Fuminobu Takahashi

Development of Signal Processing Methods for Imaging Buned Pipes

A new imaging technique for subsurface radars is described for reconstructing clear images of buried pipes in soil. The method developed has two signal processing stages; preprocessing and aperture synthesis. The preprocessing extracts signals scattered from the pipes by reducing clutter noise. The synthetic-aperture processing analyzes only the scattered signals derived by the first stage and reconstructs high-quality images in a short processing time. The imaging technique developed was successfully applied to the imaging of actual buried metallic pipes. It was experimentally confirmed that the new imaging method was capable of reconstructing clear images in a short time without losing image quality.

Development of an ultrasonic inspection system using array transducers

Abstract A new ultrasonic inspection system was developed to obtain ultrasonic images of defects. This system adopts an electronic beam control method using array transducers. The beam control modes are a compound scanning mode and a linear scanning mode. Both modes are performed by timing control of ultrasonic wave transmission and reception at each transducer element. In the focal beam, the refraction of the ultrasonic wave at the boundary between water and metal in immersion testing is utilized to improve the lateral resolution of the ultrasonic beam. In steel, the improvement is a maximum of 25% for focal lengths from 5 to 35 mm as compared to lateral resolution not utilizing refraction. This system successfully imaged two side drilled holes in a steel block.

Digital Signal Processing in Acoustical Focused Image Holography

This paper presents a new concept of signal processing in acoustical focused image holography, named “digital accustical holography”. Presented here is a method based on time coincidence measurement between digitized reflected pulses and digital clock pulses for phase detection instead of heterodyne phase detection used in conventional acoustical holography. This digital phase detection permits the use of a wide band (spike shaped) transmitted pulse which increases the depth resolution remarkably. Furthermore, fringe representation corresponding to the deviation in the propagation path length of less than half a wave length can be easily achieved by changing the clock pulse frequency independently of the carrier frequency of the transmitted waves.

Application of Shear Wave Focused Image Holography to Nondestructive Testing

This paper describes a method for sizing vertical and oblique flaws or defects within metal structures be the use of scanned acoustical holographic interferometry in the focused image hologram mode. The image of an internal flaw obtained from focused image holography consists of interference fringes or contour lines across the flaw’s surface. The fringe separation represents half wavelength deviations in depth from the scanning plane and the length of the fringes corresponds to the width of the flaw. Thus, it is possible to evaluate flaw size by measuring the number and length of fringes appearing on the focused image hologram.