Session: 17-04-01: Posters Related to Advances in Aerospace Technology

Paper Number: 99540

99540 - Simulation, Fabrication, and Experimentation of Levitating Three-Dimensional Structures 

We report levitating three-dimensional (3D) structures that provide five times the photophoretic lift forces compared to two-dimensional (2D) plates in low Reynolds number environments. We previously used Knudsen-pump-based techniques [1] to levitate 2D nanostructured disks ~1 cm in diameter and 1-2 g/m² areal densities at near-space pressures with no moving parts [2,3]. We fabricate nanostructured films of carbon nanotubes (CNTs), Mylar, and alumina to take advantage of the photophoretic levitation mechanism. The CNTs absorb incident light and create a temperature difference from the surrounding gas molecules. CNTs trap the gas molecules where they increase velocity due to increasing temperature, creating a recoil force as they escape. At certain lower pressures, this creates a force large enough to levitate the structures. These “microflyers” provide critical insights into the mesosphere and Mars, where conditions make traditional flight mechanisms impossible but are optimal for this light-induced levitation. The atmospheric research could include lightweight sensors [4] for things like GPS wind pattern tracking or CO₂ concentration measurements to benefit climate modeling [5].

We plan to expand the original 2D concept to new 3D microflyers featuring porous walls that form a hollow interior cavity with a nozzle for exit flow. The walls act as Knudsen pumps to move gas into the inner cavity and elevate the pressure, forcing gas out through the nozzle, providing greater thrust and lift over the original 2D plates. We designed the micro-architected structures using a custom in-house analytical model to optimize the walls’ porosity parameters, choose ideal geometries, and determine the structures’ payload capabilities. The analytical model builds upon previous theory centered around the nanocardboard levitation theory [1] to provide ideal porosity parameters for the 3D geometries. We are testing the methods for the optimal fabrication of the structures corresponding to the simulations. To simplify the process, we have not yet added porosity, leading to solid-film centimeter-scale conical geometries, since conical geometries are easiest to fabricate and maintain their shape well.

A new levitation mechanism emerged from the solid-film concept, the solar balloon. The incident light from the LEDs heats up the air inside the sealed structure, decreasing the density and allowing it to float at atmospheric pressure. We spin-coat a water-based CNT solution onto the Mylar, then deposit alumina through atomic layer deposition.  A micromachining laser cuts the final samples from the composite film, and we solder the pieces together into the 3D shape. The photophoretic levitation is best for low pressure environments, but the solar balloon functions at much higher pressures. Therefore, we began testing the solar balloons using the LED light chamber at atmospheric pressure. We successfully achieved lift-off for cones several centimeters in height and diameter and are still working on achieving consistent repeatable results for multiple sized cones to better understand the limits. Our next step is to include the porosity and test the structures at lower pressures for their original proposed levitation mechanism. The analytical model provides proof of payload capabilities, which will be integrated after consistent levitation success at the necessary air pressures. Successful levitation of the 3D structures will lead to brand new atmospheric research methods for the mesosphere and Mars.

References:

[1]   Pharas, Kunal et al. (2010) Journal of Microelectrical Mechanical Systems 20.12

[2]   Cortes, John et al. (2020) Advanced Materials 32.16:1906878.

[3]   Azadi, Mohsen et al. (2021) Science Advances 7.7.

[4]   Niccolai, Lorenzo et al. (2019) Progress in Aerospace Sciences 106:1-14

[5]   Goessling, Helge et al. (2016) Earth System Dynamics 7.3:697-715

Presenting Author: Thomas Celenza University of Pennsylvania

Presenting Author Biography: Tom is a third year PhD student working on photophoretic levitation of ultrathin, ultralight structures made of microfabricated composite films with sensor-based payloads for atmospheric research applications on Mars and in Earth’s upper atmosphere. Before coming to Penn, he received his bachelor’s degree in Mechanical Engineering from the University of Delaware.

Authors:

Thomas Celenza University of Pennsylvania
Andy Eskenazi University of Pennsylvania
Zhipeng Lu University of Pennsylvania
Lorenzo Yao-Bate University of Pennsylvania
Matthew Campbell University of Pennsylvania
Igor Bargatin University of Pennsylvania