Research has been conducted on acoustic metamaterials that control the transmission characteristics of reflected and refracted waves using phase delay by resonators. Using one-dimensional theory, the phase delay equations for the 1/4 wavelength and Helmholtz resonator are presented. These one-dimensional analysis results are compared with the results predicted by three-dimensional FEM. The advantages and disadvantages of 1/4 wavelength and Helmholtz resonator were confirmed in implementing phase delay. An acoustic metamaterial with a refraction angle of 30° was manufactured using multiple tubes and then the sound pressure distribution was measured. A relatively large sound pressure was measured at the target position of 30°, which was compared with the 3D FEM analysis results. Simulations confirmed that a phase delay range closer to 2π was more effective in refraction, but varying the number of resonators was found to have minimal impact on which additional research is needed for generalization.

The purpose of this study is to investigate basic parameters which are essential for tidal correction of gravity data. This study involves computation of the theoretical values and laboratory measurements of tidal force of gravity. The theoretical variation of tidal force was computed according to the relative position of moon and sun on the celestial sphere by using a computer program Gravity measurements were carried out in Seoul University for 120 operation-hours, and also in coastal area in Incheon for 48 operation-hours. The gravimetric factor (δ) and phase delay were determined by comparing theoretical values with measured gravity data. Summarized results of this study are as follows ; (1) The gravimetric factor in Seoul is in the range of 1.22∼1.36(avg.=1.28) and the phase delay is in the range of 0.1∼0.3 hours (avg.=0.16 hours). (2) The mean garvimetric factor in Incheon is 1.31 and mean phase delay is 0.025 hours (3) The difference of mean gravimetric factor between in Seoul and in Incheon is 0.03 and that of phase delay is 8 minutes.