Low‐Cost and High‐Speed Fabrication of Camouflage‐Enabling Microfluidic Devices using Ultrahigh Molecular Weight Polyethylene

Abstract

This study presents in this work a demonstration of multi‐spectrum camouflage control via microfluidic methods within a thermally and visibly semi‐transparent polymer (polyethylene). Microfluidic devices have a high potential for achieving 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. However, most traditional polymers used for microfluidics are not very transparent in the thermal IR region (≈8–14 um wavelengths), which limits their effectiveness in this spectrum. It develops 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 show fast and high 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.

The thermal ‘Buddha Board’—application of microstructured polyolefin films for variable thermal infrared transparency materials

“… (a ) Thermal scattering and low attenuation effect of cylindrical lens structures with 40 µm pitch manufactured from PE. ( b ) shows an edge detection algorithm applied to the thermal images [ 13 ]. As different distances from the hot source are tested, larger features lose their ability to be resolved by the thermal camera.…”

“…While occasionally this is done directly by switching surfaces entirely [ 8 ], other solutions have drawn inspiration from mechanisms akin to those observed in a Buddha Board, where water-induced changes lead to temporary changes in surface transparency [ 7 , 9 – 12 ]. Virtually all these solutions, however, are focused on transparency in the visible and near IR range to change the amount of solar energy heating up the solution, but future work could alter the transparency of surfaces so that thermal emission can be high or low [ 13 ] in addition to absorbing or reflecting incoming solar energy. It is the extension of switchable materials to the thermal IR spectrum (~8–14 µm) that corresponds to the atmospheric window that our work focuses on.…”