 Waffle @-@ iron filters are used in industrial microwave processes . The many industrial applications of microwave energy include drying of food products and industrial films , heating , such as in polyurethane foam production , melting , rendering , sterilising , and <unk> . In high @-@ volume production the process is continuous necessitating openings to the microwave chamber where the product can be fed in and exit . Steps need to be taken to prevent unsafe levels of microwave radiation escaping from these apertures which are often large to accommodate the product . It is usual to line the product feed ducts with microwave absorbent material for this purpose . However , the absorbed microwaves have a heating effect and this can be severe enough to damage the absorbent material . Waffle @-@ iron filters are a useful alternative because the product can be passed between the filter 's teeth . An ideal filter will reflect all the unwanted radiation rather than absorbing it so will not suffer from overheating . This is an example of a filter being used in a choke application . In some processes both techniques are used simultaneously . The waffle @-@ iron is placed nearest the microwave chamber to first reduce the energy to a level which will not cause the absorbent lining to overheat . The absorbent lining then removes the small residue . 
