  Nanoelectromechanical systems (NEMS), utilising localised mechanical
vibrations, were pioneered for sensors, signal processors and to study
macroscopic quantum mechanics. Increasingly the concept of integrating multiple
mechanical elements via electrical/optical means has emerged as a challenge
towards NEMS circuits. Here we develop phononic crystal waveguides (PnC WGs),
using a 1-dimensional array of suspended membranes, that offer purely
mechanical means to integrate isolated NEMS resonators. In the first steps to
this objective, we demonstrate the PnC WG can support and guide mechanical
vibrations where the periodic membrane arrangement also creates a phonon
bandgap that enables the phonon propagation velocity to be controlled.
Additionally embedding a phonon-cavity into the PnC allows mechanical
vibrations in the WG to be dynamically switched or transferred to the cavity,
illustrating the availability of WG-resonator coupling. These highly functional
traits of the PnC WG architecture exhibit all the ingredients necessary to
permit the realisation of all-phononic NEMS circuits.
