Hideo Oka

Mn–Zn ferrite with higher magnetization for temperature sensitive magnetic fluid

A growth-assisted coprecipitation process is proposed to achieve highly magnetic Mn–Zn ferrite particles. In this method, first, the particles were synthesized by coprecipitation under optimum condition. Then, further enhancement in particle size was obtained by using the already prepared particles as seed. The average crystallite size of the particles prepared by the proposed method was 12 nm. Furthermore, the magnetization at 1 T applied field was 50 emu/g compared to 37 emu/g of coprecipitated particles. It should be noted that the Curie temperature of the particles remained similar to the coprecipitated particles suggesting that the composition of the Mn–Zn ferrite particles has not been affected by the modified synthesis technique. The gradient of the magnetization-temperature curve was enhanced as a consequence of the rise in magnetization. These particles could be used for the synthesis of temperature sensitive magnetic fluid with higher magnetization and magnetization-temperature gradient.

Experimental results on indoor electromagnetic wave absorber using magnetic wood

The purpose of this paper is to propose a new type of indoor electromagnetic wave absorber using magnetic wood. This magnetic wood has good electromagnetic wave absorbing characteristics, a low specific gravity, a wood texture and other wood characteristics and can be easily processed. Electromagnetic wave absorbing characteristics were measured for four types of magnetic wood. The sandwich-type magnetic wood demonstrated the best wave absorbing characteristics among the four types of magnetic wood that were studied. The experimental results showed that the proposed indoor electromagnetic wave absorber can be used to suppress the transmission and reception of cellular phone and Personal Handy Phone System (PHS) signals and can be used as a cross protection for indoor wireless Local Area Networks (LAN). This wood can be processed for use in furniture, building materials, and other applications.

Experimental study on magnetic and heating characteristics of magnetic wood

Magnetic wood, wood which demonstrates magnetic characteristics, was introduced by the Oka group in 1991. Based on previous studies, we have proposed that magnetic wood can be used as a heating board by induction heating, applying a high frequency magnetic field. This article covers experimental magnetic and heating characteristics for three types of magnetic wood: an impregnated type (the wood is impregnated with a water-based magnetic fluid), a powder type (Mn–Zn ferrite powder and wood powder are mixed and pressed into boards), and a coating type (Mn–Zn ferrite powder is coated onto a fiber board). Our results showed that the coating-type magnetic wood had the highest surface temperature when using a solenoid excitation coil. In this case the surface temperature rose 50 °C. The heating board we propose can be used in furniture and medical equipment that require a warm and smooth surface.Magnetic wood, wood which demonstrates magnetic characteristics, was introduced by the Oka group in 1991. Based on previous studies, we have proposed that magnetic wood can be used as a heating board by induction heating, applying a high frequency magnetic field. This article covers experimental magnetic and heating characteristics for three types of magnetic wood: an impregnated type (the wood is impregnated with a water-based magnetic fluid), a powder type (Mn–Zn ferrite powder and wood powder are mixed and pressed into boards), and a coating type (Mn–Zn ferrite powder is coated onto a fiber board). Our results showed that the coating-type magnetic wood had the highest surface temperature when using a solenoid excitation coil. In this case the surface temperature rose 50 °C. The heating board we propose can be used in furniture and medical equipment that require a warm and smooth surface.

Wood construction and magnetic characteristics of impregnated type magnetic wood

The results of experiments involving the AC and DC magnetic characteristics of impregnated type magnetic wood were studied by taking into consideration the wood construction and fiber direction. The experimental results show that the sufficient amount of impregnated magnetic fluid varies depending on the fiber direction and length, and the grain face of the wood material. The impregnated type magnetic wood sample that is fully impregnated by magnetic fluid has a 60% saturation magnetization compared to the saturation magnetization of magnetic fluid. Samples for which the wood fiber direction was the same as the direction of the magnetic path had a higher magnetization intensity and permeability.

