Ryoichi Tsuda

Investigation of electric discharge sound in atmospheric pressure plasma using optical wave microphone

Abstract The light diffraction technique, which we call the “Optical Wave Microphone (OWM)” technique, is an effective sensing method to detect the sound and is flexible for practical uses as it involves only a simple optical lens system. This technique is also very useful to detect the sound wave without disturbing the sound field. Moreover, OWM can be used for sound field visualization by computerized tomography (CT) because the ultrasmall modulation by the sound field is integrated along the laser beam path. The characteristics of the coplanar DBD (Dielectric Barrier Discharge) operated in air is investigated. Applied voltage, current and the electrical discharge sound of coplanar DBD are measured, and examined the relationship between the micro discharge and the acoustic properties. We expect that understanding of acoustic properties gives more details of electric discharges. These are the first experiments to verify the feasibility of the OWM-CT method for the visualization of the sound field of DBD discharge.

Investigation of electric discharge sound in atmospheric pressure plasma

Abstract The characteristics of the Coplanar DBD (Dielectric Barrier Discharge) operated in air, argon or helium are investigated. Applied voltage, current and the electrical discharge sound of Coplanar DBD discharge are measured, and examined the fundamental relationship between the micro discharge and the acoustic properties. We expect that the understanding of acoustic properties gives more details of electric discharges and also develops new applications in the field of medical diagnostics, environment system, etc. We apply the new method to examine the electric discharge sound using Fraunhofer diffraction effect of visible laser beam. This new system is called the optical wave microphone by us and is very useful for the detection of sound wave without disturbing the sound field. The Fast Fourier Transform (FFT) is applied to discriminate the acoustic sound of the Coplanar DBD discharge and the dominant frequency components.

Acoustic signal analysis in the creeping discharge

We have previously succeeded in measuring the acoustic signal due to the dielectric barrier discharge and discriminating the dominant frequency components of the acoustic signal. The dominant frequency components appear over 20kHz of acoustic signal by the dielectric barrier discharge. Recently surface discharge control technology has been focused from practical applications such as ozonizer, NOX reactors, light source or display. The fundamental experiments are carried to examine the creeping discharge using the acoustic signal. When the high voltage (6kV, f = 10kHz) is applied to the electrode, the discharge current flows and the acoustic sound is generated. The current, voltage waveforms of creeping discharge and the sound signal detected by the condenser microphone are stored in the digital memory scope. In this scheme, Continuous Wavelet Transform (CWT) is applied to discriminate the acoustic sound of the micro discharge and the dominant frequency components are studied. CWT results of sound signal show the frequency spectrum of wideband up to 100kHz. In addition, the energy distributions of acoustic signal are examined by CWT.

Source localization of visually evoked magnetic fields to stimuli in apparent motion

When at least two spatially separated visual stimuli are delivered sequentially under appropriate temporal conditions, a continuous moving sensation, which is called apparent motion, can be perceived. To investigate the cortical activation associated with visual apparent motion, brain evoked magnetic fields in response to visual half field apparent motion stimuli were measured using a whole-head magnetometer. Peak magnetic fields were observed in the latency range of 170-190 msec after the stimulus onset. The neural sources in this epoch were estimated to lie in the border between occipital and temporal areas in the contralateral hemisphere, which corresponds to the extrastriate visual cortex, including the middle temporal area. The results suggest that the activities in the extrastriate cortex reflect apparent motion perception.

Spatial distributions of evoked potentials associated with visual apparent movement

Spatio-temporal properties of evoked potentials associated with the perception of visual apparent movement were studied. Optimal stimulus conditions were obtained in the psychological measurement. Based upon the results, evoked potentials related to visual apparent movement were measured, and topographic maps were constructed to evaluate the active areas of visual apparent movement. The topographic maps show that parietal scalp regions are activated about 300msec after the onset of the second stimulus of the apparent stimulation. The results suggest that visual apparent movement occurs in the visual association area or higher levels in the central nervous system.

Visualization of sound field using Optical Wave Microphone coupled with computerized tomography

The novel method, which we call the “Optical Wave Microphone (OWM)” technique, is based on a Fraunhofer diffraction effect between sound wave and laser beam. The light diffraction technique is an effective sensing method to detect the sound and is flexible for practical uses as it involves only a simple optical lens system. In this work, fibered OWM which is improved in signal-noise ratio of the conventional OWM, was developed. This new method can realize high accuracy measurement of slight density change of atmosphere. Moreover, fibered OWM can be applied for sound field visualization by computerized tomography (CT) because the ultra-small modulation by the sound field is integrated along the laser beam path.

Thermal treatment of carbon nanotubes film by a pulsed Nd: YAG laser irradiation

Multi-walled carbon nanotubes (MWCNTs) film have been analyzed by Raman spectroscopy to clarify the effect of a pulsed Nd: YAG laser heating. The MWCNTs film surface was flashed with the fundamental harmonic (λ=1064 nm) or the second harmonic (λ=532 nm) of a single pulse of Nd: YAG laser in the air. The dynamics of pulsed nanosecond laser heating process was simulated by the solution of the one-dimensional heat conduction equation. Raman spectroscopy of MWCNTs films before and after irradiation were measured. The intensity of the two characteristic Raman shifts ID (defect-mode) and IG (graphite-mode) was measured by the Raman spectroscopy. The maximum surface temperature was calculated and compared with the IG/ID ratio of MWCNTs film. The heating process by a pulsed Nd: YAG laser was further examined in the context of atmosphere (oxygen, ozone, nitrogen or partial vacuum).

Analysis of acoustic signal in the MICRO discharges using continuous wavelet transform

Abstract To examine the tracking phenomenon that was one of the main causes of fire breaking, fundamental experiments were carried out. To one of the electrodes AC high voltage was applied. The following samples: the mesh plate, the flat ribbon cable and the ignition plug were prepared as the electrode. Current, voltage waveforms of micro discharge and the sound signal detected by the condenser microphone were stored in the Hi-coder memory. In this paper, Continuous Wavelet Transform (CWT) was applied to determine the acoustic sound of the micro discharge and to study its dominant frequency components. Additionally, the energy distribution of acoustic signal was examined by CWT, when the frequency of power supply increased from 10 kHz to 30 kHz.

Breakdown effects and steady-state visual evoked potentials in short-range apparent motion

In the presentation of repetitive motion stimuli the perception of apparent motion is replaced by the impression of break down, that is, the cessation of the experience of motion. This perception is called breakdown effect. This study is focused on the stimulus conditions eliciting the breakdown and steady-state visual evoked potentials responded to the repetitive apparent motion stimuli.

Perception of visual apparent movement and topographic analysis of related evoked potentials.

SummaryMost of the studies in long-range apparent movement have been concerned with the psychophysical properties in central vision. However, apparent movement in peripheral vision is not clearly understood. This study focuses on the properties of the perception of apparent movement between central and peripheral vision. The results show that judgments of apparent movement in central vision indicate high performance at less than 4° of spatial separation, and that judgments in peripheral vision indicate high performance at greater than 4°. Evoked potentials associated with long-range apparent movement were also measured, and topographic maps were constructed to evaluate the active areas corresponding to visual apparent movement. The topographic maps show that the central regions are activated above 300 msec after the onset of the second apparent-movement stimulation. The results suggest that visual apparent movement occurs in the visual association area, or at higher levels in the central nervous system.