The human ear has a specific, biological structure and functions like a natural battery.
In the inner ear, there is an ion-filled chamber that produces electricity to drive neural signals. This is part of the process in which the vibrations of the eardrum are converted into electrical signals that the brain can recognise and interpret.
Researchers from Massachusetts Institute of Technology (MIT) and Harvard Medical School have invented devices that can draw power from this natural battery in our inner ear.
This means that in the future, hearing aids could be powered by the human body itself.
The researchers used guinea pigs in their research. Electrodes were planted into the biological batteries in the ears of guinea pigs and connected to low-power electronic devices.
The guinea pigs were able to respond normally to hearing tests afterwards and the devices were able transmit data about chemical conditions within the ear to an external receiver.
Even though the ear's natural battery has the highest voltage of any part of the body, the voltage is still very low. Any device that is plugged into the ear can therefore only harvest a small fraction of its power from this source, or else the ear's ability to communicate with the brain would be disrupted, which would lead to some hearing loss.
The researchers have therefore devised a special low-power chip in order to avoid this, which has an ultra low-power radio transmitter. The power circuit in the transmitter still requires a higher voltage than the ear can provide and it requires a kick start before it can become self-sustaining.
Implantable hearing aids
Even so, the researchers believe that further answers can be found if they are able to tap into the natural power source of the cochlea.
The technology of the future could then produce hearing aids that draw their power from the cochlea.