NC State: laser plasma filament antenna transmits 30 MHz

Researchers at North Carolina State University have demonstrated a technique that uses a laser to produce a plasma beam antenna capable of transmitting radio waves, according to news.ncsu.edu. The work is published open access in the IEEE Journal of Microwaves under the title "Laser-Induced-Plasma-Filament Antenna Transmitting 30 MHz VHF" ncsu.edu. Authors say it is the first demonstration of this concept ncsu.edu.

The study was led by Ph.D. student Prya Darshni together with Paul Franzon. Arthur Dogariu of Texas A&M University and Princeton University helped with measurements ncsu.edu.

How the plasma antenna works

A laser beam of a specific power and diameter ionizes a thin beam of air and creates a defined shaft of plasma, called a plasma filament ncsu.edu. According to the authors, electrons on the edge of the filament behave like the skin electrons of a conductor, so the filament has the basic elements needed to act as an antenna ncsu.edu.

A direct metallic contact would distort the filament, so the team built a contactless feed. It is a metal ring that acts as a capacitor; the laser passes through the ring, and the plasma filament is surrounded by it ncsu.edu. A radio-frequency generator feeds a signal into the capacitor, which creates an electromagnetic field, and the field makes the filament transmit radio waves at the required frequency ncsu.edu.

The authors state that the laser parameters set the properties of the filament, including its length. Length matters because it determines the frequencies an antenna can transmit and receive ncsu.edu. The angle of the antenna can be changed by shifting the direction of the laser, that is, by beam steering ncsu.edu.

Measurement results

In the experiment, a 30 MHz signal was fed into the filament through the capacitive feed ncsu.edu. The transmitting filament and the receiving antenna were linearly polarized with the same orientation and placed about 5 cm apart, within the unobstructed near field ncsu.edu. The received signal strength was first recorded with the capacitive feed alone, with the laser blocked, and then with the filament present ncsu.edu. With the filament as the antenna, the signal strength increased 2.5 times (150%) ncsu.edu.

The team has not demonstrated reception of radio signals by the plasma antenna, though Darshni says there is no reason to believe it would not work as a receiver ncsu.edu. The paper also examines the feasibility of such antennas for HF/VHF applications on small to large satellites and aircraft. Franzon notes that in low Earth orbit there is enough air to form a plasma ncsu.edu. According to Darshni, the next step is to improve the antenna's performance ncsu.edu.

NC State demonstrates a laser-induced plasma filament antenna transmitting 30 MHz radio waves in the lab

How the plasma antenna works

Measurement results

Sources · 2

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