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A Stanford researcher has discovered a way to charge devices deep within living bodies, potentially opening the gates to embedded sensors and “microimplants” that weren’t possible before.

More immediately, the development, published Monday in the Proceedings of the National Academy of Sciences, promises pacemakers, nerve stimulators and other existing medical devices that can be smaller, longer-lasting and implanted more deeply within the brain and body.

Currently, many of these devices run on big, long-lasting batteries that still eventually die, generally requiring another round of surgery. Others are equipped with rechargeable batteries that require large receiving coils on the implant (at least a centimeter in diameter) that strictly limit where and how they can be used.

The new approach, dubbed “mid-field wireless transfer,” could allow doctors to rely more on electronics and less on drugs to treat various diseases, according to the researchers.

“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, an assistant professor of electrical engineering at Stanford, in a statement.

Poon led the research team, which has already developed a pacemaker smaller than a grain of rice that can be powered or recharged simply by holding a credit card-size power source above it.

Different versions of the device could potentially be used for “deeper” deep-brain stimulation, sensors to monitor vital functions throughout the body and drug delivery systems that transport medicines directly to their target, the researchers said. Further down the theoretical road lie all sorts of those half exciting, half creepy possibilities for brain chips, bionics, eyeball displays, dial pads on your palms and on and on.

Wireless charging has existed for some time for smartphones and some medical gadgets embedded just below the skin, taking advantage of a type of electromagnetic wave known as near-field waves. But guess what? Near-field waves don’t travel far.

Poon and her team’s new power source emits a particular type of near-field wave. When it hits the skin, the waves actually propagate, rather than being absorbed or reflected away. And they seem to do so within the range of safe exposure levels.

They’ve tested the technology on a pig and a rabbit, and are preparing to evaluate it in humans. Any commercial device, however, would still have to work through years of safety and efficacy trials.

“The Poon lab has solved a significant piece of the puzzle for safely powering implantable microdevices, paving the way for new innovation in this field,” said William Newsome, director of the Stanford Neurosciences Institute, in a statement.