Your proposal, writeup, etc, should completely describe the technical aspects of your project. Good technical writing should include textual descriptions, block diagrams, circuit schematics, mechanical drawings, and other details (as appropriate). Browsing through patents at the US Patent Office is one source of examples (both good and bad). In particular, Professor Leeb's patent 6,198,230: Dual-use Electronic Transceiver Set for Wireless Data Networks has good examples of the kind of stuff we're looking for.
These are just some ideas to help you come up with a project. Some of these are not complete projects on their own or may be too difficult.