The bulky batteries and clumsy recharging systems often prevent medical devices from being more widely used. The size of the device makes brain implants difficult.
"We need to make these devices as small as possible to more easily implant them deep in the body and create new ways to treat illness and alleviate pain," said Ada Poon, assistant professor of electrical engineering at Stanford University in the US.
The researchers built an electronic device smaller than a grain of rice that could act as a pacemaker.
It can be powered or recharged wirelessly by holding a power source about the size of a credit card above the device, outside the body.
The technology paves way for a new type of wireless power transfer - using roughly the same power as a cell phone - that can safely penetrate deep inside the body as the researchers discovered a new way to control electromagnetic waves inside the body.
This wireless charging system was tested in a pig and used it to power a tiny pacemaker in a rabbit.
The work created the potential to develop "electroceutical" treatments as alternatives to drug therapies, said William Newsome, director of the Stanford Neurosciences Institute.
The study appeared in the journal Proceedings of the National Academy of Sciences.
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