Basically ears work by converting vibrations of the eardrum into electrochemical signals that can be interpreted by the brain, and the current for those signals is supplied by an ion-filled chamber deep within the inner ear. This is essentially a natural battery.
Scientists are now looking at using that battery to power devices that could be implanted in the ear, without affecting the recipient’s hearing. A team of scientists from MIT (The Massachusetts Eye and Ear Infirmary), and the Harvard-MIT Division of Health Sciences and Technology have recently succeeded in running an ultra-low-power radio-transmitting chip using power from these battery chambers in guinea pigs’ ears.
According to Gizmag, The “battery chamber” is located in the cochlea. It is internally divided by a membrane, some of the cells of which are designed to pump ions. The arrangement of those specialized cells, combined with an imbalance of potassium and sodium ions on opposite sides of the membrane, are what creates the electrical voltage.
The chip is not located in the guinea pigs’ ear but is on the outside, but it is small enough to fit inside of the ear. The voltage generated by the chamber isn’t enough to continually power the chip, however. Therefore, the chip incorporates power conversion circuitry, that allows a charge to build up in a capacitor.
Once that capacitor is sufficiently charged, the chip transmits a signal to an external receiver, it can take anywhere from 40 seconds to four minutes to build up enough power to do this. This also allows for the timing of the chip’s transmissions to be used as a measure of the electrochemical properties of each guinea pig’s ears.
An external burst of radio waves is used to supply that initial boost to initially power the chip’s control circuit. Once it’s going, the circuit is able to sustain itself using only ear-power.
Even if the battery chamber did provide a stronger current, the chip could still only use a fraction of it, because if there were too much power being drawn from the chamber it would effect the guinea pigs’ hearing. The guinea pigs used in the experiments showed no loss of hearing, however, when tested.