# Applications of Nanomaterials in RFID Wireless Sensor Components
## 3 RFID Sensor Technology  
The principles of systems operating through inductive coupling, such as LF and HF, are as follows (Figure 2b) [51]. The process initiates by creating a magnetic field in the RFID reader antenna through a driving current. When the tag is positioned in the corresponding magnetic field region, current is induced, resulting in the generation of voltage, ultimately activating the RFID system. The signal transmitted from the reader is modified by the unique pattern of the tag, and the reader decodes this information through demodulation. In this case, since the current flowing through the tag is very weak, only short-range transmission is possible. Nevertheless, it exhibits less sensitivity to interference, allowing signals to be transmitted and received through objects such as metals or liquids [52]. LF  
Figure 2: (**a**) Classification by radio frequency range. Operating procedures of (**b**) inductive coupling-based and (**c**) backscattering-based RFIDs. RFID is effectively used in underground object detection such as mines, military munitions management, and urban construction tasks like subterranean manholes [53; 54; 55; 56]. HF RFID, with its relatively higher frequency, achieves improved reading range and processing speed, making it suitable for applications that require a slightly longer distance, such as library management, animal identification, and cold chain tracking [57; 58; 59]. On the other hand, in scenarios operating through backscattering, such as UHF, the RFID reader transmits an electric field signal to the tag to initiate the process (Figure 2c) [60]. The tag, activated by the signal from the RFID reader, conveys its information to the reflected signal by altering the RFID reader's radio signal. Subsequently, the RFID reader processes the information by recognizing the difference between the transmitted and received information. RFID, utilizing radio signals and receiving energy from its own battery, can continuously transmit and receive signals over much longer distances. In modern society, where there is a growing demand for automation and remote monitoring, the interest in UHF RFID applications, which offer a wide reading range and enable rapid data processing, continues to rise. UHF RFID, well suited for large-scale inventory management, is used in various fields such as supply chain management of large supermarkets, farm machinery, and automatic machine identification [61; 62; 63]. However, this outstanding performance not only increases the price but also increases the size and shortens the lifespan. Therefore, for effective RFID utilization, understanding the usage environment and necessary conditions is crucial, necessitating optimized design considerations. Research on utilizing active substances with specific sensing capabilities for materials in RFID system tags to construct sensing tags and employ them as wireless sensors is being actively conducted. As shown in Figure 3a, a wireless sensor using a RFID system consists of a substrate, IC chip, sensing area, and antenna [64]. The operational principle of RFID-based wireless sensors involves a sensing tag, which carries the detection material, modulating and reflecting the signal transmitted by the RFID reader to interpret the reflected signal and acquire detection information (Figure 3b). Specifically, the RFID reader initiates the operation by transmitting the initial signal, P1, to the sensing tag. The sensing tag receives P1, and the detection area, occupying a small portion within the sensing tag, detects external stimuli. The detection area reacts to chemical environmental changes, causing a resistance change in the detection material. This change leads to alterations in reception signal parameters such as amplitude, frequency, and phase within the sensing tag. The modified reflected signal, P2, resulting from the material detection, is backscattered from the sensing tag to the RFID reader.