Skip to Content

Wireless Power for Minuscule Medical Implants

A novel way of powering implanted devices could enable new ways to control appetite, regulate insulin, and treat brain injuries.
August 21, 2014

Medical implants like pacemakers, deep brain stimulators, and cochlear implants could someday be joined by still more bioelectronic gadgets—devices that regulate insulin levels, control appetite, lower blood sugar, or treat brain injuries (see “Nerve-Stimulating Implant Could Lower Blood Pressure”).

Tiny ticker: Researchers used midfield radiation to wirelessly power this rice-size pacemaker, which was implanted in a rabbit.

But before we’re all riddled with electronics, researchers have to figure out how to power it all. Pacemaker batteries are too clunky for tiny devices saddled up to nerves, and existing wireless methods, such as those used for cochlear implants, won’t work with devices buried deep in the body.

That’s where electrical engineer Ada Poon and her team at Stanford University say they might be able to help. The group has developed a new method of sending magnetic fields well below skin level to power devices that would otherwise need batteries.

Wireless systems like the one used in cochlear implants sit permanently on the skin and derive power from electromagnetic induction, in which a current running through a coil of wire generates a magnetic field that then induces a current in a nearby device. The problem is that a field generated this way decays exponentially with distance from the generating coil, so it only works with devices close to the skin’s surface.

Poon and her team found a way to use electromagnetic induction through biological tissue without that exponential decay. They call the technique midfield wireless powering (as opposed to near-field, which refers to the exponentially decaying radiation, and far-field, which refers to the kind of radiation emitted from a cell tower).

The key, Poon says, is that instead of using a coil of wire, they use a flat plate adorned with a specially designed four-line pattern of conductive material. When they send current through the plate, that pattern produces a magnetic field capable of propagating through biological material without decaying over a short distance. The plate would most likely sit on the skin, providing constant power to an implant.

Morris Kesler, vice president of research and development at WiTricity, a Massachusetts-based company that develops wireless powering systems, says Poon’s technique would be particularly useful for powering tiny devices.

To test their new powering scheme, the Stanford group implanted a pacemaker about the size of a grain of rice in a rabbit and then powered the device using a plate about six centimeters on a side. The setup worked with about 0.1 percent efficiency—meaning that nearly all the energy sent from the conductive material to the pacemaker was wasted. Nonetheless, Poon says that is sufficient for this kind of low-power medical device. It also met safety regulations limiting the amount of radiation delivered to a given amount of tissue in humans.

In the future, Poon says, the group plans to develop flexible versions of the plate that will be more comfortable against skin. One of her graduate students is also designing plates that will penetrate materials other than biological tissue.

Kip Ludwig, the program director for neural engineering at the National Institute of Neurological Disorders and Stroke at the National Institutes of Health, says Poon’s method is promising but years from any clinical application. Still, there is so much promise in bioelectronics, he says, and the powering issue needs to be addressed.

Keep Reading

Most Popular

wet market selling fish
wet market selling fish

This scientist now believes covid started in Wuhan’s wet market. Here’s why.

How a veteran virologist found fresh evidence to back up the theory that covid jumped from animals to humans in a notorious Chinese market—rather than emerged from a lab leak.

light and shadow on floor
light and shadow on floor

How Facebook and Google fund global misinformation

The tech giants are paying millions of dollars to the operators of clickbait pages, bankrolling the deterioration of information ecosystems around the world.

masked travellers at Heathrow airport
masked travellers at Heathrow airport

We still don’t know enough about the omicron variant to panic

The variant has caused alarm and immediate border shutdowns—but we still don't know how it will respond to vaccines.

egasus' fortune after macron hack
egasus' fortune after macron hack

NSO was about to sell hacking tools to France. Now it’s in crisis.

French officials were close to buying controversial surveillance tool Pegasus from NSO earlier this year. Now the US has sanctioned the Israeli company, and insiders say it’s on the ropes.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.