## 2 Device Design  
### Device Model and Topology  
The non-contact electret-piezoelectric coupling structure is shown in Figure 1.  
In this structure, the rotor consists of curved wind blades, an electret layer, and a support layer, all of which are connected to the rotating shaft. The stator is composed of a piezoelectric layer, a copper electrode layer, and outer shell. The mechanical structure is described sequentially from top to bottom. The wind blades adopt a curved vertical-axis design, which generates relatively smaller lift and drag forces under the same wind speed, allowing for a lower starting wind speed. Additionally, vertical-axis wind blades exhibit low sensitivity to wind direction and greater structural stability. The piezoelectric layer consists of four identical optimized double-layer piezoelectric cantilever beams arranged at equal intervals. Their fixed ends are attached to the outer shell, while the active ends have magnets attached at the bottom to generate magnetically actuated vibrations. The electret support layer comprises 16 evenly spaced sector-shaped insulating supports with a sector angle of 18\({}^{\circ}\). During rotation, four magnets attached to the supports at equal intervals periodically attract the piezoelectric layer, inducing vibrations and enabling output. The electret layer, composed of flexible electret films arranged in alternating positive and negative polarities, is tightly affixed to the electret support layer, which has the same surface area. The copper electrode layer shares a structure identical to that of the electret support layer. Adjacent pairs of copper plates form an electrode pair, resulting in eight parallel pairs totally. The outer shell layer serves to fix the copper electrode and piezoelectric layers while providing isolation and protection.  
Figure 1: Diagram of the non-contact electret–piezoelectric coupling structure model.  
The outputs from the piezoelectric and electrostatic components are stored in energy storage elements via an energy management circuit and subsequently processed for external output. The topology structure of the system is illustrated in Figure 2.  
The output from both the piezoelectric and electrostatic components needs to undergo rectification, voltage reduction, and voltage stabilization before charging the energy storage capacitor. Both the piezoelectric and electrostatic low loss energy management circuit is based on the LTC3588-1, which enhance charging efficiency and reduce input voltage by charging a small capacitor and then deeply discharging it to a larger capacitor, ultimately outputting at the same voltage level. The electrostatic energy management circuit is designed to accommodate its high open-circuit voltage characteristics, thus employing external rectifier bridge with better voltage-resistant components. Diodes are employed to mitigate the impact of current backflow between power sources and reduce loop losses. The enable pin detects when the energy storage capacitor reaches the threshold voltage before providing output. Notably, the super capacitor's capacity is matched to the power level of the energy-harvesting components, supplying power to the demand device after DC/DC voltage regulation based on SX1308.