記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Inorganic Chemistry  

Co-Ni alloy nanoparticles, a potential candidate for microwave absorption material, were successfully synthesized by tuning the reduction timing of Co and Ni ions by introducing oleylamine as a complexing agent and 1-heptanol as a reducing solvent. The formation mechanism elucidated using time-resolved sampling and in situ X-ray absorption spectroscopy (XAS) and ultraviolet-visible (UV-vis) spectrophotometry measurements suggested that the delay in the reduction of Co ions via complexation with oleylamine facilitated the co-reduction of Co with Ni ions and led to the formation of Co-Ni alloys. The successful synthesis of Co-Ni alloys experimentally confirmed the differences in magnetic properties between alloy and core-shell structured Co50Ni50 particles. Further, the syntheses of Co-Ni alloys with different compositions were also possible using the above technique. In addition, the microwave absorption properties were measured using the free-space method utilizing a vector network analyzer of Co50Ni50-polyethylene composite with different sheet thicknesses. A reflection loss (RL) value of -25.7 dB at 13.6 GHz for the alloy structure was more significant than the core-shell counterpart. The above values are high compared to results reported in the past. The validity of the measurements was confirmed by utilizing the parameter retrieval method to extract permittivity and permeability from the scattering parameter (S) and recalculation of the RL as a function of frequency.

DOI： 10.1021/acs.inorgchem.2c02633

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85140324092&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Proceedings in Complexity  

Route planning in logistics, in which multiple pickup and delivery positions exist in a road network, is a complicated task with many choices in a path selection and their influences on the following procedures. Solving this task by multi-agent simulations, we examine the route optimization process by monitoring motions in networks based on simple or higher-order Markov chains (MCs). Agent footprints in the networks, which spread over the entire network at the initial phase, converge on small number of edges as the transportation path gets shortened. When we increase the order of MCs in agent mobilities, the MC networks are enlarged and possess a large number of nodes and edges with structural regularity so that one node contains partial trace history, while the optimized route that frequently overlaps edge groups with high transition probabilities is equivalent to a smaller and more noticeable subgraph around a local optimal solution. In other words, this localization of the traces indicates a convergence level in optimization, which can be a measure for route planning in logistics.

DOI： 10.1007/978-3-030-81854-8_4

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85113302052&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Scientific Reports  

© 2021, The Author(s). In situ sensing with wireless digital-data transfer is a potential processing scheme that works very closely to the location of an event monitored by a sensor and converts the sensor’s raw output into digitized and informative small-volume bits, as suggested by recent proposals for edge computing and the Internet of Things (IoT). Colour perception may be a target of in situ sensor data acquisition; however, in contrast to from other sensing devices, colour sensors that detect visible light signals are usually located away from light-emitting sources, collecting light transmitting through the space and attenuating it in some manner. For example, in a vacuum chamber whose gas pressure is much less than the ambient atmosphere in which the sensors usually work, there are many veiled light sources, such as discharge plasma, for various industrial purposes including nanoscale manufacturing. In this study, we designed an in-vacuum colour sensor that can work with analogue-to-digital conversion and transfer data by wireless communication; this sensor is active in a low-pressure plasma chamber, detecting light signals and transferring them to a personal computer located outside the vacuum chamber. In addition to detecting lights with controlled spectra from outside successfully, we achieved complete operation of our in-vacuum active sensor for plasma emissions generated at 100 Pa. Comparing the signals with data from simultaneous monitoring by a monochromator, we established that the recorded signals arose from the plasma, confirming successful direct detection of low-pressure plasma emissions without any filtering effects between the sensor and the target object.

DOI： 10.1038/s41598-020-80501-z

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85099396381&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Studies in Computational Intelligence  

Vehicle mobility in urban traffic systems is complex, partly because it reflects mobility of a human who drives a vehicle, and partly because it depends on many roles which the vehicle plays. Previous studies on human mobility revealed that it includes Lévy-flights-like motions and memoryless deterministic walks as well as random walks, but the mobility of vehicles may be more biased due to their functions. Focusing our research target on a sightseeing vehicle with sufficiently limited functions, we show a method to measure regularity of visitation patterns, quantified by order(s) of Markov chains in their mobility. Graphs of higher-order Markov chains, which are representatives of mobility in a network style, possess statistical properties; in our observation dataset, they include degree distributions similar to scale-free networks. The detection of mobility in real social experiments, which is also assumed on these graphs, yields the order of Markov chains inside it with its comparison with the results of agent-based simulations. Centrality indices of the mobility networks well coincide with prediction of these analytical and numerical results.

