  Surface acoustic wave devices are key components for processing radio
frequency signals in wireless communication because these devices offer
simultaneously high performance, compact size and low cost. The optimization of
the device structure requires a quantitative understanding of energy conversion
and loss mechanisms. Stroboscopic full-field diffraction x-ray microscopy
studies of a prototypical one-port resonator device revealed the existence of
unanticipated acoustic loss. A non-uniform acoustic excitation in the active
area was responsible for the substantial end and side leakages observed at the
design frequency. Quantitative analysis of the strain amplitude using a wave
decomposition method allowed the determination of several key device
parameters. This high-resolution spatiotemporal strain imaging technique is,
more generally, suited for studying nanophononics, specifically when the
feature size is smaller than optical wavelengths. The strain sensitivity allows
precise measurement of acoustic waves with picometer-scale amplitude.
