Considering that the single microwave mode can improve the energy stability, in order to effectively reduce electromagnetic wave modes inside the microwave absorption cavity 102, the length and width dimensions of a bottom surface of the microwave absorption cavity 102 (that is, a face perpendicular to a material transmission direction) are designed to be the same as the cross-sectional length and width dimensions of the cavity of rectangular waveguide 101 used in this application. Therefore, in the present example, the microwave absorption cavity 102 being a rectangular cavity is taken as an example for description, and the length and width dimensions of a bottom surface of the microwave absorption cavity 102 (that is, a face perpendicular to a material transmission direction) are the same as the cross-sectional length and width dimensions of the cavity of rectangular waveguide 101 used.

If single-mode microwaves are not required, the microwave absorption cavity 102 may also be designed as a cavity of other shapes according to actual needs.

The waveguide system is composed of a plurality of rectangular waveguides 101 arranged in a staggered manner. A microwave feed port is formed in the outer wall of the microwave absorption cavity 102. For convenience of description, adjacent wall surfaces among four wall surfaces of the microwave absorption cavity 102 are respectively marked as an E plane and an H plane, that is, the microwave absorption cavity 102 has two E planes and two H planes.