Faculty Profiles - TSURUTA Kenji

A density functional study of vacancy formation in grain boundaries of undoped alpha-alumina Reviewed

Takafumi Ogawa, Akihide Kuwabara, Craig A. J. Fisher, Hiroki Moriwake, Katsuyuki Matsunaga, Kenji Tsuruta, Satoshi Kitaoka

ACTA MATERIALIA 69 365 - 371 2014.5

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Recent oxygen permeation experiments with cc-alumina have shown that the two major diffusing species at the grain boundaries, i.e. oxygen and aluminum vacancies, switch over in terms of their dominance depending on the oxygen partial pressure at high temperatures (the so-called p-n transition). In order to investigate this transition behavior the formation energies of charged oxygen and aluminum vacancies at Al2O3 grain boundaries were evaluated using density functional theory. The electronic structures affecting the carrier concentrations are assessed for three types of grain boundaries. The ratios of the grain boundary band gaps relative to the bulk value lie in the range of 0.6-0.85 depending on the degree of grain boundary misorientation. From the formation energies we find that, at band gaps around 60% compared to the bulk value, the dominant vacancy alters depending on the pressure, consistent with the oxygen permeation experiments. Our results suggest that the band bap narrowing occurring at grain boundaries enhances the creation of oxygen vacancies and conduction electrons, facilitating the observed transition. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2014.01.059

Core structure and dissociation energetics of basal edge dislocation in alpha-Al2O3: A combined atomistic simulation and transmission electron microscopy analysis Reviewed

Kenji Tsuruta, Eita Tochigi, Yuki Kezuka, Kazuaki Takata, Naoya Shibata, Atsutomo Nakamura, Yuichi Ikuhara

ACTA MATERIALIA 65 76 - 84 2014.2

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Using large-scale molecular dynamics (MD) simulations, we investigate the energetics and local structures/stresses of partial dislocations, 1/3 < 01 (1) over bar0 > and 1/3 < 10 (1) over bar0 >, dissociated from the 1/3 < 11 (2) over bar0 > perfect basal edge dislocation in alpha-Al2O3. The validity of the model adopted in the simulation is confirmed by comparing with theoretical stress/strain distributions and with those experimentally obtained from a high-resolution transmission electron microscopy (HRTEM) observation. Partial dislocation pairs have a stable inter-core distance (similar to 2 nm), which is also a phenomenon that is observed in the HRTEM experiments. The distance between the partials can be explained quantitatively by the balance between an elastic core core repulsion and an effective attractive force against the extension of stacking faults (SFs). A comparison is made for two types of core structures of partial dislocations: a pair of partials with Al-terminated/O-terminated extra-half planes and that with Al-/Al-terminated ones. The overall tendency of the inter-core interaction and the equilibrium distances are the same in both cases, whereas the Al-O-terminated pair is slightly favourable in energy at the equilibrium distance. A residual shear stress on the SF plane is observed in the MD results, which can be attributed to local atomic structure in the SF. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2013.11.035

Phononic-Crystal Acoustic Lens by Design for Energy-Transmission Devices Reviewed

Yusuke Kanno, Kenji Tsuruta, Kazuhiro Fujimori, Hideki Fukano, Shigeji Nogi

ELECTRONICS AND COMMUNICATIONS IN JAPAN 97 ( 1 ) 22 - 27 2014.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

The lens effect of acoustic waves in a two-dimensional (2D) phononic crystal is studied by numerical simulation based on the finite-difference time-domain (FDTD) method. We calculate the phonon band structure of 2D phononic crystals, consisting of metal/ceramic cylinders placed periodically in water. The lens effect is observed for the far-field wave in phononic crystals with two-layered and graded-index structure. We compare the focal intensity and the energy transmission efficiency in these numerical experiments, and show that a novel energy-transmission device can be designed using phononic crystals. (c) 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 97(1): 22-27, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11491

