Article Article
A Rotationally Invariant Capacitive Probe for Materials Evaluation

Motivated by potential applications, such as anomaly detection in aircraft radome sandwich structures, a rotationally invariant capacitive probe with concentric coplanar electrodes was designed based on a previously published theoretical model. Two versions of the probe, with different target sensing penetration depths, were constructed in such a way that removal of parasitic capacitances could be achieved. Capacitance measurements for the probes in surface contact with laminar structures showed agreement to within 10% of theoretical predictions. Important factors governing the penetration depth of concentric capacitive sensors were investigated numerically, followed by experimental investigation on stepped samples, where results were found to be in accordance with numerical predictions. The effect of probe liftoff on inferred permittivity of dielectric slabs was also investigated. As liftoff increased, uncertainty in inferred permittivity increased dramatically. On the other hand, the capacitive probes show good sensitivity to low-contrast inhomogeneities embedded in laminar structures; 1 mL of a low contrast liquid injected into the core of a glass fiber-honeycomb-glass fiber sandwich structure was successfully detected.

Abou-Khousa, M.A., A. Ryley, S. Kharkovsky, R. Zoughi, D. Daniels, N. Kreitinger and G. Steffes, “Comparison of X-Ray, Millimeter Wave, Shearography and Through Transmission Ultrasonic Methods for Inspection of Honeycomb Composites,” AFRL-ML-WP-TP-2006-477, WrightPatterson Air Force Base, Ohio, August 2006. Bourasseau, N., E. Moulin, C. Delebarre and P. Bonniau, “Radome Health Monitoring with Lamb Waves: Experimental Approach,” NDT&E International, Vol. 33, 2000, pp. 393–400. Chen, T. and N. Bowler, “Analysis of a Concentric Coplanar Capacitive Sensor for Nondestructive Evaluation of Multi-layered Dielectric Structures,” IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17, 2010, pp. 1307–1318. Chen, T., J.M. Song, J.R. Bowler and N. Bowler, “Analysis of a Concentric Coplanar Capacitive Sensor Using a Spectral Domain Approach,” Review of Progress in Quantitative Nondestructive Evaluation, Vol. 30, 2011, pp. 1647–1654. Chung, Y.C, N.N. Amarnath and C.M. Furse, “Capacitance and Inductance Sensor Circuits for Detecting the Lengths of Open- and Short-Circuited Wires,” IEEE Transactions on Instrumentation and Measurement, Vol. 58, 2009, pp. 2495–2502. Duling, I. and D. Zimdars, “Terahertz Imaging Revealing Hidden Defects,” Nature Photonics, Vol. 3, 2009, pp. 630–632. Igreja, R. and C.J. Dias, “Analytical Evaluation of the Interdigital Electrodes Capacitance for a Multi-layered Structure,” Sensors and Actuators A, Vol. 112, 2004, pp. 291–301. Li, X.B., A.S. Zyuzin and A.V. Mamishev, “Design Principle of Multichannel Fringing Electric Field Sensors,” IEEE Sensors Journal, Vol. 6, 2006, pp. 434–440. Li, Y., N. Bowler and D.B. Johnson, “A Resonant Microwave Patch Sensor for Detection of Layer Thickness or Permittivity Variations in Multilayered Dielectric Structures,” IEEE Sensors Journal, Vol. 11, 2011, pp. 5–15. Mamishev, A.V., K. Sundara-Rajan, F. Yang, Y. Du and M. Zahn, “Interdigital Sensors and Transducers,” Proceedings of IEEE, Vol. 92, 2004, pp. 808–845. Nassr, A.A. and W.W. El-Dakhakhni, “Non-destructive Evaluation of Laminated Composite Plates Using Dielectrometry Sensors,” Smart Materials and Structures, Vol. 18, 2009. Nassr, A.A., W.H. Ahmed and W.W. El-Dakhakhni, “Coplanar Capacitance Sensors for Detecting Water Intrusion in Composite Structures,” Measurement Science and Technology, Vol. 19, No. 7, 2008, pp. 75702–75800. Shay, I.C. and M. Zahn, “Cylindrical Geometry Electroquasistatic Dielectrometry Sensors,” IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 12, 2005, pp. 41–49. Shull, P.J., A.V. Clark, P.R. Heyliger, J.C. Moulder and B.A. Auld, “Characterization of Capacitive Array for NDE Applications,” Research in Nondestructive Evaluation, Vol. 2, 1990, pp. 11–27. Zaretsky, M., “Parameter Estimation Using Microdielectrometry with Application to Transformer Monitoring,” PhD Thesis, Massachusetts Institute of Technology, 1987.
Usage Shares
Total Views
87 Page Views
Total Shares
0 Tweets
0 PDF Downloads
0 Facebook Shares
Total Usage