Kageyoshi Katakura

Multiple acoustic beamformer step scanner

In an ultrasonic imaging system including an array of ultrasonic oscillators, ultrasonic beams are electronically scanned by sequentially selecting a plurality of oscillator sets for beam transmission and reception. For one transmission of ultrasonic waves, at least two receiver oscillator sets having at least some oscillators in common are simultaneously selected, and the respective outputs from the oscillators in the at least two receiver oscillator sets are phase-adjusted so that echoes received by the at least two receiver oscillator sets effectively correspond to echoes substantially emanating from at least two respective different points on a depth level distanced from the plane of the oscillator array by a predetermined depth, whereby at least two signals and hence at least two successive scan lines relating to the echoes from those respective different points are produced. As a result, improved line resolution and rapid line acquisition can be obtained.

Ultrasonic velocity meter

A phase difference comparison type of ultrasonic velocity meter repeatingly transmitting acoustic waves in the form of pulses at alternate time intervals: T-TS and T+TS, receiving reflected waves generated by the transmission of these waves and reflected on an object, forming first and second mixed waves by mixing the reception signal obtained from the reflected waves with two reference waves having phases shifted 90 degrees from each other, detecting the phase difference between the present vectors representing the first and second mixed waves and similar vectors which have been obtained with respect to the preceding pulse transmission, detecting the phase difference Q between the phase difference caused in relation to the time interval T-TS and the phase difference caused in relation to the time interval T+TS with respect to a phase difference obtained each time a pulse is transmitted, and calculating the Droppler shift angle frequency ωd from ωd=Q/2TS.

Proposal of Non Contact Inspection Method for Concrete Structures Using High-Power Directional Sound Source and Scanning Laser Doppler Vibrometer

Maintenance for concrete structures such as buildings, bridges, and tunnels is necessary, because it is thought that a lot of them show deterioration. As a periodic inspection, a hammering test is the most popular method. However, it has several problems. One of the problems is that it is difficult to inspect the places where people cannot reach. Therefore, non contact inspection methods have been developed. As a non-contact inspection method, we propose a system consisting of a high-power directional sound source and a scanning laser doppler vibrometer (SLDV). In this method, an air-borne sound wave is used for the excitation of a concrete wall, and then the vibration velocities on the concrete wall are measured two-dimensionally by the SLDV. From the vibration velocity, defective parts can be detected. In this paper, we describe two types of experiment on the feasibility of our proposed method. In these experiments, concrete wall test pieces, which have artificial defects, are used. From the experimental results, we confirmed the effectiveness of our proposed method as a non contact inspection method for concrete structures.

Measurement of a damaged layer thickness with reflection acoustic microscope

An acoustic microscope was used for determining the frequency dependence of surface acoustic wave (SAW) velocity on a specimen whose silicon single-crystal surface was machined under various conditions. Consequently, thickness of the damaged layers could be estimated from the curvature points of frequency dispersion curves of the SAW velocity. It was revealed that thicknesses of the damaged layers can be estimated through rough approximation by about one-half the wavelength determined by the frequency at curvature points. From specimens possessing two damaged layers, frequency dispersion curves with two curvature lines can be obtained. From the curvature point at high frequencies the thickness of the top damaged layer can be determined. On the other hand, from the curvature point at low frequencies, the thickness of the inner damaged layer can also be determined. By choosing an acoustic lens as the condition for exciting SAWs, images can be observed while varying the frequency. From observation results obtained with this method, the distribution in the depth direction can be clarified.<<ETX>>

Convex array ultrasonic probe

An ultrasonic probe used for ultrasonic diagnosis apparatus. A plurality of ultrasonic transducer elements are provided in a convexity at the tip of a probe so as to constitute a convex array ultrasonic probe. The curvature radius of the convexity is set at not greater than 12 mm and the pitch of adjacent transducer elements is set at not greater than 1/30 of the curvature radius and a ratio Δ/Y is set at not greater than 1/35, where Y represents the beam focal distance and Δ represents the lateral resolution of the probe.

Multi‐element ultrasonic transducer

A multi-element ultrasonic transducer in which elements are arrayed and in which a plate-shaped piezoelectric material has its one face formed with a uniform electrode and its other face formed alternately with electrodes corresponding to the respective elements and electrodes for separating the elements. These electrodes for the element separation are connected the uniform electrode opposed thereto and is fed with a ground potential. On the other hand, the electrodes corresponding to the respective elements are fed individually with transmitting and receiving signals independently of the elements so that the electronic scanning or focusing operations can be achieved.

