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The high stability of the dual-excited synchronous generator (DESG) can enhance the reliability of power supply for critical users. Based on the traditional synchronous generator (TSG), a DESG with two sets of symmetrical field windings on the rotor is presented in this paper. The rotor slots are spaced equally over the whole rotor surface of DESG, which is different from the structure of TSG. Such structures of DESG are expected to enhance the reliability and give the electromagnetic performances, such as air-gap flux density and electromotive force (emf) that are close to those of TSG. For this purpose the relationship between the excitation magnetomotive forces (mmf) of the single- and dual-axis excited DESG is investigated. The mmf with a different rotor pitch is calculated by the finite-element simulation, and the simulation results agree with those by the theoretical derivation. The excitation air-gap flux density, emf, and the magnetic saturation in stator and rotor cores are calculated under different excitation modes, and the results are compared with those of TSG. In order to validate the simulation results, the emf of 10 kW DESG model machine is measured under different excitation modes. This paper provides the theoretical basis for the design and manufacture of large DESGs.

We fabricate granular Fe 3 O 4 nanoparticles with tunable particles sizes ranging from 20 to 250 nm using the solvothermal method. Magnetic stirring during the fabrication can further reduce the size of the particle. To investigate the high-frequency dynamic magnetic properties, the complex permeability and complex permittivity of the composites are measured in a frequency range of 1-15 GHz, and the reflection loss can be obtained through further calculation. The results show that the granular size strongly influences the permeability and the absorbing property of the material. The intrinsic permeability can be derived from the extended Bruggeman effective medium theory. The Fe 3 O 4 nanoparticles assisted by magnetic stirring with a size of 20 nm shows high performance in absorption compared with other bigger counterparts prepared without magnetic stirring.

Cobalt ferrite (CoFe2O4) nanowire arrays with different diameters were prepared in porous anodic aluminum oxide (AAO) template by a sol-gel template method. A magnetic field annealing procedure was performed in the direction along wire axis (out of sample planes) at 600°C under 10-T applied magnetic field to orient the spinel CoFe2O4 crystalline. The morphology was studied by scanning electron and transmission electron microscope. X-ray diffraction (XRD) patterns show that samples performed by the magnetic field annealing procedure have a 〈110〉 texture along the nanowire axis, while those annealed without applied magnetic field show a nonoriented polycrystalline phase of spinel type structure. Vibration sample magnetometer (VSM) test shows the difference between CoFe2O4 nanowire arrays samples annealed with or without applied magnetic field. This difference shows the magneto-crystalline anisotropy with the easy magnetization direction along the nanowire axis, and is caused by the resultant effect of the easy magnetization direction distribution of the crystalline.

The thickness of SnO2 buffer layers has been found to considerably affect the structure and magnetic properties of Sn1-xCoxO2 films. As the buffer-layer thickness increases, the lattice constant a and Co-O bond length of the Sn1-xCoxO2 films contract, which suggest the gradual relaxation of the accumulated tensile strain. Simultaneously, the amount of structural defects in Sn1-xCoxO2 films decreases significantly and the grain size increases with increasing buffer-layer thickness. All the Sn1-xCoxO2 films exhibit intrinsic ferromagnetism at room temperature and the saturated magnetic moment varies with the buffer-layer thickness. The dependence of ferromagnetism on the buffer-layer thickness can be explained on the basis of the variations in the density of structural defects and Co-O bond length in Sn1-xCoxO2 films.

FeCoB nanocomposites coated with FeCo-oxide layers were synthesized by a simple wet chemical method. Postannealing treatment was carried out from 400°C to 600°C. TEM observations show that the FeCoB particles have an average diameter of several tens of nanometer. The FeCoB nanoparticles are coated with 3 nm thick FeCo-oxide layers, exhibiting good core/shell structure. X-ray diffraction analysis demonstrates that the samples have bcc FeCo structure. A maximum saturation magnetization of 173.9 emu/g and a minimum coercivity of 169.1 Oe are obtained. Microwave absorption measurements show that the as-synthesized FeCoB nanocomposites exhibit a minimum reflection loss (RL) of -29.3 dB at the frequency of 13.2 GHz. Bandwidths of 4.1 GHz (11.0-15.1 GHz) for an RL of -20 dB and 7.4 GHz (9.1-16.5 GHz) for an RL of -10 dB are estimated, respectively.