This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers have demonstrated a technique that uses a laser to produce a plasma beam antenna capable of transmitting radio waves. The article, "Laser-Induced-Plasma-Filament Antenna Transmitting 30 MHz VHF," is published in the IEEE Journal of Microwaves.
"The plasma beam antenna looks like a lightsaber and is tunable, meaning we should be able to transmit across a broad range of frequencies," says Prya Darshni, corresponding author and a Ph.D. student at North Carolina State University. "And while we have not demonstrated its ability to serve as an antenna that can receive radio signals, there's no reason to believe it wouldn't also work as a receiver." "This is an exciting new concept that enables one to be able to have a customized antenna without complex mechanical deployment mechanisms," says Paul Franzon, co-author of the paper and the Cirrus Logic distinguished professor of electrical and computer engineering at NC State. The length of an antenna is important because it controls the frequencies at which radio waves can be transmitted and received.
But manipulating the length of antennas to sweep a desired range of frequencies can be challenging in some applications—such as space exploration technologies. "One of the questions we wanted to explore with this work was whether it would be possible to create plasma antennas using lasers, which would allow us to generate antennas at whatever length was needed," says Darshni. "And we have now shown that it is possible." By firing a laser beam of a specific power and diameter, the researchers are able to ionize a thin beam of air, creating a defined shaft of plasma called a plasma filament.
But to make the plasma antenna a practical tool, the researchers also needed to develop a way to connect the antenna to radio technology to transmit a radio signal. To solve that problem, the researchers also created and demonstrated a contactless antenna feed, which consists of a metal ring that serves as a capacitor. The laser passes through the ring, creating a plasma filament that is surrounded by the capacitor.
By generating an electromagnetic field with the capacitor, the researchers are able to interact with the plasma beam without touching it. Altogether, the process works like this: A radio-frequency generator feeds a signal into the capacitor, generating the appropriate electromagnetic field, which then causes the plasma filament antenna to transmit radio waves at the appropriate frequency. "By controlling the parameters of the laser, you can control the characteristics of the plasma filament—including its length," says Darshni.
"This is valuable for applications where you need an antenna that can sweep all frequencies. But there's another benefit as well. "There are also applications where it is important to be able to control the angle of the antenna, in order to target the direction of radar sweeps or to improve the strength of a signal you want to pick up," says Darshni.
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