| Summary: | 碩士 === 國立成功大學 === 製造資訊與系統研究所 === 102 === The permittivity and permeability are the basic quantity of electromagnetics in physics. Although almost all of natural material properties are positive, however, negative material properties can be realized by using artificial structures. Thus, what so-called “Metamaterial” is that materials have properties don’t exist in nature. Acoustic metamaterials, as a counterpart to electromagnetic metamaterials, can be explored as well. The novel properties of acoustic metamaterial will develop many possibilities in wave propagation design.
Resolution of conventional lens is generally constrained by diffraction limit. Therefore, we study the imaging properties of spiral acoustic hyperlens which can achieve far-field subwavelength imaging with high resolution. Based on effective medium theory, a hyperlens can be realized by an alternating layered structure of water and negative mass density that has nearly flat eguifrequency contours. To accomplish such an anisotropic medium, we had derived the relation between density and wave vector in a homogeneous material and calculated the effective dynamic mass density in acoustic metamaterial by multiple scattering theory. Simulation results have showed the spiral acoustic hyperlens has better amplification of image which can be used to propagate delicate details of a source for deep-subwavelength imaging. Furthermore, it can be applied to sonar, nondestructive testing, medical and biological examinations through a proper design.
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