Researchers from the King Abdullah University of Science and Technology (KAUST) have developed smart threads that can detect the strength and location of pressures exerted upon them—which they say could help advance the development of electronic skins for use in robots and medical prosthetics.

Fabrics containing flexible electronics are appearing in many novel products, such as clothes with built-in screens and solar panels. Most flexible sensors function by detecting changes in the electrical properties of materials in response to pressure, temperature, humidity or the presence of gases.

Electronic skins are built up as arrays of several individual sensors. But these arrays currently need complex wiring and data analysis, which generally makes them too heavy, large or expensive for large-scale production.

Yanlong Tai and Gilles Lubineau, of the KAUST Division of Physical Science and Engineering, have found a different approach. They built their smart threads from cotton threads coated with layers of single-walled carbon nanotubes (SWCNTs).

The twisted smart threads can be woven into pressure-sensitive electronic skin fabrics for use in clothing, robots or medical prosthetics. Image credit: KAUST.The twisted smart threads can be woven into pressure-sensitive electronic skin fabrics for use in clothing, robots or medical prosthetics. Image credit: KAUST.“Cotton threads are a classic material for fabrics, so they seemed a logical choice,” says Lubineau. “Networks of nanotubes are also known to have piezo-resistive properties, meaning their electrical resistance depends on the applied pressure.”

The researchers demonstrated that their threads had decreased resistance when subjected to stronger mechanical strains and, crucially, that the amplitude of the resistance change also depended on the thickness of the SWCNT coating.

These findings led to a breakthrough: the development of threads with a thick SWCNT layer at one end tapering to a thin layer at the other end. Then, by combining threads in pairs—one with graded thickness and one of uniform thickness—the researchers could detect not only the strength of an applied pressure load, but also the position of the load along the threads.

“Our system is not the first technology to sense both the strength and position of applied pressures, but our graded structure avoids the need for complicated electrode wirings, heavy data recording and analysis,” says Tai.

The researchers have used their smart threads to build two- and three-dimensional arrays that accurately detect pressures similar to those that real people and robots might be exposed to.

“We hope that electronic skins made from our smart threads could benefit any robot or medical prosthetic in which pressure sensing is important, such as artificial hands,” says Lubineau.

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