Double-Spun PVDF Nanofibers Deliver Sensitive Flexible Sensing, Energy Harvesting for Wearables

Made using two sizes of PVDF nanofibers, these sensors are robust and flexible yet offer a wide sensing range and high sensitivity.

Researchers from Shinshu University and the Tokyo Institute of Technology have developed a material well-suited to building low-cost and flexible piezoelectric sensors — capable of tracking everything from walking to the pulse in your wrist.

"Despite the current challenges, humanoid robots are poised to play an increasingly integral role in the very near future," corresponding author Ick Soo Kim, a distinguished professor in Shinshu University's Nano Fusion Technology Research Group, claims. "Considering high-tech sensors are currently being used to monitor robot motions, our proposed nanofiber-based superior piezoelectric sensors hold much potential not only for monitoring human movements, but also in the field of humanoid robotics."

The team's sensor is built using a composite two-dimensional nanofiber membrane, spun from polyvinylidene fluoride (PVDF). The secret to its success, though, is that it's spun twice: once using larger 200nm fibers to provide a base, then again with much smaller 35nm fibers that fill in the gaps and complete a PVDF network capable of delivering a piezoelectric response — turning force into electricity.

The prototype sensors proved to offer a wide response range rated at 1.5-40 Newtons, high durability, and an excellent response to weak forces below 4 Newtons, the team claims — the latter helping it operate as a sensor for movement as small as the pulse point of a user's wrist. Other tests included wearable sensors for finger tapping, the bending of knees and elbows, foot-stamping, and speaking — plus a demonstration of energy-harvesting potential in which LEDs light according to the strength of the user's slap.

To extend the work, the researchers are planning on finding ways to boost the energy output to directly drive other electronics without the need for an external power supply. "Overall," the team concludes, "due to the simple fabrication and high piezoelectric performance, we believe that the present work would provide a beneficial idea for the construction of PVDF-nanofiber membranes based piezoelectric sensors for various wearable electronic products."

The team's work has been published in the journal Advanced Fiber Materials under open-access terms.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire:
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