Simulations and experiments of electromagnetic problems involving materials in motion

The object of investigation in this work is electromagnetic waves in the presence of moving media. The study focuses on the effects induced directly by the motion of the media on incident radio-frequency time-harmonic electromagnetic fields. To restrict the consideration to frequency domain effects, a number of constraints were introduced in the formulation. We consider the motion of the media under the conditions that its boundaries remain stationary, the linear velocity vector field does not vary over time, and no transient processes occur in the system domain. The main attention is given to slow material motion, corresponding to the deeply non-relativistic state. The magnitude of these effects is extremely small, making them weak in comparison with the secondary scattering and refraction fields. For this reason, computing such effects with traditional techniques is challenging. To address this issue, a novel methodology is proposed. It relies on the Born approximation applied to electromagnetic problems involving moving media. The formulation employs equivalent field sources and is specifically designed to analyse the effects of motion on the electromagnetic field. One of the key aspects discussed in this work is the implementation of the new methodology in the commercial CAD environment, namely COMSOL Multiphysics. This opens up broad opportunities for the practical application of the methodology, particularly for modeling and designing new devices and sensors for detecting moving effects, such as electromagnetic flowmeters. To add more specificity, the methodology was adapted for operation within the COMSOL Time Explicit EMW module. The methodology was verified for a two-dimensional problem of electromagnetic wave scattering by an infinite circular cylinder moving along its axis of symmetry. The results obtained using the methodology were compared with the semi-analytical solution as well as with traditional numerical difference methods. The methodology was partially verified for a three-dimensional problem in which the scatterer was a finite-length cylinder, with all other conditions remaining the same. We evaluated the efficiency of the methodology in solving problems that extend beyond the sensitivity limits of double precision arithmetic. Traditional difference methods, even when combined with semi-analytical solutions, do not provide reliable results in this case, whereas only the new methodology can yield consistent outcomes. We also verified the algorithm for applying the methodology within COMSOL. The work presents a description of a series of experiments on the interaction of electromagnetic waves with a moving medium. These experiments were carried out using a waveguide transmission line, inside the cavity of which a pipe with moving water was placed. To date, the results of these experiments have not been rigorously interpreted, and we present only a descriptive analysis. Nevertheless, the experiments conducted demonstrate the presence of a reproducible effect and provide substantial information regarding the requirements for designing an optimal study. The verification of experimental data is one of the priority tasks for future developments. In addition, a number of tasks were identified for generalizing the methodology and expanding its range of applicability as well as for conducting new experiments. In one group of experiments, the interaction of electromagnetic radiation with a moving gas is planned to be investigated. Another direction involves the design of fundamentally new laboratory setups, the schematics of which are presented in the work. The main tasks of future developments are divided into three areas, systematized, and prioritized according to their complexity and the consistency of the results.