Decrease Of Magnetic Flux Density Research Articles

Pulse Field Magnetization of GdBCO Without Rapid Decrease in Magnetic Flux Density

Pulse Field Magnetization of GdBCO Without Rapid Decrease in Magnetic Flux Density

Three-degree-of-freedom positioning control of magnetically levitated permanent magnet planar motor using active disturbance rejection control scheme

Magnetically levitated permanent magnet planar motor is a new-generation motion device in modern precision industry, and the design of advanced motion controller has always been a main concern in the research and development of magnetically levitated permanent magnet planar motor. Due to the decrease in electromagnetic force caused by the deflection of the mover or the sharp decrease in magnetic flux density with height, it is very difficult to realize accurate positioning control of 3 degrees of freedom. In this article, an active disturbance rejection control scheme is adopted. The extended state observer is used to estimate the comprehensive disturbance and motion state in real time. Then, according to the value estimated by the extended state observer, the active disturbance rejection control motion controller can compensate the electromagnetic force in time to achieve good anti-jamming performance. Simulation and experimental results demonstrate that the adopted active disturbance rejection control scheme has good dynamic performance and uncertain disturbance robustness.

Effects of different rotation speeds on microstructure, hardness and corrosion resistance of the Au-Cu alloy

In this work, Au-Cu alloys were prepared using the permanent magnetic stirring method. A pair of permanent magnets driven by a rotating motor was selected to induce the rotating magnetic field. The influences of different rotation speeds on secondary dendrite arm spacing, dendritic segregation, hardness, and corrosion resistance of Au-Cu alloys were investigated. The experimental results revealed that the secondary dendrite arm spacing (SDAS) first decreased with the rotation speed increasing, and thereafter increased due to the sharp decrease of magnetic flux density. Generally, the dendritic structure of alloys can be refined remarkably by a rotating magnetic field, but with a too high rotation speed, the degree of grain refinement was reduced. Moreover, it was found that, the segregation of Au element only was slightly improved, but that of Cu was obviously increased by the permanent magnetic stirring. Along with the refinement of SDAS, the hardness and the corrosion resistance of Au-Cu alloys were significantly increased.

Magnetic Flux Density of Different Types of New Generation Magnetic Attachment Systems

The purpose of this study was to analyze the static magnetic flux density of different types of new generation laser-welded magnetic attachments in the single position and the attractive position and to determine the effect of different corrosive environments on magnetic flux density. Magnetic flux densities of four magnetic attachment systems (Hyper slim, Hicorex slim, Dyna, and Steco) were measured with a gaussmeter. Then magnetic attachment systems were immersed in two different media, namely 1% lactic acid solution (pH 2.3), and 0.9% NaCl solution (pH 7.3). Magnetic flux densities of the attachment systems were measured with a gaussmeter after immersion to compare with measurements before immersion (α = 0.05). The data were statistically evaluated with one-way ANOVA, paired-samples t-test, and post hoc Tukey-Kramer multiple comparisons tests (α = 0.05). The highest magnetic flux density was found in Dyna magnets for both single and attractive positions. In addition, after the magnets were in the corrosive environments for 2 weeks, they had a significant decrease in magnetic flux density (p < 0.05). No significant differences were found between corrosive environments (p > 0.05). The leakage flux of all the magnetic attachments did not exceed the WHO's guideline of 40 mT. The magnets exhibited a significant decrease in magnetic flux density after aging in corrosive environments including lactic acid and NaCl.

