## 5 Results and Discussion  
The electrochemical emission signals collected by the wireless corrosion monitoring sensor SN0 of the passive state reinforced concrete panel, including the potential and the current data, are presented in Figure 6a,b, respectively. According to Figure 6a, the potential emission is within a narrow band whose amplitude is no more than 3 mV (_vs_. SSRE). Besides, the current emission also shows a narrow-band-like distribution, and the amplitude is no more than 2 \(\times\)10\({}^{-7}\) A/cm\({}^{2}\). Which is close to the resolution of the wireless mote itself. The signal could be caused by the white noise of the acquisition system implanted in MicaZ mote or the passive steel/concrete system itself. These results indicate that the amplitude of potential or current emission of the reinforcing steel at passive state is very low, and the high pH value of the hydrated products of cement provides a safe environment to keep the r steel bar immune to chloride ions. Also, the wireless mote SN0 obtains the effective data correctly. Figure 7 exhibits the potential and the current emissions of the wireless motes SN1, SN2 and SN3 located along the diagonal line of the RC panel in Figure 5 with 3.5% NaCl solution. Lots of potential and current transients appear in the data. The amplitude of the potential emission transients and  
Figure 6: Electrochemical emission data of the passive state reinforced concrete panel. (**a**) and (**b**) are the electrochemical potential emission and the electrochemical current emission of the wireless mote SN0, respectively. current emission transients achieve even hundreds of millivolts (_vs._ SSRE) and several of \(10^{-4}\) A/cm\({}^{2}\), respectively. The typical attenuation life of electrochemical emission ranges from tens of seconds to a few hundreds of seconds. Note that the pitting corrosion presents stochastically on the surface of the working electrode. Generally, the pitting corrosion process of the steel bar in Cl\({}^{-}\) solution includes four  
Figure 7: The electrochemical emission data of the active state RC panel. (**a1**), (**a2**), (**a3**) and (**b1**), (**b2**), (**b3**) are the electrochemical potential emission and electrochemical current emission of the wireless motes SN1, SN2 and SN3 located along the diagonal line of the RC panel in Figure 6, respectively. steps as follows: the adsorption of Cl\({}^{-}\), the nucleation of metastable pits, collapse of the metastable pit and the formation of the new pit, and the formation and development of the stable pit. The measured current embodies the superimposed effect of the pitting process. This process simultaneously includes the nucleation of the metastable pit and the repassivation processes. During the developing stage of the pitting corrosion caused by Cl\({}^{-}\), two of the typical events emerge on the surface of the specimen: one part is the passivating film and the other part is the active pits. In the later part, the active steel directly contacts with solution, and then the anode current becomes much larger. As such a large current flows through the solution in the pit, there exists a large voltage drop. According to the point defect model [31], the aggressive anion Cl\({}^{-}\) is able to enhance the flux of cation vacancies through the barrier layer during the pitting corrosion process. With the favorable conditions (voltage, pH, [Cl\({}^{-}\)]), vacancy condensation will occur at the metal/barrier layer interface, and hence passivity breakdown will is confirmed, so the fresh surface of the metal will generate an electrochemical potential and current transients. We can also see that the wireless corrosion monitoring sensors and networks could effectively capture and transmit these electrochemical emission signals. To identify the pitting corrosion qualitatively, the energy distribution algorithm of the electrochemical emission signal in wavelet domain described in Section 3 of this paper is applied to analyze the potential and current emission data in Figures 6 and 7.