누설표면파의 전파특성과 박막 두께 측정에의 응용

Abstract

In the layered structure of fluid/solid, several kinds of leaky surface waves are able to propagate on the surface of the solid substrate radiating a part of energy into the fluid. The LSAW(Leaky Surface Acoustic Wave), as one of such waves in the field of ultrasonics, has longitudinal and horizontal displacements simultaneously. On the other hand, the lateral wave in the field of underwater acoustics has a longitudinal displacement only. However, those two waves propagate with similar aspects having linear wave fronts in the fluid although their velocities are different. In this study, we simulated the propagation phenomena of the two waves, which can be confused in measurement, using commercial simulation software Wave2000Pro so as to distinguish them clearly. By the simulation, the wave velocities of the LSAWs and lateral waves were obtained for several isotropy solids, and those velocities were compared with theoretical results and measurement results which were obtained by a PVDF line-focus-beam transducer. It was confirmed that the simulation results are very accurate within 1% error, approximately. On the basis of the accuracy, the velocities of LSAWs for the structure of water/copper thin films/isotropic solids were simulated. The large velocity variation about 792 m/s was shown in the film thickness of 0.1 wavelength. Consequently, it is known that the film thickness can be evaluated by the LSAW velocity measurement.