PHYSICAL PROPERTIES OF LARGE AND SMALL GRANULES IN SOLAR QUIET REGIONS

The normal mode observations of seven quiet regions obtained by the Hinode spacecraft are analyzed to study the physical properties of granules. An artificial intelligence technique is introduced to automatically find the spatial distribution of granules in feature spaces. In this work, we investigate the dependence of granular continuum intensity, mean Doppler velocity, and magnetic fields on granular diameter. We recognized 71,538 granules by an automatic segmentation technique and then extracted five properties: diameter, continuum intensity, Doppler velocity, and longitudinal and transverse magnetic flux density to describe the granules. To automatically explore the intrinsic structures of the granules in the five-dimensional parameter space, the X-means clustering algorithm and one-rule classifier are introduced to define the rules for classifying the granules. It is found that diameter is a dominating parameter in classifying the granules and two families of granules are derived: small granules with diameters smaller than 144, and large granules with diameters larger than 144. Based on statistical analysis of the detected granules, the following results are derived: (1) the averages of diameter, continuum intensity, and Doppler velocity in the upward direction of large granules are larger than those of small granules; (2) the averages of absolute longitudinal, transverse, and unsigned flux density of large granules are smaller than those of small granules; (3) for small granules, the average of continuum intensity increases with their diameters, while the averages of Doppler velocity, transverse, absolute longitudinal, and unsigned magnetic flux density decrease with their diameters. However, the mean properties of large granules are stable; (4) the intensity distributions of all granules and small granules do not satisfy Gaussian distribution, while that of large granules almost agrees with normal distribution with a peak at 1.04 I 0.

Microstructure and temperature dependence of magnetic properties of CuO-added MnZn ferrites

MnZn ferrites with the chemical formula Mn0.68Zn0.25Fe2.07O4 have been prepared by a conventional ceramic technique. Then, the effects of CuO addition on the microstructure and temperature dependence of magnetic properties of MnZn ferrites were investigated by characterizing the fracture surface micrograph and measuring the magnetic properties over a temperature ranging from 25 to 120°C. The results show that the lattice constant and average grain size increase with the increase of CuO concentration. When the CuO concentration is below 0.07 wt.%, the initial permeability and saturation magnetic flux density increase monotonously, and the temperature of the secondary maximum peak in the curve of initial permeability versus temperature and the lowest power loss shift to a lower temperature with the increase of CuO concentration. However, excessive CuO concentration (>0.07 wt.%) results in abnormal grain growth and porosity increase, which causes the initial permeability and saturation magnetic flux density decrease and the power loss increase at room temperature. Furthermore, the temperature of the secondary maximum peak in the curve of initial permeability versus temperature and the lowest power loss shift to a higher temperature.

Effects of Ta 2O 5 addition on the microstructure and temperature dependence of magnetic properties of MnZn ferrites

MnZn ferrites with the chemical formula Mn 0.68Zn 0.25Fe 2.07O 4 have been prepared by the conventional ceramic technique. Toroidal cores were sintered at 1350 °C for 4 h in N 2/O 2 atmosphere with 4% oxygen. Then the influence of Ta 2O 5 addition on the microstructure and temperature dependence of magnetic properties of MnZn ferrites was investigated by characterizing the fracture surface micrograph and measuring the magnetic properties over a temperature ranging from 25 to 120 °C. The results show that, when the Ta 2O 5 concentration is not more than 0.04wt%, the grain size has a slight increase with the increase of Ta 2O 5 concentration, the temperature of secondary maximum peak in the curve of initial permeability versus temperature and the lowest power loss shift to lower temperature. However, excessive Ta 2O 5 concentration (>0.04wt%) results in the exaggerated grain growth and porosity increase, which make the initial permeability and saturation magnetic flux density decrease and the power loss increase at room temperature. Furthermore, the temperature of secondary maximum peak in the curve of initial permeability versus temperature and the lowest power loss shift to about 100 °C.

The effects of Nb 2 O 5 and TiO 2 on electrical and magnetic properties of Mn‐Zn ferrites

Mn-Zn ferrites among iron oxide magnetic materials are widely used for high frequency magnetic core materials because they have low power loss and high initial permeability up to several MHz range. In this paper, the small amount of Nb2O5 and TiO2 were added to the Mn-Zn ferrites to study their effects on electrical and magnetic properties of the Mn-Zn ferrites. The amount of Nb2O5 and TiO2 was in the range of 0 ∼0.02 wt% and 0–0.6 wt% respectively. The effects of additives were studied in view of change in core loss, maximum flux density, specific resistivity, inductance and permeability. Adding both TiO2 (0.6wt%) and Nb2O5 (0.01wt %), the core loss was lowest. It was decreased to 50% at 500 kHz. In this case, the maximum flux density was depressed by only 2%. This means that the additives could drastically decrease the minimum core loss with penalty of a little decrease in magnetic flux density. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)