Yorinobu Murata

Optimal wavelength pair selection and accuracy analysis of dual fiber grating sensors for simultaneously measuring strain and temperature

We investigate the wavelength selection of dual fiber grating sensors for strain and temperature measurements. Temperature and strain coefficients of fiber gratings are measured in the wavelength range of 600 to 1600 nm in Corning Flexcor-980™ fiber. Theoretical fits are estimated using Ghoshs temperature-dependent refractive index model for optical fiber glasses. Moreover, the effect of apparent thermal strain due to the structural thermal expansion on the temperature coefficient in a surface-bonded fiber grating sensor is investigated, and numerical re- sults for the accuracy of temperature and strain are presented. It is shown that the structural thermal properties have a large influence on the resolution and measurement accuracy of dual fiber grating sensors.

A new vector velocimetry by real time ultrasonic imaging using M-sequence encoding array transducer

In order to measure velocity vector of moving object in water, we have developed a new vector velocimetry using ultrasound. Velocity vector was measured by real-time ultrasonic imaging using M-sequence encoding array transducer. When this array transducer was applied to ultrasonic imaging, a cross section image was obtained by a transmitting and receiving process. In experiment, we tried to measure the two dimensional velocity vector of a wire target moving at a constant velocity of 10.0 mm/s and at a constant angle of 45/spl deg/ away from the transducer surface. An ultrasonic pulse was transmitted with a constant interval time of 10.0 ms, and We obtained ultrasonic images of 16. The system was operated at the frequency of 2.5 MHz. Images at each acquisition were reconstructed by correlation method. The velocity vector was calculated by the trajectory of target in each image. In conclusion, it was found that the velocity vector of the target be measured with accuracy 4% by the developed vector velocimetry.

High-speed height measurement by a light-source-stepping method using a linear LED array

High-speed height measurement is required in industrial fields for analyzing the behavior of a breaking object, a vibrating object or a rotating object. A shape measurement performed using a phase-shifting method can measure the shape with high spatial resolution because the coordinates can be obtained pixel by pixel. A light-source-stepping method (LSSM) that uses a linear LED array by means of a whole-space tabulation method (WSTM) has been proposed. Accurate shape measurement can be performed using this method. The response speed of the LED array is greater than 12 kHz. In this paper, height measurement is performed using WSTM and LSSM with a linear LED array and a high-speed camera. It was verified that the response speed of the linear LED is greater than 200 kHz. The phase shifting was performed at 12 kHz, and the height measurement of the vibrating woofer was performed at 4 kHz using a 3-step phase-shifting method.

GENERATION OF AN ENHANCED ACOUSTIC STREAMING IN A BOUNDED SPACE

A procedure to generate enhanced acoustic streaming into a bounded space has been studied. Under continuous ultrasound radiation, it was difficult to generate enhanced acoustic streaming in bounded space because of disturbances by reflected waves. Efforts were made to remove the disturbances by adjusting the repeat time of tone bursts of ultrasound. An experimental system has been developed for visualizing acoustic streaming. As a consequence of experiments, the streaming velocity in the bounded space has been enhanced by about 2.5 times by using a series of tone bursts of ultrasound.

Design of an Acoustical Imaging Operator Based on the Singular Value Decomposition Method

A new imaging operator has been developed for acoustical imaging using a 2ch m-sequence encoding array transducer. The new imaging operator has the ability to correct the poor orthogonal property of a transfer matrix. Moreover, images with many image points have been reconstructed by the new imaging operator. The new imaging operator has been composed on the basis of the singular-value decomposition (SVD) of the transfer matrix in the frequency domain. Characteristics of the new imaging operator are discussed by simulating the two-dimensional point spread functions (2-D PSFs). An image with a high dynamic range was obtained for a single object on the sampling image points by the method. Moreover, the method was able to reconstruct the image of the existing object outside the sampling image points.

2-CH M-Sequence Encoding Array Transducer System for Acoustical Imaging

The “Encoding Array (EA)”, proposed by the authors1, represents a new concept in image sensors. With this EA, an image can be reconstructed without resort to either mechanical or electrical scanning—something that we, the authors, have already proposed the benefits of in previous papers2–5.

Deformation Distribution Measurement from Oblique Direction Using Sampling Moire Method

A sampling Moire method is one of a deformation measurement method of a large structure such as a building and a bridge. The accuracy of phase difference analysis is from 1/100 to 1/1,000 of the grating pitches. This method can analyze two-dimensional phases from a two-dimensional grating image attached on the surface of a specimen. The phase difference distribution before and after deformation gives displacement distributions for the x- and the y-directions. Grating phase also gives position for the x- and the y-directions. Therefore, the relationship between a point on an image and the corresponding point on the object can be obtained without any calibrations. A sampling Moire camera we proposed has an FPGA with an algorithm of the sampling Moire method inside the camera. It can output two-dimensional phases and phase differences from a single shot two-dimensional grating image in real-time. In this paper, a measurement accuracy of the deformation distribution measurement using the sampling Moire camera placed in the oblique direction is estimated. Experimental result of the time-series deformation measurement of a moving cantilever is shown.

Development of a Focused Ultrasonic Transducer for the Testing of the Wheel Seat in the Hollow Axle of Shinkansen Vehicles

In order to test the fretting fatigue cracks with high sensitivity, which occurred on the wheel seat of hollow axles of Shinkansen vehicles, the design of a focused ultrasonic transducer was proposed by a new method. The method was achieved by designing a suitable surface shape of the ultrasonic transducer through a reverse analysis of the wave propagation in the axle so that all radiated waves from the transducer were focused into a point region of the wheel seat with a same phase. A composite piezoelectric material was applied to the focused ultrasonic transducers in order to test with a shorter ultrasonic pulse. As the result of evaluating the performance of the developed focused ultrasound transducer, comparing with the previous plate-like ultrasonic transducer made using PZT, a great improvement was demonstrated in respect of sensitivity and directivity. Furthermore, the method inclining the ultrasonic beam slightly to the circumference direction and the method making the frequency characteristic of the transducer high were devised in order to reduce the influence of echoes by press fit. Consequently, it was demonstrated that a focused incline ultrasonic transducer of 10 MHz was possible to evaluate up to an artificial crack of about 0.17 mm depth with the SN ratio of 9 dB.Copyright

Acoustical Imaging Using M-sequence Encoding Array Transducer

An experimental study on an ultrasonic camera has been carried out using a pair of m-sequence encoding transducer made of VDF-TrFE copolymer. The ultrasonic camera can construct an image without mechanical or electrical scanning. The transducer must have wide-band characteristics. The system operates at the frequency of 10 MHz. A two dimensional point spread function of the camera system was calculated by both the correlation procedure and the pseudo-inversion matrix method, and the results were compared with the previous encoding aperture receiver system.

Application of Phase-Shifted Fringe Projection Method with Linear Fiber Arrays Using Talbot Effect to Height Measurement of BGA

Recently, authors were proposed a small pitch fringe projection method using Talbot effect with an SLD (super luminescent diode) with inclining the appearing area of the fringe pattern. The phase of the projected fringe is shifted using a linear fiber array with four cores. In this paper, an application of these methods to height measurement of BGA (ball grid array) is performed.