S. Adachi

Seikei University, Edo, Tōkyō, Japan

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Publications (307)522.28 Total impact

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    ABSTRACT: Highly-sensitive HTS-SQUIDs are applied to various systems such as eddy-current non-destructive evaluation (NDE) and compact magnetometer systems. To avoid unstable operation of the SQUID due to an excitation field, a flux transformer made of normal Cu wire is used to separate the pickup coil and SQUID. However, the resistance of the flux transformer generates thermal noise and reduces the signal bandwidth at low frequencies. In this study, we investigate use of a superconducting flux transformer with resistive connections (SFTR). The SFTR consists of pickup and input coils made of HTS thin films. The two coils are connected by using an HTS coated conductor. The input coil is stacked on an HTS thin film gradiometer. From the measured results of resistances of the connections between each coil and the coated conductor, it was found that the resistance of bonding wire was a dominant component. The estimated resistance of the SFTR was 7.2 mΩ, corresponding to a lower cut-off frequency of 11.7 Hz.
    Physics Procedia 12/2014; 58. DOI:10.1016/j.phpro.2014.09.056
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    ABSTRACT: Direct detection of magnetic fields generated by the ion currents in electrolytic cells was performed and the ion currents were mapped during a cyclic voltammetry experiment. A high-TC superconducting quantum interference device (SQUID) gradiometer with ramp-edge Josephson junctions was used as the detector and thus the first derivative of the magnetic field along the electrolytic cell surface was obtained. The electric potential vs. the reference electrode was measured between −0.3 V and 0.8 V and the hysteresis signals caused by the redox reactions of the electrolyte were observed. The vector component of the ion current during cyclic voltammetry was mapped along the electrolytic cell. As a demonstration of visualization of ion transportation, the magnetic signal was also measured at various positions above the electrolytic cell surface.
    Physica C Superconductivity 09/2014; 504. DOI:10.1016/j.physc.2014.04.024 · 1.11 Impact Factor
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    ABSTRACT: We developed a highly sensitive HTS SQUID system for liquid-phase detection of biological targets using magnetic markers. The SQUID consists of a ramp-edge Josephson junction made using an RE123-based multilayer process, and it showed a flux noise of 7.5 $muPhi_{0}/hbox{Hz}^{1/2}$ in the white noise region. The $1/f$ noise was 14 $muPhi_{0}/hbox{Hz}^{1/2}$ at $f = 1 hbox{Hz}$ when the SQUID was operated in AC bias mode. Using the SQUID system, we detected a biological target called biotin. In the experiment, biotins were fixed to a large polymer bead 3.3 $muhbox{m}$ in diameter. Streptavidin-coated magnetic markers were used for the detection. The bound and unbound (free) markers were magnetically distinguished using the difference in their Brownian relaxation time, i.e., without using a washing process to separate them. The minimum detectable number of biotins was as low as $2times 10^{4}$, corresponding to a sensitivity of $9.5times 10^{-19} hbox{mol/ml}$ . This result indicates that the developed method is highly sensitive. We also show the effect of the excitation field on the signals from free and bound markers for quantitative evaluation of the immunoassay.
    IEEE Transactions on Applied Superconductivity 08/2014; 24(4):1-5. DOI:10.1109/TASC.2014.2311449 · 1.32 Impact Factor
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    ABSTRACT: BaFe2(As0.67P0.33)2 (Ba122:P) thin films were fabricated on (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7 (LSAT) (100) substrates by a pulsed laser deposition method using a second-harmonic Nd:YAG laser. Superconducting Ba122:P thin films with c-axis orientation and in-plane alignment were successfully obtained. Detailed structural properties on the films were investigated by X-ray diffraction. The X-ray pattern suggested the existence of some apatite-type phase. Transmission electron microscope observation revealed the formation of a reacted layer between the film and the substrate. The reacted layer had a Ba(Sr)-rich and P-rich composition. These analyses indicated the formation of an apatite material at the interface of the film and the substrate.
