Antennas just got a whole lot smaller.
Tiny chips that communicate via radio waves are a tenth to a hundredth the length of current state-of-the-art compact antennas. At only a couple hundred micrometers across — comparable to the thickness of a piece of paper — these next-gen antennas can relay the same types of signals as those used by TVs, cell phones and radios, researchers report August 22 in Nature Communications. The technological advance could pave the way to create wearable, or even injectable, electronics, says study coauthor Nian Sun, an electrical and computer engineer at Northeastern University in Boston.
Antenna miniaturization has been stalled out for decades, so these minuscule devices are “a huge deal,” says John Domann, who wasn’t involved in the work.
A traditional antenna picks up signals when electromagnetic waves moving through the air wash over it, causing the antenna’s electrons to flow through it in an electric current. That current creates an electric voltage, essentially a readout of whatever message those electromagnetic waves carried.
But the longer the wavelength, the longer an antenna must be to generate a voltage big enough to convey that message clearly, explains Domann, a biomedical engineer at Virginia Tech in Blacksburg. A conventional antenna typically needs to be at least one-tenth the length of the electromagnetic waves it’s picking up. For instance, cell phones tuned into 11- to 15-centimeter-long radio waves have to contain antennas at least a few centimeters long to get good reception.
In the new study, researchers overcame that long-standing size limit by fashioning antennas that use a different method to translate signals. When electromagnetic waves pass over one of these chip antennas, the waves activate atoms in a layer of magnetic material. Similar to the way sport spectators stand and sit to create waves that ripple across a stadium, the atoms switch their magnetic alignments back and forth to create a magnetic current that runs through the chip.
That magnetic current vibrates an underlying layer of piezoelectric material — a kind of material that generates voltage when bent or squeezed (SN Online: 9/1/15). Since the vibrations create much shorter waves than those from incoming airborne electromagnetic signals, an antenna can be much smaller and still work.
Researchers built tiny antennas that could communicate at the radio frequency ranges used by GPS, Wi-Fi, FM radio and broadcast TV. These newfangled antennas have “enormous potential,” Sun says. He imagines attaching them to devices that could be embedded in people’s clothing or even inside their bodies (SN: 9/10/11 p. 10). “You can also design really, really compact GPS receivers,” he adds, which could help track everything from easily misplaced household items to military equipment.
Domann says he’s most excited about potential biomedical uses for these antennas. “You could imagine some sort of a device where you have an implantable lab-on-a-chip, where you have something inside of a patient that can actively monitor them and then relay information to their physician in real time.”