Piezoelectric Transduction of a Wavelength-Scale Mechanical Waveguide

We present a piezoelectric transducer in thin-film lithium niobate that converts a 1.7-GHz microwave signal to a mechanical wave in a single mode of a 1-$\ensuremath{\mu}\mathrm{m}$-wide waveguide. We measure a $\ensuremath{-}12$-dB conversion efficiency that is limited by material loss. The design method we employ is widely applicable to transduction in wavelength-scale structures in emerging phononic circuits such as those needed for efficient piezo-optomechanical converters and spin-phonon transducers.