## 1 Introduction  
In order to make full use of the vibrational energy and wind energy in the environment and solve the problem of self-supply of microelectronic devices such as low-power sensors, more and more scholars have begun to study environmental energy harvesting [1]. The case for the use of microelectronic devices is involved in places such as vehicle driving, bridge monitoring, energy consumption monitoring, and structural health monitoring and airfoil vibration monitoring and other places [2; 3; 4; 5]. The design of an energy harvester for wind energy harvesting and conversion to replace traditional forms of chemical batteries to supply power to microelectronic devices [6] can effectively solve the places of limited use, high manufacturing costs, environmental pollution and other problems caused by conventional batteries [7]. The energy harvester can be used in a variety of ways. Depending on the principle of operation, they can be divided into a piezoelectric energy harvester [8; 9; 10], an electromagnetic energy harvester [11], an electrostatic energy harvester [12] and a frictional energy harvester [13]. Among these, a piezoelectric energy harvester has the advantage of higher operating frequency range and higher energy density [14]. Depending on the different mechanism of wind-induced vibration, a piezoelectric energy harvester mainly includes a vortex-induced energy harvester [15; 16], a flutter energy harvester [17; 18], a galloping energy harvester [19] and a wake energy harvester [20]. Vortex excitation usually occurs in cylindrical structures, where the air flow acts on the surface of the cylinder, resulting in alternating shedding of vortices on both sides of the cylinder to form alternating vortex excitation forces, which excite the cylinder to produce vortex vibration [21; 22]. A classical vortex-induced energy harvester is generally composed of a terminal cylinder and a piezoelectric cantilever beam, which usually vibrates in a single degree of freedom [23]. [PERSON] [24] studied the output characteristics of the double-beam vortex-induced vibration piezoelectric energy harvester through numerical analysis, and the results showed that the maximum output voltage was 8.42 V when the flow velocity was 5.6 m/s. [PERSON] et al. [25] studied a suspended piezoelectric energy harvester with the upper end of the piezoelectric cantilever fixed and the lower end connected to a cylindrical blunt body. After the water flows through the cylindrical blunt body, high- and low-pressure vortices are formed. The cylinder vibrates periodically under the action of hydrodynamic force. When the water velocity is 0.48 m/s, its maximum output power is 1.064 mW. [PERSON] et al. [26] designed a vortex-induced energy harvester consisting of a cylindrical harvester body and a single degree of freedom piezoelectric cantilever beam at the rear and installed a blade at the free end of the cantilever beam. When the wind velocity was 5 m/s, the output power was 3 mW, but it is difficult to miniaturize the energy harvester. Flutter is a self-excited divergent vibration, which is suitable for higher flow rate conditions, characterized by self-excitation, nonlinearity, large amplitude and large deformation, but with low stability [27]. A wind belt harvester is a taut belt with a high spreading ratio moving at low wind velocities. [PERSON] et al. [28] have proposed a similar energy harvester that converts mechanical vibrations into electrical energy via an electromagnetic transducer. [PERSON] [29] designed a T-shaped double-crystal cantilever beam rigid flutter energy harvester, which has an output power of 4 mW when the wind velocity is 4 m/s. [PERSON] et al. [30] designed an aeroelastic energy trap based on the nonlinear limit cycle oscillation phenomenon, and obtained an average output power of 2.5 mW at a wind velocity of 27 m/s. [PERSON] and [PERSON] [31] proposed a flutter-based aeroelastic energy harvester that undergoes limit cycle oscillations at higher wind velocities above the critical wind velocity.