The occurrence of limit-cycles during feedback control of microwave heating

The microwave heating of one- and two-dimensional slabs, subject to linear feedback control, is examined. A semianalytical model of the microwave heating is developed using the Galerkin method. A local stability analysis of the model indicates that Hopf bifurcations occur; the regions of parameter space in which limit-cycles exist are identified. An efficient numerical scheme for the solution of the governing equations, which consist of the forced heat equation and a Helmholtz equation describing the electric-field amplitude, is also developed. An excellent comparison between numerical solutions of the semianalytical model and the governing equations is obtained for the temporal evolution of the temperature in a number of different heating scenarios. It is also found that the region of parameter space, in which limit-cycles can occur, and their amplitude and period are all accurately all predicted by the semianalytical model.