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Sensors 2018, 18(12), 4286; https://doi.org/10.3390/s18124286

Lift-off Effect for Capacitive Imaging Sensors

Centre for Offshore Engineering and Safety Technology, China University of Petroleum (East China), Qingdao 266580, China
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Received: 6 November 2018 / Revised: 3 December 2018 / Accepted: 4 December 2018 / Published: 5 December 2018
(This article belongs to the Section Physical Sensors)
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Abstract

Capacitive Imaging (CI) sensors are capable of non-destructively detecting both surface and hidden defects in dielectric materials and characterizing conducting surfaces through a relatively thick insulation layer. However, the complex Measurement Sensitivity Distribution (MSD) of CI sensors render the sensor capacitance variation with lift-off highly non-linear, which may lead to misinterpretation of defect indications. This work systematically studied the lift-off effect using both Finite Element (FE) analysis and experimental approaches. Sensor MSD was used as a tool to predict the imaging performance. Normalized Variation Ratio (NVR) was introduced and used to characterise sensor responses due to defects for a CI sensor. Both the FE analysis and experiments suggest that the lift-off effect for a CI sensor is specimen type and condition dependent. For a given defect, the NVR may vary non-monotonically with increased lift-offs. A case study on a glass-fibre composite/aluminium hybrid structure with multiple artificial defects demonstrated the feasibility of defects discrimination using multiple CI scans with increased lift-offs. View Full-Text
Keywords: capacitive imaging; lift-off; non-destructive evaluation; defect discrimination capacitive imaging; lift-off; non-destructive evaluation; defect discrimination
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Yin, X.; Li, C.; Li, Z.; Li, W.; Chen, G. Lift-off Effect for Capacitive Imaging Sensors. Sensors 2018, 18, 4286.

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