The capture volume of near field communication (NFC) systems is limited by adverse scaling laws, antenna perimeter restrictions, and hardware overhead costs. Here, we develop complete, modular, and easily scalable NFC communication and localisation systems based on slow wave antennas.
A review of conventional NFC is conducted, the history of radio-frequency identification discussed, and modern capture volume enhancement techniques considered. New methods for power flow modelling in periodic waveguides with complex characteristic impedance are developed and used to design directional filters for receiver isolation and carrier suppression. The tuneable filters comprise coupled sections of magneto-inductive (MI) waveguides and enable infinite carrier rejection and multiple-passband responses.
We then develop a novel bistatic tag localisation method for slow wave MI antennas. ISO/IEC 14443 Type-A queries are injected as MI waves and corresponding tag signatures extracted from either antenna end via matched filter-couplers. Pair-wise cross-correlation of tag identifiers is used to calculate the differential TOF, which is converted to a position estimate using the antenna group velocity. Accurate localisation is demonstrated using a planar MI antenna, a custom reader, and off-the-shelf tags. We then design flexible antennas with distributed sensors by periodically loading coaxial cable with field-generating nodes. Various sensor topologies are considered and used in experimental antennas up to 48.5 metres long. Accurate one- and quasi-two-dimensional bistatic localisation is demonstrated, and the feasibility of longer antennas discussed.
Finally, we develop monostatic localisation, whereby tag location is achieved with a single receiver using the absolute TOF variation in the delay between the injected reader query and the tag response. Response characteristics of multiple tag classes are characterised, and the effects of carrier power, phase, and sensor-tag separation measured. Accurate one-dimensional positioning is achieved using a flexible loaded transmission line antenna. Conclusions are drawn and the outlook and limitations of slow wave NFC considered.