Human Ear As A Battery

Inner ear's energy can work like a battery, can power tiny devices .

For the first time, an electrical device has been powered by the ear alone. The team behind he technology used a natural electrochemical gradient in cells with the inner ear of a guinea pig to power a wireless transmitter for u to five hours. The technique could one day provide an autonomous power source to the brain and cochlear implants, says Tina Stankovic, an auditory neuroscientist at Harvard University Medical School in Boston, Massachusetts. 

Cochlear cells from mammalian inner ear

Nerve cells use the movement of positively charged sodium and potassium ion across a membrane to create an electrochemical gradient that drives neural signals. SOme cells in the cochlear have the same kind of gradient, which is used to convert the mechanical force of the vibrating eardrum into electrical signals that brain can understand.

Tiny Voltage

A major challenge in tapping such electrical potential is that the voltage created is tiny – a fraction of that generated by a standard AA battery. Now, Stankovic and her colleagues have developed an electronic chip containing several tiny, low resistance electrodes that can harness a small amount of this electrical activity without damaging hearing. The implant was inserted into a guinea pig's inner ear and the electrodes attached to both sides of cochlear cell membranes. Attached to the chip was a low power radio transmitter.

Guinea Pig

The device needed kick-starting with a short burst of radio waves, but was then able to use the electrical gradient running across the membrane to sustain the transmitter for up to five hours. Tests showed that the guinea pig's hearing was not affected.The device works well for short durations but long-term use of the electrodes risks damaging the sensitive tissue inside the ear. The next step will be to make the electrodes even smaller, reducing their invasiveness.