Cool! I came across some quoras that suggested the electronics were easy for 2.4, but didn't give further detail. Noisy harmonics does sound useful for cooking!
In 1952, a paper called Tubes for dielectric heating at 915 megacycles said this, "Dielectric heating can be much faster at microwave frequencies. Because leakage radiation is large enough to interfere with communications, heating is best done at assigned frequencies. The bands at 915 and 2,450 megacycles are most useful."
"The plan which is, recommended by the United States provides for certain discrete frequencies, with appropriate guard bands, for those industrial scientific and medical devices which cannot be shielded effectively. This assures a minimum disruption of vital communication services. The allocation of frequencies for this purpose is justified because of the tremendous investments in equipment and the public demand for the various services performed, together with the harmful interference to radio communications which would result if such devices were scattered indiscriminately throughout the spectrum. The frequencies proposed are:
Yeah, I do not think I have a good source at hand, this is a fun fact from an E&M lecture we had.
I also wonder if anyone actually experimented with microwaving their dinner at 10GHz or if that was just an educated guess. X-band magnetrons for radars are widely available though, so I would not be surprised if that was coming from practical experience...
A review of the history of microwave cooking implies that the interaction of 10 GHz microwave radiation with water was understood by WWII.
"effective penetration and heating favors wavelengths in the cm range (1–30 GHz). Higher frequencies cannot penetrate sufficiently, and much lower frequencies require very high fields, and can have poor coupling unless
making use of direct contact or inductive heating. In the years following WWII, emphasis was thus placed on frequencies in the low GHz region, where both the historic development of microwave power sources and serendipity converged."
