Resonance-based extremely compact elastic transmissive metasurface and its applications

Abstract

This thesis is dedicated to engineer the extremely compact structure, called elastic metasurface, to ma- nipulate the wave propagating direction and amplitude arbitrarily. In elastics, the tensorial characteristics demands own unique physics, theories, and technologies. Here, elastic metamaterials have been stud- ied, followed by the elastic metasurface which is one of the metamaterial branches with the advantage of extreme compactness. However, in previous elastic transmissive metasurface studies could not suc- ceed in perfectly controlling elastic wave transmission within truly compact structure. i.e., the previous elastic metasurface studies could not achieve the full control on transmission amplitude or needed thick structure due to the periodicity to control elastic wave propagation perfectly. Also, although the unique physics of elastics stem from the co-existence and interactions between multi-modes, only single mode was considered in each metasurface research. Thus, in this thesis, for the truly thin structure, resonance- based single structure which can perfectly tailor multi-mode elastic waves will be suggested. Then using the unit, the various compact metasurface designs will be suggested. First, since the mode coupling be- haves as noises in the practical applications, the mode-selective metasurface which perfectly filters out the unwanted wave mode with perfect tailoring the target mode is proposed. On the other hand, the mode-converting metasurface which exploits the mode-coupling phenomenon to convert the incident longitudinal wave into shear wave entirely was secondly suggested. Also, the limitation of the proposed unit was examined; using the proposed unit structure, simultaneous achieving perfect transmission and wave tailoring was not available at interface between different media. Here, the double unit/layer meta- surface was suggested to realize impedance matched full wave tailoring at the interface. Finally, an active sensor-actuator pair metasurface which generates the desired transmission and reflection by con- structive/destructive interference was suggested as a further work. The mainly suggested single structure design is expected to achieve more efficient elastic applications.