The dissertation is devoted to research of processes of radiation and propagation of transient electromagnetic fields in unbounded nonlinear, nonstationary, layered inhomogeneous, transversely inhomogeneous, and, also, biological media by time domain methods.
The evolutionary approach to the problems of radiation and propagation of transient electromagnetic waves, which reduces the dimension of such problems by two units in the case of an unbounded transversely inhomogeneous, radially inhomogeneous, nonlinear, nonstationary medium, has been developed. General analytical solutions of the problems for the case of radially inhomogeneous medium by the Laplace transform method, for the case of weak nonlinear medium by perturbation approach are constructed. As an example, the problem of impulse wave radiation by a small loop excited by transient current surrounded by the sphere of radially inhomogeneous dielectric is solved by means of analytical and numerical-analytical methods. The development of the evolutionary approach to such problems allows to optimize effectively the electromagnetic devices by significant acceleration of the calculation of their characteristics and reducing the amount of RAM needed. The problem of propagation of a transient wave in a nonlinear medium is analytically solved in time domain by the method of evolutionary equations and perturbation theory. For the case of weak Kerr cubic nonlinearity, modal wave transformations, time forms of distorted fields are obtained for the first time.
For the first time, the corrected analytical expressions for the transient near fields of Hertz dipole were obtained using the vector potential method in time domain. The obtained improvement allows, in comparison with classical expressions, to describe correctly the formation of an electromagnetic wave in the near zone of the radiator. The analytical expressions for the fields are obtained by taking into account the bigger number of terms of the series, which expands the solution of this problem for the vector potential in the form of quadrature.
The phenomena of transient electromagnetic wave formation in near zone of several radiators, i.e. open ends of rectangular, circular, coaxial waveguides, are investigated. The ultrawideband analogue of the Klevin vibrator-slotted radiator based on the impulse slot antenna by Barnes and ultrawideband short-circuited dipoles in the form of metal cones was created and studied. The operator of wave propagation in a waveguide and a new diffractive distortion correction operator were used to generate short sounding field pulses in space using traditional transmission lines with strong frequency dispersion. The analytical solutions of the problem of radiation of impulse electromagnetic fields by powerful railguns in the moment of break of its electrical circuit are obtained. Time forms of fields at arbitrary distances and values of distances to the boundary of the far zone of such a radiator are received. The peculiarities of such nonstationary radiation in the immediate vicinity of the aperture are analyzed.
The transient electromagnetic fields in biological structures and organisms are studied. The setup for irradiation of biological solutions by ultrawideband fields with high uniformity of field distribution was calculated. For remote sensing problems of geometric and electrical parameter determination of layered structures, the use of artificial neural networks in time domain was proposed and implemented for the first time, when the input data are time samples of field amplitude without pre-processing, including spectral. The similar approach solves the problem of detecting metal objects situated underground and determining the depth of their occurrence by irradiating the ground surface with impulse ultrawideband field of a plane wave or point irradiator and analysis of the reflected wave by an artificial neural network. The pre-processing of the received signals based on the approach of discrete tomography is proposed, which allows improving the recognition at certain depths and significantly reduce the amount of processed data and simplify the structure of the neural network. The new system of local positioning on impulse ultrawideband fields is proposed and calculated. It is based on the approach of determining the angles of arrival of the wave and is realized due to the exceptional property of ultrawideband pulsed radiators to change the time shape of radiated pulses depending on the angle of radiation and extremely high sensitivity of the artificial neural networks for the changes. Such a system does not require the time synchronization of transmitters both with each other and with the receiver. It is resistant to intentional or accidental interference due to the ultrawide bandwidth used.
