• Journal of Power Electronics
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• v.16 no.1
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• pp.48-56
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• 2016

This paper proposes a method for detecting irreversible demagnetization using the harmonic analysis of back electromotive force (BEMF) in interior permanent magnet-type brushless DC motors. First, demagnetization patterns, such as equality, inequality, and weighted demagnetizations, are defined and classified by considering the possibility of demagnetization resulting from motor operating characteristics. Second, an available diagnostic model for the harmonic analysis of BEMFs is defined according to pole-slot coefficients because the characteristics of BEMFs under demagnetization conditions are affected by the combination of poles and slots. Third, BEMFs and their harmonic components under normal and demagnetization conditions are analyzed through simulation and experiment to verify the proposed demagnetization detection technique.

• Proceedings of the Korean Magnestics Society Conference
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• 2013.05a
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• pp.74-75
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• 2013

In summary, the ferromagnetic resonance experiments was applied to investigate the magnetic properties of $Co_{16}Fe_{64}B_{20}$ thin films and nanowire patterns. We find that the saturated magnetization and demagnetization factors. And we will compare experimental result with the micromagnetic simulations.

• Ocean and Polar Research
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• v.36 no.4
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• pp.395-405
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• 2014

A 570 cm-long sediment core was retrieved at $9^{\circ}57^{\prime}N$ and $131^{\circ}42^{\prime}W$ in 5,080 m water depth from the northeast equatorial Pacific and its stratigraphy was established with $^{10}Be/^9Be$ and paleomagnetic measurements. Successive AF demagnetization reveals eight geomagnetic field reversals. In the reference geologic time scale, the eight reversal events correspond to an age of about 4.5 Ma. However, $^{10}Be/^9Be$-based age yields 9.5 Ma at a depth of 372 cm. Such a large discrepancy in determined ages is attributed to an extremely low sedimentation rate, 0.4 mm/kyr on average, of the study core and resultant loss or smoothing of geomagnetic fields. The composite age model reveals a wide range in the sedimentation rate - varying from 0.1 to 2.4 mm/kyr. However, the sedimentation rate shows systematic variation depending on sedimentary facies (Unit II and III), which suggests that each lithologic unit has a unique provenance and transport mechanism. At depths of 110-80 cm with a sedimentation rate of about 0.1 mm/kyr, ancient geomagnetic field reversal events of at least a 1.8 Myr time span have not been recorded, which indicates the probable existence of a hiatus in the interval. Such a sedimentary hiatus is observed widely in the deep-sea sediments of the NE equatorial Pacific.