A study on the bandwidth increment of vertically spatial frequency for the enhancement of inner stainless steel image

The ultrasonic test for maintaining the integrity of the primary loop in nuclear power plants is restricted by the structure and shape of the material. The size of material crystalline becomes the cause of scattering noise. In this paper, the internal image of stainless steel specimen same material nuclear power plants is to be improved through the band width increment of the verify spatial frequency. Generally, the ultrasonic image obtained from ultrasonic microscope is acquired using a operational frequency and the resolution is confined by the spatial frequency determined by the operational frequency and ultrasonic convertor. In this study, an improved image acquiring method was investigated, which was obtained from synthesizing the images varying the operational frequency in the ultrasonic microscope and then increasing the vertically spatial frequency bandwidth. In the experiment, an ultrasonic microscope was assembled using an ultrasonic convert of which operational frequency was 5MHz and ratio bandwidth is 95%, and a quadrature detector is used to acquire the amplitude and phase simultaneously because the amplitude and phase image data are required for the signal processing. A specimen with four round flat type for detector was fabricated, which is in different depths. Although the shape of the defects was appeared using a single frequency, the strength of the images was not proportional to the depth of the defects. On the other hand, the strength of the images was proportional to the depth of the defects in the improved image.