By Jof Enriquez
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By coupling the acoustic resonance of a small antenna with the electromagnetic wave, researchers at the Air Force Research Laboratory Materials and Manufacturing Directorate have succeeded in scaling antenna sizes down to 90 percent smaller than state-of-the art compact antennas. The ultra-compact antenna design could find myriad applications in electronic devices used by military and civilian organizations.
Standard small antennas rely on electromagnetic wave resonance and can be shrunk no smaller than 1/10th of the electromagnetic (EM) wavelength. The long-standing challenge for researchers, including those in the U.S. military, has been to push past that limit and build antennas as small as 1/10,000 of the EM wavelength.
“We identified ultra-compact antennas as the critical last step in true device miniaturization,” said Dr. Brandon Howe, AFRL materials scientist. “Researchers had successfully shrunk most electronic components, but the true miniaturization of antennas was still a missing piece.”
Scientists know that it is possible to make tinier antennas if they are made to resonate with much shorter acoustic waves, rather than with electromagnetic waves alone. So, the AFRL scientists made acoustically actuated ultra-compact NEMS magnetoelectric (ME) antennas that receive and transmit electromagnetic waves through the ME effect at their acoustic resonance frequencies.
"We miniaturized the antennas by borrowing a trick from acoustic filters in cellphones, which convert microwave voltages to strain waves. Strain waves travel much slower than the speed of light, so by doing this, we are able to shrink the wavelengths while keeping the frequency the same. This allowed us to make the antennas much smaller," said Dr. Michael McConney, an AFRL materials scientist.
The AFRL team, with help from colleagues from Northeastern University, claims to have reduced the size of a standard small antenna by over 90 percent.
"The ME antennas (with sizes as small as one-thousandth of a wavelength) demonstrates 1-2 orders of magnitude miniaturization over state-of-the-art compact antennas without performance degradation," said the researchers, who coated conventional bulk acoustic wave filters with a low-loss, highly-sensitive magnetic material to convert slower strain waves to radiation, in order to retain efficiency as they shrunk the antennas from roughly a half inch to less than one millimeter in size.
The miniaturized antenna design could find many military and commercial communication applications, including wearable antennas, bio-implantable and bio-injectable antennas, smart phones, and wireless communication systems, according to the Air Force.
"The miniaturization of military electronics is of significant benefit to the warfighter, not only in terms of device size, but in transportability, space requirements, weight, and many factors," said Howe. "It can allow us to fit more into a given space, whether that be in a field pack or on an aerial platform. It gives us greater capability in a smaller space."