The entire electrode plates were about 0.2 mm thick and the electrode layers (anode on one side and cathode on the other) were only about 40 µm thick. This makes traditional NDE techniques difficult to apply.
This paper describes the results obtained by three techniques: ultrasonic through-transmission, ultrasonic pulse-echo and thermography. For the through-transmission technique two focused 50 MHz transducers were used. By measuring the amplitude of the transmitted ultrasonic signal through the sample, defects could be revealed. Also the time-of-flight of the received signal was evaluated.
The electrode plates were too thin to separate the interface echo and the back-wall echo using the pulse-echo technique. The back-wall echo interferes with the repetition echoes arising from reflected waves between the surface and the back-wall. However, a short gate starting with a delay relative to the interface echo was selected. The echo amplitude measured in this gate is influenced by delaminations and variation in electrode thickness. When a delamination is present the repetition echoes are damped by the lack of connection between the layers and signal was evaluated.
A thermographic technique measuring the thermal waves reflected from the samples was applied. Both conventional thermographics and a special lock-in technique (using a modulated heat source) was used. The ultrasonic findings were correlated with the results from thermographic techniques and with destructive characterization of the defects.
Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00
Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:
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