  Elastic waves propagating in piezoelectric materials are accompanied by a
time-varying electric potential, which is of critical importance for
acousto-electronic applications. The spatial mapping of such a potential at
microwave frequencies is challenging since the characteristic length scale is
determined by the acoustic wavelength of several micrometers. In this work, we
report the visualization of surface acoustic waves (SAWs) on ferroelectric
samples by transmission-mode microwave impedance microscopy (T-MIM). The SAW
potential launched by the interdigital transducer is detected by the tip and
demodulated by the microwave electronics as time-independent spatial patterns.
Wave phenomena such as interference and diffraction are imaged and the results
are in excellent agreement with the theoretical analysis. Our work opens up a
new avenue to study various electromechanical systems in a spatially resolved
manner.
