  We extend a previously developed ultrafast ultrasonic technique [Gallot et
al., Rev. Sci. Instrum. 84, 045107 (2013)] to concentration field measurements
in non-Brownian particle suspensions under shear. The technique provides access
to time-resolved concentration maps within the gap of a Taylor-Couette cell
simultaneously to local velocity measurements and standard rheological
characterization. Benchmark experiments in homogeneous particle suspensions are
used to calibrate the system. We then image heterogeneous concentration fields
that result from centrifugation effects, from the classical Taylor-Couette
instability and from sedimentation or shear-induced resuspension.