DOI： 10.1002/ecj.11491

Effect on acoustic wave propagation by the interior structure of waveguide filled up with water

Graphene metasurface for THz wavefront control Reviewed

Yatooshi T, Ishikawa A, Tsuruta K

JSAP-OSA Joint Symposia, JSAP 2014 2014

Tsubouchi Kazuya, Tadokoro Masaaki, Fujimori Kazuhiro, Ishikawa Atsushi, Tsuruta Kenji, Fukano Hideki

The Proceedings of The Computational Mechanics Conference 2014.27 325 - 326 2014

Optically Powered Voltage Supply Device for Effective Utilization of Optical Energy in the Fiber-to-the-Home Network Reviewed

Hideki Fukano, Takeshi Shinagawa, Kenji Tsuruta

ELECTRONICS AND COMMUNICATIONS IN JAPAN 96 ( 10 ) 37 - 42 2013.10

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

SUMMARYAn optically powered device using an InGaAs photodiode has been developed. This study aims to harvest light energy (2.8 to 500 mu W) from the FTTH (fiber-to-the-Home) network and to utilize it for operating remote sensors without an external energy source. We designed the booster circuit and evaluated its characteristics, confirming that it could boost an input voltage of 0.3 V to 3.0 V. We also evaluated the characteristics of an InGaAs photodiode and confirmed that it could output a voltage over 0.3 V using 10-mu W input light. We demonstrate that a ready-made sensor can be operated with an input optical power as low as 10 mu W. (c) 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(10): 37-42, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11472

DOI： 10.1002/ecj.11472

Design and development of highly ecient transducer for ultrasonic wireless power transmission system Reviewed

Yuki Hori, Kazuhiro Fujimori, Kenji Tsuruta, Shigeji Nogi

ELECTRICAL ENGINEERING IN JAPAN 184 ( 3 ) 27 - 35 2013.8

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

In this paper, a transducer that is suitable for the ultrasonic wireless power transmission system is discussed. The transducer is designed based on Mason's equivalent circuit theory, basically. The transducer was developed using design parameters optimized by multiphysics analysis. As a result, it is confirmed that the transmission eciency is drastically improved to more than 50%. This result suggests that wireless power transmission by acoustic wave is feasible. (c) 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(3): 2735, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22406

DOI： 10.1002/eej.22406

Interaction between Atomic Vacancies in Crystalline Si Wafer: A Tight-binding Molecular Dynamics Study Reviewed

K. Takata, K. Tsuruta, T. Ogawa, H. Iyetomi

Trans. Meter. Res. Soc. J 37 ( 2 ) 143 - 146 2012.4

Language：English Publisher：The Materials Research Society of Japan

Vacancy interaction in crystalline Si wafer is studied by numerical simulation based on the Tight-Binding Molecular Dynamics (TBMD) method. We evaluate an effective interaction between vacancy pair in bulk and in a thin slab as model systems of a Si wafer. In the case of vacancy pair in bulk crystal, results reveal that there is an effective "capture radius" of the vacancies to form a divacancy at around 8Å at 300K and 13Å at 600K. Surface structure involving vacancies in Si slab undergoes a reconstruction accompanying dimer-rows in [110] direction initiated by the vacancies. The capture radius is also found to exist in the slab and binding energy of the divacancy has depth dependence due to the surface effect.

DOI： 10.14723/tmrsj.37.143

CiNii Article

Experimental Analysis of Optical Fiber Multimode Interference Structure and its Application to Refractive Index Measurement Reviewed

