In the last years, there has been an outstanding growing interest in active matter. In these complex systems, a number of interacting
agents consume and convert energy into mechanical motion, representing nice examples of out-of-equilibrium behavior. Such
systems are important because they can be found in nature ranging from the microscopic to the macroscopic scale, e.g. molecular
motors, cells, bird flocks, or human crowds. Interestingly, and despite the obvious differences among the agents that compose these
systems, common behavioral patterns have been identified such as collective motion, anomalous diffusion, segregation, or clogging
in the flow through constrictions. Aiming for a better understanding of these complex active systems a reductionist strategy is
necessary, and this is why the study of active granular matter (very simple self-propelled agents that interact uniquely by contacts) is
widely acknowledged.
Within active grains, we can distinguish between internally excited ones (such as Hexbugs) or externally forced ones. Certainly, the
former have the advantage to closely resemble real active matter but, to date, also have the drawback of not allowing testing their
response to external stimulus. My proposal, PhotoActive, aims to fill this gap by designing novel macroscopic self-propelled agents
that are internally excited but can be driven by an external stimulus as it occurs with all natural systems. The idea is to develop and
implement Hexbug-like particles whose source of energy comes from a photovoltaic cell. The great advantage of these novel agents
concerns the versatility that provides using a fully controllable illumination panel with which we can impose spatial intensity
gradients or temporally evolving patterns. In this way, and applying an interdisciplinary approach involving experiments, numerical
modeling, and simulations, we ambition boosting the existing understanding of active matter systems.
