Tiny Battery-Free Implantable Devices Powered Wirelessly Using Radio Frequency Waves
Scientists at MIT have developed a wireless system that can power tiny implantable devices in the body, without the need for batteries. The system relies on radiofrequency waves emitted by an antenna outside the body, which can then power the implants from as far away as one meter and as deep as 10 cm below the body surface. At present, the devices are as small as a grain of rice, but because they do not require a battery, the researchers believe that they could be miniaturized further. The system could provide power for a variety of implantable sensors and drug delivery devices.
One of the current limitations of electronic implantable devices is the need to include a battery or pass wires through the skin. Both of these approaches have safety issues, and wires limit where a device can move or be implanted, whereas batteries limit how small a device can be and come with a limited lifespan.
To address these issues, the MIT researchers have developed a way to wirelessly power an implantable device, using radiofrequency waves. This has been difficult to achieve so far, because the waves tend to dissipate during their journey through the body. However, by using a variety of antennas that emit radio waves at different frequencies, the researchers were able to make them combine and overlap so that they produce enough energy to power a device.
“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. When they reach their highs at the same time, they are able to overcome the energy threshold needed to power the device,” said Fadel Adib, a researcher involved in the study. “Even though these tiny implantable devices have no batteries, we can now communicate with them from a distance outside the body. This opens up entirely new types of medical applications.”
The system has significant potential. From powering ingestible devices, such as smart drug delivery capsules and gastrointestinal sensors, to brain implants for deep brain stimulation or optogenetics, wireless power would provide a huge advantage.
The researchers are currently working to increase the range of the system. So far, they can achieve wireless power up to 10 cm deep in the body from antennas up to 1 meter away, but if the sensor is placed just under the skin, the range increases to 38 meters. “There’s currently a tradeoff between how deep you can go and how far you can go outside the body,” said Adib.