In the classic sci-fi film, “Predator,” starring Arnold Schwarzenegger, a brutal alien hunts down a team of hired soldiers. Using advanced wearable technology, the creature can make himself invisible and also view the world in infrared. One-by-one, the alien kills the soldiers. But when Schwarzenegger’s character, Dutch, discovers that by smearing himself in cool mud, he can squelch his body heat signature and become invisible to the creature, victory is his.
Now, a more practical, 21st-century solution could render a solider just as invisible to alien predators and nighttime nemeses. Researchers from the University of California, San Diego and the National University of Singapore have, for the first time, created wearable technology that blends a person’s own body heat signature into the surrounding environment’s temperature, adapting to temperature changes and effectively hiding the person from thermal cameras and night vision goggles. The idea is to scale the device so that it can be worn like a jacket or full-body armor.
In a research paper published in Advanced Functional Materials, the team writes that the device shows “promise for a broad range of potential applications, such as security, counter‐surveillance, and adaptive heat shielding and thermal control.”
Coatings and Metamaterials
Invisibility provides obvious advantages for soldiers, who often use the cover of darkness to perform covert operations. Thermal sensors, such as those in night vision goggles, thwart such attempts. The sensors reveal people (and animals) by distinguishing body heat from the temperature of the surrounding air. Technology that can match the radiating heat from a body to that of the background makes it invisible to thermal imagers.
Proposed solutions have included surface coatings that, when applied to fabric for instance, change how much heat an article of clothing emits. But it’s only effective within predetermined temperature ranges, and if the air gets colder or hotter than the setting, the tech “no longer works,” the researchers write. Other solutions include so-called metamaterials engineered with specific microstructures so small and artfully crafted that they can alter the physics of light, sound and heat. But according to the UC San Diego and National University of Singapore research team, although “Metamaterial‐based thermal camouflage holds great promise … their applications on human subjects are yet to be realized.”
The new device is made from a combination of phase-change materials and metal alloys that change to a specific temperature in response to an electrical current. Both work together to change a person’s body temperature to match the air temperature, without overheating or freezing them, reports PhysOrg.
The metal alloys, which are sandwiched between stretchy elastomer sheets and are thin enough to stitch into clothing, quickly cool down or heat up in response to electricity. Tests showed that the device went from 50 degrees F to 100.5 degrees F in less than a minute in order to match the surrounding temperature and camouflage the wearer’s body heat, according to a UC San Diego press release.
At the same time, the inside of the device has phase change materials that keep the person comfortable. These waxlike materials can be tuned to melt at a specific temperature. In this case, they’re tuned to melt at about 86 degrees F, which is the surface temperature of a person’s skin. According to the press release, “If the temperature on the outside of the device is higher than that, the material will melt and stabilize, insulating the wearer; if colder, it will slowly solidify, still acting as an insulating layer.”
For the next stage of research, the team will be investigating how to embed the wearable technology in a jacket. To do that, they’ll have to lighten the technology’s load and increase its energy efficiency. Currently, a garment using the proof-of-concept device would weigh about 4.5 pounds and only function for one hour.
And to make such wearable technology completely foolproof, the research team will have to deal with the heat emitted when a person breathes. Team leader, Renkun Chen, associate professor of mechanical and aerospace engineering at UC San Diego, told Popular Science that they haven’t solved that issue yet, but think a temperature-regulating face mask might work.
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