THESIS
2002
xiv, 93 leaves : ill. (some col.) ; 30 cm
Abstract
Two impedance tubes method was employed for measuring the Resonance Sonic crystals with high impedance, in the wavelength regime that is several times the physical size of the sample. By varying the length of the back impedance tube, the shifted resonant peak of the transmission amplitude shows the presence of multiple-reflection of the plane sound waves in the tube system. The method provides a reliable means to measure the complex transmittance even at resonant frequency of the tube. Low transmission amplitude including the important phase information can be measured by using high gain transmission sensor mounted in the back impedance tube....[
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Two impedance tubes method was employed for measuring the Resonance Sonic crystals with high impedance, in the wavelength regime that is several times the physical size of the sample. By varying the length of the back impedance tube, the shifted resonant peak of the transmission amplitude shows the presence of multiple-reflection of the plane sound waves in the tube system. The method provides a reliable means to measure the complex transmittance even at resonant frequency of the tube. Low transmission amplitude including the important phase information can be measured by using high gain transmission sensor mounted in the back impedance tube.
Due to cracking of the gypsum medium, a mixed medium of epoxy and gypsum powder was developed to hold the position of the coated spheres in the different orientations. Several sonic crystals embedded in either gypsum or in epoxy/gypsum mixture were fabricated in the geometries of [100], [110] or [111] directions. All the samples are measured from 100Hz to 1200Hz. Experimental data reveal transmission dips at low frequency region, showing acoustic insulation for low frequency. The experimental data are compared with theoretical predictions, and the results, including the discrepancies, are discussed.
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