Shuji Taue, Yoshiki Matsumoto, Hideki Fukano, Kenji Tsuruta

JAPANESE JOURNAL OF APPLIED PHYSICS 51 ( 4 ) 2012.4

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

We investigated a fiber-based multimode interference phenomenon in the wavelength domain by using a white light source and an optical spectrum analyzer. This phenomenon was produced by a larger-core optical fiber joined at both ends with smaller-core optical fibers. We examined the variation of interference wavelength with changes in the length of the larger-core fiber. The interference wavelengths were blue-shifted and the interference signals were sharpened with an increase in the length of the larger-core fiber. The calculated results agreed well with the measured results. Next, we investigated how the input and output fibers with a small core influence the interference signal characteristics. By comparing the amplitude differences of the interference signal we find the conditions of input and output (I/O) fibers for higher sensitivity. In addition, an interference-signal shift was observed by changing the medium surrounding an multimode interference (MMI) structure. The amount of shift increased at a longer wavelength. This leads to the sensitive detection of the refractive index. Finally, a demonstration of the optical fiber refractometer with a multimode interference structure was given by refractive-index measurements of ethanol/water solutions. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.04DG14

An investigation for optimum design of matching circuit in highly efficient RF-DC conversion circuit by genetic algorithm Reviewed

Kondo Y, Fujimori K, Tsuruta K

IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) 194 - 197 2012

Characteristics of RF-DC conversion circuit for wireless power transmission using the low resistance GaN schottky barrier diode Reviewed

Fujimori K, Wagi T, Tsuruta K, Nogi S, Ozawa Y, Furukawa M, Fujiwara T

IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) 190 - 193 2012

Design and development of highly efficient transducer for ultrasonic wireless power transmission system Reviewed

Yuki Hori, Kazuhiro Fujimori, Kenji Tsuruta, Shigeji Nogi

IEEJ Transactions on Electronics, Information and Systems 132 ( 3 ) 1 - 343 2012

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical Engineers of Japan

In this paper, the transducer that is suitable for the ultrasonic wireless power transmission system is discussed. The transducer is designed based on the Mason's equivalent circuit theory, basically. Design parameters of the transducer are optimized for by using the multi physics analysis and developed. As results, it is confirmed that the transmission efficiency is drastically improved to more than 50%. This result suggests that the WPT by acoustic wave is practicable. © 2012 The Institute of Electrical Engineers of Japan.

DOI： 10.1541/ieejeiss.132.337

Frequency characteristic of transmission efficiency depended on matching condition of transducer in ultrasonic wireless power transmission system Reviewed

Fujimori K, Tominaga S, Tanda K, Tsuruta K, Nogi S

IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) 166 - 169 2012

An ab initio analysis of electronic states associated with a silicon vacancy in cubic symmetry Reviewed

OGAWA Takafumi, TSURUTA Kenji, IYETOMI Hiroshi

Solid State Communications 151 ( 21 ) 1605 - 1608 2011.11

Negative Refraction and Energy-Transmission Efficiency of Acoustic Waves in Two-Dimensional Phononic Crystal: Numerical and Experimental Study Reviewed

Yuuki Kasai, Kenji Tsuruta, Kazuhiro Fujimori, Hideki Fukano, Shigeji Nogi

JAPANESE JOURNAL OF APPLIED PHYSICS 50 ( 6 ) 2011.6

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN SOC APPLIED PHYSICS

The negative refraction of acoustic waves in a two-dimensional phononic-crystal slab is studied by numerical simulation based on the finite-difference time-domain (FDTD) method and by ultrasonic measurement. The incident-angle dependences of energy-transmission efficiency in the simulation and experiment are in good agreement in the frequency range of approximately 1.2 MHz. Using the FDTD method, we optimize the efficiency by varying structural parameters such as filling fraction and slab thickness. The effect of deviation from the ideal crystallinity is also evaluated quantitatively via the simulation. These results indicate that an energetically efficient acoustic lens can be fabricated by carefully optimizing the structure of the phononic crystal. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.067301

Structures and Local Electronic States of Dislocation Loop in 4H-SiC via a Linear-Scaling Tight-Binding Study Reviewed

