Interaction of microwaves with atmospheric pressure plasmas

In this paper, the interaction of microwaves with a plasma, generated at atmospheric pressure, is studied. The refractive index, attenuation index, skin depth, attenuation coefficient, phase coefficient, and reflectivity are investigated as functions of the plasma number density, the wave frequency and type of polarization, and the grazing angle. It is found that two frequency regimes characterize these type of plasmas. The first is a range where the phase velocity and attenuation of the wave both increase with frequency. The second is a frequency range in which the phase velocity and attenuation of the wave remain constant. It is also found that to have a shallow skin depth, the plasma number density has to be in the 10¹³ cm^?3 range. The reflectivity is found to be an increasing function of the number density. In horizontal polarization, the reflectivity is a decreasing function of the grazing angle. But in vertical polarization and for grazing angle less than 20°, the reflectivity has a maximum at a frequency $f = f_s = \frac{{2\pi f_{pe}^2 }}{\nu }$ , where f_pe is the electron plasma frequency and v is the collision frequency.