Abstract
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.
Highlights
Vegetation fires are slightly ionised gaseous medium
When the ionised medium is illuminated with microwaves, incumbent electrons are accelerated by electric field set by the incident electromagnetic energy
The electrons undergo repetitive collisions with relatively stationary heavier neutral incumbent flame particles. They transfer some of the incident electromagnetic energy into the fire medium
Summary
Vegetation fires are slightly ionised gaseous medium. When the ionised medium is illuminated with microwaves, incumbent electrons are accelerated by electric field set by the incident electromagnetic energy. The electrons undergo repetitive collisions with relatively stationary heavier neutral incumbent flame particles. As they do, they transfer some of the incident electromagnetic energy into the fire medium. We consider a plane polarised electromagnetic wave which traverses a fire plume in x-direction. The electromagnetic energy dissipates such that its electric field strength (E(x)) varies as [1];
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