METHOD FOR CONTROLLING AND OPTIMIZING MICROWAVE HEATING OF PLASTIC SHEET

A method for processing a thermoplastic material (46), the method including: passing a thermoplastic material through a microwave heating apparatus (40) a a selected feed rate; wherein the microwave heating apparatus comprises: a microwave emitter for supplying microwave energy to a resonant cavity (43); the resonant cavity comprising at least one inlet and at least one outlet, the inlets and outlets collectively forming a passageway (49) for passing the thermoplastic material through the resonant cavity; and a movable piston (48) configured to adjust a length of the resonant cavity; exposing the thermoplastic material to microwaves in the resonant cavity, wherein the exposing causes an increase in temperature of at least a portion of the thermoplastic material; measuring an e-field generated by the microwave emitter; and adjusting a position of the movable piston in response to the measured e-field; and, processing the thermoplastic material.