Using wirelessly powered implantable devices with radio waves emitted by antennas outside the body has been difficult to achieve, as radio waves tend to dissipate as they pass through the body, ending up too weak to supply enough power. To overcome this, the researchers developed a system, which they call “In Vivo Networking,” that 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.
Working with scientists from Brigham and Women’s Hospital (Boston, MA), the MIT researchers showed that their wireless system can power devices located 10 centimeters deep in tissue, from a distance of one meter.
“Even though these tiny implantable devices have no batteries, we can now communicate with them from a distance outside the body,” says Fadel Adib, an assistant professor in MIT’s Media Lab and a senior author of a paper on the research. “This opens up entirely new types of medical applications.”
The prototype device used in this research was about the size of a grain of rice, but the researchers anticipate that it could be made even smaller.
“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,” says Adib. “When they reach their highs at the same time, they are able to overcome the energy threshold needed to power the device.”
With their system, say the researchers, they 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 that 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.
“Having the capacity to communicate with these systems without the need for a battery would be a significant advance,” says Giovanni Traverso, an assistant professor at Brigham and Women’s Hospital (BWH), Harvard Medical School, a research affiliate at MIT’s Koch Institute for Integrative Cancer Research, and an author of the research paper.
“These devices could be compatible with sensing conditions as well as aiding in the delivery of a drug.”Such devices, say the researchers, could offer doctors new ways to diagnose, monitor, and treat many diseases. Traverso’s lab, for example, is currently working on a variety of ingestible systems that can be used to deliver drugs, monitor vital signs, and detect movement of the GI tract.
Looking ahead, the researchers are working on making the power delivery more efficient and transferring it over greater distances. This technology, say the researchers, 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 communication.
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