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

12 4

reader and tag; and the tag, which contains a microchip (with a microprocessor) and an antenna. Depending on the operating frequency, RFID systems can be classified as low-frequency (LF), high-frequency (HF), or ultra-high frequency (UHF), each offering different reading distances and sensitivity to environmental factors by Meng and Li (2016). In passive RFID systems, which are the most suitable for structural health monitoring, the tag does not include any internal power supply. Instead, it harvests energy from the reader’s field through electromagnetic coupling (Figure 1). When the reader emits an electromagnetic wave, a voltage is induced in the tag’s antenna, charging a small capacitor that powers the microchip. Once energized, the tag communicates with the reader by modulating and reflecting part of the incident signal, a process known as backscatter modulation. Information is transmitted by varying the impedance of the tag’s antenna-chip interface, which alters the amplitude and phase of the reflected wave. This mechanism allows RFID tags to operate not only as identifiers but also as sensors by Bouzaffour et al. (2021), by exploiting the sensitivity of their electromagnetic response to environmental changes. When a sensing material or structure is integrated into the tag’s antenna (for example, a corrosion-sensitive metallic layer or a humidity-responsive dielectric), variations in the surrounding medium lead to measurable shifts in the antenna’s impedance, resonance frequency, or backscatter power. These variations can be interpreted as indicators of physical, chemical, or mechanical processes occurring near the tag by Zhang et al. (2017). 2.2. Relationship between signal attenuation RSSI and environmental/chemical changes The Received Signal Strength Indicator (RSSI) represents the power level of the backscattered signal received by the RFID reader from the tag. It is one of the most accessible parameters for characterizing the interaction between the tag and its environment, since it directly reflects the efficiency of power transfer and communication between the two devices. In ideal conditions, the RSSI depends on the distance between the reader and the tag, the transmission power, and the antenna design. However, in real applications, the surrounding medium strongly affects the propagation of the electromagnetic field and the coupling efficiency, leading to changes in RSSI that can be related to material or environmental variations. In corrosion or durability monitoring, this principle can be exploited by coupling the RFID antenna with a conductive or reactive element. As corrosion progresses, corrosion products alter the local dielectric constant and magnetic permeability of the medium surrounding the RFID device, affecting both the impedance of the antenna and the energy reflected back to the reader. The result is a measurable attenuation of the RSSI, which can be correlated to the degradation state of the sensing element. Similarly, the presence of moisture or chloride ions in concrete modifies its dielectric properties, influencing the propagation path and the intensity of the received signal. By tracking these changes over time, it is possible to monitor the initiation and evolution of corrosion or other degradation processes in a fully passive and wireless manner. 2.3. Advantages for RFID sensors integration in concrete and for long-term monitoring RFID-based sensors offer several advantages when used in concrete structures. Because passive tags do not require a power supply or wiring, they are easy to embed in cementitious materials and can remain functional for long periods with any maintenance. Their small size and chemical stability make them compatible with harsh environments, such as those characterized by high alkalinity, humidity, or chloride presence. Moreover, RFID signals can pass through non-metallic materials like concrete, enabling the sensors to be interrogated from the surface without damaging the structure. This makes that technology particularly attractive for non-destructive, long-term monitoring. Finally, the relatively low cost and scalability of RFID systems make them suitable for creating dense sensor networks capable of monitoring corrosion initiation and progression over large areas, which is crucial for assessing the durability of reinforced and prestressed concrete structures. 3. Experimental application example In this study an experimental investigation was conducted to evaluate the feasibility of using RFID sensors for corrosion monitoring under controlled environmental conditions. The test setup consisted of plastic supports equipped with two RFID sensor tags: a reference tag and a working tag shielded by a thin metallic layer acting as the corrosion-