A Millimeter-scale, Wirelessly Powered Cardiac Device

In their paper, the researchers demonstrated wireless power transfer to a millimeter-sized device implanted five centimeters inside the chest on the surface of the heart—a depth once thought out of reach for wireless power transmission.

The paper's senior author was Ada Poon, a professor of electrical engineering at Stanford. Sanghoek Kim and John Ho, both doctoral candidates in Poon's lab, were first authors.

The engineers say the research is a major step toward a day when all implants are driven wirelessly. Beyond the heart, they believe such devices might include swallowable endoscopes—so-called "pillcams" that travel the digestive tract—permanent pacemakers and precision brain stimulators; virtually any medical applications where device size and power matter.

Implantable medical devices in the human body have revolutionized medicine. Cochlear implants and drug pumps are today helping people live relatively normal lives, but these devices are not without engineering challenges.

First off, they require power, which means batteries, and batteries are bulky. In a device like a pacemaker, the battery alone accounts for as much as half the volume of the device it drives. Second, batteries have finite lives. New surgery is needed when they wane. "Wireless power solves both challenges," said Poon.

Poon’s device works by a combination inductive and radiative transmission of power. Both are types of electromagnetic transfer in which a transmitter sends radio waves to a coil of wire inside the body. The radio waves produce an electrical current in the coil sufficient to operate a small device.

There is an indirect relationship between the frequency of the transmitted radio waves and the size of the receive antenna. That is, to deliver a desired level of power, lower frequency waves require bigger coils. Higher frequency waves can work with smaller coils.

"For implantable medical devices, therefore, the goal is a high-frequency transmitter and a small receiver, but there is one big hurdle," explained Kim.

COMPAMED.de; Source: Stanford School of Engineering