Piezoelectric bimorph cantilever is a typical structure for vibration energy harvesting. This paper studies the method to improve the accuracy of FEA (finite element analysis) simulation for piezoelectric bimorph cantilever. The COSMOL simulation methods based on 1 D (dimension) model of Euler Bernoulli beam, as well as 2 D and 3 D models of solid mechanics are proposed respectively. Compared with the theory and experiment results given by Erturk A, the influences of 1 D and 3 D piezoelectric material parameters on simulation accuracy in FEA modeling is discussed. The simulation error can be reduced to less than 1.2% by using 1D piezoelectric material parameters in COMSOL simulation, while the maximum simulation error can be up to 28% by using 3D piezoelectric material parameters. Comparing serial and parallel configurations of piezoelectric bimorph cantilever, the output electrical powers, varying with the excitation frequency and load resistance, are also discussed in COMSOL simulation. Performance comparation of three kinds of piezoelectric bimorph cantilevers with tip mass shows that the modelling and simulation in finite element methods by COMSOL are simple and convenient, and are suitable for the electromechanical coupling analysis and optimization of complex topological structures.

Electrostatic nanogenerators or capacitive sensors that leverage electrostatic induction for power generation or sensing, has attracted significant interests due to their simple structure, ease of fabrication, and high device stability. However, in order for such devices to work, an additional power source or a post-charging process is necessary to activate the electrostatic effect. In this work, an electrostatic nanogenerator is fabricated using electrospun polystyrene (PS) mats and dip-coated graphene oxide (GO) films as the self-charged components. The electret performances of the PS mats and GO films are characterized via the electrostatic force microscopy phase shift and surface potential measurements. With a multilayer device structure that consists of top electrodes/GO films/spacer/electrospun PS mats/bottom electrodes, the resultant device acts as an electrostatic generator that operates in the noncontact mode. The nanogenerator can output a peak voltage of ca. 6.41 V and a peak current of ca. 6.57 nA at a rate of 1 Hz of mechanical compression, and with no attenuation of electrical outputs even after 50 000 cycles over a 13 h period. Furthermore, this as-prepared device is also capable of serving as a self-powered capacitive sensor for detection of tiny mechanical impacts and measurement of human finger bending. This results of this work provides a new avenue to easily fabricate electrostatic nanogenerators with high durability and self-powered capacitive sensors for the detection of small impacts.

Wireless sensor nodes (WSNs) for temperature and humidity monitoring are commonly used in a cold chain logistics container. Energy harvesting technology is expected to realize the sustainable self-power supply for the WSN. Low amplitude and broadband vibration energy harvesting performance are the key points in train application. In this study, two piezoelectric vibration energy harvesters (PVEHs) are designed and simulated via COMSOL. Their low resonant frequencies and high electromechanical sensitivities are realized by big L-shaped mass blocks with different material densities. Their broadband vibration energy harvesting performance is achieved by the stopper and series connection. Experimental data are shown at an acceleration of 0.5 m/s²; PVEH-1 and PVEH-2 have maximum powers of 0.24 mW and 0.1 mW when excited at the resonant frequencies of 13.1 Hz and 18.8 Hz, respectively, and they both have the optimal load resistance of 40 kΩ. Two circuit design styles of two PVEHs, independent and series styles, are proposed for broadband vibration energy harvesting. Experimental results show that the series style has a wider operating frequency bandwidth and shorter charging time. Two PVEHs in series style can be effectively used for power supply of the temperature and humidity WSN in the broadband frequency range of 8.7–22.0 Hz above charging root mean square voltage of 5 V at the acceleration of 3.0 m/s². This scheme is promised to be applied to the cold chain logistics train container.

The piezoelectric cantilever with a large proof mass is a classic vibration energy harvesting structure. In this study, in order to harvest much more energy from low frequency vibration in the finite volume, a novel L type mass block is proposed and compared with a traditional rectangular mass block for the piezoelectric cantilever. A theoretical modeling of lumped parameter system is carried out considering the effect of mass block length on mass, stiffness and damping. A series of PZT bimorph cantilevers with brass proof mass prototypes are fabricated for the experimental verification. Their eigenfrequency and maximum piezoelectric power output are analyzed by the experiment and simulation. The piezoelectric cantilever with L type mass block avoids the weakness of decreasing the effective length of piezoelectric cantilever, and has lower eigenfrequency and larger piezoelectric power output than that with rectangular mass block. Its piezoelectric power output of 192 mW/(g²) can be obtained at the low resonant frequency of 18.1 Hz and the optimal load impedance of 5kΩ, and the unit volume power density is as high as 24.6 mW/(cm³×g²).