Yoshiaki Akematsu

Doppler effect in flexible and expandable light waveguide and development of new fiber-optic vibration/acoustic sensor

New principle and a geometrical arrangement of an optical fiber for a vibration/acoustic measurement are proposed in the present paper. The sensor is based on a new finding that a frequency of light wave transmitted through a bent optical fiber is shifted by vibration at the bent region. The phenomenon can be explained as Dopplers effect in flexible and expandable light waveguide. Several configurations of the sensor have been designed, and very high sensitivity is achieved in the extremely wide frequency range. Principle, sensor configuration and theoretical sensitivity, measurement system, and some experimental consideration are described in the present paper. The sensor sensitivity was examined experimentally in the low and middle frequency range, and the detectability was confirmed experimentally in the frequency range of acoustic emission signals.

Detection of acoustic emission wave by using optical fiber sensor during single pulse discharge

This paper describes some experimental results on a fundamental phenomenon of the single pulse discharge. The single pulse discharge phenomenon was measured by using the optical fiber sensor, piezoelectric sensor and current transducer. In order to investigate the generation factor and propagation characteristic of acoustic emission (AE) by single pulse discharge in oil, the voltage across the gap, the discharge current and the displacement velocity were measured. Detected the signals using the optical fiber sensor and piezoelectric sensor have been compared with each other. As the results, optical fiber sensor was more resist than piezoelectric sensor in an electromagnetic noise. It is likely that the optical fiber sensor was more useful than piezoelectric sensor for AE detection with electromagnetic field. In order to investigate the relationships between the single pulse discharge phenomena and the detected AE signals, numerical analysis by using finite element method (FEM) was adapted. The numerical analysis result using the FEM and the experiment result along with the single pulse discharge was compared. As the result, it was estimated that the generation factor of the AE wave was the 1μs duration force. The signal detected by the optical fiber sensor has a good agreement with the signal from the FEM one. It is found that optical fiber sensor can detect the displacement velocity with wide band. Moreover, it was considered that frequency response of the optical fiber sensor is approximately flat. The optical fiber sensor was effective in analysis of AE source.

Measurement of Acoustic Emission Wave by Using Optical Fiber Sensor during Microsecond Discharge

In this study, we investigate the effect of discharge current on the occurrence of burst AE wave caused by microsecond discharge. Electrical discharge duration was changed from about 1µs to 8µs by using condenser circuit. Effect of current behavior was estimated by comparing with experimental signal and simulation one. AE wave was detected by optical fiber vibration sensor. The optical fiber vibration sensor is located on an aluminum work-piece (cathode) plate. Simulation was carried out with MSC. Marc. As the results, it was found that AE wave was occurred by a force depending on electrical current behavior. The force direction was machining direction. The force has been occurred during microsecond discharge.

Effect of Arc Discharge Pressure on Discharge Current in EDM

In electrical discharge machining (EDM), an electrical discharge occurs between a tool electrode and a work-piece, and removal of materials is carried out by vaporized explosion between the electrode and the work-piece. However, the mechanism of material removal in EDM is not well understood. In order to clarify this issue, the acoustic emission (AE) method has been applied to examine the force of explosion, and the Schlieren visualization method has been applied to observe the explosion. In this study, we investigate the effect of discharge current behavior on the occurrence of the AE waves by means of an optical fiber vibration sensor.

Effects of Leading and Trailing Edge of Current Pulse on Ae Wave

In this study, the mechanism of pressure occurrence in Electrical discharge machining (EDM) was investigated by Acoustic emission (AE) technique. AE wave was detected by optical fiber vibration sensor during single pulse discharge. This paper describes some experimental results on AE wave characteristics during single pulse discharge. The generation factor and propagation characteristic of AE wave were investigated. Numerical analysis by using finite element method (FEM) was adapted on the assumption that the AE wave was only depending on a force. In order to investigate the effect of current behavior on AE propagation, the numerical analysis result using the FEM and the experimental result along with the single pulse discharge were compared.

Possibility of electrical discharge pulse sound for hammering test

In this study, it was investigated that the possibility of electrical discharge pulse sound for new inspection technologies instead of hammering test. Electrical discharge pulse sound was applied for hammering sound and sensor by using sound detection was applied for optical fiber vibration sensor. The numerical analysis result using the FEM and the experiment result along with the single pulse discharge was compared. As the result, it was estimated that the generation factor of the elastic wave was same as the current duration. These results become possible to estimate the propagation characteristic of elastic wave. Evaluation of electrical discharge sound for hammering test by using optical fiber sensor was investigated. Defect shape and scale was estimated from comparison with detected waveform by using optical fiber vibration sensor and simulated waveform. As the results, it was considered that electrical discharge sound was available for hammering test.

Characteristics of Electrical Discharge Pulse Sound for Hammering Test

In this study, the possibility of electrical discharge pulse sound for new inspection technologies instead of hammering test was investigated. Electrical discharge pulse sound was applied for hammering sound and sensor by using sound detection was applied for the optical fiber vibration sensor. Elastic wave was detected by optical fiber vibration sensor during electrical discharge. The plate thickness was changed from 0.5mm to 10mm. On the assumption that generation factor of elastic wave was only depending on a force, numerical analysis by using the finite element method (FEM) was adapted. The numerical analysis result using the FEM and the experimental result along with the electrical discharge were compared. The plate thickness was estimated by comparing with experimental signal and simulation one. It was found that plate thickness was able to estimate from comparing with experimental signal and simulation one. Moreover, a quasi-defect was created the plate by comparing with experimental results and simulation one. It was found that the defect shape was able to estimate by comparing with experimental results and simulation one.

Acoustic emission and elastic wave measurements by using a new fiber-optic (DEFEW) sensor

A new fiber-optic acoustic/vibration sensor has been developed. The sensor is based on Doppler effect in flexible and expandable light-waveguide (DEFEW). The DEFEW sensor has extremely high sensitivity in wide band of frequency range. The sensing technology is applied to high speed phenomena, for examples, breakage of carbon fiber in matrix resin and elastic wave propagation impacted by electrical discharge. The demonstrated results show that the DEFEW sensor is applicable to nondestructive damage detection for structural health monitoring.