Tunability of a One-Dimensional Elastic/Piezoelectric Phononic Crystal Using External Capacitances

A superlattice made of alternate rods constituted of piezoelectric ceramic and elastic material is shown, theoretically and experimentally, to exhibit wide Bragg band gaps. The width of these stop bands is affected not only by the elastic impedance ratio between the constituent materials but also by the electrical boundary condition imposed on both ends of the piezoelectric rods. With an adequate choice of this electrical boundary condition (open circuit, short circuit, piezoelectric rods connected to an external capacitance), full tunability of the stop bands can be achieved.