There's lots of prior art here, thinking of patents.
You might want to look at Atmel's maXTouch capacitive sensors. In particular what's going on with the noise floor, or signal to noise that's a relevant factor for resolution [1]. And a side band attack btw.
Infrared sensors are affected greatly by environmental infrared, so dual transmitter types and fast switch sampling and interferometric approaches.
You'll need to consider high sampling rates both in the time and frequency domains.
You might want to look at Atmel's maXTouch capacitive sensors. In particular what's going on with the noise floor, or signal to noise that's a relevant factor for resolution [1]. And a side band attack btw.
Infrared sensors are affected greatly by environmental infrared, so dual transmitter types and fast switch sampling and interferometric approaches.
You'll need to consider high sampling rates both in the time and frequency domains.
There's other stuff but I'll keep mum about that.
1. http://www.atmel.com/microsite/maxtouch_eseries/