Method for imaging cross section of object by ultrasound using synthetic aperture technique.

The synthetic aperture imaging technique has recently become popular in the field of non-destructive testing (NDT), but its image reconstruction process takes a time too long to be applied practically. We have developed a real-time ultrasonic imaging system based on the synthetic aperture focusing technique (SAFT). The system provides a cross-sectional image as a picture-scroll of an object.Computer simulation was conducted to study effects of various essential parameters for the system, such as directivity of ultrasonic transducer, temporal or spatial sampling period etc., on the resulting image and the resolution. Also, the relation between the lateral length of object and the point spread function (PSF) was studied, and the resolution in the slice direction of the system was examined in comparison with the directivity in the direction.The imaging experiments using line-focus type transducers were conducted with the imaging system on two test specimens, plate and pipe, having artificial defects, to confirm and demonstrate the applicability of the system to NDT fields and to examine the resolution in the resulting image. The obtained results in the experiments were well explained by the analytical method, and the applicability of the system to NDT fields was confirmed.