DOI： 10.1007/978-3-030-65351-4_19

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85101814485&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Studies in Computational Intelligence  

Chemistry in plasma is complicated because it has so many reactions in parallel and in series. A complex network is suitable for the visualization and the analysis of its complexity. A numerical calculation based on hundreds of rate equations is a typical tool for plasma chemistry, but such a computational process does not clarify the undergoing physical and chemical properties that stabilize many industrial plasma processes for a number of applications. In this study, we focus on low-temperature plasma in which high-energy electrons are activators for chemical reactions, and investigate the origin of the stability by examining the statistical properties of networks for silane (SiH ) plasma. There is only one seed species in the initial space, SiH , which is surrounded by high-energy electrons. SiH is decomposed into several fragments composed of Si and/or H atoms with possible charges, and such radical and ion species are decomposed or synthesized into other species, leading to the formation of temporal reaction networks in chemistry. With the effects of rate constants that determine chemical reaction rates, we create temporal networks and observe preferential attachments that induce a new reaction in a transient state. The centrality indices for participant species and degree distributions reveal what is occurring in this complex system, and during the sequential process we observe an exponential-tail degree distribution, which is a significant source of reaction stability. 4 4 4

DOI： 10.1007/978-3-030-65351-4_32

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85101815755&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Scientific Reports  

© 2020, The Author(s). A metal plate array (MPA) which is a structure complimentary to a metal hole array (MHA), supports spoof surface plasmon polaritons (SSPP) as well as an MHA does. Babinet’s principle attributes the phenomenon of duality to transmission characteristics of the complimentary impedance surfaces because of the symmetry of the behaviors of electric and magnetic fields. However, it is also a fact that the complimentary structures do not follow this principle if they have wavelength-size thickness, because electromagnetic waves do not treat such thick structures as a boundary surface but as propagation spaces with the specific boundaries such as a waveguide which shows SSPP modes. If the thickness is so small that it is negligible, Babinet’s principle is still valid, while it has been uncertain how the layer thickness works to break the principle as it is increased. The unconfirmed transformation is revealed analytically and experimentally with the use of MPAs and MHAs of varying thicknesses.

DOI： 10.1038/s41598-020-67923-5

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85087404276&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Plasma Sources Science and Technology  

© 2020 IOP Publishing Ltd. We propose graph-theoretical analysis for extracting inherent information from complex plasma chemistry and devise a systematic way to rescale the network under the following key criteria: (1) maintain the scale-freeness and self-similarity in the network topology and (2) select the primary species considering its topological centrality. Network analysis of reaction sets clarifies that the scale-freeness emerging from a weak preferential mechanism reflects the uniqueness of plasma-induced chemistry. The effect of chemistry rescaling on the dynamics and chemistry of the He + O2 plasma is quantified through numerical simulations. The present chemical compression dramatically reduces the computational load, whereas the concentration profiles of reactive oxygen species (ROS) remain largely unchanged across a broad range of time, space and oxygen admixture fraction. The proposed analytical approach enables us to exploit the full potential of expansive chemical reaction data and would serve as a guideline for creating chemical reaction models.

DOI： 10.1088/1361-6595/abbdca

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85097937713&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Healthcare (Switzerland)  

Swallowing sounds from cervical auscultation include information related to the swallowing function. Several studies have been conducted on the screening tests of dysphagia. The literature shows a significant difference between the characteristics of swallowing sounds obtained from different subjects (e.g., healthy and dysphagic subjects; young and old adults). These studies demonstrate the usefulness of swallowing sounds during dysphagic screening. However, the degree of classification for dysphagia based on swallowing sounds has not been thoroughly studied. In this study, we investigate the use of machine learning for classifying swallowing sounds into various types, such as normal swallowing or mild, moderate, and severe dysphagia. In particular, swallowing sounds were recorded from patients with dysphagia. Support vector machines (SVMs) were trained using some features extracted from the obtained swallowing sounds. Moreover, the accuracy of the classification of swallowing sounds using the trained SVMs was evaluated via cross-validation techniques. In the two-class scenario, wherein the swallowing sounds were divided into two categories (viz. normal and dysphagic subjects), the maximum F-measure was 78.9%. In the four-class scenario, where the swallowing sounds were divided into four categories (viz. normal subject, and mild, moderate, and severe dysphagic subjects), the F-measure values for the classes were 65.6%, 53.1%, 51.1%, and 37.1%, respectively.

