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This paper presents the reduction of noise and vibration concerning the magnetostriction effects for a single-phase power transformer with a large capacity of 200 MVA. Two magnetic core shapes are investigated: 1) D-yoked core and 2) square-yoked core. The D-yoked core is used for the construction of the transformer prototype in this paper. The magnetostriction and the hysteresis loop of the core material are measured for the simulation and analysis of noise and vibration. The transformer prototype is assembled with an external clamping force applied on the core, and the core vibration and sound-level are observed. The transformer operates with a periodic excitation that may induce resonance in the core. To avoid this, a finite-element analysis is used for modal analysis to identify the natural frequencies of the core. A tank is also designed with a sufficiently rigid structure to avoid resonances. The sound-level of the fully assembled transformer prototype is measured, and it is found to have a low-noise level below 65 dB.

This paper presents a miniature autofocus (AF) voice coil motor (VCM) actuator with retaining force in a restricted space that can be applied in an optical AF apparatus. A position encoder consisting of a permanent magnet (PM) and a Hall-effect sensor is used to detect magnetic signals; the displacement of the AF VCM actuator can be obtained from the encoder, thus enabling closed-loop control. The proposed miniature AF VCM actuator consists of a high-permeability magnetoconductive plate and a PM on another side to generate a retaining force when the exciting current is switched off. Using a 3-D finite-element analysis simulation and the Maxwell stress tensor method, the electromagnetic Lorentz force within a movable displacement was determined to be ~16 mN. Blur caused by variable force and load disturbance was observed in images captured during AF operation. This adaptive fuzzy proportional-integral-derivative (PID) control approach compensates for the nonuniform friction, disturbance variation, and even load changes of the movable part of the AF VCM actuator that occur when a subject is photographed in various positions. The adaption mechanism reduced control effort, despite the variable force and load disturbance, and exhibited fast dynamic performance and minimal steady-state error.

When designing an auto-focusing actuator for use in cell phone cameras, it is important to maximize the positioning repeatability while simultaneously minimizing the device size, the power consumption, the response time, and the dynamic tilt angle. In a previous study (Liu and Lin, Opt. Express, vol. 17, pp. 9754-9763, 2009), the current group designed a miniature auto-focusing voice coil motor (VCM) actuator in which the lens was held in position using a magnetoconductive plate and a closed-loop control mechanism. The aim of this study is to characterize the performance of this device using an experimental approach. The results show that the proposed actuator has a high positioning repeatability, a low dynamic tilt angle, a rapid response, and a low power consumption.

When designing an auto-focusing actuator for use in cell phone cameras, it is essential to minimize the device size, maximize the positioning repeatability, and minimize the power consumption. In a previous study, we presented a miniature auto-focusing voice coil motor (VCM) actuator for cell phone camera applications in which the lens was precisely positioned by a closed-loop feedback signal generated by a Hall element. Our study characterizes the performance of this device by using an experimental approach. The results show that the proposed actuator is not only smaller than a conventional VCM actuator with an open-loop positioning system, but also has improved positioning repeatability, a more rapid response, and lower power consumption.

This paper presents the effects of the fluid dynamic bearing (FDB) design on the rotational precision of a spindle motor used for drivers requiring higher recording density and data transfer rate. Adopting the numerical flow field analysis on the FDB, the developed motor has robust operating stability in an operational window. The FDB provides the optimal load capacity demonstrated by the experimental results. In addition, the developed motor has excellent axial repeatable run-out performance less than 4 mum

This paper presents the development of a miniature axial-field spindle motor. Such a spindle motor could play a very important role in modern storage devices, which demand increasingly large storage capacity under limited physical space, especially for the miniature hard-disk drive or small-form-factor optical (SFFO) storage drive developments. In the present paper, an axial-field motor structure was employed to facilitate the design of a miniature spindle motor of a low profile height. In addition, the axial spoolless coil windings, which eliminate the cogging torque due to slot, serve as the electromagnetic exciting source.

This report deal with the influence of particle size of MnZn ferrite powder on the preparation of monodomain structure. It is found that when samples were sintered at low temperature (1170/spl deg/C), the power loss and microstructure of MnZn ferrite prepared from powder particle size above 1.3 /spl mu/m are dominated by sample density. On the other hand, the existence of silica still induce exaggerated grain growth for samples prepared from powder below 1 /spl mu/m and added with CaO-SiO/sub 2/ more than 0.1 wt.%. In this study, sample prepared from powder with particle size of 1 /spl mu/m and added by 0.07 wt.% CaO-SiO/sub 2/ exhibits optimum power loss.

The core loss mechanism of low loss grade Mn-Zn ferrite in the frequency range from 1 MHz to 10 MHz was investigated. Under the condition of f.B=25 kHz. T, it was found that dielectric loss dominated the core loss at frequencies between 1.1 and 3 MHz, while eddy current loss dominated the core loss at frequencies higher than 3 MHz. It is suggested that decrease of grain boundary capacitance and increase of grain resistivity of the core may be the suitable ways for the Mn-Zn ferrites to be used at this frequency region. >