Engineers transmitted radio through a laser-made plasma filament instead of a metal antenna

The plasma-filament antenna starts with a laser aimed through ordinary air. Prya Darshni, a doctoral student and the paper’s corresponding author, says “it is the first time anyone has ever demonstrated that plasma-filament antennas can work,” a claim the team rests on a short-range laboratory test.

The result is a lab proof of concept, a short-range test of one frequency, and the team is explicit about what remains unshown. Nothing about it is ready to replace a mast or a satellite whip.

A column of ionized air that behaves like a wire

North Carolina State University engineers have transmitted a radio signal at 30 megahertz through a plasma filament made by a laser, a thin column of ionized air, which serves as the radiating element in place of a conventional metal antenna. According to the ScienceDaily copy of the university’s release, the team sets the laser’s power and beam diameter so that a narrow channel of air is ionized, producing what the researchers call a plasma filament. That filament conducts electricity well enough to radiate when a radio-frequency signal reaches it. The demonstration used a transmission at 30 megahertz, which sits in the very high frequency band.

The appeal, in the researchers’ account, is that the antenna is defined by the laser rather than by a fixed piece of hardware. Darshni says that controlling the laser’s parameters controls the characteristics of the plasma filament, and the filament’s length in turn sets which frequencies it can handle. She also describes the device in plain terms: “The plasma beam antenna looks like a lightsaber and is tunable,” a line The Debrief quotes. Conventional antennas are cut or built to suit particular wavelengths, so a length that can be changed with laser settings alone is the feature the team stresses most.

Steering works the same way. Shifting the direction of the laser changes the angle of the antenna, which Darshni says could suit radar sweeps or improving received signal strength, without any mechanical extension, retraction or rotation of a physical structure. Dogariu, who is affiliated with Texas A&M University and Princeton University, contributed to the experimental measurements, and NC State Instrument Shop staff Chris Hewett, Byron Goode and Joe McElveen are credited with manufacturing the components used in the setup, which gives a sense of how bespoke the apparatus still is.

The metal ring behind the claim

The idea of dropping the metal antenna needs one qualification, which the NC State release supplies. Radio energy gets into the filament through a metal ring that acts as a capacitor, with the laser passing through the ring’s center. A radio-frequency generator drives the capacitor, the resulting electromagnetic field couples to the plasma, and the filament then transmits at the chosen frequency. The release says direct metal contact would distort the plasma, which is why the feed is contactless.

So the radiating element is air, but the system around it still contains a metal ring, a signal generator and a laser. The accurate claim is that the part of the apparatus doing the radiating is a plasma filament and not a metal conductor. Whether the whole assembly ends up lighter or simpler than a conventional antenna is not something the sources address, and the release gives no figures for the laser’s type, power, or the filament’s length.

What a five-centimeter test showed

The study itself, “Laser-Induced-Plasma-Filament Antenna Transmitting 30 MHz VHF” by Darshni, Arthur Dogariu of Texas A&M University and Princeton University, and NC State’s Paul D. Franzon, appeared in IEEE Journal of Microwaves and is open access. According to the NC State release’s summary of the abstract, the transmitter and receiver were linearly polarized in the same orientation and sat about five centimeters apart in the near field. The received signal was 2.5 times stronger, a 150 percent increase, with the plasma antenna running than with the laser blocked. Short range matters here because a near-field reading at five centimeters says little about how a signal would travel across a room, let alone to an aircraft or satellite, and the sources report no longer-range figures.

That is a modest test by the standards of radio engineering, and the authors do not present it as more. On reception, Darshni says plainly that the team has “not demonstrated its ability to serve as an antenna that can receive radio signals.” She adds that there is no reason to believe it would not work as a receiver, but that remains an expectation and not a measurement. Operation across a broad range of frequencies also still needs testing, the release notes.

Space ambitions and an earlier patent

The researchers point to satellites and spacecraft, where weight and size limits make deployable antennas awkward. Franzon is quoted saying that “in low earth orbit, there is sufficient air to form a plasma,” though the release treats this as a possibility and says nothing of performance in actual space conditions. Darshni says the next job is optimization, since showing the idea is possible lets the team begin improving its performance.

The priority claim deserves a footnote. A U.S. Navy patent, Patent 11,024,950, granted in June 2021, describes antennas built on laser-induced plasma filaments in air, including dipole arrangements, and its claims cover femtosecond-laser designs. That patent is a paper description and not a reported transmission, and The Debrief, which covered the NC State work on October 9, repeats Darshni’s “first” without checking it against earlier work. Whether the NC State test is the first measured radio transmission through such a filament is therefore Darshni’s assertion, and the open question is how the filament performs once a receiver sits farther than five centimeters away.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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