| With the development of wireless sensing technology,providing electrical energy for low-power electrical appliances is a problem that must be solved.The battery is currently used widely as a traditional style,but it is very difficult or impossible to replace the battery in many specific environments and conditions.Therefore,it is expected to supply the electricity demand of low-power electrical appliances by harvesting the surrounding environmental energy.Vibration energy,as a kind of ambient energy that exists widely in nature and has not been fully utilized,makes researchers over the world have a great interest to study how to harvest it for self-powered appliances.At present,the technology of harvesting vibration energy is mainly based on electromagnetic conversion,electrostatic conversion,and piezoelectric conversion.The energy conversion density of piezoelectric ceramics is more than three times higher than the other two.Therefore,it has been widely attended by domestic and foreign researchers.However,for piezoelectric coupled cantilever harvesters with constant and variable cross-sections,their output powers are very limited at present since they can not fully utilize the positive piezoelectric effect of piezoelectric patches.Therefore,in order to solve the above problem,a bow-shaped piezoelectric coupled unit is proposed to harvest vibration energy,which can make piezoelectric patches produce uniformly deformed.Through conducting a series of free vibration and forced vibration tests,the effect of some factors,including the length of the piezoelectric coupling segment,the length of the force arm,the position and value of the proof mass,the excitation frequency,and the load resistance,on the energy harvesting of the bow-shaped piezoelectric coupled unit are analyzed.The experimental results indicate that the bow-shaped piezoelectric coupled unit has a high energy harvesting efficiency,it is because its piezoelectric coupled segments have a uniform strain in the process of vibration.Taking a piezoelectric patch with a dimension of 40 mm×10 mm×0.5 mm as an example,when the bow-shaped piezoelectric coupled unit is excited by forced vibration and free vibration,their output power densities can reach up to 0.1 m W/mm~3and 0.281 m W/mm~3,respectively.In order to further broaden the application of the aforesaid bow-shaped piezoelectric coupled unit,through combining vibration control and energy harvesting,an energy-capturing shock absorber is proposed by circularly arranging the bow-shaped piezoelectric coupled units.According to the combination of the energy-absorbing shock absorber made of bow-shaped piezoelectric coupled units and the main vibration system,the overall vibration control equations are developed.The influences of some factors,such as the mass ratio and frequency ratio of the shock absorber to the main vibration system,the damping ratio of the shock absorber,the dimension of the shock absorber,and the length of the force arm,are analyzed through the MATLAB platform.Some valuable rules are obtained to guide the selection and installation position of the bow-shaped piezoelectric coupled unit to complete the vibration control of a specific target in the application process of the shock absorber.In addition,through theoretical analysis and experimental results,it is concluded that the vibration control effect of the shock absorber can not only be optimized by selecting the appropriate bow-shaped piezoelectric coupled unit and installation position but also can be further improved by adjusting the load resistance in the circuit.The proposed bow-shaped piezoelectric coupled unit in this research is an efficient and practical unit to harvest vibration energy,which also induces a new idea for structural vibration control by assembling a series of bow-shaped units to form all kinds of energy-harvesting shock absorbers. |
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