Research On Miniature Piezoelectric-Electromagnetic Hybrid Energy Harvester Arrays

Despite widespread use of microelectronic devices and wireless sensors,the power has become a limitation to further development.Most of the microelectronic devices are still powered by regular chemical batteries,however,chemical batteries suffer from environmental pollution,high replacement cost and short life and so on.Vibration energy harvesting technology is an effective solution to address this challenge.Vibration energy harvesting technology is a technology which transforms energy from the surrounding environment into electrical energy through piezoelectric effect,electromagnetic induction effect,triboelectric effect or other energy transformation mechanisms,and harvests and stores the energy through energy harvesting circuits.In this work,an array dual-cantilever beam piezoelectricelectromagnetic hybrid energy harvester is designed based on the piezoelectric effect and electromagnetic induction effect.The parameters of the hybrid energy harvester are determined through finite element analysis and experiments,and the energy harvesting circuit is designed according to its output features.Fundamentals of the piezoelectric effect are analyzed and the output power expression of the piezoelectric energy harvester based on the structure of the cantilever beam is derived.A finite element simulation of the piezoelectric energy harvester is carried out using COMSOL to analyze the effect of external load,mass block quality and vibration acceleration on the output performance.The optimum load resistance for the piezoelectric energy harvester is 12 kΩ,which results in the output power of 12.66 m W at 0.6 g vibration acceleration.Fundamentals of electromagnetic induction are analyzed and the output power expression of the moving magnet mode electromagnetic energy harvester is derived.The finite element simulation model is established to analyze the influence of such parameters as the distance between the induction coil and the permanent magnet,the external load,the frequency and amplitude of the magnet motion function on the output power of the electromagnetic energy harvester.Combined with the finite element analysis of the piezoelectric energy harvester,the output voltage and output current of the electromagnetic energy harvester based on cantilever beam vibration are obtained with a peak voltage of 2.06 V,a peak current of 4.08 m A and an output power of 5.25 m W for the external 100 Ω load.The single-cantilever beam piezoelectric-electromagnetic hybrid energy harvester was modelled with a spring-mass-damping system and analyzed theoretically.The finite element analysis model of the hybrid energy harvester is established based on the piezoelectric and electromagnetic finite element analysis models,with a 16% and 31.8% decrease in output power for piezoelectric energy harvester and electromagnetic energy harvester after the hybrid,respectively.However,the total output power after the hybrid is 14.21 m W,which increases by12.3% and 170.66% compared to the output power of the independent piezoelectric energy harvester and electromagnetic energy harvester.Based on the simulation model,the singlecantilever beam piezoelectric-electromagnetic hybrid energy harvester is fabricated and the experimental test platform is constructed to determine the basic structural parameters and experimental parameters,which include vibration acceleration,external load,quality of the permanent magnet and the distance between the permanent magnet and the coil.The array dualcantilever beam piezoelectric-electromagnetic hybrid energy harvester with a dimension of 90 mm × 90 mm × 50 mm is designed based on the single-cantilever beam structure,and the resonant frequency changed by controlling the size of the cantilever beam,and the upper and lower cantilever beams are coupled by permanent magnets.After coupling,the cantilever beam possesses two vibration peaks.Experimental results demonstrate that the total output power at the resonant frequency of each cantilever beam reached more than 18 m W,and the total output power of the array dual-cantilever beam piezoelectric-electromagnetic hybrid energy harvester is above 3.5 m W in the frequency interval from 24 Hz to 38 Hz.Experimental results indicate that the design extends the bandwidth of the system effectively.The piezoelectric energy harvesting circuit and the electromagnetic energy harvesting circuit have been designed to address the output features of the piezoelectric and electromagnetic energy harvesting technologies respectively.The test platform for the energy harvesting circuit is constructed and the results demonstrated that the piezoelectric energy harvesting circuit is stable in outputting both 3.6 V and 5.0 V DC voltages and the electromagnetic energy harvesting circuit is stable in outputting 3.3 V DC voltages.Experiments are conducted on the hybrid energy harvester to charge a 1 m F capacitor.The results show that the hybrid energy harvester can charge the capacitor to a higher peak and at a faster rate than the independent piezoelectric energy harvester and the independent electromagnetic energy harvester.The array dual-cantilever beam piezoelectricelectromagnetic hybrid energy harvester demonstrates that it has a wider effective charging bandwidth and the charging time to peak voltage is significantly shorter than that of the singlecantilever beam hybrid energy harvester.The wider effective charging bandwidth,shorter charging time and well-balanced output voltage indicate that the array dual-cantilever beam piezoelectric-electromagnetic composite energy harvester possesses a great potential for application.