Ultrasonic detection of electrical breakdown region in filler-added epoxy resin

Use of 15 MHz ultrasound makes it possible to detect the electrical breakdown region in epoxy resin added with inorganic filler powder. The only practical method to observe electrical breakdown paths, let alone electrical trees, in filler-added epoxy resin has long been to section a specimen with diamond cutter, since it, is completely opaque and hard. The ultrasonic method we propose provides an effective way to detect or even to visualize the electrical breakdown region in such an epoxy specimen. In the experiment, the breakdown path was formed in a disc specimen using point-to-plane electrode geometry. The 15 MHz ultrasonic transducer was energized by electrical impulses with repetition frequency of 1 kHz, and the reflected signals from the electrical breakdown region were detected by the same transducer. By scanning it over the specimen, ultrasonic images of breakdown path through the specimen were obtained