Proving the Business Case for the Internet of Things

MIT scientists use RF to power implanted devices

Steve Rogerson
June 19, 2018

Researchers at the Massachusetts Institute of Technology, working with scientists from Brigham & Women’s Hospital, have developed a way to power and communicate with devices implanted deep within the human body.
Such devices could be used to deliver drugs, monitor conditions inside the body, or treat disease by stimulating the brain with electricity or light.
The implants are powered by radio frequency waves, which can safely pass through human tissues. In tests in animals, the researchers showed that the waves can power devices located 10cm deep in tissue, from a distance of 1m.
“Even though these tiny implantable devices have no batteries, we can now communicate with them from a distance outside the body,” said Fadel Adib, an assistant professor in MIT’s Media Lab. “This opens up entirely new types of medical applications.”
Adib is a senior author of the paper, which will be presented at the Association for Computing Machinery’s Sigcomm special interest group on data communications conference in August in Hungary.
Because they do not require a battery, the devices can be tiny. In this study, the researchers tested a prototype about the size of a grain of rice, but they anticipate that it could be made even smaller.
“Having the capacity to communicate with these systems without the need for a battery would be a significant advance,” said Giovanni Traverso, assistant professor at Brigham & Women’s Hospital and an author of the paper. “These devices could be compatible with sensing conditions as well as aiding in the delivery of a drug.
Other authors of the paper are Media Lab postdoc Yunfei Ma, Media Lab graduate student Zhihong Luo, and Koch Institute and BWH affiliate postdoc Christoph Steiger.
Medical devices that can be ingested or implanted in the body could offer doctors new ways to diagnose, monitor and treat many diseases. Traverso’s lab is now working on a variety of ingestible systems that can be used to deliver drugs, monitor vital signs and detect movement of the GI tract.
In the brain, implantable electrodes that deliver an electrical current are used for a technique known as deep brain stimulation, which is often used to treat Parkinson’s disease or epilepsy. These electrodes are now controlled by a pacemaker-like device implanted under the skin, which could be eliminated if wireless power is used. Wireless brain implants could also help deliver light to stimulate or inhibit neuron activity through optogenetics, which so far has not been adapted for use in humans but could be useful for treating many neurological disorders.
Currently, implantable medical devices, such as pacemakers, carry their own batteries, which occupy most of the space on the device and offer a limited lifespan. Adib, who envisions much smaller, battery-free devices, has been exploring the possibility of wirelessly powering implantable devices with radio waves emitted by antennas outside the body.
Until now, this has been difficult to achieve because radio waves tend to dissipate as they pass through the body, so they end up being too weak to supply enough power. To overcome that, the researchers devised a system that they call in vivo networking (IVN). This relies on an array of antennas that emit radio waves of slightly different frequencies. As the radio waves travel, they overlap and combine in different ways. At certain points, where the high points of the waves overlap, they can provide enough energy to power an implanted sensor.
“We chose frequencies that are slightly different from each other and, in doing so, we know that at some point in time these are going to reach their highs at the same time,” said Adib. “When they reach their highs at the same time, they are able to overcome the energy threshold needed to power the device.”
With the system, the researchers don’t need to know the exact location of the sensors in the body, as the power is transmitted over a large area. This also means they can power multiple devices at once. At the same time that the sensors receive a burst of power, they also receive a signal telling them to relay information back to the antenna. This signal could also be used to stimulate release of a drug, a burst of electricity or a pulse of light, the researchers say.
In tests in pigs, the researchers showed they could send power from up to a metre outside the body, to a sensor that was 10cm deep in the body. If the sensors are located very close to the skin’s surface, they can be powered from up to 38m away.
“There’s currently a trade-off between how deep you can go and how far you can go outside the body,” Adib said.
The researchers are now working on making the power delivery more efficient and transferring it over greater distances. This technology also has the potential to improve RFID applications in other areas such as inventory control, retail analytics and smart environments, allowing for longer-distance object tracking and communications.
The research was funded by the Media Lab Consortium and the National Institutes of Health.