An Acoustic Microscope for Subsurface Defect Characterization

Abstmct-A scanning acoustic microscope operating in the frequency range 0.1 - L GHz has been developed. The acoustic micrographs obtained have clearly demonstrated that this device can be used nondestructively to observe spike defects at the edge of the local oxidation of silicon structures in semiconductor devices and hydrogenion-doped regions in silicon crystals. The acoustic data have been compared with results obtained through the scanning electron microscope and the optical microscope. ICROANALYSIS techniques used to measure and examine microscopic regions in materials with highfrequency ultrasound waves have recently received a great deal of attention as a new and highly promising means for measurement and observation. Typical of these new methods is the mechanical scanning acoustic microscope developed by Professor C. F. Quate at Stanford University in 1973 [l]. This device directs a narrow focused acoustic beam at a specimen being scanned two-dimensionally, and detects acoustic waves that are reflected from or transmitted through the specimen to obtain a two-dimensional image. The image contrast obtained reflects changes in the mechanical properties of materials in the specimen, such as elasticity, density, and viscosity. Applications of the acoustic microscope include, for example, fault detection in materials, the examination of semiconductor devices, and materials evaluation using surface acoustic waves [2]-161. In this paper we report the results of studies conducted on spike defects that arise in isolation regions between elements in semiconductor devices and regions bombarded by hydrogen ions on silicon substrates. 11. CONSTRUCTION OF THE ACOUSTIC MICROSCOPE The operating principles and construction of acoustic microscopes in general have already been described in a number of papers and will be omitted here. We intend to discuss here only several specific features particular to our reflection scanning acoustic microscope. The most important technical problems that had to solved during development of this device were the development of a process for forming high-performance piezoelectric film; a process for fabricating microspherical

Study on detectable size and depth of defects in noncontact acoustic inspection method

We study a noncontact inspection method for large-scale structures such as tunnels and bridges. This method involves the use of a high-powered sound source and a scanning laser Doppler vibrometer (SLDV). In our previous study, we proposed a tone burst wave method to improve the signal-to-noise ratio (SNR) of the measured result. Using this method, a defect that was difficult to detect using our previous method was detected. In this study, we examined the detectable size and depth of the defect by using a model wall with circular defects. The distance between the sound source and the concrete test piece was 5 m, and the output sound pressure was about 100 dB near the surface of the concrete test piece. As the transmitted wave, tone burst waves with different center frequencies from 500 to 7000 Hz were used. A conventional investigation by the hammer method was also simultaneously carried out for comparison and almost identical performance was confirmed. From the experimental result, we confirmed that the bending resonance frequency detected was proportional to the depth of the circular defect, and was in inverse proportion to the plane size (area) coincident to the analytical result for a circular plate. We also found that the vibration energy of the defect shows a strong dependency on its depth. Therefore, the possibility of defect depth estimation using the resonance frequency and the vibration energy ratio is expected. In the future, a practical investigation system that will replace the hammer method might be developed.

Experimental observation of plastic deformation areas, using an acoustic microscope

Novel techniques are described for the observation of plastic deformation areas by using an acoustic microscope. On a test piece subjected to plastic deformation, an area was found that had an abnormal contrast in the crystal grain and a pointed end at the V notch. Calculation of the propagation velocity of the surface acoustic wave (SAW) showed a difference of several percent between this area and the rest of the test piece. It has been presumed that this difference reflects the local plastic deformation, and that the abnormal contrast area corresponds to the image of the two-dimensionally distributed plastic deformation area of metals.<<ETX>>

Ultrasonic vector velocity measurement by projection Computed Velocimetry

A new method of measuring complete vector components of target velocity is proposed. This method makes it possible to measure target velocity components both along and transverse to the beam axis in two steps. The first step is Fourier transformation of the received signals in the direction of the time-axis (the ultrasonic pulse emission number). The second step is projection integration in the polar-axis direction. These two steps provide the two velocity components along and transverse to the beam axis. The new method is similar to the Computed Velocimetry method (CV) proposed previously by the authors, except that it does not require Fourier transformation in the polar-axis direction. The theory for this method and results of numerical simulation are presented.<<ETX>>