Stretchable wearable device uses tiny magnets to generate electricity
While we've been hearing a lot about wearable piezoelectric devices that produce electricity from people's movements, such gadgets don't work well under certain conditions. A new bioelectric wearable, however, could excel where they falter.
Whereas piezoelectric devices generate an electrical current when squeezed or pressed, the new tool is a bit different. It utilizes what is known as the magnetoelastic effect, which involves utilizing mechanical pressure to push together and draw apart magnets within a material, thus generating an electrical current as the strength of that material's magnetic field changes.
Previously, magnetoelastic generators had been constructed out of rigid metal alloys, which were too stiff to be comfortably worn on the body. Led by Asst. Prof. Jun Chen, however, a team at UCLA has created one that is soft and flexible enough to be worn on frequently moving body parts. It's composed of a platinum-catalyzed silicone polymer matrix, suspended inside of which are nanoscale neodymium-iron-boron magnets.
When attached to a volunteer's elbow via a silicone band, the device generated electrical currents of 4.27 milliamperes per square centimeter. It did so as the person's elbow moved, causing the tiny magnets to repeatedly be pulled apart and pushed back together. What's more, the experiments indicated that the device was sensitive enough that it could even convert human pulse waves into electrical signals – this means it could be integrated into a self-powered heart rate monitor.
And according to Chen, the generator does have some key advantages over the existing alternatives.
"Current biomechanical-to-electrical energy conversion technologies, including triboelectric and piezoelectric nanogenerators, confront unavoidable challenges such as very low current density and high internal impedance," he tells us. "More importantly, their electrical output performance is vulnerable to ambient humidity caused by sweating and the fluidic environment of the human body, which severely limits their practical on-body applications."
By contrast, the soft magnetoelastic generator has a higher output, and it isn't affected by moisture. Chen adds that while other types of generators could be protected against humidity via a waterproof coating, adding such a coating typically decreases their biomechanical-to-electrical energy conversion efficiency.
The research is described in a paper that was recently published in the journal Nature Materials.