Hiroshi Waki

Estimation of effective permeability of magnetic composite materials

This paper describes a method to estimate effective permeability of magnetic composite materials for static field. In the present method, the structures of the composite materials are assumed to be periodic, and the unit cell is defined. The effective permeability is determined on the basis of magnetic energy balance in the unit cell. The present method considers magnetic interaction between inclusions of the composite materials, and is more accurate and useful. Therefore, the present method can be more widely applied than conventional models, for example, the Maxwell-Garnett formula and the Bruggeman formula. Validity of the present method is confirmed by numerical analyses. This approach can be applied also to nonlinear magnetic composite materials.

Analysis of magnetic shielding effect of layered shields based on homogenization

This paper describes a nonlinear analysis of magnetic field based on homogenization. The analysis of a magnetic field is time-consuming when the problem includes magnetic substance with fine structure. Simplification of the fine structure by homogenization makes it possible to analyze them efficiently. The authors have introduced a homogenization method to estimate effective permeability of magnetic composite structure for a static field. This method can be applied not only for linear problems but also nonlinear ones. In this paper, the magnetic shielding effect of layered nonlinear material is analyzed by using the homogenization method, and the applicability of this method is discussed

Numerical analysis of magnetization of a bulk high T/sub c/ superconductor

Magnetization of a bulk high T/sub c/ superconductor (HTSC) is evaluated with the numerical simulation codes. The field-cooled magnetization of the HTSC is analyzed by using the critical state model. The pulse magnetization process is also analyzed by using the flux creep-flow model. The numerical solutions are discussed to clarify the time dependent effects in the reported experimental results on the pulse magnetization.

Numerical evaluation of pulsed field magnetization of a bulk high Tc superconductor

Abstract Pulsed field-magnetization process of a bulk high Tc superconductor (HTS) is analysed by using a macroscopic numerical simulation code. The non-linear dependence of shielding current on a dynamic magnetic field is evaluated with the Kim model and the flux flow-creep model. In the present macroscopic simulation, local heat generation in the HTS is roughly estimated with macroscopic values. Reported experimental results are explained by the decrease of the shielding current caused by the local heat generation. The effects of the local heat generation are discussed to clarify the dynamic magnetization process.

Numerical analyses of trapped field magnet and stable levitation region of HTSC

Stable levitation with a permanent magnet and a bulk high T/sub c/ superconductor (HTSC) is examined numerically by using the critical state model and the frozen field model. Differences between a permanent magnet and a trapped field magnet are discussed in terms of the levitation force property. The stable levitation region of the HTSC on a ring magnet and on a solenoid coil are calculated using numerical methods. The obtained results are discussed from the point of view of differences in magnetic field configuration. >

An analysis of magnetic shielding against DC power lines based on homogenization

Purpose – To analyze effectively magnetic shielding effects by shields with fine structure.Design/methodology/approach – Simplification of the fine structure makes it possible to analyze them efficiently. The authors have introduced a homogenization method to estimate effective permeability of magnetic composite structure for the static field. The homogenization method is applied to the analysis of magnetic shields composed of steel plates and steel rods against DC power lines to test its feasibility.Findings – The properties of the magnetic shielding are analyzed by using the homogenization method. The errors of the magnetic fields increase in case of very few layers.Originality/value – The simplification of the magnetic shields with fine structure by using the homogenization method makes it possible to analyze efficiently magnetic shielding effects, although the accuracy becomes worse in case of very few layers.

Double antennas for passive long range UHF-band RFID

This paper proposes double antennas which consist of receiver and backscatter antennas for passive long range UHF-band IC (Integrated Circuit) tags. The passive IC tags reply to readers queries by using backscatter modulation. For this purpose, variable impedance elements are inserted between the antenna and a voltage multiplier which generate dc power. This decreases the efficiency of received power in the voltage multiplier and reduces the communication range. To solve this problem, we propose to use an independent antenna for backscatter modulation. Experimental results and numerical simulation results show that the double antennas successfully reply data from IC tag to the reader.