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Reconfigurable Metasurface for Microwave Energy Absorption and Reflection in Next Generation Wireless Systems

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Thesis embargoed until 13th April 2027(4.46 MB)

Date

2026

Authors

Ojukwu, Henry

Supervisor

Seet, Boon-Chong
Rehman, Saeed Ur

Item type

Thesis

Degree name

Doctor of Philosophy

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Publisher

Auckland University of Technology

Abstract

This thesis presents the design, development, and experimental validation of a functionally reconfigurable metasurface capable of dynamically switching between electromagnetic (EM) energy absorption and reflection within the 4–6 GHz microwave frequency band. The proposed metasurface addresses the growing demand for adaptable and multifunctional platforms in next-generation wireless systems for energy and spectrum management. By integrating a single PIN diode into each unit cell, the design achieves dynamic reconfigurability with reduced structural complexity, offering a compact and efficient solution compared to existing architectures. The research begins with a comprehensive review of the theoretical foundations of metasurfaces, their electromagnetic properties, and their applications in wireless systems. A critical analysis of existing literature identifies key challenges, including design complexity, scalability, and the inability to achieve simultaneous multifunctionality. These insights inform the development of a novel metasurface unit cell, optimized for dual-mode operation. The unit cell design incorporates a split-ring resonator (SRR) and an inner square patch (ISP), with a PIN diode enabling seamless switching between absorption and reflection modes. Full-wave simulations using the Finite Element Method (FEM) validate the unit cell’s performance, achieving high absorption efficiency and strong reflection characteristics. An 8×8 metasurface, constructed from the optimized unit cells, is fabricated and experimentally characterized. In reflective mode, the metasurface demonstrates high reflection efficiency across the 4–6 GHz band, with measured results closely aligning with simulations. In absorptive mode, the metasurface achieves peak absorption efficiencies of 95–98% within its primary absorption band (4.74–5.0 GHz) and exhibits relatively broadband performance, maintaining over 80% absorptivity across the 4.6–5.2 GHz range. The metasurface is further evaluated for RF energy harvesting, integrating a power combining network (PCN) to aggregate captured energy. Experimental results demonstrate a maximum DC output of 370.8 mV at the optimal absorption frequency of 4.74 GHz, confirming the metasurface’s practical viability for energy harvesting applications. A novel hybrid operational paradigm is introduced, enabling simultaneous absorption and reflection within the same metasurface structure. By spatially partitioning the array into absorptive and reflective regions, the metasurface achieves concurrent dual-mode functionality, validated through both simulations and experiments. The hybrid configuration demonstrates effective absorption in the lower frequency range (4.0–4.75 GHz) and strong reflection at higher frequencies (5.0–6.0 GHz), showcasing its potential for adaptive spectrum management and interference mitigation. The thesis concludes by highlighting the metasurface’s versatility and scalability, with potential applications in wireless sensor networks, electromagnetic interference suppression, and self-sustainable communication systems. While minor discrepancies between simulated and measured results are attributed to fabrication tolerances and environmental factors, the overall performance validates the design methodology. Future work will focus on improving fabrication precision, optimizing hybrid configurations, and advancing the metasurface toward reconfigurable intelligent surfaces (RIS) with dynamic phase control and beam steering capabilities. This research contributes a significant advancement in metasurface technology, offering a multifunctional, reconfigurable platform that bridges the gap between energy harvesting and wave manipulation, paving the way for innovative solutions in next-generation wireless systems.

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http://hdl.handle.net/10292/20902

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Doctoral Theses