S. Parameswaran

Experimental and theoretical results with plasma antennas

This report is a summary of an extensive research program on plasma antennas. We have found that plasma antennas are just as effective as metal antennas. In addition, they can transmit, receive, and reflect lower frequency signals while being transparent to higher frequency signals. When de-energized, they electrically disappear. Plasma noise does not appear to be a problem.

Atmospheric pressure resistive barrier cold plasma for biological decontamination

Steady-state atmospheric pressure nonthermal plasmas can splendidly debilitate bacteria in liquids, gases, and on surfaces, as well as can disintegrate hazardous chemicals. The nonthermal resistive barrier gas discharge at atmospheric pressure is currently investigated for low-temperature sterilization purposes. We have carried out electrical, chemical, optical, and biological studies of the discharge, with the intent of identifying the chemically and biologically active species produced. In this paper, we have demonstrated that effective decontamination can be achieved without causing any damage to the active media.

Advances in Plasma Antenna Design

Summary form only given. We have made significant progress in developing plasma antennas. Our antennas have been operating in the region 1 to 10 GHz. The basic advantages of plasma antennas over metal antennas are threefold. First, the plasma antennas are reconfigurable. When one plasma antenna is de-energized, the antenna reverts to a dielectric tube, and a second antenna can transmit through it. This allows us to use several large antennas stacked over each other instead of several small antennas placed next to each other. This results in better sensitivity and directivity. Second, the plasma antenna is stealthy. When de-energized, the plasma antenna does not reflect incident, probing RADAR signals. Third, the plasma antenna is resistant to electronic warfare. An operating plasma antenna can be at the same time transparent and immune to incident high frequency, high power electronic warfare pulses. The question is, how well do plasma antennas operate? Our tests at the Malibu Research Corporation in California have shown that an energized plasma reflector is essentially as effective as a metal reflector. However, when de-energized, the reflected signal drops by over 20 dB. Three remaining questions are, first, how to increase the operating plasma density without overloading the plasma discharge tubes? Second, how can we reduce the power required? And third, how can we reduce plasma noise caused by the ionizing power supply.

An experimental study of ball lightning

This paper presents a study of one possible form of ball lightning. Plasma spheres several centimeters in diameter were produced in atmospheric pressure air. These spheres persisted for up to a half-second after the power supply was turned off. A mathematical theory was derived that predicts the observed lifetime. The theory predicts that the sphere lifetime should scale as the sphere radius squared, which means that large spheres should persist for many seconds.

An observation of synthetic ball lightning

Ball lightning has been extensively researched for many centuries. Here, in this paper, we present one form of ball lightning where plasma spheres several centimeters in diameter were produced in atmospheric pressure air. These spheres persisted for up to a half second after the power supply was turned off. A mathematical theory was derived that predicts the observed lifetime. The theory predicts that the sphere lifetime should scale as the sphere radius squared, which means that large spheres should persist for many seconds.

Ambient pressure resistive barrier cold plasma discharge for biological and environmental applications

Summary form only given. We have carried out electrical, chemical, optical, and biological studies on both He and atmospheric air plasma. A microwave absorption method was used for average electron density measurements. The ion measurements were done by collecting the ion current over an interval in time in a capacitor, and measuring the collected charge with a nanometer after the discharge was turned off. This method prevents RF noise from the discharge from jamming the nanometer. The measurements indicated that an ion density of 10/sup 12/ ions per cubic centimeter was present in the discharge. The results of both He and atmospheric air plasma show that the overwhelming production was of ozone. A trace of NO was found. The analysis of optical characteristics shows that the far ultraviolet light production was negligible as compared to that of a 150 Watt mercury arc in a quartz tube. Biological studies have been carried out with samples of XL-1Blue/sup TM/, E. coli and attained promising results.

Experimental results of plasma antennas

Summary form only given. Considerable progress has been made on plasma antennas of which the major advances are: operation at higher plasma densities in the steady state, considerable reduction of power consumption and reduction of noise from the electrical current, which generates the plasma. We have performed experiments concerning transmission and reception, stealth, reconfigurability, shielding, protection from electronic warfare, mechanical robustness, mechanical reconfigurability, plasma waveguides and noise reduction of plasma antennas. In the past, our plasma tubes were ionized by steady state DC current. If the tubes are ionized by extremely short bursts of DC current, we find that the plasma is produced in an extremely short time of about 2 microseconds. However, the plasma persists for a much longer time of about 1/100 second. This is the reason why fluorescent lamps can operate on 60 or 50 Hz electric power. In the new mode of operation, we observe that the plasma density produced by the pulsed power technique is considerably higher than the plasma density produced by the same power supplied in the steady state, which produces two beneficial results: we can operate at much higher plasma densities and at several giga Hertz. In addition, we can operate during the long, non-current carrying phase, which should not have noise generated by current-driven instabilities. We have also operated our plasma antennas at several megawatts using a spark-gap-driven separate RF power supply. We find that even at very high power levels, the plasma antenna operates as efficiently as a metal antenna. We also find that with the proper operating mode, the plasma antenna will not ignite even in the presence of a megawatt RF field. In conclusion, our recent inclusion of a pulsed power supply for our plasma tubes provides reduced noise, higher steady state DC plasma density and reduced power consumption. There are possibly minor problems because of a slight plasma density fluctuation during the pulsing cycle, which will be addressed in the future work

Atmospheric Pressure Resistive Barrier Cold Plasma for Biological Decontamination

Steady-state atmospheric pressure nonthermal plasmas can splendidly debilitate bacteria in liquids, gases, and on surfaces, as well as can disintegrate hazardous chemicals. The nonthermal resistive barrier gas discharge at atmospheric pressure is currently investigated for low-temperature sterilization purposes. We have carried out electrical, chemical, optical, and biological studies of the discharge, with the intent of identifying the chemically and biologically active species produced. In this paper, we have demonstrated that effective decontamination can be achieved without causing any damage to the active media.

A simple model of ball lightning

Summary form only given, as follows. We have completed a simple model of ball lightning that includes a theory, a scaling law, an experimental measurement of the lifetime, and photographs of the discharge. The conclusion is that a sphere 10 cm in radius should persist for about 1 sec. The scaling law predicts that the lifetime scales as the radius squared.

Characteristics of the steady-state atmospheric pressure DC discharge

Summary form only given, as follows. We have carried out chemical, optical, and electrical studies of the steady-state, atmospheric pressure DC discharge, with the intent of identifying the chemically and biologically active species produced. The first investigation was a discharge in air. Chemical analysis was performed by a commercial unit used in environmental monitoring. Our results comprise measurements of ozone, NO, NO/sub 2/, and methane. The results show that the overwhelming production was of ozone. A trace of NO was found. No NO/sub 2/ or methane was found. The optical investigation was looking for far (chemically active) ultra violet light. As a tool we used a crystal of calcite (calcium carbonate) naturally activated with mercury. This crystal is phosphorescent for several seconds when activated with far ultraviolet, but ignores near (chemically inactive) ultraviolet or visible light. The result is that the far ultraviolet light production was negligible as compared to that of a 150-Watt mercury arc in a quartz tube.