DOI： 10.3390/healthcare8020103

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85088588517&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.5112077

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Electronics (Switzerland)  

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. Vehicle mobilities for passengers in a city’s downtown area or in the countryside are significant points to characterize their functions and outputs. We focus on commercial sightseeing vehicles in a Japanese city where many tourists enjoy sightseeing. Such mobilities and their visualizations make tourist activities smoother and richer. We design and install a low-power, wide-area positioning system on a rickshaw, which is a human-pulled, two-or three-wheeled cart, and monitor its mobility in Hikone City. All the spatial locations, which are recorded in a time sequence on a cloud server, are currently available as open data on the internet. We analyze such sequential data using graph topology, which reflects the information of corresponding geographical maps, and reproduce it in cyberspace using an agent-based model with similar probabilities to the accumulated rickshaw records from one spatial node to another. Although the numerical results of the agent traced in a simulated city are partially consistent with the rickshaw’s record, we identify some significant differences. We conclude that the rickshaw’s mobility observed at the actual sightseeing sites is partially in the random motion; some cases are strongly biased by memory routes. Such non-randomness in the rickshaw’s mobility indicates the existence of specific features in tourism sources that are identified for each sightseeing activity and affected by local sightseeing resources.

DOI： 10.3390/electronics9010116

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85078313908&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Electronics (Switzerland)  

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. A novel 2D imaging method for permittivity imaging using a meta-structure with a functional scanning defect is proposed, working in the millimeter wave-range. The meta-structure we used here is composed of a perforated metal plate with subwavelength-holes and a needle-like conductor that can scan two-dimensionally just beneath the plate. The metal plate, which is referred to as a metal hole array (MHA) in this study, is known as a structure supporting propagation of spoof surface plasmon polaritons (SSPPs). High-frequency waves with frequencies higher than microwaves, including SSPPs, have the potential to detect signals from inner parts embedded beneath solid surfaces such as living cells or organs under the skin, without physical invasion, because of the larger skin depth penetration of millimeter wave-bands than optical wave-bands. Focused on activated SSPPs, the localized distortion of SSPP modes on an MHA is used in the proposed method to scan the electromagnetic properties of the MHA with a needle-like conductor (conductive probe), which is a kind of active defect-initiator. To show the validity of the proposed method, electromagnetic analyses of the localized distortions of wave fields were performed, and one-and two-dimensional imaging experiments were conducted with the aim of detecting both conductive and dielectric samples. The analytical results confirmed the localized distortion of the electric field distribution of SSPP modes and also indicated that the proposed method has scanning ability. In experimental studies, the detection of conductive and dielectric samples was successful, where the detected dielectrics contained pseudo-biological materials, with an accuracy on the order of millimeters. Finally, a biomedical diagnosis in the case of a rat lung is demonstrated by using the experimental system. These results indicate that the proposed method may be usable for non-invasive and low-risk biomedical diagnosis.

DOI： 10.3390/electronics8020239

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85066860208&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Series in Materials Science  

© Springer Nature Singapore Pte Ltd 2019. Discharge plasmas are composed of electrons and ions, and their permittivity is dynamic and tunable. Conventional metamaterials are composed of designed functional microstructures of solid materials, and become extraordinary wave media such as negative-permeability materials. The composites of the plasmas and the metamaterials are well mixed to show dynamic properties coming from plasmas and extraordinary outputs based on metamaterials. Here, we describe their theoretical basis and topical features observed in microwave experiments. Beyond properties of tunability, such composite “plasma metamaterials” work well as nonlinear and high-energy-carrier metamaterials, unlike conventional solid-state metamaterials.

