Iwao Matsuya

Enhancement of field emission characteristics of tungsten emitters by single-walled carbon nanotube modification

We present a simple method for improving the field emission performance of tungsten-tip electron sources based on single-walled carbon nanotube (SWCNT) modification. By coating a sandwich-like thin film of Al–Fe–Al (with Fe as a catalyst) on a tungsten tip, SWCNTs were synthesized at 600 °C in a chemical vapor deposition (CVD) reactor. The influence of CNT modification on the electron emission characteristics of the emitters was investigated by means of a triode structure. We have found that CNT-modified tungsten tips exhibit low threshold-voltage for electron emission, and improved emission-current stability, compared with nonmodified and Al–Fe–Al-coated needles.

Measuring Relative-Story Displacement and Local Inclination Angle Using Multiple Position-Sensitive Detectors

We propose a novel sensor system for monitoring the structural health of a building. The system optically measures the relative-story displacement during earthquakes for detecting any deformations of building elements. The sensor unit is composed of three position sensitive detectors (PSDs) and lenses capable of measuring the relative-story displacement precisely, even if the PSD unit was inclined in response to the seismic vibration. For verification, laboratory tests were carried out using an Xθ-stage and a shaking table. The static experiment verified that the sensor could measure the local inclination angle as well as the lateral displacement. The dynamic experiment revealed that the accuracy of the sensor was 150 μm in the relative-displacement measurement and 100 μrad in the inclination angle measurement. These results indicate that the proposed sensor system has sufficient accuracy for the measurement of relative-story displacement in response to the seismic vibration.

Accuracy Evaluation of Surface Temperature Profiling by a Laser Ultrasonic Method

Accuracy in measuring surface temperature distributions by a laser ultrasonic method is examined. Surface temperature distributions of an aluminum plate whose single side is heated up to 110 °C are estimated by the inverse analysis coupled with surface acoustic wave (SAW) measurements, and the results are compared with those measured by an infrared radiation method. A random fluctuation in the temperature estimated by the ultrasonic method is observed and decreases with an increase in the distance from the heating area. The standard deviation in fluctuation is estimated to be about 2 °C at the heating area. Furthermore, the systematic errors in the temperature estimation due to the deviations in the temperature dependence of SAW velocity and thermal diffusivity are investigated. It is found that the temperature dependence of SAW is an important factor affecting the systematic error, but the influence of the deviation in thermal diffusivity is negligible.

A Novel Process for Fabrication of Gated Silicon Field Emitter Array Taking Advantage of Ion Bombardment Retarded Etching

A novel process for the fabrication of a gated silicon field emitter array is proposed. The process involves complete self-alignment of gate electrodes taking advantage of ion bombardment retarded etching. The ion-irradiated regions serve as masks for subsequent silicon etching resulting in the formation of tabletop structures. The structures are suitable for both the formation of pyramidal emitters and the arrangement of gate electrodes adjacent to each emitter. We integrate this silicon etching into a self-align process for the fabrication of gated emitter array. The emission characteristics of 100 emitters are tested, and the emission at a gate voltage of 30 V is detected. The results indicate that the proposed process is applicable to the fabrication of gated silicon emitters.

Measuring Liquid-Level Utilizing Wedge Wave

A new technique for measuring liquid-level utilizing wedge wave is presented and demonstrated through FEM simulation and a corresponding experiment. The velocities of wedge waves in the air and the water, and the sensitivities for the measurement, are compared with the simulation and the results obtained in the experiments. Combining the simulation and the measurement theory, it is verified that the foundation framework for the methods is available. The liquid-level sensing is carried out using the aluminum waveguide with a 30° wedge in the water. The liquid-level is proportional to the traveling time of the mode 1 wedge wave. The standard deviations and the uncertainties of the measurement are 0.65 mm and 0.21 mm using interface echo, and 0.39 mm and 0.12 mm utilized by end echo, which are smaller than the industry standard of 1.5 mm. The measurement resolutions are 7.68 μm using the interface echo, which is the smallest among all the guided acoustic wave-based liquid-level sensing.

