RFID solution for cat feeder with 12" or greater range (and electric eye too)?

I want to build a cat feeder that's basically a plexiglas box with a sliding door that will close whenever our fat cat gets near it, and re-opens when he moves away. Normally it'll remain open so our other two cats can eat (they're skittish so it's better if it doesn't have to react to them, and instead can react to the fat cat). To drive the door I thought I could use an old CD ROM drive (kind of like https://www.instructables.com/id/RFID-pet-feeder/). I'd like the tag on the fat cat's collar to be waterproof(able) and not require batteries. The antenna can be as big/complicated as necessary, as long as I can get the desired range of 12-24" or so. Any suggestions for an RFID setup that'll work for this?

Also, I should set up an electric eye around the opening so it doesn't activate (close) when a cat has its head in the opening. Something like we have on our garage door to prevent it closing on someone, but smaller would be ideal. Any suggestions?

Thanks!

If your cats are chipped, you can read their RF tags at that kind of range.
It sounds like you have the basic needs of your system well defined.

I don't know if the drive from an old CD drive will have enough travel length (only about the diameter of a CD) to allow the other cats to get their heads inside to access the food. The concept seems sound though. I think that CD drives use kind of a rack and pinion type mechanism to drive the tray out using a small motor. You can get small plastic rack gear stock and compatible gears at www.mcmaster.com

As for the electric eye sensor, I would just use an infrared LED and photo transistor pair. These are inexpenisve and easy to use. The LED can just be on all the time. The phototransistor is just a small semiconductor switch that will turn on when the LED illuminates it, and is off otherwise. This will need to interface to additional circuitry, as the phototransistor itself won't directly handle the current of the door drive motor. You'll need some additional logic or at least a limit switch type of arrangement to control the direction of door travel.

I'm not familiar enough with the off the shelf RFID solutions out there, but the related projects that appear to the right on the screen show a few RFID pet door type applications, and so they may contains good ideas and sources. The 12" to 24" range you desire shold be feasible. Also check out places like www.sparkfun.com for easy to use RFID products geared toward hobbyist applications.

One suggestion I would have for the "box" would be to modify a transparent storage tote.