so that the toner image melts and fixes to the printed material when it cools outside of the resonators 2 3 the resonators 2 and 3 are arranged offset from each other by a fourth of a wavelength of the microwaves 5 in order to obtain a corresponding offset of the maxima of the microwave 5 and to heat up the printed material and the toner image in a relatively uniform manner in addition it is noted that the wavelength of this standing microwave 5 hereinafter indicated by u201c u03bb u201d which corresponds to the progression of the energy input into the printed material corresponds to only half of the wavelength of the originally free microwave that was supplied through the hollow guide in order to form the microwave field resonators 2 and 3 are connected via hollow guides depicted as lines in the diagram to a suitable system for microwave generation 6 the conveyor belt 1 and the printed material located on it move in the direction of the arrow 7 through the resonators 2 3 and to be precise for example at a speed of up to one meter per second the leakage radiation that emerges out of the through put openings of the resonators can be reduced by the assembly of a so called choke structure or by using absorbing materials outside of the resonator fig4 shows schematically a preferred sequence of resonators 8 to 11 in an overhead view onto the conveyor belt 1 on which a substrate or a printed material is conveyed in the conveyor direction 7 in fig4 for example four resonators 8 to 11 are arranged one.