Study On Acoustic Devices Based On Acoustic Artificial Materials

In recent decades, the realization and application of acoustic artificial materials have attracted wide attention. Acoustic artificial materials generally exhibit unusual acoustic properties which are not found in nature materials. These special acoustic properties are not only affected by the component materials, but depend on the their specially designed structure more. Due to the modulation of the periodic of special microstructures of the acoustic artificial materials, a series of physical phenomenon such as negative refraction, self-collimating, perfect transmission and so on have been observed. Therefore, we can freely manipulate the propagation of the acoustic waves and design novel acoustic functional devices with the assistant of the rebolutionary design concepts, such as acoustic cloaking, acoustic superlens, integrated acoustic devices, etc. In this dissertation, some novel acoustic devices are proposed based on acoustic artificial materials and the acoustic transmission properties of these devices are theoretically and experimentally studied. The novel acoustic devices include phase controlled acoustic switch and logic gates, Fano resonant acoustic senser and the unidirectional transmission of self-collimatted sound beam in 2D sonic crystals (SCs).In the first chapter, the study background and related progress on the acoustic artificial materials are reviewed briefly and then, a brief outline of this dissertation is presented.In the second chapter, we have proposed acoustic logic gates based on the linear interference of self-collimated beams in 2D sonic crystals (SCs) with line-defects. The line defects on the diagonal of the 2D square SCs are actually functioning as a 3 dB splitter. By adjusting the phase difference between two input signals, the basic Boolean logic functions such as XOR, OR, AND, and NOT are achieved both theoretically and experimentally. Due to the non- diffracting property of self-collimation beams, more complex Boolean logic and algorithms such as NAND, NOR and XNOR can be realized by cascading the basic logic gates.In the third chapter, we report compact transformable acoustic logic gates with a subwavelength size as small as 0.82?. based on Density-near-zero (DNZ) acoustic metamaterials (AMs). The basic acoustic logic gates, composed of a tri-port structure filled with space-coiling DNZ AMs, enable precise direct linear interference of input signals with considerably small phase lag and wavefront distortion. We demonstrate both theoretically and experimentally the basic Boolean logic operations such as OR, AND, XOR and NOT with wide operational frequency ranges and controllability, by adjusting the phase difference between two input signals. More complex logic calculus, such as "I1+I2×I3", are also realized by cascading of the basic logic gates.In the fourth chapter, we demonstrate tunable Fano resonances of self-collimated sound beams in two-dimensional sonic crystals (SCs). The Fano resonator is composed of a single-or multi-layer zigzag line defects (ZLDs) sandwiched by two columns of zigzag steel rods. It is shown that the discrete mode and the continuum mode of the Fano resonance can be tuned independently or simultaneously by adjusting the structure parameter of the SC-based resonator, which allows for a free and continuous way to control the resonance position and the asymmetric line shape of Fano resonance. The Fano resonance position varies with the physical properties, such as density and sound speed of the host fluid of the SCs. We finally use these features for sensitive sensing to different ethanol weight fractions.In the fifth chapter, we theoretically realized the one-way self-collimation effect of acoustic beam in two dimensional sonic crystals composed of irregular rigid rods surrounded by circulating fluids. The space and time-reversal symmetries of the circulating fluids sonic crystals (CFSCs) are broken by asymmetric crystal lattice and the circulating fluids. The sound intensity levels difference between the two output acoustic beams launched at opposite direction is around 30 dB in a relative broad frequency band. By applying gradient angular velocities of the circulating fluids, the propagation direction of the one-way self-collimated acoustic beam can be tuned gradually and bent in the CFSCs. The designable one-way self-collimation in CFSCs provides an avenue for manipulating the acoustic beams.In the sixth chapter, we present the summary of this dissertation and some prospects for the future study.