Automatic self-matching network for industrial microwave heating based on conjugate gradient algorit - Electronics Letters

Introduction: One of the main problems regarding the efficiency of industrial heating systems using high power microwaves is related to uncontrolled changes in the load. These changes can be caused both by the different kinds of materials to be processed in the same oven and by the temperature rise which modifies the material’s physical properties, particularly its dielectric permittivity. Usually, the microwave generator is matched to the oven by means of a waveguide matching system, typically a two, three or four capacitive-screw tuner empirically adjusted for a given load [l]. Once the heating process is started, the temperature dependence of the complex permittivity usually changes the impedance seen by the generator, worsening the mismatch factor and reducing the efficiency of the heating process. A similar problem affects an oven with inhomogeneous and discontinuous loads; it is not feasible to manually readjust the matching network for every different sample processed. Until now the solution has been simple but highly inefficient: to increase the incident power in order to overcome the mismatching effects. In this Jitter we describe an autonomous system which is able to detect load mismatches and reduce them automatically.