An M-shape flexible 3D piezoelectric energy harvester simultaneously achieving low-frequency, multi-directional vibration energy harvesting and high-voltage output

• M-shaped energy harvester achieves 19.9 V output at a low frequency of 14.12 Hz. • Successfully harvests energy from human motion, generating a maximum peak voltage of 20.4 V. • Produces 10.3 μW power and 0.1 μW/cm³ power density under 1 mm excitation. • Exhibits robust three-directional energy harvesting capability. Piezoelectric energy harvesting (PEH) technology converts ambient vibrational energy into electric energy through an electromechanical mechanism, enabling self-powered devices. However, existing piezoelectric vibration energy harvesters (PVEHs) struggle to simultaneously achieve low-frequency response, multi-directional response, and high-voltage output. To address these limitations, this paper proposes an M-shaped flexible three-dimensional (3D) piezoelectric vibration energy harvester (MF-3D-PVEH), which is capable of capturing low frequency vibration energy from multiple directions. The incorporation of proof mass significantly reduces the resonant frequency of the harvester. The inertial effect induces significant strain on both sides of the beam, thereby enabling the generation of a high voltage output. Systematic investigations into the vibrational and electromechanical coupling behavior of the harvester are conducted. An electromechanical coupling model is established and validated through finite element analysis (FEA) and experiments. The influence of various structural parameters on the dynamic characteristics and voltage output response is discussed. Results demonstrate that the resonant frequencies of the device under different structural parameters all fall below 20 Hz while exhibiting significant advantages in harvesting vibrational energy from multiple directions. When the external excitation amplitude is only 1 mm, the output voltages measured across all three directions in the low-frequency range of 9–20 Hz reach values between 0.763 V and 7.812 V. The maximum power and power density can reach 10.306 μW and 0.1 μW/cm³, respectively. When the excitation amplitude is increased to 5 mm, the output voltage substantially increases to 19.9 V. These characteristics indicate excellent application potential for the harvester in low-power electronic devices.