Ultrasonic measurement of three-dimensional structure of electrical trees using characteristics of tree structure

In this paper we propose a method to distinguish noise-covered ultrasonic signals by making use of the distinguishing features of signals reflected from electrical trees extending toward the direction of depth within the specimen. This method utilizes the characteristics of signals due to the spatial continuity of a tree branch and also to the change of the delay time of the signal reflected from the electrical tree when the ultrasonic transducer is moved slightly near the target point. As a result, it is shown that the three-dimensional structure of the bush-type tree in polyethylene can be visualized in a nondestructive way. The resultant shapes of the trees agreed well with those obtained by actual sectioning of the specimen using a microtome.