Similar to the other piezoelectric materials, zinc oxide results in an electrical current whenever it is subjected to mechanical stress. These very same nanorods will bend in response to sound waves, hence creating stress, where voltage will then be harvested as the nanorods remain sandwiched between a couple of electrical contact sheets. Most of the time, such contacts will be made out from gold, but with the insane price of gold, the researchers have successfully replaced the use of gold with a cost saving technique, allowing them to utilize ordinary aluminum foil instead.
The energy harvesting device is no larger than that of your regular smartphone, and hopefully it will be mass produced in due time for the world to enjoy cheap power regardless of where they are.