The Study On Electromechanical Interaction Between Electromagnetic Wave And Moving Medium

The electromechanical interaction between electromagnetic wave and moving medium is a fundamental problem in electrodynamics. The moving velocity of a macroscopic object is much smaller than the speed of light, and the impact of the movement is often ignored in the reported research. However, for particular parameters of electromagnetic wave and moving medium, there may be some significant physical effects depended on the moving velocity, even if the velocity is much smaller than the speed of light. The systematic and thorough study is of great significance for the advance of electromagnetic theory and microwave technology.Based on the Special Relativity and the microwave electromagnetic field theory, this dissertation focuses on the scientific problem-the electromechanical interaction between electromagnetic wave and moving medium, considers the uniform movement of macroscopic medium, and emphatically studies the electromechanical interaction in the moving direction.To establish the basic principles and methods of studying the electromechanical interaction between electromagnetic wave and moving medium, the eigenmode of electromagnetic field excited out of the homogeneous medium under the influence of periodic medium or boundary condition, i.e. Floquet mode, of which the electromagnetic force in moving medium is studied at first. The time-and-space Floquet mode in moving periodic structure is analyzed. The general formulas of calculating effective electromagnetic force on temporal and spatial periods are derived. Starting from the Lorentz force density of electric field and charge density, and that of magnetic field and current density, it is shown that under some preconditions, stable effective electromagnetic forces between Floquet mode and moving dielectric with charge or moving conductive medium is feasible.In the study of the electromechanical interaction between Floquet mode and moving dielectric layer, electromagnetic scattering and force on the moving dielectric layer incident by TE and TM waves are analyzed, respectively. The results show that: reflected and transmitted coefficients under the incidence of two polarizations of slow-waves can resonate and have scattering anomalies in the range of the velocity much smaller than the speed of light, which is obviously different from the case of fast-wave incidence; at the same time, as long as the permittivity has a very small imaginary part, the effective electromagnetic force is non-zero and can be enhanced much more than that under the incidence of fast-wave, and it also has an extremum at the corresponding resonance point.In the study of the electromechanical interaction between Floquet mode and moving periodic structure, by analyzing the electromechanical interaction between TE wave and moving periodic thin-film with periodic conductivity distribution, it is recognized that for slow-wave incidence, although the scattering has no resonance, the effective electromagnetic force is much bigger than that for fast-wave incidence and the force is very sensitive to the period and the conductivity. While from the analysis of the electromechanical interaction between TM wave and moving periodic thin-film with periodic permittivity distribution, it is obtained that:under the incidence of slow-wave, the scattering anomalies may exist, and the effective electromagnetic force can be extreme in a very small velocity, that makes the electromagnetic force enhance significantly and greatly influenced by the period, the incident angle and the dielectric constants.The electromechanical interaction between TE polarized slow-wave and a moving anisotropic conductive thin-film with dyadic conductivity is also studied. The reasonableness of slow-wave excitation is demonstrated, an equivalent current wave is proposed to realize the slow-wave excitation, and the effective electromagnetic force under the excitation of such a current slow-wave is analyzed. The effective electromagnetic force has tight relationship with the velocity:its starting value at zero velocity is non-zero, it has maximum value at one certain velocity, and then, it vanishes when the velocity synchronous with the phase velocity of the exciting slow-wave. The amplitude of the electromagnetic force may be positive or negative, corresponding to the velocity less or greater the phase velocity. Besides, the electromagnetic force is very sensitive to the conductivity.Finally, a primary model is designed and manufactured, and the measurable interaction between slow-wave and moving conductive thin-film is experimentally verified. In the model, the moving part (rotor) has an anisotropic conductive thin-film; while the stationary part (stator) is a high-pass lumped element transmission line that converts high-frequency voltage into exciting slow-wave current. It is the first time in the associated researches domestic and international to observe by experiment the rotation of the macroscopic rotor driven by high-frequency electromagnetic wave, in which the rotating direction is depended on the exciting frequency; and the dependence of starting torques on frequencies is recorded. The experimental results are consistent with the theoretical calculations, and this can give a convinced explanation to the complex behavior of electromagnetic wave in a composite right/left-handed transmission line.The contributions of the study in this dissertation are as following:unlike the excitation of a general plane wave (fast-wave), the concept of the excitation of Floquet mode is proposed, the electromagnetic scattering and the electromagnetic force under the excitation of Floquet mode is studied, and the effects of scattering anomaly and electromagnetic force enhancement for the slow-wave excitation in different moving mediums are discovered, which will enrich the theory of electromagnetic scattering and force; according to Floquet theorem and Galilean transformation, the time-and-space Floquet mode function in moving periodic structure is proposed and studied, its form-invariance and time-and-space orthogonality are proved, and this provides the basis and foundation for further studying the electromagnetic problems of moving periodic structure; based on the theoretical analysis, a primary model is designed and manufactured, the movement of macroscopic object driven by high-frequency electromagnetic wave is observed and measured by experiment for the first time, and it verifies experimentally that the electromechanical interaction between electromagnetic slow-wave and moving conductive thin-film can produce a measurable effective electromagnetic force, which can realize the direct conversion from RF and microwave electromagnetic energy to mechanical energy. The results of this dissertation can direct the development of continuous moving part in MEMS (Microelectromechanical systems) technology, novel propulsion system in Aeronautics and Astronautics technology, etc., and potentially be applied to electrical machinery, measurement, microwave, etc. and many other related fundamental fields.