Sensor measurements obtained from glass polyimide specimens demonstrate very similar behavior to coated metals because of the nonconductive nature of the composite. Two sensor electrodes were placed on the same side of the composite to simulate inspection of an aircraft where two-sided access was not available. Complementary measurements on opposite sides of the panel gave very similar results. Representative spectra and low-frequency impedance measurements are shown in Figure 11. The spectra showed a mainly capacitive impedance behavior al-though a resistive low-frequency region is seen following moisture adsorption. The low-frequency impedance versus moisture content relationships are given for both sensor orientations. Two points can be immediately derived from these spectra:
In-Situ Sensor to Detect Moisture Intrusion and Degradation of Coatings, Composites, and Adhesive Bonds, G.D. Davis, C.M. Dacres, and L.A. Krebs, DACCO SCI Inc.