Naoyuki Kono

3-D Modelings of an Ultrasonic Phased Array Transducer and Its Radiation Properties in Solid

Ultrasonic phased array technology has become popular in the field of industrial nondestructive testing (NDT). The technology is notable for its capability to provide images of the inside of a target in real time. Since the image quality results from rapid steering and focusing of the radiation beam from an array transducer, it is essential to have well understood characteristics of the radiated beam. Even though fundamental concepts of the array transducer in medical fields were introduced over 30 years ago (Macovski, 1979), the beam modeling and optimization of the array transducer for the NDT have only been investigated intensively in the past decade (Azar et al., 2000; Song & Kim, 2002). The characteristics of the radiated beam from the ultrasonic phased array transducer vary according to the transducer parameters such as frequency, aperture size, number of elements, pitch(inter-element spacing), element width, layout dimensions and so forth. If these parameters are not chosen properly, spurious grating lobes or side lobes with high amplitude will exist in the radiation beam field. Consequently, the image quality will be deteriorated significantly.

COMPARATIVE STUDY ON ULTRASONIC IMAGING METHODS WITH ARRAY TRANSDUCERS

The performance of ultrasonic imaging methods developed in time domain and frequency domain algorithms is investigated in this study. The sectorial synthetic aperture focusing technique (S–SAFT) outputs the flaw image by superposing the sector–scan images obtained at various measurement points in the time domain. The inverse scattering imaging method (ISIM) is based on the elastodynamic inversion in the frequency domain and reconstructs the mathematical function which represents the flaw shape. The advantages and usabilities of these methods are discussed, taking into account the practical application to the NDE field.

DEVELOPMENT OF 3D PHASED ARRAY SYSTEM “3D FOCUS‐UT”

Ultrasonic phased array inspection systems have been used the in various industrial fields recently. For instance, power plants have used these systems to maintain their reliability. The phased array is advantageous because it improves efficiency by imaging the inside of the test subject. This inspection image is obtained by electronic scanning of a focused ultrasonic beam using a phased array sensor. We have developed a 3‐dimensional volume inspection technology to make further efficiency and accuracy improvements in ultrasonic inspections. This study presents the innovative 3D phased array inspection system “3D Focus‐UT” for 3D volume inspection. This system employs (1) a 3D ray‐trace simulator to set up the delay time for the elements in the array sensor and the delay pattern for 3D volume scanning; (2) high sensitivity phased array equipment that has a 256 ch pulsar/receiver to drive/receive a 2D matrix array transducer simultaneously; and (3) high‐speed 3D data processing software. The software conve...

Numerical Simulation of Scattered Waves from Flaws for Ultrasonic Array Transducer

To enhance the detectability in the phased array UT, it is essential to have well knowledge on the characteristics of ultrasonic waves from array transducers. This paper proposes a mathematical model of the array transducer and a simulation tool to predict the flaw echoes. The modeling of an array transducer is based on the Rayleigh‐Sommerfeld integral and the scattered waves from flaws are calculated with the fast multipole BEM (FMBEM). By using the FMBEM, we can solve large scale scattering problems with relatively low computational cost. Here we focus on the transient wave analysis, in which a pulse‐shaped wave is used for exciting elements of the array transducer.

Approximate Evaluation of Acoustical Focal Beams by Phased Array Probes for Austenitic Weld Inspections

Phased array techniques are capable of the sensitive detection and precise sizing of flaws or cracks in components of nuclear power plants by using arbitrary focal beams with various depths, positions and angles. Aquantitative investigation of these focal beams is essential for the optimization of array probes, especially for austenitic weld inspection, in order to improve the detectability, sizing accuracy, and signal‐to‐noise ratio using these beams. In the present work, focal beams generated by phased array probes are calculated based on the Fresnel‐Kirchhoff diffraction integral (FKDI) method, and an approximation formula between the actual focal depth and optical focal depth is proposed as an extension of the theory for conventional spherically focusing probes. The validity of the approximation formula for the array probes is confirmed by a comparison with simulation data using the FKDI method, and the experimental data.

Development of localization system using ultrasonic sensor for an underwater robot to survey narrow environment

ABSTRACT This paper describes a localization system for a swimming robot to survey underwater narrow environments. In that environment, external sensors cannot be set up to localize the robot position, as there are many structures and the robot moves three-dimensionally. Therefore, the position needs to be calculated only by internal sensors. In this work, a new localization method based on map-matching is proposed, referring to cross-sectional shape data cut from a three-dimensional computer-aided design (CAD) data as an environmental map and structural shapes measured by a range sensor. As a range sensor, an ultrasonic sensor which is two-dimensional scanning-type was developed. The reflected signals of the ultrasonic sensor have some noise. Only structural shape data are extracted from the reflected signals. The image correlation is used as the matching method. Experiments to evaluate the performance of the proposed system were implemented at a mock-up environment. As a result, it was confirmed that the position was detected with an accuracy of 100 mm. The error is mainly caused by measurement error of the ultrasonic sensor that is used to calculate structural shapes. We concluded to improve the measurement accuracy of the ultrasonic sensor to reduce localization error.

Semi-analytical modeling of acoustic beam divergence in homogeneous anisotropic half-spaces

Beam divergences of acoustical fields in semi-infinite homogeneous anisotropic media are calculated based on a semi-analytical model. The model for a plane source in a semi-infinite homogeneous anisotropic medium is proposed as an extended model for a point source in an infinite medium. Beam divergences propagating along crystallographic axes 〈100〉, 〈110〉, and 〈111〉 in a cubic crystal, a single crystalline Ni-based alloy, are measured and compared to calculation results for verifying the model. The contribution of beam divergence attenuation to the total attenuation for propagating in anisotropic polycrystalline materials is quantitatively evaluated in isolation from scattering attenuation effects.