Abstract
In the method of non-destructive testing in ultrasonics, the sound pressure and sound intensity in acoustic field is a function of distance. If there are flaws exist in the medium, they will make discontinuities to reflection or refraction a part of energy of the wave. According to this phenomenon, we can defect whether there is any flaw in the medium or not. Here the cement is used as the material of the specimens and detected by the through transmission method in ultrasonic. First of all, in order to get the properties of the wave transferring in the specimen, such as uniformity of the concrete, concrete strength, pulse velocity, angle of divergence, and the transmission time of each skip distance, the flawless one is detected. In the second step, we evaluate the depth of the crack and compare it with the value shown on the instrument to find out the approach which the instrument uses to do. In the final step, the block with a spherical cavity in, regarded as a black-box system, is detected. Combine the transmission time with other information from the measurement in reference block to find out the position, depth, shape, and diameter of the spherical cavity. After comparing these experimental results with predetermined data, we can get the accuracy of this experiment method so as to be the base of measuring other more complex systems in the future.