Self-powered e-watch harvests energy with the aid of the movement of our hands


Self-powered – the ‘holy grail’ technological scope that pertains to a state of independence from any kind of fuel. In this case, such a self-powered credential is showcased by a special electronic watch devised by the collaborative effort of researchers from Beijing Institute of Nanoenergy and Nanosystems (in China) and Georgia Institute of Technology (in United States). Now we say ‘special’ because this e-watch has the impressive capacity to generate its own energy by using the movement of the wearer’s hand. This is made possible with the combination of two energy conversion mechanisms – electromagnetic and triboelectric, both of which are integrated into the device’s hybrid nanogenerator. As a result, the e-watch was found to harvest significantly greater energy than conventional setups that only depend on a single energy mechanism.

So how exactly does this special hybrid generator work? Well in physical terms, the bantam gizmo consists of a small box (3.6 cm x 3.6 cm x 3 cm) with a magnetic ball incorporated on the inside. Now when the user moves his hand, the motional effect instigates the ball to hit the six metal coils that are arranged on the side of the box. This initiates an electromagnetic effect, and thus the magnetic ball’s mechanical energy is converted into electricity.

As we mentioned before, the other part of this e-watch’s energy harvesting scope pertains to triboelectric effect (the same effect that causes static electricity when we rub our hair with a ruler). To that end, the researchers crafted the inconspicuous watch strap as the primary triboelectric component; as it was made from two materials – nylon and a polymer composite, both of which have different polarities. These materials are hooked up to the bottom of the box and also with two electrodes. So when the magnetic ball presses down on this strap’s juncture, the materials come in contact and create the resultant triboelectric charges, while also allowing for the flow of electrons.


Credit: Quan, et al. Copyright: 2015 American Chemical Society

From the practical perspective, the researchers found that the twisting motion of our wrists relates to a better efficiency when it comes to the self-generating energy of the device. In terms of figures, this translates to 12 mA of current, thus signifying that 39 continuous seconds of the twisting motion can power the e-watch for 7.5 minutes. On including an improvised Li-ion battery (that could store the harvested charges over time), the scientists found out that 32 minutes of the twisting motion can power the watch for 3.5 hours, while 3.6 hours of the same motion can power the electronic device for an entire day.

Judging from these figures, suffice it to say that the e-watch still has some kinks that need to worked out before its possibility in the commercial realm. And since we brought up the commercial side of affairs, the scientists are also looking forth to streamline the design element of the rather cumbersome-looking watch. According to them, this can be achieved by reducing the size factor of the hybrid nanogenerator – though the process might not be that easy considering the importance and effectiveness of the magnetic ball. However on the brighter side, the intrinsic hybrid nanogenerator has its potential beyond just powering e-watches. As Ya Yang, who was one of the project heads, said (to Phys) –

This kind of nanogenerator can also be utilized to power other wearable electronic devices, such as a wireless smart pedometer for reading data on walking steps, distance, and energy consumption.

He further added –

The future plan is to solve the power source issue of the wearable electronic device, so that these devices can work sustainably without being charged by the external power source. Ideally, the motion of human-body-induced energy will be enough to power these devices.

The study was originally published in the journal ACS Nano.

Source: Phys

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