The demand for high-power density motors has been increasing due to their remarkable output capability and compact construction. To achieve a significant improvement in motor power density, lightweight design methods have been recognized as an effective enabler. Therefore, extensive investigations have been conducted to reduce motor mass and achieve lightweight configurations through the exploration of lightweight materials, structures and manufacturing techniques. This article provides a comprehensive review and summary of state-of-the-art lightweight implementation methods for electrical machines, including the utilization of lightweight materials, structural lightweight design, and incorporation of advanced manufacturing technologies, such as additive manufacturing techniques. The advantages and limitations of each approach are also discussed in this paper. Furthermore, some comments and forecasts on potential future methodologies for motor lightweighting are also provided.

With continuously growing heat loads of microelectronic and aerospace equipment, spray cooling stands out as an effective high-heat-flux thermal management technology. Though room-temperature spray cooling has been extensively explored, liquid nitrogen spray cooling, a competitive cryogenic cooling approach, still lacks clear parametric laws and heat transfer limits due to harsh and unstable low-temperature test conditions. In this paper, experiments are carried out on a semi-closed liquid nitrogen spray cooling test rig to investigate how spray flow rate, chamber pressure and spray height affect the critical heat flux (CHF) and cooling efficiency of heated surfaces. Experimental results reveal that the maximum CHF reaches 284 W·cm⁻². Increasing flow rate raises the heat transfer limit but cuts cooling efficiency, while both CHF and efficiency are barely sensitive to chamber pressure. The spray height enabling full wall coverage is optimal, delivering a peak cooling efficiency of 32.9%. The simulation explains the relationship between liquid film evolution and CHF/cooling efficiency. Simulations demonstrate that liquid film thickness rises first and then decreases moderately with growing spray height, inconsistent with the conventional view that thinner films yield superior heat transfer. The findings provide useful guidance for the design and optimization of cryogenic spray cooling systems.