A smart granular intruder

Abstract

It has been recently reported that irregular objects sink irregularly when released in a granular medium: a subtle lack of symmetry in the density or shape of a macroscopic object may produce a large tilting and deviation from the vertical path when released from the free surface of a granular bed. This can be inconvenient—even catastrophic—in scenarios ranging from buildings to space rovers. Here, we take advantage of the high sensitivity of granular intruders to shape asymmetry: we introduce a granular intruder equipped with an inflatable bladder that protrudes from the intruder's surface as an autonomous response to an unwanted tilting. So, the intruder's symmetry is only slightly manipulated, resulting in the rectification of the undesired tilting. Our smart intruder is even able to rectify its settling path when perturbed by an external element, like a vertical wall. The general concept introduced here can be potentially expanded to real-life scenarios, such as “smart foundations” to mitigate the inclination of constructions on a partially fluidized soil.