Electrical capacitance sensor array to measure density profiles of a vibrated granular bed

Monitoring the dynamical evolution of the solids distribution within vibrating granular beds is of key importance to control a variety of industrial processes and to assist basic studies on phenomena like segregation and convection. One of the most used techniques is video analysis, however it is restricted to quasi-two dimensional beds and may need considerable postprocessing time. Here we explore an alternative technique based on a simple linear capacitor array that is able to resolve variations of the solid fraction along a single direction. This method has potential to be used in real-time control applications due to the simple signal processing needed and it's suited to probe three dimensional beds. We show a comparison between spatiotemporal density profiles of a quasi two dimensional vertically vibrated bed obtained with video and capacitive methods, and discuss on the advantages and downsides of each one. We also present spatiotemporal density profiles of a three dimensional vertically vibrated bed using the capacitive technique, illustrating the distribution of material along the direction of vibration when the bed performs bouncing motion and when the forcing is enough to obtain a granular Leidenfrost effect.