Polyethylene-based Microfluidic System Approaches to Achieve Adaptive Visible and Thermal Camouflage Applications
Creators: Sun, Xiaoruo
Publisher: name: University of Alberta Library
Year: 2024

<p>Camouflage represents a critical skill in both nature and combat zones, as it enables concealment from potential threats. With the advancement of visual and infrared-sensitive surveillance equipment, adaptive camouflage across the visible and infrared (IR) spectrums has become increasingly important due to the advantage of blend in the background. Therefore, the low-cost, high-speed fabrication of adaptive visible and infrared camouflage control system has gained significant attention. Microfluidic devices have a high potential for achieving adaptive multiband camouflage including both visible and infrared (IR) spectrums because they can manipulate fluids that may be dyed, transparent, or opaque to different parts of the electromagnetic spectrum. In the initial phase of this thesis work,  we developed a high-speed, low-cost robust process to fabricate microfluidic devices entirely made from polyethylene using xurography and thermocompression molding techniques. Moreover, a novel method that thermally bond macro-scale polyethylene tubing to micro-scale channels is developed. The simplicity and flexibility of the method allow the fabrication of devices with different channel heights, widths, and patterns. Upon filling the microfluidic devices with dyed liquids and testing them with different backgrounds, the devices showed fast and high adaptive visible camouflage capabilities. Moreover, the thermal IR appearance of microfluidic systems can be altered without changing temperature by incorporating a metalized surface which can be covered by an IR opaque liquid to alter the apparent temperature when reflecting IR sources. However, the long actuation times and unfavorable scaling laws for pressure-driven flows in smaller channels posed challenges for rapid fluid actuation. To address this, the second phase of this work focused on replacing the pressure-driven flow with an electrowetting system, capable of fast-actuating droplets using low voltage while preserve the capabilities to achieve adaptive infrared camouflage. We developed and conducted an initial feasibility test for an electrowetting on dielectric (EWOD) system based on simple fabrication techniques without atomic deposition for adaptive infrared camouflage. The electrowetting of a drop of water within an IR transparent oil (dodecane) can occur between an aluminum electrode surface with a self-assembled lipid bilayer as the dielectric. This lipid dielectric bilayer both reduces required electrowetting voltage to below 5V and is spontaneously formed in the system. More importantly, the thermal appearance of the electrodes can be altered upon wetting the droplet when reflecting IR sources with a fast actuation time (about one second). The thickness of the dodecane must be less than 1 mm before it is sufficiently transparent for thermal IR to function effectively as an IR variable pixel, but this technique may hold promise to produce faster switching and more effective microfluidic-based thermal camouflage in the future. </p>