The Study About The Design And Application Of Acoustic Metamaterials

Traditional acoustic imaging depends on the collection of sound scatteringacoustical Information to get the geometric morphology or identify internal defects ofobject. However, this method is limited by the sound wave diffraction limit. Thereason is that the evanescent waves which contain the near-field detail of object willbe exponential attenuation with the increase of the propagation distance. In order toovercome the diffraction limit of traditional acoustic imaging, we design and fabricatesuch metamaterial lens based on clamped paper membrane units. The zero-massfrequency is determined by normal incidence acoustic transmission measurement andalso be verified. The theory by using flexural wave to realize the super-resolutionimaging was developed. A invisible acoustical pathway was also designed and tested.The major research works can be summarized as follows:1, Anisotropic zero-mass acoustic metamaterials are able to transmit evanescentwaves without decaying to a far distance, and have been used for near-field acousticsubwavelength imaging. In this work, we design and fabricate such metamaterial lensbased on clamped paper membrane units. The zero-mass frequency is determined bynormal incidence acoustic transmission measurement. We also demonstrate that theimaging frequency is invariant to the change of the lens thickness. For instance thefeasibility of active control about super resolution imaging in the magnetic field orelectric field is proved.2. The given functions of flexural wave in homogeneous and orthotropic plateare devolped. Compared with the acoustic subwavelength imaging, the theory offlexural evanescent wave for subwavelength imaging is proposed. The simulationresult of flexural wave in metamaterial plate indicate that metamaterial can be used innondestructive test by using flexural wave.3. Based on the transformation method, a ways to realize the invisible pathway isproposed. The special negative effective mass density and bulk modulus of acousticmetamaterial is obtained. The real structure of invisible pathway is fabricated by3Dprinter, and also tested in acoustic test system.