Study On Band Gap Characteristics And Acoustic Energy Harvester Of Phononic Crystals

The normal operation and production of the hydro-power plant will produce strong noise and vibration,and long-term exposure to this environment will cause serious harm to workers’ health.Phononic crystal is made with different elastic properties of periodic composite materials.They are characterized by bandgap and defect states and can regulate the propagation of elastic waves.Based on the characteristic of phononic crystal,it is widely used in vibration reduction and noise reduction.Besides,phononic crystals also exhibit abundant physical phenomena,such as defect states,localization and surface states.According to the local characteristics of the phononic crystal point defect structure to the elastic wave,the elastic energy is limited to the vicinity of the defect to form a microcavity resonance,and then the acoustic energy is harvested through the force-electric conversion characteristics of the piezoelectric material,so that the phononic crystal has a broader development space.In this paper,the two-dimensional phononic crystal plate is taken as the research object.Through the idea of “local resonance”,four local resonance acoustic metamaterial scatterers models are designed to study their band gap characteristics and verified by numerical simulation.An acoustic energy harvester using the defect modes characteristics of phononic crystals was designed to study the effect of magnets on energy harvesting.The main research work and conclusions of the full text are as follows:(1)Taking the two-dimensional phononic crystal as the research object,the band gap opening frequency of the local resonance acoustic metamaterial is dynamically estimated.The analytical models of the axial resonance of the four types of scatterers are established and the calculation method of the band gap opening frequency is given.Through the numerical simulation of the structure of the four types of scatterers unit cells,the energy band structure and the eigenmode are analyzed,compared with the theoretical model solution,verifies the correctness of the mathematical model.The conclusions obtained are: the band gap opening frequency is inversely proportional to the height of the scatterer;the tapered scatterer can reduce the band gap opening frequency;for double-layer composite scatterers,the heavier surface layer is beneficial to reduce the band gap opening frequency;the bandgap opening frequency of the necked composite scatterers is the lowest.(2)In order to carry out the targeted design of vibration isolation and noise reduction,the influence of the specific modulus,height,taper ratio,radius ratio and height ratio of the scatterer on the bandgap opening frequency was studied.The results show that the band gap opening frequency decreases with increasing taper ratio and height;for composite cylindrical scatterers,when the height ratio and height increase,the band gap opening frequency drops sharply;for necked composite scatterers,as the height ratio increases,the band gap opening frequency decreases first and then begins to increase,but as the radius ratio increases,the band gap opening frequency continues to increase.For different height values,these changes are similar.(3)A variable-frequency phononic crystal plate energy harvester that can extract energy from environmental sounds is designed.Put a magnet behind the phononic crystal plate,and change the distance between the magnet and the phononic crystal plate by moving the position of the magnet,causing the force between the magnet and the upper steel column of the composite cylinder to change,thereby changing the acoustic energy harvester frequency to realize the adjustment of acquisition frequency.Based on this,the experiment was designed.By adding a magnet directly behind the point-defect phononic crystal plate and moving the position of the magnet,the relationship of the harvested voltage with the sound wave frequency,load resistance,and sound pressure at the different magnet positions was measured.The experimental results show that: within the experimental frequency range of 1-7000 Hz,there are three peak voltages;there is an optimal resistance value in different frequency bands;at low frequencies,with the distance between the magnet and the phononic crystal plate decreasing,the power increases and the frequency increases slightly;at mid-frequency,when the magnet is add,the power decreases,with the distance between the magnet and the phononic crystal plate decreases,the power increases,and the frequency also increases slightly;at high frequencies,adding a magnet leading to the power is increases,with the distance between the magnet and the phononic crystal plate decreases,the power increases,and the frequency gradually decreases.In different frequency bands,as the sound pressure increases,the voltage increases almost linearly;for different distances between the magnet and the phononic crystal plate,the properties are similar.