| Phononic crystals,as typical representatives of acoustical metamaterials,are artificially composed of different materials according to different structures.The periodic structure's Bragg scattering and local resonance characteristics make it produce a bandgap,which is also the biggest difference from traditional materials.In order to bring new ideas to the military industry,the application of this feature in vibration reduction and noise reduction has also become a hot topic.The passband portion outside the band gap has an extraordinary dispersion characteristic and is These frequency bands have negative effective elastic parameters,which make it have negative refraction characteristics,and the acoustic focusing phenomenon based on this,which brings many new acoustic propagation effects for the future scientific development.The applications are very extensive,such as modern In the study of marine military industrial devices,acoustic focusing can be used to achieve high-resolution imaging sonars,which can be better detected and checked in marine military;or in modern medical sensors,the acoustic focusing characteristics provide a treatment for humans that are afraid of tumors.A safer and more effective way,but there is still too little research and application in this area.Therefore,the application of acoustic focusing technology has great technical advantages and practical value.The use of acoustic metamaterials to realize the focusing of sound waves is a trend trend of scientific and technological progress.It has great application prospects in the research and development of scientific devices,and it explores its theoretical principles and designs.It is very necessary to have a device with higher application value.Based on the theory of elastic wave dynamics and multiple scattering theory of phononic crystals,this paper deduces the transmission coefficient and pressure field theory of acoustic waves propagating in phononic crystals,and sets up a two-dimensional local resonance phononic crystal plate as a model.The negative refraction feature changes some of the physical quantities that enter the phononic crystal to study the negative refraction imaging influencing factors in the phononic crystal,as well as the imaging law and characteristics,and further explores how to obtain a “perfect image” with no loss of energy.Secondly,a specific model of phononic crystal is designed and the converging characteristics of scattered waves in flat panel imaging are analyzed.It has been found that negative refracting imaging in phononic crystals can only form sound waves at certain frequencies or frequency bands in certain flat plate structures,material combinations,filling rates,specific sound source locations,and incident angle sizes.Negative refractive imaging features.Finally,using COMSOL Multiphysics software,the finite element method was used for simulation analysis,and the three-dimensional effect of the sound field after the transmission of the photoacoustic signal through the lens and the two-dimensional transmission characteristic curve were obtained.In the simulation results,it was observed that the waveforms of the incident wave and the outgoing wave are basically close to each other without loss of the sound source information,and all the energy is completely transmitted to the image point.The simulation results are in good agreement with the theory.This is what is being explored.To achieve "perfect imaging". |
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