PIER C | PIER Journals

2026-08-28

PIER C

Vol. 173, 41-52, 2026

doi:10.2528/PIERC26072401

download: 21

A Hybrid-Magnet Rotor Topology for Demagnetization-Resistant PMaSynRMs Using Kriging-NSGA-III Optimization

Fangrong Wang, Wen Kuang and Chaozhi Huang

Conventional ferrite-based permanent magnet-assisted synchronous reluctance motors (PMaSynRMs) suffer from low torque density and are vulnerable to irreversible demagnetization under heavy-load conditions due to the reverse armature field. To address this, this paper proposes a hybrid-magnet rotor topology in which ferrite and NdFeB magnets are arranged in series along the flux path within each U-type flux barrier (NdFeB on the airgap side, ferrite on the inner side), while the three radially layered U-type branches are connected magnetically in parallel. Within each barrier, the magnetomotive forces of the two magnet types superpose to enhance the excitation flux; meanwhile, a dual synergistic mechanism - outer NdFeB shielding and flux shunting via parallel rotor bridges - suppresses the demagnetizing field. To tackle the 15-dimensional optimization problem, a Kriging-NSGA-III framework incorporating Pearson sensitivity screening is established. Finite-element results show that, compared to the benchmark all-ferrite machine, the optimized motor achieves a 20.78% increase in average torque, torque ripple reduction from 18.80% to 8.07%, and 89.49% efficiency. The benchmark exhibits local irreversible demagnetization at 3 times rated d-axis current, whereas the proposed topology shows no observable demagnetization even at 6 times rated current, validating the effectiveness of the proposed hybrid topology and optimization strategy.

A Hybrid-Magnet Rotor Topology for Demagnetization-Resistant PMaSynRMs Using Kriging-NSGA-III Optimization

2026-08-25

PIER C

Vol. 173, 31-40, 2026

doi:10.2528/PIERC26071704

download: 45

An Ultra-High-Performance Wideband Reflective Frequency Selective Surface for Linear Y to X Polarization Conversion Suitable for Target Detection Systems

Shanmugam Muni Rathnam, Veparala Kishen Ajay Kumar, Ramamoorthy Raman, Gajendran Srihari, Shaik Mahaboob Basha and Kattela Pavan Kumar

This manuscript presents a novel compact reflective frequency selective surface (FSS) for wideband polarization conversion, enabling efficient polarization manipulation over the frequency range of 8.2 GHz to 9.5 GHz, which is the X-band spectrum for electromagnetic applications. The proposed FSS consists of a metallic pattern printed on an FR4 substrate with a relative permittivity of ε_r = 4.4, loss tangent of tanδ = 0.02, and thickness of 1.6 mm, backed by a ground plane. This configuration enables reflective-mode operation with a tunable frequency range typically spanning X-band, achieved by optimizing the unit cell's geometrical parameters. The proposed structure provides efficient linear-to-orthogonal polarization conversion over 8.2-9.5 GHz (1.3 GHz bandwidth, center frequency of 8.85 GHz), with a polarization conversion ratio (PCR) exceeding 98%. This frequency range lies within the X-band and provides a fractional bandwidth of approximately 14.69. Under oblique incidence, the proposed FSS maintains a PCR above 90% up to 40°, with only a slight bandwidth reduction, and shows good agreement between simulated and measured results. Owing to its compact nature, excellent angular stability and wide operating bandwidth, the proposed FSS is suitable for radar and wireless communication applications.

An Ultra-High-Performance Wideband Reflective Frequency Selective Surface for Linear y to x Polarization Conversion suitable for Target Detection Systems

2026-08-26

PIER C

Vol. 173, 20-30, 2026

doi:10.2528/PIERC26071404

download: 31

A Decoupling-Stub-Free Flexible MIMO Antenna with Ultra-High Isolation for Ka-Band Conformal Terminals