    Physica C Superconductivity 07/2014; 502. DOI:10.1016/j.physc.2014.04.028 · 1.11 Impact Factor
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    ABSTRACT: Solar panels are expected to play a major role as a source of sustainable energy. In order to evaluate solar panels, non-destructive tests, such as defect inspections and response property evaluations, are necessary. We developed a DC current distribution mapping system of the solar panels using a High Critical Temperature Superconductor Superconducting Quantum Interference Device (HTS-SQUID) gradiometer with ramp edge type Josephson junctions. Two independent components of the magnetic fields perpendicular to the panel surface (∂Bz/∂x, ∂Bz/∂y) were detected. The direct current of the solar panel is visualized by calculating the composition of the two signal components, the phase angle, and mapping the DC current vector. The developed system can evaluate the uniformity of DC current distributions precisely and may be applicable for defect detection of solar panels.
    Journal of Physics Conference Series 05/2014; 507(4):042026. DOI:10.1088/1742-6596/507/4/042026
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    ABSTRACT: To clarify the relationship of the crystal structure, the critical temperature (Tc) and the gap structure in iron pnictide superconductors, the studies on 1111-type iron pnictides with the highest Tc are important. However itis well known that the single crystal growth of 1111-compounds is difficult. In this work, we have established a method for reproducible growth of high quality crystals using high pressure synthesis technique and successfully obtained NdFeAs(O, F) singlecrystals (Tc = 43.5 K) with a typical size of 5002 × 30 µm3.
    Proceedings of the 12th Asia Pacific Physics Conference (APPC12); 03/2014
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    ABSTRACT: In the quest to increase the critical temperature Tc of cuprate superconductors, it is essential to identify the factors that limit the strength of superconductivity. The upper critical field Hc2 is a fundamental measure of that strength, yet there is no agreement on its magnitude and doping dependence in cuprate superconductors. Here we show that the thermal conductivity can be used to directly detect Hc2 in the cuprates YBa2Cu3Oy, YBa2Cu4O8 and Tl2Ba2CuO6+δ, allowing us to map out Hc2 across the doping phase diagram. It exhibits two peaks, each located at a critical point where the Fermi surface of YBa2Cu3Oy is known to undergo a transformation. Below the higher critical point, the condensation energy, obtained directly from Hc2, suffers a sudden 20-fold collapse. This reveals that phase competition-associated with Fermi-surface reconstruction and charge-density-wave order-is a key limiting factor in the superconductivity of cuprates.
    Nature Communications 02/2014; 5:3280. DOI:10.1038/ncomms4280 · 10.74 Impact Factor
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    ABSTRACT: For the transient electromagnetic (TEM) method using a high-temperature superconducting interference device (HTS-SQUID), we have developed a magnetometer system with a wide dynamic range, a high slew rate, and superior transportability. To achieve high tolerance to a higher excitation magnetic field, we utilized a SQUID magnetometer containing ramp-edge junctions with La0.1Er0.95Ba1.95Cu3Oy and SmBa2Cu3Oy electrode layers, which was fabricated by using an HTS multi-layer fabrication technique. To operate the magnetometer stably in a rapidly changing magnetic field, we chose the proper materials for the RF shield of liquid nitrogen (LN2) glass Dewar and cables. The white noise level and the slew rate of the system were measured to be 30 fT Hz-1/2 and 10.5 mT s-1, respectively. The resultant signal-to-noise ratio was higher than that of the previous system and improved the exploration depth, which was successfully demonstrated in field tests. The weight of the Dewar, which retains the LN2 for 17 h, is 2.5 kg. The total weight of our system including the LN2 Dewar, a probe with a flux-locked loop (FLL) circuit, a battery, a receiver, and a 30 m-long cable between the FLL and the receiver is as low as 25.6 kg.
