Chipless radio frequency identification (RFID) sensors have enormous potential for underground mining applications since this technology has the potential to meet all the requirements, such as wireless communication, maintenance-free, long lifespan, and battery-free, required to deploy in harsh underground environments. This paper has analysed existing frequency domain chipless RFID sensor technologies to understand suitability for potential applications, such as environmental condition monitoring, support system stability detection, and health monitoring of mining structures in underground mining sites. In light of the analysis, the paper has presented a new classification based on sensing materials and intrinsic sensing parameters such as effective length, coupling, conductivity and permittivity. Furthermore, the analysis has considered accuracy, performance and readability using 3D Electromagnetic (EM) analysis software, CST Studio Suite. Finally, based on our critical analysis and experimental simulations, the paper has identified challenges that need to be addressed by future research for chipless RFID sensors in the underground mining application domain.

Accurate dielectric constant measurements are crucial in Internet of Things (IoT) sensing applications to characterize materials and their properties. This article introduces an innovative capacitor-based chipless radio frequency identification (RFID) sensory array tailored specifically for precise measurements of dielectric constants in IoT contexts. The array incorporates Pi-shaped resonators and cylindrical capacitors, addressing challenges, such as low accuracy, limited $\varepsilon _{r}$ measuring range, and the reliance on bulky vector network analyzers (VNAs) as readers. Theoretical modeling, design considerations, sensor calibration, and validation processes are detailed, highlighting the array’s precision and adaptability. Real-world IoT applications are demonstrated, showcasing the array’s potential with a low-cost portable multiple-input-multiple-output (MIMO) reader, Walabot. This cost-effective solution overcomes conventional limitations, offering a versatile approach to dielectric constant measurements and opening up new possibilities for diverse IoT sensing applications. The integration of this sensory array with IoT technologies demonstrates the feasibility of smarter material characterization.

The accurate detection and reliable performance of chipless radio frequency identification (RFID) tags and sensors present significant challenges due to their inherently low radar cross section (RCS) and pronounced mutual coupling effects. These limitations adversely influence the quality (Q) factor and overall detectability, complicating the optimisation of chipless RFID systems for practical applications. This study investigates the performance characteristics and trade-offs among RCS, Q-factor, and detectability in Pi-shaped array configurations of chipless RFID tags. A comprehensive analysis of various array configurations is conducted, supplemented by a link budget evaluation to elucidate how different array structures impact system performance. The simulation results reveal that planar arrays outperform linear arrays in both RCS and Q-factor, highlighting essential trade-offs between tag identification range and angular coverage, which are influenced by array size and electromagnetic coupling. The findings emphasise optimising resonance quality and scattering efficiency to tailor chipless RFID systems for specific application requirements. This research provides valuable insights into the design and operation of chipless RFID arrays, contributing to their advancement in practical applications.

This paper introduces an innovative approach to measuring the dielectric constants of solid geological samples using a crosspolarised chipless radio frequency identification (RFID) sensor. Copolarised RFID sensors often face interference from the material under test (MUT), resulting in significant deviations in resonance frequency. To address this issue, we developed a cross-polarised chipless RFID sensor that transmits and receives signals in different polarisation directions, enhancing measurement accuracy. Our sensor features resonatorintegrated ground plane cylindrical capacitors designed to detect variations in the dielectric properties of minerals and rocks. Both simulation and experimental validation indicate that the sensor can identify dielectric constant variations ranging from 1 to 10, with a frequency shift sensitivity of 63.5 MHz per dielectric unit. The sensor was tested on various mineral and rock samples, demonstrating alignment with established dielectric values. Operating effectively across a wide frequency range of 3.1 to 10.6 GHz, the system is well-suited for ultra-wideband (UWB) applications. This proposed method is cost-effective, compact, and compatible with remote sensing platforms, presenting a promising alternative for mineralogical and geophysical testing applications.