Structural Design And Analysis Of Low Frequency And Large Bandwidth Energy Harvester Based On Pre-stress

With the increasing attention of new energy car technology,the research on the vehicle vibration energy collection has become a hot spot for scholars.In several existing vibration energy harvesting technologies(electrostatic,the electromagnetic and piezoelectric,etc.),due to the advantages of high efficiency of energy conversion,easy production and application,the design of piezoelectric energy harvesting system has become the focus of domestic and foreign scholars.The traditional piezoelectric energy harvesting system is mainly composed of cantilever structures,and this type of piezoelectric energy harvesting system uses ambient vibration to induce the bending deformation of the cantilever beam.The piezoelectric material laid on the surface of the structure produces the polarization voltage and produces the electrical energy.The related research shows that when the natural frequency of the cantilever beam is close to the frequency of the ambient vibration,the harvesting device produces the larger amplitude and the higher power output.However,most of the vibration excitation of the vehicle is in the lower frequency range,and the energy generation of the cantilever piezoelectric energy harvesting is proportional to the cube of the frequency and the square of the amplitude,so the piezoelectric energy harvester based on the resonance mechanism is difficult to apply because of the low efficiency of the harvesting energy.Considering the randomness of the vehicle vibration and the low-frequency band,it is necessary to improve the efficiency of the harvesting energy under the excitation of the broadband low frequency environment.The design of the structure should have the characteristics of a high response to low frequency excitation and the conversion to high frequency vibration(up-frequency).The urgent need of the harvester in a low frequency band has led to the development of new technologies.Mechanical frequency upgrading technology has become an important way to solve the energy collection in low frequency environment.However,the current research works for low-frequency energy collection only in the narrow band(<2Hz),so to achieve the purpose of low frequency efficient energy collection,we must effectively solve the problem of narrow banding on the basis of the structure frequency upgrading,broaden the working frequency of the energy harvesting system and improve the energy collection efficiency.In this paper,the natural frequency of the structure is tuned to the low frequency vibration environment by applying the axial load at the end of the fixed beam,which effectively improves the band-width and the energy harvesting efficiency.Based on the study of the mechanism of axial load,this paper presents a new type of cross-type pre-stressed energy harvester,which uses mechanical impact to convert low-frequency vibration energy into high-frequency vibration of attached cantilever beam,so as to enhance the efficiency of captive energy.The concrete work of this paper is composed of the following parts:(1)The two kinds of working modes of the piezoelectric harvesters are analyzed.The kinetic equation of the single mode of the harvester is obtained by Hamilton's principle and the lateral dynamic displacement response and the output voltage of the piezoelectric harvester are also obtained by the pre-stressed energy device in any position.(2)The finite element model of the axially loaded energy harvester is established,and the distribution of piezoelectric piece is optimized by the ANSYS finite element software.On this basis,the influence of the axial load on the energy harvesting efficiency was analyzed.(3)A new type of cross-type axially loaded energy harvester is proposed by using the mechanical impact at the end of the attached cantilever to induce high frequency vibration.The novel harvester achieves the purpose of widening the frequency band.In this paper,for the demand of broadband and low frequency energy harvester,we proposed a pre-stressed structure and a new cross-type pre-stressed up-frequency energy harvester structure to realize the broad-band and low-frequency energy harvesting.The work of the paper provides a new idea for the design of low frequency energy harvester.