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Engineers Discover How To Make Antennas For Wireless Communication 100x Smaller Than Their Current Size (sciencemag.org)
Engineers have figured out how to make antennas for wireless communication 100 times smaller than their current size, an advance that could lead to tiny brain implants, micro-medical devices, or phones you can wear on your finger. Science Magazine reports: The new mini-antennas play off the difference between electromagnetic (EM) waves, such as light and radio waves, and acoustic waves, such as sound and inaudible vibrations. EM waves are fluctuations in an electromagnetic field, and they travel at light speed -- an astounding 300,000,000 meters per second. Acoustic waves are the jiggling of matter, and they travel at the much slower speed of sound -- in a solid, typically a few thousand meters per second. So, at any given frequency, an EM wave has a much longer wavelength than an acoustic wave. Antennas receive information by resonating with EM waves, which they convert into electrical voltage. For such resonance to occur, a traditional antenna's length must roughly match the wavelength of the EM wave it receives, meaning that the antenna must be relatively big. However, like a guitar string, an antenna can also resonate with acoustic waves. The new antennas take advantage of this fact. They will pick up EM waves of a given frequency if its size matches the wavelength of the much shorter acoustic waves of the same frequency. That means that that for any given signal frequency, the antennas can be much smaller. The trick is, of course, to quickly turn the incoming EM waves into acoustic waves.
The team created two kinds of acoustic antennas. One has a circular membrane, which works for frequencies in the gigahertz range, including those for WiFi. The other has a rectangular membrane, suitable for megahertz frequencies used for TV and radio. Each is less than a millimeter across, and both can be manufactured together on a single chip. When researchers tested one of the antennas in a specially insulated room, they found that compared to a conventional ring antenna of the same size, it sent and received 2.5 gigahertz signals about 100,000 times more efficiently, they report in Nature Communications.
The team created two kinds of acoustic antennas. One has a circular membrane, which works for frequencies in the gigahertz range, including those for WiFi. The other has a rectangular membrane, suitable for megahertz frequencies used for TV and radio. Each is less than a millimeter across, and both can be manufactured together on a single chip. When researchers tested one of the antennas in a specially insulated room, they found that compared to a conventional ring antenna of the same size, it sent and received 2.5 gigahertz signals about 100,000 times more efficiently, they report in Nature Communications.
The Chu Limit applies to passive antennas. The antenna described in your citation isn't passive; that "non-Foster" term means it's an active antenna. The phys.org title implying some sort of breakthrough physics is click bait.
The acoustic antenna they design is passive and does not exceed the Chu limit, keeping in mind that the Chu limit accounts for the speed of propagation, i.e. light vs sound.
From the Paper, "We note that the demonstrated ME antennas are pure passive devices, no impedance matching circuit, or an external power source was used during the measurement. And its maximum achievable bandwidth is within Chu–Harrington limit (Method)"
The whole thing is really about their novel magnetic piezo material and device construction. The Ultra-small antenna is just buzzword tack on that the new material work could enable.