Three-dimensional tracking of sensor capsules mobilised by fluid flow

A new technique for simultaneously measuring particle trajectories and temperature in fluids using specially designed light-emitting sensor capsules/particles is reported. The sensor capsules each contain a microcontroller (with integrated temperature sensor), uniquely coloured light emitting diodes (LEDs), a battery, and other components. When inserted into a fluid, the sensor capsules are mobilised by fluid flow. As they emit light they can be readily tracked and their 3D position over time measured, using an externally positioned camera along with a planar mirror in a calibrated set-up. The capsules can also take intra-fluid temperature measurements and transmit encoded data by modulating their LEDs whilst moving. Controlled experiments with a sensor capsule placed on a rotating turntable and unconstrained fluid-driven motion of multiple sensor capsules placed in a mixing tank are reported. The results demonstrate how the pathlines of capsules (and instantaneous velocities) and temperature can be simultaneously measured. (paper)