    Superconductor Science and Technology 11/2013; 26(11):5003-. DOI:10.1088/0953-2048/26/11/115003 · 2.80 Impact Factor
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    ABSTRACT: The high upper critical field and low anisotropy of the iron-based superconductor BaFe2As2 make it promising for its use in the construction of superconducting magnets. However, its critical current density in high magnetic fields needs to be improved. Here we demonstrate a simple, one-step and industrially scalable means of achieving just this. We show that introducing controlled amounts of uniformly dispersed BaZrO3 nanoparticles into carrier-doped BaFe2As2 significantly improves its superconducting performance without degrading its structural or superconducting properties. Our BaFe2(As0.66P0.33)2 films also exhibit an increase in both the irreversibility line and critical current density at all magnetic-field orientations. These films exhibit nearly isotropic critical current densities in excess of 1.5 MA cm(-2) at 15 K and 1 T-seven times higher than previously reported for BaFe2As2 films. The vortex-pinning force in these films reaches ~59 GN m(-3) at 5 K and 3-9 T, substantially higher than that of the conventional Nb3Sn wire.
    Nature Communications 09/2013; 4:2499. DOI:10.1038/ncomms3499 · 10.74 Impact Factor
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    ABSTRACT: We studied the anisotropy and superconducting properties of BaFe2(As1-xPx)(2) films with various phosphorus contents x (= 0.19-0.45) fabricated on MgO by pulsed laser deposition. We demonstrated that the x = 0.28 film with optimal critical temperature (T-c,T-zero = 26.5 K) has the lowest anisotropy of upper critical field (gamma(H) = 1.54), as well as the highest irreversibility field. This is different from the case of cuprate superconductors, and preferable for application. Moreover, the minimum angular dependence of the critical current density for the x = 0.28 film at 1 T and 10 K is over 1.0MA/cm(2), indicating that this film could be a promising candidate for in-field application. (c) 2013 The Japan Society of Applied Physics
    Applied Physics Express 09/2013; 6(9):093101. DOI:10.7567/APEX.6.093101 · 2.57 Impact Factor
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    ABSTRACT: To improve the field resolution of a magnetometer for use in the Earth's field, we have developed a new magnetometer using a hybrid superconducting quantum interference device (SQUID). A multi-turn input coil (Ni turns) is inserted between a directly-coupled SQUID and a pickup coil in series in the hybrid SQUID. Screening current couples with the SQUID by both direct current injection and magnetic coupling. To avoid flux trapping, which occurs during cooling in the Earth's field, the width of the SQUID is restricted to be 5 μm. Therefore, the input coil is not stacked on the SQUID inductor like a conventional integrated SQUID but formed around the SQUID. There is an optimal Ni as a result of the trade-off relationship between the increase of the coupling strength and the decrease of the screening current with increasing Ni. The magnetometer using the hybrid SQUID with a slit hole inductor showed an effective area of 0.45 mm>;2 at the optimal Ni of 3. The magnetic coupling was enhanced by using a square hole inductor that had a larger flux capturing area. The obtained Aeff (~ 0.6 mm2) was almost doubled from that of the conventional directly coupled magnetometer, resulting in a field noise as low as 18 fT/Hz1/2 (white).
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3):1600304-1600304. DOI:10.1109/TASC.2012.2227652 · 1.32 Impact Factor
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    ABSTRACT: A battery-operated wireless flux-locked-loop (FLL) circuit for operating a high-Tc superconducting quantum interference device (SQUID) was developed and tested. This wireless battery-type FLL circuit consists of an FLL unit and a PC interface. A local area network with the TCP-IP protocol for wireless mode was used for communication between the PC interface and a controlling PC. The battery unit can power the FLL circuits for four hours. The FLL circuit had two bias modes: ac and dc. When the wireless-battery-type FLL circuit was implemented in a SQUID, the system noise generated by a wireless network became intrinsic high-Tc SQUID noise. Also, a 1/f noise was reduced in the case of the ac-bias-current mode. Consequently, the wireless-battery-type FLL circuit can operate a high-Tc SQUID with high sensitivity.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3):1601204-1601204. DOI:10.1109/TASC.2012.2231713 · 1.32 Impact Factor
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    ABSTRACT: We have fabricated a large high-Tc superconducting (HTS) SQUID gradiometer with a baseline length of 130 mm for geophysical application. It consists of an HTS-SQUID gradiometer chip with an integrated input coil and a large pickup coil made of an HTS coated conductor (CC). In this work, fabrication of the chip containing ramp-edge Josephson junctions and multilayer structures is reported. An MgO(1 0 0) substrate with a size of 15 × 15 mm2 was used. The half area of the substrate was occupied by gold pads for connection with an HTS-CC. A directly-coupled thin-film gradiometer with a baseline length of 7 mm was prepared in the remained half area. SmBCO and La-doped ErBCO having Tc’s around 90 K were used for base- and counter-electrodes, respectively. A 5.5-turn input coil made of La-doped ErBCO was formed on the thin-film pickup coil made of SmBCO. The fabricated gradiometer chip was operated by supplying electrical current through the input coil, but modulation corresponding to only three flux quanta was observed in the V–Φ curve. We found that the critical current density of the thin-film pickup coil was insufficient. We speculated that the rather wide pickup coil was not fully oxygenated. After longer annealing treatment, the number of modulation peaks in the V–Φ curve was significantly increased.
