Researchers designed a bracelet that harvests bio-mechanical energy from the wearer’s wrist movements, which can convert into electricity and used to extend the battery lifetime of personal electronics.
energy harvesting bracelet
The energy-harvesting bracelet could potentially be used to help power activity trackers, smart watches, and even some health-monitoring applications. The bracelet works due to electromagnetic induction. In which the interaction between a moving magnetic field and an electrical conductor generates a voltage.
In the bracelet’s outer shell, electrically conductive copper coils wind around an inner shell. Inside this inner shell is two moving magnets that rotate around the bracelet in response to the wearer’s wrist movements. As the magnets move through the copper coils, they generate a voltage due to electromagnetic induction.
According to Faraday’s Law, the amount of voltage generated is proportional to the number of 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 velocity of between 100 and 300 revolutions per minute, depending on the type and intensity of the wrist movements. The researchers also demonstrated that, when a single shake of the wrist, the bracelet can charge a small capacitor to approximately 1 volt in a fraction of a second and generate an average power of more than 1 milliwatt.
Advantages of the bracelet
The advantages of the bracelet design are its symmetry, which allows to transform motion in any orientation into the rotational motion of the moving magnets. Other types of electromagnetic energy harvesters have limited degrees of freedom and only work in certain orientations.
In the future, the researchers plan to investigate several different areas. One idea is to use a circular magnetization magnet to fabricate the magnets. They also want to further reduce friction in the bracelet and introduce triboelectric energy-harvesting technology to use the remaining friction.
More information: [Applied Physics Letters]