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Mammals have natural batteries within their ears. Image by אני, CC license.

Did you know there’s a battery in your inner ear? It was news to me when I found this on Turns out not only is there a natural battery, but a group is working to utilise it to run medical devices.

The natural role of your ear battery is to turn sound vibrations into electrochemical signals, which travel down nerves to the brain. An imbalance of sodium and potassium ions (as with nerve cells) is created using cells that pump ions back and forth across a membrane – this is the battery.

It’s crucial for good hearing, and could be tapped to power devices.

Though it is very low voltage, the team was able to harness a small proportion of the natural battery to power a radio transmitter. In the future, this transmitter would be coupled to a sensor, and send data about how the ear is performing to a nearby computer.

During the experiment they used a guinea pig (literally) as a substitute for a human ear. The guinea pig responded normally to hearing tests, even with the implant. The chip itself was located outside of the guinea pig’s ear, but would fit inside a human’s middle ear cavity. We have got bigger ears than guinea pigs, after all.

They estimate it would take between 40 seconds to four minutes to build up enough juice to run the radio transmitter, but after that it keeps itself going.

To get around the lag time, they could send a burst of radio waves to provide that initial power – a kick-start.

It’s one of many developing technologies to explore new ways to tap into existing energy. Cell phones that can power themselves from the mechanical vibrations of being tapped, touched or carried are also in the pipeline. Rolex has been powering its wristwatches for decades using movement energy it collects when worn.

This research could open new ways to study the inner ear for people with hearing difficulties or problems with balance. It could also provide treatments, such as by improving hearing aids. All with the battery in your ear!