DOI： 10.1007/978-981-13-8649-7_10

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85072821574&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Sciences (Switzerland)  

© 2018 by the authors. Fractal-like nanoparticle two-dimensional patterns forming in diffusion-limited aggregation show variant spatial patterns. However, they have invariant statistical properties in their network topologies, even though their formation is completely in self-assembled processes. One of the outputs from these topological properties is optical resonances at invariant frequencies, which is a required feature of a metamaterial alternative. Fractal-like metallic patterns studied here in both experiments and theoretical models exhibit similar resonance frequencies in the infrared-ray range, and they depend on the unit length of nanoparticles composing arbitrary fractal-like structures. The scheme of analysis applied here using complex network theory does not only reveal the topological properties of the nanoparticle network, but points out their optical and possibly other physical potentials arising from their geometrical properties.

DOI： 10.3390/app8081310

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85075768667&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Advances in Physics: X  

© 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. The concept of metamaterials has led to extraordinary schemes of wave propagation, which has been verified using various meta-atoms, constituent units of metamaterials, as well as applied to a number of categories in physics. Although its definition clarifies the maximum size of meta-atoms as a fraction of one wavelength, the size may vary by several orders, like from millimeters (‘macroscopic level’) to atomic scales (‘microscopic level’) for microwaves. This review surveys several patterns of parameter combinations, like permittivity and permeability in electromagnetic metamaterials, which have been achieved at either macroscopic or microscopic levels, with the similar analogy under the concept of metamaterials. Various experimental and theoretical efforts reported so far and shown here verify that the parameter identification of these values (permittivity, permeability, and refractive index) is independent of meta-atom sizes, with importance of spatial integration procedure on the order of a wavelength.

DOI： 10.1080/23746149.2018.1433551

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85064523651&origin=inward

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE SA  

Non-thermal plasmas in electrode configurations are designed in this study and investigated at atmospheric pressure for generation of reactive fields. A combination of insulated wire electrodes and bare metal wire electrodes makes it possible to obtain a filter-like assembly of microplasmas, even in ambient air or in aqueous solutions. Oxidation and reduction fields are obtained by controlling the gas supply of hydrogen, oxygen, and water vapor, and these fields benefit various functional processes such as recycling CO(2), decomposing organic molecules, and increasing the work function on metal surfaces. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2011.01.225

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

In order to investigate the effect of accumulated charge on a substrate surface in the deposition of a SiO(2) film with an atmospheric-pressure plasma jet, we have measured the discharge current flowing into a copper substrate, which was placed 20 mm from the exit of the plasma jet and connected to a variable capacitor in series. We found that the discharge current decreased markedly when the capacitance of the substrate was below 100 pF, and the deposition rate of SiO(2) traced the variation of the capacitance. To analyze the behavior of the plasma jet, we considered an equivalent circuit of our system and verified the validity of our supposition that the accumulated charge restricts the deposition rate. Thereby, we found that the discharge current and deposition rate were determined by the capacitance of both the glass tube wall and the substrate. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.49.066201

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Microplasmas have a number of potential roles to control propagating electromagnetic waves. This report focuses on novel physics of periodic microplasma assembly for electromagnetic media, which is verified by experimental results and analyzed by numerical methods. Using an assembly composed of microplasmas, novel functions are expected due to its complex dielectric function arising from dielectric and lossy properties. The dielectric property creates photonic band gaps, and the lossy property drastically changes transmittance around the photonic band gaps, leading to an attenuation gap. As a result, a "complex" dispersion relation or a band diagram in the three-dimensional space of real and imaginary wavenumbers and wave frequency will open new possibilities to control electromagnetic waves by complex-variable filters composed of microplasma assemblies. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3314334]

DOI： 10.1063/1.3314334

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We have diagnosed the electron density in nitrogen plasma generated in a device composed of coaxial-hollow microdielectric-barrier discharges using a millimetre-wave transmission method. At atmospheric pressure the generated plasma occupied almost the entire hollow-electrode space, and the electron density was estimated as 10(12)-10(13) cm(-3). This value is in good agreement with theoretical prediction in a simple particle-balance model. We also studied the effect of small admixtures of H(2)O and O(2) into nitrogen discharges at atmospheric pressure. In the case of H(2)O addition, the measured electron density was lower than that in pure nitrogen, in particular at high reduced electric fields, due to the increase in the loss processes of electrons. In the case of O(2) addition, the electron density decreased with an increase in O(2) concentration due to the additional loss process through the formation of negative ions.

