Challenges of 'imaging' particulate materials in three dimensions

In this perspective article, we discuss the challenges of imaging assemblies of particles in three dimensions. Starting from a brief motivation for the investigation of particulate materials, we provide an overview of experimental approaches developed for imaging particles. We list the challenges and existing solutions associated with X-ray tomography, one of the standard methods to study statics. Subsequently, we discuss challenges and opportunities arising from emerging new techniques such as radar tracking and ‘smart’ tracers for exploring granular dynamics. We close with a tentative view on the outstanding problems and potential solutions in the future.