In this thesis, I present the fabrication process of three-dimensional (3D) solid-in-solid phononic crystals (PCs) and experimentally studied their ultrasonic properties by measuring their underwater transmissions. Most of the PCs are in body-centered-tetragonal (BCT) structure with spherical scatters. They can be cataloged into three general types by the matrix material: paraffin-matrix, polystyrene-matrix and Aluminum-matrix. In all three types, full band gaps were observed in the transmission coefficient curves, at least for the longitudinal modes. The 1^st type of PCs exhibit the widest gap while the 3^rd type exhibit the narrowest gap. Different sizes of scatters were used for verification of the gap location and width using the scalability principle in the 1^st and 2^nd types of PCs....[ Read more ]

In this thesis, I present the fabrication process of three-dimensional (3D) solid-in-solid phononic crystals (PCs) and experimentally studied their ultrasonic properties by measuring their underwater transmissions. Most of the PCs are in body-centered-tetragonal (BCT) structure with spherical scatters. They can be cataloged into three general types by the matrix material: paraffin-matrix, polystyrene-matrix and Aluminum-matrix. In all three types, full band gaps were observed in the transmission coefficient curves, at least for the longitudinal modes. The 1^st type of PCs exhibit the widest gap while the 3^rd type exhibit the narrowest gap. Different sizes of scatters were used for verification of the gap location and width using the scalability principle in the 1^st and 2^nd types of PCs. And phase curves provide additional information in confirming the gap existence in the 3^rd type of PCs, most of which are composed of 1mm-diameter tungsten carbide (WC) beads embedded in Aluminum (Al). Both defect states and collimation were experimentally demonstrated for the first time in the 3D solid-in-solid type of PCs. In the WC/Al PCs, defect states were experimentally demonstrated in the gap regime, by introducing a cluster defects of Si₃N₄ beads of the same size. It was confirmed by both the spectral curve and the transmitted pressure field patterns. Collimation occurring in the 2^nd pass band was also recognized in mapping the transmitted pressure field patterns through a WC/Al PC doped with 3D cluster defects of Si₃N₄ beads of the same size. Multiple Scattering Technique (MST) was used to calculate the band structures of the undoped PCs in BCT. Some discrepancies are explained by two-dimensional PCs simulations using Comsol.