By what mechanism do you think the IR will propagate through various wall materials?

I'd start by conducting tests (is there a pun there?) on variouswall materials (thin samples) with a standard IR transmiter and receicer pair like you'd find in any TV remote control. Pulsing the transmitter at high intensity may help, pulsing will also help the receiver differentiate signal from noise, as it can look for the appropriate puls spacing...

Del

I'm wondering too. As I know even sheet of paper is a significant barrier for IR transmitting.

Pardon me for being blunt, but I think you might want to consider a project based on something you actually have knowledge of, since you think there would be an antenna involved with receiving IR waves.

Also, I think the only wall you will be able to transmit IR through would be made of glass, or other clear/translucent material, since IR is Infrared light.

Tom