ICM system, valiate the effectiveness of the ICM system under operational environment and summarize on the experiences and lessons from the study. 2. Description of ICM Technology 2.1. Principle of sensor The core of ICM technology is intelligent coating sensor which comprises of three layers: the driving layer, the sensing layer and the protective layer，as shown in Figure 1. The driving layer is made of bifunctional nonconductive materials: one function is that crack will also form on the driving layer once cracks generate on the substrate, and further makes the sensing layer split at the same time; secondly the driving layer spaces out the substrate and the sensing layer with good insulating efficiency in conformity to the design requirement. The sensing layer is made up of conductive materials such as Cu, Ag, C, etc and can detect the crack length in the substrate by the variation of electric resistance. As the ICM sensor is about several tens of micrometers, a small surface crack will cause the sensor cracking and the electric resistance rise accordingly, as shown in Figure 2. The increase of electric resistance of the sensor corresponds to the crack growth. The method of ICM is very simple and stable measurement system, which consists of a DC power source, an electric resistor and a data recorder. Figure 1 A formation of the intelligent coating sensor Figure 2 The relationship of eletricc resistance and crack length 2.2. ICM system construction A typical ICM system consists of hardware and software. The on-board hardware parts include virus sensors, sub-interrogators and main-interrogators, see figure 3. Each sub-interrogator, a chip microcomputer system, consists of switches for signal channel of multi path sensors, conversion circuits for A/D modulus, central process units, digital communication circuits and power circuit and other auxiliary circuits. The sub-interrogators can realize the online measuring and processing of the electric resistance value detected by each cable-connected sensor and transmit the digital
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