Tiny Membrane-Based Acoustic Antennas Could Shrink Electronic Devices

By Jof Enriquez,
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Nanoelectromechanical system (NEMS) antennas that resonate with acoustic waves, rather than with electromagnetic waves alone, could significantly reduce the size of electronic devices, according to a team of scientists at Northeastern University in Boston.

State-of-the-art compact antennas rely on electromagnetic wave resonance, which limits their miniaturization to one-tenth of the EM wavelength. However, further reduction of antenna size — to as small as one-thousandth of the wavelength — is possible if antennas are made to resonate with much shorter acoustic waves, according to the research team who designed the new antenna system.

In order to achieve this, a piezomagnetic layer of iron, gallium, and boron in the antenna picks up an incoming EM wave and converts it into acoustic vibrations. The piezomagnetic material is paired with a piezoelectric material, which converts the vibrations to an oscillating electrical voltage. If transmitting, the antenna vibrates under an alternating voltage input, which generates a magnetic current, which then radiates EM waves.

Since these NEMS antennas operate at their acoustic resonance, which is five orders of magnitude shorter than the EM wavelength, it is then possible to make antenna sizes much smaller than state-of-the-art antennas, without performance degradation.

In experiments detailed in Nature Communications, one antenna sent and received 2.5 gigahertz signals about 100,000 times more efficiently than a conventional ring antenna of the same size. Each antenna is less than a millimeter across. Both types — one with a circular membrane for frequencies in the gigahertz range, and one with a rectangular membrane for megahertz frequencies — can be fabricated together on a single chip.

“This acoustic antenna concept changes the fundamental principle on which antennas have been designed for over a century, and can lead to dramatically compact antennas with improved performance,” says study senior author Nian-Xiang Sun, an electrical engineer and materials scientist at Northeastern, reports Spectrum.

This design, which relies on relatively simple electronic circuitry and does not require batteries, would make it possible to manufacture tiny antennas systems for internet of things, wearable antennas, smart phones, wireless communication systems, ingestible devices, and injectable implants, according to the researchers.

Sun is collaborating with Massachusetts General Hospital to integrate these tiny antennas into brain implants to treat epilepsy, and to create brain-computer interfaces he described as "like science fiction" into reality, reports Science Magazine.

Challenges include the inherent difficulty in fabricating antennas in miniaturized scale, and potential heating of biological implants that can damage tissue.

“These are the first magnetoelectric antennas that have been demonstrated, which are not perfect,” Sun told Spectrum. “We see a lot of room of improvement.”