    Physica C Superconductivity 01/2013; 484:186–190. DOI:10.1016/j.physc.2012.03.053 · 1.11 Impact Factor
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    ABSTRACT: We have investigated the fabrication of a high-temperature superconducting (HTS) gradiometer with long baseline for geophysical applications. The proof-of-concept gradiometer using a 1-turn pickup coil made of a GdBa2Cu3Oy coated conductor (GCC) and 5.5-turn input coil integrated on a SQUID was fabricated in our previous work. In this study, we have optimized the device structure to improve the frequency response, gradient field sensitivity and gradiometer balance. The fabricated flux transformer consists of a 6-turn planar gradiometric pickup coil and a 26-turn input coil made of an HTS thin film. A low-melting-point alloy was used to connect polished Ag surfaces of the CGG pickup coil and Au pads of the input coil. An HTS SQUID was formed on another substrate and stacked on the input coil. A mechanical balancing structure using three pieces of GCC as a superconducting shield was also implemented. The fabricated gradiometer showed a gradient field noise of 0.8 fT/cm Hz1/2 in the white noise regions, a gradiometer balance of 1/142, and a cutoff frequency of 9 Hz corresponding to a 2 mΩ contact resistance between the pickup coil and the input coil.
    Physica C Superconductivity 01/2013; 484:191–194. DOI:10.1016/j.physc.2012.03.006 · 1.11 Impact Factor
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    ABSTRACT: We developed a highly sensitive HTS SQUID system for liquid-phase detection of biological targets using Brownian relaxation of magnetic markers. The SQUID was made of a ramp-edge Josephson junction using RE123-based multilayer process, and it showed a flux noise of 7.5 micro flux-quantam/Hz1/2 in the white noise region. The 1/f noise was 14 micro flux-quantam/Hz1/2 at f = 1 Hz when the SQUID was operated with AC bias mode. Using the SQUID system, we detected a biological target called biotin. In the experiment, biotins were fixed to a large polymer bead with a diameter of 3.3 micron meter. Streptavidin-coated magnetic markers were used for the detection. The bound and unbound (free) markers were magnetically distinguished using the difference in their Brownian relaxation time, i.e., without using the washing process to separate them. The minimum detectable number of biotins was as low as 104, corresponding to a sensitivity of 4.8×10-19 mol/ml. This result indicates a high sensitivity of the developed method.
    Superconductive Electronics Conference (ISEC), 2013 IEEE 14th International; 01/2013
  • TEION KOGAKU (Journal of the Cryogenic Society of Japan) 01/2013; 48(1):4-11. DOI:10.2221/jcsj.48.4
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    ABSTRACT: Step-by-step tensile tests were applied to flat-braided carbon-fiber-reinforced polymers with and without added dispersions of carbon nanofibers (CNFs) and with and without sample sides cut off to study their mechanical properties and destructive mechanisms by means of in situ observation and stress–strain measurements. An ex situ nondestructive evaluation technique, using a high-temperature superconductor superconducting quantum interference device gradiometer, was also applied to the samples to study their electrical properties; the relationships between the mechanical and electrical properties by visualizing current maps in the samples during ac current injection was also studied. Clear differences were observed in the mechanical and electrical properties and the destructive mechanisms between the samples with and without CNFs and with and without cut off sides. These differences were mainly attributed to the addition of CNFs, which enhanced the mechanical and electrical connections between the carbon fiber bundles.