DOI： 10.1088/0963-0252/19/2/025006

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE SA  

Plasma enhanced chemical vapor deposition using a non-thermal plasma jet was applied to deposition of ZnO films. Using vaporized bis(octane-2,4-dionato)zinc flow crossed by the plasma jet, the deposition rate was as high as several tens of nm/s. From the results of infrared spectra, the films deposited at the substrate temperature T(sub) = 100 degrees C contained a significant amount of carbon residue, while the films prepared at T(sub)=250 degrees C showed less carbon fraction. The experimental results confirmed that the plasma jet decomposed bis(octane-2,4-dionato)zinc in the gaseous phase and on the substrate, and that there should be the critical Tsub to form high-quality ZnO films in the range from 100 to 250 degrees C. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2009.11.034

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE SA  

Metamaterial effects emerging from a spatially-arranged microplasma array was investigated at microwave frequencies. With elaborated spatial designs of periodic columnar microplasmas, they serve as a converter of microwaves in the complex plane with various functions. Composites of microplasmas and metal wires show extraordinary properties for electromagnetic waves, such as negative-refractive index, which have not been naturally available. These two aspects of microplasma arrangement will open novel features beyond the conventional materials, which can be referred to as plasma metamaterial effects. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2009.11.040

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

We have investigated the discharge mechanisms in a helium plasma jet with a coaxial dielectric barrier discharge (DBD) configuration, which can generate low-temperature plasma plume mainly by positive corona streamer propagation. In this study, we focused on the relationships between the coaxial DBD inside a glass tube and the positive streamer propagating in the plasma plume, using novel types of electrode configurations composed of insulated electric wires. The discharge characteristics were investigated by measuring plume length, discharge currents of the DBD, and the line-integrated density of helium metastable atoms in the plume. The experimental results indicate that the excited-species density in the plume is largely dependent on surface-charge density accumulated by the DBD. Moreover, we analyzed the spatiotemporal distribution of electrical potential around the tube exit by the finite element method, and discussed the mechanism determining plume length. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.49.106001

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOCIETY APPLIED PHYSICS  

A microplasma device fabricated on a silicon substrate with a floating electrode inside the microdischarge space was investigated-to determine the dependences of discharge properties in neon gas on the gas pressure p and the characteristic-dimension D. With a decrease in p towards the condition of the minimum ignition voltage, the spatial emission distribution in the negative phase of the applied bipolar pulsed voltage changed from a hollow pattern with a bright periphery to a concentrated bright pattern in the central area above the floating electrode, which was similar to that in the positive phase. This observation encourages us to make this device structure to provide a brighter light source at the microscales for various photonic applications. (C) 2009 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.48.106002

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

CO2 as a solute of aqueous solution was deoxidized by hydrogen microplasmas generated in an electrolyte. Dielectric barrier discharges were generated in H-2 microbubbles created by electrolysis, and optical emission spectra included carbon-oriented lines as well as an atomic H line. From a chromatogram of a gas in a trap on the electrolyte surface, CO was detected, which was a product of the reduction reaction of CO2 induced by underwater hydrogen microplasmas.

DOI： 10.1088/0022-3727/42/20/202004

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOCIETY APPLIED PHYSICS  

Metal plates with two-dimensional hole arrays showed unusual responses of electromagnetic waves, and in this study microplasmas were generated in the holes to deform their properties dynamically and to induce novel frequency-dependent permittivity. Transmitted electromagnetic waves in millimeter wavelength range exhibited attenuation of anomalous transmittance around cutoff frequency of equivalent waveguide when microplasmas were present. On the contrary, the reflected waves were significantly enhanced around such a frequency, where reflectance is at minimum in the case without microplasma generation. These experimental results indicated resonance phenomenon which is usually called spoof surface plasmons, and dynamic change of dielectric constant in the medium inside the holes induced by microplasmas shifts their resonance frequency. (C) 2009 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.48.062004

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Pulsed microdischarge was generated in microbubbles produced by electrolysis in an electrolyte solution without external gas feed by using a fabric-type electrode. The electrode structure not only allowed low-voltage ignition of the atmospheric-pressure discharge in hydrogen or oxygen containing microbubbles but also worked effectively in producing and holding the bubbles on its surface. The generation of reactive species was verified by optical emissions from the produced microplasmas, and their transport into the solution was monitored by the change in hydrogen concentration.