Fusanori Hamasaki, Kenji Tsuruta

MATERIALS TRANSACTIONS 52 ( 4 ) 672 - 676 2011.4

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

The atomic- and electronic-level structures of a dislocation loop and a stacking fault in 4H-SiC crystal are investigated by using large-scale tight-binding (TB) molecular-dynamics simulation. We employ a linear-scaling TB method implemented on a parallel computer in order to accelerate the 9,600-atoms calculation which is required for such a nanoscale simulation. We find that the initial configuration that involves unstable C-C networks around the dislocation loop is relaxed to a structure having six-membered rings, and that the distribution of electron populations is inhomogeneous on the loop. The local electronic density of states shows two peaks in the bulk band gap, where one of these peaks may correspond to the defect state observed in EBIC and CL experiments. [doi:10.2320/matertrans.MBW201024]

DOI： 10.2320/matertrans.MBW201024

Design of Anti-Resonance Transducer and Its Abilities for Efficient Ultrasonic Wireless Power Transmission System Reviewed

Yuki Hori, Yusuke Shigeta, Kazuhiro Fujimori, Kenji Tsuruta, Shigeji Nogi

2011 41ST EUROPEAN MICROWAVE CONFERENCE 67 - 70 2011

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

We developed a fundamental testbed and investigated the suitable transducer for the wireless power transmission (WPT). We also had reported experimental results of the transmission efficiency in water by using the commercial transducer (COM) which only designed to match to the acoustic impedance of water by its structure and the electric impedance of the transmitter and receiver by matching networks. In this paper, we investigate the transducer (DEV) for improving the transmission efficiency based on the Mason's equivalent circuit. For deciding a structure and materials of the transducer, we used ANSYS well-known as the multi-physics simulator.
In this result, it is confirmed that the transmission efficiency is drastically improved from less than 1% to 60% compared to our previous report. In addition, we manufactured designed transducer, and confirmed the system's efficiency is about 50 % experimentally. This result also suggests that WPT by the acoustic wave be practicable.

The Influences of Diode Parameters on Conversion Efficiency of RF-DC Conversion Circuit for Wireless Power Transmission System Reviewed

Kazuhiro Fujimori, Sho-ichi Tamaru, Kenji Tsuruta, Shigeji Nogi

2011 41ST EUROPEAN MICROWAVE CONFERENCE 57 - 60 2011

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

RF-DC conversion circuit is one of the most important components in the wireless power transmission technologies. For realizing highly efficient wireless power transmission, it is necessary to design the RF-DC conversion circuit with high conversion efficiency, and the designing method of the circuit is actively studied. In this paper, the influences of diode parameters, such as its resistance, junction capacitance, parasitic reactance, and so on, on the conversion efficiency of the RF-DC conversion circuit are investigated to clarify the characteristic of the diode for obtaining highly efficient RF-DC conversion circuit.

Development of highly efficient transducer for wireless power transmission system by ultrasonic Reviewed

Yusuke Shigeta, Yuki Hori, Kazuhiro Fujimori, Kenji Tsuruta, Shigeji Nogi

2011 IEEE MTT-S International Microwave Workshop Series on Innovative Wireless Power Transmission: Technologies, Systems, and Applications, IMWS-IWPT 2011 - Proceedings 171 - 174 2011

Language：English Publishing type：Research paper (international conference proceedings)

We developed a fundamental testbed and investigated the suitable transducer for the wireless power transmission (WPT). We also reported experimental results of the transmission efficiency in water by using the commercial transducer (COM) which only designed to match to the acoustic impedance of water and the electric impedance of the transmitter and receiver. In this paper, we investigate the transducer for improving the efficiency based on the Mason's equivalent circuit. For deciding a structure and materials of the transducer, we used ANSYS well-known as the multi-physics simulator. In this result, it is confirmed that the transmission efficiency is drastically improved from less than 1% to 60%. In addition, we made designed transducer, and confirmed the systems' efficiency is about 50 %. This result suggests that the WPT by acoustic wave is practicable. © 2011 IEEE.

DOI： 10.1109/IMWS.2011.5877115