midi zones in air. A 'D' beam from a keyboard, or a theramin wand. Proximity midi zones.

Question

Im looking to make a midi controller. A proximity controller. Essentially, a way to cut up the proximity of an object to an electric field (or light field). As in the the Roland Theramin. You can control pitch, as you normally can, by moving your hand closer to the wand. This is cut up into midi zones. I'd like to have a fast, responsive but accurate midi trigger type event in each zone, using this method. The theramin wand is best suited for my application. Any help would be highly appreciated. I'm researching for a product to release as an MVP, if I can get the tech sorted. MAny thanks in advance! ( I have looked around and found one YT video that touches on this. There is the Alesis AirFx, but I need more of a wand type, not a dome.