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Resonant amplification in particles charged to a surface potential of 20 V. The amplification is shown as a function of refractive index (n) and particle size (x=2r/) for weakly (A), medium (B) and strongly absorbing (C) materials. The parameter r is the radius of the particle and  is the wavelength of the MW radiation

Scientists clarified some anomalous microwave phenomena in the atmosphere

10. 9. 2021 | 683 visits

A joint team of researchers from SAS and the Faculty of Mathematics, Physics and Informatics UK recently published the theoretical principle of how excess free electrons in the surface layer of particles affect incident microwave radiation. Changes in the electromagnetic field occur in the vicinity of the particles and the so-called far zone. However, these phenomena can only be observed if the frequency of the radiation and the size of the particles are in a certain resonant relationship. The amplitude and width of the resonance depend on the dielectric function of the material and the number of free charge carriers on the surface of the particles.

A team of authors from the Institute of Construction and Architecture SAS, FMFI UK and the US Army Research Laboratory showed that this effect can clarify some anomalous microwave phenomena observed in the Earth's atmosphere - especially some seemingly incomprehensible failures of microwave communication lines during dust storms. “Due to contact electrification, even non-absorbing dust particles tend to acquire an excess electric charge in such conditions, thereby their surface layer acquires ´metallic´properties,” explains Mgr. Miroslav Kocifaj, PhD., from ÚSTARCH SAS and adds that these phenomena can be interpreted by an increase in the complex refractive index and impedance.

The work was published in the Journal of Geophysical Research: Atmospheres and the joint team showed that a significant increase in resonance phenomena in charged particles compared to electrically neutral particles occurs mainly at frequencies of the order of gigahertz units (1-10 GHz). "This is an area in which meteorological radars and communication systems also work. Charge-induced resonance in charged particles at the lower limit of this frequency band proved to be significant enough to explain the increase in microwave attenuation, which is otherwise difficult to achieve by increasing the relative humidity - i.e. parameter, which contributes to the additional increase of microwave attenuation (MW),” M. Kocifaj explains the results of research. According to the scientist, the finding that the excess charge on the surface of the particles affects the lower part of the GHz frequency band has led ä to a new application based on the numerical reconstruction of the optical properties of particles so that microwaves at a specific frequency can be targeted. “By distributing suitable particles in the environment between two communication nodes, it is possible to purposefully cancel selected frequencies of MW communication lines," adds Miroslav Kocifaj from the Institute of Construction and Architecture SAS.

Edited by Andrea Nozdrovická

Graph: Miroslav Kocifaj

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