Material Alert

Soldiers have to be on top of what’s going on around them; their lives depend on it. Technology helps: for example, night-vision goggles that amplify the ambient light either in the visible or near-infrared ranges. A great gadget, except for its weight, bulk, and need for batteries. Nanotechnology may provide some new great gadgets that are smaller, lighter, and more integrated.

What if you could integrate capabilities into soldiers’ kits and clothing that would dramatically enhance their ability to monitor themselves and their surroundings? At MIT’s Institute for Soldier Nanotechnologies (ISN), researchers are developing new materials that can sense changes in a soldier’s body surface temperature and even tell whether he or she is being targeted by a laser.

Designing clothes that can “see and feel” is a goal of ISN materials scientist Yoel Fink and physicist John Joannopoulos, who are fabricating novel sensor fibers arranged from a semiconductor, metals, and insulators. The concept is to choose materials that become soft and highly deformable at a particular temperature.

Fink and Joannopoulos chose the amorphous semiconductor arsenic selenide for the fiber core, with parallel contacting wires made out of tin, surrounded by the mechanically tough insulating polyethersulfone polymer. These materials are used to create a “preform” that is tens of centimeters long and a few centimeters in diameter. The preform is inserted into a specially built “draw tower,” and a much smaller-diameter fiber is drawn out. It’s tens of meters long but has a cross-section architecture identical to that of the preform.

The fibers can be designed to detect a specific color of light. The team incorporates a dielectric stack-reflecting layer into the fiber, a layer that is concentric with and surrounds the core semiconductor device. The reflector has a cavity in it that allows only light of a specific wavelength to pass through to the semiconductor core; that a fiber has been illuminated by a particular color of light is detected via a drop in the semiconductor’s electrical resistance. Simply changing the thickness of the cavity in the reflecting layer makes the fiber sensitive to a different color of light.

The same approach works for temperature sensing, only the core semiconductor material is chosen so that temperature variations change its resistance, enabling body surface temperature to be monitored and mapped. A fabric that can see in color and feel heat and cold can be made through the cross-weaving of only a few thousand fibers. Inputs and outputs for power and control are still needed. But since the clothing has these fibers woven into it, it will provide 360 degrees of sensing in a package that is small and lightweight.

Edwin L. Thomas is Morris Cohen Professor of Materials Science and Engineering at MIT and directs the Institute for Soldier Nanotechnologies.