Wireless power comes to patient microimplants

Wireless power comes to patient microimplants

The technology, invented by a Stanford researcher, could lead to new ways of treating pain

A Stanford electrical engineer has invented a way to wirelessly transfer power to miniscule medical devices embedded deep inside the body.

Until now, there has been no safe method for wirelessly powering deep-tissue microimplants, which include pacemakers, sensors and nerve stimulators, according to Stanford researcher Ada Poon.

Poon, an assistant professor of electrical engineering, said her wireless charging method eliminates bulky batteries and clumsy recharging systems that prevent medical devices from being more widely used.

An electrostimulator next to pills. The microimplant stimulator has no battery and the new wireless power technique allows the device to be wirelessly powered deep inside the body, in locations such as the heart or brain. (Image: Austin Yee)

The microimplant technology could open up new ways of treating diseases with devices the size of a grain of rice.

"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," Poon said in a Stanford Press statement.

Wireless charging works by creating an electromagnetic field between two copper coils that are tuned to resonate at the same frequency, which then allows electricity to be transferred. There are two types of wireless charging: near- and far-field inductive resonance.

Progress in miniaturizing semiconductor technology has lead to huge advances in medical implants, some of which are less than a millimeter in size. But, with that miniaturization have been challenges in power sources.

Poon's research, published in the Proceedings of the National Academy of Sciences, shows a new way to control electromagnetic waves inside the body.

Far-field electromagnetic waves, such as those broadcast from radio towers, can travel over long distances.

Although wireless charging is a widely used technology that is rapidly expanding to handheld mobile devices and other electronics, energy transfer beyond superficial depths in tissue has so far been limited by large coils (at least a centimeter in diameter) "unsuitable for a microimplant."

The problem is that when they come in contact with living tissue or other conductive materials, they can heat up. So medical science has avoided using them for implants and opted instead for batteries connected by wires through the skin to the medical device.

Unlike conventional near-field inductive coils, Poon's method uses a technique called "midfield powering" to create a high-energy density region deep in tissue that allows the power receiver to be made extremely small.

The power transfer technology has been tested on a microimplant that was 2mm in size, but capable of closed-chest wireless control of the heart that is orders of magnitude smaller than conventional pacemakers.

The midfield power transfer sent mere milliwatts of power to a deep-tissue microimplant for both complex electronic function and physiological stimulation.

An independent laboratory that tests cell phones found that Poon's system fell well below the danger exposure levels for human safety.

The Stanford lab has so far tested the wireless charging system in a pig and used it to power a tiny pacemaker implanted in a rabbit.

Poon is now working on a system for testing in humans.

"Should such tests be approved and prove successful, it would still take several years to satisfy the safety and efficacy requirements for using this wireless charging system in commercial medical devices," the statement said.

Poon believes this discovery will spawn a new generation of programmable microimplants -- sensors to monitor vital functions deep inside the body; electrostimulators to change neural signals in the brain; and drug delivery systems to apply medicines directly to affected areas.

Electrical engineer Ada Poon has invented a way to wirelessly transfer power deep inside the body. The technology could provide a path toward new medical devices.

Lucas Mearian covers consumer data storage, consumerization of IT, mobile device management, renewable energy, telematics/car tech and entertainment tech for Computerworld. Follow Lucas on Twitter at @lucasmearian or subscribe to Lucas's RSS feed. His e-mail address is

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