Chipless Microwave RFID based on Printed Circuit Technology: Sensor Integration, Tag Localization and Robustness Optimization
Final Report Abstract
Chipless RFID is a comparatively young technology which can help to overcome limits of conventional, chip-based RFID. The chipless approaches enable specific applications with requirements such as tag operation in harsh or extreme environments, long-term dependability or extremely low tag cost due to the lack of the microchip and a tremendous range of usable materials and production technologies. However, the chipless tag technology is still behind the ‘classical’, chip-based UHF and SHF RFID solutions with regard to one central item: information content. Where the EPC standard foresees unique IDs of up to 204 bit length, there highest absolute number of bits reached with chipless approaches is 35 bits. While this may be sufficient for many applications, the situation is even worse for time-domain chipless tags. In this field, information content did not exceed the 1 digit range. Since time-domain has, on the other hand, several benefits over frequency-encoded techniques, the project “Chipless Microwave RFID based on Printed Circuit Technology: Tag Localization and Optimization of Information Content and Reading Range” researches solutions for the information content challenge. For this purpose, two strategies have been targeted within the project: new approaches for geometrically short, low dispersive delay lines based on filter structures (opposed to metamaterial lines that have been already used) and new phase modulators to increase the modulation efficiency of the tag. For that purpose, classical filter design methods have been extended to allow for group delay being a design requirement rather than a given filter design outcome. The new method treats both, magnitude and phase response equally relevant. To implement higher order modulation, three new modulator circuits have been designed and carefully compared. These exceed the state of the art 2 bit phase modulation with subpar phase distance towards flexible QAM modulation with at least 2 methods covering the entire symbol space. The QAM modulation has furthermore been extended by time position modulation to further increase the information content. All described methods have been tested in practically implemented demonstrators. The chipless time-domain tag technology requires tailored RFID reader approaches due to its inherent properties, especially its high bandwidth requirement, to name just one. Therefore, a new reader technology has been developed based on the well-known FMCW approach. The reader is small, modular and inexpensive, and, therefore well suited for the usual applications of chipless RFID. Furthermore, it allows the implementation of localization approaches in principle by simply complementing the basic reader circuitry with inertial sensors or extending it to a multi-reader setup, allowing for the implementation from simple triangulation methods up to highly sophisticated SAR techniques. First steps into that field have been performed within the current project as well. The reader implementation proved rather time-consuming as did the filter delay line development. Nevertheless, the methods investigated show a tremendous progress for chipless time-domain RFID which brings the information density back into a reasonable range that is comparable with frequency domain approaches. Phase modulation has been implemented up to 8-PSK and has been complemented by 2-PPM, resulting in a 4 bits per symbol. In terms of the figure of merit defined without pulse position modulation a FoM=0,02 GHz^-1 mm^-2 has been reached, which is only a factor of 4 below the highest information density reached so far for chipless RFID. Towards an application as well as further research on localization techniques, the modular reader implementation is a huge benefit. For an RFID system as presented, sensing and localization applications are of special interest and the next step towards a final product.
Publications
- (2016) Potential and Practical Limits of Time-Domain Reflectometry Chipless RFID. IEEE Trans. Microwave Theory Techn. (IEEE Transactions on Microwave Theory and Techniques) 64 (9) 2968–2976
Popperl, Maximilian; Parr, Andreas; Mandel, Christian; Jakoby, Rolf; Vossiek, Martin
(See online at https://doi.org/10.1109/TMTT.2016.2593722) - “Filter-based slow wave structures for application in chipless microwave RFID”, in German Microwave Conf., Nuremberg, Germany, 2015, pp. 68-711
M. Nickel, C. Mandel, M. Schüßler and R. Jakoby
(See online at https://doi.org/10.1109/GEMIC.2015.7107754) - “Higher Order Pulse Modulators for Time Domain Chipless RFID Tags with Increased Information Density”, in European Microwave Conf., Paris, 2015
C. Mandel, M. Schüßler, M. Nickel, B. Kubina, R. Jakoby, M. Pöpperl and M. Vossiek
(See online at https://doi.org/10.1109/EuMC.2015.7345709) - “An Ultra-Wideband Time Domain Reflectometry Chipless RFID System with Higher Order Modulation Schemes”, in German Microwave Conf., Bochum, Germany, 2016
M. Pöpperl, C. Carlowitz, C. Mandel, R. Jakoby and M. Vossiek
(See online at https://doi.org/10.1109/GEMIC.2016.7461640) - „A 3D-modulated delay-line based chipless TDR UWB RFID system with high suppression of multiple reflections“, 46th European Microwave Conference (EuMC) 2016, S. 57-60
M. Pöpperl, T. Frank, C. Mandel, R. Jakoby and M.Vossiek
(See online at https://doi.org/10.1109/EuMC.2016.7824276)
