This Smart Bracelet Can Efficiently Charge Your Wearable

An energy harvesting bracelet.

This Smart Bracelet Can Efficiently Charge Your Wearable
(Left) Broken-out sectional view of the energy-harvesting bracelet, in which magnets moving through copper coils generate a voltage. (Right) Photo of the bracelet. Credit: Wu et al. ©2017 American Institute of Physics

Getting bracelet as per the latest trend is the requirement of every person. The smart bracelet is a customized bracelet that harvests biomechanical energy from the wearer’s wrist movements. Scientists at the Chongqing University of Technology and the China Academy of Engineering Physics in Sichuan have developed this smart bracelet.

By getting energy from wearer’s wrist movements, it converts biomechanical energy into electricity. A user can then use the electricity to extend the battery lifetime of personal electronics or even fully power some of these devices.

Research led Zhiyi Wu said, “The energy-harvesting bracelet could potentially be used to help power activity trackers, smartwatches, and even some health-monitoring applications.”

This Smart Bracelet Can Efficiently Charge Your Wearable
Broken-out sectional view of the energy harvesting bracelet, showing the two movers that repelled each other are located in the tube and the four coils are winded around the tube.

The bracelet works on electromagnetic induction, where the interaction between a moving magnetic field and an electrical conductor generates a voltage.

Scientists attached electrically conductive copper coils outside bracelet and around the inner shell. There are two moving magnets inside the inner shell that rotate around the bracelet in response to the wearer’s wrist movements. When these magnets start moving, they generate a voltage due to electromagnetic induction.

The whole mechanism works according to Faraday’s Law. The amount of voltage generated is proportional to the several times the magnets rotate around the bracelet. So the faster the motion, the greater the power generated by the bracelet. Tests showed that the magnets can move with an average rotational speed of between 100 and 300 revolutions per minute, depending on the type and intensity of the wrist movements.

From a single shake of the wrist, the bracelet can charge a small capacitor to about 1 volt in a fraction of a second and generate an average power of more than 1 milliwatt (mW).

This Smart Bracelet Can Efficiently Charge Your Wearable
(a) Photograph of four shake excitation types. (b) Schematic of the up-shake excitation type. (c) Mechanics analysis diagram of the movers under the worst excitation condition.

Wu noted, “The greatest advantage of the bracelet is that it can transform translational motion in any orientation into rotational motion, starting from any initial position of the magnets.”

Other advantages include, its symmetrical design allows it to transform motion in any orientation into the rotational motion of the moving magnets. Other types of electromagnetic energy harvesters, such as those in the shape of tubes or flat objects, have limited degrees of freedom and only work in certain orientations.

Now, scientists are planning o investigate several different application areas. They also want to introduce triboelectric energy-harvesting technology to use the remaining friction.