Understanding the performance of resonators introduced in elastic and/or acoustic circuits is important for conceiving complex and efficient guiding structures. In this work, we reported upon the experimental characterization of hollow pillars in different waveguides with 90° corners by measuring the displacement on top of hollow pillars. The air-coupled method, laser ultrasonic technique and the newly developed method based on polypropylene (PP) piezoelectret film have been adopted during this process. In such way, we experimentally show the quadrupolar resonance of hollow pillars that corresponds well to the whispering-gallery modes in numerical results in several types of waveguides for guiding Lamb wave.
