| Summary: | 博士 === 國立中央大學 === 光電科學與工程學系 === 103 === In this thesis, we studied the one-dimensional (1D) grating structures of the Helmholtz resonator (HR) array and the Morpho butterfly wing. The HR array can absorb sound waves in specific frequencies by the locally resonant effect. By adjusting the structural parameters of the HR array, we can observe the behavior of the resonant frequency shift. The mapping between the two-spring-mass model and the finite-difference time-domain results can help us to understand the acoustic resonance inside the HR structure. Furthermore, we discover that the Fabry–Pérot-type interference occurs in this structure, and that the resonant frequencies are proportional to the thickness of the substrate. This resonant effect can be obviously observed in the field pattern of the quasi-steady state, and it resonates from the HR and substrate structure. Besides, HR array is rather sensitive to the variation of the liquid parameters. Therefore, this kind of structure is suitable for sensing the liquid concentration.
In the acoustic measurement system, we adopt the ultrasonic immersion transmission technique in our experimental setup. In the two experimental stages of the structural parameters and liquid concentration sensing, we set the two different types of the experimental setups. The measured results show that the extinction ratio is larger than 20dB, and the sensitivity to the variation of the liquid concentration is up to 1757 kHz/Molar ratio unit during the Molar ratio 0-0.035.
We adopt the rigorous coupled-wave analysis algorithm (RCWA) and plane wave expansion (PWE) method to investigate the optical properties of wing structure of the Morpho butterfly. The results show that the displacement between the lamellae is the main condition for reflected the stable wavelength (color) in the oblique incidence. Besides, adjusting the period in the vertical direction can linearly modify the reflection (wavelength) color. The wing structure can be regarded as a two dimensional photonic crystal (2D PC) structure and we analyze the optical behavior by using the plane wave expansion (PWE) method and the photonic density of states (PhDOS). The results show that the partial band gap does not usually exist in the direction of the normal incidence. Furthermore, we improve the calculation of the PhDOS for the condition in the oblique incident light. The property of the reflection light can be observed in the results obtained from the modified PhDOS results which consist with that of the RCWA. The consistency between the two methods also implies that the wing structure can be regarded as a 2D periodic structure.
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