Sadao Yamazaki

Basic analysis of a metal detector

Metal detectors are extensively used to find undesirable metal objects in processed food. In such a typical metal detector, the coils are coaxially arranged with the transmitting coil in the center and two receiving coils on the sides. The receiving coils are connected to a differential amplifier. When the magnetic field generated in the transmitting coil is disturbed by metal objects, the amplitude and phase of the output voltage of the differential amplifier change and thus the existence of foreign metal pieces are detected. The relationship between the amplitude and phase of the output and the electromagnetic properties of the metal objects, however, has only been discussed experimentally so far. The authors have already developed the SRPM method to simultaneously estimate the electrical and magnetic properties of a spherical sample by vectorially measuring the difference in the impedance of two circular solenoid coils, one with and the other without a sample. An attempt is made to theoretically analyze the properties, such as size, conductivity and permeability of the metal objects from the output, i.e., amplitude and phase of the metal detector. Based on this method an equation to estimate the vector voltage induced in the receiving coil by the metal object is derived by using a spherical sample to simplify the analysis. The validity of the new formula was confirmed by experiments using iron, aluminum and SUS304 objects.

Analysis of fluctuation conductivity in melt-textured DyBa2Cu3Oy superconductors

Abstract We evaluated the superconducting properties of DyBa 2 Cu 3 O x (Dy123) with different amounts of Dy 2 BaCuO 5 (Dy211) phase. The samples were melt-textured DyBaCuO superconductors, which were made from the mixtures in molar ratios of Dy123:Dy211=1: x ( x =0.03, 0.05, 0.08 and 0.1). The temperature dependence of resistance of DyBaCuO superconductors on different amounts of 211 phase was measured. The data of fluctuation amplitude and the dimension of conduction were obtained from analyzing the fluctuation. The results show that coherence length obtained from this analysis becomes larger as amounts of 211 phase increase. The evidence is found that the pinning force in the sample is well correlated with the characteristic length of superconductivity.

A study on the development of an open-gradient magnetic separator under dry condition

This is an attempt to explore feasibility to develop an open gradient magnetic separator for mixed powder under dry condition. The magnetic separator proposed here is intended to separate the ferromagnetic particles from mixed powder, being based on the consideration that the separation efficiency depends upon changing systematically the particle sizes and its surface properties such as hydrophobicity and cohesive force. As a result, it is found that the separation efficiency became lower as the particle size of the mixed particles became smaller. This is supposed to be caused by the cohesive force between the particles of ferrite and alumina which are easily affected by the magnetic drag force and the gravity difference. But the result is encouraging because the separation efficiency will be enhanced if the magnetic gradient is increased and if air flow in the separator is optimized in the appropriate system of the open-gradient magnetic separator proposed in this paper.

Analysis of fluctuation conductivity in melt-textured YBa2Cu3O7−y superconductors with Ag-doping

Abstract The difference in the properties between Ag-doped and undoped YBa 2 Cu 3 O 7− y (YBCO) melt-textured samples was investigated by fluctuation-conductivity analysis. The temperature dependence of the resistance in those samples was measured. Data about the dimensionality and amplitude of the fluctuation were obtained by analyzing the fluctuation conductivity on the basis of the Aslamazov–Larkin theory. The fluctuation conductivity of the undoped sample shows three-dimensional behavior in the mean-field region (MFR) with a one-dimensional (1D) character at further higher temperature. The effect of a small amount of Ag addition is manifested on a fractal conduction behavior in the 1D region of the undoped sample. Upon further Ag-doping, the conduction behavior is two-dimensional in the MFR with evidence for a rapid suppression of the short-wavelength fluctuation. The conduction behavior is discussed on the relevance to structural features of melt-textured YBCO samples with and without Ag-doping.

Microstructure of Bi-2223 Phase in oxide/Ag Multi-Layered Bulk

Bi-2223 is suitable to be applied under low field and near liquid nitrogen temperature. Jc value of the bulk materials is much smaller than that of the wire and tape materials. This should limit application field of the bulk. Then, we tried to improve Jc properties of Bi-2223 bulk by inserting Ag sheets into oxide. It was found that Jc values of the multi-layered bulk were improved in proportional to the number of Ag sheets. We investigated the microstructure of the Bi-2223/Ag multi-layered bulk. As a result, good alignment and dense structure of the oxide phase was observed near the interface between Bi-2223 layer and Ag sheet.

A new field-of-view autotracking method for online tomography reconstruction based on back-projected ray image cross-correlation

We devised a new field-of-view autotracking method for online tomography reconstruction based on a cross-correlation between a pair of neighbours, called back-projected ray images, among a specimen tilt sequence. One ray image is calculated through normal filtered back-projection only in the cross-sectional plane from each projection image. This ray-image matching can reliably track the field-of-view because a pair of neighbouring ray images mostly cross-correlates at the existing three-dimensional object position. Online experiments using real specimens resulted in successful autotracking performance with high accuracy, and online tomograms were obtained immediately after the final tracking at the last tilting angle.

Simultaneous measurement of size and electromagnetic property of multilayered spherical sample

Basic theoretical analyses to detect undesirable foreign metal pieces in the meat being processed have already been carried out. In this study, taking the low conductivity of meat into account, a double-layered spherical sample structure which enables easy analyses was selected. In order to detect these conductive materials, analyses of the difference in the impedance of a circular coil with, and another one without, a double-layered spherical conductor were made. In this way, a new formula for obtaining the electromagnetic properties of a double-layered spherical sample was derived. The process of deriving the new formula is explained. The calculated value was compared with the experimental value. Their values had a close correlation.

Defining regions of normal and anomalous skin effect of sintered Bi-based superconductors by the SRPM method

An attempt to develop a method to simultaneously estimate both the resistivity /spl rho/ and the magnetic penetration depth /spl lambda/ by vectorially measuring the difference in the impedance between two circular solenoid coils, one with and the other without a cylindrical superconductor, has been made. It was ascertained that the regions of normal and anomalous skin effect can be defined from the frequency dependence of the difference in the impedance between the two coils. The mean free path of electrons l is evaluated by applying the frequency dependence of the difference in the impedance of the coils to the anomalous skin effect region. The values of /spl rho/, /spl lambda/ and l of Bi-based sintered bulks with different J/sub c/ were evaluated at liquid N/sub 2/ temperature.

An analysis of the properties of a Bi-2223/Ag multi-layered plate samples measured by the SRPM method

Abstract Laminated bulk samples consisting of alternate layers of Bi-2223 and Ag were prepared to improve the J c of sintered Bi-2223 plate samples. Two to seven Ag sheets were inserted between six plate samples and the difference in the impedance between two sets of detecting coils was vectorially measured at 10 kHz in the temperature range of 77.3–120 K by the simultaneous resistivity and magnetic penetration depth measurement (SRPM) method. The difference in the impedance was analyzed by treating it as a serial circuit having resistance R s and inductance L s . It was clarified that as the number of Ag sheets is increased, J c and the quality factor Q (= ωL s / R s ) increase in proportion, where ω is the angular frequency.

Low Temperature Properties of HoSb, DySb, and GdSb

Materials including rare-earth and Sb compounds were developed as regenerator materials for a 4K GM refrigerator. Sb compounds have a remarkably large peak value of specific heat in the low temperature range. First, the heat capacities, thermal conductivity, and thermal expansion of HoSb, DySb and GdSb, which are anti-ferromagnetic with a large spin value in the low temperature range, were measured. Then, the results of these measurements were used to analyze the problems encountered when Sb compounds were used as the regenerative materials in a GM refrigerator.