Abstract. An eddy current method was developed to inspect cup-shaped steel parts from the I.D. side. During the manufacturing process of these parts, a thin Al tape foil is applied to the I.D. side of the part. One of the critical process parameters is that only one foil layer can be applied. An eddy current inspection system was developed to reject parts with more than one foil layer. The Al tape foil is cut to length to fit the inner diameter, however, after application of the foil there is a gap created between the beginning and end of the foil. It was found that this gap interfered with the eddy current inspection causing a false positive indication. To solve this problem a sensor design and data analysis process were developed to overcome the effects of these gaps. The developed system incorporates simultaneous measurements from multiple eddy current sensors and signal processing to achieve a reliable inspection.

This paper discusses our effort to develop advanced pulsed electroacoustic (PEA) measurement system capabilities that incorporate (1) improved signal processing tools for increased signal/noise ratios; and (2) integrated PEA modeling tools. In addition, we emphasize state-of-the-art system electronic components, integrated environmental controls, and sensor improvements required to achieve high spatial resolution while maintaining reasonable temporal resolution for both ambient and in vacuo measurements of thin dielectrics charged using electron beam injection, which is most applicable for spacecraft charging tests. PEA measurement systems provide an important tool to investigate the spatial extent and dynamic evolution of embedded charge distributions in thin dielectric materials. This knowledge has important applications in spacecraft industries, as well as for semiconductors, high-power electronic devices, high-voltage DC power cable insulation, and high-energy and plasma physics apparatus. The emphasis of this paper is on improved signal processing methods and integrated PEA modeling tools.

The media chosen to couple the PEA stack (electrode/sample/sensor/backing) can affect the spatial resolution and shape of the response from a Pulsed Electroacoustic (PEA) system significantly. The PEA stack layers must be electrically and acoustically coupled to optimize the amplitude, quality, and spatial resolution of the PEA measurements. Various coupling layer materials were used with 250 µm thick polymethylmethacrylate (PMMA) samples and a standard ~10 μm thick PVDF sensor. Coupling layers tested in this study include no media (with substantial pressure applied), light machine oil, silicone oil, and cyanoacrylate (super glue). Pulse amplitudes of 2000 V and 5 ns width were used. Static 8 kV DC bias was applied to the sample in order to detect a signal, as the samples were initially free of charge, and to see the interfaces more clearly and showcase the differences in response from the various coupling media. The best option was found to be a single layer of cyanoacrylate at the ground electrodesample interface; this is the only viable option for in vacuo PEA measurements of the media tested.

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