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Sensors 2018, 18(12), 4286;

Lift-off Effect for Capacitive Imaging Sensors

Centre for Offshore Engineering and Safety Technology, China University of Petroleum (East China), Qingdao 266580, China
Author to whom correspondence should be addressed.
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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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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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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