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Researchers Create Stretchable, Multi-Functional Fiber for Strain Sensing and Energy Harvesting Applications

It has been predicted that fiber-based electronics will play an important role in sophisticated wearable electronics.

Schematic illustration of an SMF fiber and its piezoelectric voltage output and response to strain. (Image credit: KAIST)

Fiber-based electronics, when woven into textiles, can offer greater comfort, durability, and built-in multi-functionality. Now, researchers at KAIST have developed a new kind of stretchable multi-functional fiber, or SMF, that has the ability to harvest energy and sense strain, thereby making it useful for applying to upcoming wearable electronics.

With the help of wearable electronics, physical and health conditions can be checked by examining the human body’s biological signals, like the movements of pulse and muscles. Fibers, in particular, are extremely suited for upcoming wearable electronics, as they can be easily woven into textiles, which are fabricated such that they are easy to wear and can be conformed to curvilinear surfaces. In addition, the fibers’ weave structures provide support that makes them impervious to fatigue. In this regard, a number of research teams have created fiber-based strain sensors to detect external biological signals, but their sensitivities were shown to be rather low.

At present, the applications of wearable devices are restricted by their power source, because the battery’s weight, size, and lifetime tend to reduce their versatility. One potential solution to overcome these restrictions is to harvest mechanical energy from the human body by using different types of motions, for example, pressing, stretching¸ and bending. Conversely, formerly reported, fiber-based energy harvesters were not flexible and also incapable of fully harvesting the available mechanical energy.

Professors Steve Park and Seungbum Hong from the Department of Materials Science and Engineering and their group created a stretchable fiber by utilizing a ferroelectric layer made of P(VDF-TrFE)/PDMS stacked between elastic electrodes containing a composite of poly 3,4-ethylenedioxythiophene polystyrene sulfonate (PEDOT:PSS) and multi-walled carbon nanotubes (MWCNT).

Cracks, which were formed in the MWCNT/PEDOT:PSS layer, allowed the fiber to exhibit high sensitivity in comparison to the earlier reported fiber strain sensors. The novel fiber can also harvest mechanical energy under different mechanical stimuli like tapping, stretching, and injecting water inside the fiber by means of the piezoelectric effect of the P(VDF-TrFE)/PDMS layer.

This new fiber has various functionalities and makes the device simple and compact. It is a core technology for developing wearable devices with energy harvesting and strain sensing capabilities.

Seungbum Hong, Professor¸ Department of Materials Science and Engineering, KAIST.

The article, headed by PhD candidate Jeongjae Ryu, has been reported in the January 2019 issue of Nano Energy.

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