## 1 Introduction  
Environmental energy-harvesting devices are one of the key technologies for achieving intelligent and sustainable development in the Internet of Things (IoTs) [1, 2, 3]. For intelligent online monitoring devices installed along transmission lines and on poles, traditional battery storage structures will eventually deplete energy and cannot meet the long-term stable power supply needs. Continuously harvesting the abundant environmental energy around monitoring equipment and converting it into electrical energy through transduction structures to form a self-powered system is advantageous for reducing the maintenance and replacement pressures of power sources [4, 5, 6, 7]. Wind energy is a relatively abundant form of environmental energy and aligns with the principles of environmental protection. Currently, wind energy conversion technologies are mainly applied in large wind turbines, while research and application of small wind turbines for powering monitoring equipment focus on addressing issues such as low conversion efficiency, high device losses, and poor performance in low wind speed ranges [8; 9; 10]. Small wind turbines convert wind energy into mechanical energy through the rotation of blades induced by wind, thus converting wind energy into mechanical and then electrical energy. This process primarily includes electromagnetic (EMEH), triboelectric (TEH), piezoelectric (PEH), and electrostatic (EEH) energy harvester types [11; 12; 13]. Electromagnetic systems have high-excitation-frequency requirements and face challenges in miniaturization of multi-turn coil structures, making them suitable mainly for large wind turbine systems or high-speed applications in strong winds. Triboelectric converters are almost always subject to wear due to contact methods, and their impediment to the blade shaft results in higher-starting-wind-speed requirements. In contrast, piezoelectric and electrostatic systems are more conducive to miniaturization and non-contact designs. The piezoelectric structure, compared to electrostatic and triboelectric structures, is small in size and weight while being able to output considerable power and mitigate the vibration [12; 13]. However, they can only output significantly higher energy near their resonant frequency, limiting their effectiveness in a broader frequency range. Expanding the operating range, utilizing non-resonant methods, and optimizing low wind speed performance are important research directions for piezoelectric converters under random excitation in natural environments. Electrostatic systems, based on the principle of electrostatic induction, offer reliable isolation and low component wear, showing significant application potential. However, low energy conversion rates and instability of the electrostatic field source remain the primary issues to be addressed. Electret materials, capable of retaining polarized charges for extended periods, can maintain surface electric potentials ranging from several hundred volts and can be easily formed into various thin film shapes [14; 15; 16; 17]. They are promising electrostatic field sources for wind energy conversion. Reference [18] designed a rotating electrostatic generator structure based on the advantages of electret materials, enhancing output capacity through multiple stacked electrostatic conversion components. Reference [19] further analyzed factors affecting the structure, such as duty cycle and number of electrodes, optimizing the performance of the generator. Nevertheless, the output power density and energy conversion efficiency of electrostatic converters remain relatively low. Each type of wind energy converter has distinct characteristics with respective advantages and disadvantages. Designing coupled structures to integrate and complement different types of converters is an efficient and feasible approach.