What I am looking for is a cheap, lightweight way to generate a range of specific frequencies. To expand a little, a microwave uses a constant frequency but may vary its power to cook the food. I've heard it tries to match the resonant frequency of the water molecule in order to agitate it which in turn creates heat. What I'd like is a way to input the desired frequency and amplitude and if possible have as many emitters as possible (think max. potential emission) per unit of surface area. I was thinking for starters just a flat board with unidirectional emitters hooked up to a power source with some kind of frequency control piece in the middle. I'm new to electronics but am reasonably intelligent. What I'm looking for specifically is if this kind of thing already exists and if not can it be built cheaply and if so what is the parts list looking like? Thanks.