No one's attempted this in a commercial product before, but Nihon Dengyo Kosaku Co has reportedly developed a device that makes it achievable: a 'rectenna' that can fit inside a microwave oven and recycle unused
wave energy. The palm-sized gadget combines both an antenna for catching waves and a rectifier for converting them into DC current, with a maximum output of 100 watts. Foods with a low water content have the worst heating efficiency, which means they offer the best opportunity for reclaiming energy -- so stodgy
Christmas cuisine would be perfect.
