Absorption of Microwaves in Low Intensity Eucalyptus Litter Fire


A fuel bed was constructed where various vegetation species could be used as combustion fuel. The fuel bed was equipped with a thermocouple to measure fire temperature and a two-port automatic network analyser to measure microwave scattering parameters in flame medium. The parameters are then used to determine microwave propagation characteristics in fire. The measurements have implications on radio wave communication during wildfire suppression and in remote sensing. The attenuation data also provide an estimation of vegetation fire ionisation and conductivity. Eucalyptus litter fire with a maximum flame temperature of 976 K was set on the fuel bed and X-band microwaves (7.00 - 9.50 GHz) were caused to propagate through the flame. Attenuation of 0.35 - 0.90 dB was measured for microwaves in the frequency range. For the low intensity fire, conductivity was measured to range from 0.00021 - 0.00055 mho/m and electron density was to be the range of 1.83 - 2.24 × 1015 m-3.

Share and Cite:

Letsholathebe, D. and Mphale, K. (2015) Absorption of Microwaves in Low Intensity Eucalyptus Litter Fire. Journal of Electromagnetic Analysis and Applications, 7, 217-224. doi: 10.4236/jemaa.2015.78023.

Conflicts of Interest

The authors declare no conflicts of interest.


[1] Santoru, J. and Gregorie, D.J. (1993) Electromagnetic Wave Absorption in Highly Collisional Plasma. Journal of Applied Physics, 74, 3736-3743.
[2] Schneider, J. and Hofmann, F.W. (1959) Absorption and Dispersion of Microwaves in Flames. Physical Review, 116, 244-249.
[3] Belcher, H. and Sudden, T.M. (1950) Studies on the Ionisation Produced by Metallic Salts in Flames II. Reactions Governed by Ionic Equilibrium in Coal-Gas/Air Flames Containing Alkali Metal Salts. Proceedings of the Royal Society of London Series A, 202, 17-39.
[4] Radojevic, M. (2003) Chemistry of Forest Fires and Regional Haze with Emphasis on Southeast Asia. Pure and Applied Geophysics, 12, 157-187.
[5] Jensen, A.P., Frandsen, F.J., Dam-Johansen, K. and Sander, B. (2000) Experimental Investigation of the Transformation and Release to Gas Phase of Potassium and Chlorine during Straw Pyrolysis Conditions. Energy and Fuels, 11, 1026-1032.
[6] Mphale, K.M., Heron, M. and Verma, T. (2007) Effect of Wildfire Induced Thermal Bubble on Radio Communications. Progress in Electromagnetics Research (PIER), 68, 197-228.
[7] Boan, J. (2007) Radio Experiments with Fire. IEEE Antennas Wireless Propagation Letters, 6, 411-414.
[8] Williams, D.W., Adams, J.S., Batten, J.J., Whitty, G.F. and Richardson, G.T. (1970) Operation Euroka: An Australian Mass Fire Experiment. Report 386, Defense Standards Laboratory, Maribyrnor.
[9] Boan, J. (2006) Radio Communication in Fire Environments. Proceedings of the Wars 2006 Conference, Leura,
[10] Hata, M. and Shigeyuki, D. (1983) Propagation Tests for 23GHz and 40 GHz. IEEE Journal on Selected Areas in Communications, 1, 658-673.
[11] Okuno, T., Sonoyama, N., Hayashi, J., Li, C., Sathe, C. and Chiba, T. (2005) Primary Release of Alkali and Alkaline Earth Metallic Species during Pyrolysis of Pulverized Biomass. Energy and Fuels, 19, 2164-2171.
[12] Nesterko, N.A. and Taran, E.N. (1971) Ionization and Radiation of Alkali Metals in Acetylene—Air Flame Plasma, with Halogen Additions. Journal of Applied Spectroscopy, 14, 242-244.
[13] Vodacek, A., Kremens, R.L., Fordham, S.C., Van Gorden, S.C., Luisi, D., Schott, J.R. and Latham, D.J. (2002) Remote Optical Detection of Biomass Burning Using Potassium Emission Signature. International Journal of Remote Sensing, 23, 2721-2726.
[14] Latham, D. (1999) Space Charge Generated by Wind Tunnel Fires. Atmospheric Research, 51, 267-278.
[15] Alkemade, M.A. (1979) Fundamentals of Analytical Flame Spectroscopy. Hilger, Bristol.
[16] Bjorkmann, E. and Stromberg, B. (1997) Release of Chlorine from Biomass at Pyrolysis and Gasification Conditions. Energy and Fuels, 11, 1026-1032.
[17] Mphale, K.M. and Heron, M. (2008) Nonintrusive Measurement of Ionization in Vegetation Fire Plasma. European Physical Journal: Applied Physics, 41, 157-164.
[18] Uhm, H.S. (1999) Properties of Plasmas Generated by Electrical Breakdown in Flames. Physics of Plasmas, 6, 4366-4374.
[19] Sicha, M. (1979) Measurement of the Electron Energy Distribution Function in a Flame Plasma at Atmospheric Pressure. Czechoslovak Journal of Physics, 29, 640-645.
[20] Kadaba, P.K. (1984) Simultaneous Measurements of Complex Permittivity and Permeability in the Millimeter Region by a Frequency-Domain Technique. IEEE Transactions on Instrumentation and Measurement, 33, 336-347.
[21] Varadan, V.V., Jose, K.A. and Varadan, V.K. (2000) In Situ Microwave Characterization of Nonplanar Dielectric Objects. IEEE Transactions on Microwave Theory and Techniques, 48, 388-394.
[22] Koretzsky, E. and Kuo, S.P. (1998) Characterization of an Atmospheric Pressure Plasma Generated by a Plasma Torch Array. Physics of Plasmas, 5, 3774-3780.
[23] Adler, F.P. (1954) Measurement of Conductivity of a Jet Flame. Journal of Applied Physics, 25, 903-908.

Copyright © 2022 by authors and Scientific Research Publishing Inc.

Creative Commons License

This work and the related PDF file are licensed under a Creative Commons Attribution 4.0 International License.