Dynamic resistance, which occurs when a HTS coated conductor carries a DC current under an AC magnetic field, can have critical implications for the design of HTS machines. Here, we report measurements of dynamic resistance in a commercially available SuperPower 4 mm-wide YBCO coated conductor, carrying a DC current under an applied AC magnetic field of arbitrary orientation. The reduced DC current, It/Ic0, ranged from 0.01 to 0.9, where It is the DC current level and Ic0 is the self-field critical current of the conductor. The field angle (the angle between the magnetic field and the normal vector of the conductor wide-face) was varied between 0° and 90° at intervals of 10. We show that the effective width of the conductor under study is ~12% less than the physical wire width, and we attribute this difference to edge damage of the wire during or after manufacture. We then examine the measured dynamic resistance of this wire under perpendicular applied fields at very low DC current levels. In this regime we find that the threshold field, Bth, of the conductor is well described by the non-linear equation of Mikitik and Brandt. However, this model consistently underestimates the threshold field at higher current levels. As such, the dynamic resistance in a coated conductor under perpendicular magnetic fields is best described using two different equations for each of the low and high DC current regimes. At low DC currents where It/Ic0 0.1, the non-linear relationship of Mikitik and Brandt provides the closest agreement with experimental data. However, in the higher current regime where It/Ic0 ≥ 0.2, closer agreement is obtained using a simple linear expression which assumes a current-independent penetration field. We further show that for the conductor studied here, the measured dynamic resistance at different field angles is dominated by the perpendicular magnetic field component, with negligible contribution from the parallel component. Our findings now enable the dynamic resistance of a single conductor to be analytically determined for a very wide range of DC currents and at all applied field angles.
Magnetic small-scale robots are devices of great potential for the biomedical field because of the several benefits of this method of actuation. Recent work on the development of these devices has seen tremendous innovation and refinement toward improved performance for potential clinical applications. This review briefly details recent advancements in small-scale robots used for biomedical applications, covering their design, fabrication, applications, and demonstration of ability, and identifies the gap in studies and the difficulties that have persisted in the optimization of the use of these devices. In addition, alternative biomedical applications are also suggested for some of the technologies that show potential for other functions. This study concludes that although the field of small-scale robot research is highly innovative there is need for more concerted efforts to improve functionality and reliability of these devices particularly in clinical applications. Finally, further suggestions are made toward the achievement of commercialization for these devices.
High-T c superconducting (HTS)-coated conductors are a promising option for the next-generation power devices. However, their thin-film geometry incurs dynamic loss when exposed to a perpendicular external ac magnetic field, which is difficult to predicate and estimate. In this paper, we propose and verify a numerical simulation model to predict the dynamic loss in HTSthin-coated conductors by taking into account their J c-B dependence and I-V characteristics. The model has been tested on a SuperPower YBCO-coated conductor, and we observed a linear increase of dynamic loss along the increasing field amplitude after the threshold field. Our simulation results agree closely with experimental measurements as well as an analytical model. Furthermore, the model can predict the nonlinear increase of dynamic loss at high current, while the analytical model deviates from the measurement results and still shows a linear correlation between the dynamic loss and the external magnetic field. In addition, we have used this model to simulate the distributions of magnetic field and current density when dynamic loss occurs. Results clearly show the flux traversing the coated conductor, which causes dynamic loss. Q1 The distributions have also been used to analyze the dynamic loss when the transport current and the magnetic field increase individually, while the other factor remains constant. The simulation analysis on dynamic loss is done for the first time in this paper, and our results clearly demonstrate how dynamic loss changes and its dependence on transport current and magnetic field. Index Terms-Coated conductor, current distribution, dynamic loss, magnetic field distribution, perpendicular magnetic field. I. INTRODUCTION D YNAMIC loss occurs when a superconductor carrying dc transport current is exposed to an external alternating magnetic field [1]-[3]. This is particularly important to high-T c-superconducting (HTS)-coated conductors, which have emerged as a promising option for the next-generation power devices, such as rotating machines [5]-[7] as well as associated
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