This letter proposes improved time-frequency maps for separating multiple partial discharge (PD) sources in cable terminations. PD signals are acquired through a digital measurement system and a high frequency current transformer. The waveform of each pulse is analyzed by synchrosqueezed wavelet transform, and six representative feature parameters are proposed to form time–frequency maps. The results show that the proposed algorithm is effective for discriminating mixed PD sources in cable terminations and pulses from power electronic devices detected simultaneously by the PD measurement system.

Although understanding the wetting behavior of solid surfaces is crucial for numerous engineering applications, the mechanisms driving the motion of Wenzel drops on rough surfaces remain incompletely clarified. In this study, the contact angle and contact angle hysteresis of Wenzel drops on superhydrophobic surfaces are investigated from a thermodynamic perspective. The free energy of the system is theoretically analyzed, thereby determining the equilibrium contact angle. Based on the sessile drop method, the relationship between the free energy barrier and the drop volume is calculated quantitatively, enabling the determination of advancing and receding contact angles under zero free energy barrier conditions. The theoretical calculations agree well with the experimental data. These findings enhance the understanding of the interfacial interactions between Wenzel drops and superhydrophobic surfaces.

The low adhesion of water drops on superhydrophobic surfaces is a prerequisite for their widespread potential industrial applications. The wetting transition between different wetting states significantly influences the dynamic behavior of water drops on solid surfaces. Although some theoretical studies have addressed wetting transitions, the underlying mechanisms by which local micro- and nanostructure parameters on superhydrophobic surfaces affect the wetting transition have not been fully elucidated. This study investigates three-dimensional micropillared and micro/nanopillared superhydrophobic surfaces, deriving thermodynamically the equation for the free energy barrier of wetting transition, which is influenced by the overall roughness of the entire superhydrophobic surface and its local micro/nanostructures. Theoretical calculations are performed to investigate the effects of various micro- and nanostructure parameters on the free energy barrier and wetting transition. Based on the principle of energy minimization and the calculated free energy barrier, the possible wetting states on superhydrophobic surfaces are analyzed and compared with experimental results. This study contributes to the theoretical understanding of wetting transitions and may guide the design of superhydrophobic surfaces for diverse applications.

Wave energy, a renewable resource, has attracted global attention with extensive research and applications. This paper proposes an innovative Mechanical Rectification Buoy Energy Harvester (MRBEH) based on piezoelectric generation, designed to power low-power devices on cross-sea bridges. Anchored to bridge column bases, the device restricts the buoy to single-degree-of-freedom heave motion. The buoy captures wave motion and converts it into ball-screw rotation. Via a oneway bearing, the ball-screw unidirectionally transmits motion to a planetary gear torque amplifier, which then drives the rotor for unidirectional rotation. Non-contact magnetic repulsion between rotor and PZT-unit magnets induces high-frequency mechanical oscillations in piezoelectric sheets, generating electrical output processed by a power management module. This wave energy converter addresses key challenges of low output power and cumbersome installation in existing systems, ensuring stable power supply with easy installation and maintenance. Under 0.4 Hz and 40 mm amplitude, MRBEH achieves an average output power of 1.89 W, outperforming most existing piezoelectric wave energy harvesters for cross-sea bridge applications. The generated electricity can power 136 LED lamps, GPS and temperature-humidity sensors, and rapidly charge a large-capacity capacitor from 0 V to 10 V. MRBEH proposes a novel concept for energy harvesting in extreme environments.