Hiroshi Nakane

Bio: Hiroshi Nakane is an academic researcher from Kogakuin University. The author has contributed to research in topics: Electromagnetic coil & Superconductivity. The author has an hindex of 11, co-authored 50 publications receiving 280 citations.

Basic analysis of a metal detector

Abstract: 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 is 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.

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.

Fluctuation conductivity analysis for Bi-2223 superconductors with different sintering time

Abstract: In a Bi-based superconductor, the critical current J c increases in accordance with the length of the sintering time and further increase is attained by cold isostatic pressing (CIP) The temperature dependence of the resistivity in polycrystalline Bi-2223 superconductors with different sintering time (t s ) of 10-200 h was measured In order to investigate the mechanism to improve J c , the excess conductivity caused by the thermal fluctuation above T c was analyzed using the Aslamazov-Larkin theory It was found that the samples show a two-dimensional fluctuation in conductivity irrespective of t s , and that the amplitude of fluctuation increases with t s The analysis indicates that the correlation length, which is inversely proportional to the amplitude, decreases with the length of t s Therefore, it can be deduced that J c of the samples improves as the crystals become more uniformly aligned with increased t s , resulting in a shorter correlation length as confirmed by the SEM study A similar result has been obtained for the samples with the CIP process

Simultaneous measurement of electrical and magnetic properties of a spherical sample

Abstract: A method using a solenoid coil for simultaneously estimating the electric and magnetic properties of a spherical conductor was studied. These properties are estimated by finding the difference in the complex impedance of the coil with and without a sample to find out the measuring value that best coincides with the theoretical value. A new formula applicable to a nonmagnetic, a magnetic or a superconductive spherical sample was derived. The conductivities a and permeabilities /spl mu/ measured by this method and by the conventional methods were compared using various samples. The deviations were no larger than 3% for a nonmagnetic samples, and 1.5% for /spl mu/ of magnetic samples.

Large domain growth of Ag-doped YBaCuO-system superconductor

Abstract: The effect of Ag addition on the phase diagram, solidification conditions and fabrication of large domain YBaCuO-system has been studied. Calcined powder of composition Y1.8Ba2.4Cu3.4O9-x with 0.5 wt.% Pt and 0, 1, 5, 10, 20 and 30 wt.% Ag was prepared. The melting point of each powder was measured by differential thermal analysis (DTA). A large domain (45 mm diameter and 20 mm thick) of the Ag-doped YBaCuO-system superconductor was prepared for each composition by a seeding and unidirectional growth technique which involved controlling the furnace temperature gradient. In order to assess the quality of the crystal orientation, the distribution of trapped flux density was measured. The entire sample was magnetized uniformly and the trapped magnetic field observed to form a single dome shape.

A Combined Inductive–Capacitive Proximity Sensor for Seat Occupancy Detection

Abstract: This paper presents a simple and efficient seat occupancy detector. A seat occupancy detector is an integral part of the airbag safety system and, in its simplest form, provides the (occupied or vacant) status of the seat to the airbag control unit. Although the occupancy sensing methods based on a capacitive principle are efficient, they typically require electrodes to be placed in the surface layer of the sitting and backrest areas of the seat. The proposed sensor uses a simple electrode structure, and it is placed below the seat foam in the sitting area of the seat. These features promise a less-expensive sensor as it can be easily manufactured and installed in a seat. The new sensor combines inductive and capacitive proximity sensing principles. The sensor detects the presence of an occupant exploiting the shielding effect of the electric field while its inductive proximity feature senses the presence of conductive objects (e.g., laptop) that may be placed in the seat and helps to achieve reliable occupancy sensing. The measurement system uses a signal conditioning unit based on a carrier frequency principle. A prototype sensing system has been built, and its application as a seat occupancy sensing system in a vehicle has been verified. The developed system successfully senses human proximity and distinguishes it from other conductive objects.

Self-Inductance-Based Metal Object Detection With Mistuned Resonant Circuits and Nullifying Induced Voltage for Wireless EV Chargers

Abstract: In this paper, a metal object detection (MOD) system, a kind of foreign object detection (FOD), which is based on mistuned resonant circuits and utilizes the variation of self-inductance of a sensing pattern, is newly proposed for wireless electric vehicle (EV) chargers. The sensing pattern that consists of multiple loop coil sets is mounted on the transmitting (Tx) pad of an EV charger, where a loop coil set has two coils connected in series with the opposite polarity to cancel out the induced voltage generated by the Tx coil. Variation of self-inductance of the loop coil set is detected by a parallel-resonant circuit, driven by a current source and operating at near 1 MHz, in order to enhance the resolution of the proposed MOD system. To increase the detection sensitivity of the proposed MOD system, instead of an exact resonant frequency, a mistuned operating frequency near the –3 dB point is utilized for the parallel-resonant circuit. In this way, the proposed MOD system can detect very small metal objects regardless of their position and orientation on the Tx coil without any blind zone. Through simulations and experiments, it is found that the proposed MOD system detects not only horizontal but also standing upright metal objects. A prototype MOD system, operating at 85 kHz to satisfy the standard J2954, was fabricated to verify its feasibility. The results showed that output voltage change of the proposed MOD system becomes 22.7% for a piece of the aluminum foil of 3 × 3 cm2 and 40.9% for 100 Korean Won coin.

Basic analysis of a metal detector

Abstract: 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 is 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.

Superconducting high gradient magnetic separation for purification of wastewater from paper factory

Abstract: High gradient magnetic separation (HGMS) can be one of the promising ways for a new environmental purification technique because of producing no contamination such as flocculants and having possibility of treating large amount of wasted water within a short time. The magnetic separation system for purification of wastewater from the paper factory has been developed. The test plant of 2000 ton/day was set up in the actual paper manufacturing process and a purification test of the wastewater was performed. The magnetic seeding of the organic pulp and dyes were successfully performed and the Chemical Oxygen Demand (COD) value for recycling was reached to less than 40 ppm after magnetic separation. The superconducting magnet for the system is 3 T, 680 mm long and 400 mm bore NbTi solenoid. The system mainly consists of a mixing tank (magnetic seeding tank), a settling tank, and a superconducting magnet. Floating magnetic flocks composed of magnetite particles and organic polymers such as pulp and dye are captured by magnetic force in the superconducting magnet chamber. Some magnetic flocks are precipitated at the settling tank by the gravity, which helps to reduce the amount of magnetic flocks going through the magnet chamber. The system has been successfully operated for several months