The 4-inch-tall device could be used in portable transmitter...
Physics

The 4-inch-tall system might be utilized in moveable transmitter…

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A brand new sort of pocket-sized antenna, developed on the Division of Vitality’s SLAC Nationwide Accelerator Laboratory, might allow cellular communication in conditions the place typical radios do not work, resembling underneath water, via the bottom and over very lengthy distances via air.

The system emits very low frequency (VLF) radiation with wavelengths of tens to tons of of miles. These waves journey lengthy distances past the horizon and might penetrate environments that might block radio waves with shorter wavelengths. Whereas in the present day’s strongest VLF expertise requires gigantic emitters, this antenna is barely 4 inches tall, so it might doubtlessly be used for duties that demand excessive mobility, together with rescue and protection missions.

“Our device is also hundreds of times more efficient and can transmit data faster than previous devices of comparable size,” stated SLAC’s Mark Kemp, the mission’s principal investigator. “Its performance pushes the limits of what’s technologically possible and puts portable VLF applications, like sending short text messages in challenging situations, within reach.”

The SLAC-led crew reported their outcomes in the present day in Nature Communications.

A large problem

In trendy telecommunications, radio waves transport info via air for radio broadcasts, radar and navigation methods and different functions. However shorter-wavelength radio waves have their limits: The sign they transmit turns into weak over very lengthy distances, cannot journey via water and is definitely blocked by layers of rock.

In distinction, the longer wavelength of VLF radiation permits it to journey tons of of ft via floor and water and hundreds of miles past the horizon via air.

Nonetheless, VLF expertise additionally comes with main challenges. An antenna is best when its measurement is akin to the wavelength it emits; VLF’s lengthy wavelength requires huge antenna arrays that stretch for miles. Smaller VLF transmitters are a lot much less environment friendly and might weigh tons of of kilos, limiting their supposed use as cellular gadgets. One other problem is the low bandwidth of VLF communication, which limits the quantity of knowledge it could possibly transmit.

The brand new antenna was designed with these points in thoughts. Its compact measurement might make it attainable to construct transmitters that weigh only some kilos. In assessments that despatched alerts from the transmitter to a receiver 100 ft away, the researchers demonstrated that their system produced VLF radiation 300 instances extra effectively than earlier compact antennas and transmitted knowledge with nearly 100 instances higher bandwidth.

“There are many exciting potential applications for the technology,” Kemp stated. “Our device is optimized for long-range communication through air, and our research is looking at the fundamental science behind the method to find ways to further enhance its capabilities.”

A mechanical antenna

To generate VLF radiation, the system exploits what is called the piezoelectric impact, which converts mechanical stress to a buildup {of electrical} cost.

The researchers used a rod-shaped crystal of a piezoelectric materials, lithium niobate, as their antenna. After they utilized an oscillating electrical voltage to the rod it vibrated, alternately shrinking and increasing, and this mechanical stress triggered an oscillating electrical present whose electromagnetic vitality then bought emitted as VLF radiation.

The electrical present stems from electrical costs transferring up and down the rod. In typical antennas, these motions are near the identical measurement because the wavelength of the radiation they produce, and extra compact designs sometimes require tuning models bigger than the antenna itself. The brand new strategy, then again, “allows us to efficiently excite electromagnetic waves with wavelengths that are much larger than the motions along the crystal and without large tuners, which is why this antenna is so compact,” Kemp stated.

The researchers additionally discovered a intelligent manner of tweaking the wavelength of the emitted radiation, he stated: “We repeatedly switch the wavelength during operation, which allows us to transmit with a large bandwidth. This is key to achieving data transfer rates of more than 100 bits per second — enough to send a simple text.”

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