Sensor material characterisation for magnetometer application

Pengukuran dan gangguan medan magnet arus terus dan arus ulang-alik memerlukan penderia medan magnet yang mempunyai kepekaan yang tinggi dan stabil. Untuk menghasilkan penderia tersebut, ciri-ciri bahan magnet yang baik telah dikenalpasti. Beberapa jenis bahan magnet yang berbeza telah digunakan untuk mengkaji ciri-ciri dan kesannya terhadap medan magnet. Teras gelang yang diperbuat daripada bahan-bahan magnet tersebut direkabentuk dengan dimensi yang sama bagi membolehkan perbandingan dibuat dengan mudah. Selain itu, rod tunggal dan berkembar juga telah digunakan sebagai teras penderia fluxgate, untuk melihat prestasi setiap jenis penderia tersebut. Kedua-dua penderia tersebut telah diuji dengan menggunakan dua sumber bahan magnet iaitu bar magnet tetap dan solenoid dengan diameter dawai yang berbeza. Isyarat keluaran bagi setiap penderia fluxgate seterusnya diproses bagi mengenalpasti hubungannya dengan ketumpatan medan magnet

Analytical Model of Magnet Eddy-Current Volume Losses in Multi-phase PM Machines with Concentrated Winding

Thanks to IEEE. The original PDF of the article can be found at: http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6342330&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D6342330 MHYGALE, project managed by VALEO-EEMthis paper studies magnet eddy-current losses in permanent magnet (PM) machines with concentrated winding. First of all, space harmonics of magnetomotive force (MMF) and their influence on magnet losses in electrical machines are investigated. Secondly, analytical model of magnet volume losses is developed by studying the interaction between MMF harmonics wavelengths and magnet pole dimensions. Different cases of this interaction are studied according to the ratio between each harmonic wavelength and magnet pole width (following flux density variation). Then various losses sub-models are deduced. Finally, using this analytical model, magnet volume losses for many slots/poles combinations of 3, 5, and 7 phase machines with concentrated winding are compared. This comparison leads to classify combinations into different families depending on their magnet losses level. Besides, in order to validate the theoretical study, Finite Element models are built and simulation results are compared with analytical calculations.MHYGALE/ADEM

Superconducting pipes and levitating magnets

Motivated by a beautiful demonstration of the Faraday's and Lenz's law in which a small neodymium magnet falls slowly through a conducting non-ferromagnetic tube, we consider the dynamics of a magnet falling through a superconducting pipe. Unlike the case of normal conducting pipes, in which the magnet quickly reaches the terminal velocity, inside a superconducting tube the magnet falls freely. On the other hand, to enter the pipe the magnet must overcome a large electromagnetic energy barrier. For sufficiently strong magnets, the barrier is so large that the magnet will not be able to penetrate it and will be suspended over the front edge. We calculate the work that must done to force the magnet to enter a superconducting tube. The calculations show that superconducting pipes are very efficient at screening magnetic fields. For example, the magnetic field of a dipole at the center of a short pipe of radius $a$ and length $L \approx a$ decays, in the axial direction, with a characteristic length $\xi \approx 0.26 a$. The efficient screening of the magnetic field might be useful for shielding highly sensitive superconducting quantum interference devices, SQUIDs. Finally, the motion of the magnet through a superconducting pipe is compared and contrasted to the flow of ions through a trans-membrane channel

Iron loss in permanent-magnet brushless AC machines under maximum torque per ampere and flux weakening control

The airgap flux density distribution, flux density loci in the stator core, and the associated iron loss in two topologies of brushless AC motor, having a surface-mounted magnet rotor and an interior-mounted magnet rotor, respectively, are investigated when operated under maximum torque per ampere control in the constant torque mode and maximum power control in the flux-weakening mode. It is shown that whilst the interior magnet topology is known to be eminently suitable for flux-weakening operation, due to its high demagnetization withstand capability, its iron loss can be significantly higher than for a surface-mounted magnet machine

Association of Magnet Status With Hospitalization Outcomes for Ischemic Stroke Patients.

BACKGROUND: It is not clear whether Magnet recognition by the American Nurses Credentialing Center (nursing excellence program) is associated with improved patient outcomes. We investigated whether hospitalization in a Magnet hospital is associated with improved outcomes for patients with ischemic stroke. METHODS AND RESULTS: We performed a cohort study of patients with ischemic stroke from 2009 to 2013, who were registered in the New York Statewide Planning and Research Cooperative System database. Propensity-score-adjusted multivariable regression models were used to adjust for known confounders, with mixed effects methods to control for clustering at the facility level. An instrumental variable analysis was used to control for unmeasured confounding and simulate the effect of a randomized trial. During the study period, 176 557 patients were admitted for ischemic stroke, and met the inclusion criteria. Of these, 32 092 (18.2%) were hospitalized in Magnet hospitals, and 144 465 (81.8%) in non-Magnet institutions. Instrumental variable analysis demonstrated that hospitalization in Magnet hospitals was associated with lower case-fatality (adjusted difference, -23.9%; 95% CI, -29.0% to -18.7%), length of stay (adjusted difference, -0.4; 95% CI, -0.8 to -0.1), and rate of discharge to a facility (adjusted difference, -16.5%; 95% CI, -20.0% to -13.0%) in comparison to non-Magnet hospitals. The same associations were present in propensity-score-adjusted mixed effects models. CONCLUSIONS: Using a comprehensive all-payer cohort of patients with ischemic stroke in New York State, we identified an association of treatment in Magnet hospitals with lower case-fatality, discharge to a facility, and length of stay. Further research into the factors contributing to the superiority of Magnet hospitals in stroke care is warranted

Interaction of a Magnet and a Point Charge: Unrecognized Internal Electromagnetic Momentum

Whereas nonrelativistic mechanics always connects the total momentum of a system to the motion of the center of mass, relativistic systems, such as interacting electromagnetic charges, can have internal linear momentum in the absence of motion of the center of energy of the system. This internal linear momentum of the system is related to the controversial concept of "hidden momentum." We suggest that the term "hidden momentum" be abandoned. Here we use the relativistic conservation law for the center of energy to give an unambiguous definition of the "internal momentum of a system," and then we exhibit this internal momentum for the system of a magnet (modeled as a circular ring of moving charges) and a distant static point charge. The calculations provide clear illustrations of this system for three cases: a) the moving charges of the magnet are assumed to continue in their unperturbed motion, b) the moving charges of the magnet are free to accelerate but have no mutual interactions, and c) the moving charges of the magnet are free to accelerate and also interact with each other. It is noted that when the current-carrying charges of the magnet are allowed to interact, the magnet itself will contain internal electromagnetic linear momentum, something which has not been presented clearly in the research and teaching literature.Comment: 23 pages. This manuscript is related to arXiv:1408.3741, but has been thoroughly revised with a different focu