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F. Rauscher, M Bayray:
"Acoustic Emission Measurements on Shell Structures with Directly Attached Piezo-Ceramic";
Journal of Acoustic Emission, 20 (2002), 188 - 193.

When coupling acoustic emission sensors to curved shells by means of fluid coupling medias, as often done in pressure equipment applications, disadvantages arise: Due to fluid coupling, the in-plane movements are not transferred to the sensor, and due the coupling to a curved surface the repetitive accuracy is relatively low.
The investigation dealt with the idea to build a simple sensor by gluing a piezo ceramic directly to the vessel. To protect the simple sensor from electrical noise, a simple case was also glued to the shell, such that a shield was built around the ceramic by this case and by the tested shell itself. To compare with a sensor using the same piezo ceramic, a simple sensor was built. This simple sensor was coupled by gluing, and also, in a separate test, with silicon grease to the test specimen.
The response of the investigated arrangements to small band pulses was recorded and plotted versus the centre frequency of the pulses. The ratio of the sensitivity to the in-of-plan waves to the sensitivity to the out-of-plane wave was evaluated using pencil lead breaks. In addition to that the sensitivity to electrical noise of the arrangements was checked.