Rainbow guiding of the lowest-order antisymmetric Lamb mode in phononic crystal plate

The modern acoustic circuits have experienced significant progress with the development of artificial structures, including phononic crystals, metamaterials or metasurfaces. Among the most intensive topics, the reconfigurable acoustic guides are achieved through several mechanisms. In this work, we report on the rainbow guiding for the lowest-order antisymmetric Lamb (A(0)) mode in a phononic crystal plate, where the linear waveguides are constituted by erecting aligned pillars either solid or hollow. We show both numerically and experimentally that the whispering gallery modes (WGMs) in the hollow pillars can be generated by the defect mode that propagates in the waveguide. Then, the reemission of A(0) mode by the WGMs to the outer lateral areas can lead to spatial control of frequency selective wave guidance called rainbow guiding. Our approach allows for an accurate control of the wave guiding and facilitates the integration of waveguides within other devices in the acoustic circuits.