Study Of Phononic Crystal In Two-Channel Filtering

Phononic crystals(PCs)are a kind of synthetic composite materials with spatial periodicity.In the energy band structure of PCs,the phenomenon of band gap can be observed: the acoustic/elastic wave will be restricted from propagating in such frequency range.This feature makes PCs have broad application prospects in shock absorbing,noise reduction and acoustic device design.Therefore,in recent years,the band gap characteristics of PCs attract extensive attention.Among them,the filter characteristics of PCs have always been a hot topic of research.In this article,the commercial finite element(FE)software COMSOL is used to study the effect of geometric parameters and configuration on the band distribution of the PCs.Two kinds of two-channel filtering based on PCs are investigated.The band gap characteristics are analyzed by FE simulation and experimental test.The main research contents and results are as follows:1)The energy band structure and transmission characteristics of single-phase polymethyl methacrylate(PMMA)open-cell materials and two-phase fluid-solid(steel/water)PCs are analyzed by FE method.In addition,the experimental platform of wave propagation for the PCs is built and the method for testing transmission spectra of pure solid open-cell materials is designed.2)Based on the combination of point and line defects,a Y-channel PC filter is designed,and the energy band structure of the unit cell under different impedance ratios is analyzed.The influence of point defects on the band gap structure of PCs is studied by using the supercell model.The narrow pass band constructed by setting periodic holes in solid matrix can be further adjusted by changing the inner hole radius of steel.The application of filtering and separating elastic waves with PCs at specific frequencies is realized.Then the influence of the regular polygon hole structure on the output frequency of Y-channel PCs is studied.It is concluded that when the radius of the circumscribed circle is kept constant,the output frequency will decrease as the number of regular polygon edges increases.3)According to the formation mechanism of the bragg scattering PCs,a twochannel PC plate with periodic cross-elliptical holes is designed and fabricated.The transmission characteristic of the structure along the ΓX direction is analyzed by the FE simulation as well as the experimental test.Based on that,the PCs with two cross-band gaps are obtained through the design of geometric parameters.Thereby the elastic wave can propagate in accordance with the set frequency range and direction.In addition,the effects of different thicknesses and number of periods on the filtering effect of twochannel PCs are also studied.The results show that the thinner the thickness,the better the filtering effect,and less number of periods leads to obvious filtering effect.At the same time,a two-channel PC plate of PMMA is designed and fabricated according to the simulation results,and the wave experiment is carried out.The test data verifies the accuracy of the simulation results to some extent.In summary,the study in this paper provides us a new idea and direction for the structural design and application exploration of PCs,which has certain theoretical and application value.