Power/Performance Bits: Aug. 17

Digital fiber
Researchers at MIT, Harrisburg University of Science and Technology, and Rhode Island School of Design developed a digital fiber that can sense, store, analyze, and infer activity after being sewn into a shirt.

“This work presents the first realization of a fabric with the ability to store and process data digitally, adding a new information content dimension to textiles and allowing fabrics to be programmed literally,” said Yoel Fink, a professor of material sciences and electrical engineering at MIT and a Research Laboratory of Electronics principal investigator.

Hundreds of silicon chips were placed in a preform used to create a polymer fiber, with continuous electrical connection between the chips over a length of tens of meters. The fiber can be threaded through a needle, sewn into fabrics, and watched at least ten times before breaking down. It isn’t obtrusive, according to Gabriel Loke, an MIT PhD student: “When you put it into a shirt, you can’t feel it at all. You wouldn’t know it was there.” In tests, the fiber was woven into a knitted garment sleeve.

The digital fiber enables control of individual elements within it using an addressing method that enables switching on of one element without turning them all on.

The researchers were able to write, store, and read information on the fiber, including a 767-kilobit full-color short movie file and a 0.48 megabyte music file. The files can be stored for two months without power.

The fiber also includes a neural network of 1,650 connections. After sewing it around the armpit of a shirt, the researchers used the fiber to collect 270 minutes of surface body temperature data from a person wearing the shirt, and analyze how these data corresponded to different physical activities. Trained on these data, the fiber was able to determine with 96% accuracy what activity the person wearing it was engaged in.

Currently, the fiber is controlled by a small external device. The team said the next step is designing a microcontroller that can be connected within the fiber itself.

Washable smart clothes
Engineers at Purdue University propose battery-free smart clothing that can be easily washed by using a combined spray and sewing application.

The smart clothing can harvest energy from Wi-Fi or radio waves in the environment using flexible, silk-based coils sewn onto the garment. The team has created several proofs of concept, including a glove that illuminates a fingertip when near a live electrical cable and a sweatband containing a miniaturized cardiac monitoring system.

“Such wearable devices, powered by ubiquitous Wi-Fi signals, will make us not only think of clothing as just a garment that keeps us warm but also as wearable tools designed to help us in our daily life, monitor our health and protect us from accidents,” said Ramses Martinez, an assistant professor in Purdue’s School of Industrial Engineering and in the Weldon School of Biomedical Engineering.

In addition, a coating is used to make the clothing machine washable.

“By spray-coating smart clothes with highly hydrophobic molecules, we are able to render them repellent to water, oil and mud,” said Martinez. “These smart clothes are almost impossible to stain and can be used underwater and washed in conventional washing machines without damaging the electronic components sewn on their surface. Thanks to their ultrathin coating, our smart clothes remain as flexible, stretchable and breathable as conventional cotton T-shirts.”

The team said the technology can be fabricated in conventional, large-scale sewing facilities. They have applied for a patent.

Lithium from the sea
Researchers from King Abdullah University of Science and Technology (KAUST) found a way to cost-effectively extract lithium from seawater. As demand for lithium-ion batteries increases, so has concern over the cost and continued availability of the element.

While the ocean contains vast amounts of lithium, it is in very low concentrations, about 0.2 parts per million. Complicating the picture is the presence of larger ions such as sodium, magnesium, and potassium, making extraction of lithium alone difficult.

To tackle the problem, the researchers built an electrochemical cell with a ceramic membrane made from lithium lanthanum titanium oxide (LLTO) with a crystal structure containing holes just large enough to allow lithium ions through while blocking larger metal ions.

Made up of three compartments, the cell has a central chamber into which seawater flows. Positive lithium ions pass through the LLTO membrane to a side compartment with a buffer solution and copper cathode coated with platinum and ruthenium. Negative ions exit the central chamber through a standard anion exchange membrane to a third compartment with a sodium chloride solution and platinum-ruthenium anode.

In tests using seawater from the Red Sea and with a voltage of 3.25V, the cell generated hydrogen gas at the cathode and chlorine gas at the anode, driving the transport of lithium through the LLTO membrane. The lithium-enriched water was passed through the device four more times, eventually reaching a concentration of more than 9,000 ppm. Solid lithium phosphate pure enough for use in batteries was created by adjusting the pH of the solution.

The team estimates 1kg of lithium could be extracted for $5 in electricity, with the value of hydrogen and chlorine produced offsetting that cost. The left over seawater could be used in desalination plants.

“We will continue optimizing the membrane structure and cell design to improve the process efficiency,” said group leader Zhiping Lai of KAUST. The team also hopes to collaborate with the glass industry to produce the LLTO membrane at large scale and affordable cost.