# Applications of Nanomaterials in RFID Wireless Sensor Components
## 3 RFID Sensor Technology
Particularly, by analyzing the degree of change in the modulated P2 signal received by the RFID reader, one can calculate the quantity of the detected material. The reflected signal information read by the RFID reader is transmitted to the server via wireless communication methods, enabling users to utilize the collected information [65]. The substrate serves as the foundational material supporting various elements in constructing a sensing tag. It determines aspects such as the tag's size, shape, and strength, providing the mechanical structure for the sensing tag. The selection of the substrate must accommodate all components of the sensing tag without affecting the operating principles and antenna design frequencies. Substrates can be chosen from a variety of materials, including metal, ceramic, textile, plastic, and more [66; 67; 68]. Recently, attempts have been made to develop RFID yams that can be immediately integrated into tag manufacturing, considering the widespread use of RFID in the clothing market. Additionally, there is growing attention to substrates that can provide flexibility and stretchability, especially with increasing demand for wearables (Figure 3c) [69]. The flexibility of the substrate allows it to withstand external mechanical impacts and makes it more suitable for attachment to the human biome. Stretchability, based on high elasticity and reversibility, demands properties that do not deform even with repeated strain and release. Research on flexible and stretchable RFID substrates is ongoing, with expectations that it will lead to various applications. The Integrated Circuit (IC chip) is responsible for storing tag information and processing data. Sensing tags are distinguished based on the presence of the IC chip [70]. A sensing tag with an attached IC chip follows a conventional structure, where the IC chip not only handles the ID, data, and encryption key storage and processing but also includes digital logic required for data processing (Figure 3d) [71]. Such sensing tags allow for long-distance data reading and complex data processing. However, due to the inclusion of semiconductor-based IC chips, the manufacturing cost is higher. To address the need for more affordable and simpler sensing tags, a structure without the necessity of an IC chip has emerged. In cases where there is no IC chip, integrated patterns made of materials such as metal nanoparticles, conductive polymer inks, carbon materials, etc., serve as substitutes for IC chips [72; 73; 74]. Patterns replacing IC chips can be designed using various methods such as ultra-wide band (UWB), polarization diversity, phase quantization encoding, etc. [75; 76; 77]. This structure is cost-effective, has a long lifespan, and is suitable for use in harsh environments [78]. However, compared to cases with IC chips, sensitivity and selectivity are limited, requiring further research [79]. A certain portion of the sensing tag is configured as a sensing area using active substances to induce changes in the properties of the active substances in response to external physical or chemical stimuli (Figure 3e) [80]. Specifically, materials such as PEDOT, which changes in electrical conductivity based on pH, phenanthrene with a discontinuous dielectric constant above a certain temperature, and CNT, which alters resistance upon gas molecule adsorption, fall into this category [81; 82; 83]. The changes in the properties of the active substances result in impedance variations in the sensing tag, and the detection process is completed as the RFID reader detects these changes. This sensing area can detect various elements such as light, moisture, and temperature, making it applicable to diverse fields such as environmental monitoring, healthcare, agriculture, and food [84; 85; 86].