PIER B | PIER Journals

2026-07-25

PIER B

Vol. 118, 42-55, 2026

doi:10.2528/PIERB26061003

download: 14

Doppler-Aware Robust Quantized RIS Phase Optimization for Physical Layer Security in 6G Vehicular Networks under Imperfect CSI

Ravi Patel and Atul Patel

Reconfigurable Intelligent Surfaces (RISs) can support physical-layer security in sixth-generation (6G) vehicular networks by reconfiguring the wireless channel. However, RIS-assisted vehicular links are affected by Doppler-induced channel aging, imperfect channel state information (CSI), feedback delay, and finite-resolution phase control. This paper develops a bounded-uncertainty Doppler-Aware Robust Quantized Alternating Optimization (DA-RQ-AO) framework for secure RIS-assisted 6G vehicular communication under imperfect and delayed CSI. The system includes a multi-antenna transmitter, a legitimate receiver, a passive eavesdropper, and a roadside RIS. A robustness-aware secrecy-rate surrogate is formulated by jointly optimizing the transmit beamformer and quantized RIS phase shifts under power, unit-modulus, CSI-uncertainty, and discrete-phase constraints. The non-convex problem is addressed through alternating optimization, where the beamformer is updated using a conservative generalized eigenvector-based solution, and the RIS phase vector is refined using an explicitly derived chain-rule-based phase-gradient update followed by finite-resolution quantization with an acceptance safeguard. Numerical results show improved secrecy rate and lower secrecy outage probability than no-RIS, random-RIS, Q-AO, and robust AO benchmarks. For N=64, the proposed scheme improves secrecy rate by 118.8% over no-RIS and 73.8% over random RIS, while 2-bit RIS control shows only 5.94% loss relative to continuous phase control.

Doppler-Aware Robust Quantized RIS Phase Optimization for Physical Layer Security in 6G Vehicular Networks under Imperfect CSI

2026-07-20

PIER B

Vol. 118, 30-41, 2026

doi:10.2528/PIERB26051401

download: 50

Well-Posed and Effective High-Order Absorbing Boundary Conditions for the Time-Harmonic Solution of Maxwell's Equations

Bruno Stupfel

For the time-harmonic solution of Maxwell's equations, absorbing boundary conditions (ABCs) are widely used to approximate the Silver-Muller radiation condition at infinity on the boundary Γ terminating the computational domain. An original high-order ABC (HOABC) is proposed that links the tangential components of the electric and magnetic fields on Γ via surface differential operators multiplied by coefficients. These coefficients are determined so as to minimize the reflection of a propagative or evanescent wave incident on a planar or spherical Γ - while taking its radius into account - and guarantee a well-posed Maxwell's problem. Numerical results are presented on a plane and coated spheres that demonstrate its efficiency even when evanescent waves are present. If it is implemented in a finite element formulation its numerical complexity is expected to be low.

Well-Posed and Effective High-Order Absorbing Boundary Conditions for the Time-Harmonic Solution of Maxwell's Equations

2026-07-14

PIER B

Vol. 118, 16-29, 2026

doi:10.2528/PIERB26033104

download: 65

Electric-Field Distribution Characteristics and Insulation Assessment for Typical Capacitive Core Defects of Oil-Immersed Bushings

Gang Xu, Yangyang Li, Shuo Zhou, Liehong Huang and Yechuan Luo

Oil-immersed transformer bushings are critical power system components, whose internal defects can cause electric-field distortion and insulation breakdown. In this study, a three-dimensional finite element model of a transformer bushing is established via COMSOL Multiphysics using actual structural parameters. The baseline electric field and voltage distributions under defect-free conditions are analyzed, and systematic simulations and quantitative evaluations are conducted to explore electric-field distortion and corresponding insulation risks under four typical defects: capacitor core metal particle contamination, insulating oil gas bubbles, capacitor final screen grounding loss, and capacitor screen damage. The results demonstrate that all defects break the inherent electric-field uniformity and induce local field intensification. Metal particle contamination and capacitor screen damage pose the greatest risks of distortion and insulation breakdown, while grounding loss causes the most extensive overall electric-field disturbance. This study clarifies the defect-induced electric-field response mechanisms, providing theoretical support for fault early identification, risk warning, and optimized operation of oil-immersed transformer bushings.

Electric-Field Distribution Characteristics and Insulation Assessment for Typical Capacitive Core Defects of Oil-Immersed Bushings

2026-07-01

PIER B

Vol. 118, 1-15, 2026

doi:10.2528/PIERB26030401

download: 107

CRLH-TL-Hilbert Structure Inspired Antenna Loaded with AMC Reflector for Wireless Applications

Marwa M. Ismail, Saif Mohamed Baraa Alsabti, Raya Adel Kamil, Mohammed Abdulrahman Dawood Al-Obaidi, Bashar S. Bashar, Yaser Amer Jassim and Taha Ahmed Elwi

High-gain reconfigurable antennas have become a crucial component of 5G systems. However, traditional Composite Right-Left-Hand Structure (CRLH) and Artificial Magnetic Conductor (AMC)-based designs suffer from high complexity, via losses, and complex biasing circuits. In this work, a CRLH transmission line integrated with a Hilbert Electromagnetic Band Gap (EBG) structure and a zero-phase AMC reflector is proposed for sub-6 GHz band. The proposed design integrates CRLH minimization, AMC gain enhancement, and Light-Dependent Resistor (LDR) bias-free reconfiguration within a unified low-complex framework. The design consists of 17-unit cells of a CRLH coupled to an EBG of Hilbert inclusions. An AMC reflector with zero phase shift is designed in the interested band to reduce back lobes and increase gain in forward direction. A maximum gain of 16 dBi was achieved at 5.5 GHz, and an increase of 4 dBi was achieved with the introduction of the AMC. An optical switch of LDR controls antenna performance, where different scenarios are investigated to achieve reconfiguration and beam scanning. The antenna gain is highly affected by changing the LDR switching status; for example, at 5 GHz, the antenna gain varies between 9 dBi and 11 dBi. At 5.5 GHz, the gain varies between 18 dBi and 20 dBi. In addition, the antenna achieved a scan of ∓5° with a consistent gain at 5 GHz by changing the LDR states. Therefore, the proposed antenna is an excellent candidate for direct amplitude modulation. Finally, the simulated results were validated through experimental measurements.