Flexible Radio Frequency IDentification Tags and System (FlexID)
Final Report Abstract
The main objective of the FlexID project was to realize a mechanically flexible, low-power and low-cost chipless RFID tag system, which operates in the GHz-range in order to be able to store a relevant amount of information in the frequency-domain using spectral signatures. The main challenges for this objective were I. to enable a printable Si technology for the formation of GHz capable Schottky diodes making clutter suppression concepts possible, II. to investigate and reduce the influence of mechanical tag deformation on the frequency signature, and III. to enable error correction in a defined coding bandwidth, without paying an information penalty e.g. by the integration of error-correction bits. The obtained progress with regard to these challenges is described in the following: I. To enable clutter suppression for passive chipless tags, the integration of a non-linear element into the antenna structure of the tag is beneficial, as it allows the use of higher order harmonics as the frequency response of the tag. This enables the RFID system to separate the tag response from the influence of clutter. However, such a concept requires a non-linear element with switching speeds in the GHz range, which is not possible with current printable low-cost semiconductor technologies. The FlexID project has developed a solution for that, making printable Si Schottky diodes a reality. The developed diode structure is based on printing nanoparticles which are laser modified to form highly crystalline cone shaped microstructures. Using these microstructures in the FlexID diode architecture, we were able to realize printable devices functioning at 4GHz with 2nd and 3rd order harmonics at 8GHz and 12GHz. While this demonstrates the ultra-high frequency functionality of the FlexID diode concept, it should be noted, that the developed theoretical diode equivalent circuit model predicts a diode operation at frequencies significantly above 10GHz. The investigation of fundamental diode operation at such frequencies, is however currently not possible, due to the limitations of our measurement setup. II. Passive chipless RFID tags are predestined for the use with mechanically flexible substrates and the associated low-cost application use cases. However, the flexing or the crumpling of a tag can negatively influence is spectral signature and thereby make the tag readout difficult. This was quantified using an electromagnetic simulation based on the boundary element method for a patch antenna crumpled between 0° and 60°, demonstrating a clear change in signal intensity as well as a clear shift in resonance frequency in dependence of the crumpling angle. This result could be verified experimentally using multi-bit frequency coded chipless tags, substantiating the strong implications tag crumpling may have on the readout of this type of system, and thus the requirement for good error correction strategies. III. Such error correction strategies where therefore pursued for challenge III. To mitigate coding capacity penalties for error correction purposes, such as by the integration of error correction bits (ECB) for a defined bandwidth, instead of reducing the number of information bits, the bandwidth occupied by and the resonance magnitude of a single information bit was reduced. It could be demonstrated, that the successful reading rate for the tag ID could be improved, as long as the number of ECBs does not exceed K0 × (1/rB − 1), where K0 is the number of information bits without integrated ECBs, and rB represents the bit bandwidth reduction ratio. Further, a new interrogation algorithm called the majority rule interrogation (MRI) was introduced, where multiple tag readouts are used to form an average codeword. By combining the MRI interrogation technique with the error-correcting code (ECC) discussed above, the advanced ECC-MRI algorithm was obtained, which yields a significant improvement in successful reading rates for passive chipless RFID systems. In summary, the FlexID project was able to make significant progress towards a real-world application of a passive chipless RFID system in terms of tag read-out strategies and technological implementation. By doing so, a new printable Si technology was introduced, which was able to surpass the 1GHz barrier for printable electronics.
Publications
- "Silicon nanoparticle inks for RF electronic applications," FLEX Europe 2017/SEMICON Europa 2017, Nov. 15-16, Munich, Germany, session 3 ’Materials Advancement’, 2017
L. Kuehnel, D. Pandel, R. Schmechel, J. Moeller, K. Neumann, A. Rennings, D. Erni, A. Hierzenberger, M. Schleberger, O. J. Nguon, J. Duvigneau. G. J. Vancso, and N. Benson
- "Modeling of random nanostructures based on SEM images and analysis of resulting RF-performance," COMSOL Conference 2018, Oct. 22-24, Swisstech Convention Center, EPFL Lausanne, Lausanne, Switzerland, Session: ’Electromagnetic 3 – Quasi-Static Fields’, paper 2, pp. 12, and Poster Session, poster no. 97, pp. 19, 2018
K. Neumann, J. Moeller, L. Kuehnel, A. Rennings, N. Benson, R. Schmechel and D. Erni
- “On the coding of chipless tags,” IEEE J. Radio Frequency Identification, vol.2, no.4, pp.170-184, 2018
F. Zheng, Y. Chen, T. Kaiser, and A. J. H. Vinck
(See online at https://doi.org/10.1109/JRFID.2018.2877054) - "Analysis of stochastic Schottky barrier variations within printed high frequency rectifiers for harmonics generation," IEEE MTT-S Int. Microwave Workshop Series on Advanced Materials and Processes (IMWS-AMP 2019), July 16-18, Bochum, Germany, Session TH2.2: ‘Advanced Devices and Circuits’, paper no. TH2.2-1, pp. 169-171, 2019
K. Neumann, L. Kuehnel, F. Langer, A. Rennings, N. Benson, R. Schmechel, and D. Erni
(See online at https://doi.org/10.1109/IMWS-AMP.2019.8880082) - "New approach for the simulation of bent and crumpled antennas on a flexible substrate," IEEE MTT-S Int. Microwave Workshop Series on Advanced Materials and Processes (IMWS-AMP 2019), July 16-18, Bochum, Germany, Session WE1.1: ‘Antennas and Simulation Techniques’, paper no. WE1.1-1, pp. 61-63, 2019
K. Neumann, A. Rennings, and D. Erni
(See online at https://doi.org/10.1109/IMWS-AMP.2019.8880127) - “An Information-Theoretic Approach to the Chipless RFID Tag Identification,” IEEE Access, vol.7, pp.96984-97000, 2019
Y. Chen, F. Zheng, T. Kaiser, and A. J. H. Vinck
(See online at https://doi.org/10.1109/ACCESS.2019.2929243) - "A stochastic large-signal model for printed high-frequency rectifiers used for efficient generation of higher harmonics," IEEE Trans. Microw. Theory Techn., vol. 68, no. 6, p. 2151-2160, June 2020
K. Neumann, L. Kuehnel, F. Langer, A. Rennings, N. Benson, R. Schmechel, and D. Erni
(See online at https://doi.org/10.1109/TMTT.2020.2990561) - "Nanoparticle ink-based silicon Schottky diodes operating up to 2.84 GHz," Nano Select, vol. 1, no. 6, pp. 659-665, Dec. 1, 2020
L. Kuehnel, K. Neumann, J. Neises, F. Langer, D. Erni, R. Schmechel, N. Benson
(See online at https://doi.org/10.1002/nano.202000102)
