This study proposes and experimentally validates a multifunctional, ultra-wideband polarization conversion metasurface. The design integrates polarization conversion and electromagnetic scattering functions into a single structure, enabling applications in polarization conversion, beam control, and effective reduction of the radar cross-section (RCS). The metasurface achieves linear-to-circular polarization conversion with an axial ratio (AR) of less than 3 dB across dual-band ranges of 14.6–26.8 GHz and 31–33.5 GHz. Additionally, by adjusting metallic resonant rings within the unit structure, cross-polarization conversion with a polarization conversion ratio (PCR) greater than 0.9 is realized in the 13.6–29.8 GHz frequency range, maintaining excellent stability even at oblique incidence angles up to 50°. Leveraging the phase cancellation principle, various coding arrays are designed to precisely control the scattered beams, reducing the RCS by more than 10 dB. The comparison of simulation and experimental results further validates the wide application potential of this polarization converter in fields such as wireless communication, antenna engineering, and radar stealth.

For high-speed permanent magnet machines (HSPMMs), the precise analysis of rotor stress and rotor dynamics is essential to ensure the stable operation of rotor under high-speed conditions. This work conducts an in-depth research on the rotor of an HSPMM for a micro gas turbine with predetermined geometrical sizes. Firstly, the mechanical and electromagnetic losses are investigated by both, empirical methods and finite element method (FEM) respectively, and then the 3D steady-state temperature distribution of the HSPMM is evaluated on this basis. Then, considering the non-isothermal temperature field of the rotor, the 3D thermal-structural coupling method is adopted to analyze the influence of the carbon fiber wrapping direction and the epoxy resin adhesive between permanent magnets (PMs) and rotor core on the rotor thermal stress. Furthermore, in the steady-state thermal field, considering the change in elastic modulus and the generation of thermal stress caused by temperature rise, the results of the modal analysis are compared with those of room temperature to analyze the effect of temperature on the natural frequency of the rotor. Finally, two prototypes of 80 kW, 60000 rpm HSPMMs are fabricated to test the capability of the HSPMM. The experimental results of back-to-back drag test and modal test verify the accuracy of the temperature characteristics and modal analysis, respectively.

This article proposes a model framework coupling in-nozzle flow and external spray and presents its application to the simulation of a commercial pressure-swirl atomizer, focusing on the transient characteristics of the internal flow and subsequently the impact on the spray characteristics. High-fidelity in-nozzle simulation of the liquid–gas interactions is performed using the volume-of-fluid (VOF) method. Then, a corresponding Lagrangian simulation of sprays is performed where the parcels are injected using the information from the VOF predictions instead of phenomenological models. Both the internal flow and the spray are compared to the experimental data that are available in the literature, and satisfactory agreement is obtained in terms of the in-nozzle velocity, film thickness, and Sauter mean diameter. The effect of the different liquid properties and geometric features on the air–core formation, and consequently, on the spray characteristics have been obtained directly through spray simulation coupled with nozzle flow. As indicated by the Eulerian simulation results, the viscosity plays a key role in the formation of the air core, as the hollow-cone shape can degenerate into a solid cylindrical liquid jet under high viscosity conditions. Additionally, significantly distinct spray characteristics in terms of droplet velocity, mean diameter, and penetration were predicted depending on the formation of air core. Even if there is no stable air core in the nozzle, the spray is still discharged in a swirling motion. As opposed to the converging angle and orifice length, the nozzle diameter has a direct correlation with the formation of air core and spray atomization. This study implies that the in-nozzle flow field, which is usually ignored in fuel spray simulation, has a substantial impact on the spray characteristics and should be taken into account for design optimization by applying the developed one-way coupling approach.

Wavelet neural network (WNN), which combines the capability of neural network in learning from process and that of wavelet decomposition, was used to study geometry factors on rotating stall in vaneless diffusers. A new error function called cross entropy squared (CSE) function was derived and put forward for the purpose of convergence acceleration. WNN was trained and validated with experimental data from literature. Comparison results showed the reliability. With the trained WNN, detailed investigation was carried out mainly to understand the effects of impeller blade number, blade-exit angle, impeller rotating speed, diffuser radius ratio, and width ratio on stall inception and cell speed of vaneless diffuser. Network results clearly show the existence of distinct stall mechanisms for narrow and wide diffusers, which also make different responses to variation of the above- mentioned parameters.

The high temperature superconducting homopolar inductor machine (HTS-HIM) is identified as a promising candidate for the high-speed field of superconducting machine. The reliability and performance of HTS-HIM is closely related to the critical current of its HTS excitation coil. However, the critical current is limited by the turn with the highest risk of quench, which means that not all the turns of HTS coil can achieve the best performance. Targeting ensures the reliability of HTS-HIM and enhance the utilization rate of HTS tape, the HTS coil is designed considering the critical current reduction of local turn in this paper. Firstly, the operation principle of HTS-HIM is illustrated, and the design process is given. Then, the feasibility of calculating critical current using constant sweep rate method is described, and the HTS coil of a 10 kW HTS-HIM is designed utilizing the MAX criterion. Thirdly, the external field of the HTS coil is analyzed based on the simplified model of HTS-HIM. According to the external field distribution, an easily installed L-shaped flux diverter is proposed to suppress critical current reduction of local turn of HTS coil. The results show that the current safety margin is increased by 24 % at the cost of very little extra loss and weight through the proposed method.

To improve the precision of the position and speed estimation in ultra-high-speed (UHS) permanent magnet synchronous motors (PMSM) without position sensors, multiple refinements to the traditional extended electromotive force (EEMF) estimation algorithm are proposed in this paper. The key improvements include discretization compensation, high-frequency harmonic filtering, and the real-time adjustment of the phase-locked loop (PLL) bandwidth. Firstly, a discrete model is introduced to address EMF cross-coupling issues. Secondly, an improved proportional resonant (IPR) controller eliminating static errors is utilized in place of the conventional proportional-integral (PI) controller and low-pass filter (LPF) to enable precise electromotive force extraction, effectively filtering high-frequency harmonics that arise in low carrier ratio conditions. Based on a standard PR design, the IPR controller offers a streamlined calculation for target leading angles in delay compensation schemes to effectively mitigate discretization and delay errors. Additionally, an adaptive phase-locked loop (AQPLL) dynamically adjusts its bandwidth during acceleration to balance noise rejection and phase delay, reducing position estimation errors and optimizing torque. Simulations and experimental analyses on a motor (90,000 rpm, 30 kW) validate the effectiveness of the proposed sensorless driving techniques and demonstrate enhanced performance in position and velocity estimation, compared to the conventional EEMF approach.