Research On Microwave Nonlinearity Of High-temperature Superconductor Thin Film Based On Full-wave Analysis

Microwave nonlinear performance of the high-temperature superconductor thinfilm has an important significance, and extensive researches have been conducted inexperimental and theoretical aspects either at home and abroad. With the deepening ofthe study, the development of the nonlinearity research turns to practical application.Nevertheless, there is no accurate method for nonlinear analysis at present, how toestablish an effective technique for nonlinear study has become an urgent problem to besolved.This dissertation combines the finite difference time domain method and finitedifference method for solving the Ginzburg-Landau equations for full-wave analysis ofhigh-temperature superconductor microwave nonlinearity. In this dissertation Thecurrent density distribution and nonlinear transmission characteristics of superconductorare simulated with different transmitted power. Also the transition point of power forsuperconducting transimission line with certain line width is predicted. Such contentsinvolved in this dissertation are as following:1. The FDTD algorithm suitable for microstrip type is studied, such as dispersiveabsorbing boundary conditions, non-uniform mesh, as well as the differential forms forfields in a good conductor to ensure stability on the time iteration. All of these works isto smimulate the electromagnetic field in high-temperature superconductor.2. some neural network models are proposed for computing some eigenvaluesproblems of normal matrices, and also extended to arbitary real matrices eigenvaluesproblems by matrix norm reducing technique, a complex nueral network model is setupto calculate the modulus largest eigenvector and the corresponding eigenvalue, in thesame time the convergency is improved also. these methods can be applied to the studyof stability problems from numerical computation of Ginzburg-Landau equations infull-wave analysis.3. The finite difference numerical solution for the GL equations is studied,including finite difference discrete approximation of the GL equations, treatment ofboundary conditions of the two GL equations discretized by finite difference, the Newton iteration method for solving system of linear equations produced by GLequations’ discretization, and internal and boundary field interpolation algorithm.4. Full-wave simulation is conducted for superconducting thin film transmissionline by the combination of FDTD method and GL equations numerical solution. Thecurrent density distribution is analyzed when different power is transmitted. Thetransition point of power needed for the transition between low-loss superconductingstate to the high loss state is estimated in the situation of different linewidth.5. Experiments are designed to mearsure the power nonlinear propagationproperties of high-temperature superconductor coplanar waveguide transmission line.The estimation for the power transition point is verifying by full-wave analysis. Themeasurements show that the estimation is close to the tested value, and this proves thatfull-wave analysis is effective, we also find that transmission line method for measuringsurface resistance is failure.