Yes, Some Metals CAN be placed in the Microwave!
In fact, the same walls of the microwave are covered with metal to enhance the reflections of the microwaves, working similar to mirrors. Only the shape of metal determines if a metal can or cannot be introduced in the microwave.
When the metals placed in the microwave are solid pieces, without sharp edges, nothing will really happen. A lightning rod effect, forming some sparks, occurs if a metal object very thin or with tips (such as a fork or crumpled silver paper) is introduced, however. This happens because the electrons accumulate in the tips crashing between them.
A secret of the Lékué Microwave Grill is that it has rounded edges and the precise shape so that there is no problem when it is used in the microwave. Made of the material Susceptor, which transforms the electromagnetic energy into heat and transmits it to the grilling plates to grill the food through pressure. Safe and convenient!