This EArly-concept Grant for Exploratory Research (EAGER) project builds upon preliminary demonstrations of untethered microfliers, that is, free-flying microscale structures. A temperature gradient across the microflier chassis drives a net flow of air from hot to cold side, and lift is generated by momentum transfer from this flow to the microflier body. Known as "radiometric force," this effect has been an object of study by physicists and fluid dynamicists for over a century, but only recently has a comprehensive understanding begun to emerge. Though too weak to affect larger objects at atmospheric pressures, radiometric forces scale advantageously for characteristic lengths less than a millimeter. Together with advances in fabrication of micro electro mechanical systems (MEMS), laser-driven opto-radiometric microfliers have the potential to push the envelope of human controlled flight to unprecedented levels of miniaturization. This project will advance towards that goal, with complementary theoretical and experimental components. The results will pave the way for a new class of aerial microrobots with applications such as surveillance, microassembly, airborne pollution monitoring and airborne threat detection.
Despite the existence of microscale flying insects, aerial microrobots have not been previously investigated. Thermal (radiometric) forces have been shown to move micron-sized particles in air, and radiometric forces caused by optical heating of light-absorbing structures have been studied since the invention of the Crookes Radiometer in 1873. This project will validate the feasibility of achieving untethered, controlled opto-radiometric microscale flight, i.e. flight propelled by forces generated via a thermal gradient from a focused optical beam illuminating untethered microfabricated structures. The research team will develop new theory of opto-radiometric microscale flight at atmospheric pressures, investigate novel materials and microfabrication processes that increase the opto-radiometric power transfer without increasing the microflier mass, fabricate and test prototypes of untethered microscale flying robots using a combination of microfabrication technologies and 2-photon stereolithography, and investigate biologically-inspired mechanism for attaining in-flight stability and control.
