Real-time identification, tracking, and sensing of single living cells have the potential to transform cellular biology by enabling unprecedented insight into cellular behaviour and interactions, with applications in diagnostics and treatment of complex diseases such as cancer. One promising approach is near-field radio-frequency identification (RFID), particularly in the UHF band (300 MHz - 3 GHz), where identification ranges on the order of one wavelength can be achieved.

An RFID system consists of a tag that provides a unique identifier, a reader that establishes wireless communication, and a backend system that processes the measured data. For single-cell identification, however, two major challenges arise. First, living cells have dimensions ranging from a few to several hundred micrometres, constraining tag antennas to micrometre-scale sizes that must be internalized within cells. At UHF frequencies, this leads to electrically small antennas (ESAs) with inherently low efficiency. Second, cells must be maintained in highly lossy dielectric media, such as cell culture media or balanced salt solutions, which further degrade antenna performance and complicate reliable detection.

In light of these constraints, this thesis investigates the feasibility of using RFID technology to identify ultraminiature implantable chipless RFID tags. A theoretical analysis of wireless power transfer (WPT) systems based on ESAs is first conducted using a two-port network model to evaluate fundamental performance limits. Electrically and magnetically coupled ESAs are analysed in free space and lossy media, establishing upper bounds on system efficiency. The results show that electrically coupled systems outperform in free space, whereas magnetic coupling provides superior performance in lossy environments, indicating that magnetic near-field RFID is the most suitable approach for single-cell identification.

To assess practical detectability, a complete UHF magnetic near-field RFID system operating in air is designed and experimentally validated. The system comprises ultraminiature chipless tags, a frequency-reconfigurable segmented loop reader antenna, and a backend system based on the Frequency Sweep Envelope (FSE) method. Two tag types are developed: LC resonators and NEMS-loaded resonators based on surface acoustic wave devices. Tags with areas ranging from 17.89 mm2 to 0.25 mm2 and resonant frequencies between 1.18 GHz and 1.66 GHz are fabricated and tested. Experimental results show that LC-based tags provide better detection for larger dimensions, whereas NEMS-based tags outperform at the smallest sizes due to their high quality factor and narrow spectral signatures, which are advantageous in multi-tag scenarios.

Finally, the dielectric properties of common cell culture media and balanced salt solutions are measured from 200 MHz to 20 GHz using an open-ended coaxial probe and fitted to a two-pole Cole-Cole model. Additionally, since the dielectric properties of these media resemble those of biological tissues, broadband tissue phantoms (400 MHz - 6 GHz) are developed using PBS as base compound.

Although a complete single-cell RFID system is not yet achieved, this work establishes fundamental limits, validates the detectability of ultraminiature chipless tags, and provides a foundation for future magnetic near-field RFID systems in lossy biological environments.