Abstract: A uniplanar capacitive sensor, with 8-electrode on one plane substrate, is designed to detect the subsurface anomalies or damage of non-metallic materials. A 2D finite-element method is employed to simulate the electric potential distribution, the sensitivity distribution, capacitance measurements and capacitance variations for the sensor. A kind of engineering plastic slab is used as a sample for the experiment of detecting the subsurface anomalies of nonmetallic material. A principal component analysis is employed for anomaly discrimination according to the simulated capacitances and the measured capacitances, and the subsurface anomaly or damage of non-metallic materials can be well distinguished by principal component analysis. Both of the simulation and the preliminary experimental results show that, compared with the healthy material, the measured capacitances decrease after anomaly or damage occurs in the subsurface of nonmetallic material, and that the proposed approach can effectively detect the subsurface anomalies of nonmetallic material and can be practically used for anomaly detection and health monitoring of nonmetallic materials.

Key words: Nonmetallic materials, Principal component analysis, Sensitivity distribution, Capacitive sensor, distribution, Electric potential, Finite element method