Tatsuya Doi

Crack identification in metallic materials

A novel formulation for the crack identification problem is proposed. In this formulation, cracks are regarded as the equivalent field or potential sources due to the discontinuity of conductivity at the crack positions. This means that crack identification problems are reduced to the inverse problems of searching for equivalent sources. The system equation of the inverse problems, derived by discretizing the integral equation, is successfully solved by the sampled pattern matching method. As a consequence, fairly good results are obtained even in the case of plural defect problems. >

Defect recognition in conductive materials by local magnetic‐field measurement

Among the various nondestructive testing methods, the electric potential method requires relatively simple device and measurement. However, because of the high electrical contact resistance, sometimes it is difficult to measure the correct local electric potentials by direct contact. In order to overcome this difficulty, method is proposed which involves substituting the local magnetic field for electric potential measurements. The comparison with the conventional electric potential method demonstrates the usefulness this method, especially for materials with low resistivity.

Wavelet solution of the inverse source problems

Generally, the inverse source problem is reduced into solving an ill-posed system of equations. This article proposes a novel approach for the inverse source problem employing the wavelet analysis. The wavelet analysis has two distinguished abilities; one is the image data compression ability and the other is the spectrum resolution ability of the waveforms. The key idea is that the system matrix of the inverse source problems is regarded as a two-dimensional image data. The two-dimensional wavelet transform is applied to this system matrix. Finally, we can obtain an approximate inverse matrix of the system. A simple example concerning the estimation of the current distribution from the locally measured magnetic fields demonstrates the validity of our approach.

Magnetic field distribution caused by a notebook computer and its source searching

Previously, we have proposed a method of solution for the inverse problems, and successfully applied it to the biomagnetic fields. In the present article, we apply our inverse approach to the leakage magnetic field source searching for the notebook computers. As a result, it is found that our inverse approach is quite effective in searching for the leakage magnetic field source. The validity of our solutions is carefully examined by comparing the measured and calculated magnetic field distributions.

Inverse analysis for magnetic field source searching in thin film conductor

Previously, we have proposed the sampled pattern matching (SPM) method solving for the inverse problem. In the present paper, we propose a generalized SPM method. The generalized SPM method makes it possible to estimate both the direction and magnitude of currents. We apply this new method to the current estimation in a thin film conductor. Numerical simulation suggests the validity of the method. As a result, this paper presents an effective methodology to estimate a current distribution in a thin film conductor.

Wavelet solution of the inverse parameter problems

Previously, we have proposed a method of solving inverse problems, and successfully applied the method to biomagnetic fields as well as the nondestructive testing in metallic materials. In the present article, we propose a novel inverse approach for the parameter determination problems employing wavelet analysis. A simple example of parameter determination demonstrates the validity of our wavelet approach.

An application of the wavelets to the magnetic field source searching

Recently, the waveletanalysis is being applied to the various fields, such as image data compression in informatics and spectrum analysis of the electrocardiogram. In the present article, we propose the two approaches, employing the waveletanalysis for the human heart diagnosis. One is the data base approach, and the other is an inverse approach searching for the magnetic field source of the human heart. The data base approach is an application of the data compression to the magnetocardiogram. Also, the magnetic field source searching is an application of the spectrum analysis to the magnetocardiogram. The results reveal that the data base approach makes it possible to identify the normal or abnormal heart, and the magnetic field source search is capable of estimating the current distribution of a distinct heart.

Hybrid MCG and ECG approach to medical diagnosis in human heart

This paper proposes one of the novel approaches for human heart diagnosis. Synchronizing with blood pressure pulse, it is possible to measure the electrocardiogram as well as the magnetocardiogram. Taking a gradient of electric potentials of the electrocardiogram yields an electric field vector arrow map. Similarly, taking a rotation of the magnetocardiogram yields an electric current density vector arrow map. Taking a correlation of both maps, it is possible to estimate the electric power density distribution in the human heart. Finite elements (FEM) simulation of this power density distribution shows that the power density distribution corresponds to the electrical conducting path. Thus, it is possible to examine the human heart condition, because most of the human heart problems is caused by the electrical conducting path defect. >

An Examination of Optimum Design of Magnetic Field Source

Recently, it is important to control the LF (low frequency) magnetic fields within a target area. In this paper, equivalent circuit approach using the coefficients of inductance as the objective function has been applied to the optimum design of magnetic field source. The approach is based on the FEM analysis. Simulation has been shown a correlation between the inductance coefficients and a calculated vector potential.

Leakage Magnetic Field Distribution Analysis Using The Wavelets Transform

In recent years, rapid growth of high frequency techniques causes an electromagnetic compatibility (EMC) problem. Leakage magnetic fields out of the printed circuit boards (PCB) stimulate the miss operation and mutual action among the electronic devices.This paper proposes an application of the 3-dimensional wavelets transform to the measured leakage magnetic field distributions along with a time. As a result, a simple example has demonstrated that the 3-dimensional wavelets approach exhibits its usefulness to identifying major dominant magnetic field source searching from the locally measured magnetic fields.