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.

동해 남서해역 퇴적물의 현장 음파전달속도를 파악하기 위하여 신호투과법을 이용하여 퇴적물의 실험실 음파전 달속도를 측정하였다. 측정된 실험실 음파전달속도는 해저면 온도, 해수 음파전달속도, Kim et al. (2004)과 Hamilton (1980) 모델을 적용하여 현장 음파전달속도로 보정하였다. Kim et al. (2004)과 Hamilton (1980)의 현장 음파전달속도는 연구지역 퇴적물 특성을 반영하며, 유사한 분포를 보인다. 현장 음파전달속도 보정에는 해저면 온도의 영향을 크게 받 는 것을 확인할 수 있다. 따라서 퇴적물의 실험실 음파전달속도를 통해 현장 음파전달속도를 파악하기 위해서는 해저 표층 온도 자료를 통한 온도 보정이 반드시 수행되어야 한다.

In this paper, the propagation characteristics due to the horizontal water temperature variations in the sea such as thermal fronts is analyzed by the ray theory. Two models for the temperature anomaly layer are chosen. One is a plane type and the other is a cylindrical type. In the plane type, the temperature increases linearly from a isothermal region to 5km with the gradient of about 2℃./km, and decreases with the same gradient in next 5km. In the cylindrical type, water temperature increases only with the same gradient from a half cylindrical thermal boundary surface. The result showed that the gradient of acoustic rays decreases in the temperature increasing region and vice versa in temperature decreasing region. And, the transmission loss due to the temperature variation was less than O.2dB in the plane type model as well as in the cylindrical one.

In patients with acute cerebral infarction, taranscranial ultrasonography is helpful in assessing blood flow, but in some patients, failure to detect cerebral blood flow through the temporal window is an important problem in expansion of clinical indications for transcranial ultrasonography. This study was performed between May 2016 and September 2016 in patients admitted to the neurology department of Chosun University Hospital with cerebral infarction and underwent transcranial ultrasonography and brain magnetic resonance image. Of the 129 patients, 47 were female (36.4%). The mean age of the patients was 80.7±8.0 years. Fifty patients (38.8%) did not showed any blood flow signal due to poor temporal window. The mean age of patients with temporal window failure (83.8±6.0 years) was significantly higher than without temporal window failure (78.7±8.5), and the temporal window failure was significantly higher in women. In conclusion, temporal window failure was more common in elderly and women in this study. In addition to temporal bone thickness and heterogeneity of temporal bone due to osteoporosis, hyperlipidemia may also be associated with temporal window failure and future prospective studies will be needed.