Wind dispersal of battery-free wireless devices

Plants cover a significant fraction of the earth's land mass despite most species having limited to no mobility. To transport their propagules, many plants have evolved mechanisms to disperse their seeds using wind. A dandelion seed, for example, has a bristly filament structure that decreases its terminal velocity and helps orient the seed as it wafts to the ground. Inspired by this, we demonstrate wind dispersal of battery-free wireless sensing devices. Our millimeter-scale devices weigh 30 mg and are designed on a flexible substrate using programmable, off-the-shelf parts to enable scalability and flexibility for a variety of sensing and computing applications. The system is powered using lightweight solar cells and an energy harvesting circuit robust to low and variable light conditions, and has a backscatter communication link enabling data transmission. To achieve wide-area dispersal and upright landing necessary for solar power harvesting, we developed dandelion inspired thin film porous structures that achieve a terminal velocity of 0.87 ± 0.02 m/s and aerodynamic stability with over 95% probability of upright landing. Our results in outdoor environments demonstrate that these devices can travel 50-100 m in gentle to moderate breeze. Finally, in natural systems, variance in individual seed morphology causes some seeds to fall closer and others to travel farther. We adopt a similar approach and show how we can modulate the structures' porosity and diameter to achieve dispersal variation across devices.