Open up the average laptop and you’ll see two things: a processor about the size of a half-dollar and the relatively massive parts needed to power it—most notably, the battery.

The same applies to electronic medical implants, such as pacemakers. But inside the human body, there often isn’t room for a big power pack. So a team of researchers, led by Ada Poon, an assistant professor of electrical engineering at the Stanford University School of Engineering, have developed a way to wirelessly charge devices implanted inside the body—allowing for medical devices as small as a grain of rice.

The team’s charging system is a riff on the technology used to power electric toothbrushes, smartphones and other small devices. In those setups, electricity passes through a coil in a power source, creating an electromagnetic field. A corresponding coil in the device itself collects energy from that field, which induces a current that can power the device or charge a battery. This type of wave, known as “near-field,” however, can't travel very far or pass through tissue.

While there is room for a pacemaker with a battery pack near the heart, other parts of the body provide less area to work with. In the brain, for instance, there isn’t room for an implant to sit right at a treatment site. Instead, doctors would need to place it where there’s a relatively open area, such as the back of the neck, and use wires to reach the target site.

“We’re by no means the first people to do wireless powering for medical implants,” explains John Ho, a graduate student who co-authored the study. “[Implants are] used for things like cochlear implants, but the [power source] itself has to be fairly large and the implant has to be very shallow. They can’t reach the important places in the body, like the heart or the brain.”

That’s why Poon’s work aims to explore how to use “biological tissue to transport energy,” she says. Her 2-mm-by-3-mm electronic implant is powered through the body with a credit-card-sized source (charged independently) outside it.

Her team found a unique method to manipulate the waves so that they propagate and pass through live tissue. The power source generates near-field electromagnetic waves of a specific pattern. As the pulses hit and interact with live tissue, they become a new type of wave, called “mid-field.” “When you place [our power source] over the body, the properties of your tissue actually convert the waves,” she explains.

The implant is part of a class of medical therapies known as “electroceuticals.”

Many of our body’s functions are electrical in nature, so an electronic implant placed close to a nerve fiber could deliver small pulses that provide a more-targeted therapy than drugs, which act globally.

“We want to see if electronics can be used to treat diseases as a complement to drug therapy or as a replacement for the drug therapy,” Poon says

The method, so far, appears safe. The team was able to transmit power to an implant in a pig—an animal similar to a human in scale—and set the pace of a rabbit’s heart. And an independent lab in the Bay Area found that the radio waves produced by Poon’s system are no more dangerous than those of a cellphone.

She hopes to begin human trials within a year. The initial trials will focus on pain management.. But Ho says that’s only the tip of the iceberg; the team is working with labs at the university’s medical school to find potential uses for other conditions, which may include epilepsy, Parkinson’s or urinary incontinence.

It will be several years before a system like Poon’s will reach consumer medical devices. But the stage for a new era of electronic medicine has certainly been set.