1) pay attention to the structure of closed magnetic circuit, so that the device can effectively use magnetic energy, greatly improve the energy conversion; 2) aiming at the limitation of low frequency vibration, a multi-tooth structure is designed to produce multiple alternating magnetic fields in one vibration, which greatly improves the induction electromotive force and power generation; 3) magnetic field formed by the multi-tooth structure of the yoke limits the range of motion of the vibrator. no need to install special spring or permanent magnet limit, protect vibrator from impact, simplify structure and assembly.