Guided Lamb waves in reconfigurable phononic crystal waveguides

We demonstrate experimentally the manipulation of Lamb waves guided along reconfigurable phononic circuits created by defects composed of threaded rods held with nuts in a perforated solid phononic crystal slab. Adjusting the free length of the rod, the resonant frequency of the defect can be tuned, without any change in the supporting phononic crystal slab. Both straight and bent waveguides are fabricated and measured in an aluminum sample with a lattice constant of 20 mm and a complete bandgap extending from 50 to 70 kHz. Guidance of Lamb waves is clearly observed by a Doppler vibrometer, even after 90° bends. The eigenmodes of guided waves are obtained using finite element analysis to explain the tuning of resonances through a bending cantilever model. Numerical and experimental results are generally found to be in fair agreement. They also suggest that the guiding frequency is rather independent of the details of the waveguides. They are of significance for the design of reconfigurable phononic devices.