Papers by Author: Kenji Sakai

Abstract: In order to design a ferrite absorber that can be used at frequencies of several GHz, the frequency dependences of the relative complex permeability μ_r^*, the relative complex permittivity ε_r^*, and return loss were investigated for a composite made of Ni-Zn ferrite and SiO₂. When ferrite particles were dispersed and isolated in an SiO₂ medium, the frequency dependence of μ_r^* was different from that for a composite made of SiO₂ particles dispersed and isolated in the ferrite medium. Moreover, when ferrite particles were isolated and a suitable mixture ratio of ferrite and SiO₂ was selected, the return loss was less than −20 dB at frequencies of several GHz. The dispersion states of ferrite and SiO₂ particles are thus important factors to design an absorber, and improvement in the absorption characteristics of the ferrite tile which is used as a practical absorber could be achieved using a composite made of Ni-Zn ferrite particles dispersed and isolated in an SiO₂ medium.

Abstract: To design an electromagnetic wave absorber with good absorption properties at frequencies above 1 GHz, the frequency dependences of the relative complex permeability μr*, the relative complex permittivity εr*, and return loss were investigated for the composite made of both sendust (an alloy of Al 5%, Si 10%, and Fe 85%) and aluminum particles dispersed in polystyrene resin. It was found that the frequency dependence of μr* for this composite can be changed by adjusting the particle size of aluminum and the volume mixture ratio of sendust and aluminum. Therefore, a flexible design of an absorber with good absorption characteristics was proposed based on the ability to control μr*. The composite made of both sendust and aluminum was found to exhibit a return loss of less than −20 dB in the frequency range of not only several GHz but also around 20 GHz if appropriate volume mixture ratio and particle size were selected.

Abstract: The effects of the particle size of sendust, which is an alloy of Al 5%, Si 10%, and Fe 85%, on the absorption characteristics of composite electromagnetic wave absorbers made of polystyrene resin and sendust were investigated in the frequency range from 1 to 40 GHz. The size of sendust particles was varied between approximately 5 and 20 m. A metal-backed single-layer absorber made of 20 m sendust particles absorbed more than 99% of electromagnetic wave power at frequencies above 20 GHz. Meanwhile, a composite made of 5 m particles exhibited a return loss of less than −20 dB in the frequency range of not only several GHz but also above 30 GHz. In addition, the relative complex permeability r* was shown to be controlled by adjusting the particle size of sendust, and an electromagnetic wave absorber with a flexible design was proposed.

Abstract: Composite electromagnetic wave absorbers made of a soft magnetic material (permalloy or sendust) and polystyrene resin were investigated [1]. The volume mixture ratio of magnetic material was varied in the range from 18 vol% to 75 vol%. The composites with the low volume mixture ratio of soft magnetic material absorbed more than 99 % of electromagnetic wave power in the frequency range from 1 GHz to 10 GHz. The values of the real part
r’ of the relative complex permeability
r * for both magnetic materials were less than unity at frequencies above approximately 6 GHz as the volume mixture ratio of magnetic material increased. This result suggests the possible realization of an electromagnetic wave absorber that can operate above 10 GHz.

Abstract: The frequency dependences of the complex permeability μ r*, complex permittivity ε r*, and return loss were investigated for composite electromagnetic wave absorbers made of soft magnetic materials (permalloy or sendust) and polystyrene resin. For permalloy, two types of particle shape were used: grain-type or flake-type. The volume mixture ratio of magnetic materials was varied in the range from 40 % to 70 %. The values of the real part μ ’ and imaginary part μ ” of μ r * increased with increasing mixture ratio of magnetic materials. The frequency dependence of μ r * for flake-type permalloy composite was similar to that for sendust composite. All absorbers showed the absorption of electromagnetic waves in the frequency range above 1 GHz.

Abstract: The purpose of this study is to prepare high-quality TiO2 thin films for dye-sensitized solar cells using the electrophoresis method. A high-quality TiO2 thin film has a thickness of approximately 10 μm and no crack on the surface. In this study, TiO2 thin films were deposited by changing the configuration of electrophoresis electrodes. When electrodes were set parallel to horizontal and ITO glass substrate was set in the upper electrode, an excellent TiO2 thin film of approximately 10 μm thickness was obtained by depositing very thin TiO2 films as a buffer layer. The new film has the highest open-circuit voltage and short-circuit current density.

Abstract: TiO2 thin films for the dye sensitized solar cell have been deposited by the electrophoresis method using the ultra fine particles of TiO2. To adsorb much dye molecules on the TiO2 film, electrophoresis method and vacuum impregnation have been tried. The quality of TiO2 thin film and the amount of the dye molecules adsorbed on the thin film affect the energy conversion efficiency of the dye sensitized solar cell. The condition to adsorb large amounts of dye molecules on the TiO2 film was discussed. The values of open-circuit voltage and short-circuit current increased using both vacuum impregnation and electrophoresis method to adsorb dye molecules.

Abstract: It is found through simulation that composite electromagnetic wave absorbers made of Ni-Zn ferrite and SiO2 particles, which are isolated in the continuous medium of Ni-Zn ferrite, show good absorption. In particular, absorbers show absorption in the frequency regions both below and above 1 GHz for the mixing ratio of SiO2 of 80 mol%. To simulate the complex permeability of the composite materials, we considered some arrangements of SiO2 in the Ni-Zn ferrite medium. Measured values of complex permeability are close to simulated ones above 1 GHz.