Study On A Piezoelectric Broadband Vibration Energy Harvester With A Frequency Adaptability

As a cornerstone of the digital age,wireless sensing networks are used in lowpower modes to monitor condition parameters in complex environments,where some sensing nodes are under extreme operating conditions and power supply units are difficult to replace or maintain on a routine basis,significantly reducing the operating life of the sensing nodes.To this end,researchers have harvested vibration energy commonly found in the environment and converted it into electrical energy to power the sensing nodes to reduce maintenance costs and prolong the service life of wireless sensing networks.Conventional piezoelectric vibration energy harvesters are mostly cantilever beam type structures,which have good harvesting efficiency only near the resonance peaks and are difficult to adapt to complex excitation environments.Therefore,in order to broaden the effective working bandwidth of the harvest,this paper proposes a frequency adaptive broadband piezoelectric vibration energy harvest based on an in-depth discussion and analysis of the current status of research at home and abroad.The main research content of this paper are as follows.(1)Design a frequency adaptive wide-band piezoelectric vibration energy harvesting scheme and study the frequency adaptive process of the harvester under the action of different excitation sources.The resonant frequency of the harvest is passively adjusted by releasing the axial movement degrees of freedom of the cantilever beam,and the frequency adaptive energy harvesting mechanism is established.Analyze the frequency adaptive process of the harvest under the action of two excitation sources:fixed frequency excitation and variable frequency excitation,and study the energy exchange law between two degrees of freedom of vibration and movement.(2)Construct a theoretical model of the frequency adaptive wide-band piezoelectric vibration energy harvesting system and discuss the coupling relationship between the two degrees of freedom of transverse vibration and axial movement.A dynamic model of a beam with variable length is established by using Lagrange equation.,and the expression of the output response amplitude is obtained by solving the multi-scale method.Combined with the stiffness coupling term between vibration and movement,the matching relationship between excitation frequency and resonance frequency is investigated,and the influence of the change of the beam overhang length on the output response amplitude is analyzed to determine the key structural stiffness parameters affecting the operating bandwidth of the harvest.(3)Numerical simulation of the theoretical model to analyze the variation law of the harvest output response during the frequency adaption adaptation.The electromechanical coupled system is modelled in Simulink to study the variation law of the harvest output voltage and resonant frequency under simple harmonic excitation to verify the feasibility of the frequency adaptive mechanism.A comparison is made with a cantilever beam type harvester to study the effect of the frequency adaptive mechanism on the output performance,and the effect of the structural stiffness parameters on the operating bandwidth and peak output voltage of the harvester is analyzed.(4)To build a prototype energy harvester and construct a test platform to carry out frequency adaptive performance verification experiments and parameter optimization experiments.The above experiments were carried out under constant frequency excitation and variable frequency excitation conditions to verify the bandwidth expansion capability and environmental adaptability of the frequency adaptive harvester in complex excitation environments,and to optimize parameters such as the initial length of the beam,equivalent mass,effective stiffness of the elastic element and the limiting length of the harvester to maximize the effective operating bandwidth.