Structural Design And Performance Investigation Of Low-Frequency Broadband Beam-Type Piezoelectric Energy Harvesters

Vibration and noise reduction is the key to improving vehicle ride comfort and structural performance,and is an important part of automobile design.In addition to using shock absorbers to dissipate vibration energy,vibration energy harvesting is another feasible method to reduce vibration and noise of vehicles,and the direction of green energy development.The harvested energy can power onboard wireless sensors,controllers and other electronic devices.To meet their self-powered demand,high-performance energy harvesters need to be developed.Vehicle vibration is usually composed of multiple vibration source frequencies below 300Hz,which has the characteristics of low-frequency broadband.Commonly used piezoelectric energy harvesters have narrow-band frequency response and low conversion efficiency,which seriously restricts the application of piezoelectric energy harvesters in vehicle vibration.Therefore,the research of low-frequency broadband piezoelectric energy harvesters has important theoretical significance and application value.Based on characteristics of vehicle vibration,the design method of pre-compressed bistable structures with local reinforcements is proposed,which can realize the integration of bistable structure design and preparation,and provide the theoretical basis for designing bistable piezoelectric energy harvesters using snap-through properties to improve the energy harvesting efficiency.The design method of a low-frequency broadband piezoelectric energy harvester based on preloading and attached structures is presented,which can reduce resonant frequency of the energy harvester and increase its broadband response by collaboratively design preloading and attached structures.To use the maximum piezoelectric strain constant d₁₅ to improve harvested vibration energy,the design method of piezoelectric energy harvesters based on d₁₅ mode and asymmetric attached structures is proposed.The main research contents and results are as follows:(1)To simplify the complex design process of bistable structures,a design method of specific properties for bistable structures based on local reinforcements and preloading is proposed.Based on the equilibrium equation,boundary conditions and constraints,etc.,the theoretical model of the pre-compressed bistable structure with local reinforcements is established.Effects of local reinforcements,pre-compression and actuation position on snapthrough properties are analyzed.The spectrums of bistable structures are obtained.When the vibration environment changes,the bistable structure with different snap-through properties is required.According to determined snap-through properties to traverse the obtained model spectrum,multiple design schemes with desired properties can be obtained,which extend the design domain of bistable structures and realize the integration of bistable structure design and preparation.Experimental results agree well with analytical results,verifying the effectiveness of the proposed design method.(2)Aiming at the problem of limited frequency modulation range of commonly tuned piezoelectric energy harvesters with a single variable,a symmetric cruciform tuned piezoelectric energy harvester based on preloading and side beams(attachment structures)is investigated.Based on Euler-Bernoulli beam theory,piezoelectric constitutive equations and Hamiltonian principle,the electromechanical coupling model of the proposed harvester is established,and effects of preloading and side beams on its resonant frequency,output voltage and available bandwidth are analyzed.Researches demonstrate that when the preloading and total mass are constant,lengthening side beams contributes to reducing the resonant frequency of the proposed harvester,and increasing its output voltage and bandwidth at low frequencies.Compared with the tuned energy harvester commonly used,the collaborative design of preloading and side beams can further improve the voltage of the proposed energy harvester and broaden its broadband at lower frequencies.The theoretical,simulation and experimental results are basically consistent,validating the effectiveness of the design of the tuned piezoelectric energy harvester with a symmetrical cruciform.(3)To use the maximum piezoelectric strain constant d₁₅ to harvest more energy from low frequency and wide frequency vibrations,low frequency and wide frequency characteristics of an asymmetric cruciform piezoelectric energy harvester with d₁₅ mode are researched.Based on Euler-Bernoulli beam theory,beam torsion equation and Hamiltonian principle,a bendingtorsion coupling governing equation of the asymmetric cruciform piezoelectric energy harvester is established,effects of bending and torsion deformation,asymmetric side beams and added mass on properties of the proposed harvester are analyzed.Researches indicate that the proposed harvester can output higher power at lower frequencies when the asymmetric coefficient is larger.Under a smaller asymmetric coefficient,its bandwidth is expanded by multiple vibration modes.Additionally,the asymmetric cruciform piezoelectric energy harvester has high performance stability even with large manufacturing tolerance of piezoelectric position.The good agreement between numerical and experimental results verifies the effectiveness of the asymmetric cruciform piezoelectric energy harvester for performance improvement.(4)To fully use the torsional deformation energy caused by vibration and further enlarge the bandwidth of d₁₅ mode piezoelectric energy harvesters,a multi-mode piezoelectric energy harvester based on d₁₅ mode and branch beams(attachment structures)is investigated.The proposed harvester uses multiple vibration modes induced by three attached branch beams to harvest broadband vibration energy.Based on Euler-Bernoulli beam theory,beam torsion equation and Euler-Lagrange equation,the electromechanical coupling governing equation of the proposed harvester is established.Effects of parameters of branch beams on resonant frequencies,output power and bandwidth are analyzed.An optimization model with the maximum bandwidth as design goal is proposed,which is solved by genetic algorithm.Researches show that by reasonably designing parameters of branch beams,the multi-mode piezoelectric energy harvester can have a large bandwidth,which corresponds to the continuous frequency band.Multiple optimization configurations can be obtained by solving the optimization model,which are conducive to expanding the design domain of multi-mode piezoelectric energy harvesters,then laying a foundation for further optimization design of the presented energy harvester.The numerical results are consistent with the experimental results,validating the accuracy of the optimized design.The research of this dissertation is supported by the National Natural Science Foundation of China(11572073),and enriches the design,theoretical model and numerical analysis of lowfrequency broadband piezoelectric energy harvesters.