PSI - Issue 84

Martina Giglio et al. / Procedia Structural Integrity 84 (2026) 9–16 M. Giglio et al. / Structural Integrity Procedia 00 (2026) 000–000

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provides a visual representation of RSSI dynamics within an RFID tag monitoring system, serving as a reference model for degradation progression. The X-axis “Dates” represents the temporal scale of observation in [days], and the Y-axis “RSSI” indicates signal power in [dBm]. The plot illustrates the intrinsic signal fluctuation through the superposition of four reference curves, corresponding to four working tags from different samples. These curves establish a baseline for environmental variation that is unaffected by shielding. Crucial for data interpretation is the horizontal dashed line, which defines the minimum reading threshold of the reader, set at -70 dBm. The core of the analysis resides in the conceptual progression curve, plotted in black, which models the expected behavior of a working tag in response to the deterioration of a metallic shielding layer (in this case equal to 30  m). In an initial, hypothetical phase of complete shielding, this curve remains below the threshold, indicating that the working tag is not detected due to total signal reflection back. Subsequently, the curve exhibits a rapid increase until it intersects the reading threshold, defining the critical point where the degradation of the metallic layer is sufficient to permit the pass-through of the electromagnetic signal. The crossing of this threshold corresponds to the beginning of the effective detection phase, during which the instrument begins registering the RSSI values of the working tag, adding to the values recorded for the reference tag. Finally, the curve stabilizes at significantly higher RSSI values, following the fluctuations of the real data. This stabilization is attributed to the almost complete degradation of the metallic layer, which eliminates the shielding effect and permits the full detection of the signal transmitted by the working tag (Figure 5). This progressive curve, which graphically represent the behavior (in terms of RSSI parameter) of the shielding metal layer exposed to a degrading environment, therefore, illustrates the expected relationship between physical degradation (ineffective shielding) and the measurable variation in signal power, providing a predictive framework for monitoring tag performance under environmental conditions.

Fig. 5. Shielding metal layer after the degradation exposure.

4. Conclusion The present study investigated the application and the effectiveness of passive RFID sensors for monitoring corrosion processes in metallic layers under controlled environmental conditions. The results confirmed that the variation of the Received Signal Strength Indicator (RSSI) can be effectively used to identify the progression of corrosion phenomena. When the working tag becomes detectable, it indicates that the metallic layer covering the chip has reached an advanced stage of degradation, allowing the electromagnetic signal to penetrate the corroded film and activate the sensor. Passive RFID sensors are battery-free, low-cost and wireless allowing continuous long-term monitoring without physically altering or compromising the tested samples or structures. The high temporal resolution of RSSI measurements, collected at frequent time intervals, enables the detection of early-stage corrosion phenomena, which would otherwise be difficult using conventional inspection methods. That allows considering this technology as a promising complementary tool to the well-established NDTs, offering the potential for scalable and remote monitoring in real structures. However, the current approach provides only qualitative information on the corrosion state. The detection of the working tag only confirms that the protective metallic film has degraded sufficiently to allow signal transmission, but it does not provide direct quantitative data such as corrosion rate or the amount of material loss. The