Tag Archives: thermal insulator

How To Hide Hot Objects From Infrared Detection

Hiding an object from heat-sensing cameras could be useful for military and technology applications as well as for research. Efforts to develop such a method have been underway for decades with varying degrees of success. Now, researchers report in ACS Nano that they have fabricated an inexpensive, easy-to-produce film that makes objects completely invisible to infrared detectors.

Several prior systems have been developed to mask the difference in temperature between an object and its surroundings. But each of these alternatives has weaknesses, such as difficulty in making the devices, the need for a power supply, the use of rigid materials or the addition of thick and heavy thermal blankets that can lead to heat buildup. Xuetong Zhang and colleagues wanted to find a better way.

A new, flexible infrared stealth cloak is made of a porous film of Kevlar nanofibers impregnated with polyethylene glycol.

The researchers fabricated an aerogel film made of DuPont™ Kevlar® fibers. By itself, the aerogel turned out to be a good thermal insulator, but the researchers enhanced its capabilities by coating its fibers with polyethylene glycol (PEG) and a protective waterproof layer. PEG stores heat when it melts and releases heat when it solidifies. In simulated sunlight, the composite film covering an object soaked up heat from the sun while only slowly increasing in temperature, just like the surroundings, making the object invisible to a thermal camera.

When the light was turned off to simulate night, the coating gradually surrendered its stored heat energy to match the surroundings. Without the coating, the object heated up or cooled off much faster than its environment, making it visible. In a second type of application, a combined structure consisting of aerogel films and the PEG composite film could hide hot targets from a thermal camera. The researchers say their film performs comparably to other stealth films but is simpler and cheaper to make.

Source: https://www.eurekalert.org/
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https://cen.acs.org/

Ultrathin, Ultralight NanoCardboard For Aerospace

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure. Now, a team of Penn Engineers has demonstrated a new material they call “nanocardboard,” an ultrathin equivalent of corrugated paper cardboard. A square centimeter of nanocardboard weighs less than a thousandth of a gram and can spring back into shape after being bent in half.

Nanocardboard is made out of an aluminum oxide film with a thickness of tens of nanometers, forming a hollow plate with a height of tens of microns. Its , similar to that of corrugated cardboard, makes it more than ten thousand times as stiff as a solid plate of the same mass.

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Nanocardboard is made out of an aluminum oxide film with a thickness of tens of nanometers, forming a hollow plate with a height of tens of microns. Its sandwich structure, similar to that of corrugated cardboard, makes it more than ten thousand times as stiff as a solid plate of the same mass. A square centimeter of nanocardboard weighs less than a thousandth of a gram and can spring back into shape after being bent in half.

Nanocardboard‘s stiffness-to-weight ratio makes it ideal for aerospace and microrobotic applications, where every gram counts. In addition to unprecedented mechanical properties, nanocardboard is a supreme thermal insulator, as it mostly consists of empty space. Future work will explore an intriguing phenomenon that results from a combination of properties: shining a light on a piece of nanocardboard allows it to levitate. Heat from the light creates a difference in temperatures between the two sides of the plate, which pushes a current of air molecules out through the bottom.

Igor Bargatin, Assistant Professor of Mechanical Engineering, along with lab members Chen Lin and Samuel Nicaise, led the study.

They published their results in the journal Nature Communications.

Source: https://phys.org/