Oscillating gradient measurements of fast oscillatory and rotational motion in the fluids.

We demonstrate the combination of oscillating gradient waveforms with single-point imaging techniques to perform measurements of rapidly oscillating and/or rotating fluid motion. Measurements of Fourier components of motion can be performed over a wide range of frequencies, while the immunity of single-point imaging to time-evolution artefacts allows applications to systems with great susceptibility variations. The processing approaches, displacement resolution, and the diffusive attenuation are analyzed. Measurements of high-speed flow rotation in a spiral phantom, periodic displacements of oscillating gas in a thermoacoustic device and of cavitating liquid reveal a variety of motion spectra. The potential systems for study with the technique include turbulent motion, cavitation, and multiphase flows in general.