Magnetic devices with a cloth structure have a plain shape, large inductance value and large current capacity. By introducing the idea of divided windings, we realized a cloth-transfer which has an arbitrary winding ratio and small stray capacitance between the windings. In order to improve the characteristics of the device, we tried to use both annealed amorphous wire and thinner wire in the device core. The permeability of the amorphous wire is controlled by the tension during annealing. It was suggested that improvement of the frequency characteristics can be achieved by decreasing the wire diameter.

Cloth-Transformer with Divided Windings and Tension Annealed Amorphous Wire

Recent efforts to miniaturize one common type of power supply, the dc/dc converter, raise the internal switching frequency of the power circuit from the 20-200 kHz range to the 1-10 MHz range in an effort to reduce the size of the energy storage components that dominate the converter volume. Because of the difficulty of analyzing the power dissipation in the magnetic components, it has been unclear whether present designs represent the smallest components that can be achieved, or whether their size can be reduced further. This thesis, which is part of an MIT project to develop a miniaturized 10 MHz dc/dc converter, shows that by carefully analyzing copper and core loss, the physical size of the magnetic components can indeed be reduced significantly. Both types of power dissipation, winding loss and core loss, are difficult to analyse. Above 1 MHz skin and proximity effects in the conductors greatly increase the copper loss and are difficult to analyse in closed form. Core loss predictions, unlike copper loss predictions, cannot be made from theory alone, but rather require measured data. Such data is generally unavailable for magnetic materials at these frequencies (1-10 MHz) and flux densities (above 50 G). In order to make quantitative predictions of the copper loss, finite element analyses were employed. In order to make quantitative predictions of the core loss in the ferrite magnetic materials, whose permeability and loss vary greatly with flux density and frequency, a detailed measurement and analysis procedure was developed and used to measure

Development of magnetic components for 1-10 MHZ DC/DC converters

A cloth inductor with planar shape and meander magnetic path is considered. The relationship of inductance per unit volume to the permeability of the amorphous wire and to the diameters of the winding and warps is calculated. The results indicate the existence of a suitable ratio of winding to warp diameter. The characteristics of the device are also calculated using an equivalent circuit. and desirable characteristics of the amorphous wire determined on the basis of the analysis. It is demonstrated that the quality factor can be improved by increasing both permeability and resistivity while reducing the diameter of the amorphous wire. >

Design of miniaturized cloth inductor

A design method of cloth-structured magnetic device was obtained and it made clear the optimized relation between amorphous fiber and conductive fiber in size. At the design method, inductance, equivalent resistance and quality factor of cloth-structured magnetic devices were obtained analytically. It was close agreement between the measured value and the computed one. Furthermore, the stray capacitance of the device was estimated from the analysis of equivalent circuit. The analysis showed very small capacitance in the cloth-structured device.

An optimum design method used for cloth-structured magnetic device

In recent years, the new field of micromagnetic devices has drawn the attention of an increasing number of researchers. The objective in this field is to develop very small magnetic microdevices with a planar structure for high-frequency applications. Three technologies are being exploited in order to achieve higher scales of integration: the development of new materials, microlithography and dry etching techniques, and microdevice analysis and design. This paper reviews recent research on micromagnetic devices.

Recent Developments in the Field of Micro Magnetic Components

Design and characteristics of miniaturized magnetic device in cloth structure are discussed by using machine -made devices. The method of optimization of size of amorphous fiber and conductive fiber is made clear. The inductor with quality factor Q\simeq20 and inductance per unit volume L d >10µH/mm3is realized.

T. Yamamoto

Papers

Performance of miniaturized magnetic devices in cloth structure