Abstract
In the inspection of defect in billet using ultrasonic CT method, real diameter of defect and width of defect in visualized image are difference, and that is the problem because the size of defect can't be estimated accurately. Then, we simulate by numerical calculation in order to lead relationships between parameters (center frequency of transmitted signal, diameter of defect and width of defect image … etc.). As the calculation method, we use Finite-Difference Time Domain (FDTD) method that is faster in calculation than Transmission-Line Matrix (TLM) method. As the simulation result, we found that there is a linear relationship between diameter of defect and amount of decrease in velocity of visualization image, and that there is a relationship between wavelength of signal and width of defect image. On the other hand, there is no correlation between diameter of defect and width of defect image. Therefore, we should apply the relashionship equation that is led by the linear relationship to the estimation of the size of defect.
