Control of Plasma Collision Frequency for Alleviation of Signal Degradation

Hoffman, J.

doi:10.1109/tcom.1966.1089325

Cited by 8 publications

(3 citation statements)

References 2 publications

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“…When the probe signal of an interferometer is HF or VHF, radio waves (u eff /x) [ 1 and (x p /x) [ 1. In this case, propagation theory, e.g., in Hofmann 1966, predicts transmission through a wildfire with significant attenuation.…”

Section: Theorymentioning

confidence: 99%

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Interferometric measurement of ionization in a grassfire

Mphale

Heron

Ketlhwaafetse

et al. 2010

Meteorol Atmos Phys

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Grassfire plumes are weakly ionized gas. The ionization in the fire plume is due to thermal and chemiionization of incumbent species, which may include graphitic carbon, alkalis and thermally excited radicals, e.g., methyl. The presence of alkalis (e.g., potassium and sodium) in the fires makes thermal ionization a predominant electron producing mechanism in the combustion zone. Alkalis have low dissociation and ionization potentials and therefore require little energy to thermally decompose and give electrons. Assuming a Maxwellian velocity distribution of flame particles and electron-neutral collision frequency much higher than plasma frequency, the propagation of radio waves through a grassfire is predicted to have attenuation and phase shift. Radio wave propagation measurements were performed in a moderate intensity (554 kW m-1) controlled grassfire at 30-and 151-MHz frequencies on a 44 m path using a radio wave interferometer. The maximum temperature measured in the controlled burn was 1071 K and the observed fire depth was 0.9 m. The radio wave interferometer measured attenuation coefficients of 0.033 and 0.054 dB m-1 for 30-and 151-MHz, respectively. At collision frequency of 1.0 9 10 11 s-1 , maximum electron density was determined to be 5.061 9 10 15 m-3 .

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Section: Theorymentioning

confidence: 99%

“…The researchers acknowledged that very high intensity wildfires could significantly affect radio signal strength due to heat-generated weakly ionized plasma in the plume. The generated plasma may lead to communication malfunction or even blackout (see for example , Hofmann 1966).…”

Section: Introductionmentioning

confidence: 99%

Interferometric measurement of ionization in a grassfire

Mphale

Heron

Ketlhwaafetse

et al. 2010

Meteorol Atmos Phys

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“…[2,3] In order to clarify the phenomenon, the non-steady interaction of plasma with the aircraft in its near wake region has been studied. [4] Hoffman [5] indicated that the interaction of an electromagnetic wave with the flame and reentry plasma has received considerable attention because of the need to maintain the effective linkage between a station and a space vehicle. In the past, microwave and radio waves were widely used as the means of communication, thus much research was conducted on microwave and radio wave attenuation.…”

Section: Introductionmentioning

confidence: 99%

Absorption characteristic of arc plasma in the infrared region

陈云云¹,

宋旸²,

李振华³

et al. 2011

Chinese Phys. B

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In this paper, argon arc plasma is chosen as an example to study the absorption characteristics of arc plasma in the infrared region. Firstly, the phase and the attenuation constants are deduced for the given temperature, pressure and probe wavelength regions. Based on those constants, the dependence of the attenuation constant on the temperature and pressure in the vicinity of a certain probe wavelength is found. Then, theoretical analysis and discussion are conducted. Maximal absorption occurs at the position where the contributions of neutral particles and electrons come to a balance in a physical point of view, which may provide some measures to take for decreasing or controlling the plasma absorption of electromagnetic waves.

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Ectopic rhythms originating anteriorly in the left atrium

Mirowski

1967

American Heart Journal

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Control of Plasma Collision Frequency for Alleviation of Signal Degradation

Cited by 8 publications

References 2 publications

Interferometric measurement of ionization in a grassfire

Interferometric measurement of ionization in a grassfire

Absorption characteristic of arc plasma in the infrared region

Ectopic rhythms originating anteriorly in the left atrium

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