DOI： 10.1063/1.3006348

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

The complex wave number in lossy photonic crystals composed of microplasmas was verified experimentally by measuring the refractive index and the transmittance in a microwave range. These experimental results coincide with the dispersion relation obtained by a modified plan-wave expansion method. In particular, an extraordinary reduction of attenuation was observed in a certain frequency band, which is attributed to a loss term in the dielectric function and periodicity in the structure. These results indicate that a method of dynamic control for electromagnetic waves can be realized using of the dispersion relation in complex space. (C) 2008 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.1.066003

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Functional arrays of microplasmas were designed for the purpose of controlling electromagnetic waves in the range 10 - 100GHz. A two-dimensional square-lattice array of microplasma columns was proved to have photonic-crystal-like properties showing the presence of photonic band gaps and flat bands. A one-dimensional linear array of cold cathode fluorescent lamps (CCFLs) embedded in between the truncated strip lines showed the resonant transmission characteristics due to the surface-wave modes corresponding to the flat-band frequencies. Another one-dimensional configuration of CCFLs vertically aligned along both sides of a coplanar strip line showed peculiar behavior at the lower and higher edges of the band gap. These unique wave-propagation properties are attributed to the periodic structures of which pitches are comparable to or smaller than the wavelengths of electromagnetic waves. Therefore, these artificial arrays are potential metamaterials, which can be used for plasma devices controlling electromagnetic waves.

DOI： 10.1088/0741-3335/49/12B/S43

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Millimeter plasmas were tailored to play a role as dynamic devices of microwave components, that is, to control electromagnetic wave propagation dynamically on a microstrip line. The generation of millimeter plasmas with their relatively long discharge channel (similar to 3 mm) was in high-pressure (20-200 torr) Ne, and they were successfully arranged near and on the conductor of microstrip lines. When such a plasma was set perpendicularly to the conductor to form a T junction, a significant reduction of electromagnetic wave transmission along the metal conductor was observed. The reduction rate depended on the discharge current and the number of T junctions. These experimental results are compared with the case of 2 MHz launching for crude electron density measurements and the numerical results of propagating electric fields in a two-dimensional model.

DOI： 10.1109/TPS.2005.863594

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Propagation of electromagnetic waves in several types of microplasmas has been examined experimentally in a frequency range 10-75 GHz. Firstly, the fundamental characteristics of the propagation were investigated using a planar geometry of microplasma assembly, and the electron density was derived by a comparison of the transmittance with the theoretical analyses using a Drude type model with collisional effects. Secondly, an extraordinary propagation phenomenon such as the focusing effect was observed in a two-dimensional periodical microplasma array. This kind of anomalous refraction cannot be interpreted only by predictions based on the dielectric property of bulk plasma, and it is suggested that a photonic-crystal-like periodical dielectric structure may play a significant role. Thirdly, it was demonstrated that the T-junction formed by a microplasma connected to a microstrip line can control the transmission of microwaves. An attenuation (or modulation) depth of about 35% was obtained with a series of two T -junctions connected to the strip line at the right-angled corners. All the above features come from (a) the relatively high electron density of the microplasmas near 10(13) cm(-3), (b) the complex dispersion relation with collisional effects and (c) the spatial arrangement with a characteristic scale of the same order of the wavelength of microwaves.

DOI： 10.1088/0741-3335/47/12B/S45

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

We experimentally verified that a microplasma assembly can create a functional dielectric layer for the propagation of electromagnetic waves as a "plasma photonic crystal." A two-dimensional array in a square lattice was composed of columnar plasmas of about 2 mm in diameter, and the transmitted microwaves at 70-75 GHz showed a change of energy flow direction. This result is attributed to the fact that periodical structure is composed of individual plasma columns with a different dispersion than the ambient part and the experimental frequency range lies in the vicinity of the lowest band gap of the photonic crystal calculated theoretically. (c) 2005 American Institute of Physics.

