The effects of chemical composition and deformation temperature on the magnetic properties of hot-deformed Nd-Fe-B magnets were studied systematically, with the following results: 1) all magnet samples consisted of single- and multi-domain grains, 2) single-domain grains increased with decreasing crystal grain sizes, and 3) both coercivity and its temperature coefficient were strongly related to crystal grain size and total rare earth content. By optimizing the chemical composition and the hot-deformation conditions, Dy-free magnets with a coercivity of 1600 kA/m, which is 23% higher than that of conventional magnets, were fabricated.

抄録全体を表示

  A very sensitive thin film sensor was developed using a transmission line. The sensor element consisted of a coplanar line fabricated from Sr₃₃Ti₁₆O₅₁ (STO) film (6 μm thick), morphous CoNbZr film (5 μm thick), and Cu/Cr film (4 μm/0.2 μm). The deposited STO film had high permittivity of around 31. The STO film enhanced the sensitivity of the sensor and a phase change of more than 100 degrees/Oe and gain of over -40 dB were achieved simultaneously. These characteristics are very similar to those of a large sensor with a bulky ceramic substrate⁶⁾.

抄録全体を表示

  A highly sensitive and broadband method of obtaining thin film permeability without sample-size limitations was developed based on the change in high-frequency impedance due to the skin effect. A microstrip probe with impedance matching of 50 Ω was fabricated, and placed in proximity to a magnetic thin film. The permeability was optimized with the Newton-Raphson method. The permeability of CoFeB film (45 mm × 25 mm and 0.5 μm in thickness) and that of FeCoB/Ru film (50 mm × 40 mm and 0.2 μm in thickness) were evaluated using a permeameter. The measured values were in rough agreement with theoretical values based on the Landau-Lifshitz-Gilbert equation and eddy current generation up to 30 GHz. The proposed method offers promise for measuring the permeability of wafer-sized samples in line because it is not restricted by size limitations.

抄録全体を表示

  Current transformers and Rogowski coils are used to measure electric current in power distribution equipments. In recent years, wide-range current sensors have had strong demands to standardize current sensors in those various equipments. However, it has been difficult to make a trade-off between the sensitivity and the size of a conventional current sensors. To overcome the difficulty, we developed a new current sensor where magnetic pieces are regularly arrayed inside the Rogowski coil. We made a comparative evaluation of the performances of the conventional and developed sensors with magnetic field analysis, and we achieved that the S/N ratio of the developed sensor was approximately 4.5 times higher than that of a Rogowski coil, and that the developed sensor had the measurement range of the current approximately 8 times wider than common current transformers. We also built a prototype which has the precision of the current sensing comparable to conventional current transformers.

抄録全体を表示

  Functionalities of thermoresponsive molecules immobilized on iron-oxide magnetic nanoparticles were non-invasively controlled by the application of alternating magnetic field keeping the solution temperature unchanged. Hydrodynamic particle sizes of iron oxide nanoparticles functionalized with thermoresponsive polymers were successfully controlled. The activity of the thermoresponsive enzymes immobilized on iron oxide was significantly enhanced by the application of alternating magnetic field.

抄録全体を表示

  Magnetic hyperthermia (MHT) is of considerable practical interest as a new less invasive local tumor treatment. MHT requires a uniform alternating magnetic field (AMF) over a wide volume. However, it is very difficult to actually generate the exchange magnetic field of completely uniform amplitude over a wide area such as a human body. We used electromagnetic-field simulator, Maxwell 3D, to design AMF generator. Before designing AMF generator, reliability of simulation was checked. We measured temperature changes of a magnetic fluid (ResovistⓇ) in an AMF to determine the tolerance range of the magnetic field amplitude suitable for MHT. Then, we designed an AMF generator, optimizing the magnetic circuit parameters such as the diameter of the ferrite core, the coil current and the capacitor voltage using the simulator.

抄録全体を表示