Dielectric Characterization of Fog in the Terahertz Regime

Abstract

Electromagnetic radiation at millimeter and sub-millimeter (terahertz) wavelengths are being considered for various applications, including remote sensing, wireless communications, and radars. However, wireless links implemented in millimeter wavelengths above 30 GHz suffer from absorption and dispersion effects in air, which emerge mainly due to oxygen molecules, humidity, and water droplets. Such frequency dependent atmospheric propagation effects become more severe as the frequency is increased to the terahertz regime. Moreover, weather conditions like haze, fog, and rain cause a further decrease in the overall link-budget leading to a degradation in the channel performance. In the current paper, the physical properties of the atmosphere and their effect on the electromagnetic radiation within the sub-millimeter wavelengths are studied theoretically and experimentally. Expressions for the attenuation and group delay are presented in terms of the electric susceptibility of the atmospheric medium in the presence of suspended water droplets. The analytical estimations are demonstrated experimentally in a controlled water fog chamber.

Experimental Study of Fog and Suspended Water Effects on the 5G Millimeter Wave Communication Channel

“…Preliminary experimental study was conducted in sub-millimeter waves with an artificial fog seeded by high volume 'smoke machines'. It was found that the fog generates attenuation, and group delay may affect radar accuracy [16,17]. These findings led to further experimental study of the radiation dispersive effects emerging in the presence of fog, on wireless communication links operating in mmW frequencies designated for the 5G cellular communication, which is described in this paper.…”

“…The visibility measurements were discussed elsewhere [17]. However, we will concentrate more on the experimental technique here.…”

“…According to Ref. [17], the instantaneous visibility at a 1 Hz is calculated via the following expression:…”

Detection of Low RCS Supersonic Flying Targets with a High-Resolution MMW Radar

“…They are employed as detection measures in many applications, such as collision avoidance radars in automobiles [12,13]. Detecting a target with a Doppler MMW radar has several advantages compared to other remote sensing technologies operating in infrared or optical wavelengths, mainly in foggy conditions and stationary background clutter scenarios [14][15][16]. Although millimeter waves are attenuated by fog, haze, and rain [17], they still can be used for short-range detection, where optical sensors completely fail.…”