Researchers at North Carolina State University have demonstrated a laser-powered plasma antenna that transmits radio signals without a conventional metal radiating element. Resembling a lightsaber, the device uses a laser to ionise air and create a thin plasma filament that transmitted a 30 MHz radio signal during laboratory tests. According to the study published in the IEEE Journal, titled ‘Laser-Induced-Plasma-Filament Antenna Transmitting 30 MHz VHF’, the received signal strength increased by approximately 2.5 times when the plasma filament was used as an antenna. The technology could eventually support reconfigurable antennas for satellites and aircraft, although further development is needed.
How does the laser-powered plasma antenna work
The antenna relies on a process in which a laser beam ionises air, producing a narrow channel of plasma known as a laser-induced plasma filament. The research paper explains that electrons become concentrated around the filament’s outer edges, giving the structure characteristics similar to those of a conventional electrical conductor. When electromagnetic energy is coupled into the filament, these electrons can support the propagation and radiation of electromagnetic waves.The researchers used a laser with a pulse duration of 100 femtoseconds, a repetition rate of 1 kilohertz and a pulse energy of approximately 5 millijoules. A converging lens with a focal length of two metres was used to produce a plasma filament measuring approximately 20 centimetres in length and 0.1 millimetres in diameter. These dimensions describe the experimental prototype rather than the larger antenna structures the researchers hope to develop in the future.
Plasma antenna transmits radio signals without direct contact
One of the main challenges was introducing a radio-frequency signal into the plasma filament without disrupting its structure. A conventional metal connection would distort the filament and interfere with its formation, so the researchers developed a capacitively coupled antenna feed that transfers electromagnetic energy without making direct contact with the plasma.The feed consists of a metal structure that generates an electromagnetic field around the filament. A radio-frequency generator supplies a 30 MHz signal to this structure, allowing the field to couple energy into the plasma. The resulting electromagnetic waves propagate along the filament and radiate outwards. The feed itself also has radiation characteristics, making it necessary for the researchers to distinguish its contribution from that of the plasma antenna.To test the arrangement, the team measured the received signal under two conditions. First, the laser was blocked, leaving the radio-frequency feed operating without the plasma filament. The researchers then repeated the measurements with the laser unblocked and the plasma filament present. A receiving antenna was positioned approximately five centimetres from the transmitter, with both antennas sharing the same linear polarisation and orientation.
How did researchers achieve 150% stronger radio signals
The experimental results showed that the received signal was stronger when the plasma filament was present and capacitively fed than when the laser was blocked. According to the research paper’s abstract, the received signal strength increased by approximately 2.5 times, equivalent to a reported increase of 150%, compared with the feed-only configuration.The researchers reported that the measurements supported the feasibility of using a laser-induced plasma filament as an antenna capable of radiating its own electromagnetic field. The conclusion of the paper states that the experiment represents the first demonstration of this concept to the authors’ knowledge. The work establishes a proof of concept for transmitting a 30 MHz radio-frequency signal; it does not demonstrate a fully developed antenna ready for operational use.The researchers noted that the laboratory-scale antenna had relatively low gain and lacked the beamforming precision required for operational synthetic-aperture radar systems or satellite and aircraft applications. Further work will focus on improving the antenna’s radiation performance, increasing the efficiency of the contactless feed and developing more accurate methods for characterising its electromagnetic properties.
How could plasma antennas improve satellite communications
The researchers are investigating whether laser-induced plasma filament antennas could eventually be used in satellites and aircraft. Antenna length influences the frequencies at which radio waves can be transmitted and received, but changing the length of a conventional antenna can be difficult in applications where space, weight and mechanical deployment are important constraints.Because the plasma filament is generated by a laser, its length can be controlled through the laser’s operating parameters. The NC State news release also describes the possibility of changing the filament’s direction by steering the laser beam. This could provide a means of adjusting antenna orientation without physically moving a conventional antenna structure. However, these capabilities are potential applications of the technique rather than fully demonstrated operational functions of the current prototype.
How could plasma antennas transmit and receive radio signals
The research paper discusses the longer-term possibility of producing plasma filaments several metres long or more for high-frequency and very-high-frequency applications, as well as very-low-frequency systems. It also identifies the possibility of using the same configuration as a receiving antenna, based on electromagnetic reciprocity; this capability remains to be validated in future work. The demonstration therefore establishes an initial step towards antennas whose radiating elements can be generated and reconfigured using laser-produced plasma. The researchers’ next task is to improve performance and address the technical limitations that remain before the technology can be considered for practical satellite or aircraft systems.
