromagnetic SDOF harvester whereas the second optimisation stage can be easily modified to suit different structural considerations. Additionally, both stages can also be slightly modified to account for rotational systems. </p
Structural optimisation through material selections for multi-cantilevered vibration electromagnetic energy harvesters
No full textThis study investigates the structural optimisation of a multi-cantilevered electromagnetic anti-phase energy harvester by considering the optimum material choice. The mathematical model for the harvester was first developed, displaying an excellent correlation when compared with the experimental results. Afterwards, the anti-phase harvester was structurally optimised under a defined set of constraints while only considering a single material for all cantilever beams. Here, three materials with low damping capacity were considered. It was found that if the beam thickness was unchanged, the optimisation for certain materials would not converge due to high stress levels exceeding the fatigue safety factor of 80.0%. The safety factor was implemented in the optimisation to ensure the device's durability. However, the unsuccessful material exhibited the lowest damping capacity among other materials. Hence, a mixed material approach was attempted which produced an optimum power output of 119.6 mW and a 1.76 V voltage output under a base acceleration input of 0.1 g and a practical volume constraint of 600 cm3. This corresponds to a 33.3% increase in power output when compared to the single material harvester. Further analysis demonstrated that if the fatigue safety factor was lowered to 60%, the optimised power output would drop by 26.5% to 87.9 mW whereas a slight increase in voltage was recorded. Finally, the optimum material for the masses on the harvester was examined, suggesting that a high-density material must be used for the beam clamp and the proof masses on the magnet beams whereas the mass on the support beam must be minimized.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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