I dimly remember from the early 60s (before they were the 60s) the Student Union had what they called an infrared oven that they used to heat sandwiches and the like but I think it acted more like a toaster oven. What freq range is infrared? In the Navy we used to refer to the communications ETs as DC techs because they worked with low frequencies around 5-10 MHz. Our lowest frequency radar was around 500 MHz.