DOI： 10.1063/1.2147709

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Atmospheric pressure discharges in Ne, N-2 and N-2/O-2 gases have been investigated with a novel high-voltage pulse power supply. Three characteristic types of discharge modes were observed: (1) diffuse glow discharge seen in Ne gas both with the eye and high-speed camera; (2) diffuse glow-like discharge in N-2 gas observed with the eye, but seen as a vague filamentary discharge with a high-speed camera; and (3) clear filamentary discharge in N-2/O-2 gas mixture both with the eye and high-speed camera. Characteristics in the current and voltage waveforms revealed that the existence of the second voltage with opposite polarity following the first impulse voltage was important to have a diffuse glow-like discharge. This suggests that elimination of the memory effect by non-uniformly distributed charges on the surface is important for obtaining the diffuse mode because the non-uniformity triggers a positive feedback to the current constriction at the points with higher charge density, and results in filamentation of the discharge.

DOI： 10.1088/0022-3727/38/12/010

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

We have measured the density of metastable He atoms in the lowest triplet state (2(3)S(1)) with a diode-laser absorption spectroscopic technique in atmospheric pressure plasmas produced by dielectric barrier discharge schemes. Two different types of electrode configuration are employed: one is a conventional parallel-plate system and the other is a microdischarge integrated system with stacked metal-mesh electrodes covered by insulating films. We have analyzed the pressure-broadened spectral line corresponding to the 2(3)S(1)-> 2(3)P(J) (J=0-2) transition to derive the broadening coefficient and to calibrate absolute densities. The measured density ranges from 10(11) to 10(12) cm(-3), but the values in the mesh-type system are larger than those in the parallel-plate system by about one order of magnitude. The density, however, depends strongly on the gas flow rate, showing the influence of quenching by the Penning-ionization process with impurities. Those behaviors are consistent with the variation of the electron density estimated by millimeter-wave transmittance measurement.(c) 2005 American Institute of Physics.

DOI： 10.1063/1.1922581

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Two different types of microdischarge-integrated plasma sources have been operated at around the atmospheric pressure range. The discharge characteristics were diagnosed by optical emission spectroscopy (OES), laser absorption spectroscopy (LAS) and microwave transmission (MT) techniques. The dynamic spatiotemporal behaviour of excited atoms was analysed using OES and LAS and the temporal behaviour of the electron density was estimated using the MT method. In Ar and Xe/Ne gases, waveforms of the NIT signal followed the current waveform in the rise period and lasted longer according to the recombination losses. However, in He the waveform followed the density of metastable atoms, reflecting the production of a large amount of electrons by the Penning ionization process with impurities. The estimated peak electron density in those plasma sources is of the order of 10(12) cm(-3), and the metastable atom density can reach 10(13) cm(-3). Thus, it is suggested that these sources can be potentially applied to convenient material processing tools of large area operated stably at atmospheric pressure.

DOI： 10.1088/0741-3335/47/5A/012

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

An integrated structure of coaxial-hollow micro dielectric-barrier-discharges has been developed by stacking two metal meshes covered with insulating material. The test panel has an effective area of 50 mm diameter in which hundreds of hollow structures are assembled with a unit hollow area of 0.2 x 1.7 mm(2). He or N-2 was used as the discharge gas in the pressure range from 20 to 100 kPa and the firing voltage was less than 2kV, even at the maximum pressure. The intensity of each microdischarge was observed to be uniform over the whole area throughout the pressure range, and its time evolution during one discharge pulse was analysed through two-dimensional microscopic observation with a gated CCD camera. In a gas flow regime through the coaxial hollow structures, several significant changes of the discharge properties were observed, such as impurity reduction, decrease in discharge voltage and cooling of the neutral gas. The fundamental plasma parameters were measured using a single probe in the downstream region of microdischarges using an auxiliary flat electrode set apart from the mesh electrode plane. The occurrence of an extended glow with a length of some millimetres was observed in He but not in N-2. The electron density derived by the probe data in He at 100 kPa was similar to3 x 10(11) cm(-3), suggesting a value of more than 10(12) cm(-3) in the active microdischarge region.

DOI： 10.1088/0022-3727/38/3/012

Web of Science