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2026-06-15
Near-Field SAR-Aware Power Control and Beamforming for Reconfigurable Intelligent Surfaces with Electromagnetic Safety Guarantees
By
Sohel Rana,

    Dr. Sohel Rana

    Department of Electronics and Communication Engineering

    Shreeyash College of Engineering and Technology (SYCET)

    India

    Homepage

Nagendranath,

    Prof. Nagendranath

    Department of CSE

    Sasi Institute of Technology and Engineering

    India

    Homepage

Shaik Md. Rafee,

    Prof. Shaik Md. Rafee

    Sasi Institute of Technology and Engineering

    India

    Homepage

Venkata Krishnamoorthy,

    Dr. Venkata Krishnamoorthy

    Department of ECE

    Sasi Institute of Technology and Engineering

    India

    Homepage

Ravi Sankar,

    Dr. Ravi Sankar

    Department of Electronics and Communication Engineering

    Sasi Institute of Technology and Engineering

    India

    Homepage

Tukaram Shep,

    Dr. Tukaram Shep

    CSMSS Chh. Shahu College of Engineering

    India

    Homepage

Kiranmayi Sridhara

    Dr. Kiranmayi Sridhara

    Department of Electronics and Communication Engineering

    Aditya University

    India

    Homepage

Progress In Electromagnetics Research B, Vol. 117, 214-230, 2026
doi:10.2528/PIERB26050302 | Google Scholar

Abstract
Existing electromagnetic (EM) safety analyses for reconfigurable intelligent surface (RIS) systems rely on the far-field equivalent plane-wave density (EPD) formula, which systematically underestimates tissue exposure when the user equipment (UE) operates in the radiating near-field (NF) zone (dU ≲ dR/2, where dR = 2D2/λ is the Rayleigh distance, and D = (N-1)λ/2 is the aperture length). This paper presents five analytically rigorous contributions to NF-aware power allocation and beamforming for RIS-assisted 5G/6G systems. (1) A conservative Fresnel-envelope correction factor κ(d,N) with a provable non-negative overestimation error ε(d,N) ≥ 0 (Propositions 1-2, Lemma 1). (2) Closed-form NF-corrected SAR power ceiling P∗NF and minimum exclusion radius dNFmin; the 1-D Fresnel bound is conservative for 2-D uniform planar arrays (UPAs) with a separability gap up to 13.2 dB, confirmed by exact 2-D spherical-wave summations (SAR1D ≥ SARFF ≥ SAR2D). (3) A closed-form NF phase-taper Δϕn recovering up to 0.4 bit/s/Hz SAR-constrained spectral efficiency (SCSE) at dU = 1 m (Proposition 3). (4) A two-stage NF-SAR alternating-optimisation (NF-SAR-AO) algorithm with O(N) per-iteration complexity, hard guard margin (deff = 1.1dU), and proved monotone convergence under line-of-sight (LOS) channels (Algorithm 1, Proposition 4). (5) 2-bit phase quantization incurring < 0.3 bit/s/Hz SCSE loss with 100% ICNIRP 2020 compliance for all dU ≥ 0.5 m. Validated over 5 × 103 Monte Carlo (MC) trials at 3.5 GHz (N = 64, Pmax = 200 mW): dNFmin = 0.727 m1 vs. dFFmin = 0.498 m - far-field models underestimate the required safety exclusion radius by 46%, risking ICNIRP 2020 non-compliance.
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Citation
Sohel Rana, Nagendranath, Shaik Md. Rafee, Venkata Krishnamoorthy, Ravi Sankar, Tukaram Shep, and Kiranmayi Sridhara, "Near-Field SAR-Aware Power Control and Beamforming for Reconfigurable Intelligent Surfaces with Electromagnetic Safety Guarantees," Progress In Electromagnetics Research B, Vol. 117, 214-230, 2026.
doi:10.2528/PIERB26050302
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