    Physica C Superconductivity 01/2013; 484:195–201. DOI:10.1016/j.physc.2012.03.059 · 1.11 Impact Factor
  • S. Adachi, Y. Murai, K. Tanabe
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    ABSTRACT: We prepared polycrystalline samples with nominal compositions of (Ba0.5Sr0.5)Fe2(As1−xPx)2 (x = 0. 2, 0.3, 0.35, 0.4, 0.5, 0.6). Nearly single-phase samples were successfully obtained. Rietveld refinements of the powder XRD data revealed that the cell volume was gradually reduced with increasing the P content x. Comparing with the reported data for P-substituted Ba122 (Ba122:P) and Sr122 (Sr122:P), the P-substituted (BaSr)122 exhibited intermediate structural properties. The structure of the Fe2(As, P)2 block was almost identical regardless of different alkaline earth elements. The sample with x = 0.4 showed the highest Tc of 29 K, being nearly identical to those of Ba122:P and Sr122:P.
    Physica C Superconductivity 12/2012; 483:67–70. DOI:10.1016/j.physc.2012.07.005 · 1.11 Impact Factor
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    ABSTRACT: We have developed HTS SQUID modules applicable to various systems, such as nondestructive evaluation and low-field NMR/MRI systems. The SQUID module consists of a directly coupled HTS planar gradiometer and a HTS multi-turn input coil, which are fabricated on separate substrates and stacked with a flip-chip configuration. Two types of input coils, 26-turns and 59-turns, are fabricated. The SQUID module is mounted on a printed circuit board with large electrodes for soldering to the external pickup coil. The mutual inductances between the input coil and SQUID varied from 0.5 to 2.3 nH, depending on the number of turns of the input coil and the inductance of the SQUID. The SQUID modules with an external pickup coil made of normal metal showed a lower cut-off frequency of 45 Hz and a field noise as low as 35 fT Hz−1/2 (>4 kHz).
    Superconductor Science and Technology 11/2012; 26(1):015013. DOI:10.1088/0953-2048/26/1/015013 · 2.80 Impact Factor
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    ABSTRACT: Superconducting BaFe2(As0.6P0.4)2 (Ba122:P) thin films were fabricated on MgO(100) substrates by a pulsed laser deposition (PLD) method using a second-harmonic Nd:YAG (yttrium aluminum garnet) laser. Structural investigation by means of x-ray diffraction confirmed both c-axis orientation and in-plane alignment, or epitaxial growth on the substrate. The film exhibited Tc(onset) = 26.5 K and Tc(zero) = 24.0 K. High Jc values of 3.5 MA cm−2 at 4.2 K in the self-field and over 1 MA cm−2 at 10 K under 1 T were also obtained. Fabrication of Ba122:P film by Nd:YAG PLD seems to be a promising approach for preparing superconducting tapes, since a high-Tc and high-Jc film can be relatively easily obtained.
    Superconductor Science and Technology 09/2012; 25(10):105015. DOI:10.1088/0953-2048/25/10/105015 · 2.80 Impact Factor

Publication Stats

3k Citations
522.28 Total Impact Points

Institutions

  • 2013
    • Seikei University
      Edo, Tōkyō, Japan
    • Kyushu University
      • Department of Electrical Engineering
      Hukuoka, Fukuoka, Japan
  • 1992–2013
    • International Superconductivity Technology Center
      Sakado, Saitama, Japan
  • 2005–2006
    • Nihon University
      Edo, Tōkyō, Japan
  • 2003
    • Osaka Prefecture University
      Sakai, Ōsaka, Japan
  • 2002
    • The University of Tokyo
      • Department of Advanced Materials Science
      Tokyo, Tokyo-to, Japan
  • 2000–2002
    • Hitachi, Ltd.
      Edo, Tōkyō, Japan
  • 1999
    • Tanta University
      • Department of Chemistry
      Ṭanṭa, Muḩāfaz̧at al Gharbīyah, Egypt
  • 1995
    • Chinese Academy of Sciences
      Peping, Beijing, China