We adopted a combination of pieces of permanent magnets and a single-channel (SC) shim coil to shim the magnetic field in a magnetic resonance imaging system dedicated for skeletal age assessment of children. The target magnet was a 0.3-T open and compact permanent magnet tailored to the hand imaging of young children. The homogeneity of the magnetic field was first improved by shimming using pieces of permanent magnets. The residual local inhomogeneity was then compensated for by shimming using the SC shim coil. The effectiveness of the shimming was measured by imaging the left hands of human subjects and evaluating the image quality. The magnetic resonance images for the child subject clearly visualized anatomical structures of all bones necessary for skeletal age assessment, demonstrating the usefulness of combined shimming.
Shingo Inamura, Student Member, Hironori Shibayama, Non-member, Koichiro Sawa, Member (Keio University)With recent remarkable development of power electronic technology, a Switched Reluctance Motor (SRM) has been widely studied for practical use. There still remain some problems to improve, e.g. relatively high torque ripples, electromagnetic noise and iron loss.We have concentrated on iron loss and discussed simple method to estimate it. The analysis of iron loss enables us to know not only total loss but also its distribution, therefore it would be possible to calculate the temperature analysis. A proposed method is based on 2D static Finite Element Analysis(FEA) and loss data given by open circuit test. Eddy current loss is evaluated by the frequency analysis of flux density waveforms using Fourier transform, while hysteresis loss is evaluated by the classification of the waveforms in each position of the magnetic circuit. The total loss and loss distribution are obtained. The validity of this method is verified in comparison with measured values in two types of SRM with different material property.
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