Air-coupled method to investigate the lowest-order antisymmetric Lamb mode in stubbed and air-drilled phononic plates

In this work, we applied a robust and fully air-coupled method to investigate the propagation of the lowest-order antisymmetric Lamb (A0) mode in both a stubbed and an air-drilled phononic-crystal (PC) plate. By measuring simply the radiative acoustic waves of A0 mode close to the plate surface, we observed the band gaps for the stubbed PC plate caused by either the local resonance or the Bragg scattering, in frequency ranges in good agreement with theoretical predictions. We measured then the complete band gap of A0 mode for the air-drilled PC plate, in good agreement with the band structures. Finally, we compared the measurements made using the air-coupled method with those obtained by the laser ultrasonic technique.