Noncontact Temperature Profiling of Rotating Cylinder by Laser-Ultrasound

In the fields of engineering and manufacturing industries, it is often required to know quantitative information about surface and internal temperatures of rotating objects. In this work, a new ultrasonic method for measuring such temperatures of a heated rotating cylinder is presented. A laser-ultrasonic technique which provides noncontact ultrasonic measurements is employed in the present method. To make a quantitative evaluation of the internal temperature distribution in the radial direction of a heated rotating cylinder having axisymmetric temperature distribution, an effective method consisting of surface temperature measurements with a laser-ultrasonic technique and one-dimensional unsteady heat conduction analyses with a finite difference calculation is developed. To demonstrate the feasibility of the method, experiments with heated steel cylinders of 100 mm and 30 mm in diameter rotating at 300 min− 1 are conducted. A pulsed laser generator and a laser Doppler vibrometer are used for generating and detecting surface acoustic waves (SAWs) on the steel cylinder, respectively. Measured SAWs are used for determining both surface and internal temperatures of the cylinder. The estimated temperature distributions during heating almost agree with those measured by an infrared radiation camera. Thus, it has been shown that the noncontact temperature measurement technique with laser ultrasound is a promising tool for on-line monitoring of heated rotating cylinders.

Application of Laser Ultrasound to Noncontact Temperature Profiling of a Heated Hollow Cylinder

A new ultrasonic method to monitor the temperature distributions of a thick-walled hollow cylinder whose inner surface is heated is presented. This method basically consists of laser ultrasonic measurements and a heat conduction analysis of the heated hollow cylinder. Both longitudinal wave (LW) and surface acoustic wave (SAW) are used for estimating the temperature distribution of the cylinder. To demonstrate the validity of the proposed method, a numerical simulation and an experiment are carried out. In the numerical simulation, a steel hollow cylinder (the inner and outer diameters are 20 mm and 100 mm, respectively) is uniformly heated by a constant heat flux at the inner surface. It has been verified in the simulation that temperature distributions estimated by the proposed method completely agreed with the theoretical results. In the experiment, an aluminum hollow cylinder (the inner and outer diameters are 20 mm and 50 mm, respectively) is heated by pouring molten metal at 300 °C into the hollow cavity of the cylinder. A laser ultrasonic system is used for measuring both LW and SAW of the heated cylinder. It has also been demonstrated that the proposed method can measure the change in the temperature distribution during heating.

A Feasibility Study on Generation of Acoustic Waves Utilizing Evanescent Light

A new approach of generating acoustic waves utilizing evanescent light is presented. The evanescent light is a non-propagating electromagnetic wave that exhibits exponential decay with distance from the surface at which the total internal reflection of light is formed. In this research, the evanescent light during total internal reflection at prism surface is utilized for generating acoustic waves in aluminium and the feasibility for ultrasonic measurements is discussed. Pulsed Nd:YAG laser with 0.36 J/cm2 power density is used and the incident angle during the total internal reflection is arranged to be 69.0° for generating the evanescent light. It has been demonstrated that the amplitude of the acoustic waves by means of evanescent light is about 1/14 as large as the one generated by the conventional pulsed laser. This reveals the possibility of using a laser ultrasonic technique with near-field optics.

Experimental study on liquid-level measurement based on laser ultrasonic technique and tip-generated wedge wave

A method for measuring liquid-level utilizing wedge wave generated by a pulsed laser is presented. The sound velocity of wedge wave is slow compared to the other types of guided waves, so the measurement accuracy which is closely related to the time resolution of measurement equipment can be improved. This method is utilizing the difference of wedge wave velocity in the air and in the water. It is demonstrated that the liquid level is proportional to the elapsed time difference of the propagated wedge wave. The wedge wave velocities in the air were experimentally obtained 1375 m/s for mode 1 and 2362 m/s for mode 2. It is confirmed that mode 1 is suitable for the measurement because of its slowness and clear signal. The liquid-level sensing was carried out by laser ultrasonic technique using aluminum 30° wedge in the water. The relationship between the liquid-level and the elapsed time of the wedge wave showed high linearity. The standard deviation of data plots was 0.88 mm, the measurement resolution was...

Ultrasonic Lateral Displacement Sensor for Health Monitoring in Seismically Isolated Buildings

An ultrasonic lateral displacement sensor utilizing air-coupled ultrasound transducers is proposed. The normally-distributed far field of an ultrasound transducer in a lateral direction is taken advantage of for measuring lateral displacement. The measurement system is composed of several air-coupled ultrasound transducers as a receiver and several transmitters. The transmitters are immobilized at a fixed point, whereas the receiver set-up is separately arranged on the opposite side. In order to improve measurement accuracy, a correction method that utilizes polynomial approximation is introduced. The difference between the corrected lateral displacement and the reference displacement is estimated to be 0.2 mm at maximum for the two transmitters system. A good responsiveness is demonstrated by conducting a dynamic response experiment. When five transmitters are arranged, their measurement range is easily extended up to ±60 mm with an accuracy of 0.7 mm. In both cases, the fluctuations to the measurement ranges show less than 1%. These results indicate that the developed sensor system is useful for measuring relative lateral displacement of a seismically isolated building in the field of structural health monitoring.