| Summary: | 碩士 === 國立雲林科技大學 === 機械工程系 === 103 === Surface acoustic wave (SAW) devices have been widely used to develop acoustic filters and delay lines. This study proposes the combination of SAW devices with two-dimensional nickel pillar surface phononic crystals (PnCs) to discuss the filtering effect of PnCs. The physical parameters of PnCs that influence and determine the appearance of band gaps includes the periodic array arrangement, pillar height, and constitutive materials. The three-dimensional finite-element models are established to calculate the band structure of the PnCs with different geometrical parameters and to analyze the transmission spectra. Several designs are fabricated by MEMS process. The PnCs in this study are composed of an array of nickel pillars, deposited on a LiNbO3 substrate (128°Y cut-X propagating) between two SIDTs. The measured signals and results of simulation were compared with each other, and discussions about the theoretical and experimental results were addressed.
According to the simulated results, The position of locally resonant band gap is changed by pillars height. When the height of pillars increase, the position of locally resonant band gap decreased. Correspond with the measured signals, the signal significantly reduced by the impact of PnCs in the locally resonant band gap ranges. On the other hand, the results of transmission spectra show SAW energy loss follow the row of PnCs increase, and the honeycomb lattice symmetries better than square lattice symmetries of PnCs. Although different from the 12 row and 20 row of lattice symmetries of PnCs frequency signal, but still exist the effect of band gap. Observed the part of SAW propagation time it can be found situation of time delay that means PnCs produce the effect of slow down the speed of wave.
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