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Analysis of energy conversion capability among various magnetostrictive materials for energy harvesting

Abstract This work addresses vibrational energy harvesting using magnetostrictive materials. In this field, materials with exceptional magneto-mechanical coupling properties (e.g., Galfenol, Terfenol-D) have attracted significant attention. Only a few magnetostrictive materials have been tested in devices, however, leaving the actual influence of these materials’ properties on the energy harvesting device open to question. This work compares an extensive range of ferromagnetic materials through analysis of their magnetic behavior under static stress. To enable fair comparison of the materials, a model was developed to interpolate their magnetic anhysteretic curves under fixed stress of σ = ±50 MPa. The energy harvesting process was then simulated using a theoretical Ericsson thermodynamic cycle, where the area represents the energy density. This approach estimates the ultimate energy density of the materials using a fair approach, without placing conditions on the applied magnetic field. The correlation between ultimate energy density and the magnetoelastic coefficient show that highly magnetostrictive materials achieve higher ultimate energy densities, as expected. In the low field range, it is however concluded that all materials exhibit energy densities of the same order of magnitude. Secondly, the magnetoelastic coefficient versus excitation field characteristics revealed an optimal bias magnetic field for each material. Finally, for realistic implementation, the paper considers a pre-stress in combination with a bias magnetic field and the small dynamic variations that result from currents induced in surrounding coils. A model was developed and revealed an optimum output energy density that was independent of the geometry and the coil. An energy harvesting figure of merit was then defined to enable a final comparison of the materials, encompassing both material characteristics and realistic applications. Under these working conditions and with all costs considered, some low-magnetostriction materials appeared able to compete with giant magnetostriction materials.

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Analogous piezoelectric network for multimodal vibration attenuation of a thin circular ring

Structural vibrations can be reduced by coupling to a piezoelectric electrical network that exhibits analogous modal properties of the structure. This paper considers the multimodal vibration damping of a thin circular ring using this method. The electrical network is derived by applying a finite difference model to the governing equations of motion for a segment of a thin curved beam. An electromechanical analogy is then applied to the physical constants. The resulting passive electrical network unit cell is a topology of capacitors, inductors, and transformers analogous to the dynamics of a segment of curved beam. The electrical network for a curved beam is simplified by considering an inextensional assumption and combining edge components in adjacent unit cells. The resulting simplified discrete network for a curved beam segment is assembled into a complete network for a circular ring. The electrical network for a circular ring displays modal properties similar to its mechanical analogue in both the spatial and frequency domains. As a result of the analogous modal properties across the frequency spectrum, it is shown that the network can be used to achieve multimodal vibration attenuation across a large frequency spectrum. Piezoelectric patches are used to couple the two domains. Numerical simulation of the coupled system demonstrates the effectiveness of the broadband damping effects from the analogous network. Notably, this research establishes a novelty in the field, as it not only introduces experimental validation of curved beam analogues, but also extends the investigation to encompass the coupling between a circular ring and its piezoelectric electrical network counterpart. Further experimental network optimization demonstrate the possibility of tuning the network to adapt to an imperfect mechanical ring.

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An ensemble approach for enhancing generalization and extendibility of deep learning facilitated by transfer learning: principle and application in curing monitoring

Machine learning (ML) and deep learning (DL) have exhibited significant advantages compared to conventional data analysis methods. However, the limitations of poor generalization and extendibility impede the broader application of these methods beyond specific learning tasks. To address this challenge, this study proposes a transfer learning-based ensemble approach called SMART. This approach incorporates synthetic minority oversampling technique, average reinforced interpolation, series data imaging, and fine-tuning. To validate the effectiveness of SMART, we conduct experiments on curing monitoring of polymeric composites and construct a hybrid dataset with highly heterogeneous features. We compare the performance of SMART with exemplary ML algorithms using conventional evaluation indicators, including Accuracy, Precision, Recall, and F1-score. The experimental results demonstrate that the SMART approach exhibits superior generalization capacity and extendibility, achieving indicator scores above 0.9900 in new scenarios. These findings suggest that the proposed SMART approach has the potential to break through the limitations of conventional ML and DL models, enabling wider applications in the industrial sectors.

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Parametric investigations of wireless energy transfer using strain-mediated magnetoelectric transmitter-receiver

Magnetoelectric (ME) composites inherently convert magnetic energy to electrical energy and vice-versa, making them a viable technology in wireless energy transfer (WET) applications. This article focuses on identifying the optimal configuration for achieving relatively high ME power conversion efficiency in a fully ME-based transmitter/receiver composite system. Two configurations of ME composites, one in concentric composite rings and the other in layered laminate formation, have been fabricated and used alternately as transmitters and receivers. The influence of three important parameters has been experimentally studied and reported, including the effect of (1) the magnetization state of the magnetostrictive components and (2) the relative orientation of and (3) the separation distance between the transmitter and the receiver. It has been found that a higher energy conversion efficiency is obtained in a configuration where the laminated plate was used as the transmitter while the ring composites acted as the receiver. Furthermore, the location and alignment of the receiver significantly influence the output transferred power. Lastly, the distance between the transmitter and the receiver has been observed to have an exponential inverse influence on the performance of the investigated WET system. These results have been deciphered by experimentally generating horizontal and vertical magnetic field mapping around the composite systems and capacitance measurement of the piezoelectric element. Thus, this article presents a detailed study of the parameters and their influence on the performance of the ME-based WET technology, which would be extremely useful in designing and optimizing devices based on this technology.

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Full-field deformation reconstruction for large-scale cryogenic composite tanks with limited strain monitoring data

Online deformation monitoring, while of paramount importance in safety evaluation for aerospace composite tanks, is highly challenging due to the complex strain distributions in the composite tank and the strict restrictions of sensor placement. In this study, full-field deformation of large-scale cryogenic composite tanks were reconstructed under thermo-mechanical coupling conditions. In essence, the inner surface strains in the junction area of the head and cylindrical shell of the tank, defined as the ‘H-C portion’, was derived theoretically based on outer-surface strain measurement. The inverse finite element method (iFEM) was then applied using the measured and derived strains to reconstruct the full-field deformed shape of the tank. A systematic and efficient parametric discussion was conducted using an orthotropic model equivalent with composite laminated models with different lay-ups. The influences of various factors relevant to the material and geometries of the tank on the accuracy of deformation reconstruction were unveiled. Finally, a numerical experiment was carried out to reconstruct the full-field deformation of a large-scale aerospace composite tank with a specific lay-up, where limited strain data analogous to those sparely measured using distributed optical fiber sensors was used. It was found that the sensor placement strategy markedly affects the accuracy of deformation reconstruction.

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