Electromagnetic Wave Absorption Characteristics of Half Carbonized Powder-Type Magnetic Wood

A new technique for designing the material composition for a powder-type magnetic wood to achieve a specific matching frequency for an electromagnetic wave absorber is proposed and validated experimentally. The complex permittivity of the wood powder is changed by heating the powder-type magnetic wood until the surface is carbonized (referred to as half- carbonized) and has a conductive property. The changed complex permittivity of the wood powder alters the frequency at which peak absorption takes place. The experimental results for this study show that the electromagnetic wave absorption characteristics of the half- carbonized Mn-Zn ferrite powder-type (40 volume%) magnetic wood can be controlled by adjusting the processing temperature. The correct matching frequency and an acceptable bending strength are achieved if the material is processed at 250°C. The powder-type magnetic wood boards used in these experiments satisfy JIS standards for wood surface materials in terms of bending strength. The results from our studies can be used to design indoor powder-type magnetic wood wave absorbers with a specified absorption frequency.

A new frequency modulator using ferrite orthogonal cores

A new frequency modulator circuit is presented, which is a new application of small size orthogonal cores. The circuit proposed here has a number of excellent operating characteristics and an extremely simplified construction. The wide variable frequency range is obtained by a small input power. Furthermore, large output voltage, high reliability, isolation characteristic, and low input impedance can be expected from this device. The proposed circuit can be used as a power controlled device and a power telemeter. The operation and circuit configuration of the new frequency modulator are described. The flux behavior of the circuit under frequency modulated condition is examined.

Study of electromagnetic wave absorption characteristics and component parameters of laminated-type magnetic wood with stainless steel and ferrite powder for use as building materials

The purpose of this paper is to propose that a laminated-type magnetic wood using ferrite powder and stainless steel powder can serve as a wood building material of suitable quality for an indoor electromagnetic wave absorber. The experimental results for the gigahertz frequency band show that the laminated-type magnetic wood which has volume content ratio of 20vol%, an inside ratio of stainless steel to ferrite powder 2:3, and a thickness of magnetic layer 4.0mm has an electromagnetic wave absorption characteristic of 45.18dB at 2.62GHz. This laminated board can be used to prevent radio interference for indoor wireless LANs, which mainly use the 2.4GHz frequency band.

Heating characteristics of magnetic wood by induction heating

The purpose of this article is to examine the possibility of using magnetic wood as a heating board. This article covers top and side surfaces of heating characteristics for three types of magnetic wood (impregnated, powder and coating types) when using three different excitation coil types (solenoid, meander and spiral coil). Our results showed that the coating type magnetic wood had the highest top surface temperature when using a spiral excitation coil. In this case the top surface temperature rose 60/spl deg/C and good net heat. The temperature difference was 15/spl deg/C. The heating board we propose can be used in floor heating and for medical equipment that require a safe, warm and smooth surface.

Electromagnetic Wave Absorption Characteristics Adjustment Method of Recycled Powder-Type Magnetic Wood for Use as a Building Material

The purpose of this paper is to demonstrate the electromagnetic wave absorption characteristics of powder-type magnetic wood by changing the mixing ratios for the Mn-Zn ferrite and Ni-Zn ferrite powder. The results show that the matching frequency of the electromagnetic wave absorption characteristics can be controlled by changing the mixing ratios of the magnetic materials and the thickness of the board. We obtained electromagnetic wave absorption of close to 20 dB over the 2.5 GHz-6.2 GHz frequency range. The powder-type magnetic wood boards used in these experiments satisfy JIS standards for wood surface materials in terms of bending strength and deflection. The results from our studies can be used to design indoor powder-type magnetic wood wave absorbers for a specified absorption frequency.

Laminated impregnated type magnetic wood manufacturing methods and magnetic characteristics from DC to 13.5 GHz band

Summary form only given. Since the introduction of magnetic wood, the authors have proposed various functions such as heating, attraction and electromagnetic wave absorption. The impregnated type magnetic wood, which is manufactured by impregnating magnetic fluid through conduit pipes, has the best woody characteristics among the three types of magnetic woods (impregnated type, powder type and coating type). In spite of the merits, the manufacturing methods up until now have been unsuccessful in producing an impregnated type magnetic wood with good magnetic characteristics, because it is difficult to impregnate a sufficient amount of magnetic fluid into the wood board. The purpose of this paper is to suggest a new impregnating method and report on the experimental results of DC and AC magnetic characteristics. The manufacturing method involves taking a thin layer of film from the wood and impregnating this section with a magnetic fluid. Next, these layers are laminated and adhered to create a board. Comparative measurements were made of the specific gravity of the laminated impregnated type and impregnated type magnetic woods. The experimental results for the proposed laminated impregnated type show that uniform magnetic characteristics are obtained and apparently good characteristics are shown from DC to 13.5 GHz.