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Friday, August 10, 2018

Researchers incorporate optoelectronic diodes into washable fabrics.

By Nick Flaherty

Researchers at MIT have embedded high speed optoelectronic semiconductor devices, including light-emitting diodes (LEDs) and diode photodetectors, within fibres that were then woven ito soft, washable fabrics and made into communication systems. 

This is a key step to washable, wearable systems that will potentially be on the market next year. 

A spool of fine, soft fibre made using the new process shows the embedded LEDs turning on and off to demonstrate their functionality. The team has used similar fibres to transmit music to detector fibers, which work even when underwater. 

Optical fibers have been traditionally produced by making a cylindrical object called a “preform,” which is essentially a larger version of the fibre, then heating it. Softened material is then drawn or pulled downward under tension and the resulting fibre is collected on a spool.

The key breakthrough for producing these new fibres was to add the heat tolerant LEDs to the pre-from alongside a pair of copper wires. When heated in a furnace during the fibre-drawing process, the polymer preform partially liquified, forming a long fibre with the LEDs and photodiodes lined up along its centre and connected by the copper wires. “Both the devices and the wires maintain their dimensions while everything shrinks around them” in the drawing process, says researcher Michael Rein at MIT. 

The resulting fibres were then woven into fabrics, which were laundered 10 times to demonstrate their practicality as possible material for clothing.

“This approach adds a new insight into the process of making fibres,” said Rein. “Instead of drawing the material all together in a liquid state, we mixed in devices in particulate form, together with thin metal wires.”

One of the advantages of incorporating function into the fibre rather than the material is that the result is inherently waterproof. To demonstrate this, the team placed some of the photodetecting fibers inside a fish tank and a lamp outside the aquarium transmitted music through the water to the fibres in the form of rapid optical signals. The photodiodes converted the light pulses to electrical signals, which were then converted back into music. The fibers survived in the water for weeks.

Making sure that the fibres could be manufactured reliably and in quantity has been a long and difficult process. Staff at the Advanced Functional Fabric of America Institute (AFFOA), led by Jason Cox and Chia-Chun Chung, developed the pathways to increasing yield, throughput, and overall reliability, making these fibers ready for transitioning to industry. At the same time, Marty Ellis from Inman Mills in SOuth Carolina developed techniques for weaving the fibres into fabrics using a conventional industrial manufacturing-scale loom.

“This describes a scalable path for incorporating semiconductor devices into fibre. We are anticipating the emergence of a ‘Moore’s law’ analog in fibers in the years ahead,” said Yoel Fink, MIT professor of materials science and electrical engineering and CEO of AFFOA. “It is already allowing us to expand the fundamental capabilities of fabrics to encompass communications, lighting, physiological monitoring, and more. In the years ahead fabrics will deliver value-added services and will no longer just be selected for aesthetics and comfort.”

The first commercial products incorporating this technology will be reaching the marketplace as early as next year. “It's going to be the first fabric communication system. We are right now in the process of transitioning the technology to domestic manufacturers and industry at an unprecendented speed and scale,” said Fink.

Beyond communications, the fibres could potentially have significant applications in the biomedical field, the researchers say. For example, devices using such fibres might be used to make a wristband that could measure pulse or blood oxygen levels, or be woven into a bandage to continuously monitor the healing process.

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