High frequency electromagnetic field generator is the hart of any microwave oven (a.k.a.  Microwave) . These waves cause to vibrate any electric charge careers inside the oven (food) bringing up the temperature. Since water molecules (in food) don’t have free electrons, the whole molecule is shaken effectively with altering electric field heating up the food placed inside microwave oven. For safety reason the generator is placed inside the metal box to prevent its effect on surrounding objects outside the Microwave.

If the object inside Microwave contains free electrons, as metals do, that will cause very high temperature due to strong electric currents induced in metal. Temperature can be high enough to melt down or burn out the metal object. It may cause damage to oven and electric circuit. For that reason you may not put any metal containing object in a Microwave.

Interestingly, the new approach in medicine to cure cancer is based on using radiofrequency electromagnetic waves  with combination of nanoparticles (metal particles about the size of small molecules). The idea is the following: The suspension of metal nanoparticles with attached antibodies to tumor cells is injected into bloodstream to target the cancer cells. These particles easily penetrate and bind cancer cells. Than the body of patient is placed into the radiofrequency electromagnetic field to heat the metal particles and destroy cancer cells. There are some laboratories that do experiments on animal models using this technique and they have come up with some positive results.