Chenmeng Wang, Lingming Tong and Wendong Yang

Devices such as drones and low Earth orbit satellites demand antennas that are lightweight, thin, and sufficiently flexible to conform to curved surfaces. At millimetre wave frequencies, however, closely placing multiple antennas inevitably introduces mutual coupling, which degrades communication quality. This paper presents a four element antenna array fabricated on a flexible polyethylene ter-ephthalate (PET) substrate, operating in the 26.21-29.64 GHz band. Unlike conventional approaches that rely on additional decoupling components, our design eliminates interference solely through a centrosymmetric four quadrant layout of the radiating elements, without any auxiliary structures. Measurements show that isolation among all four ports exceeds 46.95 dB; the envelope correlation coefficient (ECC) reaches as low as 0.0000312; and the diversity gain approaches the theoretical limit of 10 dB. The antenna maintains a radiation efficiency above 90% and a gain of 2.40-3.20 dBi, with stable coverage patterns across the entire band. With a thickness of only 0.12 mm, this flexible antenna offers a simple, low cost, high performance solution for conformal ap-plications. The work demonstrates that careful layout design can replace complex decoupling networks, providing a new pathway for lightweight, flexible, large scale antenna arrays in future 5G/6G communication systems.

A Decoupling-Stub-Free Flexible MIMO Antenna with Ultra-High Isolation for Ka-Band Conformal Terminals

2026-08-26

PIER C

Vol. 173, 9-19, 2026

doi:10.2528/PIERC26062903

download: 13

Unbalance Vibration Compensation Control of Outer Rotor Coreless Bearingless Permanent Magnet Synchronous Motor Based on Optimized Secondary-Path Estimation VSS-FXLMS Algorithm

Zelong Zhao, Huangqiu Zhu and Yichen Liu

Rotor mass eccentricity in an outer-rotor coreless bearingless permanent magnet synchronous motor (ORC-BPMSM) causes synchronous unbalance vibration, which degrades suspension stability and limits high-speed operation. To suppress this vibration, an optimized secondary-path estimation variable-step-size filtered-x least mean square (OSPE-VSS-FxLMS) feedforward compensation method is proposed. First, the rotor unbalance vibration mechanism is derived from the suspension force model. Then, a hyperbolic tangent-exponential (tanh-exp) function is introduced to adaptively regulate the FxLMS step size, improving the trade-off between convergence speed and steady-state error. Meanwhile, a normalized least mean square (NLMS)-based online secondary-path estimation strategy is developed to reduce gradient deviation caused by secondary-path mismatch. Simulations and experiments are conducted under constant-speed and acceleration conditions. Compared with the uncompensated condition at 3000 r/min, the displacement vibration amplitudes in the x- and y-direction are both reduced to 11 μm, corresponding to a reduction of about 69.4%. The effectiveness of the proposed unbalance vibration compensation method is confirmed by both simulated and experimental results.

Unbalance Vibration Compensation Control of Outer Rotor Coreless Bearingless Permanent Magnet Synchronous Motor Based on Optimized Secondary-Path Estimation VSS-FxLMS Algorithm

2026-08-25

PIER C

Vol. 173, 1-8, 2026

doi:10.2528/PIERC26060705

download: 26

Accurate Modelling of the Nonlinear Magnetic Restoring Force and the Electromechanical Transduction Coefficient in an Electromagnetic Vibration Energy Harvester

Merwan Hebbache, Naamane Mohdeb, Hocine Bouchekhou, Nabil Ikhlef, Hicham Allag and Abdelghani Kimouche

Electromagnetic harvesters based on magnetic levitation have emerged as particularly attractive systems owing to their contactless suspension, low mechanical damping, and inherently nonlinear stiffness behavior, which are suited to low-frequency ambient excitation. The investigated harvester consists of a levitating magnet suspended between two fixed outer magnets via repulsive magnetic forces, with a pickup coil converting oscillatory motion into electrical energy under base excitation. The primary source of difficulty in this system is the nonlinear magnetic restoring force F_mag and the electromechanical transduction coefficient γ, which must be pre-characterized via semi-analytical or finite element methods before any solution can be attempted. Therefore, the accurate pre-characterization of both F_mag and γ is the essential foundation of the entire modelling process. A Fourier space semi-analytical approach is proposed and developed, transforming a three-dimensional magnetostatic problem into a computationally efficient one-dimensional spectral calculation without remeshing. The semi-analytical predictions were validated against COMSOL finite element simulations, and their strong mutual agreement confirmed the accuracy of the proposed method before embedding it into the motion's coupled nonlinear equations.