PIER B | PIER Journals

2026-08-01

PIER B

Vol. 118, 72-86, 2026

doi:10.2528/PIERB26041302

download: 63

SMS Optical Fiber Laser Sensor for Transformer Oil Temperature Monitoring-Based IoT of AI Control

Jawad Kadhim Raham, Maather Alshaibi and Taha Ahmed Elwi

This paper presents the design, fabrication, and characterization of a novel optical fiber temperature sensor based on a single-mode-multimode-single-mode (SMS) structure for real-time monitoring of transformer oil temperature in high-voltage environments, addressing the limitations of conventional electronic sensors such as electromagnetic interference, electrical safety hazards, and restricted spatial coverage. The sensor, fabricated with corning single mode fiber (SMF)-28e+ single-mode and Thorlabs FG050UGA multimode fibers (5 cm active section), operates on the Mach-Zehnder interferometer principle, where temperature-induced refractive index changes in transformer oil modulate light propagation. Systematic experiments over a 30-90 °C range using a 1550 nm tunable laser, temperature‑controlled oil bath, Pt100 reference, and optical spectrum analyzer yielded a wavelength sensitivity of 4.17 × 10^-3 nm/°C with excellent linearity (R² = 0.9646), a standard error of 4.45 °C, repeatability better than 0.5 % coefficient of variation, and progressive OSNR improvement from 0 dBm at 30°C to 2.26 dBm at 90 °C. The wavelength-based calibration method significantly outperformed the power-based approach, offering 1.36× lower error (4.45 °C vs. 6.04 °C) and higher correlation, with expanded uncertainty (95 % confidence, k = 2) calculated as 6.14°C. Compared to fiber Bragg grating and fiber-loop mirror sensors, the proposed SMS sensor provides electromagnetic immunity, cost-effective fabrication, high stability, and a simple all-fiber configuration, making it a reliable and practical solution for continuous thermal monitoring in power transformers and laying the foundation for comprehensive fiber-optic sensing networks in high-voltage power systems.

SMS Optical Fiber Laser Sensor for Transformer Oil Temperature Monitoring-Based IoT of AI Control

2026-07-29

PIER B

Vol. 118, 56-71, 2026

doi:10.2528/PIERB26061101

download: 56

Software-Validated Computational Framework for Axial and Radial Magnetic Force Prediction in Misaligned Air-Core Coil Systems with Surrogate Modeling

Ali Jebelli, Nafiseh Lotfi, Arezoo Mahabadi and Mustapha C. E. Yagoub

Accurate prediction of magnetic forces in air-core coil systems is essential for the design and optimization. Accurate magnetic-force prediction in air-core coil systems is essential for electromagnetic actuators, wireless power transfer, inductive coupling, magnetic calibration, and coil-based positioning systems. This paper presents a software-validated computational framework for predicting axial and radial magnetic forces in practical air-core coil systems under aligned and misaligned conditions. The framework extends ideal coaxial coil-force analysis by including lateral offset, angular tilt, finite coil dimensions, discrete winding geometry, helical winding pitch, finite conductor diameter, and nonuniform conductor placement. Three complementary physics-based methods are implemented and compared: a semi-analytical elliptic-integral method for rapid coaxial and near-coaxial evaluation, a direct numerical-integration method based on the Lorentz-force interaction integral, and a filament-based discrete-winding method for practical conductor geometry. Independent Ansys Maxwell simulations are used as the finite-element software-validation reference under identical geometric and electrical conditions. This work is limited to software-based validation; physical experimental validation using real coil pairs is identified as future work. The validation results show strong agreement among the proposed methods and Ansys Maxwell simulations. The final software mesh-independence change is 0.15%, the boundary-domain sensitivity is 0.12%, and the maximum relative half-spread among the physics-based methods is 0.55%. The maximum axial-force deviation in the coaxial separation sweep is 0.62%, and the radial-force sign-symmetry error remains below 0.23%. Including practical winding details reduces the model-to-software vector error from 2.87% for the continuous-current approximation to 0.10% for the full practical winding model. A feedforward neural-network surrogate model trained using 12,000 validated samples is also introduced for rapid interpolation within the sampled design domain. The surrogate achieves R²=0.996-0.998, mean relative error below 1.20%, and maximum relative error of 5.00% on unseen test data. The proposed framework provides an accurate, efficient, and physically interpretable tool for axial and radial force prediction in practical misaligned air-core coil systems.

Software-Validated Computational Framework for Axial and Radial Magnetic Force Prediction in Misaligned Air-Core Coil Systems with Surrogate Modeling

2026-07-25

PIER B

Vol. 118, 42-55, 2026

doi:10.2528/PIERB26061003

download: 43

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: 65

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: 79

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: 127

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.