Research On The Chiral Acoustic Artificial Materials

Recently, the research on various kinds of artificial structure materials have acquired fruitful achievement. Photonic crystal(PTc)and phononic crystal(POc) can be used to control electromagnetic (EM) wave and sonic wave. In the process, the periodical structure plays a key role. The performance is different for different periodical structure metarials. Particularly, it is show some interesting properties for the chiral structure metarials. For instance, EM wave in the chiral PTc split into two modes and displays the polarization gaps, In this thesis, we are focused on the properties of the chiral acoustic artificial structure materials. The degenerate transverse wave split into two modes like EM wave when bring in chiral structure in solid/solid POc. In addition, chiral structure elastic metamaterials can realize the double negative property, and the effective parameters are controlable through adjusting the structure. The surface wave(SW) of the metamaterials is related to the effective parameters. When the parameters satisfy specific condition, the SW will occur like the EM wave. It is of great significance that in the practical application, which is attributed to the shorter wavelength and strong localization. It can break the diffraction limit and realize the subwavelength imaging.In the first chapter of the thesis, we gave an outline of the development of the POc and acoustic metamaterials(Ac-meta), introducing the SW and the background and significance of the thesis. In the second chapter, we present the common research method of the POc, and describe the theory of elastodynamics briefly. We are focused on the calculation of the band with Multiple scattering theory(MST). Finally, we give an outline of the finite element method.In the third chapter, on the ground of MST, we introduce the Layer Multiple scattering theory(Layer-MST), and then, designing a three-dimension chiral structure with spherical scatters. We use the L-MST calculate the band with different periodic chiral layers structure. According to the band structure we can come to a conclusion that the transverse band split into two polarization band, due to the destruction of the space symmetry in the crystal structure. Locally resonant behavior of the same system can be achieved by introducing a soft coat to the spheres. The first transverse split into two on the resonant band gap. However, it is not occur that the negative group velocity of the split band.We design a two dimension chiral structure elastic metamaterials in fourth chapter. Both the effective parameters of the metamaterials, effective mass density and effective modulus, can change to negative at the same time. Realizing the double negative metamaterials with just one single unit cell. Adjusting the construction will change the effective parameters. It will generate the SW when the parameters satisfy the conditionλ+μ= 0. The SW is called Rayleigh wave. The dispersion curve of the Rayleigh wave is similar to the SPP of EM wave. This analogous acoustical SPP possesses numerous value of application.In the fifth chapter, we design the experimental scheme to demonstration the acoustical SPP and trying the test preliminarily. The sample is a piece of stainless steel plate with the chiral unit structure. Exciting the lower order symmetric Lamb wave(S0) of the sample by the Piezo-electric Transducer (PZT). The vibration displacement of S0 model is in the plane of the sample, which is well approximate the longitudinal model in the two-dimension elastic metamaterials, it can be measured by the 3D-Doppler laser vibrometer.