Design And Experimental Study Of Single-phased Solid Double Negative Elastic Wave Metamaterial

In the past ten years,people have designed many different types of acoustic and elastic-wave metamaterials through analogy of electromagnetic metamaterials.In particular,the study of negative equivalent parameters including negative equivalent mass density,negative equivalent bulk modulus,negative equivalent shear modulus,and negative equivalent refractive index has attracted attention of a large number of scholars.Thanks to these negative equivalent parameters,acoustic and elastic-wave metamaterials have been proven to exhibit anomalous physical phenomena,and therefore have many potential applications that break through the performance of natural materials,such as negative refraction and subwavelength imaging,etc.However,compared with acoustic metamaterials,the elastic-wave metamaterials have more intrinsic parameters,which provides more possibilities for implementing a richer equivalent parameter combination.Therefore,this rich possibility combined with topology optimization may create a new metamaterial,breaking the limitations of artificial and empirical designs.In this thesis,based on the results of topological optimization of double-negative elastic wave metamaterials,the simplest unit geometry configuration is proposed to make it easy for fabrication and experimental processing under the premise of retaining negative refraction characteristics.The parametric analysis is then performed to give an optimized structure;and the negative refraction and subwavelength imaging of the metamaterial are verified numerically.Finally,the negative refraction characteristics are verified by experiments.The main contents and results include:1.Based on the results of topology optimization calculations,a preliminary simplified structure is proposed.The energy band structures,equal-frequency curves,transmission spectra and equivalent parameters of the model were calculated by using the finite element COMSOL software;and based on the results,the unit cell model was optimized.The influences of the geometric parameters of the model on the fourth band(the negative band),equal-frequency curves and equivalent parameters were analyzed.A double-negative elastic-wave metamaterial with an ultra-wide frequency domain,which is easily processed and manufactured in a given frequency range,is designed.The imaging and image point resolution of the elastic-wave metamaterial plate was analyzed.The variations of the resolutions with different frequencies,different point source locations and different panel widths were discussed.It was found that the pixel resolution is non-monotonic.Finally,the geometrical parameters corresponding to the highest resolution at 20KHz were given.2.The negative refraction characteristics of the single-phased solid double-negative elastic-wave metamaterial was studied and the negative refraction phenomenon was confirmed in the experiment.First,the negative refraction characteristics in the two-dimensional finite system and the three-dimensional metamaterial plate were simulated and compared;and the negative refraction of an incident wave with different positions and different frequencies was discussed.The amplitudes of the signals in the ceramic piezoelectric strips at the positive and negative refraction areas in the sample were compared statistically to illustrate the phenomenon of the negative refraction.Through the analysis of the experimental data,in a statistical sense we can see that the amplitudes of the signals in the negative refraction region are significantly higher than those in the positive refraction region.It can be shown that the emergent wave mainly propagates in the negative refraction region,which proves that the designed double negative elastic-wave metamaterial can indeed exhibit negative refraction.