Development of L-Shaped Ultrasonic Waveguide Using Elastic Metamaterial

In this study, we developed a new ultrasonic L-shaped waveguide that can be installed on a specimen with insufficient room to install a long-straight beam-type waveguide. The proposed L-shaped waveguide was designed using elastic metamaterial technology and can control the wave propagation direction to 90 degrees without mode conversion. To design the waveguide, we firstly investigated the L-shaped ultrasonic waveguide without metamaterial. Motivated by acoustic waves in fluids, which can easily convert horizontal wave motion into vertical motion even if the fluid in the duct is bent to 90 degrees, we designed an elastic metamaterial whose unit cells represent horizontal and vertical wave motions simultaneously. Next, we derived the frequency at which the elastic metamaterial exhibits the desired motion and verified the performance of the designed metamaterial. Subsequently, using numerical simulations, we successfully tested wave-direction conversion to 90 degrees without mode conversion for the various elastic metamaterial-based L-shaped ultrasonic waveguides. In the future, we will perform experimental studies on fabricated waveguide to determine the possibility for field tests.