Challenges and solutions of metasurface based reconfigurable intelligent surfaces

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2025-08-29
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Date

2025

Department

Elektroniikan ja nanotekniikan laitos
Department of Electronics and Nanoengineering

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Mcode

Degree programme

Language

en

Pages

104 + app. 80

Series

Aalto University publication series Doctoral Theses, 146/2025

Abstract

Reconfigurable Intelligent Surfaces (RISs) have emerged as a transformative technology in wireless communications, promising enhanced signal propagation, interference management, and energy efficiency. This thesis develops novel methodologies for designing RISs with improved electromagnetic parameters. In the first part of the thesis, a key focus is done on relationships between reflection locality, physical optics, and angular stability of a uniform metasurface. We show that angular stability of a uniform metasurface is crucial for a RIS implemented as its periodically non-uniform analogue (with tunable period). Through analytical modelling, numerical simulations, and experimental validation, our study results in such binary metasurfaces (BMSs) that possess following advantages compared to previously known ones: higher angular stability of the reflection phase, true polarization insensitivity of the scattering pattern, broader operation band, and what is not less important, possibility to accurately predict the operation characteristics with the use of simple analytical models. In the second part of the thesis, we aim to achieve higher scattering efficiency. With this purpose our research advances the discrete sheet impedance approach for periodically non-uniform metasurfaces of general type. We optimize their beamforming efficiency, overcoming the previously adopted limitations of conventional (diagonal matrix) techniques. A novel framework for RIS with multiple reradiation modes is developed, leveraging both unequal coefficient superposition and discrete impedance optimization. The methodologies proposed and validated in this thesis contribute to the realization of highperformance, cost-effective RISs for future wireless networks – 6G and beyond.

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Supervising professor

Simovski, Constantin, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland

Keywords

RIS, wireless communication, angular stability, metasurfaces, beamforming

Other note

Parts

  • [Publication 1]: J. Shabanpour, V. Lenets, G. Lerosey, S. Tretyakov and C. Simovski. Engineering of intelligent reflecting surfaces: Reflection locality and angular stability. IEEE Transactions on Antennas and Propagation, vol. 72, no. 5, pp. 4198-4211, May 2024.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202405293965
    DOI: 10.1109/TAP.2024.3375659 View at publisher
  • [Publication 2]: J. Shabanpour, Y. Li, S. Tretyakov and C. Simovski. Physical Optics and Reflection Locality in Designing Reconfigurable Intelligent Surfaces. IEEE Open Journal of Antennas and Propagation, vol. 5, no. 6, pp. 1571-1579, Dec 2024.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202412177896
    DOI: 10.1109/OJAP.2024.3422681 View at publisher
  • [Publication 3]: J. Shabanpour and C. R. Simovski. Angular and Polarization Stability of Broadband Reconfigurable Intelligent Surfaces of Binary Type. IEEE Access, vol. 10, pp. 126253-126268, 2022.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202301021051
    DOI: 10.1109/ACCESS.2022.3226264 View at publisher
  • [Publication 4]: Javad Shabanpour, Xuchen Wang, Sergei Kosulnikov, Constantin Simovski. Advancing RIS Beamforming Efficiency: Moving Beyond Diagonal Matrix Techniques. Accepted in IEEE Transactions on Vehicular Technologies, 14 pages, July 2025.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202507045560
    DOI: 10.1109/TVT.2025.3583421 View at publisher
  • [Publication 5]: Javad Shabanpour, Constantin Simovski. On the design of reflecting intelligent surfaces for multi-user NOMA communication networks. 2024 IEEE International Symposium on Circuits and Systems (ISCAS), Singapore, pp. 1-5, 2024.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202502052282
    DOI: 10.1109/ISCAS58744.2024.10558543 View at publisher
  • [Publication 6]: Javad Shabanpour, Constantin Simovski, Giovanni Geraci. Physically Consistent RIS: From Reradiation Mode Optimization to Practical Realization. Accepted in 2024 IEEE Globecom Workshops, 6 pages, 2024.

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https://urn.fi/URN:ISBN:978-952-64-2661-7

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[diss] Sähkötekniikan korkeakoulu / ELEC